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Method
Measurement of arterialised venous pH and partial pressure of carbon dioxide
An arterialised venous blood sample was collected from a 20 gauge cannula that was inserted into a
vein on the dorsum of the wrist or forearm. A 12 cm extension catheter was attached (dead space
0.2 millilitres) and pointed distally to allow blood to be sampled away from the hand. The cannula
was flushed intermittently with normal saline to prevent clotting. An electric heating pad
(Theratherm, Chattanooga Group, Hixon, Tennessee, USA) was wrapped around the participants
forearm and hand, covering the cannula. The temperature of the forearm was monitored using a
thermometer with the probe placed adjacent to the cannula, and an external display screen. Skin
temperature was maintained between 42 - 45ºC [1, 2]. The heating pad was in place for a minimum
of 20 minutes before sampling began. To account for dead space within the cannula and extension
catheter, one millilitre (mL) of blood was withdrawn and discarded prior to collection of the
arterialised venous sample. Then two mL of blood was withdrawn from the cannula into a three mL
heparinised syringe. Air bubbles were expelled from the syringe and the sample was stored in ice
until blood pH, partial pressure of carbon dioxide (PCO2) and lactate (La) levels were analysed
using a Corning 175 Blood Gas Analyser (Medfield, MA). This was typically within 30 minutes of
the sample being collected.
Flow
Expiratory flow was measured by a mesh screen pneumotachograph (3830B Hans Rudolph,
Shawnee, Kansas, USA) placed between the full face mask and the expiratory port within the
bilevel circuit. To keep the interface and dead space (195 mL) consistent, flow was measured
during unassisted exercise by removing the expiratory port and tubing, leaving only the full face
mask and pneumotachograph. The pneumotachograph was connected to a differential pressure
transducer (Validyne DP45-14, ± 2.25 cmH2O, Validyne Engineering Corporation, Northridge, CA,
1
USA). The pressure transducer voltage output was amplified, displayed real time and recorded on a
laptop using a data acquisition program (PhysioDAQxs, University of Sydney, NSW, Australia)
with a sampling frequency of 100Hz. The pneumotachograph was calibrated prior to each test
using a three litre syringe and the technique described by Tang et al [3]. The calibration file was
used to determine whether an offset needed to be applied to zero the baseline, and the magnitude of
the offset. A linear relationship between voltage and flow was assumed, and a conversion factor
was obtained by calculating the average voltage output for one litre/second from the calibration file.
Voltage output was converted to flow (litres/minute), and flow was integrated to give tidal volume
(VT). Respiratory rate (RR) was calculated by counting the number of breaths on the flow trace
during the final 20 seconds of the baseline period and minute ventilation (VE) was calculated by
multiplying VT and RR.
Subjective responses to pressure support during exercise
At the end of each test with pressure support (PS), participants scored the effect of PS during
exercise on the amount of “help” provided and “breathlessness” compared to usual unassisted
walking on a 10 cm visual analogue scale (VAS).
Results
Table 4 Pairwise comparisons of walking unassisted, with sham pressure support, pressure support
10 cmH2O and pressure support 20 cmH2O for endurance time (seconds) after transformation using
log(x)
Comparison
PS 20 vs UnA
PS 20 vs PS 10
PS 10 vs UnA
PS 20 vs Sham
PS 10 vs Sham
Sham vs UnA
Log(x) endurance time
Mean (SD) vs Mean (SD)
Mean difference
(95% CI)
p value
Adjusted
p value
2.446 (0.3456) vs 2.137 (0.234)
2.446 (0.3456) vs 2.217 (0.1548)
2.217 (0.1548) vs 2.137 (0.234)
2.446 (0.3456) vs 2.071 (0.2376)
2.217 (0.1548) vs 2.071 (0.2376)
2.071 (0.2376) vs 2.137 (0.234)
0.309 (0.078 to 0.540)
0.229 (0.080 to 0.378)
0.080 (-0.079 to .240)
0.375 (0.235 to 0.515)
0.146 (0.057 to 0.235)
-0.066 (-0.273 to 0.141)
0.013
0.006
0.295
<0.001
0.004
0.499
0.039
0.012
NS
<0.001
0.008
NS
Log(x) of endurance time (seconds) data are presented. PS 20: pressure support 20 cmH 2O; UnA: unassisted exercise; PS 10:
pressure support 10 cmH2O; Sham: sham pressure support; Adjusted p: p value adjusted using a sharper Bonferroni correction [17];
NS: not significant
2
Table 5 Descriptive data for physiological and subjective variables at rest, baseline, isotime and end
exercise
SpO2 %
Rest
Baseline
Isotime
End exercise
HR (beats/min)
Rest
Baseline
Isotime
End exercise
Dyspnoea (Borg)
Rest
Baseline
Isotime
End exercise
RPE (Borg)
Rest
Baseline
Isotime
End exercise
VE (L/min)
Baseline
Isotime
End exercise
RR (bpm)
Baseline
Isotime
End exercise
VT (L)
Baseline
Isotime
End exercise
pH
Rest
Baseline
End exercise
PCO2 (mmHg)
Rest
Baseline
End exercise
[La] (mmol/L)
Rest
Baseline
End exercise
SBP (mmHg)
Rest
Baseline
End exercise
DBP (mmHg)
Rest
Baseline
End exercise
MAP (mmHg)
Rest
Baseline
End exercise
Unassisted
Sham PS
PS 10
PS 20
94 ± 4
94 ± 4
84 ± 7
82 ± 10
94 ± 2
92 ± 3
82 ± 7
80 ± 7
94 ± 3
94 ± 2
87 ± 5
81 ± 7
94 ± 2
96 ± 2
88 ± 5
82 ± 8
87 ± 15
87 ± 15
116 ± 20
118 ± 23
86 ± 11
88 ± 13
115 ± 20
118 ± 18
85 ± 12
86 ± 14
113 ± 16
118 ± 16
85 ± 15
87 ± 14
109 ± 14
120 ± 18
0 (0 - 0.5)
0 (0 - 0.5)
3.7 ± 2.7
6.0 ± 2.9
0 (0 - 0.8)
0 (0 - 2.5)
4.4 ± 2.6
5.4 ± 2.4
0 (0 - 0.5)
0 (0 - 1)
2.7 ± 1.8
5.4 ± 2.6
0 (0 - 0.3)
0.5 (0 - 1)
2.0 ± 2.2
6.0 ± 2.7
0 (0 - 0.3)
0 (0 - 0.3)
4.5 ± 2.8
6.3 ± 2.8
0 (0 – 1.0)
0 (0 - 2.0)
4.5 ± 2.4
5.5 ± 2.3
0 ( 0 - 0.5)
0 (0 - 0.8)
2.9 ± 2.2
5.5 ± 2.7
0 (0 - 0.3)
0 (0 - 1.0)
2.8 ± 2.1
7.1 ± 3.0
9.237 ± 2.870
18.110 ± 5.056
19.543 ± 6.332
8.035 ± 1.693
15.265 ± 2.747
15.588 ± 2.722
9.765 ± 2.016
17.390 ± 3.390
19.023 ± 4.061
10.450 ± 3.740
17.261 ± 4.354
21.325 ± 5.293
29 ± 6
42 ± 9
47 ± 10
30 ± 8
40 ± 10
41 ± 10
28 ± 9
38 ± 9
42 ± 11
25 ± 9
34 ± 8
40 ± 9
0.332 ± 0.107
0.462 ± 0.136
0.471 ± 0.132
0.295 ± 0.094
0.412 ± 0.120
0.419 ± 0.131
0.384 ± 0.113
0.483 ± 0.143
0.505 ± 0.159
0.453 ± 0.179
0.539 ± 0.173
0.569 ± 0.174
7.379 ± 0.046
7.379 ± 0.046
7.352 ± 0.051
7.383 ± 0.039
7.374 ± 0.040
7.359 ± 0.039
7.379 ± 0.039
7.389 ± 0.040
7.356 ± 0.038
7.382 ± 0.031
7.421 ± 0.043
7.355 ± 0.048
50.7 ± 7.2
50.7 ± 7.2
53.9 ± 9.5
49.7 ± 7.4
50.3 ± 8.7
53.1 ± 8.2
49.5 ± 7.9
47.8 ± 7.1
53.4 ± 8.0
49.9 ± 6.6
43.9 ± 6.0
51.9 ± 8.6
1.1 ± 0.3
1.1 ± 0.3
1.7 ± 0.9
1.0 ± 0.2
0.9 ± 0.1
1.3 ± 0.4
1.1 ± 0.4
1.1 ± 0.4
1.7 ± 0.5
1.2 ± 0.5
1.2 ± 0.6
2.2 ± 1.0
124 ± 13
124 ± 13
158 ± 24
124 ± 11
125 ± 13
145 ± 23
121 ± 11
123 ± 14
150 ± 23
125 ± 14
118 ± 11
150 ± 20
88 ± 11
88 ± 11
90 ± 11
85 ± 11
89 ± 10
85 ± 13
85 ± 10
87 ± 11
90 ± 10
86 ± 10
85 ± 11
93 ± 11
100 ± 11
100 ± 11
113 ± 3
98 ± 10
101 ± 10
105 ± 14
97 ± 9
99 ± 11
110 ± 12
99 ± 11
96 ± 11
112 ± 12
Data are presented as mean ± SD or median (interquartile range). SpO2 %: oxygen saturation; HR: heart rate; RPE: rate of perceived
exertion; VE: minute ventilation; RR: respiratory rate; VT: tidal volume; PCO2: arterialised venous carbon dioxide partial pressure;
[La]: lactate; SBP: systolic blood pressure; DBP: diastolic blood pressure; MAP: mean arterial pressure; UnA: unassisted exercise;
Sham PS: sham pressure support, PS 10: pressure support 10 cmH 2O; PS 20: pressure support 20 cmH2O; NA: not assessed
3
Baseline
At baseline, there was a difference between the interventions with respect to SpO2, pH, PCO2 and
VT (Table 6). Pairwise comparisons of the four conditions with a sharper Bonferroni [4] correction
of p values, revealed that SpO2 was higher with PS 20 and PS 10 compared to unassisted breathing
or sham PS. Compared to unassisted breathing, sham PS or PS 10, PS 20 increased pH (less acidic)
and reduced PCO2. Pressure support 10 cmH2O at rest increased pH compared to sham PS, and
reduced PCO2 compared to unassisted breathing and with sham PS. Tidal volume was higher with
PS 20 compared to unassisted breathing and sham PS (Table 7).
Table 6 Linear mixed model analysis of breathing unassisted, with sham pressure support, pressure
support 10 cmH2O and pressure support of 20 cmH2O at baseline, isotime, end exercise and change
from baseline to end exercise on oxygen saturation, pH, partial pressure of carbon dioxide,
cardiovascular variables, dyspnoea, perceived exertion, lactate and ventilation
SpO2
HR
Dyspnoea
RPE
SBP
DBP
MAP
pH
PCO2
La
RR
VT
VE
Baseline
Isotime
End Exercise
Change from baseline
to end exercise
p
p
p
p
<0.001
0.89
0.16
0.68
0.073
0.43
0.12
<0.001
<0.001
0.16
0.11
0.002
0.09
<0.001
0.16
0.006
0.013
NA
NA
NA
NA
NA
NA
<0.001
0.018
0.13
0.38
0.79
0.67
0.061
0.092
0.002
0.007
0.94
0.27
0.002
<0.001
0.003
0.015
0.32
0.15
0.31
0.045
0.014
0.001
0.001
<0.001
0.010
0.047
0.031
0.84
0.22
SpO2%: oxygen saturation; HR: heart rate; RPE: rate of perceived exertion; SBP: systolic blood pressure; DBP: diastolic blood
pressure; MAP: mean arterial pressure; PCO2: arterialized venous carbon dioxide tension; La: lactate; RR: respiratory rate; VT: tidal
volume; VE: minute ventilation; NA: not assessed
4
Table 7 Pairwise comparisons of breathing unassisted, with sham pressure support, pressure
support 10 cmH2O and pressure support 20 cmH2O for oxygen saturation, pH, partial pressure of
carbon dioxide and tidal volume at baseline
Comparison
Mean (SD) vs Mean (SD)
Mean difference
(95% CI)
SpO2
PS 20 vs UnA
PS 20 vs PS 10
PS 10 vs UnA
PS 20 vs Sham
PS 10 vs Sham
Sham vs UnA
96 (2) vs 94 (4)
96 (2) vs 94 (2)
94 (2) vs 94 (4)
96 (2) vs 92 (3)
94 (2) vs 92 (3)
92 (3) vs 94 (4)
pH
PS 20 vs UnA
PS 20 vs PS 10
PS 10 vs UnA
PS 20 vs Sham
PS 10 vs Sham
Sham vs UnA
7.421 (0.043) vs 7.379 (0.046)
7.421 (0.043) vs 7.389 (0.040)
7.389 (0.040) vs 7.379 (0.046)
7.421 (0.043) vs 7.374 (0.040)
7.389 (0.040) vs 7.374 (0.040)
7.374 (0.040) vs 7.379 (0.046)
PCO2
PS 20 vs UnA
PS 20 vs PS 10
PS 10 vs UnA
PS 20 vs Sham
PS 10 vs Sham
Sham vs UnA
43.9 (6.0) vs 50.7 (7.2)
43.9 (6.0) vs 47.8 (7.1)
47.8 (7.1) vs 50.7 (7.2)
43.9 (6.0) vs 50.3 (8.7)
47.8 (7.1) vs 50.3 (8.7)
50.3 (8.7) vs 50.7 (7.2)
VT
PS 20 vs UnA
PS 20 vs PS 10
PS 10 vs UnA
PS 20 vs Sham
PS 10 vs Sham
Sham vs UnA
0.453 (0.179) vs 0.322 (0.107)
0.453 (0.179) vs 0.384 (0.113)
0.384 (0.113) vs 0.322 (0.137)
0.453 (0.179) vs 0.295 (0.094)
0.384 (0.113) vs 0.295 (0.094)
0.295 (0.094) vs 0.322 (0.137)
p value
Adjusted
p value
2 (1 to 4)
2 (0 to 3)
1 (-1 to 2)
5 (3 to 6)
3 (1 to 4)
-2 (-4 to -1)
0.005
0.030
0.48
<0.001
0.001
0.004
0.02
NS
NS
<0.001
0.002
0.012
.039 (0.03 to 0.05)
.026 (0.01 to 0.04)
.013 (0 to 0.03)
.047 (0.03 to 0.06)
.021 (0.01 to 0.04)
-0.01 (-0.02 to 0.01)
<0.001
0.001
0.087
<0.001
0.012
0.33
<0.001
0.003
NS
<0.001
0.048
NS
-6.3 (-8.3 to -4.3)
-3.4 (-5.4 to -1.4)
-2.9 (-4.9 to -0.9)
-6.8 (-8.9 to -4.7)
-3.4 (-5.5 to -1.3)
0.4 (-1.7 to 2.5)
<0.001
0.002
0.006
<0.001
0.003
0.68
0.001
0.006
0.030
<0.001
0.012
NS
0.130 (0.045 to 0.214)
0.068 (-0.014 to 0.150)
0.062 (-0.022 to 0.146)
0.158 (0.076 to 0.239)
0.089 (0.007 to 0.171)
-0.027 (-0.112 to 0.057)
0.004
0.099
0.145
<0.001
0.034
0.511
0.008
NS
NS
<0.001
NS
NS
SpO2%: oxygen saturation; PCO2: arterialized venous carbon dioxide tension; VT: tidal volume (L); PS 20: pressure support 20
cmH2O; UnA: unassisted exercise; PS 10: pressure support 10 cmH2O; Sham: sham pressure support; Adjusted p: p value adjusted
using a sharper Bonferroni correction [4]; NS: not significant
Change from baseline to end exercise
For the change from baseline to end exercise (where exercise endurance time varied between
conditions), there was a difference between interventions with respect to RPE, SBP, DBP, MAP,
pH, PCO2, La and RR (Table 6). Pairwise comparisons of the four interventions with a sharper
Bonferroni [4] correction of p values, revealed that the change in RPE was greater with PS 20
compared to sham. Changes in blood pressure were greater with PS 20 and unassisted exercise
compared to sham PS. Arterialised venous pH decreased to a greater extent with PS 20 during
walking compared to unassisted exercise, sham PS and PS 10, and a greater increase in PCO2 was
observed when PS 20 was used during exercise compared to unassisted exercise and sham PS. In
addition, change in blood La was significantly higher with PS 20 compared to sham PS. Lastly,
change in RR from rest to end of exercise was significantly lower with sham PS compared to
unassisted exercise (Table 8).
5
Table 8 Pairwise comparisons of walking unassisted, with sham pressure support, pressure support
10 cmH2O and pressure support 20 cmH2O for perceived exertion, cardiovascular variables, pH,
partial pressure of carbon dioxide, lactate and respiratory rate for the change from baseline to end
exercise
Comparison
Mean change (SD) vs mean change (SD)
Mean difference
(95% CI)
p value
Adjusted
p value
RPE
PS 20 vs UnA
PS 20 vs PS 10
PS 10 vs UnA
PS 20 vs Sham
PS 10 vs Sham
Sham vs UnA
6.4 (2.8) vs 5.7 (2.7)
6.4 (2.8) vs 4.8 (2.5)
4.8 (2.5) vs 5.7 (2.7)
6.4 (2.8) vs 4.4 (2.3)
4.8 (2.5) vs 4.4 (2.3)
4.4 (2.3) vs 5.7 (2.7)
0.7 (-0.8 to 2.1)
1.6 (0.2 to 3.1)
-1.0 (-2.4 to 0.5)
2.0 (0.5 to 3.4)
0.3 (-1.1 to 1.8)
-1.3 (-2.8 to 0.1)
0.38
0.035
0.20
0.011
0.64
0.084
NS
NS
NS
0.011
NS
NS
SBP
PS 20 vs UnA
PS 20 vs PS 10
PS 10 vs UnA
PS 20 vs Sham
PS 10 vs Sham
Sham vs UnA
32.4 (17.0) vs 34.6 (25.6)
32.4 (17.0) vs 27.0 (16.4)
27.0 (16.4) vs 34.6 (25.6)
32.4 (17.0) vs 20.3 (19.8)
27.0 (16.4) vs 20.3 (19.8)
20.3 (19.8) vs 34.6 (25.6)
-2.0 (-10.8 to 6.8)
5.4 (-3.2 to 14.0)
-7.4 (-16.2 to 1.4)
12.1 (3.5 to 20.7)
6.7 (-1.9 to 15.3)
-14.1 (-22.9 to -5.3)
0.66
0.23
0.108
0.009
0.135
0.003
NS
NS
NS
0.018
NS
0.003
DBP
PS 20 vs UnA
PS 20 vs PS 10
PS 10 vs UnA
PS 20 vs Sham
PS 10 vs Sham
Sham vs UnA
8.0 (8.5) vs 3.9 (6.7)
8.0 (8.5) vs 2.8 (4.4)
2.8 (4.4) vs 3.9 (6.7)
8.0 (8.5) vs -3.8 (8.0)
2.8 (4.4) vs 3.8 (8.0)
3.8 (8.0) vs 3.9 (6.7)
4.1 (-1.2 to 9.4)
5.2 (-0.1 to 10 5)
-1.2 (-6.4 to 4.1)
11.8 (6.5 to 17.1)
6.5 (1.3 to 11.8)
-7.7 (-13.0 to -2.4)
0.139
0.060
0.67
<0.001
0.020
0.007
NS
NS
NS
<0.001
NS
0.014
MAP
PS 20 vs UnA
PS 20 vs PS 10
PS 10 vs UnA
PS 20 vs Sham
PS 10 vs Sham
Sham vs UnA
16.1 (10.1) vs 13.3 (12.0)
16.1 (10.1) vs 10.9 (7.9)
10.9 (7.9) vs 13.3 (12.0)
16.1 (10.1) vs 4.3 (10.4)
10.9 (7.9) vs 4.3 (10.4)
4.3 (10.4) vs 13.3 (12.0)
2.9 (-2.6 to 8.4)
5.3 (-0.2 to 10.8)
-2.4 (-7.9 to 3.1)
11.9 (6.4 to 17.4)
6.6 (1.1 to 12.1)
-9.0 (-14.5 to -3.5)
0.31
0.068
0.40
<0.001
0.024
0.003
NS
NS
NS
<0.001
NS
0.006
pH
PS 20 vs UnA
PS 20 vs PS 10
PS 10 vs UnA
PS 20 vs Sham
PS 10 vs Sham
Sham vs UnA
-0.059 (0.040) vs -0.024 (0.027)
-0.059 (0.040) vs -0.033 (0.027)
-0.033 (0.027) vs -0.024 (0.027)
-0.059 (0.040) vs -0.015 (0.022)
-0.033 (0.027) vs -0.015 (0.022)
-0.015 (0.022) vs -0.024 (0.027)
-0.04 (-0.05 to -0.02)
-0.03 (-0.04 to -0.01)
-0.01 (-0.03 to 0.01)
-0.05 (-0.06 to -0.03)
-0.02 (-0.04 to 0)
0.010 (-0.01 to 0.03)
0.001
0.008
0.34
<0.001
0.062
0.32
0.002
0.024
NS
<0.001
NS
NS
PCO2
PS 20 vs UnA
PS 20 vs PS 10
PS 10 vs UnA
PS 20 vs Sham
PS 10 vs Sham
Sham vs UnA
7.2 (5.9) vs 3.1 (4.7)
7.2 (5.9) vs 5.8 (3.7)
5.8 (3.7) vs 3.1 (4.7)
7.2 (5.9) vs 2.5 (4.5)
5.8 (3.7) vs 2.5 (4.5)
2.5 (4.5) vs 3.1 (4.7)
4.1 (1.3 to 6.9)
1.5 (-1.3 to 4.3)
2.7 (-0.1 to 5.5)
4.3 (1.3 to 7.2)
2.8 (-0.1 to 5.8)
-0.2 (-3.1 to 2.8)
0.005
0.30
0.062
0.006
0.060
0.91
0.005
NS
NS
0.012
NS
NS
La
PS 20 vs UnA
PS 20 vs PS 10
PS 10 vs UnA
PS 20 vs Sham
PS 10 vs Sham
Sham vs UnA
0.9 (0.7) vs 0.6 (0.6)
0.9 (0.7) vs 0.6 (0.4)
0.6 (0.4) vs 0.6 (0.6)
0.9 (0.7) vs 0.5 (0.4)
0.6 (0.4) vs 0.5 (0.4)
0.5 (0.4) vs 0.6 (0.6)
0.26 (-0.03 to 0.55)
0.25 (-0.04 to 0.55)
0.01 (-0.28 to 0.30)
0.46 (0.15 to 0.77)
0.21 (-0.10 to 0.51)
-0.20 (-0.50 to 0.11)
0.087
0.097
0.96
0.006
0.20
0.22
NS
NS
NS
0.006
NS
NS
RR
PS 20 vs UnA
PS 20 vs PS 10
PS 10 vs UnA
PS 20 vs Sham
PS 10 vs Sham
Sham vs UnA
14.8 (5.9) vs 17.8 (7.7)
14.8 (5.9) vs 13.9 (7.5)
13.9 (7.5) vs 17.8 (7.7)
14.8 (5.9) vs 11.0 (6.0)
13.9 (7.5) vs 11.0 (6.0)
11.0 (6.0) vs 17.8 (7.7)
-3.1 (-7.4 to 1.2)
0.8 (-3.3 to 5.0)
-3.9 (-8.2 to 0.3)
3.4 (-0.4 to 7.9)
2.9 (-1.2 to 7.1)
-6.8 (-11.1 to 2.6)
0.17
0.70
0.081
0.086
0.18
0.004
NS
NS
NS
NS
NS
0.004
RPE: rate of perceived exertion (Borg); SBP: systolic blood pressure (mmHg); DBP: diastolic blood pressure (mmHg); MAP: mean
arterial pressure (mmHg); PCO2: arterialized venous carbon dioxide tension; La: lactate (mmol/L); RR: respiratory rate; PS 20:
pressure support 20 cmH2O, UnA: unassisted exercise; PS 10: pressure support 10 cmH2O; Sham: sham pressure support; Adjusted
p: p value adjusted using a sharper Bonferroni correction[4]; NS: not significant
6
Subjective responses to pressure support during exercise
A repeated measures ANOVA revealed a difference between exercise with sham PS, PS 10 and PS
20 with respect to VAS scores for the amount of “help” provided and “breathlessness” (p<0.001
and p<0.001 respectively, Figure 6). Pairwise comparisons are shown in Table 9.
Figure 6 Visual analogue scales representing the effect of sham pressure support (PS), pressure
support 10 cmH2O (PS 10) and pressure support 20 cmH2O (PS 20) on: a) “help during exercise”;
b) “breathlessness during exercise”. Mean scores are presented and the whiskers represent standard
deviation. Scores above the horizontal dashed line at 50% represent an advantage relative to
unassisted walking, and scores below the dashed line represent a disadvantage relative to unassisted
walking. *: p < 0.05; †: p < 0.01; ‡: p < 0.001 after the sharper Bonferroni correction[4]; * (light
grey): p < 0.05 prior to the sharper Bonferroni correction [4]
7
Table 9 Pairwise comparisons of walking with sham pressure support, pressure support 10 cmH2O
and pressure support 20 cmH2O for “help during exercise” and “breathlessness”
Comparison
Mean (SD) vs Mean (SD)
Mean difference
(95% CI)
p value
Adjusted
p value
Help during exercise
PS 20 vs PS 10
PS 20 vs Sham
PS 10 vs Sham
73.6 (21.0) vs 54.3 (24.4)
73.6 (21.0) vs 36.0 (22.0)
54.3 (24.4) vs 36.0 (22.0)
19.3 (2.7 to 35.9)
37.6 (25.7 to 49.5)
18..3 (3.5 to 33.0)
0.026
<0.001
0.019
NS
<0.001
0.038
Breathlessness
PS 20 vs PS 10
PS 20 vs Sham
PS 10 vs Sham
74.7 (20.5) vs 64.8 (17.9)
74.7 (20.5) vs 40.9 (17.1)
64.8 (17.9) vs 40.9 (17.1)
9.8 (-2.1 to 21.8)
33.8 (19.4 to 48.1)
23.9 (10.4 to 37.4)
0.097
<0.001
0.002
NS
<0.001
0.004
Data are presented as a percentage of the 10 cm visual analogue scale. Zero represents no help during exercise and no reduction in
breathlessness. One hundred represents maximum help during exercise and maximum reduction in breathlessness. PS 20: pressure
support 20 cmH2O; UnA: PS 10: pressure support 10 cmH2O; Sham: sham pressure support; Adjusted p: p value adjusted using a
sharper Bonferroni correction [4]; NS: not significant
References
[1]
Forster HV, Dempsey JA, Thomson J, Vidruk E, DoPico GA. Estimation of arterial PO2,
PCO2, pH, and lactate from arterialized venous blood. Journal of Applied Physiology. 1972
Jan;32:134-7.
[2]
Morgan EJ, Baidwan B, Petty TL, Zwillich CW. The effects of unanesthetized arterial
puncture on PCO2 and pH. American Review of Respiratory Disease. 1979 Oct;120:795-8.
[3]
Tang Y, Turner MJ, Yem JS, Baker AB. Calibration of pneumotachographs using a
calibrated syringe. Journal of Applied Physiol. 2003;95:571-6.
[4]
Hochberg Y. A sharper Bonferroni procedure for multiple tests of significance. Biometrika
1988:800-2.
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