Cardiac Oxygenation During Severe Hypothermia in Dog

Abstract

Evidence in the form of a normal coronary A-V oxygen difference at 20[degree]C is presented in support of the contention that, in the cases of the heart at least, no serious tissue hypoxia results from the leftward shift of the Hb dissociation curve in the cold. Further evidence is gained from the fact that breathing 100% oxygen, wherein the readily available physically dissolved oxygen is greatly increased in the blood, does not materially affect the coronary A-V difference. The similarity and differences between the delivery of oxygen to the tissues in CO asphyxia and hypothermia are discussed, as is the effect of oxygen tension on oxygen uptake in tissue slice work. The shape and position of the Hb dissociation curve of blood cooled in vivo to 20[degree]C is presented and compared with a published curve constructed from blood cooled in vitro (Brown and Hill). Coronary venous pO2 values of 4 and 5 mm. Hg occur frequently at 20[degree]C, with no evidence of impaired oxygenation of heart muscle.