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[Effects of mechanical ventilation with different tidal volumes on right ventricular hemodynamics in acute respiratory distress syndrome rats].

OBJECTIVE
To explore the effect of different tidal volumes (VT) on the hemodynamics of right heart in acute respiratory distress syndrome (ARDS) rats induced by oleic acid (OA).


METHODS
Sixty adult male Sprague-Dawley (SD) rats were divided into control group (n = 20), ARDS model group (n = 20), low VT (LVT) group (n = 10) and high VT (HVT) group (n = 10) by random number table. ARDS model was reproduced by injecting OA 0.15 mL/kg through a jugular vein. The control group was given the same amount of normal saline. The success of modeling was judged by the oxygenation index (PaO2/FiO2) 2 hours after modeling, at the same time, the lung tissues were collected, the wet/dry weight (W/D) ratio was determined, and the lung histopathological changes were measured by lung injury score. The rats in the LVT group and HVT group were given mechanical ventilation with VT of 6 mL/kg or 20 mL/kg for 4 hours, respectively at 2 hours after modeling. The rats in the control group and the ARDS model group maintained spontaneous breathing. After mechanical ventilation for 4 hours, the heart rate (HR), right ventricular systolic pressure (RVSP), the maximum rate of rising of right ventricular pressure (dp/dt max), and the blood pressure (BP) were measured. Meanwhile, arterial blood samples were collected for blood gas analysis, including pH value, arterial partial pressure of oxygen (PaO2), arterial partial pressure of carbon dioxide (PaCO2) and PaO2/FiO2.


RESULTS
The rats in the ARDS model group showed symptoms of respiratory distress 1 hour after modeling, and the lung tissue samples showed obvious patchy bleeding 2 hours after modeling, while the control group showed no such changes. The PaO2/FiO2 in the ARDS model group was significantly lower than that in the control group [mmHg (1 mmHg = 0.133 kPa): 294.3±5.9 vs. 459.0±4.4, P < 0.01], and the lung W/D ratio and lung injury score were significantly higher (lung W/D ratio: 8.24±0.25 vs. 4.48±0.13, lung injury score: 0.60±0.03 vs. 0.12±0.02, both P < 0.01). It indicated that ARDS model was successfully reproduced. The arterial blood gas analysis and hemodynamic parameters of the ARDS model group were significantly worse than those of the control group. After 4-hour mechanical ventilation, the blood gas parameters of the LVT group were better than those of the ARDS model group and the HVT group [pH value: 7.36±0.02 vs. 7.24±0.02, 7.13±0.01; PaO2 (mmHg): 92.4±2.1 vs. 61.8±2.3, 76.6±2.2; PaCO2 (mmHg): 49.6±1.7 vs. 61.8±1.8, 33.6±1.3; PaO2/FiO2 (mmHg): 440.0±10.2 vs. 274.3±21.4, 364.7±10.5; all P < 0.05]. HR, BP and dp/dt max in the LVT group were significantly higher than those in the ARDS model group and the HVT group [HR (bpm): 346.9±5.4 vs. 302.3±10.1, 265.5±12.2; BP (mmHg): 125.4±2.2 vs. 110.0±2.5, 89.2±2.8; dp/dt max (mmHg/s): 1 393.3±30.3 vs. 1 236.4±20.5, 896.1±19.5; all P < 0.05], and RVSP was significantly lower than that in the ARDS model group and the HVT group (mmHg: 31.3±0.4 vs. 34.0±1.0, 38.8±0.9, both P < 0.05).


CONCLUSIONS
Mechanical ventilation with low VT can improve the hemodynamic parameters of the right ventricle and protect the function of the right heart in ARDS rats.