Hypertension and Exercise

2. Hypertension and Exercise • due to hardening of arteries, excessive peripheral resistance (enhanced nervous tone or kidney malfunction) • pressures of 250-300 for systole and >90 mm Hg for diastole • aerobic exercise can modestly lower BP • extent is unclear, but beneficial for normotensive and hypertensive individuals

3. resting BP also lowers significantly, possibly due to higher circulating catecholamines after training  decreased peripheral resistance to blood flow, decreasing BP • exercise may enhance sodium elimination by kidneys

4. BP and Exercise static and dynamic resistance exercise will increase peripheral resistance to BF • even at light loads, e.g., 25% 1RM • potential for harm for those with heart and vascular disease • chronic resistance training does not appear to increase resting BP, and can blunt the response to a single bout

5. Steady State exercise • dilation of blood vessels in working muscles will decrease TPR, increase BF to working muscle • may see a small rise in systole, 140-160 mm Hg, then levels off • diastole may increase or decrease 10 mm Hg, or remain unchanged

6. Graded Exercise • Increase in systole, mean, and diastole with increase in Q • greatest changes are in systole, diastole may change only ~12%

7. Arm Exercise • systole and diastole significantly higher than with leg exercise, even at same intensity • may be due to smaller vasculature, increased resistance to flow • heart will have to work harder

8. Recovery • after submax exercise, systolic pressure can be temporarily (2-3 hrs) depressed below pre-exercise levels • B/c TPR remains low after exercise

9. Heart Blood Supply • has its own blood supply • has dense capillary network • @ rest, normal BF to myocardium is ~200-250 ml, 5% of Q

10. Myocardial oxygen utilization • @ rest, 70-80% of oxygen is extracted from the blood in coronary vessels • in other tissues, @rest, ~25% of the oxygen is extracted • coronary BF will increase during exercise to meet myocardial oxygen requirements, can increase 4-6X above resting levels

11. Two ways to increase myocardial BF 1. Increased myocardial metabolism causes dilation of coronary vessels 2. Increased aortic pressure forces a larger amount of blood into coronary circulation • coronary BF is 2.5X greater during diastole than during systole • heart has limited ability to generate energy anaerobically

12. Myocardial Metabolism • has a 3X higher oxidative capacity than skeletal muscle • have the greatest mitochondrial density, well adapted for fat catabolism as primary source of ATP resynthesis • Figure 15-9 this is the substrate use of the heart at rest, during exercise, and during recovery

13. glucose, fatty acids, and lactate provide energy for the heart • during heavy exercise, with a large concentration of lactic acid in the blood, the heart can use lactate for 50% of its total energy • during prolonged submax activity, 70% of energy comes from fatty acids • metabolic patterns are similar for TR and UNTR, but TR have a greater contribution of fats to the total energy requirement

14. Rate-Pressure Product: Estimate of myocardial work increase in myocardial contractility and heart rate will increase the demand for oxygen • estimate myocardial workload and oxygen consumption, use product of peak systole and heart rate • index of relative cardiac work

15. called the double product, or rate-pressure product • highly related to myocardial oxygen consumption and coronary BF • RPP = SBP X HR • with training in cardiac patients, a higher RPP can be achieved before ischemic symptoms appear • this measure is used in coronary heart disease patients

16. Blood Distribution • rapid adjustments are necessary during exercise, possible by constriction and dilation of smooth muscular bands of arterioles • additionally, venous capacitance vessels stiffen • can rapidly redistribute blood to meet metabolic demand of exercise, while preserving adequate flow and pressure throughout the system

17. Regulation of Blood Flow • changing diameter of blood vessels is most important factor regulating regional flow • resistance to flow changes with vessel diameter (to the fourth power) • reducing diameter by 1/2, causes flow to decrease 16X

18. Local Factors 1 in 30-40 capillaries is open at rest opening capillaries during exercise will 1. Increase muscle blood flow 2. Due to the increase in channels, increased blood volume can be delivered with only small increases in velocity of flow

19. 3. Enhanced vascularization will increased the effective surface for exchange between blood and muscle cells • local factors can increase the dilation of arterioles and precapillary sphinchters

20. Local Factors 1. Decrease in oxygen supply 2. Increase in temperature 3. increase in carbon dioxide 4. increase in acidity 5. increase in adenosine 6. increase in ions of magnesium and potassium • these are autoregulatory mechanisms

21. Neural factors • sympathetic and to small extent, parasympathetic portions of autonomic NS provide a central vascular control • muscles contain sensory nerve fibers which are sensitive to substances released in local tissue during exercise: causes vascular responses • central regulation ensures that the area with the most need for oxygen gets the most blood flow

22. norepinephrine is the general vasoconstrictor, and is released at certain sympathetic nerve fibers (adrenergic fibers) • other sympathetic fibers can release ACH, causing vasodilation (cholinergic fibers) • dilation of blood vessels is due more to a reduction in vasomotor tone than to an increase in action of either sympathetic or parasympathetic dilator fibers

23. Hormonal Factors • sympathetic nerves terminate in the medullary portion of the adrenal gland • with activation, epi is released in large quantities, norepi in small quantities • epi and norepi cause a constrictor response, except in blood vessels of the heart an skeletal muscle

24. during exercise, hormonal control is minor in the control of regional BF • BF is decreased to the skin, gut, spleen, liver, and kidneys as a general response

25. Integrated Response in Exercise • Nerve centers above the medullary region are active both before and at the onset of exercise to cause increases in the rate and contractility of the heart, as well as to change regional blood flow • sympathetic cholinergic outflow plus local metabolic factors acting on chemosensitive nerves and on blood vessels cause dilation in active muscles

26. this reduces peripheral resistance, allowing for greater blood flow • constriction adjustments will then occur in less active tissues as exercise continues, so that perfusion pressure can be eliminated factors influencing venous return: 1. action of muscle and ventilatory pumps 2. stiffening of the veins 3. increase in venous tone with an increase in Q

27. Cardiac Output • Q = HR X SV • primary indicator of the functional capacity of the circulation to meet the demands of PA

28. Four methods to determine Q: • Direct Fick • Q = O2 consumed/ (a-v)O2 Indicator Dilution: examine an indicator dilution curve • CO2 rebreathing, indirect Fick • Q = CO2 production/ (v-a)CO2 X 100

29. Impedance • SV • Preload • Afterload • Contractility • BP • Systemic Vascular Resistance (SVR) • Can index the values to body size