Temperature-induced changes in turtle CSF pH and central control of ventilation.

Cerebrospinal fluid (CSF) and arterial blood acid-base variables, as well as respiratory minute volume (RMV), were measured at three different body temperatures in unanesthetized turtles. RMV remained constant while CSF pH decreased 0.015 U/degrees C with increasing body temperature. These results show that ventilation is not tracking CSF pH when body temperature is the independent variable; however, perfusion of the brain ventricular system of turtles with mock CSF, in which ion-dependent pH decreases were produced, caused large increases in ventilation which were independent of body temperature. Comparisons between turtles and goats reveal that central chemical control of ventilation is functioning similarly in the two animals and appears to fit the alphastat model of ventilatory control proposed by Reeves. These data strongly suggest that both animals are maintaining the fractional dissociation of imidazole constant in central receptive structures, indicating that this system is the model for central chemical control of ventilation in air-breathing vertebrates.