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Efficiency of the normal human diaphragm with hyperinflation

¹Department of Pulmonary Physiology, Sir Charles Gairdner Hospital, ²West Australian Sleep Disorders Research Institute, QEII Medical Centre, and ³Department of Physiology, University of Western Australia, Nedlands, Western Australia, Australia

Submitted 15 October 2004 ; accepted in final form 10 June 2005

We evaluated an index of diaphragm efficiency (Eff_di), diaphragm power output (di) relative to electrical activation, in five healthy adults during tidal breathing at usual end-expiratory lung volume (EELV) and diaphragm length (L_{di ee}) and at shorter L_{di ee} during hyperinflation with expiratory positive airway pressure (EPAP). Measurements were repeated with an inspiratory threshold (7.5 cmH₂O) plus resistive (6.5 cmH₂O·l^–1·s) load. di was the product of mean inspiratory transdiaphragmatic pressure (Pdi_mean), diaphragm volume displacement measured fluoroscopically, and 1/inspiratory duration (TI^–1). Diaphragm activation, measured with esophageal electrodes, was quantified by computing root-mean-square values (RMS_di). With EPAP, 1) EELV increased [mean r² = 0.91 (SD 0.01)]; 2) in four subjects, L_{di ee} decreased [mean r² = 0.85 (SD 0.07)] and mean Eff_di decreased 34% per 10% decrease in L_{di ee} (P < 0.001); and 3) in one subject, gastric pressure at EELV increased two- to threefold, L_{di ee} was unchanged or increased, and Eff_di increased at two of four levels of EPAP (P 0.006, ANOVA). Inspiratory loading increased di (P = 0.003) and RMS_di (P = 0.004) with no change in Eff_di (P = 0.63) or its relationship with L_{di ee}. Eff_di was more accurate in defining changes in L_{di ee} [(true positives + true negatives)/total = 0.78 (SD 0.13)] than Pdi_mean·RMS_di^–1, RMS_di, or Pdi_mean·TI (all <0.7, P 0.05, without load). Thus Eff_di was principally a function of L_{di ee} independent of inspiratory loading, behavior consistent with muscle force-length-velocity properties. We conclude that Eff_di, measured during tidal breathing and in the absence of expiratory muscle activity at EELV, is a valid and accurate measure of diaphragm contractile function.

in vivo diaphragm length; power output; electromyogram activity; diaphragm contractile function and efficiency; fluoroscopy

This article has been cited by other articles:

				K. E. Finucane and B. Singh Human diaphragm efficiency estimated as power output relative to activation increases with hypercapnic hyperpnea J Appl Physiol, November 1, 2009; 107(5): 1397 - 1405. [Abstract] [Full Text] [PDF]