[Study of the effects of mechanical ventilation on the heart function of patients with echocardiography]

To study the effects of different positive end expiratory pressure (PEEP) levels on the heart function of patients undergoing mechanical ventilation (MV) with echocardiography.

Thirty six critical patients with respiratory failure undergoing MV were divided into two groups according to the cardiac index (CI). The left heart function was measured with echocardiography at different PEEP levels (0, 4, 7, 10, 14 cm H(2)O, 1 cm H(2)O=0.098 kPa).

In the normal cardiac function group (CI≥2.0 L×min(-1) ×m(-2) , n=17), an increase in PEEP had no significant effects on left ventricular systolic function [left ventricular end systolic volume (LVESV), left ventricular end diastolic volume (LVEDV), cardiac output (CO), ejection fraction (EF)]. The increase in PEEP had no significant effect on left ventricular diastolic function [mitral early diastolic filling velocity (E), late diastolic filling velocity (A), the ratio of E/A, early diastolic velocity (Ve), late diastolic velocity (Va), the ratio of Ve/Va, left ventricular end diastolic pressure (LVEDP)]. In the poor cardiac function group (CIP<2.0 L×min(-1) ×m(-2), n=19), when PEEP was increased to 10 cm H(2)O and 14 cm H(2)O, compared with PEEP 0, left ventricular systolic function indexes including LVESV (ml: 21.2±1.2 vs. 18.2±1.4 as 10 cm H(2)O) was significantly higher, i.e. LVEDV (ml: 42.6±2.4, 40.1±1.9 vs. 44.5±3.5), CO (L: 2.3±0.6, 2.1±0.7 vs. 2.6±0.7), EF (0.40±0.02, 0.39±0.02 vs. 0.42±0.02) were decreased (all P<0.05); left ventricular diastolic function indexes including A (cm/s: 88.5±15.2, 93.2±18.7 vs. 76.0±9.0), Va (cm/s: 14.3±4.5, 15.8±5.3 vs. 12.0±1.2), LVEDP [mm Hg (1 mm Hg=0.133 kPa): 15.3±2.0, 16.9±2.8 vs. 10.7±2.5] were significantly higher; E (cm/s: 73.6±15.4, 63.2±16.4 vs. 83.1±20.1), the ratio of E/A (0.83±0.10, 0.68±0.20 vs. 1.10±0.20), Ve (cm/s: 11.7±1.8, 10.4±2.0 vs. 13.8±2.8), the ratio of Ve/Va (0.8±0.1 , 0.6±0.2 vs. 1.2±0.2) were decreased (all P<0.05).

Under the same condition of MV, change in PEEP levels (0-14 cm H(2)O) do not produce any obvious effect in the normal cardiac function group, on the other hand when PEEP≥10 cm H(2)O left heart function is significantly lowered in the poor cardiac function group. Optimal PEEP may improve the cardiac function.