The factors that impel patients with myocardial failure of the congestive type to sit up in bed in order to breathe more comfortably have aroused the curiosity of many investigators. Numerous theories of the pathogenesis of orthopnea have been advanced, but none completely accounts for all the characteristics of the phenomenon.
REVIEW OF THE LITERATURE
The earlier writers generally believed that the sitting posture was assumed because the accessory muscles of inspiration could then be used to greater advantage. Hofbauer,1 however, showed that the chief respiratory difficulty in orthopneic patients was expiratory rather than inspiratory, and that the accessory muscles of expiration did not function more efficiently in the upright posture. According to him,2 the orthopneic position provides relief because it secures the following mechanical advantages: 1. The lower position of the diaphragm and the consequent increased capacity of the thorax increases the elastic tension of the lungs and so