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Original Research: PULMONARY VASCULAR DISEASE |

Differences in Ventilatory Inefficiency Between Pulmonary Arterial Hypertension and Chronic Thromboembolic Pulmonary HypertensionVentilatory Inefficiency in Pulmonary Hypertension

Zhenguo Zhai, PhD; Kevin Murphy, PhD; Hannah Tighe, BSc; Chen Wang, PhD, FCCP; Martin R. Wilkins, PhD; J. Simon R. Gibbs, MD; and; Luke S. Howard, DPhil
Author and Funding Information

From the Imperial College School of Medicine (Dr Zhai), the Division of Experimental Medicine and Toxicology (Dr Wilkins), and the National Pulmonary Hypertension Service (London), Hammersmith Hospital, Imperial College Healthcare NHS Trust and National Heart and Lung Institute (Drs Gibbs and Howard), Imperial College London, London, England; the Respiratory and Critical Care Department (Drs Zhai and Wang), Beijing Institute of Respiratory Medicine, Beijing Chao-Yang Hospital, Capital Medical University, Beijing, China; and the Department of Respiratory Medicine (Dr Murphy and Ms Tighe), Hammersmith Hospital, London, England.

Correspondence to: Luke Howard, DPhil, National Pulmonary Hypertension Service (London), Hammersmith Hospital, Imperial College Healthcare NHS Trust, Du Cane Rd, London W12 0HS, England; e-mail: l.howard@imperial.ac.uk


Funding/Support: Dr Zhai received financial support from the Beijing Youth Star of Science and Technology Program [No. 2007B037].

Reproduction of this article is prohibited without written permission from the American College of Chest Physicians (http://www.chestpubs.org/site/misc/reprints.xhtml).


© 2011 American College of Chest Physicians


Chest. 2011;140(5):1284-1291. doi:10.1378/chest.10-3357
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Background:  Measures of ventilatory efficiency during cardiopulmonary exercise testing (CPX) are increasingly being used as prognostic markers in heart failure and pulmonary hypertension (PH). Little is known about whether these measures can be applied to all forms of PH, in particular chronic thromboembolic pulmonary hypertension (CTEPH), wherein thrombotic vascular occlusion has an impact on gas exchange.

Methods:  One hundred twenty-seven patients, 50 with CTEPH and 77 with pulmonary arterial hypertension (PAH), underwent incremental CPX.

Results:  Physiologic ventilatory dead space fraction (Vd/Vtphys) measured at peak exercise with arterial blood gas analysis was higher in CTEPH than PAH (52.9% vs 41.8%, P < .001). The V˙ e/V˙ co2 slope was higher in patients with CTEPH than in patients with PAH (50.7 L/min/L/min vs 44.4 L/min/L/min, P = .024) and was mirrored by similar changes in the ventilatory equivalent for CO2 at anaerobic threshold (Eqco2_AT) (47.7 L/min/L/min vs 42.0 L/min/L/min, P = .008). In a multivariate linear regression analysis, disease subtype was found to be an independent predictor of Vd/Vtphys (P < .001), V˙ e/V˙ co2 slope (P = .003), and Eqco2_AT (P < .001). These three measures could distinguish between World Health Organization functional classes I/II and III/IV in PAH but not CTEPH.

Conclusion:  Significant differences in gas exchange exist between CTEPH and PAH, due to differences in Vd/Vtphys likely as a result of vascular occlusion due to thromboembolic disease. This dissociates measures of ventilatory efficiency from disease severity and also contributes to our understanding of the differences in exercise limitation and breathlessness in PAH and CTEPH. Common prognostic end points from CPX cannot be applied to all forms of PH.

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