Cardiovascular changes in anesthetized rats during exposure to 30 bar

The effect of exposure to 30 bar (PHe = 29.0 bar, PN2 = 0.8 bar, PO2 = 0.2 bar) on left ventricular pressure, cardiac contractility, heart rate (HR), and arterial pressure was studied in anesthetized rats. During compression there was a progressive increase in maximal left ventricular pressure (LVPmax), maximal velocity of LVP rise (+ dP/dtmax) and fall (- dP/dtmax), systolic pressure (APsys), and pulse pressure (delta AP). The greatest increase in contractility per bar was found between 1 and 5 bar. Immediately after 30 bar was reached, LVPmax (19%), + dP/dtmax (60%), and - dP/dtmax (22%). APsys (19%), and delta AP (43%) were significantly increased from predive values, with an additional increase detected for all these variables after 60 min at 30 bar. An increase in estimated oxygen consumption (work load) of the heart was also found during compression to and at 30 bar. No changes in HR, mean arterial pressure, and end-diastolic pressure were observed during the high-pressure exposure, indicating that the inotropic changes were not due to changes in peripheral hemodynamics.