Significance of pulmonary elastic and viscous resistance in orthopnea

The mechanical properties of the lungs were measured in the sitting and supine positions in 5 normal subjects and in 5 patients with orthopnea due to congestive heart failure. The patients had higher elastic and viscous resistances in the sitting position. Recumbency increased both resistances in both groups but there was a disproportionate increase in the viscous resistance of the patients. This increase was most marked in late expiration and early inspiration. The significance of these findings to orthopnea is discussed.