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HIGHLIGHTED TOPIC
Reflexes from the Lungs and Airways

Effects of pulse lung inflation on chest wall expiratory motor activity

¹Departments of Physiology and Biophysics, Case Western Reserve University, MetroHealth Medical Center, Cleveland; ²Louis Stokes Cleveland Department of Veterans Affairs Medical Center, Brecksville; and ³Division of Pulmonary and Critical Care Medicine, Department of Medicine, Case Western Reserve University, Cleveland, Ohio

Submitted 1 February 2006 ; accepted in final form 22 August 2006

The effects of pulse lung inflation (LI) on expiratory muscle activity and phase duration (TE) were determined in anesthetized, spontaneously breathing dogs (n = 20). A volume syringe was used to inflate the lungs at various times during the expiratory phase. The magnitude of lung volume was assessed by the corresponding change in airway pressure (Paw; range 2–20 cmH₂O). Electromyographic (EMG) activities were recorded from both thoracic and abdominal muscles. Parasternal muscle EMG was used to record inspiratory activity. Expiratory activity was assessed from the triangularis sterni (TS), internal intercostal (IIC), and transversus abdominis (TA) muscles. Lung inflations <7 cmH₂O consistently inhibited TS activity but had variable effects on TA and IIC activity and expiratory duration. Lung inflations resulting in Paw values >7 cmH₂O, however, inhibited expiratory EMG activity of each of the expiratory muscles and lengthened TE in all animals. The responses of expiratory EMG and TE were directly related to the magnitude of the lung inflation. The inhibition of expiratory motor activity was independent of the timing of pulse lung inflation during the expiratory phase. The inhibitory effects of lung inflation were eliminated by bilateral vagotomy and could be reproduced by electrical stimulation of the vagus nerve. We conclude that pulse lung inflation resulting in Paw between 7 and 20 cmH₂O produces a vagally mediated inhibition of expiratory muscle activity that is directly related to the magnitude of the inflation. Lower inflation pressures produce variable effects that are muscle specific.

respiration; control of expiration; vagal reflexes

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