Correlations between Longitudinal Corneal Apex Displacement, Head Movements and Pulsatile Blood Flow

Abstract

Determination of the phase dependencies between longitudinal corneal apex displacement (LCAD), anterio-posterior (AP) head displacements and pulsatile blood flow, using the cross-correlation function, was the main goal of our investigation. We have proposed a noninvasive method to measure signals LCAD and head movements using two ultrasonic distance sensors. Synchronically, the blood pulsation was registered with pulsoxymeter. We calculated the phase relationship between particular signals for the first four harmonics associated with the heart rate. In this paper we presented results obtained for the 3rd harmonic because of the highest value of the coherence function. We applied the time window in calculation of the correlation function due to the nonstationary nature of analyzed signals. The length of this window was selected for each harmonics. It allowed to observe more details in phase shift variations in time. Results show that the time shift between LCAD and pulse, as well as between head movements and pulse exist. We can notice more clear relationship for pair of signals: AP head displacements and blood pulsation. Obtained data are not sufficient enough to explain influence the blood pulsation on the ocular pulse. But proposed method might be helpful to acquire information about this phenomenon.