Relationship between tracheal air flow and induced changes in intrathoracic volume. A basis for calibration of...

The volume of air moved into the trachea due to ventricular activity--a record of which is the pneumocardiogram (PNCG)--is always less than true stroke volume. A new method of investigating this relationship consists of inducing a known volume change (delta V in) within the thorax and measuring the volume of air (delta V out) recorded with a pneumotachograph connected to the trachea. The range of delta V in was from 4 ml to 36 ml. A linear relationship (mean r = 0.98, p less than 0.001) between delta V out and delta V in was observed in 19 anesthetized, intubated dogs: delta V out = (f) delta V in, where f = 0.53 +/- 0.09 (mean +/- SD). The coefficient, f, ranged from 0.40 to 0.71. These results demonstrate that although f is subject-dependent, delta V out reliably reflects changes in delta V in. It is suggested that the technique of inducing a known volume change within the thorax and measuring the volume of air recovered from the trachea could be used as a method for calibrating the pneumocardiogram to obtain stroke volume.