Exercise and the Heart

O2 Delivery

Q increase is in direct proportion to the O2 demand of the muscles Heart Rate Stroke Volume

Blood pressure Systolic Diastolic

a-v O2 Difference

Redistribution of Blood Flow

Muscle blood flow to working skeletal muscle

Splanchnic blood flow to less active organs (Liver, kidneys, GI tract, etc.)

Redistribution of Blood Flow During Exercise

Fig 9.19 (c) 2004 The McGraw-Hill Companies, Inc. All rights reserved.

Redistribution of Blood Flow

Increased Blood Flow to Skeletal Muscle During Exercise

How? Withdrawal of sympathetic

vasoconstriction Autoregulation

Blood flow increased to meet metabolic demands of tissue

Vasodilation: O2 tension, CO2 tension, pH, potassium, adenosine, nitric oxide

Circulatory Responses to Exercise

Depend on: Type, intensity, and duration of

exercise Environmental condition Emotional influence

Transition From Rest Exercise and Exercise Recovery

Rapid increase in HR, SV, cardiac output

Plateau in submaximal (below lactate threshold) exercise O2 supply = O2 demand

Recovery depends on: Duration and intensity of exercise Training state of subject

Transition From Rest Exercise Recovery

O2 supply < O2 demand

O2 supply = O2 demand

Recovery

O2 supply > O2 demand What is the extra oxygen used for?

Restore O2 inside muscles (myoglobin) Removal of lactic acid Reduce body temperature

Incremental Exercise

Heart rate and cardiac output Increases linearly with increasing work

rate Reaches plateau at 100% VO2max

Systolic blood pressure Increases with increasing work rate

Incremental Exercise

Stroke Volume Reaches

plateau at 40-60% VO2max

Why?

Arm vs. Leg Exercise

At the same oxygen uptake arm work results in higher: Heart rate

Due to higher sympathetic stimulation Blood pressure

Due to vasoconstriction of large inactive muscle mass

.

Heart Rate and Blood Pressure During Arm and Leg Exercise

Prolonged Exercise

Cardiac output is maintained Gradual decrease in stroke volume Gradual increase in heart rate

Cardiovascular drift Due to dehydration and increased

skin blood flow (rising body temperature)

.

Fig 9.22

HR, SV, and CO During Prolonged Exercise

Fig 9.22

Cardiovascular Adjustments to Exercise

Fig 9.23

Summary of Cardiovascular Control During Exercise

Initial signal to “drive” cardiovascular system comes from higher brain centers

Fine-tuned by feedback from: Chemoreceptors Mechanoreceptors Baroreceptors

Fig 9.24

A Summary of Cardiovascular Control During Exercise

Fig 9.24