Arterial lactate responses in dogs made apneic or breathing nitrogen.

O2 stores are kept more intact in apnea than in N2 breathing which removes O2stores from the body. If lactate moves readily into the circulation, arterial lactate should rise sooner with N2 breathing than with apnea because tissue O2 is lowered faster. This was tested in 10 anesthetized, paralyzed dogs made hypoxic both ways. Arterial and mixed venous blood were sampled every minute until circulation began to fail. Calculated changes in O2 stores would have supported control V O2 for 1.3 min with N2 and 2.7 min with apnea. The PVO2 at those times were 23.1 and 20.1 Torr. Although arterial lactate rose sooner with N2 than with apnea, the mean values for lactate increase for both N2 and apnea were fitted by a single curvilinear relation with PVO2. The PVO2 at which lactate first rosores were depleted. Latent period for lactate rise, therefore, was nearly the same as that for development of tissue hypoxia.