Alteration of ischemic cardiac function in normal heart by daily exercise

Area of Science:

• Cardiovascular Physiology
• Exercise Physiology

Background:

• Myocardial ischemia reduces cardiac function and blood flow.
• Exercise training is known to improve cardiovascular health.
• The effects of training on myocardial response to acute ischemia require further elucidation.

Purpose of the Study:

• To investigate the impact of a 4-week treadmill exercise program on myocardial function and tissue blood flow during coronary artery occlusion in conscious dogs.
• To compare the physiological responses between untrained (UT) and partially trained (PT) states.

Main Methods:

• Utilized ultrasonic segment length gauges to assess myocardial function in the ischemic zone.
• Employed isotope-labeled microspheres to measure myocardial tissue blood flow in normal and ischemic regions.
• Studied conscious dogs under control conditions and during a 2-minute left circumflex coronary artery occlusion.

Main Results:

• Myocardial function in the ischemic zone reduced by 71% in UT dogs, but only 33% in PT dogs during occlusion.
• Heart rate increased by 46% in UT dogs versus 19% in PT dogs during occlusion.
• Tissue blood flow to the ischemic subendocardium decreased by 60% in UT dogs, compared to a 34% decrease in PT dogs (heart rate held constant).

Conclusions:

• Partial training significantly improves myocardial function during acute ischemia.
• Enhanced coronary collateral blood flow into the ischemic zone is a key mechanism for improved function after training.
• Exercise training confers protective benefits against ischemic events in the heart.