Changes in the minute ventilation of rats exposed to different concentrations of cigarette smoke

Measurements of tidal volume and breathing frequency were made in rats during a 30-min period of exposure to cigarette smoke, and were compared with those obtained during a 10-min pre-exposure period. All measurements were made in animals previously habituated to smoke exposure. Both tidal volume and breathing frequency were decreased by low-dose exposure to smoke, resulting in a 34% decrease in minute volume. At high-dose exposures (double the low-dose smoke concentration) tidal volumes showed a 23% increase over pre-exposure values with little change in breathing frequency, giving a net 20% increase in minute ventilation. This apparent inverse dose-relationship is discussed.