Estimation of regional lung volume changes by electrical impedance pressures tomography during a pressure-volume maneuver
To assess the degree of linearity between lung volume and impedance change by electrical impedance tomography (EIT) in pigs with acute lung injury and to investigate regional impedance changes during a pressure-volume maneuver.
Design and setting
Experimental animal study in a university research laboratory.
Patients and participants
Nine pigs with lung injury induced by lung lavage.
The lungs were insufflated to four different lung volumes. Next the lungs were inflated in steps up to 40 cmH2O and then in steps deflated.
Measurements and results
EIT measurements were performed. Impedance was highly linear with lung volume ( r 2=0.97). From the pressure-volume maneuver regional pressure-impedance (P-I) curves were obtained in the upper half (ventral) and lower half (dorsal) of the thoracic cross-section. Excellent fit was found of the regional P-I curves with a predefined sigmoid equation ( r 2=0.998). The P-I curves after lavage were markedly different than before lavage. The P-I curves recorded after lavage displayed a strong heterogeneity on the inflation limb: Lower corner pressure (traditionally lower inflection point) was significantly higher in the dorsal (28.3±4.1 cmH2O) than in the ventral region (17.5±4.3 cmH2O). The deflation limb displayed a more homogeneous pattern. Upper corner pressure and true inflection point, where the curve slope is maximal, in the dorsal region were only slightly higher than in the ventral region (1–2 cmH2O).
EIT and automated curve fitting provide information on regional lung inflation and deflation which may be of clinical use for optimizing ventilator settings.
KeywordsAcute lung injury Lung volume Lung compliance Electrical impedance Tomography
We are grateful to Arnold Drop and Els Duval for their assistance during the experiments. We thank Theo Faes and Rob Heethaar for their comments on the interpretation of EIT and Dick Markhorst for general discussion. The help of Tom Leenhoven in the setup of the experiments is greatly appreciated.
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