Effect of exhaustive exercise on myocardial performance

Area of Science:

• Cardiovascular Physiology
• Exercise Science
• Animal Models

Background:

• Previous studies noted ultrastructural heart changes in exercised animals.
• The functional capacity of the intact heart during exhaustion remained unclear.

Purpose of the Study:

• To investigate functional changes in the canine heart during exhaustive exercise.
• To determine if cardiac contractile function is depressed post-exhaustion.

Main Methods:

• Adult mongrel dogs (n=8) were instrumented to measure cardiac output, coronary blood flow, and pressures.
• Dogs underwent exhaustive exercise at ~70% max heart rate until refusal or inability to continue.
• Physiological parameters were recorded at rest, steady state, and exhaustion.

Main Results:

• Cardiac output and coronary blood flow increased from rest to steady state; stroke volume remained constant.
• During the transition to exhaustion, only maximal positive and negative dP/dt increased significantly.
• No significant changes in maximum cardiovascular parameters were observed before and after exhaustive exercise.

Conclusions:

• Cardiac contractile function is not depressed in dogs following exhaustive exercise.
• The canine heart demonstrates resilience and maintains function during intense physical exertion.