The broad objective is to examine the degree to which the regulation of blood pressure and heart rate changes during orthostatic stress can be modified by biofeedback and voluntary control procedures. A non-invasive tracking cuff system is used to measure systolic and diastolic blood pressure continuously while heart rate and respiration are simultaneously monitored. Healthy volunteers and patients with orthostatic hypotension are studied in sitting and standing conditions and while going from a sitting to a standing position. Blood pressure and/or heart rate feedback is presented to subjects by means of a computer display indicating beat-to-beat changes which may be compared with baseline or previous performance.
The specific aims are to examine in healthy subjects the degree to which postural cardiovascular changes can be controlled """"""""voluntarily"""""""", whether feedback is more effective than simple instructions only, whether different types of feedback procedures have different effects, how feedback results compare with the effects of other mental and physical strategies, whether control can be improved with repeated practice, and how orthostatic regulation varies according to age. Diabetic patients will be studied to characterize their degree of neuropathy using various tests of autonomic function, e.g. Valsalva, paced respiration, handgrip. A detailed examination will be made of the patients' response to orthostatic stress by itself and in combination with concurrent mental arithmetic and with concurrent handgrip. Out of this sample, patients will be selected with the most severe orthostatic hypotension to participate in a controlled clinical outcome study to determine whether the degree of hypotension can be modified by a biofeedback training method. Finally, several methodological issues will be investigated: comparison of different methods of assessing and quantifying arterial baroreceptor sensitivity, refinements in the blood pressure tracking system.
