title: Acute application of bilevel positive airway pressure influences the cardiac autonomic nervous system.
abstract: BACKGROUND
  Noninvasive positive pressure has been used to treat several diseases. However, the physiological response of the cardiac autonomic system during bilevel positive airway pressure (Bilevel) remains unclear.
  
  
  OBJECTIVE
  The aim of this study was to evaluate the heart rate variability (HRV) during Bilevel in young healthy subjects.
  
  
  METHODS
  Twenty men underwent 10-minute R-R interval recordings during sham ventilation (SV), Bilevel of 8-15 cmH(2)O and Bilevel of 13-20 cmH(2)O. The HRV was analyzed by means of the parallel R-R interval (mean R-Ri), the standard deviation of all R-Ri (SDNN), the root mean square of the squares of the differences between successive R-Ri (rMSSD), the number of successive R-Ri pairs that differ by more than 50 milliseconds (NN50), the percentage of successive R-Ri that differ by more than 50 milliseconds (pNN50), the low frequency (LF), the high frequency (HF) and SD1 and SD2. Additionally, physiological variables, including blood pressure, breathing frequency and end tidal CO(2), were collected. Repeated-measures ANOVA and Pearson correlation were used to assess the differences between the three studied conditions and the relationships between the delta of Bilevel at 13-20 cmH(2)O and sham ventilation of the HRV indexes and the physiological variables, respectively.
  
  
  RESULTS
  The R-Ri mean, rMSSD, NN50, pNN50 and SD1 were reduced during Bilevel of 13-20 cmH(2)O as compared to SV. An R-Ri mean reduction was also observed in Bilevel of 13-20 cmH(2)O compared to 8-15 cmH(2)O. Both the R-Ri mean and HF were reduced during Bilevel of 8-15 cmH(2)O as compared to SV, while the LF increased during application of Bilevel of 8-15 cmH(2)O as compared to SV. The delta (between Bilevel at 13-20 cmH(2)O and sham ventilation) of ETCO(2) correlated positively with LF, HF, the LF/HF ratio, SDNN, rMSSD and SD1. Acute application of Bilevel was able to alter the cardiac autonomic nervous system, resulting in a reduction in parasympathetic activity and an increase in sympathetic activity and higher level of positive pressure can cause a greater influence on the cardiovascular and respiratory system.
authors: Cardiopulmonary Physiotherapy Laboratory, Nucleus of Research in Physical Exercise, Physiotherapy Department - Federal University of São Carlos - São Carlos/SP, Brazil. camila_pantoni@hotmail.com
authors: Camila Bianca Falasco
authors: CB
authors: Pantoni
authors: Renata Gonçalves
authors: RG
authors: Mendes
authors: Luciana
authors: L
authors: Di Thommazo
authors: Aparecida Maria
authors: AM
authors: Catai
authors: Luciana Maria Malosá
authors: LM
authors: Sampaio
authors: Audrey
authors: A
authors: Borghi-Silva
mesh_terms: D001341:Autonomic Nervous System / Q000502:physiology*; D002320:Cardiovascular Physiological Phenomena; D004812:Epidemiologic Methods; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D008297:Male; D011175:Positive-Pressure Respiration / Q000379:methods*; D012123:Pulmonary Ventilation / Q000502:physiology; D055815:Young Adult