PHYSICAL EXERCISES AND THE CARDIOVASCULAR SYSTEM.

PHYSICAL EXERCISES AND THE CARDIOVASCULAR SYSTEM.

Carl Stuart

Stuart Medical Series

                                                          Abstract.

This paper focuses on increasing the stamina and endurance of the cardiovascular system during strenuous exercise. The paper provides a general overview of the cardiovascular system, discusses its main components, describes the principal functions of the cardiovascular system. The paper also describes exercise physiology in relation to the cardiovascular system. The paper also explains the methods of increasing the tolerance of the cardiovascular system to arduous exercises.

                                                         Introduction.

The cardiovascular system is one of the two components of the circulatory system, with the other component being the lymphatic system. The cardiovascular system is made up of the heart and an intricate network of blood vessels that conduct and propel blood and its constituents throughout the human body. The cardiovascular system supplies cells with nutrients, oxygen, hormones; and also drains the cell’s metabolic wastes which can cause cellular toxicity if allowed to accumulate (Rowell, 2010).

The following are measuring techniques used to assess the function of the cardiovascular system. Cardiac electrophysiology is assessed using ECG (electrocardiogram), while, the cardiac function is assessed by the pulse meter. Sphygmomanometer measures the blood pressure. Pulse and pulse pressure determine the heart rate. The variation in time intervals between successive heart beats is measured using heart rate variability. The level of tissue perfusion is assessed using the nail-bed blanching test (Rowell, 2010).

                                     Components of the Cardiovascular System.

Cardiovascular system constitutes the heart and the blood vessels which include arteries, veins and capillaries (Rowell, 2010).

The heart is made up of two muscular pumps that act in series to pumps blood to the pulmonary and systemic vascular circuits. Systemic veins return blood with low oxygen saturation into the right atrium via the superior and inferior vena cavae. The right atrium pumps this blood to the right ventricle during the diastole phase of the cardiac cycle. During the subsequent systole, the right ventricle pumps this deoxygenated blood to the lungs through the pulmonary arteries. The lung oxygenates this blood, while at the same time, removing carbon dioxide and other volatile excretory gases. From the lungs, the oxygenated blood is conducted by the pulmonary veins into the left atrium. This circuit, consisting of blood conduction through the right atrium, right ventricle, lungs and the left atrium, is termed the pulmonary circulation. During diastole, the left atrium pumps this blood to the thick walled left ventricle. The muscular left ventricle during systole pumps this blood to the systemic arteries which arborize into capillaries which drains into systemic venules and then ultimately into the systemic veins. This constitutes the systemic circulation. Coronary circulation is part of the systemic circulation (Rowell, 2010).

The types of blood vessels are arteries, veins and capillaries. Most of the blood vessels, except for capillaries, consist of the tunica intima, tunica media and tunica adventitia. Capillaries consist of only the tunica intima (Rowell, 2010).

The arteries conduct blood at relative high pressure (compared to the veins) from the heart to the body tissues. The artery size and type is a continuum based on morphological characteristics from the large elastic arteries (conducting arteries such as the aorta, branches of the aorta like the brachiocephalic trunk and carotid arteries; and the pulmonary trunk), medium muscular arteries (distributing arteries that have the property of vasoconstriction) and small arteries including the arterioles. Vascular anastomoses provide collateral circulation in the systemic vascular circuit (Rowell, 2010).

The capillaries connect the arterioles to the venules. Exchange of materials between blood and the interstitial fluid or the extravascular fluid compartment occurs through the capillary walls. Capillaries are arranged in capillary networks or beds. A portal venous system connects two capillary beds(Rowell, 2010).

The veins (except for the pulmonary vein which conducts oxygenated blood) conduct low-oxygen blood from the extensive capillary bed into the heart. The smallest veins that drain the capillary bed are the venules. Venules do unite in particular anatomical locations to form venous plexuses, for example, in the foot there is the dorsal venous arch. Medium veins contain the flap valves, and they drain the venous plexuses and venules. Large veins such as the superior and inferior vena cavae drain the medium veins and conduct this blood to the right atrium. The arrangement of the accompanying veins surrounding the deep arteries in a branching network serves two functions: as a countercurrent heat exchanger and as an arteriovenous pump (Rowell, 2010).

                                    Functions of the Cardiovascular System.

These functions are described below. The cardiovascular system main function is to transport essential nutrients and oxygen from the gastrointestinal tract and lungs respectively, to the tissues; and in turn, transport metabolic wastes and other related excretory products from the tissues to the excretory organs such as kidneys (Rowell, 2010).

The thermoregulatory function of the cardiovascular system prevents heat shocks and cold shocks. Thermoregulation involves the blood vessels losing or gaining heat via the countercurrent heat exchanger, superficial vessels normally dissipating excess heat, while, blood vessels in the gut transfer heat from the body’s core to the peripheral tissues (Rowell, 2010).

The cardiovascular system also transports hormones that influence cellular metabolism, for example, thyroid hormone (Rowell, 2010).

                             Exercise Physiology in Relation to the Cardiovascular System.

Exercise physiology constitutes the study of acute reactions and chronic adaptations of the body to physical exercises (Katch, 2011).

Acute reactions in the cardiovascular system to physical exercises.

There is an increase in the heart rate from the normal resting average heart beat of 60-100 beats per minute. Epinephrine and norepinephrine released from their cellular stores into synaptic synapses causes this increase in the heart rate. Anticipatory response is the increase in heart rate that occurs before the physical exercise commences, and, is caused by anticipation (Katch, 2011).

The anticipatory response is followed by increases in heart rate in direct proportion to the intensity of the physical exercises till the maximum possible heart rate is attained. This maximum possible heart rate can be estimated mathematically using the formula below:
                      Maximum heart rate possible = 220- age of subject.

If exercise intensity is increased and maintained at that level for some time, the heart rate increases then falls, and, stabilizes at a relatively constant rate termed as the steady-state heart beat. During the steady-state heart rate, the demands of the metabolically active tissues are adequately provided for by the cardiovascular system. Gradual increase in body temperature during sustained steady-state exercise cause the steady-state heart rate to progressively increase, a condition termed cardiac drift (Katch, 2011)

The left ventricle ejects a specific amount of blood during systole, the stroke volume, and, is about 50-70milliliters per heart beat in a normal resting individual. Stroke volume increases proportionally with the increasing intensity of the physical exercises; till the maximum capacity is attained and further increase in stroke volume is no longer possible until physiological exhaustion occurs. According to the Frank-Sterling mechanism, increasing the intensity of exercise causes more ventricular filling during diastole (hence greater end-diastolic stroke volume) which in turns builds up the elastic recoil energy which produces stronger contraction during systole, thus a greater percentage of the ejection fraction is forced out. Another factor for this observation is increased arteriolar vasodilatation (caused by adrenaline release which dilates distributing arteries) which causes a decrease in the peripheral vascular pressure (Costill, 2011).

Cardiac output is the product of heart rate and stroke volume. Hence, during increases in exercise intensity, cardiac output also increases proportionally. Cardiac output is approximately 5 liters per minute in an adult at rest, but, can increase up to 40 liters per minutes during arduous physical exercises (Costill, 2011).

The blood flow to skeletal muscles increases during physical exercises and can reach about four-fifths of the cardiac output. This is caused by shunting off blood from other tissues into the skeletal muscles (Costill, 2011).

The blood pressure for a normal adult ranges from 110/60 to 140/90. During exercise, the systolic pressure increases in direct proportions, but, the diastolic pressure remains relatively constant, hence, consequently causing an increase in the pulse pressure (pulse pressure is the difference between the systolic and diastolic blood pressure). Both diastolic and systolic blood pressures rise to high levels during Valsalva maneuver, a form of resistance exercise (Costill, 2011).

The difference between arterial oxygen content and the venous oxygen content is termed arterial-venous oxygen difference (a-v O₂ difference). This a-v O₂ difference is increased during physical exercises due to greater demand of oxygen by active tissues. During physical exercise, the increase in blood pressure and increased intramuscular oncotic pressure act synergistically by exerting hydrostatic and oncotic pressures that causes water to extravasate from the intravascular compartment into the interstitial tissues, hence, reducing the plasma volume. This reduction in plasma volume increases the hematocrit, which increases the oxygen carrying capacity of blood as more hemoglobin is available to transport oxygen per unit volume of blood. This causes immediate acclimatization to altitudes in athletes (Costill, 2011).

Increased anaerobic respiration in skeletal muscles causes the levels of lactic acid in plasma to increase, hence, reduction of blood pH from approximately 7.4 to about 6.5(Costill, 2011).

Chronic adaptations to physical exercises in the cardiovascular system.

Cardiac hypertrophy occurs after endurance training. The cardiac myocytes hypertrophy, with the myocytes located in the wall of the left ventricle hypertrophying to the greatest extent. The size of the heart chambers also increase in size (Clausen, 2011).

A 12-week maximal exercise program reduces the resting heart rate by about 12 beats per minute. This would enable a trained athlete to endure more strenuous exercises before fatigue occurs. Research showed that the maximum heart rate remains constant. The pace at which the heart rate returns to the normal resting level after strenuous physical exercise is used to assess the cardiovascular fitness (Clausen, 2011).

Sustained maximal and sub-maximal exercise programs increase the resting stroke volume. This increases the physical endurance of athletes during exhausting competitions (Clausen, 2011).

Maximal exercise programs cause an increase in the cardiac output as the maximal stroke volume rises, though, the maximum heart rate remains constant (Clausen, 2011).

Maximal training programs leads to the following changes in the cardiovascular system. First of all, the number of capillaries increases. Secondly, there is increased exudation and transudation of materials from the existing capillary walls. Thirdly, the skeletal muscles receive adequate blood flow because of effective blood redistribution in the body. Lastly, there is an increase in the blood volume caused by the contraction of the plasma volume which induces the production of erythropoietin by the kidney (Clausen, 2011).

Research has shown that endurance exercise causes a reduction in resting blood pressure, and during arduous exercises, the blood pressure increases with a small margin compared to the increase of the exercise intensity level (Clausen, 2011).

Increasing stamina and endurance in the cardiovascular system during exercises.

There are several ways of increasing the stamina and endurance of the cardiovascular system during physical exercises as described below.

Exercise training is the most important consideration factor. Sub-maximal training is not as effective as maximal training. Efficient endurance training attenuates the anticipatory response, thus, the trainee commences the exercise with a lower heart rate. Endurance training also promotes efficient exchange of materials in the capillary beds; builds up the cardiac capacity by causing cardiac hypertrophy, increasing the stroke volume and reducing peripheral vascular resistance. Increase in the cut-off point of both psychological and physiological fatigability of the skeletal muscles improves the stamina that the trainee has before starting the physical exercise (Clausen, 2011).

Proper diet is essential in improving the endurance of the cardiovascular system to physical exercises. Proteins are needed to repair damaged or replace dead myocytes. Lack or inadequate intake of protein in the diet will severely limit the capacity of muscles in increasing their workload, as damaged and dead myocytes cannot cope up with sustained exercises. Carbohydrates are needed for energy production. Lack or inadequate intake of carbohydrate in the diet leads to chronic fatigue and exceptionally low stamina. Inadequate production of energy by the cell affects the entire body system as it also interferes with conduction of nervous impulses. Micronutrients are necessary for normal cellular physiological processes, and, a deficiency in any one of them leads to erratic cellular physiology which manifests itself as early fatigability and low stamina. Adequate intake of micronutrients fine tunes the impulse conduction in the nervous system, hence, the trainee has improved fine motor skills that increase his/her confidence, hence, positively impacting on stamina.

Rest is an essential component in building cardiovascular fitness. Rest allows the damaged tissues to be repaired, ensures that lactic acidosis that occurred during the ‘oxygen debt’ is cleared from the body, allows regeneration and recuperation of energy. Rest also improves the mental health, and hence, increases the stamina of the trainee.

                                                      Conclusion.

Cardiovascular system main function is to transport oxygen and nutrients to tissues. Physical exercises cause both acute response and chronic adaptations in the cardiovascular system. Diet, exercises and rest are essential components in improving the endurance and stamina of the cardiovascular system.

                                         

                                                           References.

Katch, L. (2011). Principles of Exercise Physiology, 4^th Edition, Philadelphia, Lippincott Williams Press.

Costill, D. (2011). Human Kinetics, Sports Physiology and the Cardiovascular System, 5^th Edition. Chicago,  Humana Press.

Rowell, B. (2010). Human Cardiovascular System. Washington, Oxford University Press

Clausen, J. (2011). Effects of endurance training on cardiovascular responses to physical exercise in man. Physiological Reviews. 57:779-816