Mechanical output impedance of the lung determined from cardiogenic oscillations

The beating heart naturally oscillates the lung because of the close juxtap osition between these organs producing cardiogenic oscillations in flow tha t can be measured at the mouth when the glottis is open. Correspondingly, i f the mouth is occluded, the same phenomenon produces cardiogenic pressure oscillations that can be measured just distal to the site of occlusion. The Fourier-domain ratio of these oscillations in pressure and flow constitute s what we call cardiogenic respiratory impedance (Zc). We calculated Zc bet ween about 1.5 and 10 Hz in relaxed normal subjects at functional residual capacity with open glottis. Zc was insensitive to heart rate changes induce d by exercise and had an imaginary part close to zero at all frequencies in vestigated. Its real part was similar to or smaller than resistance determi ned by the forced oscillation technique. We speculate that Zc measures the flow resistance of the central and upper airways of the lung. Zc may be use ful as a means of obtaining information about lung mechanics without the ne ed for an external source of flow perturbations.