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Table 2 Respiratory variables through the ventilatory modes tested

From: Moderately high frequency ventilation with a conventional ventilator allows reduction of tidal volume without increasing mean airway pressure

Variable VT = 6 mL/kg RR = 30 HFPPV = 60 HFPPV = 90 HFPPV = 120 HFPPV = 150 HFOV p valuea
P/F ratio (mmHg) 95 [87,105] 151 [117,181]b 141 [102,189]b 132 [95,169]b 111 [86,162]b 112 [90,171]b 193 [146,216]b,c P = 0.003
Gradient (A-a)O2 480 [465,493] 396 [383,452]b 427 [378,468]b 427 [394,466] 455 [406,481] 458 [394,478] 365 [350,420]b,c P = 0.014
Minute ventilation (L/min) 6.9 [6.6,8.8] 8.7 [7.4,10.0] 11.1 [11.0,11.5]b 15.6 [14.0,17.5]b 18.6 [13.0,19.2]b 20.2 [19.5,21.3]b 27 [23.5,28.4]b,c P < 0.001
Shunt (%) 43 [41,45] 29 [26,34]b 34 [30,40] 31 [28,44] 34 [31,45] 38 [30,43] 27 [25,32]b,c P = 0.003
EtCO2 (mmHg) 58 [52,60] 43 [32,47]b 41 [37,49]b 40 [30,45]b 40 [31,48]b 34 [28,36]b 27 [23,30]b,c P < 0.001
Cstatic (mL/cmH2O) 12 [10,14] 12 [9,14] 10 [9,13] 10 [9,12]b 10 [7,11]b 9 [8,11]b - P = 0.001
Cdyn (mL/cmH2O) 8 [7,9] 9 [6,10] 7 [6,9] 7 [6,8] 6 [5,7]b 6 [5,7]b - P < 0.001
Resistance (cmH2O/L/s) 8 [8,10] 10 [9,12]b 9 [8,9]b 9 [8,9]b 8 [8,11]b 9 [8,13]b 17 [13,20]b,c P < 0.001
PEEP total (cmH2O) 14 [11,17] 14 [10,17] 14 [10,17] 13 [10,16] 13 [10,17] 13 [10,17] - P = 0.744
PEEP intrinsic (cmH2O) 0 0 0 0 [0,1] 0 [0,1] 2 [1,3]b - P < 0.001
PEEP extrinsic (cmH2O) 14 [11,16] 14 [11,16] 13 [10,17] 13 [10,16] 13 [10,16] 12 [9,14] - P < 0.001
Peak pressure (cmH2O) 45 [44,48] 54 [47,58]b 44 [42,47] 44 [41,45] 41 [38,44] 41 [38,43] 59 [51,79]b,c P < 0.001
Pmean (cmH2O) 17 [15,20] 18 [16,22]b 18 [15,22]b 20 [18,23]b 20 [18,24]b 20 [17,23]b 29 [28,30]b,c P < 0.001
Inspiratory flow (L/s) 1 1 1 1 1 1 - P = 1.000
Tinsp/Ttot (%) 15 [14,17] 19 [14,22] 24 [20,28]b 34 [30,37]b 38 [33,44]b 42 [37,49]b 56 [50,67]b,c P < 0.001
  1. Values are presented as median [P25th,P75th]. aThe p value was obtained through Friedman’s test; bStudent-Newman-Keuls’ post hoc analysis, p < 0.05 vs VT = stabilization step (VT = 6 mL/kg and RR = 35 breaths/min); cStudent-Newman-Keuls’ post hoc analysis, p < 0.05 vs HFPPV = 150.