EFFECTS OF NON-REM SLEEP ON THE RESPONSE OF RESPIRATORY OUTPUT TO VARYING INSPIRATORY FLOW

It has been shown in mechanically ventilated awake normal humans that increasing inspiratory flow rate (VI) exerts an excitatory effect on r espiratory output. It is not known if this effect persists during slee p. To test this, seven normal adults were studied during wakefulness a nd non-rapid eye movement (non-REM) sleep. Subjects were connected thr ough a nose mask to a volume-cycled ventilator in the assist/control m ode, and VI was increased in steps (3 to 4 breaths each) from 30 to 70 L/min and then back to 30 L/min. VI pattern was square, and all breat hs were subject-triggered. Forty-one trials during non-REM sleep and 1 0 during wakefulness were analyzed. Both during sleep and wakefulness minute ventilation increased and total breath duration (Ttot) decrease d significantly in a graded and reversible manner as VI increased. The se changes were complete in the first breath after VI transition. The response was significantly less during sleep than during wakefulness ( p < 0.05); at 30 L/min Ttot, expressed as percent of that at 70 L/min, was 110.2+/-1.3% during sleep and 127.8+/-3.9% during wakefulness. Du ring wakefulness, the rate of change in airway pressure before trigger ing the ventilator (dp/dt), an index of respiratory drive, increased s ignificantly (p < 0.05) with increasing VI. During sleep dp/dt was not affected by VI changes. In four sleeping subjects the increase in VI was sustained for 1.5 to 2 min. There was no evidence for adaptation o f the response; Ttot, averaged over the last three breaths, did not di ffer from that obtained when VI was sustained for only 3 to 4 breaths. We concluded that VI exerts an excitatory effect on respiratory outpu t, mediated by a reflex neural mechanism, and the gain of this reflex is attenuated by sleep.