Chest
Volume 98, Issue 4, October 1990, Pages 857-865
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Diaphragmatic Rest During Negative Pressure Ventilation by Pneumowrap: Assessment in Normal and COPD Patients

https://doi.org/10.1378/chest.98.4.857Get rights and content

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.

INPV = intermittent negative pressure ventilation; Pdi = transdiaphragmatic pressure; Edi = electrical activity of diaphragm; Pga = gastric pressure; Pes = esophageal pressure; tcCO2 = transcutaneous carbon dioxide tension; Pab = abdominal pressure; RC = rib cage: ABD = abdomen; RIP = respiratory inductive plethysmography

Section snippets

MATERIALS AND METHODS

Five normal nonsmoking subjects (one woman) and six COPD patients agreed to take part in the study. In the normal group, two of the subjects were aware of the purpose of the study, but none had previously been submitted to an INPV trial, while all the patients had received INPV sessions for the previous three days. The mean age of normal subjects was 35.6 ± 4.1 years, and their static and dynamic volumes were measured by body plethysmography and found to be within normal limits. The

RESULTS

During the first 5 to 10 minutes of INPV at the pressures of –15 cmH2O and –30 cmH2O, the response of all the variables considered was very irregular. For this reason, we only analyzed the data obtained when all the variables were stabilized. Indeed, 2 to 4 minutes were required for the pressure recorded inside the pneumowrap to reach a stable desired value, even if the pressure set on the manometer of the ventilator was fixed from the beginning. End-expiratory volume, as assessed by RIP,

DISCUSSION

In this study, we provide evidence that in normal subjects and in a group of trained COPD patients, negative pressure ventilation by pneumowrap, using pressure swings of –15 cmH2O and –30 cmH2O and after adaptation, induces partial diaphragmatic rest, as assessed by a decrease in electrical and mechanical activity of the diaphragm. After a few minutes, a 1:1 phase lock developed between the spontaneous respiratory rhythm and that of the mechanical ventilator (Figure 7, Figure 8).

A previous

ACKNOWLEDGMENT

The authors wish to thank Miss Jacqueline McKay for kindly reviewing the manuscript.

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