Korotkoff Phases and Diastolic Blood Pressure in Pregnancy

Introduction and Background

Researchers in the field of family systems medicine have long recognized the association between psychosocial stressors and the onset and exacerbation of various illnesses (McDaniel, 1992). Psychosocial distress has been implicated in the etiology and 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 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). Furthermore, the prematurity rate rises with increased blood pressure, related both to premature labor and premature termination of pregnancy; in addition, higher incidences of low birthweight have been reported among hypertensive patients 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 conditions represent an increased risk for future development of disease (Baum, McCabe, & Schneiderman, 1992). The course of both conditions is such that they may be attributed to the progressive insulin resistance characteristic of pregnancy that abates postpartum, but may have revealed an underlying predisposition to subsequent disease. Today, however, there is a lack of agreement among clinicians concerning the optimum blood pressure measurement device, and inconsistencies persist in practice with regard to the method by which blood pressure is measured. Accurate blood pressure measurement is an important clinical concern because raised blood pressure in pregnancy may have relatively acute and potentially serious consequences; consequently, accurate measurements throughout the pregnancy are essential.

In the United States, 50 million people are thought to have high blood pressure; about half are receiving treatment, and half of those treated successfully reduce their blood pressure to below 140/90. This leaves approximately 37 million people in the United States with persisting hypertension. The incidence of high blood pressure rises with age; it is more common in men under 50, but more common in women over age 65. Over age 70, the incidence of high blood pressure approaches two-thirds of the population. Hypertension is divided into two groups: primary or essential hypertension and hypertension 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 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 sampling — numerous readings are required to obtain a meaningful average; and (4) corrective action taken may be inappropriate (Kaplan, 1998). Blood pressure is a dynamic feature of pumping blood. Readings 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 during vigorous exercise (Kaplan, 1998). Because blood pressure can be affected by such a wide range of physiological and psychosocial factors, identifying the most efficacious means of measuring it, particularly during pregnancy, becomes all the more important.

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 vessels called arteries, which 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 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 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.

The increased prevalence among older women of hypertension, diabetes, and fibroid tumors 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 — placing both mother and fetus at risk for increased morbidity and mortality (Mansfield, 1986). Hypertension has also been associated with increased maternal morbidity and mortality in a number of studies. Intervening complications may include 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 the sample studied. As early as 1886, Galabin reported in his treatise on midwifery that when heart disease was "grave," one could expect 55% of cases to be fatal (p. 326, as cited in Mansfield, 1986). Patients with essential hypertension also have an increased likelihood of labor induction and cesarean section deliveries, with their ensuing complications (Mansfield, 1986).

Blood Pressure Measurement Methods and Korotkoff Sounds

Cardiac function tests are essentially attempts to measure certain variables reflecting the condition of the circulatory system under various conditions of exertion. The variables most commonly used include pulse rate and blood pressure (Matthews, 1973). Blood pressure refers to the pressure exerted by blood on the walls of the blood vessels. Systolic and diastolic blood pressure tend to increase during the performance of tasks (Baum, Krantz, & Singer, 1983). 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, both systolic and diastolic blood pressure could for the first time 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 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 from an acoustic transducer signal. The main advantages of the auscultatory method are: (1) similarity with the usual clinical measurement of BP; and (2) accurate detection of systolic and diastolic pressures on the appearance and disappearance of sounds. The main disadvantages are: (1) artifacts due to movement; and (2) difficulties in signal analysis due to physiological variations of Korotkoff sound patterns or poor signals. These difficulties can be overcome by appropriate signal processing, noise rejection, and/or ECG gating. With the oscillometric method, air volume variations in the cuff are detected during deflation. The maximum oscillation is related to mean arterial pressure; systolic and diastolic BP are determined by algorithmic interpretation of the shape of oscillometric amplitudes as well as heart rate. The main advantages of the oscillometric approach are: (1) the possibility of BP measurement when the Korotkoff signal is poor; (2) measurement of mean arterial BP; and (3) no need for a microphonic sensor. The main disadvantages are: (1) some oscillometric curves are difficult to read accurately; (2) oscillometry is very sensitive to movement; and (3) the accuracy of 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 Andreassi (2000), the true measurement of blood pressure can only be achieved through arterial penetration to insert a sensing device; however, direct intra-arterial measurement presents problems in research settings using human subjects because of discomfort 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 wrapped around the upper arm and 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 recorded as x/y: x is the systolic pressure and y is the diastolic. Systole refers to the contraction period of the heart, when blood is forced into the circulatory system, and diastole refers to the resting period, when the heart expands and receives another supply of blood. At each heartbeat, blood pressure rises to the systolic level; between beats, it drops to the diastolic level. As the cuff is inflated, a stethoscope is placed against the skin at the crook of the arm. As air is released, the first sound heard marks the systolic pressure; as the release continues, a dribbling noise is heard that represents the diastolic pressure.

In one common 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 placed over the brachial artery detects 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 second on the mercury manometer provide relatively accurate measurements of BP (Andreassi, 2000).

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). 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 associated with the five classical Korotkoff phases are clinically important for measuring systolic and diastolic blood pressures.

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 a 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 indicates diastolic pressure (DBP). Normal diastolic pressure ranges between 60 and 89 mm Hg for adults.

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 and is considered adequate for clinicians mainly concerned that patients fall within a normal range; however, for psychophysiological research, automated, accurate techniques enabling frequent measurements are necessary. According to Sebald, Bahr, and Kahn (2002), auscultatory blood pressure measurement uses the presence and absence of acoustic pulses generated by an artery — the so-called Korotkoff sounds — 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). By placing two microphones along the bicep muscle near the brachial artery under the occlusion cuff, a similar blood pressure pulse appears in both microphones with a relative time delay, while acoustic noise appears simultaneously. Subtraction of the two signals can therefore enhance the information signal and cancel the noise signal (Sebald et al., 2002).

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 phase; and to describe differences between adults and children. The researchers used 57 children (7 to 8 years old) and 59 adults (median age 47 years, range 30 to 62 years). Korotkoff sounds were recorded to MiniDisc from the bell of a stethoscope and each sound was classified as Korotkoff Phase I, II, III, or IV. The most common pattern was for all five phases to be present (children: 23/57, 40%; adults: 24/59, 41%). Phases I and IV were more common in children than in adults (Phase I: 56/57 [98%] vs. 47/59 [80%], P = .002; Phase IV: 52/57 [91%] vs. 44/59 [75%], P = .018). Phases II and III were less common in children than in adults (Phase II: 32/57 [56%] vs. 50/59 [85%], P = .001; Phase III: 27/57 [47%] vs. 45/59 [76%], P = .001). Phases I and IV were longer in children (median 3.9 [IQR 2.1 to 6.7] and 6.7 [IQR 3.2 to 9.8] seconds, respectively) compared with adults (1.3 [IQR 0.7 to 2.7] and 1.7 [IQR 0.3 to 2.6] seconds, P < .001). The researchers concluded that there are clear differences in the Korotkoff phases between adults and children, and that the length of phases II and III increases with age with a concomitant decrease in phases I and IV; however, the reasons for these differences remain unexplained (O'Sullivan, Allen, & Murray, 2002).

Another measure of blood pressure — 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 formula: MAP = 1/3(SBP − DBP) + DBP. Papillo and Shapiro (1990) observed that MAP is an important measure of BP because it reflects the average effective pressure that drives blood through the circulatory system.

Tursky (1974) reported that the auscultatory method leads to an underestimate of systolic blood pressure 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 measurement error. The presence and absence of the Korotkoff sound is used to establish a median pressure. Tests on a patient who had arterial pressure recorded directly from the brachial artery while systolic pressures were simultaneously obtained from the right arm with the constant-cuff procedure showed a close correspondence between the two methods, with all comparisons within 2 mm Hg of each other (Andreassi, 2000).

Ambulatory blood pressure monitoring devices have become increasingly miniaturized and can provide accurate measures of blood pressure over a 48-hour period. The instruments can be worn by a freely moving person, enabling continuous recording of blood pressure as the individual responds to physical or psychological demands during the course of a day (Harshfield & Pulliam, 1992). Contemporary commercially available units weigh less than 16 ounces and can record systolic, diastolic, and mean arterial pressure as well as heart rate. The aim of a study by Allen et al. (2004) was to compare features associated with the different phases of the Korotkoff sounds using a joint time-frequency analysis (JTFA) technique. A single operator recorded Korotkoff sounds from 25 healthy subjects using a cardiology stethoscope, microphone, amplifier, and recording system. The results showed that phase classification by the cardiologist was repeatable, with no significant differences in the number of sounds allocated to phases on two separate recording assessments. Phase III had the largest overall amplitude and high-frequency energy; Phase II had the greatest high-frequency component and longest murmur and was the most complex phase in terms of time and frequency content; Phases IV and V had the lowest amplitude and frequency components. 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 (0.61 to 0.10) (all p < 0.0001); and Phase IV to V with decreases in 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 can identify characteristic differences associated with the different phases as classified by an expert cardiologist (Allen et al., 2004).

Preeclampsia and Hypertensive Disorders of Pregnancy

Preeclampsia-eclampsia, 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 — and its cause remains unknown (Feinbloom, 2000). Preeclampsia is characterized by high blood pressure and the presence of protein in the urine, with or without edema of the legs, arms, and face. The condition affects up to 6 or 7% of all pregnancies and can be superimposed on preexisting hypertension (Feinbloom, 2000).

The known risk factors for developing preeclampsia include first pregnancy, age over forty, African-American background, family history of pregnancy-induced hypertension, chronic high blood pressure, chronic kidney disease, antiphospholipid syndrome, diabetes, twin pregnancy, and high levels of the amino acid homocysteine. An association between preeclampsia and mutations in genes encoding blood-clotting proteins has been found (Feinbloom, 2000).

Blood pressure and urinary protein levels are routinely checked during prenatal visits to detect preeclampsia early. While edema in the legs is normal in pregnancy, if it is accompanied by rapid, sudden weight gain, preeclampsia is suspected. Preeclampsia can also cause symptoms of upper-abdominal pain, nausea, and vomiting, sometimes without elevated blood pressure or protein in the urine. When these symptoms are present together with blood abnormalities constituting the HELLP syndrome, preeclampsia is a strong consideration.

The HELLP syndrome has three defining characteristics from which the acronym is derived: hemolysis (destruction of red blood cells), elevated liver enzymes in the blood (evidenced by liver inflammation), and low platelet counts. 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. Fatty acids not metabolized by the fetus tend to accumulate in the woman's blood and are toxic to her liver. Measurement of liver enzymes, platelets, and uric acid can help clinicians distinguish between preeclampsia and worsening chronic hypertension uncomplicated by preeclampsia (Feinbloom, 2000).

Risks to the fetus associated with preeclampsia include intrauterine growth disturbance, stillbirth, placental abruption, and prematurity. Risks to the mother include convulsions (eclampsia); hemorrhage into the brain, with possible permanent neurological deficits; loss of vision (usually temporary); hemorrhage into the liver; kidney failure; and death (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.

Although much research has been devoted to this area, the cause of preeclampsia remains unknown. One feature demonstrated in studies by German physician Hans Schobel and colleagues was a markedly increased tone of the smooth muscles in the woman's arteries, resulting from excess stimulation by the nerves that control them; however, precisely how this hyperstimulation arises remains an open question. A study organized by the National Institutes of Health demonstrated that long before preeclampsia develops, there is a reduction in blood vessels of the chemical prostacyclin — which causes dilation — relative to thromboxane, which causes constriction (Feinbloom, 2000).

Blood pressure determination is one of the most important serial measurements made in pregnancy. A reading over 140/90 occurring with protein in the urine after the twentieth week defines preeclampsia — a relatively common disorder with important risks for both woman and fetus. According to Baum et al. (1992), pregnancy is in fact 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 of the National High Blood Pressure Education Program, 1990) is distinct from preeclampsia and may foretell future risk of hypertension (Chesley, 1980).

The incidence of diabetes developing many years after gestational hypertension is four times the expected rate (Chesley et al., 1976), again demonstrating the overlap between the ultimate risk of hypertension and of diabetes. Women with hypertension during the third trimester of pregnancy have been shown to have hyperinsulinemia in response to an oral glucose tolerance test, compared to normotensive control women (Bauman, Maimen, & Langer, 1988). 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).

The condition known as toxemia includes preeclampsia and eclampsia and occurs in about 3% to 5% of all pregnancies, most typically in the third trimester. Preeclampsia 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).

Feinbloom reports that preeclamptic mothers must be carefully monitored for seventy-two hours following delivery because eclamptic convulsions can occur during this time. In some cases, headache, confusion, increased blood pressure, abdominal pain, nausea, and vomiting may signal impending convulsions. If convulsions have occurred or seem imminent, the standard treatment is magnesium sulfate administered intravenously (Feinbloom, 2000).