AORTIC PH OSCILLATIONS IN CONSCIOUS HUMANS AND ANESTHETIZED CATS AND RABBITS

Respiratory oscillations in arterial blood gas composition influence b reathing in cats and dogs. Their role in the control of breathing in h umans is less certain. To determine whether oscillations are very smal l or absent in mammals who are large or breathe fast, aortic pH oscill ations, recorded with a tridodecylamine based hydrogen-ion selective e lectrode, were compared in humans (n = 13), cats (n = 7) and rabbits ( n = 4) over a wide range of ventilation. For comparison, data were ana lysed in terms of the ratio of tidal volume to functional residual cap acity (VT/FRC). During spontaneous breathing in rabbits, cats and huma ns (mean respiratory frequency fR = 61, 20.4 and 17.5 min(-1)), mean V T/FRC were 1.35, 0.63 and 0.36 respectively. Corresponding pH amplitud es (pHamp) of 0.009 (0.004), 0.016 (0.006) and 0.013 (0.005) pH units (mean +/- 1SD) were not significantly different. The pHamp decreased e xponentially with increasing fR in each species and pHamp increased li nearly with increasing VT in the 3 cats in which this was studied. The study confirms the dependence of pHamp on fR and VT and its comparabi lity among species despite differences in body size. It also demonstra tes that oscillations can be recorded in humans at fR in excess of 20 min(-1).