A. Agrawal et Kp. Agrawal, BODY PLETHYSMOGRAPHIC MEASUREMENT OF THORACIC GAS VOLUME WITHOUT PANTING AGAINST A SHUTTER, Journal of applied physiology, 81(2), 1996, pp. 1007-1011
When a subject breathes through a pneumotachograph in a body box, the
measured value of specific airway resistance (sRaw(1)) is equal to the
product of thoracic aas volume (TGV) and the sum of the airway resist
ance (Raw) and the instrument resistance (Rins). If an additional resi
stance (Radd) is put in the breathing path, the measured specific airw
ay resistance (sRaw(2)) exceeds sRaw(1) by the product of TGV and Radd
and can be used for determining TGV. With the use of a device increas
ing Rins by a known amount (Radd) during normal breathing, sRaw(1) and
sRaw(2) were measured in 3 normal subjects, 16 asthmatic patients, 2
patients with chronic obstructive pulmonary disease, and 1 patient wit
h restrictive lung disease from the slopes of the x-y plots of airflow
vs. box signals obtained before and after adding Radd. TGV was calcul
ated by dividing (sRaw(2)-sRaw(1)) by Radd. We also determined subject
s' TGV by the panting method of A. B. DuBois, S. Y. Botelho, G. N. Bed
ell, and J. H. Comroe, Jr. (J. Clin. Invest. 35: 322-326, 1956) and fu
nctional residual capacity by the helium-dilution method. The results
of the new method were quite reproducible (coefficient of variation=5.
6) and equivalent to those obtained by the other two methods.