title: Elderly women regulate brain blood flow better than men do.
abstract: OBJECTIVE
  Orthostatic intolerance and falls differ between sexes and change with age. However, it remains unclear what role cerebral autoregulation may play in this response. This study was designed to determine whether cerebral autoregulation, assessed using transcranial Doppler ultrasound, is more effective in elderly females than in males.
  
  
  METHODS
  We used transcranial Doppler ultrasound to evaluate cerebral autoregulation in 544 (236 male) subjects older than age 70 years recruited as part of the MOBILIZE Boston study. The MOBILIZE Boston study is a prospective cohort study of a unique set of risk factors for falls in seniors in the Boston area. We assessed CO2 reactivity and transfer function gain, phase, and coherence during 5 minutes of quiet sitting and autoregulatory index during sit-to-stand tests.
  
  
  RESULTS
  Male subjects had significantly lower CO2 reactivity (males, 1.10 ± 0.03; females, 1.32 ± 0.43 (cm/s)/%CO2; P<0.001) and autoregulatory indices (males, 4.41 ± 2.44; female, 5.32 ± 2.47; P<0.001), higher transfer function gain (males, 1.34 ± 0.49; females, 1.19 ± 0.43; P=0.002), and lower phase (males, 42.7 ± 23.6; females, 49.4 ± 24.9; P=0.002) in the autoregulatory band, implying less effective cerebral autoregulation. However, reduced autoregulation in males was not below the normal range, indicating autoregulation was intact but less effective.
  
  
  CONCLUSIONS
  Female subjects were better able to maintain cerebral flow velocities during postural changes and demonstrated better cerebral autoregulation. The mechanisms of sex-based differences in autoregulation remain unclear but may partially explain the higher rates of orthostatic hypotension-related hospitalizations in elderly men.
authors.affiliation: Electrical & Electronic Engineering, School of Engineering & Informatics, NUI Galway, University Road, Galway, Ireland.
authors.forename: Brian M
authors.initials: BM
authors.lastname: Deegan
authors.forename: Farzaneh A
authors.initials: FA
authors.lastname: Sorond
authors.forename: Andrew
authors.initials: A
authors.lastname: Galica
authors.forename: Lewis A
authors.initials: LA
authors.lastname: Lipsitz
authors.forename: Gearoid
authors.initials: G
authors.lastname: O'Laighin
authors.forename: Jorge M
authors.initials: JM
authors.lastname: Serrador
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D015992:Body Mass Index; D001921:Brain / Q000098:blood supply*; D002245:Carbon Dioxide / Q000378:metabolism; D002560:Cerebrovascular Circulation; D015331:Cohort Studies; D004562:Electrocardiography / Q000379:methods; D005260:Female; D006801:Humans; D008297:Male; D054971:Orthostatic Intolerance / Q000453:epidemiology* / Q000473:pathology; D011446:Prospective Studies; D012307:Risk Factors; D012737:Sex Factors; D018608:Ultrasonography, Doppler / Q000379:methods
chemical_list: D002245:Carbon Dioxide