title: 4-Second Exercise Test: Reference Values for Ages 18-81 Years.
abstract: BACKGROUND
  Physiological reflexes modulated primarily by the vagus nerve allow the heart to decelerate and accelerate rapidly after a deep inspiration followed by rapid movement of the limbs. This is the physiological and pharmacologically validated basis for the 4-s exercise test (4sET) used to assess the vagal modulation of cardiac chronotropism.
  
  
  OBJECTIVE
  To present reference data for 4sET in healthy adults.
  
  
  METHODS
  After applying strict clinical inclusion/exclusion criteria, 1,605 healthy adults (61% men) aged between 18 and 81 years subjected to 4sET were evaluated between 1994 and 2014. Using 4sET, the cardiac vagal index (CVI) was obtained by calculating the ratio between the duration of two RR intervals in the electrocardiogram: 1) after a 4-s rapid and deep breath and immediately before pedaling and 2) at the end of a rapid and resistance-free 4-s pedaling exercise.
  
  
  RESULTS
  CVI varied inversely with age (r = -0.33, p < 0.01), and the intercepts and slopes of the linear regressions between CVI and age were similar for men and women (p > 0.05). Considering the heteroscedasticity and the asymmetry of the distribution of the CVI values according to age, we chose to express the reference values in percentiles for eight age groups (years): 18-30, 31-40, 41-45, 46-50, 51-55, 56-60, 61-65, and 66+, obtaining progressively lower median CVI values ranging from 1.63 to 1.24.
  
  
  CONCLUSIONS
  The availability of CVI percentiles for different age groups should promote the clinical use of 4sET, which is a simple and safe procedure for the evaluation of vagal modulation of cardiac chronotropism.
authors.affiliation: Clínica de Medicina do Exercício, Rio de Janeiro, RJ, Brazil.
authors.forename: Claudio Gil
authors.initials: CG
authors.lastname: Araújo
authors.affiliation: Clínica de Medicina do Exercício, Rio de Janeiro, RJ, Brazil.
authors.forename: Claudia Lucia Barros de
authors.initials: CL
authors.lastname: Castro
authors.affiliation: Clínica de Medicina do Exercício, Rio de Janeiro, RJ, Brazil.
authors.forename: João Felipe
authors.initials: JF
authors.lastname: Franca
authors.affiliation: Hospital e Maternidade Therezinha de Jesus, Faculdade de Ciências Médicas e da Saúde de Juiz de Fora, Juiz de Fora, MG, Brazil.
authors.forename: Plínio Santos
authors.initials: PS
authors.lastname: Ramos
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D004562:Electrocardiography; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test / Q000379:methods*; D005260:Female; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D012016:Reference Values; D012737:Sex Factors; D018709:Statistics, Nonparametric; D013997:Time Factors; D014630:Vagus Nerve / Q000502:physiology*; D055815:Young Adult
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