Haemodynamic effects of increasing angle of head up tilt

Abstract

Objective-To investigate the haemodynamic eVects of varying the angle of head up tilt. Methods-20 healthy subjects (12 female, eight male; mean (SD) age 33.6 (8.4) years) underwent head up tilt for five minutes to each of four angles of tilt in random order, with a five minute rest period at the horizontal between each angle. Forearm blood flow was measured using intermittent occlusion mercury strain gauge plethysmography at two and five minutes. Subjects underwent continuous monitoring of heart rate, systolic blood pressure (SBP), and diastolic blood pressure (DBP) by Finapres and cardiac output and stroke volume by impedance cardiography. Each variable was measured at two and five minutes, averaged over the period of blood flow measurement. Results-Every haemodynamic variable at each angle was significantly diVerent from supine values. Head up tilt produced progressive increases in heart rate (11-21%), SBP (12-21%), and DBP (20-33%) with increasing tilt angle. However, although 45°produced significantly less haemodynamic eVect, there were no significant diVerences for angles between 60°and 90°. Cardiac output fell on head up tilt by 17-20% and stroke volume by 28-34%, but increasing tilt angle produced no significant additional reduction in cardiac output and stroke volume because of increases in heart rate and vasoconstriction. Conclusions-Angles < 60°produce significantly less haemodynamic eVects than steeper angles. Increasing tilt angle beyond 60°produces no apparent additional eVect on cardiac output or sympathetic tone. Increasing tilt angle beyond 60°confers no additional orthostatic stress and may not aVect the sensitivity and specificity of head up tilt testing as previously thought. Sixty degrees of tilt is a more practical angle for support of a syncopal patient and is recommended.

Entropy in Investigation of Vasovagal Syndrome in Passive Head Up Tilt Test

“…We also observed a statistically significant decrease in stroke volume (SV) just after the tilt and before the loss of consciousness. The decrease in SV after tilting was also reported by other researchers [44][45][46]. The decrease in SV before the loss of consciousness directly preceded syncope.…”

The Relation Between Venous Reserve Capacity and Low Plasma Volume

“…10,19,20 Women with LPV who could tolerate head-up tilt showed a consistently higher HR and a lower SV, but no differences in response pattern, during head-up tilt when compared with the NPV group.These results suggest a resetting of the hemodynamic system in LPV women toward a higher sympathetic level without affecting the magnitude of rapid corrective autonomic responses.…”

Quantification of the distribution of blood flow pressure with postures

“…Hemodynamic variables, such as SBP/DBP, are significantly different from supine values at each tilting angle [5]. Head up tilt has produced progressive increases in SBP (12% -21%) and DBP (20% -33%) with increasing tilt angle.…”

“…There are two main types of methods. One is test method [4][5][6][7], and the other is modeling and simulation one [2,[8][9][10]. Olufsen et al [2] performed the study of blood pressure and blood flow variation during the postural change from sitting to standing by presenting a mathematical model.…”