Chest
Volume 103, Issue 1, January 1993, Pages 143-150
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Clinical Investigations
Effect of Nasal Pressure Support Ventilation and External PEEP on Diaphragmatic Activity in Patients with Severe Stable COPD

https://doi.org/10.1378/chest.103.1.143Get rights and content

Nasal pressure support ventilation (NPSV) has been shown to be useful in the treatment of acute and chronic pulmonary failure. However, little is known about respiratory muscle activity during NPSV in stable patients with COPD. The aim of this study was to test the effect of two levels (10 and 20 cm H2O) of NPSV on diaphragmatic activity, in a group of seven stable, severe COPD patients (FEV1 20 percent ± 7 of pred, FEV1/FVC 35 percent) with hypercapnic respiratory insufficiency. Since these patients had an intrinsic PEEP (PEEPi) of 2.6 ± 1.3 cm H2O, we also investigated the effect of adding 5 cm H2O external PEEP (PEEPe) during NPSV. Blood gases, ventilatory pattern by inductive plethysmography, integrated electromyogram of the diaphragm (Edi), transdiaphragmatic pressure (Pdi), and the diaphragmatic pressure time product (PTPdi) were recorded during randomized 15-min runs of both levels of NPSV with and without the addition of PEEPe. Minute ventilation did not change with the application of NPSV, but a significant decrease in breathing frequency with a parallel increase in tidal volume was observed, so that blood gas determinations improved at the higher levels of support. A marked statistically significant reduction in diaphragmatic activity, as assessed by a decrease in Pdi swings, PTPdi, and Edi, was detected at the levels of 10 and 20 cm H2O; a further significant decrease in these values was observed when PEEPe was added. PEEPi decreased significantly only with the application of PEEPe, resulting in a small increase in end-expiratory lung volume. We conclude that NPSV improves diaphragmatic function in patients with severe stable COPD; this effect may be enhanced by the applications of external PEEP.

Section snippets

MATERIALS AND METHODS

Seven patients (five male and two female) with severe COPD (FEV1 = 20 percent ± 6.9 of pred and FEV1/FVC = 35 percent ± 10.5) and respiratory muscle dysfunction (maximum inspiratory pressure [MIP] 44.6 ± 8.5 cm H2O) were studied after giving oral consent to a protocol approved by the Clinica del Lavoro Foundation of Pavia institutional ethics committee. All the patients were in a stable condition, as assessed by stability in blood gas values and pH in the preceding four weeks; indeed they had

RESULTS

One patient refused to swallow the gastric and esophageal balloons; therefore we could not record Pes and Pga swings and PTPdi. Another subject was unable to tolerate a PS of 20 cm H2O with or without PEEPe, while all the others tolerated NPSV at the different levels without any discomfort or complication. The actual pressure delivered measured at the mask for a PS of 10 and 20 cm H2O averaged 8.1 ± 0.2 and 15.9 ± 1.1 cm H2O, respectively; the effective PEEPe at the mask was 3.2 ± 0.3 cm H2O.

DISCUSSION

This study shows that NPSV acutely improves, in stable hypercapnic COPD patients, some indices of diaphragmatic activity such as Pdi, Edi, and PTPdi, increasing with the amount of PS used. These effects are enhanced by the application of external PEEP in these patients who all had auto-PEEP. Improved efficiency is not solely due to the action of NPSV in aiding the inspiratory muscles, but may also result from a different pattern of breathing, especially the marked decrease in respiratory

CONCLUSION

In conclusion, we demonstrated that NPSV is able to significantly reduce the diaphragmatic activity as assessed by a decrease in Pdi, Edi, and PTPdi in stable severe hypercapnic patients; these effects may be enhanced by the application of PEEPe in patients who showed dynamic PEEPi during spontaneous breathing. PS is usually tolerated up to values of 20 cm H2O when given by nose mask and may also acutely improve blood gases, while significantly reducing frequency.

These findings indicate that

ACKNOWLEDGMENT

As usual, the authors wish to thank Dr. R. C. Stanner for reviewing the English of the manuscript.

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    Manuscript received December 9; revision accepted May 12.

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