CIRCULATORY RESPONSE TO EXERCISE

The Circulatory System Heart Pumps blood Arteries and arterioles Carry blood away from the heart Capillaries Exchange of nutrients with tissues Veins and venules Carry blood toward the heart

Acute cardiovascular (circulatory system) responses to exercise  heart rate  stroke volume  cardiac output  blood pressure  blood flow  blood plasma volume

Circulatory Responses to Exercise Heart rate and blood pressure Depend on: Type, intensity, and duration of exercise Environmental condition Emotional influence

Changes in Cardiac Output during Exercise CO increases during exercise in direct proportion to metabolic rate required to perform the exercise task.  due to an increase in HR & SV [CO = SV x HR] BUT: In untrained & moderately trained, at work rates >40% - 60% VO2max the increase in CO is from increase in heart rate only.

As work rate increases, the following also increase: Arteriovenous O2 difference. The extent to which O2 is extracted from the blood as it passes through the body Calculated as the difference between the oxygen content of arterial blood and right atrial blood

Arteriovenous difference increases with increasing exercise intensity: more oxygen being extracted from the blood and used for oxidative production of ATP by skeletal muscle

Mean arterial pressure (MAP) 2. Blood pressure As work rate increases, BP also increases (as more blood is pumped to working muscle from the heart): Mean arterial pressure (MAP) Average pressure in the arteries Maximal CO tends to decrease in linear fashion after 30years of age. This is due to decrease in heart rate with age.

Redistribution of Blood flow during Exercise 11/13/2018

Redistribution of Blood flow during Exercise During maximal exercise: 80% - 85% of total CO goes to contracting muscles.  necessary to meet the huge increase in muscle oxygen requirements during intense exercise. Increase to muscles is due to redistribution of blood flow from inactive organs to the contracting skeletal muscles.

Vasodilation of arterioles feeding the contracting skeletal muscles:  reduces the vascular resistance and therefore increases blood flow. Also, recruitment of capillaries in skeletal muscle:  At rest only 50% - 80% are open During intense exercise almost all open

Emotional Influence Submaximal exercise in an emotionally charged atmosphere = higher heart rates & blood pressure.

Transition From Rest  Exercise  Recovery Onset of exercise = Rapid increase in HR, SV, CO If the work rate is constant & below the lactate threshold = a steady state plateau is reached (in HR, SV, CO) Recovery depends on: Duration and intensity of exercise Training state of subject

Circulatory Responses to Exercise-Incremental Exercise HR and CO increase in direct proportion to oxygen uptake. This ensures that there is enough O2 available for ATP synthesis. Both then reach a plateau at about 100% VO2max This point represents a maximal ceiling for O2 transport to exercising muscles

The elevation in mean arterial blood pressure during exercise is due to increase in systolic pressure. Diastolic pressure remains fairly constant during incremental work Increase in exercise intensity = increase in both HR and SBP =increases the work load placed on the heart.

Recovery from exercise Recovery from short term, low intensity exercise is generally rapid Recovery speed varies from individual to individual:  Trained: recover more quickly & easily than untrained.

Circulatory Responses to Intermittent Exercise Discontinuous exercise (interval training, stop/start): Recovery of HR & BP between bouts depends on: 1. Level of fitness 2. Environmental conditions (temperature, humidity) 3. Duration and intensity of exercise.

Circulatory Responses to Intermittent Exercise Light exercise in a cool environment = generally complete recovery between bouts. Intense exercise or exercise in a hot/humid environment = cumulative increase in HR between bouts recovery is not complete.

Prolonged Exercise With prolonged aerobic exercise or aerobic exercise in the heat, at a constant exercise intensity: Gradual decrease in SV (greater % of blood diverted to skin for heat loss & decrease in blood volume from sweating)  Therefore HR must increase to maintain CO

Cardiovascular drift Ability to maintain a constant CO despite a decreasing SV which is due to the increase in HR being equal in magnitude to the decline in SV

Cardiovascular drift - due to: 1. The influence of rising body temperature on dehydration: Progressive increase in the amount of CO directed to the vasodilated skin to facilitate heat loss More blood in skin to cool the body Less blood available to return to heart = decreases SV

2. A reduction in plasma volume: Reduces venous return to the heart & therefore reduces SV If prolonged exercise is performed in a hot/humid environment, the increase in heart rate and decrease in stroke volume is exaggerated

Regulation of cardiovascular adjustments to exercise Initial signal to the cardiovascular system at the beginning of exercise comes from higher brain centers. However, fine tuning of the cardiovascular response to exercise is accomplished via a series of feedback loops from: 1.Muscle chemoreceptors 2. Arterial baroreceptors 3. Others.

Arm vs. Leg Exercise At any given level of oxygen consumption both HR and BP are higher during arm work compared to leg work Higher HR from greater sympathetic stimulation (SNS) to the heart during arm work. The relatively large increase in BP for arm work is due to a vasoconstriction in the inactive muscle groups (e.g. legs) .

Heart Rate and Blood Pressure During Arm and Leg Exercise