Predicted values for closing volumes using a modified single breath nitrogen test.

The measurement of closing volumes has been proposed as a simple and sensitive test of small airway function. Prediction formulas for closing volumes, obtained from a large number of asymptomatic, nonsmoking adults have not thus far been reported. Closing volumes were measured in 284 asymptomatic, nonsmoking adults using a modification of the single breath nitrogen test. Data from these subjects were then used to derive prediction formulas for closing volume expressed as a percentage of vital capacity and for closing capacity expressed as a percentage of total lung capacity. These formulas confirmed the findings of others that closing volumes appear to increase linearly with age, presumably because of loss in lung elastic recoil. The advantages of the modified single breath nitrogen test are (1) it is suitable for use as a screening test and in epidemiologic studies because it does not require equipment that is either extremely costly or technically difficult to operate; (2) it can be used to compute tota...