Effect of alterations in blood volume on cardiac function during maximal exercise

Area of Science:

• Exercise Physiology
• Cardiovascular Physiology

Background:

• Endurance-trained individuals exhibit higher stroke volume and cardiac output than untrained individuals.
• This difference has been hypothesized to stem from enhanced diastolic filling due to larger blood volume in trained individuals.

Purpose of the Study:

• To investigate the direct impact of blood volume manipulation on cardiac function in endurance-trained and untrained males.
• To determine if blood volume is the primary determinant of enhanced diastolic filling in endurance-trained individuals.

Main Methods:

• Cardiac function was assessed in six endurance-trained and six untrained males under control conditions.
• Blood volume was manipulated by 500 mL (reduction in trained, expansion in untrained) and cardiac function reassessed.
• Key parameters measured included blood volume, maximal diastolic filling rate, maximal ventricular emptying rate, stroke volume, cardiac output, and VO2max.

Main Results:

• Endurance-trained individuals had significantly greater blood volume, maximal diastolic filling rate, stroke volume, cardiac output, and VO2max compared to untrained individuals.
• Expanding blood volume in untrained individuals increased diastolic filling rate, stroke volume, cardiac output, and VO2max.
• Reducing blood volume in endurance-trained individuals decreased diastolic filling rate, stroke volume, cardiac output, and VO2max.

Conclusions:

• Alterations in stroke volume and cardiac output due to blood volume changes are primarily mediated by changes in diastolic function.
• The enhanced diastolic filling rate observed in endurance-trained individuals is largely attributable to their larger blood volume.