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

^* From the Los Angeles Biomedical Research Institute (Drs. Hansen, Sun, and Wasserman), Harbor-UCLA Medical Center, Respiratory and Critical Care Division of Physiology and Medicine, Department of Medicine, University of California at Los Angeles, Torrance, CA; Department of Chest Diseases (Dr. Ulubay), Faculty of Medicine, Baskent University, Ankara, Turkey; and Department of Respiratory Medicine (Dr. Chow), Ruttonjee Hospital, Hong Kong, SAR.

Correspondence to: James E. Hansen, MD, FCCP, Harbor-UCLA Medical Center, 1000 W. Carson St, RB-2, Box 405, Torrance CA 90509; e-mail: jhansen{at}labiomed.org

Abstract

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 (/) 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 / mismatching in these disorders.

Key Words: congestive heart failure • COPD • exercise test • pulmonary artery hypertension • pulmonary circulation • ventilation/perfusion ratio