Combined influence of temperature and hydrostatic pressure on cardiac conduction

Interactions of temperature and hydrostatic pressure were examined in three types of cardiac tissue. Decreases in temperature from 37 degrees C to 27 degrees C and increases in pressure from 1 to 150 ATA slowed conduction significantly in rabbit atria, dog atria, and dog Purkinje fibers. The combination of lowest temperature and highest pressure produced the greatest decreases in conduction in all three tissues. Purkinje fiber action potentials revealed that slowing of conduction can be attributed to depressed excitability, decreased membrane potential, and reduced maximum upstroke velocity of the action potential. These action potential variables exhibited the greatest change at the lowest temperature and highest pressure. Cooling or elevations in pressure increased the duration of the action potential. At 27 degrees C, however, the duration was unaffected by increases in pressure. Aberrant conduction developed occasionally, at 27 degrees C and 150 ATA, and could be explained by changes in action potential variables. The significance of this finding is discussed with respect to the possible development of cardiac arrhythmias in divers exposed to cold hyperbaric stress.