To stress or not to stress? Exercise pulmonary haemodynamic testing in systemic sclerosis Edmund M.T. Lau 1,2 , Vivek Thakkar 3,4 , Marc Humbert 5,6,7 and Philippe Herve 8 Affiliations: 1 Sydney Medical School, University of Sydney, Sydney, Australia. 2 Dept of Respiratory Medicine, Royal Prince Alfred Hospital, Camperdown, Australia. 3 Dept of Rheumatology, Liverpool Hospital, Sydney, Australia. 4 School of Medicine, Western Sydney University, Campbelltown, Australia. 5 Univ. Paris-Sud, Université Paris-Saclay, Le Kremlin-Bicêtre, France. 6 Service de Pneumologie, Hôpital Bicêtre, Assistance Publique Hôpitaux de Paris, Le Kremlin-Bicêtre, France. 7 INSERM UMR_S 999, Hôpital Marie Lannelongue, Le Plessis Robinson, France. 8 AP-HP, Service de Pneumologie, Centre de Référence de l’Hypertension Pulmonaire Sévère, DHU Thorax Innovation, Hôpital Bicêtre, Le Kremlin-Bicêtre, France. Correspondence: Edmund M.T. Lau, Dept of Respiratory Medicine, Royal Prince Alfred Hospital, Missenden Road, Camperdown, NSW 2050, Australia. E-mail: edmund.lau@sydney.edu.au @ERSpublications Exercise pulmonary hypertension may have prognostic significance in patients with systemic sclerosis http://ow.ly/qkpx304uPZE Pulmonary arterial hypertension (PAH) is a leading cause of morbidity and mortality in systemic sclerosis (SSc) [1], and patients have a ∼10% lifetime risk of developing this devastating complication [2]. Despite targeted PAH therapy, outcomes of SSc-associated PAH (SSc-PAH) remain unsatisfactory, with a median survival of only 3–4 years from time of diagnosis [3, 4]. In the hope of further improving outcomes in SSc-PAH, early disease detection has been a major focus of research in the past decade [5–9]. One important and highly debated topic is the utility of exercise pulmonary haemodynamic testing for the early diagnosis of pulmonary vascular disease [10–12]. From a physiological viewpoint, exercise stress testing for the unmasking of early or silent pathology appears a worthwhile pursuit. The pulmonary circulation is unique in that >60% of its circulation must be obstructed before the resting mean pulmonary artery pressure (mPAP) rises above 25 mmHg [13], a value which represents the consensus threshold for the diagnosis of pulmonary hypertension (PH) [14]. Thus, there is the potential that clinically important pulmonary vascular disease is left undiagnosed using the current diagnostic criterion. Reliance on resting measurements may be very specific, but is perhaps not sensitive enough for the early diagnosis of pulmonary vascular disease. Furthermore, there is also now ample evidence to support that patients with normal resting mPAP but an abnormal pulmonary haemodynamic response during exercise (also known as exercise PH) develop symptoms of exertional dyspnoea [15–18]. So why do some experts remain circumspect or even oppose the concept of exercise haemodynamics testing of the pulmonary circulation? Many readers will know that exercise haemodynamics were part of the definition of PH (exercise mPAP >30 mmHg) until this was officially abandoned during the Fourth World Symposium on PH (Dana Point, USA, 2008) [19] due to uncertainties regarding the upper limits of normal exercise mPAP [20]. Exercise mPAP is also dependent on age, exercise type and exercise intensity [20]. A fundamental problem of the old definition of exercise PH was related to the fact that mPAP is a flow-dependent variable. Therefore, exercise mPAP must be adjusted for cardiac output in order to avoid false positive diagnoses of exercise PH [21], where elevated mPAP is simply driven by large cardiac output increases during exercise (as would occur in athletic individuals). To address this issue, new data have been accumulated in recent years and Copyright ©ERS 2016 Received: Sept 12 2016 | Accepted: Sept 15 2016 Conflict of interest: Disclosures can be found alongside this article at erj.ersjournals.com Eur Respir J 2016; 48: 1549–1552 | DOI: 10.1183/13993003.01809-2016 1549 | EDITORIAL PULMONARY VASCULAR DISEASES