Functional respiratory imaging, regional strain, and expiratory time constants at three levels of positive end expiratory pressure in an ex vivo pig model

Abstract

Heterogeneity in regional end expiratory lung volume (EELV) may lead to variations in regional strain (ε). High ε levels have been associated with ventilator-associated lung injury (VALI). While both whole lung and regional EELV may be affected by changes in positive end-expiratory pressure (PEEP), regional variations are not revealed by conventional respiratory system measurements. Differential rates of deflation of adjacent lung units due to regional variation in expiratory time constants (τE) may create localized regions of ε that are significantly greater than implied by whole lung measures. We used functional respiratory imaging (FRI) in an ex vivo porcine lung model to: (i) demonstrate that computed tomography (CT)-based imaging studies can be used to assess global and regional values of ε and τE and, (ii) demonstrate that the manipulation of PEEP will cause measurable changes in total and regional ε and τE values. Our study provides three insights into lung mechanics. First, image-based measurements reveal egional variation that cannot be detected by traditional methods such as spirometry. Second, the manipulation of PEEP causes global and regional changes in R, E, ε and τE values. Finally, regional ε and τE were correlated in several lobes, suggesting the possibility that regional τE could be used as a surrogate marker for regional ε.

Keywords: Positive end‐expiratory pressure; strain; time constant.

© 2016 The Authors. Physiological Reports published by Wiley Periodicals, Inc. on behalf of The Physiological Society and the American Physiological Society.

Figures

Figure 1

Pictoral representation of lung lobes and airways using composite 3D airway images at three positive end expiratory pressures. PEEP 0/5/10, positive end expiratory pressure of 0/5/10 cm H2O. Red, right anterior lobe; Yellow, right caudal lobe; Orange, right diaphragmatic lobe; Green, right internal lobe; Purple, left diaphragmatic lobe; Light blue, left caudal lobe; Dark blue, left anterior lobe.

Figure 2

The effect of positive end expiratory pressure (PEEP) in expiratory resistance as calculated by functional respiratory imaging (FRI). The extremes of the box represent the quartiles and the black line represents the median. The whiskers extend to the most extreme data point which is no more than 1.5 times the interquartile range from the box. Open circles represent data points outside of this range.

Figure 3

The effect of lobe on expiratory resistance as calculated by functional respiratory imaging (FRI). RAL, right anterior lobe; RCL, right caudal lobe; RDL, right diaphragmatic lobe; RIL, right internal lobe; LDL, left diaphragmatic lobe; LCL, left caudal lobe; LAL, left anterior lobe. The extremes of the box represent the quartiles and the black line represents the median. The whiskers extend to the most extreme data point which is no more than 1.5 times the interquartile range from the box. Open circles represent data points outside of this range.

Figure 4

The effect of positive end expiratory pressure (PEEP) in lung elastance as calculated by functional respiratory imaging (FRI). The extremes of the box represent the quartiles and the black line represents the median. The whiskers extend to the most extreme data point which is no more than 1.5 times the interquartile range from the box. Open circles represent data points outside of this range.

Figure 5

The effect of lobe in lung elastance as calculated by functional respiratory imaging (FRI). RAL, right anterior lobe; RCL, right caudal lobe; RDL, right diaphragmatic lobe; RIL, right internal lobe; LDL, left diaphragmatic lobe; LCL, left caudal lobe; LAL, left anterior lobe. The extremes of the box represent the quartiles and the black line represents the median. The whiskers extend to the most extreme data point which is no more than 1.5 times the interquartile range from the box. Open circles represent data points outside of this range.

Figure 6

The effect of positive end expiratory pressure (PEEP) on strain as calculated by functional respiratory imaging (FRI). The extremes of the box represent the quartiles and the black line represents the median. The whiskers extend to the most extreme data point which is no more than 1.5 times the interquartile range from the box. Open circles represent data points outside of this range.

Figure 7

The effect of lobe on strain as calculated by functional respiratory imaging (FRI). RAL, right anterior lobe; RCL, right caudal lobe; RDL, right diaphragmatic lobe; RIL, right internal lobe; LDL, left diaphragmatic lobe; LCL, left caudal lobe; LAL, left anterior lobe. The extremes of the box represent the quartiles and the black line represents the median. The whiskers extend to the most extreme data point which is no more than 1.5 times the interquartile range from the box. Open circles represent data points outside of this range.

Figure 8

The effect of positive end expiratory pressure (PEEP) on the expiratory time constant as calculated by functional respiratory imaging (FRI). The extremes of the box represent the quartiles and the black line represents the median. The whiskers extend to the most extreme data point which is no more than 1.5 times the interquartile range from the box. Open circles represent data points outside of this range.

Figure 9

The effect of lobe on the expiratory time constant as calculated by functional respiratory imaging (FRI). RAL, right anterior lobe; RCL, right caudal lobe; RDL, right diaphragmatic lobe; RIL, right internal lobe; LDL, left diaphragmatic lobe; LCL, left caudal lobe; LAL, left anterior lobe. The extremes of the box represent the quartiles and the black line represents the median. The whiskers extend to the most extreme data point which is no more than 1.5 times the interquartile range from the box. Open circles represent data points outside of this range.