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Sternomastoid, rib cage, and expiratory muscle activity during weaning failure

Division of Pulmonary and Critical Care Medicine, Edward Hines Jr. Veterans Administration Hospital, and Loyola University of Chicago Stritch School of Medicine, Hines, Illinois

Submitted 16 August 2006 ; accepted in final form 28 March 2007

We hypothesized that patients who fail weaning from mechanical ventilation recruit their inspiratory rib cage muscles sooner than they recruit their expiratory muscles, and that rib cage muscle recruitment is accompanied by recruitment of sternomastoid muscles. Accordingly, we measured sternomastoid electrical activity and changes in esophageal (P_es) and gastric pressure (P_ga) in 11 weaning-failure and 8 weaning-success patients. At the start of trial, failure patients exhibited a higher P_ga-to-P_es ratio than did success patients (P = 0.05), whereas expiratory rise in P_ga was equivalent in the two groups. Between the start and end of the trial, failure patients developed additional increases in P_ga-to-P_es ratio (P < 0.0014) and the expiratory rise in P_ga also increased (P < 0.004). At the start of trial, sternomastoid activity was present in 8 of 11 failure patients contrasted with 1 of 8 success patients. Over the course of the trial, sternomastoid activity increased by 53.0 ± 9.3% in the failure patients (P = 0.0005), whereas it did not change in the success patients. Failure patients recruited their respiratory muscles in a sequential manner. The sequence began with activity of diaphragm and greater-than-normal activity of inspiratory rib cage muscles; recruitment of sternomastoids and rib cage muscles approached near maximum within 4 min of trial commencement; expiratory muscles were recruited slowest of all. In conclusion, not only is activity of the inspiratory rib cage muscles increased during a failed weaning trial, but respiratory centers also recruit sternomastoid and expiratory muscles. Extradiaphragmatic muscle recruitment may be a mechanism for offsetting the effects of increased load on a weak diaphragm.

sternomastoid muscles; respiratory muscles; mechanical ventilation

This article has been cited by other articles:

				M. J. Tobin, F. Laghi, and L. Brochard Role of the respiratory muscles in acute respiratory failure of COPD: lessons from weaning failure J Appl Physiol, September 1, 2009; 107(3): 962 - 970. [Abstract] [Full Text] [PDF]