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Unformatted text preview: TITLE THE CARDIOVASCULAR RESPONSE TO AEROBIC EXERCISE - HR is proportional to power - linear relationship max HR = 220 - age the drop in stoke volume is despite the activity of the sympathetic nervous system (increase contractility) otherwise it would drop much more - stroke volume starts to decrease because of a physiological tachycardia systole time decreases a little at high activity (the duration of contraction) but diastole decreases much more - CO = HR*SV - cardiac output triples - mostly due to the increase of heart rate - analogous to minute ventilation - arterial blood pressure rises by a factor of 1.2 - MAP = CO*TPR - since CO increases by a factor of 3, then TPR must drop by a factor of 1.2/3 = 0.4 - the fall in TPR is due to dilation of arterioles in the muscles (which happens due to the buildup of waste products) - at high levels of exercise, the body extracts more oxygen from the blood than at rest - the AV difference increases by a factor of 3 Fick principle: rate of change of oxygen per unit time = flow * the difference in concentration between oxygen the artery and veins - increases by a factor of 9 - due to increase in aerobic respiration - this is achieved by the increase in CO (which increases by a factor of 3) - where is the other factor of 3 from? --> the muscles need to extract more oxygen from the blood ×3 HR ∝ Power max HR = 220 - age r ×3
↓ systole ↓↓ diastole ×3 ↓ SV at very high HR ×3 ×3 CO = HR × SV resp? ×3 ×3 ×1.2 MAP = CO × TPR ×3 ×1.2 MAP = CO × TPR ×0.4 skeletal muscle vasodilation ×3 ×3 ×9
×9 ×3 ×3 ×9
×3 Fick Principle: VO2 = CO × a-vO2 Fig. 12-61 REGIONAL BLOOD FLOWS IN EXERCISE ×3.5 angina - the supply of oxygen is not equal to the demand built up waste products bind to receptors and cause pain ×12 massive vasodilation of the arterioles in skeletal muscle due to buildup of waste products, decrease in PO2 ×5 ×0.6 ×0.5
Olympic-class endurance athlete: 35 L/min (×7) (heat loss)
allows for the cardiac output to go where it needs to muscles, heart - important for maintaining blood pressure ×3.5 TABLE 12.7 CV PARAMETERS DURING EXERCISE and skin there are four types of hearts in the body - left heart, right heart, muscle pump, lungs - lung movements aid in pumping blood Fig. 12-35 NEURAL CONTROL OF SKELETAL MUSCLE TONE Adrenal medulla Secretes NE into blood ↑ Plasma NE
strong beta agonist the large increase in flow (by a factor of 30) to the muscles during exercise is due to local control - neural control can cause an increase or decrease by a factor of 2 only local control dominates over neural and hormonal control in muscle (skeletal and cardiac) non-muscle: α >> β → constriction Fig. 12-64 ENDURANCE TRAINING higher cardiac output therefore either the max heart rate or stroke volume must increase - but max heart rate is unchanged CO = HR × SV unchanged max HR
highly trained athletes have low resting heart rates because their resting stroke volume is so high training does not effect max HR, so it cannot be the cause of increase CO stroke volume increases - cause of increased CO - cardiovascular training causes the size of the muscle cells to increase - this causes the resting heart rate to decrease because the heart can now contract with more force (more actin and myosin) hypertrophy (not hyperplasia) of ventricular muscle
the size of the muscles increase (more actin and myosin), there are not more cells Week-after next Monday: Week-after next Tuesday: last CV lecture last tutorial 5 p.m. Martin - Rm. 504 !!!!! ENJOY SPRING-BREAK WEEK !!!!! ...
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- Winter '08