[Principle of the activity-controlled rate-adaptive cardiac pacemaker: analysis of stress and environment-induced mechanical effects on the human body].

Rate-adaptive pacemakers are increasingly becoming part of clinical routine, the most widespread systems being activity-controlled. In order to shed more light on the foundations of mechanical forces which can possibly be utilized for controlling rate-adaptive systems, we conducted tests on six healthy volunteers and six pacemaker patients. With the aid of three orthogonal wide-band linear acceleration pick-ups attached to the body, the mechanical signals were recorded from the three axes during different activities. Along with standardized exercise on bicycle and treadmill ergometers, we tested the influence of household activities and interference influences. The results were analyzed in terms of the amplitude and frequency content of the signals. For walking activities we found a signal amplitude increasing in largely linear fashion with the walking speed, the signal amplitudes being approximately twice as high on the vertical axis as on the other two axes. Exercise on the bicycle ergometer produced mechanical signals of clearly lower amplitude than comparable walking activities. The Fast-Fourier analysis showed amplitude peaks in the low frequency range of 1 to 4 Hz for all forms of physiological exercise, while interference influences showed amplitude peaks mainly in the range above 8 Hz. The use of an acceleration pickup and a corresponding low pass filter might be a way of reducing the effect of nonphysiological interference influences on an activity-controlled pacemaker system. A sensor measuring in the horizontal axis appears to be the most favorable compromise for the various types of exercise. However, due to the considerable difference in signal amplitude for different types of exercise of the same intensity, an activity-controlled pacemaker system cannot entirely meet metabolic conditions and requirements.