Factors affecting variations in pulmonary diffusing capacity resulting from postural changes.
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 less than 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 less than 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.
Pistelli
R
R
Servizio di Fisiopathologia Respiratoria, Università Cattolica S. Cuore, Roma, Italia.
Fuso
L
L
Muzzolon
R
R
Canfora
M
M
Ferrante
E
E
Ciappi
G
G
D000328:Adult; D001810:Blood Volume; D002248:Carbon Monoxide / Q000032:analysis; D005260:Female; D006801:Humans; D008297:Male; D011187:Posture; D011653:Pulmonary Diffusing Capacity / Q000502:physiology*; D011897:Random Allocation; D012119:Respiration
D002248:Carbon Monoxide