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 o f relatively stable brood pressure (BP) and heart rate (HR) after 30 sec to 30 min of head-up tilt. The objective of the present study was to determin e the degree of instability of cardiovascular responses to postural challen ge in normotensive and hypertensive subjects. In the initial phase of the s tudy, two groups of age and sex-matched subjects were assessed: essential h ypertension (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 t est (HUTT). We categorised 'BP-change' as the difference between individual BP measurements during HUTT and the last recumbent BP value, divided by la tter value. The average and standard deviation (SD) of the recorded BP chan ges were calculated, and BP changes were plotted along a time curve. A comp uterised image analyser then calculated the outline ratio (OR) and fractal dimension (FD) values for each of the curves. An identical process evaluate d measurements for HR-changes. BP- and HR-changes were then converted into absolute numbers, and the average, SD, OR, and FD were calculated. A multiv ariate analysis was conducted, evaluating independent predictors of hyperte nsion. Finally, an equation for the calculation of 'haemodynamic instabilit y score' (HIS) was deduced and a cut-off between HIS of hypertensive and no rmotensive subjects was established. Independent predictors of the cardiova scular 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, DIASSD 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) we re: avg = 3.348, SD = 2.863, and 95% CI for mean = 2.008, 4.688. The HIS va lues 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 hyperten sives (sensitivity 95%) and Values less than or equal to -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, t he HIS values were: avg = -0.456, SD = 4.403, 95% CI for mean = -1.506, 0.5 93 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 dur ing postural challenge. Based on this score, a distinction between the card iovascular reactivity of hypertensives vs normotensives is drawn. possible applications of HIS are discussed.