The Relation of Postural Hemodilution to Paroxysmal Dyspnea

For many years, there has been considerable speculation about the mechanism of paroxysmal dyspnea. Changes in vasomotor, neural, cardiac, and respiratory physiology, nightmares and other trigger mechanisms, and alterations in blood volume have been variously suggested as responsible for the characteristic nocturnal attacks. The present study was undertaken to see whether shifts of body fluid to the blood stream, following rest in the horizontal position, could be correlated with the time of onset of paroxysmal dyspnea and might therefore be considered a factor in inducing acute left-sided heart failure. B6hme (1) early noted a fall in serum proteins after rest, a rise after periods of exercise; and other workers (2 to 5) have published results indicating that the change from recumbency to an upright position may be followed by a rise in protein concentration, usually ranging from 10 to 20 per cent. Similar changes in the composition and volume of the blood have also been reported (3, 5, 6). Since the introduction of the concept of cardiac asthma (7), reviewers of the subject (8, 9) have pointed out the frequently nocturnal character of these episodes, which usually occur at rest and in the horizontal position. Weiss and Robb (9) have suggested that patients with low plasma proteins are more susceptible to severe attacks.