Design and construction of a non-invasive blood glucose and heart rate meter by photoplethysmography

Abstract

This article describes the design and construction of a non-invasive blood glucose and heart rate meter that can non-invasively measure blood glucose level and heart rate from the fingertip.  This device operates on the principle of light absorption, known as the Beer-Lambert Law, tracking changes in near-infrared light absorbance of blood glucose with blood volume changes in a photoplethysmogram (PPG) using opto-electronics.  The design incorporates near-infrared 950 nm wavelength and red 630 nm wavelength LED light sources and a photodiode light receiver.  An Arduino NANO 3.0 Mini USB microcontroller was used for signal processing, enabling the meter to compute blood glucose levels in the range of 70 to 130 mg/dL and measure heart rate across the range of 60 to 100 bpm.  To validate the effectiveness of this device, it was used by a sample group of diabetic patients at the Endocrine Unit, Faculty of Medicine, Vajira Hospital.  The results of device evaluation compared with standard clinical measurements were as follows: 1) The non-invasive blood glucose meter accurately measured blood sugar levels in the range of 75 to 150 mg/dL (R² = 0.99); 2) Across the ranges of 75 to 130 mg/dL and 131 to 289 mg/dL the device had average percentage error of 3.18% and 22.14%, respectively and the overall average percentage error was 10.76%; 3) Heart rate measurements from 60 to 100 bpm showed a mean percentage error of 2.94%, and these were not statistically different from a vital sign monitor (p= 0.222), and 4) Although readings from the meter appeared to be systematically lower than results of standard blood tests, this was not a statistically significant difference (p= 0.135).  Overall, these findings indicate that this non-invasive blood glucose meter may be suitable for non-critical patient monitoring applications where patient comfort and convenience are important considerations.