Measurement of respiratory parameters using inspired oxygen sinusoidal forcing signals. Williams, E. M., R. Hamilton, L. Sutton, and C. E. W. Hahn. NUFFIELD DEPARTMENT OF ANAESTHETICS, UNIVERSITY OF OXFORD, RADCLIFFE INFIRMARY, WOODSTOCK ROAD, OXFORD, OX2 6HE, UK
APStracts 3:0140A, 1996.
A companion paper (Hahn, J. Appl. Physiol.....) described a continuous-flow gas-exchange mathematical model which predicted that forced inspired oxygen sinusoids could be used to measure respiratory parameters rapidly, in place of the inert gas argon. We therefore made simultaneous measurements of dead space volume, VD, and alveolar volume, VA, in an animal model, using argon and oxygen inspired gas concentration sinusoid forcing signals, and then compared the results. Our data confirmed the model prediction that the attenuations of the oxygen and argon sinusoid perturbations are identical in the alveolar gas space, even though there is a net uptake of oxygen by the body. Our results show that the calculated values of VD and VA, using inspired oxygen forcing signals, were independent of both the mean inspired oxygen concentration ( FIO2 range 0.18-0.80 % v/v) and the oxygen forcing signal amplitude (range +/- 2-6% v/v). In these studies, oxygen forcing signals, with forcing periods between 1 and 2 minutes, were able to measure controlled changes in instrument dead space to within 16 ml, and also measure PEEP-induced changes in VA. Under hyperoxic conditions, intravascular oxygen sensors confirmed that the sinusoidal PO2 signal passed into the arterial blood, but not into the mixed-venous blood. However, the sinusoid perturbation PO2 signal did pass into the mixed-venous blood when the mean FIO2 was mildly hypoxic (FIO2 = 0.18 % v/v). These data show that oxygen can be used instead of argon to measure airways dead space and alveolar volume. 

Received 6 January 1995; accepted in final form 21 February 1996.
APS Manuscript Number A26-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 20 March 96