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Table 2 Physiological variables and diaphragm shear modulus under the different ventilatory conditions

From: Ultrasound shear wave elastography for assessing diaphragm function in mechanically ventilated patients: a breath-by-breath analysis

Variables

Condition of ventilation

PS+25%

PS

PS-25%

PSZEEP

SBT Start

SBT End

Pressure support, cmH2O

13 (12–16)

10 (10–13)

8 (7–9)

10 (10–13)

0

0

PEEP, cmH2O

5 (5–5)

5 (5–5)

5 (5–5)

0

0

0

VT, mL/kg

5.7 (4.9–7.4)def

4.9 (4.2–6.2)ef

4.6 (4.1–5.4)ace

4.8 (3.8–6.8)ae

3.3 (3.1–4.9)abcd

3.9 (3.2–5.4)ab

Respiratory rate, cycles/min

19 (13–25)

21 (17–27)

23 (18–29)

24 (17–30)

24 (18–33)ab

26 (22–32)a

Inspiratory time, s

1.1 (1.0–1.6)

1.0 (0.9–1.3)

1.0 (0.9–1.2)a

1.0 (0.8–1.3)

1.2 (0.9–1.3)c

1.1 (0.9–1.3)a

Expiratory time, s

2.0 (1.5–2.8)

1.8 (1.3–2.4)

1.5 (1.2–2.1)

1.5 (1.2–2.2)

1.3 (1.0–1.8)ab

1.3 (1.0–1.6)

Inspiratory duty cycle

0.40 (0.37–0.45)e

0.41 (0.36–0.45)

0.39 (0.37–0.43)e

0.41 (0.38–0.43)e

0.45 (0.43–0.50)acd

0.45 (0.41–0.47)

Minute ventilation (l.min−1)

7.8 (5.8–10.4)

8.1 (6.0–10.1)

7.9 (6.1–9.5)

8.2 (5.8–9.4)

6.4 (5.2–9.0)

7.5 (5.5–8.6)

ΔPdi, cmH2O

3.9 (1.6–9.4)ef

3.2 (1.3–8.9)ef

4.3 (2.5–12.9)ef

5.8 (2.8–10.5)ef

10.3 (5.6–21.8)abcd

10.0 (7.1–23.5)abcd

PTPdi, cmH2O.s/breath

2.9 (0.8–6.7)ef

1.5 (0.7–4.1)ef

3.4 (1.3–6.9)ef

3.5 (1.8–6.4)ef

9.2 (2.7–13.7)abcd

7.4 (3.6–11.4)abcd

PTPdi, cmH2O.s/min

42 (17–131)ef

33 (16–137)ef

78 (23–128)ef

78 (34–167)f

188 (66–369)abc

178 (103–297)abcd

ΔPes, cmH2O

− 1.7 (− 8.5 to − 0.9)ef

− 1.7 (− 9.0 to − 0.9)ef

− 2.9 (− 12.2 to − 1.9)ef

− 4.8 (− 8.8 to − 2.8)ef

− 11.3 (− 18.7 to − 8.6)abcd

− 10.6 (− 23.5 to − 9.3)abcd

ΔPga, cmH2O

0.9 (0.2–2.3)

1.1 (0.2–1.9)

1.0 (0.5–2.3)

0.9 (0.3–2.4)

0.4 (0.0–1.3)

0.2 (0.0–1.0)

ΔSMdi, kPa

5.5 (3.8–9.0)ef

5.4 (3.5–8.8)ef

7.0 (5.8–8.6)ef

7.7 (4.0–11.8)ef

12.2 (7.7–14.3)abcd

7.5 (4.8–13.1)abcd

  1. Results are shown as median (Q1–Q3). PEEP, positive end-expiratory pressure; VT, tidal volume; ΔPdi, inspiratory change in transdiaphragmatic pressure; PTPdi, pressure–time product of Pdi; ΔPes, inspiratory changes in esophageal pressure; ΔPga, inspiratory changes in gastric pressure; ΔSMdi, inspiratory change in diaphragm shear modulus assessed using ultrasound shear wave elastography; PS, pressure support ventilation with baseline inspiratory support and positive end-expiratory pressure; PS+25%, PS with inspiratory pressure support increased by 25%; PS−25%, PS with inspiratory pressure support decreased by 25%; PSZEEP, PS with baseline inspiratory support and zero end-expiratory pressure; SBT, spontaneous breathing trial. a, significantly different from PS+25%; b, Significantly different from PS; c, significantly different from PS−25%; d, significantly different from PSZEEP; e, significantly different from the start of the SBT; f, significantly different from the end of the SBT; all p < 0.05