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

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Abstract
The volume of air moved into the trachea due to ventricular activity.sbd.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 of inducing a known volume change (.DELTA.Vin) within the thorax and measuring the volume of air (.DELTA.Vout) recorded with a pneumotachograph connected to the trachea. The range of .DELTA.Vin was from 4 ml to 36 ml. A linear relationship (mean r=0.98, p<0.001) between .DELTA.Vout and .DELTA.Vin was observed in 19 anesthetized, intubated dogs; .DELTA.Vout=(f) .DELTA.Vin, 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.Vout reliably reflects changes in .DELTA.Vin. 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.

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