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CV changes during exercise

CV changes during exercise. Exercise. Greatest stress on the CV system Sympathetic nervous system orchestrates many of the changes associated with exercise Cardiac output is increased 5-6 fold Blood flow is shifted primarily from organs to active skeletal muscle. The role of the SNS.

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CV changes during exercise

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  1. CV changes during exercise

  2. Exercise • Greatest stress on the CV system • Sympathetic nervous system orchestrates many of the changes associated with exercise • Cardiac output is increased 5-6 fold • Blood flow is shifted primarily from organs to active skeletal muscle

  3. The role of the SNS • SNS stimulation due to: • Cerebral cortex stimulation (central command) • Reflex signals from active joint proprioceptors and muscle spindles • Local chemoreceptor signals originating in the active muscle • SNS effects • Increased HR and SV (CO) • Induces local metabolic vasodilatation at the heart

  4. SNS effects (cont) • SNS stimulation of pre-capillary resistance vessels (organs and inactive skeletal muscle) decreases blood flow • SNS stimulation of veins causes constriction which mobilizes blood out of veins increasing venous return • Redistribution of blood volume • SNS stimulation of vascular smooth muscle in walls of arteries help maintain slightly increased blood pressure during exercise

  5. Tissues that escape SNS vasoconstriction • Heart • SNS indirectly induces local vasodilatation by increasing cardiac muscle contractility and promoting the release of local vasodilators • Brain • SNS stimulation induces a weak constrictor response that doesn’t limit blood flow • Lungs • SNS stimulation induces a mild vasoconstriction that doesn’t limit blood flow. Pulmonary blood flow = CO

  6. Increased flow to active muscle • Increased blood flow to the active muscle is NOT mediated by the SNS but by the local release of tissue metabolites in response to the increase in metabolism “Local vasodilators” (partial list) • Adenosine • CO2 • K+ • Histamine • Lactic acid

  7. Rest CO = 5.9 L/min Coronary-250 ml/min Brain-750 ml/min Organs-3100 ml/min Inactive muscle-650 ml/min Active muscle-650 ml/min Skin- 500 ml/min Exercise = 24 L/min Coronary-1000 ml/min Brain-750 ml/min Organs-600 ml/min Inactive muscle-300 ml/min Active muscle-20,850 ml/min Skin- initially↓, then ↑as body temp ↑ Blood Flow

  8. Effect of exercise on CV endpoints • HR ↑ (60-180 b/min) • SV ↑ to a point and then may ↓ • CO ↑ (5-25 L/min) • Systolic BP ↑ • Diastolic BP ↑ (slightly) • Mean arterial BP ↑ (slightly) • Total peripheral resistance ↓ • Oxygen consumption ↑ (.25-5.0 L/min) • Arteriovenous oxygen difference ↑ (25-50%)

  9. VO2 Maximum • The maximum volume of oxygen that one can take up from the lungs and deliver to the tissues/minute • Can range from 1.5 L/min in a cardiac patient to 3.0 L/min in a sedentary man to 6.0 L/min or greater in an endurance athlete • Function of CO and AV O2 difference • Proportional to increases in SV as training occurs

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