Objective To investigate the effects of mechanical ventilation( MV) via different tidal volume ( VT) in combination with positive end expiratory pressure( PEEP) on dogs with acute lung injury( ALI) . Methods Dog model of oleic acid-induced ALI was established. And after that animals were randomized into different MV groups ( included low VT group, VT =6 mL/kg; and high VT group, VT =20 mL/kg) and ventilated for 6 h with a PEEP of 10 cmH2O. Arterial blood gas wasmeasured before, during and after ALI model was established ( at 1 h,2 h, 4 h and 6 h during MV) . The albumin concentration in BALF and pathological change of the lung tissue were evaluated in order to determine the lung injury while animals were sacrificed after 6 h MV. Results ALI model was successfully established ( 2. 50 ±0. 80) hours after oleic acid injection. Arterial pH decreased much severer in the low VT group than the high VT group( P lt;0. 01) . PaO2 and SaO2 in ventilation groups decreased after modeling but increased after MV, and PaO2 and SaO2 were significantly higher in the low VT group than the high VT group after 6 h MV( P lt;0. 05) . PaCO2 fluctuated less in the high VT group, while it increased significantly in the low VT group after MV( P lt; 0. 01) . Oxygenation index( PaO2 /FiO2 ) was lowered after modeling( P lt; 0. 01) , decreased to about 190 mm Hg after 1 h MV. And PaO2 /FiO2 in low VT group was significantly higher than the high VT group after 6 h MV( P lt; 0. 05) . BALF albumin concentration and the lung injury score in the low VT group were both significantly lower than the high VT group( both P lt; 0. 05) . Conclusions Ventilation with PEEP could improve the oxygenation of ALI dogs, and low VT ventilation improves the oxygenation better than high VT. Otherwise, low VT could induce hypercapnia and ameliorate lung injury caused by high VT MV.
Objective To evaluate the influence of tidal volume on the accuracy of stroke volume variation ( SVV) to predict volume state of pigs with ventilation.Methods Thirty-six healthy pigs were anesthetized after tracheal intubation and ventilated. With the envelope method, they were randomized into a normovolemia group, a hemaerrhagic shock group, and a hypervolemia group, with 12 pigs in each group. The pigs in the hemaerrhagic shock group were removed 20 percent of blood, and the pigs in the hypervolemia group received additional infusion of 20 percent 6% hydroxyethyl starch. In each group, ventilator settings were changed in a randomized order by changing VT [ VT = 5 mL/kg ( VT5 ) , VT =10 mL/kg ( VT10 ) , and VT =15 mL/kg ( VT15 ) ] . Hemodynamic measurements [ heart rate ( HR) , mean arterial boold pressure ( MAP) , systemic vascular resistance index ( SVRI) , cardiac index ( CI) , stroke volume index ( SVI) , intrathoracic blood volume index( ITBVI) , and SVV] were obtained after 10 minutes of stabilization. Results SVV was increased in the hemaerrhagic shock group comparing with the normovolemia group for VT10 [ ( 21 ±5) % vs. ( 11 ±2) % , P lt;0. 05] , but SVV was decreased in the hypervolemia group comparing with the normovolemia group [ ( 7 ±2) % vs. ( 11 ±2) % , P lt; 0. 05] . The variation tendency for VT15 was the same with VT10 , moreover SVV were all above 12% for the hemaerrhagic shock group, the normovolemia group, and the hypervolemia group [ ( 30 ±7) % , ( 19 ±3) % , and ( 15 ±4) % ] . There were no significant diffrences among the hemaerrhagic shock group, hypervolemia group and normovolemia group [ ( 8 ±6) % ,( 7 ±5) % , and ( 7 ±4) % , P gt; 0. 05] for VT5 . Conclusions SVV was a precise indicator of cardiac preload, but SVV was less sensitive to the changes of volume during low tidal volume ( 5 mL/kg) ventilation. The threshold of SVV for predicting fluid responsiveness maybe above 12% with a high tidal volume ( 15 mL/kg) ventilation.
ObjectiveTo explore the effects of volume mechanical ventilation with different tidal on the diaphragm discharge in rats. MethodsTwenty-four SD rats were randomly divided into three groups, namely a high tidal volume group, a low tidal volume group, and a control group. The rats in the high tidal volume group and the low tidal volume group underwent volume controlled ventilation with tidal volume of 10 mL/kg and 5 mL/kg, respectively. The rats in the control group breath spontaneously after anesthetization. The EMGdi frequency, diaphragm discharge area, product of diaphragm discharge amplitude and diaphragm discharge rate (A×R) were measured every 2 hours to analyze the characteristics of diaphragm of rats under different duration of ventilation. ResultsCompared with the control group, there was no statistical difference of A×R in the high tidal volume group, but the frequency of the diaphragm discharge reduced and the discharge diaphragm area increased. When compared the low tidal volume group with the control group, only the A×R increased significantly. The transcutaneous oxygen saturation (SpO2) and end-tidal CO2 pressure (PetCO2) in the high tidal volume group decreased significantly compared to the control group while the other indexes had no difference. ConclusionsThe effects of mechanical ventilation with different tidal volume on the rat diaphragm discharge are different. The low tidal volume mechanical ventilation can excite the respiratory center and strengthen the diaphragm discharge with the stabilization of physiological index while the high tide volume inhibits diaphragm function and damages the oxygenation.
Objective To investigate the curve correlation between ventilation pressure and tidal volume in assisted mechanical ventilation with facemask during anesthesia induction. Methods Between January and August 2015, 120 patients, American Society of Anesthesiology Ⅰ-Ⅱ, undergoing selective gynecological surgery were randomly divided into four groups: groups P5, P10, P15 and P20, with 30 patients in each group. Mask ventilation pressure for the four groups were respectively 5, 10, 15 and 20 cm H2O (1 cm H2O=0.098 kPa). Patients were ventilated by preset ventilation pressure and frequency based on different groups after loss of consciousness. Mean ventilation volume (mean value of three tidal volumes) and end-tidal carbon dioxide pressure (PetCO2) were recorded for analysis. Results There was no significant difference among the four groups in patient’s general condition (P>0.05). The tidal volume of assisted mechanical ventilation increased with ventilation pressure degrees, and the differences among the four groups were significant (P<0.05). After curve regression analysis, tidal volume and ventilation pressure showed a positive linear correlation when ventilation pressure was set at 5-20 cm H2O, and the correlation equation was: tidal volume = 33.612×ventilation pressure-53.155. PetCO2 in P5 group was lower than those in the other three groups (P<0.05), while there were no significant differences among groups P10, P15 and P20 (P>0.05). Conclusion When ventilation pressure is set at 5-20 cm H2O in assisted mechanical ventilation with facemask during anesthesia induction, tidal volume and ventilation pressure show a positive linear correlation.
This paper investigates the variation of lung tissue dielectric properties with tidal volume under in vivo conditions to provide reliable and valid a priori information for techniques such as microwave imaging. In this study, the dielectric properties of the lung tissue of 30 rabbits were measured in vivo using the open-end coaxial probe method in the frequency band of 100 MHz to 1 GHz, and 6 different sets of tidal volumes (30, 40, 50, 60, 70, 80 mL) were set up to study the trends of the dielectric properties, and the data at 2 specific frequency points (433 and 915 MHz) were analyzed statistically. It was found that the dielectric coefficient and conductivity of lung tissue tended to decrease with increasing tidal volume in the frequency range of 100 MHz to 1 GHz, and the differences in the dielectric properties of lung tissue for the 6 groups of tidal volumes at 2 specific frequency points were statistically significant. This paper showed that the dielectric properties of lung tissue tend to vary non-linearly with increasing tidal volume. Based on this, more accurate biological tissue parameters can be provided for bioelectromagnetic imaging techniques such as microwave imaging, which could provide a scientific basis and experimental data support for the improvement of diagnostic methods and equipment for lung diseases.