Ventilatory response to CO2 re-breathing before and after Nocturnal Nasal Intermittent Positive Pressure Ventilation in patients with chronic alveolar hypoventilation

Long-term nocturnal nasal intermittent positive pressure ventilation (NIPPV) has beneficial effects on daytime PACO(2) in patients with chronic alveolar hypoventilation. Our aim was to investigate if these beneficial effects are related to improved respiratory drive as measured by ventilatory response to CO2. In 17 hypoventilated patients (mean age 62 years) we obtained daytime arterial blood gases, nocturnal transcutaneous oxygen saturation, nocturnal transcutaneous PACO(2), ventilatory response to CO2 re-breathing, spirometry and indices of respiratory muscle strength before and after 9 months of NIPPV. Patients served as their own controls. After 9 months of NIPPV day-time PACO(2) decreased from 7.1 kPa to 6.3 kPa, (P < 0.001) and PAO(2) increased from 8.1 kPa to 9.3 kPa, (P < 0.01). The changes in morning and daytime PACO(2) and in nocturnal transcutaneous oxygen saturation were significantly correlated to the changes in several variables derived from the ventilatory response to CO2 re-breathing. In patients with substantial improvement in daytime PACO(2) we found significant improvements in ventilatory response to CO2 re-breathing. The present study confirms the beneficial effect of long-term NIPPV on daytime arterial blood gases. The results are consistent with the hypothesis that the improvement of daytime PACO(2) is related to improved respiratory drive observed after NIPPV.