Influence of hyperbaric oxygen on left ventricular contractility, total coronary blood flow, and myocardial oxygen consumption in the conscious dog

Savitt, M.A.; Rankin, J.S.; Elberry, J.R.; Owen, C.H.; Camporesi, E.M.

Undersea and Hyperbaric Medicine Journal of the Undersea and Hyperbaric Medical Society Inc 21(2): 169-183

1994


ISSN/ISBN: 1066-2936
PMID: 8061558
Accession: 008867066

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Abstract
It is known that hyperbaric oxygenation (HBO) decreases total coronary blood flow (TCBF) and cardiac output (CO). To determine whether this is related to an alteration in myocardial contractility, 10 chronically instrumented conscious dogs were studied during pharmacologic autonomic blockade. Left ventricular (LV) volume was measured with ultrasonic transducers, LV transmural pressure with micromanometers, TCBF with Doppler-flow probes, and coronary AV-O-2 difference (A-CS-O-2) was calculated from direct LV and coronary sinus (CS) sampling. To evaluate the effect of increased oxygenation, data were obtained during resting control conditions and during dynamic vena caval occlusions (VCO), at 1 atmosphere of pressure, while breathing air (1 bar/0.21); at 3 atmospheres, breathing compressed air (3 bar/0.21), and at 3 atmospheres breathing 100% oxygen (3 bar/1.0). Because of autonomic blockade, heart rate (HR) was not statistically different in the three conditions. With increasing oxygenation, arterial oxygen tension (Pa-O-2) increased from 85 +- 5 mmHg (mean +- SD) at 1 bar/0.21, to 1374 +- 201 mmHg at 3 bar/1.0 whereas arterial carbon dioxide tension (Pa-CO-2) and pH values were not statistically different. Arterial oxygen content (A-O-2 content) and CS-O-2 content increased significantly (both P lt 0.05) with increasing Pa-O-2. LV stroke volume (SV), CO, coronary blood flow, and myocardial oxygen consumption (MV-O-2) were all significantly reduced (P lt 0.05) with increasing levels of oxygenation. Intrinsic myocardial function, as measured by the stroke-work/end-diastolic volume relationship was unchanged from 1 bar/0.21 to 3 bar/0.21, and to 3 bar/1.0 (P lt 0.20). Thus, the diminished TCBF, CO, and MV-O-2 associated with HBO do not seem to be associated with a primary alteration in myocardial contractility, but rather may result from a physiologic autoregulation of the myocardium to increasing levels of Pa-O-2.