CONTROL OF BREATHING DURING SLEEP ASSESSED BY PROPORTIONAL ASSIST VENTILATION

We used proportional assist ventilation (PAV) to evaluate the sources of respiratory drive during sleep. PAV increases the slope of the rela tion between tidal volume (VT) and respiratory muscle pressure output (Pmus). We reasoned that if respiratory drive is dominated by chemical factors, progressive increase of PAV gain should result in only a sma ll increase in VT because Pmus would be downregulated substantially as a result of small decreases in PCO2. In the presence of substantial n onchemical sources of drive [believed to be the case in rapid-eye-move ment (REM) sleep] PAV should result in a substantial increase in minut e ventilation and reduction in PCO2 as the output related to the chemi cally insensitive drive source is amplified severalfold. Twelve normal subjects under went polysomnography while connected to a PAV ventilat or. Continuous positive air pressure (5.2 +/- 2.0 cmH(2)O) was adminis tered to stabilize the upper airway. PAV was increased in 2-min steps from 0 to 20, 40, 60, 80, and 90% of the subject's elastance and resis tance. VT, respiratory rate, minute ventilation, and end-tidal CO2 pre ssure were measured at the different levels, and Pmus was calculated. Observations were obtained in stage 2 sleep (n = 12), slow-wave sleep (n = 11), and REM sleep (n = 7). In all cases, Pmus was substantially downregulated with increase in assist so that the increase in VT, alth ough significant (P < 0.05), was small (0.08 liter at the highest assi st). There was no difference in response between REM and non-REM sleep . We conclude that respiratory drive during sleep is dominated by chem ical control and that there is no fundamental difference between REM a nd non-REM sleep in this regard. REM sleep appears to simply add bidir ectional noise to what is basically a chemically controlled respirator y output.