Development and evaluation of new blood pressure and heart rate signal analysis techniques to assess orthostatic hypotension and its subtypes.

Orthostatic hypotension (OH) is a clinical condition, which frequently results in symptoms such as syncope, dizziness during standing, weakness, blurred vision and fatigue. It is defined as a sustained drop in blood pressure exceeding 20 mmHg systolic or 10 mmHg diastolic occurring within 3 min of assuming upright posture, and is a common causal factor for falls in the elderly. Since 1986, tilt-table testing has become widely used in the diagnosis of OH. The Finometer provides non-invasive monitoring of haemodynamic changes during tilt-table testing. In this study, new algorithms for parameter extraction from Finometer data were developed, with specific reference to the diagnosis of OH. Algorithms were developed to assess the rates of change of haemodynamic variables in response to head-up tilt testing, a previously unexamined aspect of tilt-table testing. These algorithms were applied to the Finometer measurements of 20 patients, who underwent tilt-table testing in the Mid-Western Regional Hospital, Limerick. The data extraction algorithms were shown to accurately record changes in haemodynamic variables for further analysis. It was also demonstrated that the rate of change of blood pressure during the head-up tilt-table testing could have prognostic significance for OH.

Orthostatic hypotension: a new classification system.

AIMS: 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. METHODS AND 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). CONCLUSION: This is a practical classification tool and when validated physiologically, this system could be useful in directing treatment of OH.