Combining Volumetric Capnography And Barometric Plethysmography To Measure The Lung Structure-function Relationship

McKayla Seymour; Elizabeth Pritchard; Hassan Sajjad; Erik P. Tomasson; Cole M. Blodgett; Harold Winnike; Oana V. Paun; Michael Eberlein; Melissa L. Bates

doi:10.3791/58238

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Method Article

Combining Volumetric Capnography And Barometric Plethysmography To Measure The Lung Structure-function Relationship

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DOI:

10.3791/58238

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January 8th, 2019

McKayla Seymour¹ , Elizabeth Pritchard¹ , Hassan Sajjad² , Erik P. Tomasson² , Cole M. Blodgett¹ , Harold Winnike⁴ , Oana V. Paun³ , Michael Eberlein² , Melissa L. Bates¹^,⁴

¹Department of Health and Human Physiology, Department of Internal Medicine, University of Iowa, ²Pulmonary, Critical Care and Occupational Medicine Division, University of Iowa, ³Hematology, Oncology and Bone Marrow Transplant Division, University of Iowa, ⁴Institute for Clinical and Translational Science and Stead Family Department of Pediatrics, University of Iowa

Summary

Here, we describe two measures of pulmonary function – barometric plethysmography, which allows the measurement of lung volume, and volumetric capnography, a tool to measure the anatomic dead space and airways uniformity. These techniques may be used independently or combined to assess airways function at different lung volumes.

Abstract

Tools to measure lung and airways volume are critical for pulmonary researchers interested in evaluating the impact of disease or novel therapies on the lung. Barometric plethysmography is a classic technique to evaluate the lung volume with a long history of clinical use. Volumetric capnography utilizes the profile of exhaled carbon dioxide to determine the volume of the conducting airways, or dead space, and provides an index of airways homogeneity. These techniques may be used independently, or in combination to evaluate the dependence of airways volume and homogeneity on lung volume. This paper provides detailed technical instructions to replicate these techniques and our representative data demonstrates that the airways volume and homogeneity are highly correlated to lung volume. We also provide a macro for the analysis of capnographic data, which can be modified or adapted to fit different experimental designs. The advantage of these measures is that their advantages and limitations are supported by decades of experimental data, and they can be made repeatedly in the same subject without expensive imaging equipment or technically advanced analysis algorithms. These methods may be particularly useful for investigators interested in perturbations that change both the functional residual capacity of the lung and airways volume.

Introduction

Gas washout techniques have been used for decades to provide important information about the structure and uniformity of the airway tree. The lung is classically described as having two compartments – a conducting zone that is comprised of the anatomic dead space and the respiratory zone where gas exchange occurs in the alveoli. The conducting airways are termed as “dead space” because they do not participate in the exchange of oxygen and carbon dioxide. In the single breath gas washout method, the concentration profile of an exhaled gas can be used to determine the volume of the anatomic dead space and to derive information about the uniformity of v....