title: Orthostatic hypotension: a new classification system.
abstract: OBJECTIVE
  Orthostatic hypotension (OH) is a common condition, which is defined as a reduction in systolic blood pressure of >or=20 mmHg or diastolic blood pressure of >or=10 mmHg within 3 min of orthostatic stress. Utilizing total peripheral resistance (TPR) and cardiac output (CO) measurements during tilt-table testing (Modelflow method), we classified OH into three categories, namely arteriolar, venular, and mixed. The principle defect in arteriolar OH is impaired vasoconstriction after orthostatic stress, reflected by absence of the compensatory increase in TPR. In venular OH, the predominant defect is excessive reduction in venous return, reflected by a large drop in CO after orthostatic stress with marked tachycardia. Mixed OH is due to a combination of both these mechanisms.
  
  
  RESULTS
  We analysed haemodynamic parameters of 110 patients with OH and categorized them as arteriolar, venular, or mixed. Significant differences between the groups were found for the magnitude and time to reach nadir of the systolic blood pressure drop post-head-up tilt. The mixed OH category had the largest systolic blood pressure reduction (42.5, 31.9, 53.3 mmHg, P < 0.001) and the longest nadir time (18.6, 20, 30.7 s, P = 0.002).
  
  
  CONCLUSIONS
  This is a practical classification tool and when validated physiologically, this system could be useful in directing treatment of OH.
authors.affiliation: Department of Electronic Engineering, National University of Ireland, Galway, Galway, Ireland. briandeegan@oceanfree.net
authors.forename: B M T
authors.initials: BM
authors.lastname: Deegan
authors.forename: M
authors.initials: M
authors.lastname: O'Connor
authors.forename: T
authors.initials: T
authors.lastname: Donnelly
authors.forename: S
authors.initials: S
authors.lastname: Carew
authors.forename: A
authors.initials: A
authors.lastname: Costelloe
authors.forename: T
authors.initials: T
authors.lastname: Sheehy
authors.forename: G
authors.initials: G
authors.lastname: OLaighin
authors.forename: D
authors.initials: D
authors.lastname: Lyons
mesh_terms: D000368:Aged; D016477:Artifacts; D001794:Blood Pressure; D002302:Cardiac Output; D002309:Cardiology / Q000379:methods; D006339:Heart Rate; D006801:Humans; D007024:Hypotension, Orthostatic / Q000145:classification* / Q000175:diagnosis*; D008875:Middle Aged; D008954:Models, Biological; D013575:Syncope; D018667:Tilt-Table Test; D013997:Time Factors; D016896:Treatment Outcome; D014661:Vasoconstriction