The Haemodynamic Instability Score (HIS) for assessment of cardiovascular reactivity in hypertensive and normotensive patients.
The normal response to postural challenge is characterised by maintenance of relatively stable blood pressure (BP) and heart rate (HR) after 30 sec to 30 min of head-up tilt. The objective of the present study was to determine the degree of instability of cardiovascular responses to postural challenge in normotensive and hypertensive subjects. In the initial phase of the study, two groups of age and sex-matched subjects were assessed: essential hypertension (n = 20) and healthy (n = 37). The BP and HR were recorded at 5-min intervals during the course of the 10-min supine-30-min head-up tilt test (HUTT). We categorised 'BP-change' as the difference between individual BP measurements during HUTT and the last recumbent BP value, divided by latter value. The average and standard deviation (SD) of the recorded BP changes were calculated, and BP changes were plotted along a time curve. A computerised image analyser then calculated the outline ratio (OR) and fractal dimension (FD) values for each of the curves. An identical process evaluated measurements for HR-changes. BP- and HR-changes were then converted into absolute numbers, and the average, SD, OR, and FD were calculated. A multivariate analysis was conducted, evaluating independent predictors of hypertension. Finally, an equation for the calculation of 'haemodynamic instability score' (HIS) was deduced and a cut-off between HIS of hypertensive and normotensive subjects was established. Independent predictors of the cardiovascular response to postural challenge of hypertensives (Group I) vs healthy (Group II) were: a.DIAST-FD, a.HR-AVG, a.HR-SD, a.HR-FD, DIAS-SD and HR-SD and HR-SD. Based on these five predictors, a linear discriminant score was computed and called the Haemodynamic Instability Score (HIS): HIS = 59.4 + (-16.6*a.DIAST-FD) + (-29.0*a.HR-AVG) + (-82.4*a.HR-SD) + (-30.1*a.HR-FD) + (-57.9*DIAS-SD) + (73.4*HR-SD) The HIS values in Group I (hypertensives) were: avg = 3.348, SD = 2.863, and 95% CI for mean = 2.008, 4.688. The HIS values in Group II (healthy) were: avg = -3.394, SD = 2.435, 95% CI for mean = -4.206, -2.582. Values of the HIS > -2.09 were generally observed in hypertensives (sensitivity 95%) and values < or = -2.09 were usually seen in the healthy (specificity 81.1%). The HIS was cross-validated in an additional group of hypertensive patients (n = 73). In the latter group, the HIS values were: avg = -0.456, SD = 4.403, 95% CI for mean = -1.506, 0.593 and 71.4% sensitivity at the proposed cut-off point. In conclusion, the HIS confers numerical expression to the degree of lability of BP and HR during postural challenge. Based on this score, a distinction between the cardiovascular reactivity of hypertensives vs normotensives is drawn. Possible applications of HIS are discussed.
Naschitz
J E
JE
Department of Internal Medicine A, Bnai Zion Medical Center and Bruce Rappaport Faculty of Medicine, Technion-Israel Institute of Technology, Haifa, Israel.
Sabo
E
E
Gaitini
L
L
Ahdoot
A
A
Ahdoot
M
M
Shaviv
N
N
Musafia-Priselac
R
R
Rosner
I
I
Eldar
S
S
Yeshurun
D
D
D000328:Adult; D001794:Blood Pressure / Q000502:physiology*; D002320:Cardiovascular Physiological Phenomena; D005260:Female; D018475:Head-Down Tilt / Q000502:physiology; D006339:Heart Rate / Q000502:physiology*; D006439:Hemodynamics / Q000502:physiology*; D006801:Humans; D006973:Hypertension / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D012107:Research Design; D016683:Supine Position / Q000502:physiology