Increased cardiac contractility in rats exposed to 5 bar

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Abstract
The left ventricular pressure, arterial blood pressure and heart rate were studied in three series of pentobarbital-anaesthetized rats exposed to 5-bar normoxic (PO2 = 0.2 bar) environments: nitrogen-oxygen (15 and 60 min) and helium-oxygen (15 min). The maximal left ventricular pressure (LVP max) and the maximal velocities of LVP rise (+dP/dt max) and fall (-dP/dt) were significantly (P < 0.01) increased immediately after reaching normoxic 5 bar (He, 13-28%; N2, 13-23%) and during the exposure at 5 bar (He, 22-44%; N2, 13-18%). The pulse pressure increased significantly (He, 50-62%; N2, 30-34%; P < 0.01) during the hyperbaric exposure. No changes in heart rate or end-diastolic and mean arterial pressure were detected. The present findings indicate an enhanced cardiac contractility (+dP/dt max) at 5 bar, with the greatest increase found when He was used as inert gas. The increased contractility was of significant duration (at least 60 min), and was not completely reversed until 5-10 min after decompression.