Dependence of phrenic motoneurone output on the oscillatory component of arterial blood gas composition.

Abstract

SUMMARY1. The hypothesis that respiratory oscillations of arterial blood gas composition influence ventilation has been examined.2. Phrenic motoneurone output recorded in the C5 root of the left phrenic nerve and the respiratory oscillations of arterial pH in the right common carotid artery were measured in vagotomized anaesthetized dogs which had been paralysed and artificially ventilated.3. The effect of a change in tidal volume for one or two breaths on phrenic motoneurone output was measured with the inspiratory pump set at a constant frequency similar to, and in phase with, the animal's own respiratory frequency. A reduction of tidal volume to zero or an increase by 30 % led to a corresponding change of mean carotid artery pH level. The changes of carotid artery pH resulted in a change of phrenic motoneurone output, predominantly of expiratory time (Te) but to a lesser extent of inspiratory time (TI) and also peak amplitude of 'integrated' phrenic motoneurone output (Phr). Denervation of the carotid bifurcation blocked this response.4. The onset of movement of the inspiratory pump was triggered by the onset of phrenic motoneurone output. When a time delay was interposed between them, the phase relationship between respiratory oscillations of arterial pH and phrenic motoneurone output altered. The dominant effect was to alter Te; smaller and less consistent changes of Phr and Ti were observed.5. When the inspiratory pump was maintained at a constant frequency but independent of and slightly different from the animal's own respiratory frequency (as judged by phrenic motoneurone output), the phase relationship between phrenic motoneurone output and the respiratory oscillations of pH changed breath by breath over a sequence of 100-200 breaths, without change of the mean level of arterial blood gas composition. Te varied by up to 30 % about its mean value depending on the phase relationship. Ti and Phr were also dependent on the phase relationship but varied to a lesser extent. The changes were comparable to the results obtained in paragraph 4.6. It was concluded that phrenic motoneurone output is dependent in part on its relationship to the respiratory oscillations of arterial blood gas composition.

Role of carbon dioxide oscillation in the control of respiration in the anesthetized dog.

“…Dependence of respiratory center output on the timing of carotid body stimulation within a respiratory cycle has been demonstrated (ELDRIDGE, 1972;CROSS et al, 1979;TEPPEMA et al, 1985). In the present experiment, vagotomy changed the phase relationship between mechanical ventilation (hence arterial C02 oscillation) and the respiratory center output of the dog.…”

Role of metabolic CO2 production in ventilatory response to steady-state exercise.

“…The magnitude (and probably instantaneous rate) of such oscillations are increased when mixed venous-arterial Pco2 differences are increased, such as during venous CO2 loading (34,35). It has not been established that such oscillations do in fact provide a stimulus to ventilation, but there is some experimental support for the possibility (36,37). Furthermore, it is of interest that the oscillations in arterial Pco2 and pH are detected by the carotid body chemoreceptors and reflected in their neural output, even under normoxic conditions (38)(39)(40).…”

“…Studies were performed in four adult sheep, weighing [35][36][37][38][39][40] kg, that were selected for study on the basis of being in good health (by veterinarian examination) and of calm temperament, and of a demonstrated ability to run on a treadmill. The sheep were trained to stand quietly in place and to run on the treadmill at speeds of0.7-2.0 mph for 20-30 min at each speed.…”

The pH oscillations in arterial blood during exercise; a potential signal for the ventilatory response in the dog

“…Further doses were given during the experiment as required. An Cross et al 1979), the amplitude of the pH cycle (pH amp); the maximum rate of fall of pH obtained from the first differential of the pH signal (dpH/dtlmax); and the C02 production (fco,). The method used for computation of breath-by-breath Tco, and its validation are given in the preceding paper (Cross et at.…”

“…Firstly there could be a very small change in the mean level of the gas tensions or pH, undetected by measurement on arterial blood samples because of the moment-to-moment variation in ventilation and the errors of measurement of pH, blood gases and ventilation. Secondly, the signal could be due to a change in the pattern of the arterial PCO, or pH oscillations in arterial blood (Yamamoto, 1960;Saunders, 1980) or alteration in their temporal relationships to the ventilatory cycle (Cross, Grant, Guz, Jones, Semple & Stidwill, 1979). Both the amplitude and the rate of change of PCO. on the upstroke of the oscillation (or rate of change of pH on the downstroke of the oscillation) are largely determined by 10co, and are therefore potential humoral signals linking ventilation and TC0.…”