Table 1 Effects of expiratory ventilation assistance on physiologic parameters in normovolemia. The end-expiratory pressures for each ventilator condition are shown in the top row. Variables are compared with the values measured at baseline on conventional positive pressure ventilation with 4 cmH20 positive end-expiratory pressure. 1a shows hemodynamic variables and 1b shows gas exchange variables
Variable | Baseline conventional ventilation + 4 cmH20 | Expiratory ventilation assistance | Conventional ventilation + 4cmH20 | |||
|---|---|---|---|---|---|---|
+ 4 cmH20 | 0 cmH20 | − 4 cmH20 | − 8 cmH20 | |||
1a | ||||||
Stroke volume (ml) | 53.8 (7.7) | 58.0 (13.2) | 64.6* (10.7) | 67.0* (11.7) | 68.1* (10.5) | 62.3* (12.8) |
Cardiac output (L/min) | 3.53 (0.46) | 3.58 (0.61) | 3.86 (0.37) | 4.01 (0.30) | 4.26* (0.27) | 3.54 (0.16) |
Left venytricular end-diastolic volume (ml) | 87.6 (17.6) | 90.0 (17.2) | 102.3 (10.8) | 102.2 (11.6) | 103.8 (10.9) | 92.3 (12.9) |
Central venous pressure (mmHg) | 6.0 (2.0) | 5.7 (1.6) | 5.3* (1.9) | 5.0* (2.0) | 4.2* (2.5) | 4.4 (2.7) |
Mean systemic arterial pressure (mmHg) | 110 (10.6) | 105 (9.0) | 104 (9.1) | 105 (10.5) | 106 (9.2) | 106 (15.5) |
Mean pulmonary artery pressure (mmHg) | 17.4 (2.5) | 17.7 (3.0) | 16.8 (2.5) | 16.4 (2.5) | 16.5 (2.3) | 15.5 (2.4) |
dP/dt (mmHg/s) | 1996 (183) | 1979 (173) | 1969 (169) | 1997 (159) | 2039 (160) | 1953 (217) |
Left ventricular ejection fraction (%) | 62.4 (9.0) | 64.7 (8.9) | 63.2 (8.0) | 65.8 (10.0) | 66.2 (11.8) | 69.7 (10.8) |
Heart rate (min−1) | 65.8 (5.6) | 62.7 (8.2) | 60.7 (8.6) | 61.0 (9.4) | 63.9 (11.3) | 58.8 (12.8) |
1b | ||||||
Minute ventilation (L/min) | 5.3 (0.3) | 5.3 (0.4) | 5.3 (0.2) | 5.5 (0.5) | 5.5 (0.4) | 5.2 (0.2) |
Peak inspiratory pressure (cmH20) | 19.5 (1.8) | 13.5* (2.6) | 10.5* (2.6) | 8.6* (3) | 7.0* (3.7) | 19 (2.9) |
pH | 7.48 (0.02) | 7.41 (0.04) | 7.42 (0.05) | 7.42 (0.05) | 7.43 (0.07) | 7.50 (0.06) |
PCO2 (mmHg) | 44.0 (5.1) | 53.4* (8.3) | 52.2* (11.0) | 51.2* (9.4) | 49.8 (12.2) | 43.4 (7.5) |
PO2/FiO2 | 487 (61) | 456 (53) | 466 (37) | 459 (69) | 431 (41) | 466 (203) |