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Representative Results






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

Published: January 8th, 2019



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

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.

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.

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....

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This protocol has been previously approved by and follows the guidelines set by the University of Iowa Institutional Review Board. Data shown were collected as part of a project approved by the Institutional Review Board at the University of Iowa. Participants gave informed consent and the studies were performed in accordance with the Declaration of Helsinki.

1. Equipment

  1. Check the equipment table to verify that all required equipment is available. Double check the configuration us.......

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Representative plethysmography results are given in Figure 4. This participant required four attempts in order to collect three FRC values with <5% variability from the mean.%Ref reflects the percent of the predicted value for each variable based on population regression equations that take into account sex, age, race, height and weight

Figure 1 (top) shows a repres.......

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Here, a protocol for the measurement of VD and airways homogeneity (slope) is provided. These measurements can be made at FRC, or as a function of lung volume. Measuring FRC before the start of the experiment and after a perturbation allows VD and slope to be plotted as a function of lung volume and may provide useful information about the structure-function relationship of the lung that is not obtained from capnography at FRC alone.

Airways volume and high-resolution str.......

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This work was funded by the Departments of Health and Human Physiology and Internal Medicine at the University of Iowa. This work was also supported by the Old Gold Fellowship (Bates) and Grant IRG-15-176-40 from the American Cancer Society, administered through The Holden Comprehensive Cancer Center at The University of Iowa (Bates)


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Name Company Catalog Number Comments
Computer with dual monitor Dell Instruments
PowerLab 8/35* AD Instruments PL3508
LabChart Data Acquisition Software* AD Instruments Version 8
Gemini Respiratory Gas Analyzer* (upgraded option) CWE, Inc GEMINI 14-10000 *indicates that part is available in the Exercise Physiology package from AD Instruments
Heated Pneumotach with Heater Controller* (upgraded option) Hans Rudolph, Inc MLT3813H-V
3L Calibration Syringe Vitalograph 36020
Nose Clip* VacuMed Snuffer 1008
Pulse Transducer* AD Instruments TN1012/ST
Barometer Fischer Scientific 15-078-198
Flanged Mouthpiece* AD Instruments MLA1026
Nafion drying tube with three-way stopcock* AD Instruments MLA0343
Desiccant cartridge (optional for humid environments)* AD Instruments MLA6024
Resistor Hans Rudolph, Inc 7100 R5
Flow head adapters* AD Instruments MLA1081
Modified Tubing Adapter (optional) AD Instruments SP0145
Two way non-rebreather valve (optional)* AD Instruments SP0146
Plethysmograph Vyaire V62J
High Purity Helium Gas Praxair He 4.8
6% CO2 and 16% O2 Calibration Gas Praxair Custom
Microsoft Excel Microsoft Office 365

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