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End-tidal PCO₂ Abnormality and Exercise Limitation in Patients With Primary Pulmonary Hypertension^*

^* From the Department of Medicine, Los Angeles Biomedical Research Institute, Harbor-UCLA Medical Center, Torrance, CA.

Correspondence to: Karlman Wasserman, MD, PhD, FCCP, Department of Medicine, Harbor-UCLA Medical Center, 1000 W Carson St, Box 405, Torrance, CA 90509-2910; e-mail: kwasserman{at}rei.edu

Objectives: Primary pulmonary hypertension (PPH) is a pulmonary vasculopathy resulting in exercise intolerance, usually due to dyspnea. We hypothesized that ventilation is increased during exercise in PPH relative to normal because the ventilated lung is underperfused, cardiac output increase is restricted, and arterial hypoxemia may develop. Our aim was to determine the size of the reduction in end-tidal PCO₂ (PETCO₂) as a reflection of the abnormality in ventilatory efficiency and ventilatory drive in PPH patients.

Methods: We performed cardiopulmonary exercise testing (CPET) in 52 PPH patients. All had hemodynamic measurements to confirm the diagnosis of PPH. A subgroup of 29 patients who underwent right-heart catheterization within 50 days of CPET were studied to compare their CPET responses to resting hemodynamics. Nine healthy volunteers matched for age and gender served as CPET control subjects.

Results: In PPH patients, the percentage of predicted peak oxygen uptake (O₂) correlated significantly with mean pulmonary artery pressure (mPAP) [r = – 0.59, p = 0.0007, n = 29]. PETCO₂ values at rest, anaerobic threshold (AT), and peak O₂ were proportionately reduced as percentage of predicted peak O₂ decreased (r = 0.66 to 0.72, p < 0.0001, n = 52). PETCO₂ values at rest, AT, and peak O₂ were also reduced as mPAP increased (r = – 0.51 to – 0.53, p < 0.005, n = 29). In contrast to normal subjects in whom PETCO₂ increased from rest to AT, PETCO₂ decreased in PPH patients, except for two patients with mild PPH in whom there was no change. Also, PETCO₂ increased rather than decreased further at the start of recovery, in contrast to normal. Although usually normal at rest, oxyhemoglobin saturation decreased during exercise in most PPH patients.

Conclusions: In patients with PPH, PETCO₂ at rest and exercise is significantly reduced in proportion to physiologic disease severity. The range of values is unusually low. Furthermore, the directional changes of PETCO₂ during exercise and early recovery are in the opposite direction of normal.

Key Words: anaerobic threshold • end-tidal CO₂ • mean pulmonary artery pressure • peak oxygen uptake • primary pulmonary hypertension • ventilatory equivalent for CO₂

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				J. E. Hansen, G. Ulubay, B. F. Chow, X.-G. Sun, and K. Wasserman Mixed-Expired and End-Tidal CO2 Distinguish Between Ventilation and Perfusion Defects During Exercise Testing in Patients With Lung and Heart Diseases Chest, September 1, 2007; 132(3): 977 - 983. [Abstract] [Full Text] [PDF]