Use of esophageal balloon pressure-volume curve analysis to determine esophageal wall elastance and calibrate raw esophageal pressure: a bench experiment and clinical study

Abstract

Background: Accurate measurement of esophageal pressure (Pes) depends on proper filling of the balloon. Esophageal wall elastance (Ees) may also influence the measurement. We examined the estimation of balloon-surrounding elastance in a bench model and investigated a simplified calibrating procedure of Pes in a balloon with relatively small volume.

Methods: The Cooper balloon catheter (geometric volume of 2.8 ml) was used in the present study. The balloon was progressively inflated in different gas-tight glass chambers with different inner volumes. Chamber elastance was measured by the fitting of chamber pressure and balloon volume. Balloon pressure-volume (P-V) curves were obtained, and the slope of the intermediate linear section was defined as the estimated chamber elastance. Balloon volume tests were also performed in 40 patients under controlled ventilation. The slope of the intermediate linear section on the end-expiratory esophageal P-V curve was calculated as the Ees. The balloon volume with the largest Pes tidal swing was defined as the best volume. Pressure generated by the esophageal wall during balloon inflation (Pew) was estimated as the product of Ees and best volume. Because the clinical intermediate linear section enclosed filling volume of 0.6 to 1.4 ml in each of the patient, we simplified the estimation of Ees by only using parameters at these two filling volumes.

Results: In the bench experiment, bias (lower and upper limits of agreement) was 0.5 (0.2 to 0.8) cmH2O/ml between the estimated and measured chamber elastance. The intermediate linear section on the clinical and bench P-V curves resembled each other. Median (interquartile range) Ees was 3.3 (2.5-4.1) cmH2O/ml. Clinical best volume was 1.0 (0.8-1.2) ml and ranged from 0.6 to 1.4 ml. Estimated Pew at the best volume was 2.8 (2.5-3.5) cmH2O with a maximum value of 5.2 cmH2O. Compared with the conventional method, bias (lower and upper limits of agreement) of Ees estimated by the simple method was - 0.1 (- 0.7 to 0.6) cmH2O/ml.

Conclusions: The slope of the intermediate linear section on the balloon P-V curve correlated with the balloon-surrounding elastance. The estimation of Ees and calibration of Pes were feasible for a small-volume-balloon.

Trial registration: Identifier NCT02976844 . Retrospectively registered on 29 November 2016.

Keywords: Bench experiment; Calibration; Esophageal balloon catheter; Esophageal elastance; Esophageal pressure.

Conflict of interest statement

Ethics approval and consent to participate

The study protocol was approved by the institutional review board of Beijing Tiantan Hospital, Capital Medical University (KY-2016-11-22). Written informed consent was obtained from the patient or appropriate substitute decision makers.

Consent for publication

Not applicable

Competing interests

The authors declare that they have no competing interests.

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Figures

Fig. 1

The bench model and experimental protocol. Panel (a) Each glass chamber had two openings: one for introducing the balloon into the chamber and the other one for adjusting and measuring the chamber pressure. Panel (b) Balloon volume tests were performed in five chambers with respective inner volume of 1000, 500, 250, 175 and 125 ml. In each chamber, baseline pressure was adjusted to 5, 10, 15, 20, 25 and 30 cmH2O. Before each balloon volume test, connections in the chamber system were sealed by silicone sealant, and systematic leaks were checked

Fig. 2

Examples of balloon pressure-volume curves. Panel (a) Balloon pressure (circles) and chamber pressure (dots) were plotted against balloon volume in the bench experiment. The balloon volume with transmural pressure (the difference between the balloon pressure and the chamber pressure) within ±1.0 cmH2O was defined as the minimal and maximal balloon volumes (VMIN and VMAX). The balloon volume with the closest to zero transmural pressure was defined as the best filling volume (VBEST). Least square fitting line between the chamber pressure and balloon volume (black line) and between the balloon pressure and balloon volume within VMIN to VMAX (red dash line) are also shown. Panel (b) Esophageal balloon pressure at end-expiratory (circles) and end-inspiratory occlusion (squares) were plotted against balloon volume in the clinical study. The lower and upper limits of an intermediate linear section on expiratory balloon pressure-volume curve were visually inspected, and were defined as the clinical VMIN and VMAX. The clinical VBEST was defined as the balloon volume with the largest difference between end-expiratory and end-inspiratory esophageal balloon pressure. Least square fitting line between the end-expiratory balloon pressure and balloon volume within clinical VMIN to VMAX (red dash line) is also shown

Fig. 3

Bland-Altman’s limits of agreements analysis for estimated chamber elastance (panel a) and baseline chamber pressure (panel b). Horizontal axis represents the average of the estimated and measured values, and vertical axis represents the difference of estimated and measured values. Bias (solid line) and upper and lower limits of agreements (dash lines) are also shown