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Table 2 Ventilatory pattern, gas exchange and respiratory effort

From: Chest wall mechanics during pressure support ventilation

Parameter

P

Pressure support (cmH2O)

  

5

10

15

25

Tidal volume (l)

<0.001

0.340 ± 0.048

0.432 ± 0.064

0.610 ± 0.063

0.852 ± 0.070

Frequency (minute-1)

<0.001

27.7 ± 2.9

22.1 ± 2.6

15.9 ± 2.2

11.9 ± 1.7

Minute ventilation (l/minute)

NS

8.5 ± 0.8

8.9 ± 1.2

8.6 ± 0.7

9.5 ± 1.2

Pao2/Fio2 (mmHg)

0.042

299.3 ± 22.0

263.1 ± 22.8

288.2 ± 22.3

320.0 ± 25.4

Paco2 (mmHg)

NS

35.4 ± 2.4

33.9 ± 2.7

33.9 ± 2.2

33.8 ± 2.0

f/Vt (1/l·minute)

<0.001

97.9 ± 15.4

61.2 ± 9.9

33.3 ± 9.3

16.2 ± 3.6

WOB (J/minute)

<0.001

4.9 ± 1.0

3.8 ± 1.7

1.2 ± 0.6

0.0 ± 0.0a

PTP (cmH2O s/minute)

<0.001

106.1 ± 18.3

61.9 ± 21.8

16.3 ± 8.6

0.1 ± 0.1

P0.1 (cmH2O)

<0.001

2.0 ± 0.5

1.5 ± 0.3

0.9 ± 0.2

0.3 ± 0.2

  1. Where applicable, values are expressed as mean ± standard error of the mean. aZero work of breathing (WOB) is the consequence of our assumption that, at 25 cmH2O, the respiratory system is in a fully relaxed state. P values refer to one-way analysis of variance on repeated measures (for different levels of pressure support). FiO2, fraction of inspired oxygen; f/Vt, frequency/tidal volume ratio; NS, not significant; P0.1, occlusion pressure; PaCO2, arterial carbon dioxide tension; PaO2, arterial oxygen tension; PTP, pressure time product.