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Monika Danielewska, D Robert Iskander, Visual Optics Group; Assessing the influence of cardiovascular signals on ocular pulse. Invest. Ophthalmol. Vis. Sci. 2013;54(15):30.
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© ARVO (1962-2015); The Authors (2016-present)
To evaluate the effect of blood pulsation and electrical heart activity on ocular pulse.
A new robust method to measure ocular pulse as corneal indentation pulse (CIP) has been proposed. CIP amplitude has been registered noninvasively with an innovative ultrasonic distance sensor working at a frequency of 0.8 MHz. To examine the heart activity, continuous measurements of signals: blood pulsation (BPL) and electrocardiogram (ECG) were taken synchronically with pulseoximeter placed on the right earlobe and in a standard three-lead system (Einthoven’s triangle), respectively. Considered signals are nonstationary meaning their frequency spectra vary in time caused mainly by heart rate variability. A way to resolve this problem is to use Discrete Time Warping (DTW) algorithm, which we applied to averaging signal shapes. Shape parameters included the time delays between: systolic BPL peak and CIP maximum, τ(BPL, maxCIP), R wave peak of ECG and CIP maximum, τ(ECG, maxCIP), R wave peak to systolic BPL peak, τ(ECG, BPL) and the crest time (CT) - time taken from CIP minimum to CIP maximum. Correlation analysis was used to identify the interactions between shape parameters of the averaged signals for all subject measurements.
It was observed that increase in τ(BPL, maxCIP) corresponds to an increase in CT (r=0.83, p<0.001) and in τ(ECG, maxCIP) (r=0.91, p<0.001). However, no significant correlation was found for the time delays calculated between τ(ECG, maxCIP) and τ(ECG, BPL) (r=0.22, p=0.19).
A new way to estimate time delays between CIP, BPL and ECG signals was proposed. The results revealed that CIP is affected by the blood inflow and electrical heart activity. These relationships confirmed that ECG, in addition to the indirect influence via blood pulsation, independently affects the CIP (see Figure). It points to a role the ECG signal may play in the ocular pulse phenomenon. The proposed noninvasive technique of ocular pulse measurement and robust method of analysis may lead in future to a tool for the assessment of ocular hemodynamics and diagnosis of ocular vascular diseases.
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