Blood nitrogen tensions of seals during simulated deep dives.

KOOYMAN, G. L., J. P. SCHROEDER, D. M. DENISON, D. D. HAMMOND, J. J. WRIGHT, and W. P. BERGMAN. Blood nitrogen tensions of seals during simulated deep dives. Am. J. Physiol. 223(5) : 1016-1020. 1972.-Three species of seal were subjected to a total of 65 simulated deep dives equivalent to depths ranging from 30 to 272 m (4-28.2 atm absolute (ATA)) in a hydraulic pressure chamber. Lung volume and arterial and venous NZ tension were measured during these dives. Mean lung volume at the beginning of the dive was 20.4 ml X kg-l in elephant seals and 22.6 ml X kgl in harbor seals. Lung volume was not determined in the Weddell seal. Soon after maximum pressure was achieved, arterial Na tension, which had risen at least 2-5 ATA, declined. It was always lower than theoretically possible considering the ambient pressure. Venous Nz tension lagged behind arterial tension, and although it was low at the beginning of the compression period, it rose to about 2 ATA in elephant seals and as high as 5 ATA in harbor seals. Based on the lung volume and low arterial Nz tensions, it was concluded that seals experience absorption collapse of the lung alveoli during time at depth and that this event is probably hastened by some degree of compression collapse during descent. In some instances with harbor seals Nz tensions were high enough to be of possible concern with regard to NZ narcosis and decompression sickness.