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