Cardiogenic oscillations in expired gas: origin and mechanism

I produced cardiogenic oscillations (C.O.) of gas concentration for Ar, N2 and CO2 in the expirate by inspiration from RV of a bolus of Ar-O2 mixture followed by O2 to TLC. In 3 out of 4 subjects, C.O. of Ar changed phase during expiration by a half cycle with respect to C.O. of CO2, as was predicted by a previously suggested model (Arieli, R., A.J. Olszowka and H.D. Van Liew (1981) J. Appl. Physiol. 51: 922-928). The model attributed the production of C.O. to fluctuation of the relative flow from two units which differ from each other in their compliance; and due to an assumed dependence of the resistance on the compliance, the time constant of each lung unit changes as a function of lung volume. By scaling the subject's lung volume to Weibel Model A and by the use of expired volume and ECG, I suggest that the origin of C.O. seen at the mouth is at the terminal bronchioles. I made use of the arrhythmic heart rate of one subject to confirm the aligning of ECG with C.O. and also to show that the volume between the site of C.O. origin and the mouth is a function of lung volume. The differences between C.O. of Ar, N2 and CO2 are attributed to their distribution pattern in the lung.