Table 3.
In vitro diaphragm muscle contractile properties with various modes of mechanical ventilation, with and without applied positive end-expiratory airway pressure a
| Control | CPAP | CPAP-8 | AMV | AMV-8 | CMV | CMV-8 | |
|---|---|---|---|---|---|---|---|
| Lo (cm) | 3.2 ± 0.1 | 3.1 ± 0.1 | 3.4 ± 0.1 | 3.2 ± 0.1 | 3.2 ± 0.2 | 2.9 ± 0.2 | 3.2 ± 0.1 |
| TPT (ms) | 67 ± 3 | 68 ± 3 | 73 ± 9 | 71 ± 3 | 71 ± 2 | 70 ± 4 | 66 ± 6 |
| RT1/2 (ms) | 84 ± 4 | 116 ± 11 | 115 ± 17 | 98 ± 5 | 96 ± 5 | 118 ± 8 | 89 ± 11 |
| Ptw (N/cm2) | 7.4 ± 0.5 | 5.9 ± 0.5 | 6.0 ± 0.8 | 6.2 ± 0.8 | 7.2 ± 0.6 | 5.7 ± 0.9 | 3.7 ± 0.4b |
| Po (N/cm2) | 24.3 ± 0.4 | 23.3 ± 1.0 | 23.0 ± 1.6 | 22.6 ± 0.8 | 23.0 ± 1.1 | 15.8 ± 1.0c | 15.0 ± 1.1c |
aValues are mean ± SE (n = 6 animals in each group). Ptw and Po are normalized for cross-sectional area (see Material and methods for calculation). AMV, Assist-control mechanical ventilation; CMV, Controlled mechanical ventilation (numerical value of 8 next to ventilatory mode denotes the set CPAP or PEEP of 8 cmH2O); CPAP, Continuous positive airway pressure; Lo, Length at which diaphragm muscle strip produced maximal isometric tension; Po, Maximum tetanic force; Ptw, Peak twitch force; RT1/2, Time required for peak twitch force to relax to one-half of peak twitch force; TPT, Time from onset of muscle contraction to peak twitch force. bFor Ptw, P < 0.01 for CMV-8 compared with control and AMV-8. cFor Po, P < 0.01 for CMV compared with control, CPAP and AMV, as well as for CMV-8 compared with control, CPAP-8 and AMV-8.