ELECTRICAL AND MECHANICAL-ACTIVITY OF THE DIAPHRAGM ACCOMPANYING BODY POSITION IN SEVERE CHRONIC OBSTRUCTIVE PULMONARY-DISEASE

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Abstract
Using a special gastroesophageal catheter, electromyographic measurements of diaphragm (Edi) and transdiaphragmatic pressure (Pdi) were taken in the supine, standing, erect sitting and leaning forward (sitting) positions in 8 normal subjects and 6 patients with severe chronic obstructive pulmonary disease (COPD) with marked hyperinflation and low flat diaphragms. Four patients had pronounced postural relief of their dyspnea from assuming the supine and/or leaning forward positions. All 8 normal subjects and 4 of the 6 patients and COPD showed substantial (2- to 5-fold) increases in .delta.Edi, the phasic inspiratory amplitude on Edi, on assuming the standing and erect sitting postures. In the normal subjects, .delta.Pdi, the phasic inspiratory increment in Pdi, was maintained in all 4 postures, whereas in all patients with COPD, it decreased significantly in the erect sitting and standing postures. In 2 of the 6 patients with COPD, the .delta.Edi did not increase in the erect postures. In these patients a reflex, which normally compensates for reduced diaphragmatic efficiency because of shortened muscle fibers in the erect postures, apparently was not operating. Although it is not clear what mechanism(s) might account for suppression of this compensatory reflex, such reflex suppression might be advantageous from the viewpoint of diaphragmatic muscle energetics. The diaphragm would be thus spared energetically wasteful attempts to accomplish a fatiguing mechanical task.

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