title: Circadian variation of haemodynamics in patients with essential hypertension: comparison between early morning and evening.
abstract: OBJECTIVE
  An increased incidence of cardiovascular accidents in the morning has been reported, but the reason why is not clear. We measured 24-h haemodynamics and focused on its change in the morning.
  
  
  METHODS
  To study the circadian variation of haemodynamics, we recorded 24-h direct blood pressure and electrocardiogram using a telemetry method, in 21 untreated inpatients with essential hypertension, and measured cardiac output using the dye-dilution method in the morning, in the evening and during sleep. We also determined the beat-to-beat cardiac output (using the pulse-contour method), the total peripheral resistance and the ratio of low- to high-frequency components (using power spectral analysis of the R-R interval during 24 h), and made comparisons between morning and evening values.
  
  
  RESULTS
  Both systolic and diastolic blood pressure increased rapidly in the early morning. Although the comparison of blood pressure between morning and evening showed no difference, total peripheral resistance and low- to high-frequency ratio were significantly higher in the morning than in the evening, but cardiac output was lower in the morning.
  
  
  CONCLUSIONS
  Sympathetic nervous activity and vascular resistance seem to be higher in the morning than in the evening, and these haemodynamic changes may stress the cardiovascular system.
authors.affiliation: Second Department of Internal Medicine, Yokohama City University School of Medicine, Urafune Hospital, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Kawano
authors.forename: O
authors.initials: O
authors.lastname: Tochikubo
authors.forename: K
authors.initials: K
authors.lastname: Minamisawa
authors.forename: E
authors.initials: E
authors.lastname: Miyajima
authors.forename: M
authors.initials: M
authors.lastname: Ishii
mesh_terms: D000328:Adult; D000368:Aged; D002940:Circadian Rhythm; D005260:Female; D006439:Hemodynamics; D006801:Humans; D006973:Hypertension / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged