It has been shown in artificially-ventilated animals and humans that the Cdyn decreases with time following a hyperinflation. The nature of the ventilation might be expected to alter the rate of fall of Cdyn, since increased ventilation has been shown by different groups to either deplete or increase alveolar surfactant. In this study we have tested whether ventilatory frequency affects this time course of Cdyn. Five mongrel dogs (30-40 lb) were anesthetized with pentobarbital and paralyzed with pancuronium. They were ventilated with a constant tidal volume (400ml) for 3 hours, the first hour at low frequency (15-18/min with I/E or 1/2), the second hour at high frequency (30-35/min with I/E of 1.5/1). and the third hour back to low frequency. At the start of each hour, the animals were hyperinflated with a 5 sec breathhold at 30 cmH2O Ptp. The conditions during high frequency were such that the peak flow rate and arterial PCO2 were the same as low frequency. The arterial PCO2 was kept constant by adding 100% CO2 into the inspired air. Results showed that the percentage decrease in Cdyn with time was less during the high frequency breathing. At low rates Cdyn fell 28% after 50 minutes, while at high rate it fell 21%. Since both tidal volume and flow rate were constant in this study, it appears that ventilatory frequency can by itself affect Cdyn. The fact that the Cdyn fell less with the higher frequency suggests both that a degradation of surfactant contributes to the fall in Cdyn with time, and that increasing breathing frequency either prevents this degradation or promotes surfactant release.
|Original language||English (US)|
|Pages (from-to)||No. 5689|
|State||Published - Jan 1 1985|
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