In normoxemic cats, acetazolamide (ACTZ) has been shown to cause a large rise in ventilation (VE) but a decrease in peripheral chemoreceptor activity. The relative contribution of the peripheral chemoreceptors to ventilation is higher during hypoxemia than during normoxemia. Therefore, what are the effects of ACTZ during steady-state hypoxemia? The aims of this study in anesthetized cats were 1) to study the effect of ACTZ (50 mg/kg iv) on mean hypoxemic [arterial PO2 (PaO2) approximately 6 kPa] ventilation and 2) to study the effect of ACTZ on the isocapnic hypoxic ventilatory response. In the first study, in six cats with an inspiratory CO2 fraction of 0, ACTZ led to an insignificant rise in mean VE of 119 ml.min-1.kg-1 after 1 h. In five other cats maintained at an inspiratory CO2 fraction of 0.015, ACTZ resulted in a significantly larger response in VE (268 and 373 ml.min-1.kg-1 after 1 and 2 h, respectively). In the second study, before infusion in five cats, an isocapnic fall in mean PaO2 from 13 to 4.7 kPa led to a significant rise in mean VE of 385 ml.min-1.kg-1; 1 h later, the response (at the same mean alveolar PCO2) was reduced to an insignificant rise of 38 ml.min-1.kg-1. Before infusion four other cats showed a significant rise in mean VE of 390 ml.min-1.kg-1 when mean PaO2 was lowered isocapnically from 12.4 to 6.8 kPa; 2 h after infusion, an isocapnic fall in mean PaO2 from 13.9 to 7.2 kPa led to an insignificant rise of 112 ml.min-1.kg-1.(ABSTRACT TRUNCATED AT 250 WORDS)
Experimental and theoretical study of processes leading to steady-state sound in annular thermoacoustic engines
