title: Biological variation, reference change value (RCV) and minimal important difference (MID) of inspiratory muscle strength (PImax) in patients with stable chronic heart failure.
abstract: BACKGROUND
  Despite the widespread application of measurements of respiratory muscle force (PImax) in clinical trials there is no data on biological variation, reference change value (RCV), or the minimal important difference (MID) for PImax irrespective of the target cohort. We addressed this issue for patients with chronic stable heart failure.
  
  
  RESULTS
  From the outpatients' clinic of the University of Heidelberg we retrospectively selected three groups of patients with stable systolic chronic heart failure (CHF). Each group had two measurements of PImax: 90 days apart in Group A (n = 25), 180 days apart in Group B (n = 93), and 365 days apart in Group C (n = 184). Stability was defined as (a) no change in NYHA class between visits and (b) absence of cardiac decompensation 3 months prior, during, and 3 months after measurements. For each group, we determined within-subject (CVI), between-subject (CVG), and total (CVT) coefficient of variation (CV), the index of individuality (II), RCV, reliability coefficient, and MID of PImax. CVT was 8.7, 7.5, and 6.9 % for groups A, B, and C, respectively. The II and RCV were 0.21, 0.20, 0.16 and 13.6, 11.6, 10.8 %, respectively. The reliability coefficient and MID were 0.83, 0.87, 0.88 and 1.44, 1.06, 1.12 kPa, respectively. Results were similar between age, gender, and aetiology subgroups.
  
  
  CONCLUSIONS
  In patients with stable CHF, measurements of PImax are highly stable for intervals up to 1 year. The low values for II suggest that evaluation of change in PImax should be performed on an individual (per patient) basis. Individually significant change can be assumed beyond 14 % (RCV) or 1.12 kPa (MID).
authors.affiliation: Department of Cardiology, Angiology, and Pulmonology, University of Heidelberg, Im Neuenheimer Feld 410, 69120, Heidelberg, Germany.
authors.forename: Tobias
authors.initials: T
authors.lastname: Täger
authors.affiliation: Department of Cardiology, Angiology, and Pulmonology, University of Heidelberg, Im Neuenheimer Feld 410, 69120, Heidelberg, Germany.
authors.forename: Miriam
authors.initials: M
authors.lastname: Schell
authors.affiliation: Department of Cardiology, Angiology, and Pulmonology, University of Heidelberg, Im Neuenheimer Feld 410, 69120, Heidelberg, Germany.
authors.forename: Rita
authors.initials: R
authors.lastname: Cebola
authors.affiliation: Department of Cardiology, Angiology, and Pulmonology, University of Heidelberg, Im Neuenheimer Feld 410, 69120, Heidelberg, Germany.
authors.forename: Hanna
authors.initials: H
authors.lastname: Fröhlich
authors.affiliation: Department of Cardiology, Angiology, and Pulmonology, University of Heidelberg, Im Neuenheimer Feld 410, 69120, Heidelberg, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Dösch
authors.affiliation: Department of Cardiology, Angiology, and Pulmonology, University of Heidelberg, Im Neuenheimer Feld 410, 69120, Heidelberg, Germany.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Franke
authors.affiliation: Department of Cardiology, Angiology, and Pulmonology, University of Heidelberg, Im Neuenheimer Feld 410, 69120, Heidelberg, Germany.
authors.forename: Hugo A
authors.initials: HA
authors.lastname: Katus
authors.affiliation: Department of Pathology, Baylor University Medical Center, Dallas, TX, USA.
authors.forename: Frank H
authors.initials: FH
authors.lastname: Wians
authors.affiliation: Department of Cardiology, Angiology, and Pulmonology, University of Heidelberg, Im Neuenheimer Feld 410, 69120, Heidelberg, Germany. Lutz.Frankenstein@med.uni-heidelberg.de.
authors.forename: Lutz
authors.initials: L
authors.lastname: Frankenstein
mesh_terms: D002908:Chronic Disease; D003964:Diaphragm / Q000503:physiopathology*; D005260:Female; D005858:Germany; D006333:Heart Failure / Q000175:diagnosis / Q000503:physiopathology*; D006801:Humans; D001239:Inhalation; D008297:Male; D008875:Middle Aged; D053580:Muscle Strength; D012016:Reference Values; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
keywords: Biological variation; Chronic heart failure; Inspiratory muscle strength; Minimal important difference; PImax; Reference change value