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Isometric exercise in the denervated heart: a Doppler echocardiographic study
S C Robson1, S S Furniss, A Heads
1Department of Cardiology, Freeman Hospital, Newcastle upon Tyne.
British Heart Journal
|March 1, 1989
Summary
Heart transplant recipients cannot increase cardiac output during isometric exercise due to a denervated heart. This study highlights the heart transplant
Area of Science:
- Cardiology
- Exercise Physiology
- Transplant Medicine
Background:
- The human heart's response to isometric exercise is crucial for understanding cardiovascular health.
- Orthotopic heart transplantation denervates the heart, potentially altering its physiological responses to stress.
- Isometric exercise involves sustained muscle contraction, demanding specific cardiovascular adjustments.
Purpose of the Study:
- To investigate the hemodynamic responses to isometric exercise in orthotopic heart transplant recipients.
- To compare the cardiovascular responses of heart transplant recipients with healthy controls during isometric exercise.
- To determine if the denervated heart can augment cardiac output during isometric exertion.
Main Methods:
- Eight orthotopic heart transplant recipients and eight healthy controls performed isometric handgrip exercise at 30% of maximal voluntary contraction for three minutes.
- Cardiac output was measured using combined Doppler and cross-sectional echocardiography before, during, and after exercise.
- Hemodynamic parameters including blood pressure, heart rate, and stroke volume were continuously monitored.
Main Results:
- Healthy controls exhibited significant increases in cardiac output and blood pressure, driven by elevated heart rate with no change in stroke volume.
- Heart transplant recipients showed no significant changes in cardiac output, heart rate, or stroke volume during isometric exercise.
- The pressor response in transplant recipients was attributed to increased peripheral vascular resistance, not cardiac output augmentation.
Conclusions:
- The denervated heart in orthotopic heart transplant recipients is incapable of increasing cardiac output during isometric exercise.
- Unlike dynamic exercise, isometric exercise elicits a pressor response mediated by peripheral vascular resistance in transplant recipients.
- These findings underscore the distinct cardiovascular limitations of denervated hearts during specific types of physical stress.