title: Differences in ventilatory inefficiency between pulmonary arterial hypertension and chronic thromboembolic pulmonary hypertension.
abstract: 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(CO(2)) 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 CO(2) at anaerobic threshold (Eqco(2)_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(CO(2)) slope (P = .003), and Eqco(2)_AT (P < .001). These three measures could distinguish between World Health Organization functional classes I/II and III/IV in PAH but not CTEPH.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Imperial College School of Medicine, Imperial College London, London, England; Respiratory and Critical Care Department, Beijing Institute of Respiratory Medicine, Beijing Chao-Yang Hospital, Capital Medical University, Beijing, China.
authors.forename: Zhenguo
authors.initials: Z
authors.lastname: Zhai
authors.affiliation: Department of Respiratory Medicine, Hammersmith Hospital, London, England.
authors.forename: Kevin
authors.initials: K
authors.lastname: Murphy
authors.affiliation: Department of Respiratory Medicine, Hammersmith Hospital, London, England.
authors.forename: Hannah
authors.initials: H
authors.lastname: Tighe
authors.affiliation: Respiratory and Critical Care Department, Beijing Institute of Respiratory Medicine, Beijing Chao-Yang Hospital, Capital Medical University, Beijing, China.
authors.forename: Chen
authors.initials: C
authors.lastname: Wang
authors.affiliation: Division of Experimental Medicine and Toxicology, Imperial College London, London, England.
authors.forename: Martin R
authors.initials: MR
authors.lastname: Wilkins
authors.affiliation: National Pulmonary Hypertension Service (London), Hammersmith Hospital, Imperial College Healthcare NHS Trust, National Heart and Lung Institute, Imperial College London, London, England.
authors.forename: J Simon R
authors.initials: JSR
authors.lastname: Gibbs
authors.affiliation: National Pulmonary Hypertension Service (London), Hammersmith Hospital, Imperial College Healthcare NHS Trust, National Heart and Lung Institute, Imperial College London, London, England. Electronic address: l.howard@imperial.ac.uk.
authors.forename: Luke S
authors.initials: LS
authors.lastname: Howard
mesh_terms: D001784:Blood Gas Analysis; D002908:Chronic Disease; D005080:Exercise Test; D005260:Female; D006801:Humans; D006976:Hypertension, Pulmonary / Q000503:physiopathology*; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D011379:Prognosis; D011659:Pulmonary Gas Exchange; D012129:Respiratory Function Tests; D013923:Thromboembolism / Q000503:physiopathology*