Chapter 13 15 Cardiovascular System E ects of Exercise Coronary Arteries Even though the heart pumps large volumes of blood the blood within the heart s chambers do not supply the heart muscle with signi cant quan es of oxygen or nutrients Instead the heart obtains oxygen and nutrients via the coronary arteries which branch o the aorta near its base and run through the heart muscle Myocardial Ischemia The heart requires high levels of oxygen even at rest because cardiac muscle has limited capacity for anaerobic glycolysis A decrease in cardiac blood ow to levels insu cient to provide adequate oxygen is called myocardial ischemia Cardiac catheteriza on is oHen performed to determine whether blockage of a coronary artery is present Myocardial Infarc on Chronic myocardial ischemia can lead to myocardial infarc on generally caused by a blood clot lodging in a narrowed coronary artery This causes irreversible damage to cardiac muscle and contrac le cells die and are replaced by scar ssue Myocardial Infarc on Myocardial Infarc on Markers Myocardial necrosis or cell death ischemia induced and other produces an ini al release of markers that di use out of the cardiac cells into the blood One of the best markers is the rise of troponin concentra on that begins approximately six hours post infarct with a peak usually at 12 24 hours and a gradual return to normal generally within 7 14 days Soreng K Bayer Health Care 2010 Heart Failure Some mes heart failure is caused by a heart aXack in which muscles cells die and the heart is weakened Once the heart muscle weakens it generates less contrac le force which reduces stroke volume and cardiac output Exercise and the Cardiovascular System 5 immediate responses of the cardiovascular system to exercise 3 long term adapta ons of the cardiovascular system to exercise The e ects of high al tude on the cardiovascular system The best life insurance policy is exercise Immediate Response of the Cardiovascular System to Exercise 1 Heart Rate Res ng heart rate averages 60 80 beats min in healthy adults During exercise heart rate increases in direct propor on to exercise intensity un l a maximum heart rate is reached Maximum heart rate is es mated with the formula 220 age Exercise and Sympathe c Ac vity During exercise sympathe c nerve ac vity to the heart increases Sympathe c ac vity not on increase heart rate but also the conduc on me through AV node so that less of a delay occurs between atrial and ventricular contrac on Exercise and Sympathe c Ac vity Sympathe c ac vity causes ventricular myocardial cells to contract faster and more strongly This ensures that both contrac on me and relaxa on me are decreased so that the me of systole declines In summary autonomic NS increases cardiac output by causing the heart to beat faster yet s ll maintaining as much lling me diastole as possible Immediate Response of the Cardiovascular System to Exercise 2 Stroke Volume Stroke volume also increases propor onally with exercise intensity In normal adults stroke volume at rest averages 50 70 ml beat increasing up to 110 130 ml beat during intense physical ac vity Crawford M H et al Circula on 1985 Cardiac Output Stroke Volume x Heart Rate Immediate Response of the Cardiovascular System to Exercise 3 Blood Pressure At rest a typical systolic blood pressure in healthy adult ranges from 110 140mm Hg During exercise systolic pressure can increase to over 250 mm Hg MacDougall J D et al American Physiological Society 1985 Immediate Response of the Cardiovascular System to Exercise 4 Blood Flow At rest 15 20 of circula ng blood supplies skeletal muscle During intense exercise this increases to 80 85 Blood ow is independently distributed according to need due to the local control of arteriolar radius Immediate Response of the Cardiovascular System to Exercise 5 Blood During prolonged exercise blood plasma volume can decrease 10 20 A reduc on in plasma increases the concentra on of hemoglobin Although no extra blood cells have been produced there is a greater concentra on of hemoglobin per unit of blood signi cantly increase oxygen carrying capacity Collins M A et al Eur J of Applied Physiology 1986 Cardiovascular Response to Light Exercise In summary even light exercise is accompanied by profound altera ons in cardiovascular func on Changes are bene cial in that they Increase delivery of oxygen and nutrients to muscles Oxygen and nutrients are conserved by curtailing delivery to ssues in which the need is not as acute Increased blood ow to through the skin aids the body in gemng rid of excess heat generated during exercise Cardiovascular Adapta ons Over Time in Response to Exercise 1 Heart Size The heart s mass and volume increase and the cardiac muscle undergoes hypertrophy The leH ventricle has been shown to adapt to the greatest extent Pluim B M et al Circula on 2000 Cardiovascular Adapta ons Over Time in Response to Exercise As well as the chamber size increasing as a result of endurance training more recent studies show that the myocardial wall thickness also increases Pluim B M et al Circula on 2000 Figure 12 Cardiac remodeling caused by long term deconditioning Maron B J Pelliccia A Circulation 2006 114 1633 1644 Copyright American Heart Association Cardiovascular Adapta ons Over Time in Response to Exercise 2 Heart Rate Res ng heart rate can decrease signi cantly following training in a previously sedentary individual During submaximal exercise heart rate is lower at any given intensity compared to pre training This di erence is more marked at higher rela ve exercise intensi es Cardiovascular Adapta ons Over Time in Response to Exercise 3 Blood Pressure Although resistance exercises can raise systolic and diastolic blood pressure signi cantly during the ac vity they lead to a long term reduc on in blood pressure Wealton S P et al Annals of Internal Medicine 2002 E ects of High Al tude Many athletes train at high al tudes where the quan ty of oxygen in the air is less than at sea level When oxygen levels in the blood are low this s mulates the release of erythropoie n the hormone responsible for More red blood cells are produced which in turn transport more oxygen to the ssues that need them Wolfel E E et al Applied Physio 1991 Erythrocytes Red blood cells are the most abundant cells in the blood 5 million per mm3 Shaped like disks and lack nuclei mitochondria and other organelles They transport oxygen and carbon dioxide in the blood for exchange with the body cells
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