Increased cardiac contractility in rats exposed to 5 bar

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.