Chest
Volume 97, Issue 1, January 1990, Pages 150-158
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Clinical Investigations in Critical Care
Ventilatory Muscle Support in Respiratory Failure with Nasal Positive Pressure Ventilation

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Long-term intermittent mechanical ventilation results in improvements in ventilatory performance and clinical status between ventilation sessions in patients with chronic respiratory failure. The application of intermittent positive pressure ventilation through a nasal mask (NPPV) is a simple, noninvasive method for the provision of chronic intermittent ventilatory support. We investigated the effects of NPPV on inspiratory muscle activity in three normal subjects and nine patients with acute or chronic ventilatory failure due to restrictive (four subjects) or obstructive (five subjects) respiratory disorders. NPPV resulted in reductions of phasic diaphragm electromyogram amplitude to 6.7 ± 0.7 percent (mean ± SEM) of values obtained during spontaneous breathing in the normal subjects, 6.4 ± 3.2 percent in the restrictive group, and 8.3 ± 5.1 percent in the obstructive group. Simultaneous decreases in activity of accessory respiratory muscles were observed. The reductions in inspiratory muscle activity were confirmed by the finding of positive intrathoracic pressure swings on inspiration in all subjects. With NPPV, oxygen saturation and Pco2 remained stable or improved as compared with values obtained during spontaneous breathing. These results indicate that NPPV can noninvasively provide ventilatory support while reducing inspiratory muscle energy expenditure in acute and chronic respiratory failure of diverse etiology. Long-term assisted ventilation with NPPV may be useful in improving ventilatory performance by resting the inspiratory muscles. (Chest 1990; 97:150-58)

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Subjects

The study population consisted of three normal subjects, four subjects with neuromuscular disorders with or without associated chest wall deformities (restrictive group), and five subjects with severe COPD (obstructive group). Subject characteristics are shown in Table 1.

In the restrictive group, two subjects (nos. 5,7) were receiving nocturnal intermittent positive pressure ventilation and one (no. 6) was on intermittent positive pressure ventilation continuously, all through fenestrated

RESULTS

One subject (no. 12) with COPD was extremely anxious and unable to synchronize his breathing with the ventilator. There were no evident clinical characteristics which distinguished him from others in the obstructive group (Table 1). This subject was not included in further analysis. The other 11 subjects tolerated NPPV well without discomfort or complications.

Figure 1 is a representative tracing from a subject with COPD (no. 10). During spontaneous breathing (Fig 1A), large negative deflections

DISCUSSION

The results of this study demonstrate that NPPV can achieve, in the short term, two major goals of assisted ventilation, namely: to provide adequate ventilation while simultaneously allowing for a significant reduction in spontaneous inspiratory effort. Other investigators have shown that long-term intermittent NPPV can result in sustained improvements in Pco2 and clinical status, as well as increased exercise tolerance in patients with chronic respiratory failure.9,10,12, 13, 14 However, the

ACKNOWLEDGMENTS

The writers thank Dr. J. Martin for thoughtful review of the manuscript, and Drs. P. Goldberg and M. Angle for referring patients.

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Supported by the Quebec Thoracic Society and the Environmental Lung Disease Research Fund.

Manuscript received March 2; revision accepted June 1, 1989.

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