VENTILATORY RESPONSE TO SPONTANEOUS RESISTIVE LOAD VARIATIONS DURING SLEEP

We investigated the ventilatory response to spontaneous changes in res istive load during sleep in nine adult asthmatic patients, four of who m were snorers. All patients had a history of nocturnal worsening of r espiratory symptoms and were submitted to a nocturnal polysomnographic study in a sleep laboratory. During the night, all patients showed sp ontaneous increases in pulmonary resistance due to bronchoconstriction . A temporary additional increase in inspiratory resistance (RI) was o bserved as a result of snoring. In all patients, a highly significant inverse linear relationship was found between ventilation (VE) and RI, but the slopes of the regressions varied considerably among patients; the decrease in VE was due to a reduced mean inspiratory flow. The mo st effective ventilatory compensation to increasing resistive load (lo west absolute values in the VE/RI slopes) was observed in two patients : one nonsnorer and one snorer. Effective VE compensation appeared to be dependent on the individual's combined adjustments of transpulmonar y pressure (Ptp) and duty cycle (TI/TT). In fact, an increase in Ptp, linearly related to RI, was observed in all patients except one (a sno rer during nonsnoring breathing); however, the Ptp increase was able t o compensate VE only when TI/TT increased. We conclude that, in sleepi ng asthmatic patients, VE adaptation to increased spontaneous load is highly variable among patients and its effectiveness is related to ind ividual strategies on the basis of adequate adjustments of neuromuscul ar output and timing of the breathing cycle.