Canadian Journal of Anesthesia, Vol 25, 479-487, Copyright © 1978 by Canadian Anesthesiologists' Society

Variability of the Pulmonary Vascular Response to Hypoxia and Relation to Gas Exchange in Dogs

¹ Departments of Anaesthesia and Medicine, McMaster University Health Sciences Centre, Hamilton, Ontario, Canada, L8S 4J9

Anaesthetized and mechanically ventilated dogs were subjected to five minutes of alveolar hypoxia with FI_OO2 ranging from 0.08 to 0.20 while pulmonary artery pressure (Ppa), pulmonary wedge pressure (Pwp) and cardiac output (Q^·) were measured. Hypoxia increased Ppa in all dogs whereas Pwp and Q^· did not change significantly. Thus pulmonary vascular resistance (PVR) increased by a mean for all dogs of 56 per cent. There was great variation in the absolute increase in Ppa and PVR between animals and these were not statistically correlated with arterial P_OO2, but highly significant and reproduceable inverse relationships were found for Ppa and PVR against arterial oxygen per cent saturation. The slopes of these responses varied between dogs from -0.013 to -0.144 for PVR and from -0.038 to -0.561 for Ppa. The alveolar-arterial oxygen gradient and the pulmonary shunt fraction were reduced in a similar way with decreasing arterial oxygen per cent saturation, but dead space/tidal volume ratio remained unchanged. Thus the slope of PVR response to hypoxia against arterial oxygen per cent saturation is unique for individual animals. This may reflect functional and likely structural adaptations of the pulmonary vascular smooth muscle.

Note:

Supported by the Canadian Medical Research Council, Grant # MA 5880. Presented in part at the Canadian Anaesthetists' Society Meeting, June 20-23, 1977.