VENTILATORY RESPONSE TO SPONTANEOUS RESISTIVE LOAD VARIATIONS DURING SLEEP

We investigated the ventilatory response to spontaneous changes in resistive load during sleep in nine adult asthmatic patients, four of whom were snorers. All patients had a history of nocturnal worsening of respiratory symptoms and were submitted to a nocturnal polysomnographic study in a sleep laboratory. During the night, all patients showed spontaneous increases in pulmonary resistance due to bronchoconstriction. A temporary additional increase in inspiratory resistance (RI) was observed 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 most effective ventilatory compensation to increasing resistive load (lowest 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 transpulmonary 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 snorer during nonsnoring breathing); however, the Ptp increase was able to compensate VE only when TI/TT increased. We conclude that, in sleeping asthmatic patients, VE adaptation to increased spontaneous load is highly variable among patients and its effectiveness is related to individual strategies on the basis of adequate adjustments of neuromuscular output and timing of the breathing cycle.