Changes in Ventilatory Muscle Function with Negative Pressure Ventilation in Patients: RESULTS

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Functional data of the three groups were summa­rized in Table 1. As shown, the study group (A) and the control group (B) exhibited similar VC, FRC, FEVi, and FEV/VC ratio, MIP and МЕР, and Pa0₂, and PaCO_z; these values being significantly different compared with the mean value of the normal control group (C group). Breathing characteristics (Table 2) were also similar in groups A and В but, compared with group C, both groups A and В exhibited a significantly lower Vt (p<0.01) and Ti (p<0.01) and a greater RF (p<0.01 and p<0.05, respectively) and lower Ttot (p<0.01 and p<0.05, respectively) and Ti/ Ttot (p<0.05 for both comparisons). The Vt/Ti was slightly greater in patients, but this difference was not significant; similarly, Ve did not significantly differ among the three groups. In addition, in groups A and В both EMGd (p<0.01) and EMGint (p<0.01) were significantly higher than in normal subjects.

Table 1—Baseline Functional Data of the Three Studied Groups

	Age, yr	vet	FRCt	FEV.t	FEV./VC, %	Pa02, mm Hg	PaC02, mm Hg	MIP, cm H20	МЕР, cm H20
Group A Group В Group С	68.4 ±4.5 71.0±6.9 62.0 ±8.7	59.6 ±8.0 52.4 ±3.2 110.7±8.6	147.8± 11.7 147.6 ±28.0 105.2 ±7.4	29.8 ±9.7 26.8 ±5.9 108.7± 11.4	38.4 ±12.0 42.4 ±10.7 70.6 ±3.4	58.2±8.0 57.2 ±4.6	60.5 ±3.4 59.6 ±9.8	40.5 ±13.9 44.0 ±10.0 99.6± 8.2	83.5 ±26.6 84.0 ±16.0 169.6 ±18.6

After a seven-day study period (Table 3), group A did not exhibit significant changes in VC, FEV,, and FRC. The MIP and МЕР measurements before and after completion of the study period are shown for group A patients in Table 3 and in Figure 1 (top). As shown in Figure 1, MIP rose in each patient; average MIP increased from 40.5 to 44.6 cm H₂0 (p<0.05); МЕР rose in five of the six patients and average МЕР increased from 83.5 to 100 cm H₂0 (p = NS). After completion of the study period, PaC0₂ decreased in each group A patient; the mean PaC0₂ decreased from 60.5 to 51.2 mm Hg (p<0.05) while Pa0₂ rose in five patients and decreased in one; the mean Pa0₂ in­creased from 58.2 to 63.75 mm Hg (p = NS). Mean and individual changes in arterial blood gas values are depicted in Table 3 and Figure 1 (bottom), respectively. The group mean effects of assisted ventilation on breathing pattern are schematized in Table 3. Both Vt and Ti increased (from 0.5 ±0.1 L to 0.67 ±0.1 L, with p<0.05, and from 1.08 ±0.2 s to 1.33 ±0.25 s, with p<0.05 respectively), whereas RF significantly decreased (from 21.6 ±3.9 cycles/min to 19.25 ±3.3 cycles/min, with p<0.05). The Ti/Ttot significantly increased (from 0.37 ±0.02 to 0.42 ±0.04 with p<0.05). The Vt/Ti was found to increase (from 0.47 ±0.06 L*s~^l to 0.52 ±0.08 L-s¹); for the group this change was not significant. Mouth occlusion pressure (Po.i) did not exhibit any significant differ­ence among the three groups (Table 2). With assisted ventilation, Po.i did not exhibit any significant change (from 2.8 ± 1.0 cm H₂0 to 2.0±0.8 cm H₂0). canadian pharmacy support net

Table 2—Breathing Battern, Po.i, and EMG Activity in the Three Groups

RF, Ve, L cycles	Vt, L	Ti, s Ttot, s	Vt/Ti, Po.i, EMGd, EMGint, 1л-1 Ti/Ttot cm H20 %TLC*s 1 %TLC*s ‘
Group A 11.2 ±1.6 21.651 ± Group В 10.3 ±3.6 19.6$ ± Group С 10.9 ±1.8 12.7t$±	3.9 0.5t ±0.09 5.0 0.49t ±0.18 1.5 0.78t±0.08	1.08t ±0.20 2.84t ±0.49 1.08t ±0.37 3.20$ ±0.80 2.13t ±0.32 4.82t$±0.54	0.47± 0.06 0.37$±0.02 2.8±1.00 45.4f±23.7 31.0t±15.0 0.47±0.21 0.35$ ±0.05 2.54 ± 0.80 34.2t±14.1 30.3t±10.6 0.41 ±0.08 0.43$±0.02 1.90±0.54 3.6t±2.3 0.9t±0.2

The EMGd at Vt was a greater fraction of the maximal EMGd activity recorded at TLC in group A and В patients (45.4 ±23.7 percent TLC^s and EMGint also decreased in each group A patient after cessation of study period (Fig 2); mean EMGint decreased from 31 percent TLOs ~¹ to 15.4 percent TLC*s^_1, with p<0.05 (Table 3). It is also worth noting that in the above-mentioned patients (1 and 3), assisted ventilation caused EMGint to decrease more than EMGd.

Table 3—Functional Data of the Study Group before and after Seven-Day Assisted Ventilation (AV) Period

	Control	Post AV	P
VC, L	1.71 ±0.36	1.98 ±0.47	NS
FRC, L	4.65 ±0.69	4.30 ±0.42	NS
FEV,, L	0.73 ±0.26	0.86 ±0.36	NS
PaOs, mm Hg	58.20 ±8.00	63.75 ±8.80	NS
PaC02, mm Hg	60.50 ±3.27	51.20 ±3.81	<0.05
MIP, cm H20	40.50 ±13.90	44.60 ±14.60	<0.05
МЕР, cm H20	83.50 ±26.60	100.00 ±17.80	NS
Po.„ cm H20	2.80 ±1.00	2.00 ±0.80	NS
EMGd, %TLC.s 1	45.40 ±23.70	31.60 ±15.20	<0.05
EMGint, %TLC .s ‘	31.00 ±15.00	15.40 ±4.70	<0.05
VE, L/min	10.77 ±1.83	12.88 ±2.30	NS
RF, cycles”1	21.65 ±3.90	19.25 ±3.30	<0.05
Vt, L	0.50 ±0.09	0.67 ±0.10	<0.05
Ti, s	1.08 ±0.20	1.33 ±0.25	<0.05
Ttot, s	2.84 ±0.49	3.19 ±0.52	<0.05
Vt/Ti, L/s	0.47 ±0.06	0.52 ±0.08	NS
Ti/Ttot	0.37 ±0.02	0.42 ±0.04	<0.05

In group В patients, no relevant changes in pulmo­nary volume, muscle strength, EMG, arterial blood gas values, and breathing pattern were observed during the study period.
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FIGURE 1. Maximal inspiratory (MIP) and expiratory (МЕР) pressures and arterial P02 and Pco2 in the study group patients before (C) and after a seven-day period of assisted ventilation (NPV).

In the two patients (2 and 5) in whom EMG was also evaluated one day after cessation of NPy both EMGd and EMGint did not exhibit substantial per­centage changes compared with the end of the seven- day period of NPV: EMGd was 105 percent ±5 percent and EMGint was 106 percent ±6 percent. Accordingly, neither Vt nor Ti nor RF exhibited substantial percent changes.

FIGURE 2. Electromyographic activity of diaphragm (EMGd) and parasternal intercostal (EMGint) muscles in the study group patients before (C) and after a seven-day period of assisted ventilation (NPV). Numbers represent individual patients (for explanations see text).

At the end of the study period each group A patient experienced a decrease in sensation of breathlessness. No ventilator-related complications were observed in them.