Blood Pressure in Pregnancy

¶ … Korotkoff Phase Should Be Used as the Endpoint for the Measurement of Diastolic Blood Pressure During Pregnancy

Literature Selection and Identification

Critical Appraisal of Selected Literature

Five Korotkoff Phases

Conducting System of Human Heart

Two of the most common complicating problems seen during pregnancy are the appearance of gestational diabetes and of hypertension. Both of these conditions are more likely to occur during late pregnancy and both generally abate in the postpartum period. Nevertheless, both of these conditions represent an increased risk for future development of disease. There is a lack of agreement among clinicians concerning the optimum blood pressure measurement device and inconsistencies in practice with regard to the method in which blood pressure is measured. Blood pressure is created by a number of physical forces related to the heart and blood vessels and regulated by hormones and other substances in the human body. The blood pressure measurement is an important clinical area because raised blood pressure in pregnancy may have relatively acute and potentially serious consequences; consequently, accurate measurements throughout the pregnancy are essential. The sounds produced by small amounts of blood passing through a blood pressure cuff are called Korotkoff sounds, after the physician who first used this method in the early 1900s, and five Korotkoff phases are described in adults. A review of the relevant and scholarly literature is followed by a critical review of selected studies to identify the most efficacious method of measuring blood pressure during pregnancy. The results of the research are followed by a discussion, conclusions and recommendations.

An Investigation as to which Korotkoff Phase Should Be Used as the Endpoint for the Measurement of Diastolic Blood Pressure During Pregnancy

Introduction/Background

Researchers in the field of family systems medicine have long recognized the association between psychosocial stressors and the onset of various illnesses and their exacerbation (McDaniel, 1992). Psychosocial distress has been implicated in the etiology and/or exacerbation of such conditions as chronic idiopathic prostatitis, somatization disorder, and adverse pregnancy outcomes (Langer et al., 1996). In an international study of medically unexplained physical symptoms, the World Health Organization concluded that psychosocial stress may be specifically responsible for many of the multiple, persistent, and medically unexplained somatic symptoms seen by primary care physicians across multiple cultures and populations (Isaac et al., 1995). Two of the most common complicating problems seen during pregnancy are the appearance of gestational diabetes (Freinkel, 1980, 1985) and of hypertension (National High Blood Pressure Education Program, 1990).

Hypertension has been linked to poor fetal development and ensuing perinatal death (Mansfield, 1986). In their study of pregnancy over 40 years, Horger and Smythe (1977) determined that fully one-third of their sample, black women of very high parity suffering from hypertension, accounted for two-thirds of all the perinatal deaths occurring during the study. These researchers attributed the link to placental malfunction. Other researchers have reported a link between hypertension and stillbirth, resulting from impaired placental circulation caused by placental infarction or abruption (Mansfield, 1986). Further, the prematurity rate rises with increased blood pressure, related both to premature labor and premature termination of the pregnancy; in addition, higher incidences of low birthweight have been reported among hypertensive patients by researchers in the Collaborative Perinatal Project (Mansfield, 1986).

Both gestational diabetes and hypertension are more likely to occur during late pregnancy and both generally abate in the postpartum period. Nevertheless, both of these conditions represent an increased risk for future development of disease (Baum, McCabe, & Schneiderman, 1992). The course of both of these conditions is such that both may be attributed to arising as a consequence of the progressive insulin resistance characteristic of pregnancy that abates postpartum, but may have revealed an underlying predisposition to subsequent disease development. However, today, there is a lack of agreement among clinicians concerning the optimum blood pressure measurement device and inconsistencies in practice with regard to the method in which blood pressure is measured. The blood pressure measurement is an important clinical area because raised blood pressure in pregnancy may have relatively acute and potentially serious consequences; consequently, accurate measurements during pregnancies are essential. The precise definition of the research question/hypothesis is presented below clarifying the explicit link to the identified clinical area of inquiry.

Statement of Problem

In the United States, 50 million people are thought to have high blood pressure; about half are receiving treatment and half of the treated are successful at reducing their blood pressure to below 140/90. This leaves about 37 million people in the United States with persisting hypertension. The incidence of high blood pressure rises with age; more common in men under 50, but more common in women over age 65 years. Over age 70 years, the incidence of high blood pressure approaches two-thirds of the population. Hypertension is divided into two groups - primary or essential hypertension and secondary to a specific disease. Diseases of the kidney and blocked kidney arteries, for example, can produce high blood pressure as a secondary effect. While no specific cause is found in 90% of hypertensives, one explanation is that the population at risk is becoming more sedentary with an increase in obesity. Their food supply is clearly suspect and it is not just the fat in the diet; these arterial problems with different and complex origins link to the diets and lifestyles that are currently popular in Europe and North America and occur less often among physically active, vegetable-eating populations who seldom eat dairy products, meat, and other high-protein-fat foods (Kaplan, 1998).

Today, there are four major concerns about blood pressure diagnosis and treatment:

1) BP readings may be inaccurate or biased;

2) White coat syndrome - higher BP readings are obtained in the doctor's office; 3) Inadequate sample (numerous readings are required to obtain a meaningful average); and 4) Corrective action taken is inappropriate (Kaplan, 1998).

Blood pressure is a dynamic feature of pumping blood. Blood pressure readings also tend to vary (BP tends to be lowest in the morning and highest in the late afternoon), and BP will rise with exertion and may be very high briefly with vigorous exercise (Kaplan, 1998). Because the blood pressure rate can be affected by such a wide range of physiological and psychosocial factors, identifying the most efficacious means of measuring blood pressure, particularly during pregnancy, becomes all the more important.

Rationale

Blood pressure is created by a number of physical forces related to the heart and blood vessels and regulated by hormones and other substances in the human body. The heart pumps blood throughout the body in blood vessels or tubes called arteries, which are similar to a garden hose carrying water from a faucet to the flower bed. Arteries branch into smaller tubes called arterioles that deliver oxygen and other nutrients to the tissues (Griffith & Wood, 1997). A number of common and uncommon factors can lead to secondary high blood pressure. The more common causes for secondary hypertension include the use of certain medications (e.g., birth control pills), hyperthyroidism, pregnancy induced hypertension, and renal artery disease (Griffith & Wood, 1997). The cause of pregnancy-induced hypertension is unknown; however, pregnancy places a greater demand on the heart to pump blood and is associated with hypertension in certain individuals. According to Griffith and Wood, pregnancy-induced hypertension (PIH) includes a spectrum of high blood pressure disorders ranging from toxemia to chronic hypertension (Griffith & Wood, 1997).

The increased prevalence among older women of hypertension, diabetes, and fibroid tumors, in particular, has been of special concern because of the link between these conditions and poorer reproductive outcomes; thyroid and kidney disorders have been implicated as well (Mansfield, 1986). Hypertension has been arbitrarily defined as a blood pressure of 140/90 or more, and has the potential for damage to vital organs such as the brain, heart, kidney, and placenta; therefore, the condition places the mother and fetus at risk for increased morbidity and mortality (Mansfield, 1986). Because blood pressure rises slowly with age, older women may be at greater risk for this disorder and its ensuing pregnancy complications.

Hypertension has also been associated with increased maternal morbidity and mortality rates in a number of studies. The intervening complications may be cerebral hemorrhage, placental abruption, heart failure, or preeclampsia. A 1982 study of maternal mortality rates found that disorders of the cardiovascular system were the predominant indirect obstetric cause of death in their sample. However, this risk is not a modern discovery. In fact, as early as 1886, Galabin reported in his treatise on midwifery that when heart disease was "grave," one could expect 55% of the cases to be fatal (p. 326 in Mansfield, 1986).

Furthermore, patients with essential hypertension have an increased likelihood of labor induction and cesarean section deliveries, with their ensuing complications (Mansfield, 1986). These are additional reasons why the hypertensive patient may be at additional risk for a number of pregnancy complications.

Data Collection

Electronic databases used included:

1) Cochrane Database of Systematic Reviews.

2) CINAHL. Cumulative Index of Nursing and Allied Health.

3) MEDLINE. Medical Literature Analysis and Retrieval System Online.

The following key words were used to search the databases:

Hypertension

Pregnancy

Pre-eclampsia

Korotkoff Phases

Sphygmomanometry

Oscillometric

Auscultatory

Electronic/automated monitoring

Subject Population

The subject population of the literature review will be limited to studies reported in English concerning pregnant women in the United States.

Literature Review

Literature Selection and Identification

The literature reviewed for this project was conducted using the search terms noted above, in isolation and in combination. Based on the appropriateness of the identified research, the following literature was selected for inclusion in this study. As with many other areas of clinical research, there is a paucity of research concerning the appropriateness of which Korotkoff phase should be used as the endpoint for the measurement of diastolic blood pressure during pregnancy. Further complicating the investigation is the wide range of confounding factors such as age (Mansfield, 1986), race, level of neonatal care and socioeconomic status of the subjects involved (Berry et al., 2000). For instance, pregnant women, especially young, single pregnant women, consistently demonstrate higher levels of prenatal care in neighborhoods with strong social networks, perhaps because these networks put pressure on them to avoid compromising the health of their fetus and also provide them with more information about what constitutes effective prenatal care (Sampson, 1992).

Background and Overview of Blood Pressure Measurement. Generally speaking, cardiac function tests are simply attempts to measure certain variables reflecting the condition of the circulatory system in adjusting to situations of exertion. The variables used most generally include pulse rate and blood pressure, which are recorded under various conditions (Matthews, 1973). Blood pressure refers to the pressure exerted by the blood on the walls of the blood vessels. Typically, systolic and diastolic blood pressure tend to increase during the performance of tasks (Baum, Krantz & Singer, 1983). The blood pressure reaches its highest levels during systole in the left ventricle. This systolic pressure increases during activity and falls during sleep. The diastolic blood pressure is the lowest point to which the pressure drops between beats (Matthews, 1973). When Dr. Nicolai Korotkoff of Leningrad added a stethoscope to Riva-Rocci's technique in order to hear the pulsations of blood in the brachial artery, for the first time both systolic and diastolic blood pressure could be gauged (Lynch, 1985).

The noninvasive methods used for the measurement of blood pressure are known as indirect techniques. Two methods of indirect blood pressure (BP) measurement are currently used for ambulatory blood pressure measurement (ABPM): the auscultatory and oscillometric methods. According to Bonnafoux (1996), the auscultatory method is based on the detection of Korotkoff sounds that are issued from the acoustic transudcer signal. The main advantages of the auscultatory method are (1) similarities with usual clinical measurement of BP; and (2) accurate detection of systolic and diastolic pressures on the appearance and disappearance of sounds. The main disadvantages associated with this method are (1) artefacts due to movements; and (2) difficulties in signal analysis due to physiological variations of the Korotkoff sound patterns or poor signals. The difficulties associated here can be overcome by appropriate signal processing (K2 recognition), noise rejection and/or ECG gating. This may allow relatively accurate BP measurement during mild exercise. With the oscillometric method, air volume variations in the cuff are detected during deflation. The maximum oscillation is related to the mean arterial pressure; the systolic and diastolic BP are determined by an algorithmic interpretation of the shape of oscillometric amplitudes as well as the heart rate. The main advantages in this approach are (1) possibility of BP measurement when the Korotkoff signal is poor; (2) measurement of the mean arterial BP; and (3) there is no need of a microphonic sensor. The main disadvantages of the oscillometric approach are (1) some oscillometric curves are difficult to read accurately; (2) oscillometry is very sensitive to movements due to the bandwidth of the signals, so the arm must be immobile; and (3) the accuracy of the systolic and diastolic BP depends on the algorithm used. "These two methods are complementary and should ideally be associated in the same device" (Bonnafoux, 1996, p. 185). According to John L. Andreassi (2000), the true measurement of blood pressure can only be achieved through the penetration of an artery to insert a sensing device; however, this direct measurement of intra-arterial BP would be a problem in the psychophysiology laboratory using human subjects, because of discomfort for participants and possible medical complications. "The most familiar blood pressure measuring technique involves the use of a sphygmomanometer (from the Greek word sphygmos, meaning "pulse").

The sphygmomanometer is comprised of an inflatable rubber cuff, which is wrapped around the upper arm and which is connected to an apparatus that records pressure, usually in terms of the height of a column of mercury or on a dial. A blood pressure reading consists of two numbers, which are typically recorded as x/y. The x is the systolic pressure, and y is the diastolic. The term, systole, refers to the contraction period of the heart, when it forces blood from the heart into the circulating system, and diastole refers to the resting period, when the heart expands and receives another supply of blood. At each heartbeat, blood pressure is raised to the systolic level, and, between beats, it drops to the diastolic level. As the cuff is inflated with air, a stethoscope is placed against the skin at the crook of the arm. As the air is released, the first sound heard marks the systolic pressure; as the release continues, a dribbling noise is heard; this sound represents the diastolic pressure (Sphygmomanometer, 2004).

One method of measuring blood pressure involves the use of a pressure cuff, a rubber bulb, a mercury (Hg) manometer, and a stethoscope (Andreassi, 2000, p. 305). In this method, the pressure cuff is wrapped around the upper arm and inflated to a level well above the expected systolic pressure (for instance, 175 mm Hg). The stethoscope, which has been placed over the brachial artery, is able to discern no sound at this level, because the artery has been collapsed by the cuff pressure. The cuff pressure is then very gradually reduced, until sounds are heard. Gradual reductions of about 2 mm Hg per sec on the mercury manometer provides relatively accurate measurements of BP (Andreassi, 2000).

Korotkoff Sounds. The sounds produced by small amounts of blood passing through the cuff are called Korotkoff sounds, after the physician who first used this method in the early 1900s (Andreassi, 2000). Five Korotkoff phases are described in adults (O'Sullivan & Murray, 2001) as shown in Figure 1 below:

Figure 1. Five Korotkoff Phases [Source: Gedney & Sorenson, 2000].

The Korotkoff sounds are divided into five phases based on the loudness and quality of the sounds. According to Allen et al. (2004), the sounds that are associated with the five classical Korotkoff phases are clinically important for measuring systolic and diastolic blood pressures.

The frequency ranges of the sounds have been described by simply using the overall peak frequencies within each phase by Fourier methods; however, Allen et al. suggest that such analysis may be missing potentially useful clinical information.

Phase 1: Loud clear tapping or snapping sounds are heard. They grow louder as the cuff is deflated.

Phase 2: A succession of murmurs is heard. Sounds may disappear during this phase if the cuff is deflated too slowly.

Phase 3: The sounds become louder and have thumping quality similar to phase 1.

Phase 4: The thumping sounds of phase 3 are abruptly replaced by a muffled sound.

Phase 5: All sounds disappear. This phase is absent in some people (Gedney & Sorenson, 2000).

The pressure on the manometer is recorded when the first sound is heard with each pulsation. This is the systolic pressure (SBP) and, for a normal adult, ranges between 95 and 140 mm Hg, with 120 mm Hg being average (Andreassi, 2000). The pressure in the cuff is then reduced further, until the sounds are no longer heard. When the sounds disappear, the manometer reading at that point indicates diastolic pressure (DBP). Normal diastolic pressure ranges between 60 and 89 mm Hg for the adult.

According to Andreassi, the Korotkoff sounds are thought to be caused by blood jetting through the partly collapsed artery. "The jet causes turbulence in the open artery beyond the cuff, and this sets up the vibrations heard in the stethoscope" (Andreassi, 2000, p. 305). This technique is known as the auscultatory method of obtaining blood pressure, and is considered to be adequate for the clinician who is mainly concerned that patients fall within a normal range; however, for psychophysiological research, it is necessary to have automated, accurate techniques that enable frequent measurements of blood pressure. According to Sebald, Bahr, and Kahn (2002), auscultatory blood pressure measurement uses the presence and absence of acoustic pulses that are generated by an artery (i.e., the so-called Korotkoff sounds), which are detected with a stethoscope or a sensitive microphone, to noninvasively estimate systolic and diastolic pressures. "Unfortunately, in high noise situations, such as ambulatory environments or when the patient moves moderately, the current auscultatory blood pressure method is unreliable, if at all possible" (Sebald et al., 2002, p. 1038). Empirical evidence to date suggests that the pulse beneath an artery occlusion travels relatively slow when compared with the speed of sound. Therefore, by placing two microphones along the bicep muscle near the brachial artery under the occlusion cuff, a similar blood pressure pulse appears in the two microphones with a relative time delay. On the other hand, the acoustic noise appears in both microphones simultaneously. With a narrowband signal, the microphone signal phasing information is adequate for distinguishing between acoustic noise and the blood pressure pulse. By selecting the microphone placement correctly, subtraction of the two signals will enhance the information signal and cancel the noise signal (Sebald et al., 2002).

It should be pointed out as well that the systolic reading is obtained when the heart is contracting to push blood into the arteries, whereas the diastolic reading is obtained when the heart relaxes between beats. However, there are no data on the pattern of the Korotkoff phases in the normal population (O'Sullivan, Allen & Murray, 2002). A study by O'Sullivan and colleagues was designed to describe the pattern of Korotkoff phase distribution in adults and children; to measure the duration of each of the phases; and to describe the differences between adults and children. The researchers used a total of 57 children (7 to 8 years old) and 59 adults (median age 47 years, range 30 to 62 years) in their study. The researchers report that the pressure in the arm cuff was deflated using a device that provided a consistent rate of deflation. The Korotkoff sounds were recorded to MiniDisc from the bell of a stethoscope and each sound was described as a Korotkoff phase I, II, III, or IV. The results of this study showed that the most common pattern of Korotkoff phase distribution was for all five phases to be present (children [23/57; 40%], adults [24/59; 41%]). Phases I and IV were reported to be more common in children than in adults (56/57 [98%] v 47/59 [80%]; P =.002 for phase I; 52/57 [91%] v 44/59 [75%]; P =.018 for phase IV). Phases II and III were found to be less common in children than in adults (32/57 [56%] v 50/59 [85%], P =.001 for phase II; 27/57 [47%] v 45/59 [76%], P =.001 for phase III). In addition, Phases I and IV were longer in children (median 3.9 [interquartile range, IQR 2.1 to 6.7] and 6.7 [IQR 3.2 to 9.8] sec, respectively) compared with the results reported for adults (1.3 [IQR 0.7 to 2.7] and 1.7 [IQR 0.3 to 2.6), P

Another measure of blood pressure determined by the difference between systolic and diastolic is called pulse pressure. Mean arterial pressure (MAP) refers to the average pressure during the cardiac cycle and is estimated by the following: MAP = a…"(SBP - DBP) + DBP. Some commercial BP measuring equipment provides digital readouts of MAP along with systolic and diastolic pressure. Papillo and Shapiro (1990) observed that MAP is an important measure of BP because it reflects the average effective pressure that drives the blood through the circulatory system. The MAP must be sufficient to cause the cardiac output of blood to flow through the resistance in the blood vessels (Andreassi, 2000).

Tursky (1974) reported that the auscultatory method leads to an underestimate of systolic blood pressure. According to Andreassi, this is because the pressure in the cuff must be lower than that in the artery in order for Korotkoff sounds to be heard. A problem also exists in measuring diastolic pressure by this means, because it, too, depends on changes in sound. Tursky et al. (1972) developed an automated constant-cuff pressure system to help overcome this error of measurement. According to Andreassi, this technique serves to determine the relationship between a fixed-cuff pressure and arterial pressure at each heartbeat.

The presence and absence of the Korotkoff sound is then used to establish a median pressure. The system was tested on a patient who had arterial pressure recorded directly from the brachial. artery of the left arm while systolic pressures were obtained from the right arm with the constant-cuff procedure. Measures on five sets of 32 beats indicated a close correspondence in systolic pressure obtained with each method (all comparisons used were less than 2 mm. Hg apart) (Andreassi, 2000).

Gunn, Wolf, Black, and Person (1972) briefly described a portable device for the automatic measurement of blood pressure. Since that time, ambulatory blood pressure monitoring devices have become increasingly miniaturized and can provide accurate measures of blood pressure over a 48-hr period. The numerous noninvasive BP measures are recorded for later downloading into a computer for detailed analyses. The instrument can be worn by a freely moving person, enabling the continuous recording of blood pressure as the individual responds to physical or psychological demands that occur during the course of a day (Harshfield & Pulliam, 1992). The use of these portable devices has great potential for researchers who wish to study BP reactions to daily events, and for physicians desiring to measure effects of antihypertensive medications. Contemporary commercially available units have become lighter in weight (less than 16 ounces) and can record systolic, diastolic, and mean arterial pressure as well as HR. A hospital nursery was the setting where ambulatory monitoring was used to measure BP and heart rate in newborn infants (Hall, Thomas, Friedman, & Lynch, 1982). The device used in this case detected pressure pulsations in the cuff and recorded them automatically. The lowest BP readings were obtained when the 77 infants were sleeping (78 systolic, 40 diastolic), and the highest (82 systolic, 45 diastolic) occurred while they were sucking. The HR was lowest while they slept (126 BPM), and it was highest when they cried (144 BPM) (Andreassi, 2000).

The Del Mar Avionics Blood Pressure Monitor is a non-invasive device which automatically records a patient's blood pressure. The compact unit allows the subject to pursue normal daily activities while blood pressure measures are computed automatically and stored in memory. In actual operation, a transducer is secured over the patient's brachial artery beneath a conventional cuff which is then inflated by a built-in pneumatic pump. As the cuff bleeds, a transducer is used to detect the Korotkoff sounds (Baum & Singer, 1982). The aim of a study by Allen et al. (2004) was to compare features associated with the different phases of the Korotkoff sounds that were obtained during blood pressure measurement using a joint time-frequency analysis (JTFA) technique. The researchers used a single operator who recorded Korotkoff sounds from 25 healthy subjects using a measurement system comprising cardiology stethoscope, microphone, amplifier and recording system for computer sound digitization, and a MiniDisc system for playback to the cardiologist for subsequent Korotkoff phase classification. The results of the Allen et al. study showed that by using this system, the phase classification by the cardiologist is repeatable, with no significant differences being shown in the number of sounds allocated to phases on two separate recording assessments.

The digitized sounds were processed using a MATLAB-based short-time Fourier transform JTFA technique and differences in time, frequency and amplitude characteristics between the phases compared. It was also shown that on average, phase III had the largest overall amplitude and high frequency energy. Phase II was reported to have the greatest high frequency component and longest murmur, and was visibly the most complex phase in terms of time and frequency content. By contrast, phases IV and V were reported to have the lowest amplitude and frequency components. Generally speaking, the statistically significant transitions between phases were:

Phase I to II with increases in high frequency (224 to 275 Hz) (p < 0.01) and sound duration (49 to 98 ms) (p < 0.0001);

Phase II to III with a significant decrease in sound duration (to 37 ms) (p < 0.0001);

Phase III to IV with decreases in maximum amplitude (0.95 to 0.25), highest frequency (262 to 95 Hz), and relative high frequency energy of the sounds (0.61 to 0.10) (all p < 0.0001); and,

Phase IV to V with decreases in the maximum amplitude (0.25 to 0.13) (p < 0.0002) and high frequency energy (0.10 to 0.03) (p < 0.005).

This study demonstrated that joint time-frequency analysis of Korotkoff sounds was able to identify characteristic differences that are associated with the different phases classified by the expert cardiologist (Allen et al., 2004).

Preeclampsia-eclampsia. This condition, also known as pregnancy-induced hypertension, is a common, multifaceted disorder of pregnancy. It manifests after twenty weeks' gestation, except in the case of gestational trophoblastic disease, when the syndrome can occur in the first trimester as well, and its cause remains unknown (Fienbloom, 2000). Preeclampsia-eclampsia is characterized by high blood pressure and the presence of protein in the urine, with or without edema (swelling) of the legs, arms, and face. In spite of almost five decades of research devoted to the problem, preeclampsia remains a major contributing factor to illness and even to death of women and babies. The condition affects up to 6 or 7% of all pregnancies and can be superimposed on the ordinary kind of hypertension (high blood pressure) that some women have prior to becoming pregnant or that develops as pregnancy progresses (Fienbloom, 2000).

The known risk factors for developing preeclampsia are first pregnancy, age over forty, African-American background, family history of pregnancy-induced hypertension, chronic high blood pressure (hypertension), chronic kidney (renal) disease, antiphospholipid syndrome, diabetes, being pregnant with twins, and high levels of the normally present amino acid homocysteine (a genetic abnormality that can be treated with large doses of folic acid). An association between preeclampsia and mutations in genes that encode for blood-clotting proteins has been found (Feinbloom, 2000).

Blood pressure and urinary protein levels are routinely checked during prenatal visits to detect preeclampsia early. The accumulation of fluid in the skin of a pregnant woman, especially in the hands and face, is a sign of preeclampsia. While edema, particularly in the legs, is normal in pregnancy, if it is accompanied by rapid, sudden weight gain preeclampsia is suspected. Preeclampsia can also cause symptoms, varying in intensity, of upper-abdominal pain, nausea, and vomiting, usually with but some times without elevated blood pressure or protein in the urine. When these symptoms are present, preeclampsia is a consideration, particularly when blood abnormalities constituting what is known as the HELLP syndrome are also present.

The HELLP syndrome has three defining characteristics, from which the acronym "HELLP" is derived: hemolysis (destruction of red blood cells), elevated liver enzymes in the blood (evidenced by inflammation of the liver), and low platelet counts. However, the HELLP syndrome can result in problems of its own. For instance, a 1999 study identified as one likely cause of the HELLP syndrome a genetic defect, shared by the fetus and the pregnant woman, in the processing of fatty acids. The rationale in this case was that fatty acids that are not metabolized by the fetus tend to accumulate in the woman's blood and are toxic to her liver because she cannot process them either. The measurement of liver enzymes, platelets, and uric acid can help clinicians in distinguishing between preeclampsia and worsening chronic hypertension uncomplicated by preeclampsia (Feinbloom, 2000).

The risks to the fetus associated with preeclampsia include intrauterine growth disturbance, stillbirth, placental abruption, and prematurity, when the baby is purposely delivered early to prevent other problems and safeguard the health of the woman; the risks to the mother include convulsions (known as eclampsia when occurring withiin the context of preeclampsia); hemorrhage into the brain, with possible permanent neurological deficits; loss of vision (usually temporary); hemorrhage into the liver; kidney failure; and, at the extreme, death (Feinbloom, 2000). Tests of fetal health in late pregnancy are used when preeclampsia is present; such tests help determine whether it is safe for the fetus for the pregnancy to continue to fruition (Feinbloom, 2000).

The only treatment for preeclampsia to date is ending the pregnancy through birth of the baby, either through induction or by cesarean section (Feinbloom, 2000).

The results of previous studies of the effectiveness of taking aspirin during the second trimester in preventing preeclampsia in women at increased risk for this disorder have been inconclusive; however, a high-calcium diet (including supplements) has been shown to be effective in prevention. Feinbloom reports that preeclamptic mothers must be carefully monitored for seventy-two hours following delivery because eclamptic convulsions can occur during this time. "In rare cases, convulsions occur after delivery when there were no signs of preeclampsia before labor and delivery" (Feinbloom, 2000, p. 304). In some cases headache, confusion, an increase in blood pressure, abdominal pain, nausea, and vomiting marked impending convulsions. If convulsions have occurred or seem imminent, the standard treatment is magnesium sulfate administered intravenously (Feinbloom, 2000).

The research was consistent in noting that although much research has been devoted to this area, the cause of preeclampsia is still unknown. One feature of preeclampsia demonstrated in the studies of German physician Hans Schobel and his colleagues was a markedly increased tone (state of constriction) of the smooth muscles in the woman's arteries, resulting from excess stimulation of these muscles by the nerves that control them; however, precisely how this hyperstimulation arises remains a question to be addressed by additional research (Feinbloom, 2000). A study organized by the National Institutes of Health has demonstrated that long before preeclampsia develops, there is a reduction in blood vessels of the chemical prostacyclin, which causes them to dilate in relation to the chemical thromboxane, which causes them to constrict. "We are just beginning to get a handle on the biochemical basis for preeclampsia" (Feinbloom, 2000, p. 309).

Blood Pressure and Testing for Preeclampsia. According to Richard I. Feinbloom (2000), blood pressure is measured at each prenatal visit. As noted above, an inflatable cuff is secured over the upper arm just above the elbow. A stethoscope is placed on the artery that passes under the crease at the elbow. The cuff is inflated to stop the pulse below the cuff and gradually deflated. The upper reading of the blood pressure, called the systolic pressure systole refers to the contraction of the heart when blood is ejected with maximum force into the blood vessels), is the reading on the gauge when the pulse sounds first become audible. The lower reading, or diastolic pressure (diastole refers to the filling, noncontracted phase of the heart cycle), is the gauge reading when the pulse is no longer audible. The gauges are calibrated in millimeters of mercury; therefore, a pressure of 120 means that the pressure will balance or support a column of mercury 120 millimeters (about five inches) high in a thin tube. The systolic and diastolic readings are expressed as a fraction: the numerator is the systolic pressure, and the denominator is the diastolic pressure (Feinbloom, 2000).

According to Lynch (1985), people have come to attach meaning to blood-pressure numbers in a way that has made it the preeminent indicator of health and illness. A pressure reading of 140/90 is regarded as the upper limit of normal; if either figure is higher, the blood pressure is considered too high (hypertension). According to Fienbloom, blood pressure tends to vary in a predictable way during pregnancy; for example, there is a normal dip of about five millimeters in the systolic and diastolic pressures during the first and second trimesters (Feinbloom, 2000).

According to Lynch, blood pressure is a measure of the force that liquid blood exerts against the walls of blood vessels throughout the body during the cardiac cycle. With each heartbeat, two or three ounces of blood is pumped under pressure into the major artery that exits the heart, the aorta. The aorta subdivides into smaller branches throughout the body. The smaller arteries lead into a system of microscopic vessels, the arterioles, which have the capacity to dilate and constrict (1985).

Blood pressure determination is one of the most important serial measurements made in pregnancy. A blood-pressure reading over 140/90 occurring with protein in the urine after the twentieth week defines preeclampsia, a relatively common disorder with important risks for the woman and the fetus. Blood-pressure readings are also essential in monitoring women who are being treated for established hypertension whether or not it is complicated by preeclampsia (Feinbloom, 2000).

The condition known as toxemia includes pre-eclampsia and eclampsia, and occurs in about 3% to 5% of all pregnancies, most typically in the third trimester. This condition, which tends to run in families, is more common in women during their first pregnancy and in those who carry twins. Pre-eclampsia is identified by protein in the urine, swelling of the extremities, increased reflexes, and an abnormal rise in blood pressure. Eclampsia is the continuing progression of this disease with advanced involvement of the liver, kidney, blood and brain, often heralded by seizure activity. Toxemia of pregnancy can result in miscarriage, intrauterine growth retardation, and death. The disorder is generally treated with bed rest, salt restriction, antihypertensive drugs, magnesium, and early delivery when indicated (Griffith & Wood, 1997). Multiple population surveys since the 1960's have shown that women have higher percentages of body fat than men. Women also have higher HDL cholesterol (the "good" type) than men at all ages. Estrogen appears to be the main factor responsible for both of these effects. High blood pressure is responsible for 39% of all congestive heart failure cases in men; however, it causes 59% of cases in women; in fact, diabetic women experience a twofold greater risk for heart disease than diabetic men (Griffith & Wood, 1997).

According to Baum et al. (1992), pregnancy is a screening test for risk of ultimate hypertension. "Women who are normotensive during pregnancy, especially after the age of 25, have a low risk of future hypertension" (p. 213). Gestational hypertension, termed transient hypertension by the newest recommendations (National High Blood Pressure Education Program, 1990), is distinct from preeclampsia and may foretell future risk of hypertension (Chesley, 1980).

Baum et al. note that the literature on this subject remains confusing, because a clear distinction has not been made in most studies between gestational hypertension and preeclampsia. The evidence to date, though, is that preeclampsia does not appear to constitute a risk factor for future hypertension (Chesley, 1980). If a clinician requires that women with a true diagnosis of preeclampsia have significant proteinuria (i.e., at least 300 mg/l in a 24-hour collection or 1 g/l in a random collection) and if it is assumed that true preeclampsia occurs in primagravida, then it can be inferred that a diagnosis of gestational hypertension either if proteinuria is absent or in the absence of data on proteinuria if the pregnancy is in a multiparous woman. The data have been analyzed in this manner by Chesley and others for a number of studies, and they find that the future prevalence of hypertension in women who have had gestational hypertension is 40%-74%. In two subsequent series, the prevalence was 36% and 42% (Lindeberg, Ayelsson, Jorner, Maluberg, & Sandstrom, 1988; Svensson, Aldersch, & Hansson, 1983).

The incidence of diabetes developing many years after gestational hypertension is four times the expected rate (Chesley et al., 1976), again demarcating the overlap between the ultimate risk of hypertension and of diabetes. According to Bauman, Maimen, and Lauger (1988), women with hypertension during the third trimester of pregnancy have been shown to have hyperinsulinemia in response to an oral glucose tolerance test, in comparison to normotensive control women. In fact, both of these groups of women experienced similar normal glucose tolerance curves, and had equivalent circulating levels of placental lactogen, thought to be one factor conferring the insulin resistance of pregnancy. Therefore, gestational hypertension, like gestational diabetes, appears to be associated with an even greater degree of insulin resistance than that normally seen in pregnancy (Baum et al., 1992).

Gender-Related Stressors. When humans are confronted with stressful situations, their bodies undergo certain physiological changes that can then be measured and studied to determine their impact, if any, on the human body. The human heart and circulatory system respond to the various metabolic requirements during periods of exercise by increasing blood flow to the active areas and by decreasing the flow to less active areas. These metabolic requirements are used by researchers to determine the baselines for comparison purposes, and for making changes in the various assessments for testing purposes. In studies of acute stress men typically respond more strongly to stressors than do women. In particular, men have been shown to exhibit greater systolic blood pressure increases than do women during and after challenge, and in some cases women show greater heart rate responses than do men (Eisler & Hersen, 2000). For instance, in a series of studies by Light, Turner, Hinderliter and Sherwood (1993), men were shown to demonstrate greater systolic blood pressure increases to a variety of stressors; however, they also showed slower return to systolic and diastolic baseline blood pressure levels as compared to the responses of women.

According to Baum, Krantz and Singer (1983), much remains unknown about precisely what events may result in a physiological reaction that may cause an imbalance in human cardiovascular homeostasis, because the sources of such catalysts are wide ranging, highly varied, and in many cases entirely subjective. Even in the case of specific physical responses, an event triggered in the kidney might in turn feed back to the central nervous system via a blood-borne or neural message, or both, to initiate a particular cardiovascular operation aimed at restoring homeostasis (Baum, Krantz & Singer, 1983). Cardiovascular endurance is the body's ability to perform large muscular activities such as running, walking, bike riding, or swimming over an extended period (McCardle, Katch & Katch, 2001). This ability is dependent on the cardiovascular system's ability to pump blood from the heart, which carries nutrients and most importantly oxygen to the working muscles. Cardio-respiratory endurance is the functional capability of the heart, lungs, and blood vessels to distribute oxygen and energy substances to the working muscles, combined with the capability of the working muscles to extract those delivered substances efficiently for energy production over sustained periods of time.

In sum, cardio-respiratory endurance is the human body's capability to receive and utilize oxygen, carbohydrates, and fats to produce energy (McCardle, Katch & Katch, 2001). The human cardiovascular system is remarkable in its ability to provide for the needs of the body in this regard. When the healthy human body is at rest, the cardiovascular system has little difficulty supplying oxygen and fuels to the tissues. The system removes waste products easily and helps maintain a stable cellular environment (Blair, 1996).

The human cardiovascular system also conveys blood through vessels to and from all parts of the body, carrying nutrients and oxygen to tissues and removing carbon dioxide and other wastes. The cardiovascular system in the human body is a closed tubular system in which the blood is propelled by a muscular heart (Cardiovascular system, 2004). Two circuits, which are known as the pulmonary and the systemic, consist of various arterial, capillary, and venous components. The primary function of the heart is to serve as a muscular pump which sends blood into and through vessels to and from all parts of the body (Cardiovascular system, 2004).

The regular beating of the heart is maintained by the inherent rhythmicity of cardiac muscle; in fact, no nerves are located within the heart itself, and no outside regulatory mechanisms are necessary to stimulate the muscle to contract rhythmically as shown in Figure 2 below (Cardiovascular system, 2004). However, these processes are significantly altered during periods of stress and threats to personal safety.

Figure 2. Conducting System of Human Heart [Source: Novartis, 1995].

Papillo & Shapiro (1990) refer to the role that the cardiovascular system plays in maintaining homeostasis. According to Gendolla (1998), this role can be described as being a transport system tasked with the function of providing the organism with nutrients and oxygen and disposing of metabolic waste. "Whenever an organism works intensively (i.e., expends a large amount of effort), the cardiovascular system also has to work with high intensity to support the functioning of the organism. Therefore, indicators of the intensity with which the cardiovascular system works should be valid measures of effort expenditure" (1998, p. 114). According to Krantz and Falconer (1995), the customary indices of the working intensity of the cardiovascular system are:

Determinations of heart rate (this is the frequency of pulse beats within a specified period of time),

SBP (maximal pressure against the vessel walls following a heartbeat); and Diastolic BP (DBP; minimal pressure between heartbeats).

As noted above, cardiovascular homeostasis in humans is a highly complex process, and may involve any number of physical and psychological responses. Obrist (1981 in Gendolla, 1998) demonstrated that cardiovascular responses are also a function of the difficulty of cognitive demands, which are less dependent on metabolic processes than are physical responses. As a result, cognitive effort (as well as physical effort) is sharply correlated with high reactivity of the cardiovascular system. "It is important to emphasize that these effects could not be explained as reflecting anxiety or threat (i.e., emotional rather than motivational processes) because they were observed in both approach and avoidance settings" (Gendolla, 1998, p. 113).. Further, according to other research since Obrist, it has been shown that heart rate increases in particular are linked to activity and motivation, while threat and anxiety are correlated with electrodermal responses (Gendolla, 1998).

Differences in adrenergic receptor distribution and sensitivity may underlie differences in vascular reactivity to acute stressors, and it is assumed that cardiovascular reactivity in the laboratory is a meaningful long-term predictor of cardiovascular disease (Eisler & Hersen, 2000).

In response to standard laboratory stressors such as mental arithmetic, males consistently show higher levels of urinary epinephrine than females. For instance, Frankenhaeuser, Dunne, and Lundberg (1976) determined that after repeated venipuncture and a frustrating cognitive task, males, but not females, showed a significant increase in epinephrine. Employing plasma rather than urinary epinephrine measures, Forsman and Lindblad (1983) discovered similar gender-related responses to a mental challenge task. Pre-task levels of epinephrine were almost identical for men and women; however, during periods of stress, men's epinephrine levels became significantly higher than women's epinephrine levels.

Gender differences in systolic blood pressure changes were also noted, with men showing greater reactivity than women; however, no gender differences in heart rate responses were identified. According to Polefrone and Manuck (1987), the absence of heart rate effects in the presence of different levels of epinephrine should not be viewed as surprising because differences in epinephrine do not necessarily predict differences in heart rate reactivity. "Direct sympathetic neural influences are often more important in regulating heart rate" (Eisler & Hersen, 2000). However, gender is not the only individual difference variable that is related to stress.

Race and Ethnicity.

Race and ethnicity also appear to be related to the hormones that may result in hypertension and research has suggested differences in biological activity and specific disease morbidity and mortality that are relevant for the study of stress. For instance, cardiovascular reactivity among African-Americans differs from that exhibited by white Americans, and essential hypertension is twice as prevalent among African-Americans; in fact, even in people without hypertension, African-Americans tend to exhibit higher rates of resting blood pressure (Eisler & Hersen, 2000). Sympathetic neural activity during stress may also serve to contribute to chronically high blood pressure, and it is possible that these adrenergic responses may contribute to cardiovascular hyperactivity in African-American individuals (Anderson, 1989). Anderson (1989) reported the importance of the fact that substantial heterogeneity exists within black populations, including variation in blood pressure, and that substantial overlap in the two populations is likely.

Hypertension, which is defined as a systolic pressure of 140 mmHg or diastolic pressure of 90 mmHg or greater, can lead to heart attacks, kidney failure, and strokes. Of the ethnic minority groups, adult African-Americans are at greatest risk with 37.2% of males and 31.1% of females having hypertension. This is compared to a hypertension prevalence rate of 25.3% and 18.3% of Euro-American males and females, respectively. Among Hispanic-Americans, hypertension is present in 26.7% of males and 21% of females (National Center for Health Statistics, 1996).

The majority of surveyed Asian-American groups showed lower rates of hypertension than found in the general population. Among a sample of Korean-Americans, 11% of males and 12% of females reported high blood pressure. However, there is little information available for hypertension among Pacific Islanders, American Indians, or Alaskan Natives, although the increasing incidence of obesity in these groups would lead to a prediction of future increases in this condition (Eisler & Hersen, 2000). Among the Navajo, 23% of the males and 14% of females had hypertension. At any rate, blood pressure can be lowered through weight reduction, limited ingestion of salty foods, and physical exercise, as well as with medication (Eisler & Hersen, 2000).