Submitted on February 1, 2006
Accepted on August 22, 2006
EFFECTS OF PULSE LUNG INFLATION ON CHEST WALL EXPIRATORY MOTOR ACTIVITY
Jaroslaw R. Romaniuk1, Thomas E Dick2, Krzysztof E Kowalski3, and Anthony F DiMarco3*
1 Departments of Physiology and Biophysics, Case Western Reserve University, Cleveland, Ohio, United States; Louis Stokes Cleveland Department of Veterans Affairs Medical Center, Brecksville, Ohio, United States
2 Division of Pulmonary and Critical Care Medicine, Case Western Reserve University, Cleveland, Ohio, United States
3 Departments of Physiology and Biophysics, Case Western Reserve University, Cleveland, Ohio, United States
* To whom correspondence should be addressed. E-mail: afd3{at}po.cwru.edu.
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 less than 7 cmH2O consistently inhibited TS activity but had variable effects on TA and IIC activity and expiratory duration. Lung inflations resulting in airway pressures greater than 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 airway pressure between 7 and 20 cmH2O produce a vagally mediated inhibition of expiratory muscle activity which is directly related to the magnitude of the inflation. Lower inflation pressures produce variable effects which are muscle specific.
