Skin blood flow in human adult thermoregulation: mechanisms and function

Skin Blood Flow

Thermoregulation is the regulation of temperature. More concretely it is the maintenance of a particular temperature of the living body. Organisms that do not have thermoregulation and protective functions would have been eliminated through natural selection. There are various strategies that the body uses to control temperature (Lim et al., 2008). These strategies are also utilized to control physiological homeostasis. When the entire body is heating there are certain temperature thresholds that are reach so that cutaneous vasodilation and sweating can take place (Charkoudian, 2003). These thresholds are referred to as the internal temperatures at which cutaneous vasodilation or sweating starts. In addition, the research found that blood skin flow control can be local and reflexive. This local control occurs as it pertains to warming and cooling of the skin. When the local area is in a warm environment veins and arteries expand to allow for blood flow. On the other hand when the local area is cold the veins and arteries narrow. There are certain factors that influence the thermoregulatory system including menopause and diabetes. These two factors can greatly alter skin blood flow and the way that the thermoregulatory system operates. During menopause hot flashes and night sweats occur as a result of hormonal fluctuations. Individuals with diabetes have a more difficult time regulating body temperature in extremely hot conditions.

Introduction

The manner in which the human body functions is intriguing on many different levels. Skin blood flow in Adult Human Thermoregulation is one of the most intriguing aspects of human function. Thermoregulation is the aspect of physiological function that ensures that human being maintain the proper temperature. There are different aspects of thermoregulation and the need for such regulation in the human body. Overall, The purpose of this discussion is to examine how Skin blood flow in Adult Human Thermoregulation works. The research will focus on the factors that can effect human skin blood flow and thermoregulation including menopause and diabetes.

Human circulatory system

Before a discussion about skin blood flow can ensue, there an explanation of the human circulatory system must occur. According to the National Institutes of health the heart and blood vessels are the two elements that compose the blood circulatory system. In addition there are four subsystems that makeup the circulatory system. These subsystems are as follows

Arterial Circulation- this is the aspect of the circulatory system that includes the arteries such as pulmonary arteries and the aorta. Arteries are defines as blood vessels that are responsible that carries blood away from the heart. According to NIH when arteries are healthy they are elastic and strong. Between heartbeats the arteries actually become narrow and arteries also assist in regulating blood pressure. Additionally the arteries branch off into arterioles which are smaller blood vessels. Both arteries and arterioles strong walls that permit them to "alter the amount and rate of blood flowing to different parts of your body ("Circulation and Blood Vessels")."

Venous Circulation - this subsystem has involves veins including the vena cavae and pulmonary veins ("Circulation and Blood Vessels"). Veins are defined as the blood vessels that are responsible for supplying blood to the heart. Veins are different from arteries in that they have thinner walls. In addition veins are able to increase in size to accommodate the quantity of blood passing through them ("Circulation and Blood Vessels").

Capillary Circulation- Capillaries are small blood vessels that are responsible for passing nutrients, oxygen, and waste between the blood and other parts of the body. In addition capillaries link the arterial and venous circulatory subsystems. . According to the NIH

"The importance of capillaries lies in their very thin walls. Unlike arteries and veins, capillary walls are thin enough that oxygen and nutrients in your blood can pass through the walls to the parts of your body that need them to function normally. Capillaries' thin walls also allow waste products like carbon dioxide to pass from your body's organs and tissues into the blood where it's taken away to your lungs ("Circulation and Blood Vessels")."

Pulmonary Circulation- Pulmonary circulation involves the movement of blood from the heart to the lungs and back to the heart again. Pulmonary circulation is inclusive of both arterial and venous circulation ("Circulation and Blood Vessels"). Blood that lacks oxygen is passed to the lungs from the heart. This is known as arterial circulation. In addition, blood with oxygen moves from the lungs to the heart through the pulmonary veins ("Circulation and Blood Vessels"). This is known as venous circulation.

Pulmonary circulation also requires capillary circulation ("Circulation and Blood Vessels").The Oxygen that is taken into the lungs through breathing passes through your lungs and into the blood through the many capillaries found in the lungs ( "Circulation and Blood Vessels"). In addition, Capillaries in the lungs also remove carbon dioxide from your blood so that your lungs can breathe the carbon dioxide out into the air ("Circulation and Blood Vessels").

The circulatory system is a critical aspect of thermoregulation. The circulatory system works in unison with the thermoregulatory system to provide skin blood flow. Now that we have provided an explanation of the circulatory system let us focus on thermoregulation.

Thermoregulation

Thermoregulation is defined as "the maintenance or regulation of temperature; specifically: the maintenance of a particular temperature of the living body ("Thermoregulation")." According to Lim et al. (2008) the capacity to perceive and normalize body temperature is an important aspect of human survival. In addition, "a deviation of ± 3.5°C from the resting temperature of 37°C can cause physiological impairments and fatality (Lim et al., 2008)."

The picture to the left is a depiction of how thermoregulation actually occurs and the process by which the body normalizes temperature. Thermoregulation is essential to the maintenance of the proper body temperature.

The authors explain that heat most likely played a significant part in the creation and continued existence of the first unicellular organism . The authors also explain that the capacity to perceive and control body temperature also contributed to the development of these unicellular organisms to multicellular cold blooded animals and warm-blooded mammals (Lim et al., 2008).

Organisms that do not have thermoregulation and protective functions would have been eliminated through natural selection. There are various strategies that the body uses to control temperature (Lim et al., 2008). These strategies are also utilized to control physiological homeostasis. For instance animals that are cold blooded regulate their temperature through reliance on external heat sources known as ectotherms (Lim et al., 2008). When the body temperature of cold blooded animals are low they are dormant. However when the body temperature rises they become active so that they can seek food and shelters. They are able to heat their bodies based on the temperature of the environment. On the other hand, people are endotherms because heat is derived from internal sources to control the body temperature. In addition in human beings body temperature is controlled by a combination of absorption, heat production and loss.

The authors explain that just as with "the first living cell on earth, thermo-sensitivity, thermoregulation, and thermo-protection remain a central part of physiological homeostasis and survival, and are necessary properties for living organisms to operate proficiently in their environment (Lim et al., 2008)."

For the purpose of this discussion the focus will be on physiological thermoregulation. According to Charkoudian (2003) physiological thermoregulation in humans is associated with s changes in heat dissipation (cutaneous vasodilation and sweating) and heat generation (shivering) which are caused by changes in both internal and external thermal stimuli (Charkoudian, 2003). The author explains that the primary control for thermoregulation is found in the preoptic/anterior hypothalamus (PO/AH) in the brain. Additionally information involving the internal (core) and surface (skin) temperatures is given to the PO/AH, which is then responsible for coordinating the applicable reaction (Charkoudian, 2003). In theory, this part of the human brain can be compared to a thermostat, that is responsible for initiating heat dissipation responses when it recognizes that body temperature is "too hot" and conserving or producing heat when body temperature is too cold (Charkoudian, 2003) .

So then it has been established that thermoregulation in the human body is responsible for regulating body temperature. Thus far the research has illustrated that cold-blooded animals are ectotherms while warm-blooded are endotherms. That is cold-blooded animals such as reptiles have thermoregulatory stems that are controlled by conditions outside of the body -- the environment. On the other hand warm-blooded animals have thermoregulatory systems that are governed by internal conditions. Now that a greater understanding of the human regulatory system has been garnered the discussion will focus on the Skin Blood Flow and Thermoregulation.

Skin Blood Flow and Thermoregulation

According to Charkoudian (2003) skin flow in human beings changes as thermal stress occurs. In fact thermoregulatory vasodilation in humans rises when thermal stress occurs. The author explains that when a human being is suffering from severe hyperthermia thermoregulatory vasodilation can increase skin blood flow to 6 to 8 L/min (Charkoudian, 2003). The skins response to extremely cold temperature is demonstrative of the role of thermoregulation in the human body.

The picture to the left depicts the various elements that are responsible for thermoregulation in human skin. The illustrations shows the various layers of skin along with the veins, arteries and capillaries of the circulatory system that assist in insuring that the thermoregulatory system works properly. The sweat glands are responsible for selectively removing materials from the blood the sweat glands then concentrates or alters these toxins, and secretes them for elimination from the body. The perspiration or sweat is then removed through the sweat pore. This has a twofold purpose: to remove toxins and thermoregulation (in this case cooling the body).

Thermoregulation involving perspiration is brought about by both internal and environmental heat and exercise. As it relates to the latter, there have been many studies related to exercise and thermoregulation. According to Marino (2004)

"thermoregulatory effector responses of humans and concluded that temperature regulation during exercise is dissimilar to temperature regulation during fever.

Essentially, Nielsen described the human thermoregulatory system during exercise as analogous to a thermostat, whereby the increase in core temperature is proportional to the metabolic rate and almost independent of the environmental conditions over a wide range. Since this early understanding of human thermoregulation during exercise, there have been a plethora of studies dealing with the human thermoregulatory system and its limitations during exercise

(Marino, 2004)."

The author also explains that this subject matter has lead to the study of thermoregulation during exercise under different types of environmental conditions (Marino, 2004). The author explains that it has been established that people have the capacity to thermoregulate proficiently during exercise when the ambient air is cool to moderate, however such thermoregulation has been more difficult during exercise in warm conditions (Marino, 2004). The author further asserts that, "an analysis of the average ambient temperatures of the cities in which the fastest times for distance events ranging from 5000 m to 100 km road race are set (are rarely above an average of ~14 8C (Marino, 2004)."

Indeed Skin blood flow responds to heat exposure and exercise. In most human beings both skin blood flow and vasodilation increase to allow for the dissipation of heat. When people are in cold environments vasoconstriction occurs (Charkoudian, 2003). The skin reduces the amount of heat that is lost and protects the body against hypothermia (Charkoudian, 2003). Therefore, altered control of skin blood flow has important clinical implications and can substantially impair the ability to maintain normal body temperatures (Charkoudian, 2003).

When environments are thermoneutral the resting skin blood flow is around

250 mL/min (Charkoudian, 2003). This results in heat dissipation of 80 to 90 kcal/h, which is identical to resting metabolic heat production (Charkoudian, 2003). When people are exposed to heat or exercise a rise in body temperature causes cutaneous vasodilation and sweating. Cutaneous vasodilation is responsible for significantly increasing blood flow to the skin (Charkoudian, 2003). This process is also responsible for convective transfer of heat from the interior of the body to the exterior of the body (Charkoudian, 2003). When Cutaneous vasodilation occurs the large increases in skin blood flow often necessitates greater cardiac output and redistribution of blood flow from other areas of the body, including the splanchnic area in which vasoconstriction occurs (Charkoudian, 2003).

The adjustments that are made are normally enough to reflect the demand for greater skin blood flow, so that the amount of oxygen getting to vital organs is not compromised. The author also explains that cutaneous vasodilation and the drying up of sweat decreases skin temperature, which is responsible for cooling the blood in the expanded skin vessels before it returns to the body's core. The author also explains that

"In general, skin blood flow and sweating continue to increase in proportion to internal temperature until a steady state is reached at which heat dissipation and heat generation are equal, and therefore body temperature is constant, or until maximal responsiveness is reached. When internal temperature decreases toward normal, sweating stops, and skin blood flow returns to normal. In this sense, thermoregulation represents a classic negative feedback loop (Charkoudian,

2003)."

When the entire body is heating there are certain temperature thresholds that are reach so that cutaneous vasodilation and sweating can take place (Charkoudian, 2003). These thresholds are referred to as the internal temperatures at which cutaneous vasodilation or sweating starts (Charkoudian, 2003). Additionally the occurrence of sweating or a vasodilator reaction as it relates to internal temperature is described as the slope of the skin blood flow or the internal temperature relationship following the reaching of the threshold (Charkoudian, 2003). This is why the body may have altered reactions in some situations. For instance, "lower skin blood flow at a given internal temperature during heat stress could be due to an increased threshold for vasodilation (such that vasodilation does not begin until a higher internal temperature is reached), a decrease in the sensitivity of the response, or some combination of both (Charkoudian, 2003)."

The picture above is a depiction of 2 cutaneous vasodilator responses as functions of internal temperature during body heating. The author explains that the responses shown have differing thresholds but their sensitivities are alike (Charkoudian, 2003). This leads to noticeable differences between responses as it pertains to the level of skin blood flow and as such heat dissipation for a certain level of internal temperature (Charkoudian, 2003). The author explains that issues that can change the threshold and/or sensitivity of cutaneous vasodilation include the status of reproductive hormones, circadian rhythm, heat acclimation, and exercise training (Charkoudian, 2003). When people are exposed to cold environments, skin blood flow is reduced as a result of cutaneous vasoconstriction (Charkoudian, 2003). The author explains "This results in a decrease in heat dissipation from the skin surface and less convective heat transfer from the core to the surface. With further body cooling, shivering begins (Charkoudian, 2003). The muscular contractions involved result in increased heat generation, which in combination with decreased heat dissipation helps to maintain core temperature in the face of cold exposure (Charkoudian, 2003)."

Thermoregulatory controls

Reflex control of Skin Blood Flow

There are different types of controls as it pertains to the human body and the thermoregulatory system. The first type of control that will be discussed is reflex control. According to (Charkoudian, 2003) cutaneous circulation in people is controlled by 2 populations of sympathetic nerves this type of control is different from other animals. The sympathetic adrenergic vasoconstrictor nerves and the sympathetic vasodilator nerves (Charkoudian, 2003). The sympathetic adrenergic vasoconstrictor nerves are generally well-known and understood (Charkoudian, 2003). On the other hand the sympathetic vasodilator nerves is not as well studied and it is only activated during hypothermia.

The author further explains that both the sympathetic vasoconstrictor and vasodilator nerves supply nerves to all areas of hairy (non-glabrous) skin. On the other hand areas of, hairless (glabrous) skin are supplied with nerves only by sympathetic vasoconstrictor nerves (Charkoudian, 2003). The author also explains that there are other factors that distinguishes glabrous and nonglabrous skin which is the presence of arteriovenous anastomoses (AVA). AVA are thick-walled, low-resistance channels for liquid that permit high flow rates directly from arterioles to venules. The authors explains that when skin is glabrous, AVA are plentiful and richly innervated by sympathetic vasoconstrictor nerves (Charkoudian, 2003). Because this is the case, the opening or closing of glabrous skin AVA can result in significant changes in skin blood flow (Charkoudian, 2003). On the other hand nonglabrous skin has limited AVA and is innervated by both sympathetic vasoconstrictor and vasodilator nerves (Charkoudian, 2003).

The author also explains that Sympathetic vasoconstrictor nerves are responsible for giving off norepinephrine. Norepinephrine combines with postsynaptic ?1- and ?2-receptors on cutaneous arterioles and AVA (Charkoudian, 2003). The article also explains that noradrenergic vasoconstrictor nerves discharges at least one co transmitter that is responsible for vasoconstriction (Charkoudian, 2003). Even studies involving animal models have found

"roles for neuropeptide Y (NPY) and/or adenosine triphosphate as adrenergic cotransmitters mediating cutaneous vasoconstriction,32,33 the identity of those that participate in human reflex vasoconstriction remains to be elucidated. The vasoconstrictor system in human skin is tonically active in thermoneutral environments. Therefore, subtle changes in the activity of this system during most daily activities are responsible for maintenance of normal body temperature with slight changes in activity or ambient temperature (Charkoudian, 2003)."

According to the author the aforementioned scenario occurs because minute fluctuations in skin blood flow can lead to significant changes as it pertains to heat dissipation. For instance, the author points out that when skin blood flow changes from resting neutral levels of 8 mL per 100 mL/min over the whole surface of the human body a doubling of heat transfer to the environment occurs. The transfer is significant because it allows an area of thermoregulation known as the "neutral" or "vasomotor" area. This is only made possible through changes in cutaneous vasomotor tone (Charkoudian, 2003). The author also explains that the vasoconstrictor system is also responsible for the decreases in skin blood flow that occur with cold exposure. Withdrawal of the activity of these nerves is responsible for 10% to 20% of the cutaneous vasodilation during hyperthermia (Charkoudian, 2003)."

When an individual is stricken with hypothermia skin blood flow can rise to as high as a 6 to 8 L/min or 60% of cardiac output (Charkoudian, 2003). The significant increass in the flow of blood to the skin are facilitated by activation of sympathetic vasodilator nerves (Johnson & Proppe, 1996; Rowell, 1983) The author explains that the sympathetic active vasodilator system in people is not tonically active in normothermia. Additionally it is only activated when internal temperature increases (Charkoudian, 2003). These increases occur during exercise or when human being spend time in the heat (Charkoudian, 2003).

Local Control of Skin Blood flow: Local Warming and Cooling of the Skin

In addition to the reflex control already described. There also exist local control of skin blood flow. This local control occurs as it relates to both the warming and cooling of the skin. Charkoudian, 2003 asserts that the local temperature any particular part of the skin is vital to the regulation of skin blood flow at that part of the skin (Charkoudian, 2003). The author explains that local warming of the skin is responsible for direct and substantial vasodilation of the part of the skin that is warmed. When people are healthy a continuous local temperature of 42°C will be responsible for the dilation of skin blood vessels as far as they can expand (Charkoudian, 2003). According to the author the vasodilator response to this local warming stimulus has two phases (Charkoudian, 2003). When skin is exposed to the aforementioned temperature for the first 3-5 minutes there is a fast rise in blood flow in the skin (Charkoudian, 2003). After this initial increase there is a small decrease and then a reduced vasodilation having a plateau after about 25 minutes (Charkoudian, 2003).

According to the author during the first rapid phase vasodilation when local warming occurs it is extremely dependent upon the local activity of sensory nerves. This dependency exist because only local neural instruments are beeded because of topical application of a local anesthetic (Charkoudian, 2003). Additionally, the sensory nerves that govern the local reaction to heat are mainly composed of C-fiber afferents that once motivated, produces localized vasodilation through antidromic release of calcitonin gene -- related peptide (CGRP),neurokinin A, and substance P (Charkoudian, 2003). These are afferents that are fueled by capsaicin (Charkoudian, 2003). Capsaicin is significant because it joins to vanilloid receptors (VR1) that are located on nerve endings. This joining results in depolarization through the opening of a cation channel (Charkoudian, 2003).

The result of this process is a local feeling of heat and vasodilation. The author further explains that VR1 is also immediately activated by heat and low pH balance (Caterina et al., 1997;Charkoudian, 2003). The author also explain that the newly found aspect of the vanilloid receptor family known as VRL3 or TRPV3 is localized to human skin (Xu et al., 2002; Smith et al., 2002). Additionally, TRPV3 has been localized in keratinocytes of the outermost portion of the skin (Charkoudian, 2003).The aforementioned receptor is perceptive of temperature but the receptor is also capsaicin insensitive. This means that it is very likely that this particular receptor contributes to stimulation of cutaneous heat-sensitive afferents at higher local temperatures along with VR1 (Charkoudian, 2003). The author also explains

"To investigate the role of these heat-sensitive afferents at lower levels of local temperature, we measured skin vasodilation at local temperatures between 20?C

and 42?C in combination with local capsaicin treatment to chemically stimulate heat-sensitive sensory nerves. Using various combinations of chemical (capsaicin)

and thermal stimulation of small areas of skin, we showed that activation of these nerves contributes to local warming vasodilation at temperatures ranging from 29?C to 40?C (Stephen et al. 2001)."

According to the author even though a barrier of local neural activity hinders the initial, rapid vasodilation to local warming, it has no effect on the second, slower phase of the response. The article also confirms that nitric oxide is significant as it pertains to both the start and the preservation of the aforementioned phase. The author further explains that "Local L-NAME (a nitric oxide synthase inhibitor) inhibits this vasodilation when administered either before local heating or after vasodilation has reached a plateau (Kellog et al., 1999; Minson et al., 2001:Charkoudian, 2003)." 60,63

Local Cooling of the Skin

In addition to local warming of the skin, the skin can also be cooled locally. According to the author Local cooling of the skin results in a substantial localized vasoconstriction that has the capacity to reduce skin blood flow to zero. The vasoconstriction is dependent upon "local activation of adrenergic nerves and is reversed by local noradrenergic inhibition with bretylium (Pergola et al. 1993).An increase in the affinity of postsynaptic ?-receptors (especially ?2-receptors) with decreasing temperature also contributes to this local vasoconstriction.(Vanhoute et al. 1985; Flavahan 1985) This response does not require intact connection to the central nervous system because it is not affected by proximal neural blockade (Charkoudian, 2003)."

This illustration is a depiction of the local warming and cooling of the skin. The illustration depicts the differences in size in the vein and arteries that occurs with a change in temperature.

Overall this section of the discussion explains that control of skin blood flow can be reflexive or local. When control is reflexive cutaneous circulation in people is governed by 2 populations of sympathetic nerves which separates people from other animals. The sympathetic adrenergic vasoconstrictor nerves and the sympathetic vasodilator nerves (Charkoudian, 2003). The sympathetic adrenergic vasoconstrictor nerves are generally well-known and understood (Charkoudian, 2003). On the other hand the sympathetic vasodilator nerves is not as well studied and it is only activated during hypothermia.

In addition the research found that local blood skin flow control. This local control occurs as it pertains to warming and cooling of the skin. When the local area is in a warm environment veins and arteries expand to allow for blood flow. On the other hand when the local area is cold the veins and arteries narrow. Now that a greater understanding thermoregulatory controls, let us focus on the factors that effect thermoregulation.

Factors that effect Thermoregulation

One of the most prominent issues that effects thermoregulation is significant changes in hormones. This change is most notable to women during menopause when women often complain of hot flashes. According to Deecher & Dorries (2007) nearly 80% of all menopausal women will have hot flashes or flushes, which are technically called menopausal vasomotor symptoms (VMS). Many women also suffer from night sweats. (National Institutes of Health 2005). Many women first notice such symptoms during the per menopausal period These symptoms can start to occur in the premenopausal period (Soules et al. 2001). The author explains that menopause is proceeded by a change in hormonal fluctuations. Menopause begins one year after a women had has her last menstrual cycle. In addition the hormonal fluctuations can continue to effect women even throughout the final phase in menopause, known as postmenopausal (Rodstrom et al. 2002; Deecher & Dorries, 2007).

According to Deecher & Dorries (2007) the intensity and duration of hot flashes vary, from person to person. The authors explain that minor hot flashes usually come in the form of a passing while warning sensation. In some cases that are several symptoms associated with the hot flashes. Typically a woman experiences a "sudden and intense heat spreading over the upper body and face, reddening of the skin or flushing, and severe perspiration. In one survey, more than half of the symptomatic women reported that flushing was followed by chills and shivering (Kronenberg 1990; Deecher & Dorries, 2007).

The author also explains that there are some of the symptoms that women may experience during a hot flash. These symptoms are inclusive of nausea, anxiety, changes in breathing and heart rate, and pressure in chest and head. Some women also experience what are known as night sweats. Night sweats involve profuse sweating that causes a woman to be deprived of sleep (Woodward and Freedman 1994; Deecher & Dorries, 2007).

The author also reports that for some women VMS result in mood disturbances and a host of other physical ailments (Dugan et al. 2006; Kronenberg 1999; Joffe et al. 2002). Although most women are able to cope with these issues that arise as a result of menopause for others these problems can be absolutely debilitating (Utian 2005). The debilitating nature of the symptoms associated with menopause include hot flush situations that can last as long as 5 minutes. Some women have even reported having hot flashes that lasted as long as 15 minutes. These episodes can be overwhelming because of how they feel and need of the woman to find external sources such as a fan or cold water to relieve the flush and bring her body temperature back into balance (Kronenberg 1990; Deecher & Dorries, 2007). The author further explains that VMA is also linked to the changes and decline in ovarian hormone levels." This occurs during and after menopausal transition. These changes are also present in women who have survived cancer. These individuals often experience a loss of ovarian function because of cancer treatment (Mom et al. 2006) Such problems may also occur in men who have had androgen ablation therapy (Holzbeierlein et al.2003).

As it relates specifically to the role of thermoregulation and VMS, the author explains that it occurs as a result of a dysfunction in the temperature circuitry of human beings. Eventually the result of this dysfunction is a drawn out activation of heat dispensation reactions. This includes both peripheral vasodilation and sweating. The author explains that certain ailments, medications and neuronal injury can also cause thermoregulatory dysfunction. Thermoregulatory circuitry three primary components: the brain, the internal body cavity, and the peripheral vasculature (Deecher 2005). All of these components work in unison to control temperature homeostasis. The author also explains that other thermoregulatory zones are responsible for supplying the body with temperature inputs. Thermoregulatory zones transmit temperature signals to the corresponding thermoregulatory centers in the brain, especially the hypothalamus. The author further explains that

"These centers use the signals to maintain optimal core body temperature (CBT) by inducing vasodilation to dissipate heat or vasoconstriction to conserve heat. Thus, an HF is a rapid, exaggerated response causing an intense heat sensation (flash), upper body skin reddening (flush), and increasedskin blood flow resulting in changes in heart rate and blood pressure. It is hypothesized that the body is not really in a "hyperthermic" state, but that there is a miscommunicationin temperature signaling that regulates normal temperature responses. Therefore, the message to rapidly reduce CBT results in extreme vasodilation followed by sweating and in some cases drenching perspiration, especially at night, which can lead to sleep disruption (Kronenberg 1990; North AmericanMenopause Society 2004a).

Often, the extreme heat loss caused by the vasodilation of blood vessels results in chills and shivering as the body attempts to compensate for the loss (Freedman 2001;).

This illustration (taken from (Deecher & Doories 2007). The illustration depict the issues that arise as it pertain to menopauses and thermoregulation.

Thermoregulation and Diabetes

In addition to menopause, illnesses such as diabetes can also effect thermoregulation. Petrofsky et al. (n.d.) explains that diabetes is a serious heath concern throughout the globe. In fact millions of people every year have to deal with illness and complications that occur as a result of diabetes (Petrofsky et al., n.d.) The authors explain that the prevalence of diabetes is heavily dependent upon race (Petrofsky et al., n.d.). In America about8% of the white population has diabetes while nearly 11% of the black population was diagnosed as diabetic (Petrofsky et al., n.d.). Rates of diabetes are also high amongst Mexican-Americans and Pacific islanders Diabetes is serious because it can be detrimental to various parts of the body including the heart (Petrofsky et al., n.d.). According to the authors those with diabetes are twice as likely to get heart disease as people without the disease (Petrofsky et al., n.d.). Additionally diabetes is the leading cause of kidney disease, blindness, and nontraumatic amputation (Petrofsky et al., n.d.).