title: Nocturnal cardiovascular activity in essential hypotension: evidence of differential autonomic regulation.
abstract: OBJECTIVE
  Essential hypotension represents a form of chronic low blood pressure (BP) not explained by medical or orthostatic conditions. The pathogenesis of essential hypotension may involve sympathetic hypoactivation and other forms of autonomic dysregulation. The aim of the current study was to investigate autonomic and cardiovascular activity during sleep in individuals with essential hypotension.
  
  
  METHODS
  A case-control study was conducted in 14 individuals with essential hypotension (mean [standard error] = 23.4 [0.6] years, all women) and 14 controls (mean [standard error] age = 22.2 [0.4] years, all women). The following measures were collected over a night of sleep: BP, heart rate (HR), stroke volume, cardiac output (CO), preejection period (PEP), total peripheral resistance, and time-domain measures of HR variability.
  
  
  RESULTS
  Hypotensive participants had consistently lower BP, HR, and CO than did normotensives. Cardiac autonomic variables revealed enhanced parasympathetic tone (proportion of adjacent normal-to-normal intervals that differed in length by more than 50 milliseconds = 40.8 [6.3] versus 23.4 [4.5], p = .03) and reduced sympathetic drive in hypotensives (PEP = 99.4 [3.6] versus 86.1 [4.3], p = .02). Analysis of temporal profiles showed that HR, stroke volume, and CO decreased throughout the night in both groups, whereas PEP and HR variability increased. Unlike controls, BP remained essentially unchanged in hypotensives, as the decrease in CO was counterbalanced by a parallel rise in total peripheral resistance.
  
  
  CONCLUSIONS
  These findings suggest that nocturnal cardiac sympathetic withdrawal combined with vagal hyperactivity is a characteristic of the autonomic regulation in essential hypotension.
authors.affiliation: Department of General Psychology, University of Padova, Via Venezia 8, 35131 Padova, Italy.  naima.covassin@unipd.it.
authors.forename: Naima
authors.initials: N
authors.lastname: Covassin
authors.forename: Massimiliano
authors.initials: M
authors.lastname: de Zambotti
authors.forename: Nicola
authors.initials: N
authors.lastname: Cellini
authors.forename: Michela
authors.initials: M
authors.lastname: Sarlo
authors.forename: Luciano
authors.initials: L
authors.lastname: Stegagno
mesh_terms: D000328:Adult; D001341:Autonomic Nervous System / Q000503:physiopathology*; D001794:Blood Pressure / Q000502:physiology; D002302:Cardiac Output / Q000502:physiology; D002307:Cardiography, Impedance; D016022:Case-Control Studies; D002940:Circadian Rhythm / Q000502:physiology*; D005260:Female; D006339:Heart Rate / Q000502:physiology; D006439:Hemodynamics / Q000502:physiology*; D006801:Humans; D007022:Hypotension / Q000175:diagnosis / Q000503:physiopathology*; D008297:Male; D017286:Polysomnography; D012016:Reference Values; D012815:Signal Processing, Computer-Assisted; D012893:Sleep Wake Disorders / Q000175:diagnosis / Q000503:physiopathology*; D013318:Stroke Volume / Q000502:physiology; D055815:Young Adult