Study objective: To evaluate the short-term physiologic
effects of two settings of nasal pressure-support ventilation
(NPSV) in stable COPD patients with chronic hypercapnia.
Design: Randomized controlled physiologic study.
Setting: Lung function units and outpatient clinic of
two affiliated pulmonary rehabilitation centers.
Patients: Twenty-three patients receiving domiciliary
nocturnal NPSV for a mean (± SD) duration of 31 ± 20 months.
Methods: Evaluation of arterial blood gases,
breathing pattern, respiratory muscles, and dynamic intrinsic positive
end-expiratory pressure (PEEPi,dyn) during both unassisted and assisted
ventilation. Two settings of NPSV were randomly applied for 30 min
each: (1) usual setting (U), the setting of NPSV actually used by the
individual patient at home; and (2) physiologic setting (PHY), the
level of inspiratory pressure support (IPS) and external positive
end-expiratory pressure (PEEPe) tailored to patient according to
invasive evaluation of respiratory muscular function and
Results: All patients tolerated NPSV well
throughout the procedure. Mean U was IPS, 16 ± 3 cm H2O
and PEEPe, 3.6 ± 1.4 cm H2O; mean PHY was IPS, 15 ± 3
cm H2O and PEEPe, 3.1 ± 1.6 cm H2O. NPSV was
able to significantly (p < 0.01) improve arterial blood gases
independent of the setting applied. When compared with
spontaneous breathing, both settings induced a significant increase in
minute ventilation (p < 0.01). Both settings were able to reduce the
diaphragmatic pressure-time product, but the reduction was
significantly greater with PHY (by 64%; p < 0.01) than with U
(56%; p < 0.05). Eleven of 23 patients (48%) with U and 7 of 23
patients (30%) with PHY showed ineffective efforts (IE); the
prevalence of IE (20 ± 39% vs 6 ± 11% of their respiratory rate
with U and PHY, respectively) was statistically different
(p < 0.05).
Conclusion: In COPD patients with
chronic hypercapnia, NPSV is effective in improving arterial blood
gases and in unloading inspiratory muscles independent of whether it is
set on the basis of patient comfort and improvement in arterial blood
gases or tailored to a patient’s respiratory muscle effort and
mechanics. However, setting of inspiratory assistance and PEEPe by the
invasive evaluation of lung mechanics and respiratory muscle function
may result in reduction in ineffective inspiratory efforts. These
short-term results must be confirmed in the long-term clinical