Regional Cardiac Hemodynamics and Oxygenation during Isovolemic Hemodilution in Anesthetized Pigs

Regulation of Coronary Blood Flow

“…2). Nevertheless, data from studies of exercise-induced increases in MVO 2 in swine [which display little change in coronary venous PO 2 (270)] and hemodilution-induced anemia (normal arterial PO 2 with progressive increases in coronary venous PO 2 [934, 935)] clearly demonstrate that reductions in tissue oxygen tension are not required for robust coronary vasodilation (Fig. 13B).…”

“…Assuming that values of coronary venous PO 2 reflect levels of myocardial tissue PO 2 (469, 919), these findings collectively support that mechanisms to invoke metabolic coronary vasodilation are progressively activated as myocardial tissue PO 2 falls below a critical threshold value. The physiologic relevance of this relationship is also supported by the essential observations that pronounced reductions in coronary microvascular resistance are also observed in response to reductions in perfusion pressure (84, 201, 252–254, 333, 690, 853), arterial PO 2 [i.e., hypoxemia; (2,22,89,205,262,376,458,608,645,670,671,708,767, 849, 917, 940, 958)], arterial oxygen content [i.e., anemia; (59, 102, 120, 204, 206–210, 323, 372, 377, 482, 486, 509, 691, 905, 934, 935, 947, 957, 976)], and overt myocardial ischemia (27–29,33,36,97,110,189,246,497,498,730–732) (see Fig. 2).…”

“…Right: Relationship between coronary blood flow and coronary venous PO 2 in response to exercise in swine [data, with permission, from Duncker et al (281)] and isovolemic hemodilution-induced anemia [data, with permission, from Van Woerkens et al (935)].…”

Hyperoxic ventilation at the critical hematocrit: Effects on myocardial perfusion and function

“…Myocardial O 2 extraction at rest is already about 50% (5). The ability to increase coronary blood flow depends upon the coronary vasodilator reserve, which may achieve a maximal increase of 400–600% (5, 6). When Hct is lowered below a threshold at which coronary blood flow cannot be adequately increased, which is when coronary vasodilatory reserve is exhausted, myocardial ischemia occurs at that critical Hct‐value (Hct crit ) (7).…”

Subcutaneous Po2 as an index of the physiological limits for hemodilution in the rat

“…Although surprising, our finding that MABP progressively fell when Hct dropped below 24% is consistent with observations in other animal species and humans. In humans (11,40,64) and animals (2,48,63), MABP rarely falls until Hct drops below 20 -25%. Because MABP is normally a regulated variable, it would be expected that the normal homeostatic response would result in an increase in peripheral resistance and/or CO to maintain MABP, the driving force for organ blood flow.…”