Factors Affecting Variations in Pulmonary Diffusing Capacity Resulting from Postural Changes

Abstract

The relation of postural changes to the diffusing capacity of the lung for carbon monoxide (DLCO) was investigated in 12 normal nonsmokers in order to evaluate the influence of body position on several components of lung resistance to gas diffusion. The well-known increase in CO diffusing capacity in the supine position was obtained only for data corrected for alveolar volume (KCO: 6.18 ± 0.75 vs. 5.45 ± 0.67 ml/min/ mm Hg/l; p < 0.005). Moreover, only the membrane component (Dm) increased significantly in supine subjects (KDm = 2.81 ± 1.32 vs. 1.82 ± 0.54 ml/min/mm Hg/l; p < 0.05), the increase in capillary blood volume (Vc) being not significant (KVc = 12.54 ± 4.22 vs. 11.17 ± 3.79 ml/l; NS). These data could be interpreted as a demonstration of a more homogeneously distributed ventilation with respect to diffusion surface in healthy young people in a supine position. The amount of surface available for diffusion seems therefore to be a limiting factor to gas flow across the lungs in these subjects. Thus a straightforward attribution of posturally influenced changes in CO diffusing capacity exclusively to factors affecting Vc is not recommended, particularly in pathological conditions, if information about variation in distribution of ventilation is unavailable

Effect of Postural Variations on Carbon Monoxide Diffusing Capacity in Healthy Subjects and Patients with Chronic Obstructive Pulmonary Disease

“…The increasing trend of gas exchange (DL CO , absolute value and % of predicted, and DL CO /VA) observed in healthy subjects with a change in position from upright to supine is totally in line with results supplied earlier and consistent with a picture of recruitment of lung capillary bed in response to the position change from upright to supine [5,6,7,8,9,10,11,12,13]. The most innovative results of this study are those about the prone posture, since the scientific literature does not provide us with enough information about the effect of the prone posture on DL CO , especially compared with the upright position.…”

“…In normal subjects, changing the body position from upright (and seated) to supine results in an increase in DL CO [5,6,7,8,9,10,11,12,13], possibly due to changes in pulmonary vascular recruitment and an increase in pulmonary capillary blood volume [5,6,7,8,9,10,11,12,13]. In particular, the mechanisms inducing the DL CO increase in the supine position may be attributed to a change in the pulmonary capillary shape from an elliptical (standing position) to a circular configuration (supine position) [10].…”

Lateral Decubitus Position Generates Discomfort and Worsens Lung Function in Chronic Heart Failure

“…This is likely attributable to differences in the age of subjects, ours being significantly older than subjects in previous reports. 6,7 We observed a significant reduction of Dlco in both lateral decubiti. This observation was unexpected and deserves some comment.…”

“…Indeed, in healthy, young subjects, Dlco is higher in the supine position, when compared with the sitting position, 6,5 because of an increase in capillary volume. 6,7 In patients with ARDS, the prone position eliminates compression of the lung by the heart, 9 and in heart failure patients, Dlco is similar in the sitting and supine positions with relevant interpatient variability. 8 However, a systematic evaluation of the effects of body position on lung function in congestive heart failure patients has never been carried out.…”

Diabetes mellitus and Lung Function

“…DL CO was measured by the single-breath method [9]. Four DL CO measurements, two in sitting and two in supine position, were performed in each subject, according to the method used in a previous study [10]. The subjects were asked to assume the appropriate position 5 min before the test with an interval of at least 15 min between each DL CO measurement (the best value as a percentage of predicted values).…”