Effect of exercise conditioning on coronary resistance

Area of Science:

• Cardiovascular Physiology
• Exercise Physiology
• Coronary Circulation

Background:

• Diastolic coronary resistance (DCR) is a key determinant of myocardial oxygen supply.
• The effects of partial exercise conditioning on DCR regulation are not fully understood.

Purpose of the Study:

• To investigate the impact of partial exercise conditioning on DCR in conscious dogs.
• To examine the role of adrenergic blockade in modulating DCR before and after training.

Main Methods:

• Measurements of aortic pressure and left circumflex coronary flow during atrial pacing in conscious dogs.
• Assessment of DCR at varying heart rates before and after exercise conditioning (partial training).
• Adrenergic blockade using propranolol (beta B) and phentolamine (alpha B); myocardial oxygen consumption (MVO2) measurement.

Main Results:

• DCR decreased with increasing heart rate in both untrained (UT) and partially trained (PT) states.
• Partial training significantly reduced DCR at rest and during pacing compared to the UT state.
• Alpha-adrenergic blockade reduced DCR, while beta-adrenergic blockade increased it; these effects were maintained in the PT condition.
• Myocardial oxygen consumption was not affected by training or adrenergic blockade but increased with heart rate.

Conclusions:

• Partial exercise conditioning alters coronary resistance vessel caliber, leading to a parallel shift in the DCR-heart rate relationship.
• The findings suggest enhanced coronary blood flow regulation following short-term exercise conditioning.