Lung stress and strain during mechanical ventilation in animals with and without pulmonary acute respiratory distress syndrome.
BACKGROUND
Mechanical ventilation is a life-saving therapy for acute respiratory distress syndrome (ARDS). However, unphysiological lung stress (transpulmonary pressure) and strain (the ratio between inflated volume and functional residual capacity) can induce lung injury. Unfortunately, both stress and strain are not measured directly because of technical limitations but predicted from airway plateau pressure (Pplat) and tidal volume (Vt). Recently, some literatures indicated that Pplat and Vt cannot be good surrogates without distinguishing pulmonary ARDS patients (ARDSp) from extrapulmonary ARDS patients. Analyzing them together might distort the truth. Thus, we established animal models of ARDSp to explore whether lung stress and strain can be surrogated precisely by Pplat and Vt.


METHODS
Fifteen Beagle dogs were recruited to establish ARDSp models by injection of oleic acids. Esophageal manometry was performed to estimate pleural pressure and lung stress. Functional residual capacity was obtained through computed tomography. In the first stage, Vt was set at 10mL/kg body weight in healthy and injured lungs and then adjusted to achieve lung strain as 1.0, 1.5, and 2.0 in sequence.


RESULTS
There was a good linear relationship between lung stress and Pplat in healthy and ARDS lungs (P<0.001). For a given Vt (10mL/kg body weight), the global lung strains varied from 0.197 to 0.416 and 0.467 to 0.715 in healthy individuals and different ARDS patients, respectively. On the contrary, Vt varied remarkably for a given lung strain.


CONCLUSIONS
Pplat is an adequate surrogate for lung stress, but Vt cannot represent lung strain sufficiently.
Respiratory Mechanics Lab, State Key Laboratory of Respiratory Disease, Guangzhou Institute of Respiratory Disease, First Affiliated Hospital of Guangzhou Medical College, Guangzhou, China.
Qi
Q
Liu
Wen
W
Li
Qing-Si
QS
Zeng
Nan-Shan
NS
Zhong
Rong-Chang
RC
Chen
D000818:Animals; D045422:Continuous Positive Airway Pressure / Q000009:adverse effects*; D004195:Disease Models, Animal; D004285:Dogs; D005652:Functional Residual Capacity; D016014:Linear Models; D008168:Lung / Q000000981:diagnostic imaging / Q000503:physiopathology*; D008297:Male; D008365:Manometry; D019301:Oleic Acid; D012128:Respiratory Distress Syndrome / Q000139:chemically induced / Q000503:physiopathology / Q000628:therapy*; D013990:Tidal Volume; D014057:Tomography, X-Ray Computed
D019301:Oleic Acid