Name: combining volumetric capnography and barometric plethysmography to measure the lung structure-function relationship
Uploaded: 2019-01-08T13:00:00
Description: Watch this Scientific Journal Video about Combining Volumetric Capnography And Barometric Plethysmography To Measure The Lung Structure-function Relationship at JoVE.com

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)

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
<ol>
	<li>Check the equipment table to verify that all required equipment is available. Double check the configuration us...

<ol>
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L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Pulmonary+function+responses+to+ozone+in+smokers+with+a+limited+smoking+history.">Pulmonary function responses to ozone in smokers with a limited smoking history.</a> Toxicology and Applied Pharmacology. 278 (1), 85-90 (2014).</li><li>Bates, M. L., Brenza, T. M., Ben-Jebria, A., Bascom, R., Ultman, J. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Longitudinal+distribution+of+ozone+absorption+in+the+lung:+comparison+of+cigarette+smokers+and+nonsmokers.">Longitudinal distribution of ozone absorption in the lung: comparison of cigarette smokers and nonsmokers.</a> Toxicology and Applied Pharmacology. 236 (3), 270-275 (2009).</li><li>Reeser, W. 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The Respiratory Dead Space.</a> American Journal of Physiology-Legacy Content. 154 (3), 405-416 (1948).</li><li>Eberlein, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Supranormal+Expiratory+Airflow+after+Bilateral+Lung+Transplantation+Is+Associated+with+Improved+Survival.">Supranormal Expiratory Airflow after Bilateral Lung Transplantation Is Associated with Improved Survival.</a> American Journal of Respiratory and Critical Care Medicine. 183 (1), 79-87 (2011).</li><li>Eberlein, M., Schmidt, G. A., Brower, R. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chest+wall+strapping.+An+old+physiology+experiment+with+new+relevance+to+small+airways+diseases.">Chest wall strapping. An old physiology experiment with new relevance to small airways diseases.</a> Annals of the American Thoracic Society. 11 (8), 1258-1266 (2014).</li><li>Taher, H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chest+wall+strapping+increases+expiratory+airflow+and+detectable+airway+segments+in+computer+tomographic+scans+of+normal+and+obstructed+lungs.">Chest wall strapping increases expiratory airflow and detectable airway segments in computer tomographic scans of normal and obstructed lungs.</a> Journal of Applied Physiology. , (2017).</li><li>Verscheure, S., Massion, P. B., Verschuren, F., Damas, P., Magder, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Volumetric+capnography:+lessons+from+the+past+and+current+clinical+applications.">Volumetric capnography: lessons from the past and current clinical applications.</a> Critical Care. 20 (1), 184 (2016).</li><li>Suarez-Sipmann, F., Bohm, S. H., Tusman, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Volumetric+capnography:+the+time+has+come.">Volumetric capnography: the time has come.</a> Current Opinion in Critical Care. 20 (3), 333-339 (2014).</li><li>Wanger, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Standardisation+of+the+measurement+of+lung+volumes.">Standardisation of the measurement of lung volumes.</a> European Respiratory Journal. 26 (3), 511-522 (2005).</li><li>Culver, B. H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Recommendations+for+a+Standardized+Pulmonary+Function+Report.+An+Official+American+Thoracic+Society+Technical+Statement.">Recommendations for a Standardized Pulmonary Function Report. An Official American Thoracic Society Technical Statement.</a> American Journal of Respiratory and Critical Care Medicine. 196 (11), 1463-1472 (2017).</li><li>Goldman, H. I., Becklake, M. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Respiratory+function+tests;+normal+values+at+median+altitudes+and+the+prediction+of+normal+results.">Respiratory function tests; normal values at median altitudes and the prediction of normal results.</a> Am Rev Tuberc. 79 (4), 457-467 (1959).</li><li>Shim, S. S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Lumen+area+change+(Delta+Lumen)+between+inspiratory+and+expiratory+multidetector+computed+tomography+as+a+measure+of+severe+outcomes+in+asthmatic+patients.">Lumen area change (Delta Lumen) between inspiratory and expiratory multidetector computed tomography as a measure of severe outcomes in asthmatic patients.</a> J The Journal of Allergy and Clinical. , (2018).</li><li>Smith, B. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Human+airway+branch+variation+and+chronic+obstructive+pulmonary+disease.">Human airway branch variation and chronic obstructive pulmonary disease.</a> Proceedings of the National Academy of Sciences of the United States of America. 115 (5), E974-E981 (2018).</li><li>Farmery, A. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Volumetric+Capnography+and+Lung+Growth+in+Children+-+a+Simple-Model+Validated.">Volumetric Capnography and Lung Growth in Children - a Simple-Model Validated.</a> Anesthesiology. 83 (6), 1377-1379 (1995).</li><li>Scherer, P. W., Neufeld, G. R., Aukburg, S. J., Hess, G. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Measurement+of+Effective+Peripheral+Bronchial+Cross-Section+from+Single-Breath+Gas+Washout.">Measurement of Effective Peripheral Bronchial Cross-Section from Single-Breath Gas Washout.</a> Journal of Biomechanical Engineering-Transactions of the Asme. 105 (3), 290-293 (1983).</li><li>Sinha, P., Soni, N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Comparison+of+volumetric+capnography+and+mixed+expired+gas+methods+to+calculate+physiological+dead+space+in+mechanically+ventilated+ICU+patients.">Comparison of volumetric capnography and mixed expired gas methods to calculate physiological dead space in mechanically ventilated ICU patients.</a> Intensive Care Medicine. 38 (10), 1712-1717 (2012).</li><li>Bourgoin, P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Assessment+of+Bohr+and+Enghoff+Dead+Space+Equations+in+Mechanically+Ventilated+Children.">Assessment of Bohr and Enghoff Dead Space Equations in Mechanically Ventilated Children.</a> Respiratory Care. 62 (4), 468-474 (2017).</li></ol>

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...

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 &#8211; 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 &#8220;dead space&#8221; 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 ventilation. Some methods rely on the breathing of inert gases to make these measures (N2, argon, He, SF6, etc.). The use of inert gas is well-established, supported by scientific consensus statements1, and there are available commercial equipment with user friendly interfaces. However, the exhaled profile of carbon dioxide (CO2) can be used to derive similar information. Evaluating the profile of CO2 as a function of the exhaled volume, or volumetric capnography, does not require the participant to breathe special gas mixtures and allows the investigator to gather additional information flexibly about metabolism and gas exchange with minimal adjustment to the technique.
During a controlled exhalation, the concentration of CO2 can be plotted against the total exhaled volume. At the beginning of an exhalation, the dead space is filled with atmospheric gas. This is reflected in Phase I of the exhaled CO2 profile where there is an undetectable amount of CO2 (Figure 1, top). Phase II marks the transition to the alveolar gas, where gas exchange occurs and CO2 is abundant. The volume at the midpoint of Phase II is the volume of the anatomic dead space (VD). Phase III contains alveolar gas. Because airways with different diameters empty at different rates, the slope (S) of Phase III provides information about airways uniformity. A steeper slope of Phase III suggests a less uniform airway tree proximal to the terminal bronchioles, or convection-dependent inhomogeneity2. In the case where a perturbation may change the rate of CO2 production, and to make comparisons between individuals, the slope can be divided by the area under the curve to normalize for differences in metabolism (NS or normalized slope). Volumetric capnography has been used previously to evaluate the changes in airways volume and uniformity following air pollutant exposure3,4,5,6.
Gas transport in the lung is governed by both convection and diffusion. Single breath washout measures are highly dependent on air flow and the measured value of VD occurs at the convection-diffusion boundary. Changing the flow rate of the exhalation or preceding inhalation changes the location of that boundary7. Capnography is also highly dependent on the volume of the lung immediately preceding the maneuver. Larger lung volumes distend the airways, resulting in larger values of VD8. One solution is to consistently make the measurement at the same lung volume &#8211; usually functional residual capacity (FRC). An alternative, described here, is to couple volumetric capnography with barometric plethysmography, in order to obtain the relationship between VD and lung volume. The participant then performs the maneuver at constant flow rates, while varying the lung volume. This still allows for classic capnographic measures to be made at FRC, but also for the relationship between the lung volume and dead space volume and between the lung volume and homogeneity to be derived. Indeed, the added value of coupling capnography with plethysmography comes from the ability to test hypotheses about the distensibility of the airways tree and the structure-function relationship of the lung. This may be a valuable tool for investigators aiming to quantify the influence of airways mechanics versus lung compliance and elastance on pulmonary function in healthy and diseased populations9,10,11. Furthermore, accounting for the absolute lung volume at which the volumetric capnographic measurements are being performed allows investigators to characterize the effects of conditions that can alter the inflation state of the lung, such as obesity, lung transplant, or interventions like chest wall strapping. Volumetric capnography may ultimately have clinical utility in the intensive care setting12,13.

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

combining volumetric capnography and barometric plethysmography to measure the lung structure-function relationship

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.

Representative plethysmography results are given in Figure 4. This participant required four attempts in order to collect three FRC values with &#60;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...

Watch this Scientific Journal Video about Combining Volumetric Capnography And Barometric Plethysmography To Measure The Lung Structure-function Relationship at JoVE.com

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

Here, we describe two measures of pulmonary function &#8211; 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 ...

This method can help answer key questions in pulmonary physiology, particularly about how the structure-function relationship in the lung contributes to disease pathology. The main advantage of this technique is that it allows measures to be made repeatedly, within the same subject, without expensive imaging equipment or technically advanced analysis algorithms. The implications of measuring the lung structure-function relationship extend toward understanding the development of lung diseases, using classic, well-established physiological tools to evaluate novel interventions.Though this method provides insights into human lung physiology, it can also be applied to animal models of lung disease. Generally, individuals new to this method may struggle with the correct coaching of participants to follow the outlined maneuvers. Several practice runs are often necessary with a first-time participant.Visual demonstration of this method is critical, as the capnographic maneuver can be difficult to learn and the flow and volume of the maneuver must be controlled carefully. Procedures involving human subjects has been approved by the Institutional Review Board of the University of Iowa. Before beginning the calibration, use a standard barometer to measure the temperature, barometric pressure, and relative humidity, and enter these values into the plethysmograph software as correction factors.To calibrate the flow sensor, use a calibrated three liter syringe at variable flow rates and use a 50 milliliter pump to calibrate the box pressure. Immediately prior to the plethysmography measurement, have the participant enter the whole-body plethysmograph and close the door. After 30 to 60 seconds of thermal equilibration, instruct the participant to place their mouth on the mouthpiece, put on the nose clips, and place their hands on their cheeks.Instruct the participant to breathe normally, allowing at least four tidal breaths to be acquired, and a functional residual capacity to be established. At the end of a normal exhalation, close the shutter and coach the participant to pant lightly at 0.5 to one breaths per second for three to four seconds. Evaluate the relationship between the mouth pressure and plethysmograph pressure to ensure that it is a series of overlapping, straight lines, without thermal drift, and open the shutter and allow the participant to take a normal breath.Then coach the participant to exhale to the residual volume. Followed by a maximal inspiratory maneuver to total lung capacity. Before the participant arrives, address and modify the variables in the table, as necessary.To calibrate the gas analyzer, attach the drying tube to the mixing chamber and flush the bag with inert gas at a rate of at least 10 liters per minute, taking care not the pressurize the system. Once the displayed concentrations of the displaced carbon dioxide and oxygen have stabilized, adjust the zero knobs until they both read zero. Next, repeat the flush with 6%carbon dioxide and room air containing 20.93%oxygen as the calibration gases, matching the concentration of the calibration gases with the span knob when the concentration of the gases stabilizes.Then, recheck the inert gas and calibration gas concentrations and adjust the zero and span knobs until both are accurate to plus or minus 0.1%To calibrate the heated pneumotach, allow the pneumotach to warm to 37 degrees Celsius for at least 20 minutes, and open the Flow Channel menu in the system software. Select Spirometer and click Zero to zero the pneumotach. Then select OK.Use a flow head adaptor to connect a three liter syringe to the pneumotach and highlight the calibration breath.Under the Flow Channel menu, select Spirometer Flow, and Calibrate, and enter three liters. Click OK.And use the syringe the inject three liters of room air into the pneumotach at varying flow rates. The difference from three liters should be less than 5%When the system is ready, coach the participant to perform a single maneuver consisting of two pairs of breaths:a coaching breath and a breath for analysis.Because we have inspiration and expiration, with inspiration. During the maneuver, coach the participant to follow the flow guide on the computer monitor. Consider adding a resistor in line with the mouthpiece to make the exhaled flow easier to control.To measure the functional residual capacity, instruct the participant to sit straight with both feet on the floor, put on nose clips, and place their mouth on the mouthpiece. Coach the participant to complete at least one minute of tidal breathing to measure the metabolic function and to allow the participant to become familiar with the mouthpiece. Stop the data collection after one minute.Before beginning the maneuver, participants should vary their tidal volume, taking either normal, smaller, or larger than normal tidal breaths, to ensure that capnograms are obtained at different lung volumes. Coach the participant to transition to performing a capnogram maneuver as soon as the flow tracings appear on the screen, and resume the data collection at a random point in the participant's respiratory cycle, to allow measurements to be obtained at different lung volumes. Finally, coach to perform a sigh at the end of each maneuver, so that the muscles of respiration are completely relaxed, to allow the functional respiratory capacity to be determined.The single most important step, is the correct measurement and completion of the maneuver performed with volumetric capnography. Then, stop the data collection and have the participant repeat the capnogram maneuvers at least six to eight more times, to obtain 12 to 16 pairs of breaths for analysis. Here, a representative single capnogram used in an analysis, and the raw data for the entire sequence of the maneuver, are shown.In the raw data, the capnogram and the flow tracing were not aligned to account for the time delay. In these representative cases, the dead space and the slope were significantly correlated to the lung volume, suggesting that the dead space and airway homogeneity increase as the lung volume increases. While attempting this procedure, it's important to remember that it is highly dependent on the participant's exhaled flow rate and the delay between the analyzer and the spirometer.The accuracy of these vales should be checked carefully. After its development, this technique paved the way for researchers in the field of pulmonology to explore the structure-volume relationship of the lung in various patient populations, and this could potentially be integrated into the standard bedside care of respiratory diseases.

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