title: Increased mortality in patients with severe COPD associated with high-intensity exercise: a preliminary cohort study.
abstract: BACKGROUND
  Intensity of exercise is believed to be a key determinant of response to chronic obstructive pulmonary disease (COPD) rehabilitation. We hypothesized that a higher intensity of exercise, in combination with physiotherapist-led instructions and education in management of breathlessness, would lead to better self-management, possibly delaying calls to the emergency service and preventing hospitalization.
  
  
  OBJECTIVE
  We aimed to test this hypothesis in a subsequent randomized trial, and in order to test study processes and estimate hospitalization rates, we did a small preliminary prospective cohort study on severe COPD patients referred to outpatient rehabilitation.
  
  
  METHODS
  In 2013, four rehabilitation courses were scheduled (spring, summer, autumn, and winter) each lasting 8 weeks and including eight to ten patients. This preliminary study was designed as a controlled cohort study. The bi-weekly exercise sessions in the spring and autumn courses included a high-intensity walking exercise at 95% of estimated VO2max for as long as possible. The other two rehabilitation courses included the usual walking exercise intensity (85% of estimated VO2max). Hospitalization rates were assessed from the participants' medical records in an 18-month period.
  
  
  RESULTS
  We were able to enroll 31 patients in total (15 in the high-intensity exercise group and 16 in regular intensity). There were no group differences in the hospitalization rates. However, during review of the medical records, we observed a striking mortality rate among participants who had attended the high-intensity rehabilitation courses (five deaths) compared to the standard rehabilitation (zero deaths). Four of the five deaths were COPD exacerbations. Fisher's exact test was statistically significant (P=0.046), as was a log-rank test (P=0.019) of the Kaplan-Meier estimated survival rates.
  
  
  CONCLUSIONS
  These results from this small preliminary cohort study are alarming and raise concerns about the possible serious risks associated with high-intensity exercise rehabilitation of severe COPD patients.
authors.affiliation: Department of Physio- and Occupational Therapy; The Parker Institute, Copenhagen University Hospital Bispebjerg-Frederiksberg, Copenhagen, Denmark.
authors.forename: Lone
authors.initials: L
authors.lastname: Schaadt
authors.affiliation: The Parker Institute, Copenhagen University Hospital Bispebjerg-Frederiksberg, Copenhagen, Denmark.
authors.forename: Robin
authors.initials: R
authors.lastname: Christensen
authors.affiliation: The Parker Institute, Copenhagen University Hospital Bispebjerg-Frederiksberg, Copenhagen, Denmark.
authors.forename: Lars Erik
authors.initials: LE
authors.lastname: Kristensen
authors.affiliation: Department of Physio- and Occupational Therapy; The Parker Institute, Copenhagen University Hospital Bispebjerg-Frederiksberg, Copenhagen, Denmark.
authors.forename: Marius
authors.initials: M
authors.lastname: Henriksen
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000553:Ambulatory Care; D003718:Denmark; D018450:Disease Progression; D005081:Exercise Therapy / Q000009:adverse effects / Q000379:methods / Q000401:mortality*; D017079:Exercise Tolerance; D005260:Female; D006304:Health Status; D006760:Hospitalization; D006801:Humans; D053208:Kaplan-Meier Estimate; D008168:Lung / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D010101:Oxygen Consumption; D010865:Pilot Projects; D016016:Proportional Hazards Models; D011446:Prospective Studies; D029424:Pulmonary Disease, Chronic Obstructive / Q000175:diagnosis / Q000401:mortality* / Q000503:physiopathology / Q000534:rehabilitation*; D018570:Risk Assessment; D012307:Risk Factors; D012720:Severity of Illness Index; D013997:Time Factors; D016896:Treatment Outcome; D016138:Walking
keywords: Chronic obstructive pulmonary disease; exercise; mortality; rehabilitation