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Determinants of diaphragm motion in unilateral diaphragmatic paralysis

¹Laboratory of Cardiorespiratory Physiology, Brussels School of Medicine, and ³Chest Service and ²Department of Radiology, Erasme University Hospital, 1070 Brussels, Belgium

Submitted 22 July 2003 ; accepted in final form 28 August 2003

Cranial displacement of a hemidiaphragm during sniffs is a cardinal sign of unilateral diaphragmatic paralysis in clinical practice. However, we have recently observed that isolated stimulation of one phrenic nerve in dogs causes the contralateral (inactive) hemidiaphragm to move caudally. In the present study, therefore, we tested the idea that, in unilateral diaphragmatic paralysis, the pattern of inspiratory muscle contraction plays a major role in determining the motion of the inactive hemidiaphragm. We induced a hemidiaphragmatic paralysis in six anesthetized dogs and assessed the contour of the diaphragm during isolated unilateral phrenic nerve stimulation and during spontaneous inspiratory efforts. Whereas the inactive hemidiaphragm moved caudally in the first instance, it moved cranially in the second. The parasternal intercostal muscles were then severed to reduce the contribution of the rib cage muscles to inspiratory efforts and to enhance the force generated by the intact hemidiaphragm. Although the change in pleural pressure (Ppl) was unaltered, the cranial displacement of the paralyzed hemidiaphragm was consistently reduced. A pneumothorax was finally induced to eliminate Ppl during unilateral phrenic nerve stimulation, and this enhanced the caudal displacement of the inactive hemidiaphragm. These observations indicate that, in unilateral diaphragmatic paralysis, the motion of the inactive hemidiaphragm is largely determined by the balance between the force related to Ppl and the force generated by the intact hemidiaphragm.

respiratory muscles; mechanics of breathing

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