A spirometer method of studying continuously the gaseous metabolism of man during and after exercise

Abstract

The instruments generally employed for the investigation of the gaseous metabolism in man are divided into two classes, the closed and open circuit systems. Apparatus belonging to the former class is naturally not suitable for a study of rapidly altering gaseous exchange; apparatus of the latter class involves the use either of a spirometer or of a bag for collecting the expired gases. A method employing a series of Douglas bags was devised by Campbell, Douglas and Hobson (1) to follow changes in the gaseous metabolism, and recently this method has been developed in a convenient way by A. V. Hill, Long, and Lupton (2). During rapid ventilation of the lungs the latter authors succeeded in obtaining reliable results by allowing as small an interval as 10 seconds for the collection of a sample of the expired air, during the early period of recovery from severe exercise. In the present paper a method is described which obviates the necessity for a series of bags, and allows a continuous determination to be made of the gaseous metabolism in man, during or after any kind of activity in which the subject does not move away from the apparatus. Principle of Method . In fig. 1 curve V denotes the total volume of the expired gas up to time t . Suppose that a sample be taken at time t n , and that the total volume of the expired gas up to that moment is V n . From the analysis of the sample and from the total volume of the expired gas we may calculate the amounts of oxygen used and of CO 2 expired by the subject during the time interval t 0 — t n . By increasing the number of samples taken we may make a continuous curve, if we please, of either ( a ) the percentage of oxygen in the total expired air up to any moment t ; ( b ) the percentage of CO 2 in the total expired air; ( c ) the total volume of oxygen used up to time t ; or ( d ) the total CO 2 expired up to the same time. In fig. 1 the curve denoted by V represents the total volume of oxygen used. From the latter curve the oxygen consumption per unit of time at any given moment t n is obviously given by the slope of the tangent to the curve at that time. The oxygen used in any finite interval is immediately obtained by subtracting the ordinates at the beginning and end of that interval. In fig. 1 the broken line represents the rate of oxygen intake obtained by measuring the slope of the curve V . In the examples given below, however, for the sake of simplicity, finite intervals are employed, and the mean value of the rate of oxygen intake' calculated by dividing the total oxygen used during the interval by its duration.