Optical Sensors

A fibre grating is an in-fibre device that consists of a periodic change in refractive index and/or geometry of the fibre. It resonantly scatters the core-guided light to other core and cladding fibre modes, thus forming characteristic resonant bands in the transmission and reflection spectra. Gratings are usually divided into fibre Bragg gratings (FBGs) and long-period gratings (LPGs). Fibre Bragg gratings (period of several hundred nanometers) are designed to couple light from the fundamental core mode into a back-propagating core-mode. Their resonances are observed as narrow peaks in reflection or as the corresponding attenuation bands in transmission spectrum. Long-period gratings (period from tens to hundreds of microns) scatter light from the fundamental core mode to co-propagating lossy modes of the cladding thus producing resonant attenuation bands in transmission spectrum.

Changes in environmental parameters or forces applied to the grating can cause changes in the magnitude and/or central wavelength of its resonant band. These easily measurable changes in the grating spectrum give information on the magnitude of the disturbance. Based on this principle numerous fibre-grating sensors of temperature, concentration, humidity, pressure, strain, curvature, etc. have been constructed. We use LPG and FBG sensors of global and local grating curvatures to measure physiological pulsations relevant to the respiratory and cardiac human body functions.

This work is done in collaboration with the Aston Institute of Photonics Technologies, UK

Optical Sensors in Pulmnology

We have devised a novel sensing scheme for the real-time monitoring of lung volume and the measurement of tidal and minute volumes during mechanical ventilation. The scheme is based on a long-period grating fibre-optic sensor of bending and the assumption of the correlation between the local torso curvature and the lung volume. By applying a two-step calibration-test measurement procedure to a series of healthy volunteers, we have found that this correlation is linear in the normal breathing range. The demonstrated technique is not affected by air-leaks and drifts that are limiting factors in the currently used air-flow measurement methods.

Moreover, a method of directly monitoring the lung volume of patients would provide a non-pneumatic ventilator trigger independent on air leaks. The ventilator trigger defines the timing of the pump activation and is crucial for achieving patient-ventilator synchronization and hence effective and nonabrasive ventilation.

Optical Sensors in Cardiology-POLYCARDIOGRAPH

Polycardiograf (PCG) is a novel device for advanced diagnostics of heart diseases and in particular the heart failure (HF). The heart failure is a fatal, disabling, difficult to diagnose and expensive condition which occurs when the heart’s pumping power is reduced. Only a timely diagnosis and treatment can stop its progression and save the patient. However, a diagnostic test suitable for screening does not exist. On one hand, in its early stages the disease cannot be detected by the standard screening ECG test. On the other hand, the golden standard HF diagnostic test, echocardiograph, has the prohibitively high cost to be used as a screening test. As a consequence, HF is often diagnosed too late to stop the process and save the patient. Finally, figures show that the treatment of the late-stage HF is the most expensive treatment in medicine, while the cost of a treatment of an early-stage HF is significantly lower.

Polycardiograph is our solution to this challenge.

The PCG is based on integration of fibre-grating sensors of cardiovascular pulsations on the surface of the human body with two conventional diagnostic technologies, electrocardiograph (ECG) and phonocardiograph. Analysis of the combined mechanical (gratings and phono) and electrical (ECG) signals enables measurement of ejection fraction - the volumetric fraction of blood pumped out of the heart in each cycle. A reduced ejection fraction is the principal indicator of heart failure.

Polycardiografic test will be accurate, non-invasive, fast (5 min), operator-independent and low-cost. If proven capable of measuring the ejection fraction, it will become the optimal candidate for an HF diagnostic test in primary care.

This work is realized within the project Multi-SENSor SysteM and ARTificial intelligence in service of heart failure diagnosis (SensSmart) funded by Science fund of the Republic of Serbia, IDEAS, Grant No. 7754338 (1. 4. 2022 – 31. 3. 2025)