CANINE VENTILATION AFTER ACID-BASE INFUSIONS, EXERCISE, AND CAROTID-BODY DENERVATION

We studied the effect of exercise and carotid body denervation on the ventilatory response which occurs following acute acid-base infusions. Studies were done in 6 dogs prepared with chronic tracheostomies and carotid loops. Ventilation (VE) and arterial pH were measured at rest and during exercise before and after infusions of lactic acid (70 meq), HCl (26 meq), NaHCO3 (45 and 90 meq), or normal saline alone (250 ml). The VE response to [H+] is expressed as l x min-1/[H+] in nmol x kg H2O-1. Before carotid body denervation (CBD), the response was 0.1 l x min-1/[H+] at rest, 1.2 l x min-1/[H+] during exercise. After CBD there was no ventilatory response to [H+] at rest during exercise. We concluded that exercise potentiates the [H+] stimulus to breathing; for small changes in arterial [H+], this exercise potentiation is a function of the carotid body; that exercise potentiates the carotid body response directly and/or the central projection of this input in the central nervous system; and finally, since carotid body denervation eliminates only 7% (0.8 l x min-1) of ventilation at pH 7.35 in these dogs, that the effective threshold for this ventilatory response approximates a pH slightly greater than 7.35.