Deposition of ethanol and acetone vapors in the upper respiratory tract of the rat.

The deposition of nonreactive gases in the lungs is well studied and is dependent on the ventilation-perfusion relationships of that organ. The current investigation was undertaken to determine if pulmonary ventilation-perfusion models could be successfully applied to quantitatively describe upper respiratory tract (URT) deposition of acetone and ethanol vapors. Toward this end, the deposition of these vapors was measured in the surgically isolated URT of the anesthetized rat at selected inspiratory flow rates (ranging from 70 to 500 ml/min) and exposure times (ranging from 3.3 to 13.3 min). The deposition of acetone in the URT followed apparent quasi-steady-state conditions, suggestive of a ventilation-perfusion relationship. Pulmonary ventilation-perfusion models predict the ratio of the amount deposited to the amount not deposited should be linearly related to the inverse of the inspiratory flow rate. Such a relationship was observed for URT acetone (r = 0.988, N = 16,p less than 0.0001) and ethanol (r = 0.963, N = 20, p less than 0.0001) deposition. From the deposition-flow relationships estimates of 0.31 and 0.33 ml/min were obtained for nasal blood flow in the ethanol and acetone studies, respectively. The 95% confidence limits for these estimates overlapped. The successful application of a ventilation-perfusion model to describe URT deposition suggests that acetone and ethanol vapors equilibrate between the inspired airstream and the capillary blood of the URT and that their deposition is dependent on both the URT ventilation and perfusion rates.