Diaphragmatic rest during negative pressure ventilation by pneumowrap. Assessment in normal and COPD patients

In the present study, we assessed the occurrence of respiratory muscle rest during long lasting INPV runs using a pneumowrap ventilator at different pressure levels. We measured two indices of diaphragmatic activity: transdiaphragmatic pressure and the electrical activity of the diaphragm. Five healthy volunteers and six COPD patients were studied during spontaneous breathing and during 30-minute runs of INPV at a pressure of -2, -15 and -30 cmH2O. Ventilation, rib cage and abdomen motion were measured by inductive plethysmography; Pdi was obtained as the difference between gastric and esophageal pressures; Edi was recorded with surface electrodes. About 10 minutes of INPV (adaptation phase) were needed to obtain stable values in all the variables recorded. Ventilation increased in both groups up to threefold by increasing the negative pressure applied, this being due to changes in tidal volume. Changes in Pga swings mainly accounted for the reduction in Pdi that became negative during the run at -30 cmH2O. In both groups, Edi, after adaptation, showed no change during INPV at -2 cmH2O but a progressive reduction from control, during INPV at -15 and -30 cmH2O. We conclude that INPV by a pneumowrap ventilator can induce partial respiratory muscle rest in normal subjects and COPD patients.