title: The Valsalva maneuver in Chagas disease patients without cardiopathy.
abstract: OBJECTIVE
  To perform a meta-analysis of studies using the Valsalva ratio (VR) in Chagas disease (ChD) patients without cardiopathy in comparison to control subjects in order to determine if vagal heart modulation is impaired in early forms of ChD.
  
  
  METHODS
  The medical literature was systematically searched and reviewed for cross-sectional studies in humans in which the Valsalva maneuver was used to evaluate the autonomic modulation of the heart in ChD patients without cardiopathy. The Hedges g statistic (software Medcalc v.9.4.0.0) was used to combine the results of all studies through the calculation of the summary standardized mean difference (SMD): the mean VR in controls minus the mean VR in ChD patients, divided by the pooled and adjusted standard deviation. The sample size necessary to detect this SMD with 80% of power was calculated using the G*Power software v.3.0.
  
  
  RESULTS
  The meta-analysis included 396 patients in 7 studies. Summary mean VRs were 1.87 +/- 0.39 ms in controls versus 1.74 +/- 0.40 ms in ChD without cardiopathy, leading to a statistically significant summary SMD of -0.310 (95% CI -0.513 to -0.106). Considering the summary SMD of -0.31, an alpha error of 0.05 and a 1:1 ratio of ChD and control patients, the estimated total sample size for a study with 80% power was 330 patients.
  
  
  CONCLUSIONS
  ChD patients without cardiopathy have reduced VR values compared to healthy controls, indicating early vagal dysfunction. Most previous studies could not detect this impairment due to small study samples and insufficient statistical power.
authors: Serviço de Cardiologia, Hospital das Clínicas, Faculdade de Medicina, Universidade Federal de Minas Gerais, Av. Alfredo Balena, 190-Campus Saúde, Belo Horizonte, 30130-100, Brazil. antonior@uai.com.br
authors: Antonio L P
authors: AL
authors: Ribeiro
authors: Marcos Soares
authors: MS
authors: Campos
authors: Leonardo Matos Gomes
authors: LM
authors: Baptista
authors: Marcos R
authors: MR
authors: de Sousa
mesh_terms: D000328:Adult; D001341:Autonomic Nervous System / Q000502:physiology; D009202:Cardiomyopathies / Q000503:physiopathology; D016022:Case-Control Studies; D014355:Chagas Disease / Q000503:physiopathology*; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D014630:Vagus Nerve / Q000503:physiopathology; D014636:Valsalva Maneuver / Q000502:physiology*