Postural and Thermal Effects on Pulmonary Diffusing Capacity at Rest

Abstract

Pulmonary diffusing capacity for carbon monoxide (DL) was measured in recumbent and sitting postures in five healthy male subjects under ambient temperatures of 12, 20, 28 and 36°C. DL increased by about 30% from 36°C to 12°C in both postures. DL in the recumbent posture was always larger than that in the sitting one and these postural change was not affected by change in ambient temperatures. Changes in DL with ambient temperature were parallel with those in pulmonary capillary blood volume (Vc) as shown in correlation coefficients of 0.54 for the recumbent position and 0.93 for the sitting one. However, the regression coefficient of DL on Vc was smaller in the recumbent posture than in the sitting one. This implies that change in DL in the recumbent posture mainly depends on pulmonary capillary dilation while change in DL in the sitting one mainly depends on pulmonary capillary recruitment. It was found out that Vc was related well with stroke volume among obtained physiological parameters. It is concluded that Vc is a primary determinant of acute change in DL induced either by postural change or by thermal condition and that alteration in Vc may be closely related with determinants of acute change in stroke volume in this study.