title: The utility of cardiopulmonary exercise testing in difficult asthma.
abstract: BACKGROUND
  Unexplained persistent breathlessness in patients with difficult asthma despite multiple treatments is a common clinical problem. Cardiopulmonary exercise testing (CPX) may help identify the mechanism causing these symptoms, allowing appropriate management.
  
  
  METHODS
  This was a retrospective analysis of patients attending a specialist-provided service for difficult asthma who proceeded to CPX as part of our evaluation protocol. Patient demographics, lung function, and use of health care and rescue medication were compared with those in patients with refractory asthma. Medication use 6 months following CPX was compared with treatment during CPX.
  
  
  RESULTS
  Of 302 sequential referrals, 39 patients underwent CPX. A single explanatory feature was identified in 30 patients and two features in nine patients: hyperventilation (n = 14), exercise-induced bronchoconstriction (n = 8), submaximal test (n = 8), normal test (n = 8), ventilatory limitation (n = 7), deconditioning (n = 2), cardiac ischemia (n = 1). Compared with patients with refractory asthma, patients without "pulmonary limitation" on CPX were prescribed similar doses of inhaled corticosteroid (ICS) (median, 1,300 μg [interquartile range (IQR), 800-2,000 μg] vs 1,800 μg [IQR, 1,000-2,000 μg]) and rescue oral steroid courses in the previous year (median, 5 [1-6] vs 5 [1-6]). In this group 6 months post-CPX, ICS doses were reduced (median, 1,300 μg [IQR, 800-2,000 μg] to 800 μg [IQR, 400-1,000 μg]; P < .001) and additional medication treatment was withdrawn (n = 7). Patients with pulmonary limitation had unchanged ICS doses post CPX and additional therapies were introduced.
  
  
  CONCLUSIONS
  In difficult asthma, CPX can confirm that persistent exertional breathlessness is due to asthma but can also identify other contributing factors. Patients with nonpulmonary limitation are prescribed inappropriately high doses of steroid therapy, and CPX can identify the primary mechanism of breathlessness, facilitating steroid reduction.
authors.affiliation: Centre for Infection and Immunity, Queen's University Belfast, Belfast City Hospital, Belfast, Northern Ireland; Regional Respiratory Centre, Belfast City Hospital, Belfast, Northern Ireland.
authors.forename: Diarmuid M
authors.initials: DM
authors.lastname: McNicholl
authors.affiliation: Regional Respiratory Centre, Belfast City Hospital, Belfast, Northern Ireland.
authors.forename: Jacqui
authors.initials: J
authors.lastname: Megarry
authors.affiliation: Centre for Infection and Immunity, Queen's University Belfast, Belfast City Hospital, Belfast, Northern Ireland.
authors.forename: Lorcan P
authors.initials: LP
authors.lastname: McGarvey
authors.affiliation: Regional Respiratory Centre, Belfast City Hospital, Belfast, Northern Ireland.
authors.forename: Marshall S
authors.initials: MS
authors.lastname: Riley
authors.affiliation: Centre for Infection and Immunity, Queen's University Belfast, Belfast City Hospital, Belfast, Northern Ireland; Regional Respiratory Centre, Belfast City Hospital, Belfast, Northern Ireland. Electronic address: l.heaney@qub.ac.uk.
authors.forename: Liam G
authors.initials: LG
authors.lastname: Heaney
mesh_terms: D000328:Adult; D001249:Asthma / Q000175:diagnosis* / Q000503:physiopathology*; D005080:Exercise Test; D005260:Female; D006801:Humans; D008297:Male; D012189:Retrospective Studies