DIAPHRAGM ACTIVITY AND THORACOABDOMINAL MECHANICS DURING POSITIVE PRESSURE BREATHING
Abstract
The electrical activity of the diaphragm and the mechanical contribution of the thorax and the abdomen through the breathing cycle were investigated in man during positive pressure breathing (PPB). The electrical activity of the diaphragm persists even at values at which inspiration should be completely passive according to the pressure volume diagram of the thorax and lung. The transdiaphragmatic pressure decreases as the value of PPB increases, but is still appreciable at values of PPB at which the inspiration appears to be completely passive by an analysis based on transthoracic pressure measurements alone. The transdiaphragmatic pressure becomes zero only at a PPB of about 30 cm. water. The persistent activity of the diaphragm during PPB is counterbalanced by an activity of the abdominal muscles in excess of that of the expiratory muscles as given by transthoracic pressure measurements. Owing to the persistence of a thoracoabdominal pressure gradient the venous return, and therefore the cardiac output, should be less reduced than in the case of a passive inspiration. The activity of the abdominal muscles is not necessarily initiated by the respiratory control system. Similarly, during PPB, the activity of the abdominal muscles could be a tonic reflex against the background of which the diaphragm behaves in its usual way. The electrical activity of the diaphragm during breath holding was studied. After a period of no, or only slight, tonic activity a marked discharge was recorded; this was followed by others at a progressively higher rate up to the breaking point. The action of the diaphragm, not balanced by antagonist muscles, caused a fall of the intrathoracic pressure.
Document Details
- Document Type
- Technical Report
- Publication Date
- Dec 01, 1964
- Accession Number
- AD0617741
Entities
People
- Emilio Agostoni
Organizations
- University of Milan