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Am J Physiol Heart Circ Physiol 281: H823-H830, 2001;
0363-6135/01 $5.00
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Vol. 281, Issue 2, H823-H830, August 2001

Right ventricular oxygen supply/demand balance in exercising dogs

Bradley J. Hart, Xiaoming Bian, Patricia A. Gwirtz, Srinath Setty, and H. Fred Downey

Department of Integrative Physiology, University of North Texas Health Science Center at Fort Worth, Fort Worth, Texas 76107-2699

This is the first investigation of right ventricular (RV) myocardial oxygen supply/demand balance in a conscious animal. A novel technique developed in our laboratory was used to collect right coronary (RC) venous blood samples from seven instrumented, conscious dogs at rest and during graded treadmill exercise. Contributions of the RV oxygen extraction reserve and the RC flow reserve to exercise-induced increases in RV oxygen demand were measured. Strenuous exercise caused a 269% increase in RV oxygen consumption. Expanded arteriovenous oxygen content difference (A-VDelta O2) provided 58% of this increase in oxygen demand, and increased RC blood flow (RCBF) provided 42%. At less strenuous exercise, expanded A-VDelta O2 provided 60-80% of the required oxygen, and increases in RCBF were small and driven by increased aortic pressure. RC resistance fell only at strenuous exercise after the extraction reserve had been mobilized. Thus RC resistance was unaffected by large decreases in RC venous PO2 until an apparent threshold at 20 mmHg was reached. Comparisons of RV findings with published left ventricular data from exercising dogs demonstrated that increased O2 demand of the left ventricle is met primarily by increasing coronary flow, whereas increased O2 extraction makes a greater contribution to RV O2 supply.

oxygen extraction; myocardial oxygen consumption


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