title: The impact of age on vascular smooth muscle function in humans.
abstract: OBJECTIVE
  Advanced age is associated with vascular endothelial dysfunction, characterized by reductions in the endothelium-dependent vasodilation of the conduit and resistance arteries, in part, from decreased nitric oxide bioavailability. Although vascular smooth muscle function (SMF), assessed by responsiveness to an exogenous nitric oxide donor, is typically reported to be intact, many of these studies are limited by a small sample size. Therefore, the purpose of this meta-analysis is to systematically review and determine whether vascular SMF is different between older versus young healthy individuals.
  
  
  METHODS
  We conducted a systematic search of MEDLINE, Cochrane and Scopus, since their inceptions until January 2014, for articles evaluating SMF in the brachial artery and/or resistance arteries (BASMF and RASMF, respectively), as assessed by the endothelium-independent vasodilator response to exogenous nitric oxide donors in older (≥60 years) and young (<30 years) groups of healthy individuals. Meta-analyses were performed to compare the mean difference in BASMF and the standardized mean difference in RASMF between older and young groups. Subgroup analyses were performed to identify sources of heterogeneity.
  
  
  RESULTS
  Fifteen studies assessing BASMF and 20 studies assessing RASMF were included, comprising 550 older and 516 young healthy individuals. After data pooling, BASMF and RASMF were lower in older compared with the young groups (mean difference = -1.89%, P = 0.04; standardized mean difference = -0.46, P = 0.0008, respectively). Significant heterogeneity was observed in the BASMF (I2 = 74%, P < 0.00001) and the RASMF (I2 = 57%, P = 0.0008) meta-analyses. Subgroup analyses revealed that studies with (predominantly) men showed similar SMF responses between the older and the young groups.
  
  
  CONCLUSIONS
  On the basis of the current published studies, vascular SMF is reduced in conduit and resistance arteries of otherwise healthy older individuals, particularly in women.
authors.affiliation: aDepartment of Internal Medicine, Maastricht University Medical Centre (MUMC) and Cardiovascular Research Institute Maastricht (CARIM), Maastricht, the Netherlands bDepartment of Health and Human Physiology, University of Iowa, Iowa City, Iowa cDepartment of Nutrition and Exercise Physiology dDepartment of Child Health eDalton Cardiovascular Research Center, University of Missouri, Columbia, Missouri, USA fDepartment of Physiology, Radboud University Medical Center, Nijmegen, the Netherlands gResearch Institute for Sport and Exercise Science, Liverpool John Moores University, Liverpool, UK.
authors.forename: David
authors.initials: D
authors.lastname: Montero
authors.forename: Gary L
authors.initials: GL
authors.lastname: Pierce
authors.forename: Coen D A
authors.initials: CD
authors.lastname: Stehouwer
authors.forename: Jaume
authors.initials: J
authors.lastname: Padilla
authors.forename: Dick H J
authors.initials: DH
authors.lastname: Thijssen
mesh_terms: D000375:Aging / Q000502:physiology*; D001916:Brachial Artery / Q000502:physiology; D006801:Humans; D009131:Muscle, Smooth, Vascular / Q000502:physiology*; D009569:Nitric Oxide; D020030:Nitric Oxide Donors; D014664:Vasodilation; D014665:Vasodilator Agents
chemical_list: D020030:Nitric Oxide Donors; D014665:Vasodilator Agents; D009569:Nitric Oxide