Vrije Universiteit Ambulatory Monitoring System: Quo vadis?

E.J.C. de Geus¹, J. den Hartog² and P.F.C. Groot²

¹Department of Biological Psychology, Vrije Universiteit, Amsterdam, The Netherlands
²Department of Instrumentation (ITM), Vrije Universiteit, Amsterdam, The Netherlands

The Vrije Universiteit Ambulatory Monitoring System (VU-AMS) plays a key role in the cardiovascular research of the department of Biological Psychology and The Netherlands Twin Registry on the (interactive) influence of genetic and environmental factors (e.g. chronic stress) on cardiovascular disease risk. This ongoing scientific demand from within has maintained the VU-AMS in a continuous state of innovation since its first prototypes in the early 1990’s. This demand for continuous innovation is reinforced by the over 40 external research groups that use the VU-AMS world-wide. To meet this demand, we will release the first VU-AMS of the new 5fs-series in the fall of 2005. The new full storage VU-AMS (version 5fs.1) will continuously record the ECG, thorax impedance and (optionally) skin conductance and store these to flash memory. The new version will not lead to a change in the main VU-AMS philosophy of rapid data-reduction based on ensemble averaging over labeled periods. Ensemble averaged values over the relevant labeled periods will still be extracted in as short a time frame as possible without compromising full visual interactive control over signal scoring. Put otherwise, the device will be downward compatible to existing software and data analysis strategies. The new device tops the old one, however, on three major accounts. A number of new variables can be extracted including the T-wave amplitude and QT interval variability (both indices of sympathetic drive that are less dependent on pre- and afterload), convergence of skin conductance and thorax impedance changes (can now jointly measured by a single device), and fourier- or wavelet-based frequency decomposition of the variance in heart period and respiration signals. Secondly, because memory is .ash-card based, repeated 24-hour measurements on the same subject can be scheduled by minimal contact of the researcher with the participant/patient. Finally, availability of continuous data sampled at a much higher frequency (1000 Hz) than before will allows us to reduce measurement error and increase automaticity of scoring of the impedance cardiogram (ICG) and the respiration signal.

Paper presented at Measuring Behavior 2005 , 5^th International Conference on Methods and Techniques in Behavioral Research, 30 August - 2 September 2005, Wageningen, The Netherlands.

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