Respiratory oscillations of the arterial PO2 and their effects on the ventilatory controlling system in the cat.

The respiratory oscillations of the arterial PO2 were measured in paralyzed, artificially ventilated cats by a small (1.2 mm) fast-responding catheter oxygen electrode. The amplitude of these oscillations could be changed independently of the mean PA,O2n by a specially designed respirator circuit. deltaPaO2 was shown to increase with increasing tidal volume or decreasing frequency of the respirator, and with increasing mean PaO2. The amplitude of the oscillations was attenuated considerably from the left atrium to the aorta. No attenuation occurred from the aorta to the carotid artery, provided that the blood flow in the carotid artery was not impeded. The measured attenuation of the oscillations was compared to that calculated by Yokota and Kreuzer (1973) and found to be quite different. The output of the ventilatory controlling system of the cat was measured from the quantified phrenic nerve activity. When only deltaPaO2 was changed at a constant level mean PaO2, the quantified phrenic nerve activity did not change, indicating that the amplitude of the oscillations does not influence the ventilatory controlling system. In vagotomized animals, the periodicities of the oscillations and the phrenic nerve activity were completely dissociated. From the fact that no Cheyne-Stokes type of breathing occurred, it was concluded that the effect of timing is negligible.