title: Morning surge in blood pressure is associated with reactivity of the sympathetic nervous system.
abstract: BACKGROUND
  An exaggerated morning surge in blood pressure (BP) closely relates to target organ damage and cardiovascular risk, but whether the causative mechanism involves greater reactivity of the sympathetic nervous system (SNS) is unknown. We determined whether the response of the SNS to a cold pressor test predicted the BP morning surge.
  
  
  METHODS
  Ambulatory BP recordings were obtained from 14 men and 19 women (age = 41±4 years), and the amplitude (day-night difference), rate of rise (RoR), rate by amplitude product (BPPower), and morning BP surge (MBPS; post-awake minus pre-awake) of morning mean arterial pressure (MAP) were determined. The reactivity of the SNS to CPT was assessed by recording of muscle sympathetic nerve activity (MSNA).
  
  
  RESULTS
  CPT induced a marked increase in MAP and all parameters of MSNA, including burst amplitude. Log-normalized BPPower positively correlated with the overall average CPT-induced increases in total MSNA (r = 0.38; P = 0.04) and burst amplitude (r = 0.43; P = 0.02) but was not related to the increase in MSNA frequency. Furthermore, a strong positive linear trend in the CPT-induced changes in burst amplitude across tertiles of BPPower and RoR was observed. BPPower and RoR were not related to CPT-induced hemodynamic changes. The MBPS did not correlate with any of the CPT-induced changes in vascular or MSNA variables.
  
  
  CONCLUSIONS
  These results suggest that the central nervous system mechanisms influencing the increase in MSNA burst amplitude during arousal may also be fundamental in determining the rate and power of BP rise during the morning period.
authors.affiliation: Human Neurotransmitters Laboratory, Baker IDI Heart & Diabetes Institute, Melbourne, Victoria, Australia.
authors.forename: Elisabeth A
authors.initials: EA
authors.lastname: Lambert
authors.forename: Kanella
authors.initials: K
authors.lastname: Chatzivlastou
authors.forename: Markus
authors.initials: M
authors.lastname: Schlaich
authors.forename: Gavin
authors.initials: G
authors.lastname: Lambert
authors.forename: Geoffrey A
authors.initials: GA
authors.lastname: Head
mesh_terms: D000328:Adult; D062186:Arterial Pressure; D017704:Baroreflex; D018660:Blood Pressure Monitoring, Ambulatory; D002940:Circadian Rhythm; D003080:Cold Temperature; D005260:Female; D006801:Humans; D006973:Hypertension / Q000175:diagnosis / Q000503:physiopathology*; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000294:innervation*; D013564:Sympathetic Nervous System / Q000503:physiopathology*; D013997:Time Factors; D014661:Vasoconstriction
keywords: ambulatory blood pressure; blood pressure; cold pressor test; double logistic equation; hypertension; microneurography; morning blood pressure surge; sympathetic nervous system.