Effects of Repetitive Airway Obstruction on O2Saturation and Systemic and Pulmonary Arterial Pressure in Anesthetized Dogs

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Abstract
We examined the effects of multiple repetitive airway obstruction (RAO) on arterial oxygen saturation (SaO2) and pulmonary and systemic arterial pressure in eight anesthetized spontaneously breathing dogs. SaO2 was monitored at the tongue with a pulse oximeter. RAO created by an electrical valve that was attached to a tracheal cannula was alternated with seven consecutive spontaneous breaths until the nadir SaO2 (nSaO2) became constant or decreased to less than 35%. Tracheal occlusion durations of 15, 30, 45 and 60 s were chosen arbitrarily. In each animal nSaO2 decreased with every trial number in an exponential fashion, and the rate of nSaO2 fall was greater for the longer occlusion duration. In each animal the increases in pulmonary arterial pressure (PAP) and systemic arterial pressure (SAP) were inversely related to the nSaO2 values, and the relationship between nSaO2 and PAP or SAP was identical for all occlusion durations. Moreover, when the animals breathed pure oxygen and SaO2 did not decrease, there were no significant increases in the PAP and SAP at similar levels of pleural pressure (Ppl). In another six dogs, the effects of RAO on PAP and SAP were compared with those of intermittent hypoxic exposure without apnea, which was achieved by the inhalation of hypoxic gas (4 to 6% O2,5% CO2 in N2) instead of RAO, to examine the effects of interruption of ventilation. The relationships between nSaO2 and both pressures did not differ significantly from those during RAO. These results suggest that the main factor in the PAP and SAP increases during RAO is hypoxemia or hypoxic exposure of the lung, and that other factors, including negative Ppl, interruption of ventilation, acidosis, and hypercapnia have no significant effects.

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