Maximal myocardial blood flow is enhanced by chronic hypoxemia in late gestation fetal sheep

Abstract

The measurement of maximal myocardial blood flow gives information about the total cross-sectional area of the coronary resistance vessels. During a continuous left atrial infusion of adenosine (60 micrograms.kg-1.min-1), maximal myocardial blood flow was measured in 4 fetuses hypoxemic for a minimum of 5-8 days (pH = 7.33 +/- 0.01, arterial PCO2 = 49.8 +/- 4.2 Torr, arterial PO2 = 16.1 +/- 1.3 Torr, and arterial concentration of O2 = 5.3 +/- 1.2 ml/dl). These data were compared with an identically instrumented group of normoxemic fetuses (n = 7) following the same study protocol (pH = 7.38 +/- 0.02, arterial PCO2 = 43.1 +/- 3.8 Torr, arterial PO2 = 19.8 +/- 2.0 Torr, and arterial concentration of O2 = 7.9 +/- 1.0 ml/dl) (P < 0.05). At comparable arterial pressures, the maximal myocardial flow (ml.min-1.100 g tissue-1) for hypoxemic vs. normoxemic fetuses was 974 +/- 273 and 630 +/- 181 for the total myocardium, 986 +/- 367 and 602 +/- 192 for the left ventricular free wall, 1,025 +/- 346 and 614 +/- 178 for the septum, and 1,231 +/- 274 and 757 +/- 269 for the right ventricular free wall, respectively (P < 0.01). These data suggest that hypoxemia in the fetus can significantly alter the coronary vascular bed, which, if confirmed, would represent an important adaptation in the developing fetus.

Intermittent high altitude hypoxia protects the heart against lethal Ca2+ overload injury

“…It is noteworthy that the CF during pre-depletion and Ca 2+ paradox was higher in IHA hypoxic hearts in the present study, which is consistent with the previous observations from IHA hypoxic hearts (Zhong et al, 2002;Zhu et al, 2003) and chronic hypoxic hearts (Reller et al, 1992;Kong et al, 2001). This phenomenon may be related to a decrease in coronary circulation resistance and/or to an increase in myocardial capillarity density in hypoxic heart (Kayar and Banchero, 1985;Reller et al, 1992).…”

“…This phenomenon may be related to a decrease in coronary circulation resistance and/or to an increase in myocardial capillarity density in hypoxic heart (Kayar and Banchero, 1985;Reller et al, 1992). Such adaptation may also contribute partly to a resumed cardiac function when the hearts subject to Ca 2+ paradox.…”

Myocardial vascular and metabolic adaptations in chronically anemic fetal sheep

“…In the ovine fetus, decreased arterial oxygen content has profound effects on myocardial blood flow (9). In response to chronic (5-8 days) hypoxemia and chronic anemia, fetal myocardial blood flow increases severalfold (9,27). This finding is not unexpected because the heart operates aerobically and coronary flow must increase to provide adequate myocardial oxygen delivery.…”

Influence of Altitude Exposure on Coronary Flow Reserve

“…2 For safety reasons, it is therefore current clinical practice to advise patients with CAD not to exceed moderate altitudes of Ϸ2000 to 2500 m. 3 Because similar conditions are encountered in most airplanes during flight, concerns have been raised about the risk of air travel for certain patients with CAD. 4 In experimental animals, acute 5 and chronic hypoxemia have been shown to increase baseline 6 as well as maximal 7 pharmacologically and exercise-induced 6 myocardial blood flow (MBF). By contrast, in humans, only scant data exist on the influence of acute hypoxia on coronary circulation.…”