Variability of Data
The within-subject coefficient of variation values were similar on air and oxygen and only those from air are given in Table 2. A marked increase in variability of all respiratory measurements occurred in changing NREM to REM sleep, but especially in the frequency of ventilation, and all save Vt and AC were more variable in REM than wakefulness.
Comparison to Normal Values
A comparison with normal data, derived using similar MLR calibration of RIP in six restrained young healthy adult males, is presented in Figure 3. This illustrates the mean values of each variable during wakefulness, slow wave (S3/4) sleep, and REM sleep in the six subjects with Duchenne MD studied on air compared to these published normal data. Significant differences between the present data and those of Stradling et al were noted for Ve in NREM sleep (p<0.05) and abdominal contribution during wakefulness (p<0.01), slow wave sleep (p<0.01), and REM sleep (p<0.05). Mean Vt/Ti fell by 17.8 percent (air) and 20.9 percent (oxygen) from awake to NREM sleep, but by only 2.9 percent in the published normal results; the further fall from NREM to REM sleep was similar to normal. other
The immobility of subjects with advanced Duchenne MD allowed a noninvasive analysis of calibrated ventilatory data from six such subjects during wakefulness and sleep. Minute ventilation when awake was similar to that reported in normal subjects* but fell in NREM and further in REM sleep to values well below normal. In two subjects, persistent paradoxical abdominal movement was observed in NREM sleep; overall, the abdominal (diaphragmatic) contribution to breathing in NREM sleep was lower than in normal subjects and correlated with the extent of subsequent oxygen desaturation in REM sleep. We have previously shown that patients with advanced Duchenne MD and only minimal scoliosis usually have no abnormal daytime sleep symptoms and often maintain near normal daytime blood gas tensions despite a severe thoracic restrictive deficit. Although the breathing pattern and oxygen saturation during NREM sleep may appear normal, REM sleep is often accompanied by repeated central hypopneas and/or apneas, with associated significant oxygen desaturation.
Table 2—Mean (and Range) Values for Coefficient of Variation cf the Measurements During Wakefulness, Stage 2 NREM, Stage 3-4 NREM, and REM Sleep in the Six Subjects with Duchenne MD Breathing Air
|Awake||S2 NREM||S3/4 NREM||REM|
|VE||7.7 (1.3-13.1)||4.0 (1.8-7.1)||6.8 (1.3-18.0)||28.8 (12.4-60.3)*## +|
|f||7.6 (2.6-15.3)||4.6 (2.7-7.5)||2.5 (1.2-4.0)t||16.0 (8.8-20.1)**###+ + +|
|VT||12.2 (2.8-37.7)||5.5 (2.4-10.0)||4.3 (1.5-7.8)||26.7 (8.0-55.7)+ +|
|VT/Ti||11.0 (6.1-28.3)||6.9 (4.0-9.4)||5.8 (1.2-10.0)||35.8 (7.6-65.8)*##+ +|
|Ti/Ttot||6.9 (4.4-8.2)||3.9 (2.5-7.8)||2.8 (1.2-5.7)||23.1 (7.2-50.3)*#+ +|
|AC||16.6 (6.5-39.9)||14.6 (8.8-27.2)||5.0 (2.9-6.3)t##||24.2 (7.5-61.6) +|
Figure 3. Mean ± SEM of frequency (f), tidal volume (Vt), minute ventilation (Ve), abdominal contribution (AC), mean inspiratory flow (Vt/Ti), and fractional inspiratory time (Ti/Ttot) in the six subjects with Duchenne MD breathing air during wakefulness (w), slow wave (S3/4) sleep (SWS), and REM sleep, compared with normal values from six adult males. Significant differences compared with wakefulness (triangle) and SWS (square) are denoted by single symbol = p<0.05, double = p<0.01, and triple = p<0.001.