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:  O 2 tension,  CO 2 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% VO 2max  Systolic blood pressure Increases with increasing work rate

Incremental Exercise  Stroke Volume Reaches plateau at % VO 2max 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 Cardiovasc ular Control During Exercise Fig 9.24