Continuous cardiac baroreceptor measurement during tilt in healthy elderly subjects

Abnormalities of cardiac baroreceptor sensitivity (BRS) may contribute towards the high prevalence of orthostatic hypotension and falls in the elderly. Most mathematical analyses used to determine BRS in the time or frequency domains assume a stationary physiological state and cannot be performed under dynamic change and therefore are not valid during tilt. We describe a new method of estimating BRS during tilt.

Twenty-five healthy elderly volunteers with a mean age of 69 +/- 3 years underwent head-up tilt to 70 degrees, within 5 s, 3 times on 2 separate visits. Blood pressure (BP) and heart rate were recorded continuously using a Finapres beat-to-beat BP monitor and surface ECG. A continuous estimate of BRS was obtained by combining beat-to-beat linear regression with Legendre polynomial interpolation.

The values for supine BRS prior to tilt on the two visits, calculated using the new regression method (10.4 +/- 8.2 ms/mmHg and 12.5 +/- 9.7 ms/mmHg) were similar to those using fast Fourier analysis (10.7 +/- 6.7 ms/mmHg and 12.4 +/- 7.1 ms/mmHg). A rapid fall in BP and pulse interval along with cardiac BRS values occurred with tilt within the first 20 s of onset on both visits and remained reduced up to 90 s post tilt (p < 0.01).

The values for cardiac BRS obtained using continuous time domain analysis agree well with those calculated using spectral methods and can be used to assess the dynamic changes in BRS to rapid perturbations in BP such as that occur with tilt.