The Cardiovascular System
3.2a The physiology of the cardiovascular system
This chapter focuses on the cardiovascular system, also known as the circulatory system. Like Section 3.1a, this section is divided into two parts. If you are using this book as a study course, then, because of its length, you are advised to work through the two parts in separate study sessions.
Part I: The vessels and the heart organ26
The cardiovascular system consists of all those structures that have the role of transporting the blood to all parts of the body. It enables the blood to perform its roles of protection, providing nutrients and removal of toxins for all the body tissues.
The cardiovascular system can be considered as comprising two main components – the blood vessels and the heart – and these are explored in turn in this section. The vessels are the channels through which the blood flows. The three main types of blood vessel are the arteries, veins and capillaries. The heart is the pump that provides the power to create the flow of blood through the vessels.
Sometimes the lymphatic system first referred to in Section 2.1d is also included as part of the cardiovascular system. However, in this book, for the sake of clarity, the lymphatic system is treated as a separate system.
The blood (hematological system) is not conventionally considered to be part of the cardiovascular system. The blood is considered to be connective tissue in nature and originates from the bone marrow. The blood is described in Chapter 3.4.
Very simplistically speaking, a typical conventional practitioner might view the cardiovascular system as a fleshy pump, albeit a rather complex one, which is linked to a series of soft-tissue pipes. Although emotions and stress in particular are recognized in modern medicine to have a bearing on the function of the cardiovascular system, the heart and vessels do not have any of the deep emotional correlations that they are ascribed in Chinese medicine and other holistic complementary medical disciplines. For example, a modern heart surgeon may not necessarily consider the part that love plays in the life of a patient to have anything to do with the task of improving the function of that patient’s heart. In contrast, a holistic practitioner is much more likely to be interested in how a person’s relationships and zest for life are linked to the health and function of the Heart Organ, the energetic system that is linked most with the heart and circulation in Chinese medicine.
The blood vessels
The vascular system is the term used to describe the vessels alone. It consists of a network of tubes lined with endothelium (a form of epithelial tissue). These tubes are at their widest as they leave the heart, and then divide, like the branches of a tree, to form thousands of tiny capillaries within the tissues. The capillaries then meet up again to form wider and wider tubes, which return the blood back to the heart.
Blood vessels that lead blood away from the heart are called arteries and those that lead blood back again to the heart from the tissues are called veins. Arterioles and venules are the names given to the smallest types of arteries and veins.
An important characteristic of arteries is that they contain both muscle and an elastic material called elastin in their wall, which means that they have the capacity to contract and expand. This means that arteries can alter the flow of blood to an area of the body by altering in width. This is a very important concept to grasp in preparation for understanding the concept of blood pressure.
The blood in arteries is under high pressure because it has just been pumped from the heart. This is why a severed artery will spurt blood in pulses. It is from the arteries, and not the veins, that a Chinese medical practitioner can sense the state of Blood and Qi when taking the pulse.
One important disease of arteries, arterial thrombosis, has already been described in this text (see Section 2.2d).
In contrast to arteries, the blood within the veins is under much lower pressure, and it is necessary for veins to contain valves to ensure that the flow of blood back to the heart remains one-way. Veins rely on the pumping action of the muscles to aid in the movement of blood back to the heart. This is partly why sedentary people may develop swollen ankles at the end of the day. Fluid accumulates in the tissues of the lower parts of the body when there is no motive force to propel it upwards against the force of gravity.
One important potentially life-threatening venous disease, deep vein thrombosis (DVT), has already been described (see Section 2.2d). The more common and benign condition of varicose veins is described later (see Section 3.2c).
Capillaries are minute vessels with walls that are only one cell thick. A significant characteristic of capillaries is that they enable the rapid transfer of nutrients, gases and waste products to and from the blood across their very thin walls.
Capillaries were introduced in Section 2.2b, where inflammation was described. In inflammation, the gaps between the cells in the capillary wall widen, making the capillaries more permeable to tissue fluid.
The transfer of nutrients from the capillaries to the tissues
Healthy blood that has just passed through the digestive system will contain a high concentration of basic nutrients, including simple sugars, cholesterol, triglycerides, fatty acids, amino acids from proteins, vitamins and minerals. Once the blood has passed through the capillaries of the lungs, it will also contain a high concentration of oxygen. Thus the blood transports both the oxygen and glucose and other simple nutrients that will be used by the mitochondria of every cell in the body to produce the energy required for many vital cellular processes.
The body relies on the transport processes of diffusion, osmosis and active transport for nutrients and oxygen to enter the bloodstream from the tissues of the digestive system and the lung. These processes are described in detail in Section 1.1c.
Oxygen, simple sugars, fatty acids, vitamins and minerals all pass with ease through the single-celled wall of the capillary by diffusion. The movement is particularly rapid when it is from a region in which these nutrients are in high concentration to one in which there is a low concentration. For both oxygen in the lungs and nutrients in the tissues of the digestive system this movement enables these substances to readily enter the circulating fluid component of the blood, the plasma.
Conversely, when the nutrient and oxygen-rich plasma reaches other tissues in which the concentration of nutrients and oxygen may be relatively low, the nutrients and oxygen tend to move out of the blood and into the tissues. This transfer of nutrients from digested food in the intestines and of air from the lungs into the tissues happens within a few seconds. Because diffusion is a spontaneous process, this process is incredibly energy efficient, requiring no extra energy over that required by the heart to pump the blood.
In addition to this energy-efficient transfer of oxygen and nutrients into the tissues, another wonderful aspect of the process of diffusion is that it underpins the movement of waste products out of the tissues. As waste products such as urea from protein metabolism and carbon dioxide from respiration build up in the tissues, the tendency is for them to move back into the bloodstream, where they are kept at a relatively low concentration. The waste products can then be carried to the liver, kidneys, sweat glands and lungs, each of which is specially adapted to remove otherwise toxic by-products from the body.
Similarly, water moves into and out of the plasma with ease. In this case, the process is called osmosis. This term describes the movement of water from a region in which it is part of a dilute solution to one in which it is part of a more concentrated solution. This is the means by which water will move from a vase into a wilted (dehydrated) flower stem. In the same way, by osmosis, water will enter the plasma from the tissues if the plasma is more concentrated than the tissue fluid. Conversely, if the plasma is relatively well hydrated, water will move out of the plasma into the tissues. This is another very energy-efficient mechanism, and it ensures that water is transported from the digestive system to the tissues that need it.
The desire for water to move from a region of low concentration to one of high concentration is described in scientific terms as osmotic pressure. This pressure relates directly to the difference in concentration between two regions, and so to the tendency that water will have to move between these regions. When the osmotic pressure is high (e.g. in a dehydrated plant stem), a lot of water can be encouraged to move (in this case, against the downward pull of gravity and into the stem). Thus, in the body, if a dehydrated person drinks some water, there will be a rapid movement of water from the digestive system, through the plasma and into the dehydrated tissues, all under the pull of the increased osmotic pressure of the concentrated tissue fluids.
One other factor needs to be considered in this description of the movement of nutrients into and out of the bloodstream, and this is the effect of the physical pressure of fluid in the vessels. Just as air in an inflated tire is under a measurable degree of pressure (which is what makes the tire feel inflated), so the blood in a blood vessel is under a degree of pressure. In the blood vessels the internal pressure varies according to the proximity to the heart. Arteries close to the heart contain blood that is being pumped by muscular contractions of the heart, and this blood is therefore under significant pressure. As the arteries branch into more and more numerous smaller vessels, the pressure within them gradually decreases, so that at the start of the capillary bed the pressure is much lower. Nevertheless, at the arterial end of the capillaries the pressure is still sufficient to force some fluid through the gaps between the cells of the capillary walls and into the tissues. This can be compared visually to squeezing an inflated bicycle tube punctured with numerous tiny holes; the greater the pressure applied, the more air that is able to escape through the holes. However, unlike the air escaping from a squeezed and punctured bicycle tube, the tendency for water to move out of the blood vessels by physical pressure is countered by the tendency of fluid to stay in the blood vessels under osmotic pressure. In health, a delicate balance between the two forces is established, ensuring that the tissues remain perfectly hydrated, becoming neither too dry nor too waterlogged.
Just under half of the volume of the blood is made up of blood cells that are too large to move between the gaps in the capillaries. A good proportion of the composition of the remaining plasma consists of dissolved protein molecules, which are also too large to pass through the gaps in the capillaries. Therefore, the movement of fluid across capillary membranes is selective for the remaining small molecules, such as water itself, salt and sugars. This is the property of semi-permeability, as first described in Section 1.1c.
An understanding of these forces that affect the movement of fluid between the blood and the tissues is a helpful foundation for the study of the important condition of edema, described in Section 3.2f.
To summarize, the balance of these forces is such that the net movement of fluid is out of the capillaries at the arterial end and into the capillaries at the venous end. This is ideal to suit the body’s needs. It means that nutrients and oxygen tend to move out into the tissue fluid from the arterial end, and wastes and carbon dioxide tend to move into the venous end of the capillaries. This is how the blood deposits its nutrients into the cells that need them, and transports away the wastes from the tissues at the capillaries.
The pathway of the arteries
Figure 3.2a-I illustrates the pathway of the major arteries that lead away from the heart. The diagram shows how the blood is directed from the heart to all parts of the body. The arch of the largest blood vessel in the body, the aorta, is shown leaving the top of the heart and then descending to run deep in the body, through the diaphragm to the pelvis. Here, it splits into two main branches, which supply blood to each leg.
Figure 3.2a-I The pathway of the arteries from the heart
The vessels: comments from a Chinese medicine perspective
Maciocia (1989)27 states that in The Simple Questions (Suwen) the vessels are said to be controlled by the Heart, but adds that the Lungs also control circulation of Blood in the vessels because of their role in Governing the circulation of Qi throughout the body.
One of the Chinese medicine functions of the Lungs is to inhale pure Qi and to exhale dirty Qi. The pure Clear Qi (derived from the air we breathe) combines with Gu Qi (derived from food) to form Gathering (Zong) Qi in the chest. True (Zhen) Qi is a further refinement of Gathering Qi and Original Qi, which also arises in the chest. The Lung then enables the dispersion of this Qi in its dual form of Nutritive (Ying) Qi and Defensive (Wei) Qi to the whole of the body. Therefore, the Lungs are important for the generation of essential energy throughout the whole of the body.
This makes an interesting comparison with the conventional medicine interpretation that the vessels permit the transportation of nutrients and oxygen to all the tissues and thus facilitate the production of cellular energy from these ingredients in the mitochondria present in all cells of the body. This is very much in keeping with the Chinese medicine association of the vessels with the Lung Organ.
Figure 3.2a-II The pathway of the left common carotid artery
Figure 3.2a-II shows how the major branches of the aorta in the neck, the common carotid arteries, branch to supply blood to the head. One branch, the internal carotid artery, divides to enter the skull and supply the brain with blood.
Now turn back to Figure 3.2a-I, which shows how arterial branches from the aorta divide down each limb to take blood to the hands and the feet. Compare this with Figure 3.2a-III, which shows the pathways of the veins that return the blood to the heart, ending in two major vessels called the superior vena cava and inferior vena cava. Note how the basic pathways of the veins mirror those of the arteries. This is the pattern for almost all parts of the body, in that an artery delivering blood to a body part runs very close to the vein that is draining the blood away from that part.
A major difference between the position of arteries and veins is that most veins tend to run closer to the surface of the body, whereas arteries generally lie much deeper. The veins that run close to the surface are called superficial veins. All the blue-colored vessels that can be seen through the skin in areas such as the back of the hand, the crooks of the elbows and the neck are superficial veins, not arteries. If these vessels are palpated, no pulse will be felt, and it will be found that they are very easy to compress.
In addition to superficial veins, there is also a system of deep veins. The blood draining from the surface of the body runs first into the superficial veins, and then enters the deep veins through vessels that penetrate the deeper tissues called perforators. It is important to be clear about the distinction between superficial and deep veins in order to understand the pathology of the conditions of varicose veins and also deep venous thrombosis, as described in Section 3.2c.
Figure 3.2a-III The pathway of the veins leading back to the heart
The structure of the heart
The heart is a fist-sized organ that sits just to the left of midline in the chest. It is situated between the two lungs, and together these organs fill the space that overlies the diaphragm. This space is known as the thoracic cavity, as shown in Figure 3.2a-IV. These organs are so closely related that the inside surfaces of the lungs bear the impression of the shape of the heart on them.
Figure 3.2a-IV The organs associated with the heart in the thoracic cavity
The heart is largely made up of cardiac muscle (the myocardium), and is divided into four chambers. It might be helpful now to turn back to the description of the tissue types given in Section 1.1d for a reminder of the characteristics of cardiac muscle, and how the cardiac muscle cells communicate with each other through specialized joints.
The healthy heart is lined with endocardium, a smooth epithelial tissue lining that is continuous with the lining of the blood vessels. The outside of the heart is protected by a tough fibrous sac called the pericardium. In between the pericardium and the heart organ is a very small space containing fluid. This fluid lubricates the movement between the heart and the pericardium, and contains immune cells. The remainder of the organ consists of the naturally contractile myocardium.
To understand the action and some of the structural disorders of the heart, it is important to understand that the heart is divided into two halves: the right half deals with the flow of the blood from the body and to the lungs, and the left half deals with the flow of the blood from the lungs and to the body. Each half has two chambers known as the atria (singular atrium) and the ventricles, and together these form the four chambers of the heart. There are two valves situated in each half of the heart. Their function is to ensure that the blood flow is always one way. Figure 3.2a-V illustrates the position and shape of the four chambers and the valves of the heart, and the direction of blood flow through the two halves of the heart.
Figure 3.2a-V The interior of the heart and its blood flow
The flow of blood through the heart
The double structure of the heart means that blood can flow through the heart twice in each full circulation of the body. It might help when reading the following description of the flow of the blood to use Figure 3.2a-V to visually trace the pathway the blood takes.
THE FLOW OF BLOOD THROUGH THE RIGHT SIDE OF THE HEART
Blood returning from most of the tissues of the body enters the right atrium of the heart from the two large veins, the superior and inferior vena cavae. This blood has given up its oxygen and is carrying relatively high levels of waste products such as carbon dioxide and urea. The right atrium contracts to force the blood through the tricuspid valve, and thus into the right ventricle. The right ventricle then contracts and this forces the blood through the pulmonary valve into the pulmonary artery. The pressure of blood in the contracting right ventricle closes the tricuspid valve, making a very subtle clapping noise. The blood rushing into the pulmonary artery does not flow back into the right ventricle when it finishes its contraction as the pulmonary valve also closes in turn, making its own clapping noise as it does so. The blood entering the pulmonary artery then passes into a concentrated network of capillaries within the tissue of the lungs.
THE FLOW OF BLOOD THROUGH THE LEFT SIDE OF THE HEART
When blood has passed through the capillary network of the lungs, it has given up its carbon dioxide and is rich in oxygen, all through the effortless process of diffusion (see Section 3.3a for more detail about the structure of the blood vessels in the lungs). This oxygen-rich blood is a brighter shade of red than the darker venous blood. It flows through the pulmonary vein and into the left atrium of the heart. The left atrium contracts to force the blood through the mitral valve, and thus into the muscular left ventricle. The left ventricle then contracts and this forces the blood through the aortic valve into the arch of the aorta, the widest part of the widest blood vessel in the body. The pressure of the blood in the contracting right ventricle closes the mitral valve, also making the valvular clapping noise. Just as was described for blood leaving the right ventricle, blood rushing into the aorta does not flow back into the left ventricle when it finishes its contraction. This is because the aortic valve also closes in turn, again, making its own clapping noise as it does so.
It might be appreciated from this description that the flow of blood in the body can be compared to a figure-of-eight, with the heart situated at the crossing point of the lines of the eight. In this delicate but powerful pumping system, both the right and the left heart contract together in a single heartbeat. This results in a double pumping action, which means that the pulse of flow of blood within the lungs and body occurs at exactly the same time, and the clapping of the four valves closing in turn makes the heart sounds that are audible by means of a stethoscope.
In summary, it is important to understand that the route of the flow of blood through the two halves of the heart is as follows:
•oxygenated blood from the lungs enters the left heart
•the left heart pumps oxygenated blood to all the tissues of the body
•tissues absorb oxygen so that the blood becomes deoxygenated
•deoxygenated blood from the body returns to the right heart
•the right heart pumps deoxygenated blood to the lungs
•blood absorbs oxygen from the lungs so that it becomes oxygenated
•oxygenated blood from the lungs enters the left heart
…and so on.
The blood supply to the heart
It might appear surprising that the heart itself requires a blood supply. However, the heart muscle is working continuously for a full lifetime, and requires a consistent supply of oxygen and nutrients. These high demands cannot be met by the blood flowing through the chambers of the heart alone.
Figure 3.2a-VI illustrates how vessels, known as coronary arteries (derived from cor, the Latin root meaning heart), branch from their origin at the aorta to wrap around the heart muscle. An understanding of this blood supply will be good preparation for the study of coronary heart disease (see Section 3.2e), which is the most important cause of death after cancer in developed countries.
Figure 3.2a-VI The blood supply to the heart
The conduction system of the heart
The conduction system of the heart is what enables the heart to contract in such a way that a wave of contraction moves from the top of the heart to the tip (apex). This means that the blood within the heart is pumped smoothly through the two chambers of the two sides.
The conduction system consists of strands of specialized cardiac muscle cells, which run from an electrically active node situated in the muscular wall between the atria in the upper part of the heart. These cells branch out from this region to connect to all parts of the heart muscle. This node (more specifically known as the sinoatrial node) is the heart’s own pacemaker. The cells of this pacemaker have an internal rhythm, giving them the property of being able to contract at a rate of just over once every second. Because of the membranous joints between cardiac cells, the contraction of the cells in the pacemaker can stimulate the contraction of neighboring cells in the conduction system, and so on, until the whole heart muscle has contracted.
Various factors can affect the rate at which the pacemaker cells contract, which explains why people can be aware of changes in their heart rate from time to time. One of these is the nerve supply to the heart. This is part of the autonomic nervous system (described in more detail in Chapter 4.1). The autonomic nervous system plays an essential role in the maintenance of homeostasis in the body, and very probably in the mechanism of many of the effects of acupuncture. For the time being, all that need be understood about this system is that it deals with the control of the involuntary aspects of the function of the body, such as breathing, digestion and sweating. It is conventionally seen as two opposing systems, the sympathetic nervous system (SNS) and the parasympathetic nervous system (PNS). Most parts of the body are under the influence of both these systems.
In the heart, the sympathetic nerves cause the pacemaker to contract more rapidly, and the heart muscle to contract more forcefully (in Chinese medicine this would be interpreted as a Yang response). The parasympathetic nerves cause the pacemaker to contract more slowly, and the heart muscle to contract less forcefully (a Yin response).
Emotional states such as fear and anxiety and also physical exercise all lead to an increased heart rate as a result of activation of the SNS. Other factors that contribute to a relatively increased heart rate include body temperature, being female and young age (infancy and childhood).
The generation of the pulse
The pulse wave, which is of interest to practitioners both of Chinese medicine and conventional medicine, is a direct consequence of the rhythmic pumping of the heart. As blood is forced through the chambers of the heart by the wave of contraction from the base to the apex of the heart, the arteries that leave the heart bulge with the increased amount of blood that has been forced into them, and this distension is propagated down the length of the major arteries. Arteries are elastic vessels that can stretch, but are not flaccid. This bulging is felt on palpation at any artery as a pushing outward of the vessel wall, and this bulge is what is known as the pulse.
When conventional medicine practitioners assess the pulse they use quite firm pressure. In this way they can feel the physical force of the blood in the artery. Practitioners of Chinese medicine apply very little pressure to assess the pulse. This is because they are less concerned with the physical force of the blood and more with the energetics of the vital substances of Blood and Qi, which are believed to move with the physical blood.
The heart sounds
Practitioners of conventional medicine use a stethoscope to listen to the heart sounds. In a healthy person, the heart sounds are like the familiar repeated “lub-dub” used so often to heighten emotion in televised hospital dramas. As mentioned previously, the heart sounds are produced by the heart valves closing as the blood is forced through them. In each chamber, one valve closes before the other, thus producing the “lub-dub” sound.
Different conditions of the heart lead to very subtle changes in these sounds. A valve that does not close properly will give a muffled sound as blood leaks through it, and this is known as a murmur.
Part II: Blood pressure and the Chinese medical view
Blood pressure is simply a measure of the force that the bulge of blood in the arteries exerts on the walls of the arteries. It can be assessed approximately by palpation of the artery. An artery that feels very tense during the pulse can reflect a high blood pressure, whereas a weak, flaccid pulse can reflect a low blood pressure.
Blood pressure oscillates up and down during the heartbeat. When the heart reaches the peak of contraction, blood pressure also reaches a peak, and this is called systolic blood pressure. When the heart relaxes after its contraction, blood pressure drops down to its lowest point, diastolic blood pressure. When a conventional doctor palpates the force of the pulse, information about the difference between systolic (peak) and diastolic (trough) pressure can also be obtained.
Adequate blood pressure is necessary for ensuring a steady flow of nutrients to all parts of the body. In times of physical stress blood pressure rises, but this is appropriate to the body’s needs. It is only if blood pressure remains at too high a level for the body’s requirements for too long that long-term damage to the circulatory system can occur. The condition of high blood pressure (hypertension) is explored in more detail in Section 3.2d.
Two important factors combine to affect the blood pressure. The first is the amount of blood being pumped by the heart at any one time. A rapid and forceful heartbeat will lead to a higher blood pressure than a slow and relaxed heartbeat. A frightening experience or strenuous exercise will both temporarily put up blood pressure, as they both lead to an increased and more forceful heart rate.
The second factor that increases blood pressure is the amount of tension in the muscles of the artery walls. If the artery walls are tightly constricted, the pressure of the blood being forced through them will be raised. There are many factors that cause the artery walls to constrict. One familiar cause is extreme cold, which causes the small arteries in the skin to constrict. This leads to cold flesh, numbness and a bluish discoloration. This is an important reflex in the body, because it means that the heat of the blood is not lost so readily from the skin, and is kept deep in the interior where it is vital for the effective function of the organs.
It is important for homeostasis that blood pressure remains generally within a certain range. It has been found that most healthy individuals have comparable ranges of blood pressure. Young people tend to have lower blood pressure than older people, and women tend to have lower blood pressure than men.
It might now be appreciated that blood pressure has to be responsive to a wide range of conditions, which include emotional stress, exercise, pain and blood volume.
As with the heart rate, the autonomic nervous system (ANS) is central in the control of blood pressure. The muscles within the small artery walls are supplied by sympathetic nerves, and thus it is the SNS that deals with increasing the heart rate. In the small blood vessels, activated sympathetic nerves lead to constriction. Conditions such as emotional stress, exercise, pain and loss of blood volume activate the SNS and lead to constriction of the vessels.
Two chemicals that are integral to the activation of the SNS are the hormones adrenaline and noradrenaline. A release of adrenaline from the adrenal glands will lead to an increased heart rate, constriction of the artery walls and an increase in blood pressure. This is explained in more detail in Chapter 5.1.
When the SNS is not activated, the action of the PNS becomes dominant. In this situation, the heart rate slows down, the blood vessels relax and blood pressure drops. A faint often occurs as a result of a strong emotional response to a shock (different to fear) or even to excessive joy. This has the effect of activating the PNS. The result of this is that the heart rate suddenly slows and blood pressure drops. This leads to a sudden drop in the supply of blood and nutrients to the brain, and the person will feel dizzy and may very briefly lose consciousness. However, the act of fainting and the drop in blood pressure that accompanies it then stimulates the SNS, which immediately reverses the situation. A hallmark of a faint is that the person very quickly begins to regain consciousness (within seconds) as the blood pressure rises and the blood supply returns to the brain.
This is also what occurs when a person receiving acupuncture experiences needle shock, which occurs very occasionally, often during a first treatment. Although alarming for the practitioner, this type of faint is usually benign, as long as the patient starts to regain consciousness immediately. It is conventionally believed to be the result of an emotional response to needling, which then leads to over-activation of the PNS. This dramatic response to needling can, however, be framed in terms of a helpful shift in energy, and case studies suggest that if interpreted in this positive light may allow long-term healing from trauma held within the body.28
Measurement of blood pressure
Although blood pressure can be roughly assessed by palpation of the pulse, the way to obtain an objective measure of blood pressure is by means of an instrument called the sphygmomanometer. This consists of an inflatable fabric cuff, which is wrapped around a limb, usually the upper arm, and a device to measure the pressure within the cuff.
The pressure can be assessed by a simple manually operated pressure gauge, similar to those used to measure car tire pressure, in which case the equipment is called an aneroid sphygmomanometer. Increasingly, in medical settings, an oscillometric assessment is made, which involves a digitally processed result drawn from the mean arterial pressure. This requires an automated digital sphygmomanometer. The British Hypertension Society (BHS) currently recommends a wide range of oscillometric models for reliable assessment of blood pressure.29
The now outmoded mercury-containing sphygmoman-ometer used to provide the gold standard for measurement. For this reason, the numerical value of blood pressure is conventionally expressed in millimeters of mercury (mmHg). A normal systolic pressure falls within the range 100–140mmHg, and a normal diastolic pressure falls within the range 65–90mmHg. Blood pressure is expressed as a combination of these two values. For example, a blood pressure of 120/80mmHg (described as 120 over 80) would be considered to be a normal blood pressure, and one of 150/99mmHg would be considered to be a high (albeit only classed as Stage 2) blood pressure.
In blood pressure assessment the cuff is inflated to a pressure high enough to totally compress the arteries within the limb. This will be equivalent to a pressure higher than the systolic pressure, and can be in the range of 200–250mmHg. At this pressure the compression of the artery leads to a total cessation of blood flow through the artery, and the pulse can no longer be felt or picked up by an oscillometer. This stage is often uncomfortable for the patient, and this level of pressure should be maintained only for a moment.
In aneroid assessment, a stethoscope is placed over the artery that is distal to the cuff. This is usually at the brachial artery, the pulse of which can be palpated at the elbow (in the region of the acupoint Qu Ze, PC-3). The pressure in the cuff is then gradually reduced. As the pressure in the cuff falls to that of the systolic pressure, squirts of blood can be forced through the now partially compressed artery. This is heard as a pulsatile rushing noise through the stethoscope. The systolic pressure is recorded as the pressure of the cuff when the rushing noises are first heard.
As the pressure in the cuff is reduced further to close the diastolic pressure, more and more blood can pass through the brachial artery. As the blood flows more easily, the rushing noises become increasingly soft. When the pressure in the cuff reaches the diastolic pressure, all the blood can pass freely through the vessel and the sounds disappear altogether. The diastolic pressure is recorded as the pressure of the cuff when the rushing noises stop altogether.
The BHS and National Institute for Clinical Health and Care Excellence (NICE) have collaborated to write guidelines for health professionals on how to take accurate blood pressure measurements and how to treat high blood pressure.30 These guidelines ask for careful repeated measurements, although this ideal may be rarely achieved in real practice because of time constraints. However, this is not a trivial issue; an inaccurate measurement will lead to a false assumption about the true level of blood pressure, and can lead to inappropriate treatment.
The guidance states that the patient should be seated and should be relaxed. The arm should be resting on a surface so that it is at the level of the heart. The cuff pressure should be deflated very slowly (no more than 2mmHg per second) so that the rushing sounds can be accurately matched with the cuff pressure. The blood pressure should be measured in both arms, and if one of the two readings is consistently higher, this should be considered to be the accurate reading. If the blood pressure measurement is high, it should be repeated after 1–2 minutes and the first reading discarded if the second reading is lower. If more readings are taken, the lowest of these is used to give the final measurement. If the clinic reading is high, the advice is that the doctor should arrange for home readings to be obtained to ensure that a “white-coat effect” (see Section 3.2b) has not raised the blood pressure to higher than its usual level. The gold standard is that the patient is given an automated ambulatory blood pressure monitor to assess blood pressure throughout their day, but the guidelines accept that readings from a simple home monitor may also be valid in the diagnosis of raised blood pressure.
Information box 3.2a-II
The heart and pericardium: comments from a Chinese medicine perspective
In Chinese medicine, the Heart and Pericardium are Organs to which specific functions are ascribed, and which are manifest on the exterior of the body in the primary Heart and Pericardium Channels respectively.
Maciocia (1989)31 again quotes The Simple Questions (Suwen) when outlining the Chinese medicine view that the Heart is “like the Monarch and it governs the mind.” He lists the six functions of the Heart Organ, which are to:
•control the blood vessels
•manifest in the complexion
•house the mind (Shen)
•open into the tongue
In order to be clear about how these functions relate to conventional medical understanding, it will help to consider each of these in turn.
First in this categorization, according to Maciocia, government of Blood refers to two aspects: the transformation of food (Gu Qi) into Blood, and also the healthy circulation of Blood. In contrast, in conventional medicine the manufacture of blood from basic nutrients takes place largely in the bone marrow, although the healthy circulation of blood is, of course, recognized as the domain of the cardiovascular system. This is one indication that the Chinese medical description of Blood does not map directly to the Western medical understanding of the blood that flows in the blood vessels. This potential source of confusion is explored in more detail in Chapter 3.4.
The control of the blood vessels is linked to two organs in Chinese medicine, the Heart and the Lungs. This partly refers to maintenance of healthy vessels, and is a reflection of healthy Gathering (Zong) Qi made by the Lung Organ from Gu Qi (from food) and Clear Qi (in air). In conventional medicine terms, the health of the blood vessels results from a healthy cardiovascular system, and does not obviously relate to the lungs. However, it is interesting to reflect that arteriosclerosis, a major cause of vascular (vessel) disease in the Western world, is the result of an activity that directly damages the lungs, namely, smoking. Also, the hormone angiotensin II that is vital for the maintenance and responsiveness of blood pressure is formed in the capillaries of the lungs where the hormone angiotensin-converting enzyme is manufactured.
The complexion is conventionally considered to be a reflection of the health of the skin rather than the heart. However, in conventional medicine it is recognized that certain cardiovascular conditions can cause signs that appear on the face. Malar flush, the pink coloration of the cheekbone area, is one example. This finding, considered an indication of Yin Deficiency in Chinese medicine, is, in a florid form, a medically recognized sign of the valvular heart disease known as mitral stenosis. From a Chinese medical viewpoint a deep branch of the Heart Primary Channel32 runs up to cross the face and open into the eye, so explaining the link with the complexion of the face.
The mind/spirit is not associated with the cardiovascular system at all in conventional medicine. However, the English language reveals that in Western culture a deep connection has been made between the heart and the emotions. Phrases such as “my heart isn’t in it,” “to be heartbroken,” “he was heartless” and “have a heart!” (to name only a few) are evidence of this connection. In many older cultures the heart is integral to the concept of mind and thought. The spirit of a person is also recognized in the eyes, and these have a direct link with the Heart Primary Channel via its deep branches that course upwards to end in the eyes.
The tongue and speech are also not associated with the cardiovascular system in conventional medicine, although one of the signs of severe heart disease is recognized to be cyanosis, in which a bluish discoloration is seen on the lips and tongue. There is also some recognition that aphasia is a frequent component of shock, which can manifest in other heart-related symptoms. In Chinese medicine the Heart Luo connecting channel connects the Heart Channel with the root of the tongue.
Sweating is not directly linked to the cardiovascular system from a conventional medicine perspective, but is a well-recognized symptom of heart attack.
The functions of the Heart according to a conventional and Chinese perspective can be summarized in the form of a correspondence table (for an introduction to the Organ correspondence tables, see Appendix I). This illustrates the idea that the functions of the fleshy pump, which conventional medicine calls the heart, may be in the domain of not only the Heart Organ in Chinese medicine, but also the Kidney and Liver Organs, and to a lesser extent all the Organ systems. This is because the body is not understood as reduced to its component parts in Chinese medicine. These correspondences are supported by the fact that deep branches of the Kidney and Liver Organs connect either directly or indirectly via the Pericardium with the Heart Organ. It will follow from this that diseases of the conventionally viewed cardiovascular system may manifest in Chinese medicine syndromes involving other Organs, including the Heart, Kidney and Liver.
The Pericardium Organ in the Chinese medicine tradition is loosely associated with the more superficial layers of the heart, the fibrous pericardium and the myocardium. The function of the Pericardium (Heart Protector) is described as similar to that of the Heart, but it also has the particular function of protection of the Heart against external pathogenic influences.33 This has some overlap with the conventional medicine view in which the pericardium and the fluid that lies between it and the myocardium are very much seen as providing mechanical and immunological protection. In addition, there is the broader role, together with the Kidneys and Triple Burner Organs, of being associated with the Gate of Vitality (Ming Men). This Heart-Master role is as an intermediary within the Heart-Kidney Shaoyin Axis, and locates the Pericardium with the Ming Men at the physical level of the kidneys.343536
Correspondence table for the functions of the Heart, as described by conventional and Chinese medicine
Functions of the heart
Acts as a pulsatile pump to enable circulation of the blood (Heart and Liver Organs)
The origin of the heart muscle impulse (the pacemaker) (Heart Organ and Kidney Yang)
Contributes to the maintenance of blood pressure (Heart Organ and Kidney Yang)
Will respond to bodily requirements by an alteration in the strength and rate of pumping (Heart Organ and Kidney Yang)
Functions of the Heart Organ
“The Heart is like the Monarch and it governs the mind”
It governs blood (bone marrow, heart, blood vessels)
It controls the blood vessels (blood vessels, adrenal glands, autonomic nervous system)
It manifests in the complexion (heart, blood vessels, blood, skin)
It houses the mind (brain and diverse neurochemical-releasing cells distributed throughout the body)
It opens into the tongue (digestive system)
It controls sweat (skin, autonomic nervous system)
Correspondence table for the functions of the Pericardium, as described by conventional and Chinese medicine
Functions of the pericardium
This is a fibrous membrane that surrounds the heart and allows its free movement. It also protects from mechanical injury. The serous fluid it encloses contains protective antibodies and immune cells (Heart, Liver and Kidney Organs)
Functions of the Pericardium35
“The Pericardium is an ambassador and from it joy and happiness derive”
Like the Heart it governs blood (bone marrow, heart, blood vessels)
Like the Heart it houses the mind (brain)
Together with the Kidneys and Triple Burner Organs it has been associated with the Gate of Vitality (Ming Men) (possibly the healthy function of the metabolic processes that go on in all the cells and particularly the sympathetic nervous system and the other diverse cells which derive from the embryonic neural crest36)