Mixed-Expired and End-Tidal CO2 Distinguish Between Ventilation and Perfusion Defects During Exercise Testing in Patients With Lung and Heart Diseases

doi:10.1378/chest.07-0619

Chest

Volume 132, Issue 3, September 2007, Pages 977-983

https://doi.org/10.1378/chest.07-0619 Get rights and content

Background

Mismatching of ventilation to perfusion is found in patients with COPD, left ventricular failure (LVF), and pulmonary vascular diseases. Such mismatching may be due to ventilation or perfusion defects or both. Our primary hypothesis was that pressures of mixed-expired CO₂ pressure (Peco₂), end-tidal Pco₂ pressure (Petco₂), and their ratios would differ between groups during exercise testing, depending on whether the ventilation/perfusion ( $\dot{V}$ / $\dot{Q}$ ) abnormality was dominantly caused by airways or perfusion defects.

Methods

We administered incremental cycle ergometry tests to 25 normal subjects and three groups of 25 patients, each group with uncomplicated COPD, LVF, or primary pulmonary arterial hypertension (PAH). We compared Peco₂, Petco₂, and their ratios at rest, unloaded pedaling, anaerobic threshold, and peak exercise.

Results

Although each patient group had mean peak O₂ uptake of approximately 50% of predicted normal, the levels and patterns of change for each group for Peco₂, Petco₂, and their ratios were surprisingly distinctive. As hypothesized, the COPD group always had markedly lower Peco₂/Petco₂ ratios than all other groups (p < 0.001). In addition, patients with LVF had slightly lower Peco₂/Petco₂ ratios at heavy exercise than normal subjects (p < 0.05). At all times, except for COPD group Petco₂ at peak exercise, each group had significantly lower Petco₂ and Peco₂ than normal subjects (p < 0.001). In patients with PAH, the Petco₂ decline with exercise was distinctive.

Conclusions

The levels and changes in Peco₂, Petco₂, and their ratios during cardiopulmonary exercise testing are distinctive and explained by the differing pathophysiologies of $\dot{V}$ / $\dot{Q}$ mismatching in these disorders.

Section snippets

Subjects

The study was approved by our institutional review board. From our recent files, the authors screened and selected cardiopulmonary exercise test results obtained with informed consent from 25 adults in each of the following four groups: normal, COPD, LVF, and PAH. All normal subjects were considered healthy. All COPD patients had FEV₁/FVC ratios < 50% and low or reduced gas transfer index; none had asthma. All LVF patients were New York Heart Association class III or IV left ventricular

Results

Demographics of the subjects are noted in Table 1. Although age and sex distributions were dissimilar, generally reflecting age and sex distributions seen in the respective disease states, disease severities (percentage of predicted peak $\dot{V}$ o₂), peak $\dot{V}$ e, and peak $\dot{V}$ co₂ for the three disease groups were not significantly different. However, FEV₁/VC, Dlco, and breathing reserve were significantly lower and residual volume/total lung capacity significantly higher in the COPD group

Discussion

Discerning the dominant disorder in patients with dyspnea can sometimes be difficult. As previously found in several studies, $\dot{V}$ / $\dot{Q}$ inequalities, increased Vd/Vt, and/or decreased Peco₂ and Petco₂ occur at rest and during exercise in COPD,⁶⁷⁸⁹¹⁰ LVF,¹¹¹²¹³¹⁴¹⁵ and PAH.¹⁶¹⁷¹⁸ The major hypothesis and finding of this study was that $\dot{V}$ / $\dot{Q}$ mismatch caused by airway defects could be differentiated from that of perfusion defects using noninvasive measures of Peco₂ and Petco₂.

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Citation Excerpt :
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This work was performed at Los Angeles Biomedical Research Institute, Harbor-UCLA Medical Center.

James E. Hansen has received consultation fees from MET-Test, LLC, and salary support from St. Jude Medical. Dr. Ulubay received support from the Turkish Scientific Research Institute (Tubitak). Dr. Chow reports no conflict of interest. Dr. Sun has received salary support from St. Jude Medical. Dr. Wasserman has received consultation fees from MET-Test, LLC, and salary support from St. Jude Medical.

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Chest

ORIGINAL RESEARCHEXERCISE TESTINGMixed-Expired and End-Tidal CO2 Distinguish Between Ventilation and Perfusion Defects During Exercise Testing in Patients With Lung and Heart Diseases

Background

Methods

Results

Conclusions

Section snippets

Subjects

Results

Discussion

Chest

Med Clin North Am

Chest

Chest

Am J Cardiol

Chest

Principles of exercise testing and interpretation

The lung: clinical physiology and pulmonary function tests

Introduction to statistical analysis

Ventilation-perfusion inequality in chronic obstructive pulmonary disease

J Clin Invest

ORIGINAL RESEARCH
EXERCISE TESTING
Mixed-Expired and End-Tidal CO₂ Distinguish Between Ventilation and Perfusion Defects During Exercise Testing in Patients With Lung and Heart Diseases