Relationship Between Tracheal Air Flow and Induced Changes in Intrathoracic Volume

A Basis for Calibration of Pneumocardiogram

抄録

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 (ΔV_in) within the thorax and measuring the volume of air (ΔV_out) recorded with a pneumotachograph connected to the trachea. The range of ΔV_in was from 4ml to 36ml. A linear relationship (mean r=0.98, p<0.001) between ΔV_out and ΔV_in was observed in 19 anesthetized, intubated dogs: ΔV_out=(f)ΔV_in, where f=0.53±0.09 (mean±SD). The coeff=icient, f, ranged from 0.40 to 0.71. These results demonstrate that although f is subject-dependent, ΔV_out reliably reflects changes in ΔV_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.