The effect of increasing levels of NPPV on phasic diaphragm EMG amplitude for individual subjects is illustrated in Figure 4. Results of surface EMG recordings are not shown for subject no. 3, since good quality signals of phasic respiratory muscle activation during spontaneous breathing and with NPPV were not obtained. Increments in peak mask pressure resulted in progressive reductions in EMGdi. There were comparable decreases in the EMGdi signals recorded from surface and esophageal electrodes in those subjects in whom both were measured (Fig 4). In the three subjects in whom recordings of accessory muscle EMGs were obtained, the application of NPPV resulted in falls in the phasic activity of these muscles which were similar to those observed for the dia­phragm (Fig 5).

FIGURE 4. The relationship between the mean

FIGURE 4. The relationship between the mean amplitude of the diaphragm EMG (EMGdi) and level of mask pressure (Pmask) during NPPV is shown. Results for individual subjects during NPPV are expressed as a percentage of control values obtained for each subject during spontaneous breathing. Subject numbers are shown. Open and closed symbols represent diaphragm activity recorded from surface and esophageal electrodes, respectively. In all subjects, NPPV resulted in substantial reductions of EMGdi amplitude. Surface and esophageal EMGdi amplitudes decreased in a similar fashion in those subjects in whom both signals were recorded. canadian cialis

Peak mask pressures which resulted in the maximal reduction of phasic EMGdi were similar between groups and averaged 16.6 ± 1.4 cmH20 for the normal group, 17.0 ± 1.8 cmH20 for the restrictive group and 13.3 ± 1.8 cmH20 for the obstructive group (Table 2). These levels of NPPV were associated with only positive inspiratory intrathoracic pressure swings (Ta­ble 2). With the highest Pmask employed, the phasic EMGdi amplitude decreased significantly (Table 2) to 6.7 ±0.7 percent of control values for the normal group, 6.4 ±3.2 percent for the restrictive group and 8.3 ±5.1 percent for the obstructive group (all p<0.01).

Ficuaı 5. The effect of mask pressure

FIGURE 5. The effect of mask pressure (Pmask) on the mean amplitudes of inspiratory muscle surface EMGs is shown for individual subjects. Control values represent those obtained during spontaneous breathing. As Pmask increased, phasic EMGs of the diaphragm, sternocleidomastoid and parasternal muscles decreased in a similar fashion.

Figure 6 illustrates the effects of NPPV on oxygen saturation and Pco2. Oxygen saturation remained stable (94.6 ±0.6 percent) as compared with control values (93.8 ± 0.6 percent) (p = NS). NPPV resulted in small but consistent reductions in arterial Pco2 from 65 ±9.9 mm Hg to 59 ±8.2 mm Hg and in end-tidal Pco2 from 54±2,1 mm Hg to 48±3.1 mm Hg (p<0.05). Pco2 did not increase in any subject with NPPV.

Ficutix 6. Oxyhemoglobin saturation

FIGURE 6. Oxyhemoglobin saturation (O, sat), arterial (PaCOJ and end-tidal Pcoa (PETCOJ are shown during spontaneous breathing (control) and with NPPV 08 sat and Pco2 were stable or improved with NPPV in all subjects.

In the five subjects who were instructed to open their mouths during NPPV, the maneuver resulted in the re-appearance of substantial phasic diaphragm EMG activity from 15.0 ±4.9 percent (mouth closed) to 98.0 ±25.5 percent (mouth open) of the value previously recorded during spontaneous breathing (Fig 7).
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Ficuaı 7. The effect ofmouth

FIGURE 7. The effect of mouth position on mean phasic diaphragm EMG during NPPV is shown. Control values represent those obtained from each subject during spontaneous breathing. The application of NPPV with the mouth closed resulted in marked reduction of the phasic surface EMGdi amplitude. With the mouth open, there was re-emergence of substantial diaphragm activity.