title: Respiratory muscle strength effect on linear and nonlinear heart rate variability parameters in COPD patients.
abstract: BACKGROUND
  Chronic obstructive pulmonary disease (COPD) is recognized as a multisystemic inflammatory disease associated with extrapulmonary comorbidities, including respiratory muscle weakness and cardiovascular and cardiac autonomic regulation disorders. We investigated whether alterations in respiratory muscle strength (RMS) would affect cardiac autonomic modulation in COPD patients.
  
  
  METHODS
  This study was a cross-sectional study done in ten COPD patients affected by moderate to very severe disease. The heart rate variability (HRV) signal was recorded using a Polar cardiofrequencimeter at rest in the sitting position (10 minutes) and during a respiratory sinus arrhythmia maneuver (RSA-M; 4 minutes). Linear analysis in the time and frequency domains and nonlinear analysis were performed on the recorded signals. RMS was assessed using a digital manometer, which provided the maximum inspiratory pressure (PImax) and the maximum expiratory pressure (PEmax).
  
  
  RESULTS
  During the RSA-M, patients presented an HRV power increase in the low-frequency band (LFnu) (46.9±23.7 vs 75.8±27.2; P=0.01) and a decrease in the high-frequency band (HFnu) (52.8±23.5 vs 24.0±27.0; P=0.01) when compared to the resting condition. Significant associations were found between RMS and HRV spectral indices: PImax and LFnu (r=-0.74; P=0.01); PImax and HFnu (r=0.74; P=0.01); PEmax and LFnu (r=-0.66; P=0.01); PEmax and HFnu (r=0.66; P=0.03); between PEmax and sample entropy (r=0.83; P<0.01) and between PEmax and approximate entropy (r=0.74; P=0.01). Using a linear regression model, we found that PImax explained 44% of LFnu behavior during the RSA-M.
  
  
  CONCLUSIONS
  COPD patients with impaired RMS presented altered cardiac autonomic control, characterized by marked sympathetic modulation and a reduced parasympathetic response; reduced HRV complexity was observed during the RSA-M.
authors.affiliation: Course of Physiotherapy, Department of Health and Physical Education, University of Santa Cruz do Sul (UNISC), Santa Cruz do Sul, Rio Grande do Sul, Brazil.
authors.forename: Cássia Da Luz
authors.initials: Cda L
authors.lastname: Goulart
authors.affiliation: Course of Physiotherapy, Department of Health and Physical Education, University of Santa Cruz do Sul (UNISC), Santa Cruz do Sul, Rio Grande do Sul, Brazil.
authors.forename: Julio Cristiano
authors.initials: JC
authors.lastname: Simon
authors.affiliation: Course of Physiotherapy, Department of Health and Physical Education, University of Santa Cruz do Sul (UNISC), Santa Cruz do Sul, Rio Grande do Sul, Brazil.
authors.forename: Paloma De Borba
authors.initials: Pde B
authors.lastname: Schneiders
authors.affiliation: Course of Physiotherapy, Department of Health and Physical Education, University of Santa Cruz do Sul (UNISC), Santa Cruz do Sul, Rio Grande do Sul, Brazil.
authors.forename: Elisabete Antunes
authors.initials: EA
authors.lastname: San Martin
authors.affiliation: Cardiopulmonary Physiotherapy Laboratory, Nucleus of Research in Physical Exercise, Federal University of São Carlos (UFSCar), São Carlos, São Paulo, Brazil.
authors.forename: Ramona
authors.initials: R
authors.lastname: Cabiddu
authors.affiliation: Cardiopulmonary Physiotherapy Laboratory, Nucleus of Research in Physical Exercise, Federal University of São Carlos (UFSCar), São Carlos, São Paulo, Brazil.
authors.forename: Audrey
authors.initials: A
authors.lastname: Borghi-Silva
authors.affiliation: Cardiopulmonary Physiotherapy Laboratory, Nucleus of Research in Physical Exercise, Federal University of São Carlos (UFSCar), São Carlos, São Paulo, Brazil.
authors.forename: Renata
authors.initials: R
authors.lastname: Trimer
authors.affiliation: Course of Physiotherapy, Department of Health and Physical Education, University of Santa Cruz do Sul (UNISC), Santa Cruz do Sul, Rio Grande do Sul, Brazil.
authors.forename: Andréa Lúcia Gonçalves
authors.initials: AL
authors.lastname: da Silva
mesh_terms: D000368:Aged; D001341:Autonomic Nervous System / Q000503:physiopathology*; D045853:Exhalation; D005260:Female; D006321:Heart / Q000294:innervation*; D006339:Heart Rate; D006801:Humans; D001239:Inhalation; D016014:Linear Models; D008168:Lung / Q000503:physiopathology*; D008297:Male; D008365:Manometry; D008875:Middle Aged; D053580:Muscle Strength; D017711:Nonlinear Dynamics; D011237:Predictive Value of Tests; D029424:Pulmonary Disease, Chronic Obstructive / Q000175:diagnosis / Q000503:physiopathology*; D012132:Respiratory Muscles / Q000503:physiopathology*; D012720:Severity of Illness Index; D012815:Signal Processing, Computer-Assisted; D013147:Spirometry; D013686:Telemetry; D013997:Time Factors
keywords: COPD; autonomic nervous system; heart rate; muscle strength; sinus arrhythmia