Mechanisms underlying effects of nocturnal ventilation on daytime blood gases in neuromuscular diseases

The hypothesis that, in neuromuscular and chest wall diseases, improvement in central respiratory drive explains the effects of night-time ventilation on diurnal gas exchanges was tested. The effects at 6 months, 1, 2 and 3 yrs of intermittent positive pressure v entilation (IPPV) on arterial blood gas tension, pulmonary function, muscle strength, sleep parameters, respiratory parameters during sleep and ventil atory response to CO2 were evaluated in 16 consecutive patients with neurom uscular or chest wall disorders. As compared with baseline, after IPPV daytime arterial oxygen tension (Pa,O -2) increased (+2.3 kPa at peak effect) and arterial carbon dioxide tension (Pa,CO2) and total bicarbonate decreased (-1.8 kPa and -5 mmol . L-1, resp ectively) significantly; vital capacity, total lung capacity, maximal inspi ratory and expiratory pressures and alveolar-arterial oxygen gradient did n ot change; the apnoea-hypopnoea index and the time spent with an arterial o xygen saturation (Sa,O-2) value <90% decreased (-24 and -101 min, respectiv ely), sleep efficiency and mean Sa,O-2 increased (+16% and +5%, respectivel y); and ventilatory response to CO2 increased (+4.56 L.min.(1).kPa.(1)) sig nificantly, The reduction in Pa,CO2 observed after IPPV correlated solely w ith the increase in the slope of ventilatory response to the CO2 curve (r=- 0.68, p=0.008), In neuromuscular or chest wall diseases, improvement of daytime hypoventila tion with nocturnal intermittent positive pressure ventilation may represen t an adaptation of the central chemoreceptors to the reduction of profound hypercapnia during sleep or reflect change in the quality of sleep.