Ventilation-perfusion ratio obtained by a noninvasive frequency response technique

Abstract

Results of animal experiments using sinusoidal changes in inspired halothane concentration showed that the ratio of variation in end-expired concentration to the variation in inspired concentration reached a plateau in the Bode diagram. With the help of an uptake and distribution model, the interpretation of the results showed that the level of the plateau is determined by the overall ventilation-perfusion ratio. With a good selection of input frequency, tracer agent, and known ventilation, the ventilation-perfusion ratio and the lung perfusion can be consequently obtained noninvasively. Mean ventilation-perfusion ratio was determined with 20 human voluteers. At rest a mean ratio was found of 0.87 +/- 0.28 (SD). At a work load of 90 W a mean ratio was found of 1.19 +/- 0.19 (SD). In two individuals reproducibility and influence of CO2 was studied. At rest without additional CO2 the ventilation-perfusion ratio was 0.71 +/- 0.06 (SD) obtained with a constant breathing rate of 10/min. At an end-expired CO2 level of 6% the ventilation-perfusion ratio was increased almost 2.5 times. The calculated perfusion with and without increased end-expired CO2 levels under the same work load were well reproducible.

Modelling Inert Gas Exchange in Tissue and Mixed–Venous Blood Return to the Lungs

“…as used with the sine-wave technique for inert gases (Barton et al, 1988;Gavaghan & Hahn, 1995Hahn et al, 1993;Williams et al, 1994Williams et al, , 1998Zwart et al, 1975). In this case, we are interested in the venous blood partial pressure, P T (t), that #ows back to the lungs.…”

“…One example is the uptake and distribution of an anaesthetic agent within tissue, (Mapleson, 1963(Mapleson, , 1973Zwart et al, 1975). Another example is to predict the onset of atelectasis (the collapse of a region of the lung), (Joyce & Williams, 1999).…”

“…A further need for an accurate description is to calculate the content of a given gas in the mixedvenous blood #owing from the body compartments back to the lungs. This is used in the sine-wave technique, an experimental technique for investigating various cardio-respiratory parameters (Barton et al, 1988;Gavaghan & Hahn, 1995Hahn et al, 1993;Williams et al, 1994Williams et al, , 1997Williams et al, , 1998Zwart et al, 1975).…”

“…The sine-wave technique (Barton et al, 1988;Gavaghan & Hahn, 1995Hahn et al, 1993;Williams et al, 1994Williams et al, , 1997Williams et al, , 1998Zwart et al, 1975) is an experimental technique designed to investigate various cardiorespiratory parameters. When being investigated with the sine-wave technique, a subject is given an inspired gas mixture containing one or more marker gases whose partial pressure varies with a sinusoidal perturbation with time about a "xed mean concentration, with a period typically between 1 and 5 min.…”

“…All of this work then uses the ODE describing gas partial pressure in the body compartment to calculate the amplitude of the resulting perturbation to the mixed-venous blood signal. Most authors, (Barton et al, 1988;Gavaghan & Hahn, 1995Hahn et al, 1993;Williams et al, 1994Williams et al, , 1997Zwart et al, 1975) on the basis of the attenuation predicted by the ODE, assume that the perturbation in the concentration of the marker gases in mixed-venous blood is negligible, and so assume that the partial pressure of the marker gas in mixed-venous blood is constant. Another work (Williams et al, 1998) has used the ODE to predict the amplitude of the perturbation to the partial pressure of mixed-venous blood under conditions where it is not negligible.…”