The Lung Volume and Its Subdivisions

Orthopnea is a common complaint in patients with chronic cardiac decompensation. The frequent association of orthopnea and pulmonary congestion has properly led many authors to regard congestion of the lungs as an important factor in the genesis of dyspnea in the recumbent position, the symptom being favorably modified in the upright position. There has, however, been no general agreement regarding the mechanism whereby pulmonary congestion induces or exaggerates dyspnea in recumbency. A number of authors have stated that dyspnea of recumbency results from increased pulmonary congestion in the recumbent position, consequent to a shift of blood from the lower part of the body (1), pressure on (2) or unfavorably hydrostatic relations within (3) the pulmonary veins, kinking of the pulmonary vessels (4), or an increase in the volume flow of blood through the lungs in the recumbent position (5, 6). The last named factor has been eliminated by the more recent studies of McMichael (7) in patients with congestive failure. The increase in pulmonary congestion by one or more of these factors is believed to induce the dyspnea of recumbency, either by influencing adversely the respiratory exchange (3), by activating reflexes initiated by changes in the parenchyma or blood vessels of the lungs (3, 5, 8), or by causing increased rigidity of the lungs (3, 9). It has been stated that the appearance of rales or an increase in their number occurs in the recumbent position (10). However, no data bearing on variations in the degree of pulmonary congestion in patients with chronic congestive failure in various positions are available except for McMichael's findings in one case (11). The deviations from the normal in the lung volume and its subdivisions, produced by passive congestion of the lungs, yield a characteristic pattern (9). The lung volume and its subdivisions have therefore been studied in orthopneic patients with chronic congestive failure to learn whether pulmonary congestion increases when orthopneic patients assume the recumbent position. Although the primary purpose was to investigate the effect of position on pulmonary congestion, data also were obtained on other pulmonary factors which might affect dyspnea of recumbency. Accordingly, the relation between various aspects of respiratory function and orthopnea will be discussed. The procedure used in the present study is applicable only to patients with mild or moderate orthopnea and therefore conclusions derived from the present experiments may not be wholly applicable to severe orthopnea.