Respiratory changes associated with rapid eye movements in normo- and hypercapnia during sleep

Rapid eye movements during rapid-eye-movement (REM) sleep are associated wi th rapid, shallow breathing. We wanted to know whether this effect persiste d during increased respiratory drive by CO2. In eight healthy subjects, we recorded electroencephalographic, electrooculographic, and electromyographi c signals, ventilation, and end-tidal PCO2 during the night. Inspiratory PC O2 was changed to increase end-tidal PCO2 by 3 and 6 Torr. During normocapn ia, rapid eye movements were associated with a decrease in total breath tim e by -0.71 +/- 0.19 (SE) s (P < 0.05) because of shortened expiratory time (-0.52 +/- 0.08 s, P < 0.001) and with a reduced tidal volume (-89 +/- 27 m i, P < 0.05) because of decreased rib cage contribution (-75 +/- 18 mi, P < 0.05). Abdominal (-11 +/- 16 mi, P = 0.52) and minute ventilation (-0.09 /- 0.21 ml/min, P = 0.66) did not change. In hypercapnia, however, rapid ey e movements were associated with a further shortening of total breath time. Abdominal breathing was also inhibited (-79 +/- 23 mi, P < 0.05), leading to a stronger inhibition of tidal volume and minute ventilation (-1.84 +/- 0.54 l/min, P < 0.05). We conclude that REM-associated respiratory changes are even more pronounced during hypercapnia because of additional inhibitio n of abdominal breathing. This may contribute to the reduction of the hyper capnic ventilatory response during REM sleep.