Abstract
Purpose :
To develop an independent algorithm for evaluating diurnal dimensional changes at the corneoscleral limbus area (CSLA) measured with the Triggerfish Contact Lens Sensor (TF-CLS) and to ascertain whether continuous 24-hour acquisition with this device can be clinically utilized for monitoring heart rate variability (HRV).
Methods :
The study involved 10 patients with primary open-angle glaucoma. 24-hour continuous monitoring of CSLA and ECG signals was performed with TF-CLS and Holter ECG, respectively. Raw TF-CLS and ECG data were numerically analysed in Matlab. Up to 288 CSLA signal packets sampled at 10 Hz for a period of 30 s at 5 min intervals were extracted, concatenating the median signal levels into a time series. Detrending of the median signal and best-sine wave fitting were performed. A corresponding time interval of the ECG recording was assigned. Using a time-domain-peak-detector a series of RR intervals and corresponding changes in time intervals between any two successive maxima of the CSLA packet were determined and used as the two estimators of the HRV within the packet. Further, spectral estimation of each pair of CSLA and ECG signals was performed to assess the correspondence between dimensional changes at CSLA and heart rate activity.
Results :
Estimation of the median signal level in each TF-CLS packet has been performed in a way to exclude sudden signal changes corresponding to blinks and other artefacts. The new methodology showed evident sine-wave diurnal dimensional changes at CSLA for all the subjects. Diurnal HRVs obtained from TF-CLS and ECG Holter were comparable. The highest frequency associated with the heart rate was confirmed in both CSLA and ECG spectra. However, such a close correspondence was difficult to identify in active time of a subject where the TF-CLS signal becomes noisier than that encountered in the resting time or sleep.
Conclusions :
Our study revealed that continuous 24-hour CSLA signals follow a sine-wave pattern typical to other diurnal changes in physiological measurements. TF-CLS can also be used as a potential clinical tool to monitor heart rate variability, particularly in a sleep period.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.