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Left ventricular oxygen extraction during submaximal and maximal exertion in ponies
1Department of Veterinary Biosciences, College of Veterinary Medicine, University of Illinois, Urbana 61801.
The Journal of Physiology
|October 1, 1988
Summary
This study shows that in ponies, increased oxygen extraction by the left ventricle during exercise is crucial for meeting heightened myocardial oxygen demand. Coronary blood flow does not appear to limit maximal exercise capacity.
Area of Science:
- Cardiovascular Physiology
- Exercise Physiology
- Myocardial Perfusion
Background:
- Understanding the limits of myocardial oxygen supply and demand is critical for assessing exercise capacity.
- The left ventricle (LV) has high oxygen requirements, especially during exercise, necessitating efficient oxygen extraction and perfusion.
- Previous studies suggest the equine heart has a high capacity for blood flow, but the limits during maximal exertion require further investigation.
Purpose of the Study:
- To investigate left ventricular (LV) myocardial oxygen (O2) extraction and consumption in ponies during rest and graded exercise.
- To determine the role of coronary vasodilator capacity and blood flow in limiting maximal exercise in ponies.
- To assess the impact of adenosine, a potent vasodilator, on myocardial O2 extraction during maximal exercise.
Main Methods:
- Healthy ponies (n=5) underwent catheterization for measurements of great cardiac vein and pulmonary artery O2 content, and aortic blood sampling.
- Phasic LV and aortic pressures, LV dP/dtmax (index of contractility), and rate-pressure product were recorded.
- Measurements were taken at rest, during graded exercise (moderate to maximal), and during adenosine infusion (3 mumol kg-1 min-1) at rest and maximal exercise.
Main Results:
- Resting LV O2 extraction was 59.9%, significantly reduced to 14.3% by adenosine, indicating superfluous perfusion.
- During maximal exercise, LV O2 extraction increased to 78%, with O2 consumption rising 13.4-fold compared to rest.
- Adenosine infusion during maximal exercise reduced O2 extraction to 45%, demonstrating that coronary vasodilator capacity was not fully utilized.
Conclusions:
- Increased LV O2 extraction, rather than solely increased coronary blood flow, meets the elevated myocardial O2 demand during maximal exercise in ponies.
- Coronary circulation is unlikely to be a limiting factor for further exertion in ponies, as vasodilator capacity remains.
- The LV myocardium receives a high level of blood flow, consistent with its high metabolic demands during exercise.