Electromyography of the diaphragm in man and transdiaphragmatic pressure

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Abstract
The electrical activity of the vertebral part of the diaphragm in man has been studied in physiological conditions through an esophageal bipolar lead; the spirogram and/or the intrathoracic and gastric pressure were simultaneously recorded. Electrical activity has been found during inspiration; it is approximately related to the transdiaphragmatic pressure as the activity found during graded inspiratory efforts at relaxation volume. At minimum lung volume the electrical activity during maximum inspiratory efforts is small notwithstanding the high transdiaphragmatic pressure. Electrical activity may persist at the beginning of expiration, showing that the diaphragm does not relax completely at the onset of expiration. At the end of maximum expiration a small electrical activity may appear, the transdiaphragmatic pressure is high and it is not clear to what extent the diaphragm is passively distended or contracted. At relaxation volume during expiratory efforts electrical activity appears only when the effort is high, while during expulsive efforts, even moderate, the activity is marked. Submitted on May 2, 1960

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