An Eddy Current System for the Study of the Cranial Rhythmic Impulse

The cranial rhythmic impulse (CRI) is an important osteopathic medicine concept that refers to the health of the individual. The technique of the eddy current (EC) sensors has the advantage to be directly sensitive to the CRI. In this paper, we present an EC system dedicated to the measurement of the CRI. To detect the CRI, a flexible aluminum foil covered with an adhesive layer is placed on the crane of the patient. The oscillations of the aluminum sheet induced by the CRI are detected by a dedicated EC sensor constituted of a printed coil. The sensing coil is put with an identical reference coil in an ac bridge. The bridge output voltage is analyzed with a lock-in amplifier. A spectral analysis is done on the output signal obtained after a 2 min long record on a patient. Different signals can be observed: 1) cardiac signal; 2) respiration signal; and 3) baroreflexe signal, showing the capability of the EC system in the analysis of the CRI.

I. Introduction

Many physiological changes happen rhythmically or cyclically within the human body [1]. Some of these rhythm fluctuations and their frequencies have been associated with physiological phenomenon. For example, studies using laser Doppler flowmetry showed that signal of 0.02 Hz frequency has been associated to thermoregulation [2], [3]. Signals of 0.1 and 0.25 Hz frequencies have been associated to baroreflexe [1], [2]. Signal of Hz frequency could be associated to thermoregulation [2], [3]. Some of these rhythms may be observed by practitioners on cranial and sacrum anatomical parts of the subject using osteopathic palpations [2]. These palpations rely on the cranial field of osteopathy originally described in [4] and [5]. This osteopathic science and practice assumed that other pulses could be observed using palpation, such as cerebrospinal fluid motion and bones, cranial sutures [1]. To our knowledge, few studies have proved a good reliability between cranial rhythmic impulse (CRI) observed by different osteopaths palpations and objective measurements [1], [2]. One argues that skull motion of very low amplitude (<0.3 mm) remains difficult to assess for researchers [1].