Exploring the Efficacy of Piezoelectric-Based Sensory Systems for Heart Rate Monitoring in Differentiating Stress vs. Relax Conditions
Authors: Zulkifli Muhammad Hafiz Zulhilmi , Jasni Farahiyah , Ghazali Aimi Shazwani , Nordin Nor Hidayati Diyana , Sidek Shahrul Na'im , Shaharum Syamimi Mardiah , Kamaru Zaman Fadhlan Hafizhelmi 
Published: July 2024

Stress has diverse effects on human physiological reactions, and one such effect is on heart rate (HR). The established methods to acquire HR is by electrocardiogram (ECG) and photoplethysmogram (PPG). ECG electrodes need to be placed on the chest, which can cause inconvenience and is not practical in daily life, while PPG signals are known to contain more noise than ECG. Thus, this work aims to investigate the efficacy of a piezoelectric-based sensory system in measuring HR and using the signal to differentiate stressed and relaxed conditions by means of statistical analysis. Two activities were conducted to achieve the goal. The first experiment involved collecting and analysing piezoelectric signals to measure the pulse rate (bpm) and compare this with the HR from PPG. For the second experiment, the piezoelectric-based HR was calculated from 20 subjects (male and female, age ranging between 20 and 25) in relaxed and stressed conditions. The stress condition was triggered using two stressors: the Stroop Colour Word Test and the Digit Span Test. Statistical analyses reveal a strong positive correlation between piezoelectric-based heart rate (HR) and oximeter readings (r(12) = 0.993, p < 0.001), despite the fact that the values are not precisely identical. In addition, the findings also indicate that there are significant effects by the mental states (stressed and relaxed) on the piezoelectric-based HR readings (p<0.05). Employing a within-subject design condition, the results further illustrated that piezoelectric readings are elevated during stressed conditions (Mean±SD = 72.395±0.097) and diminished during relaxed conditions (Mean±SD = 71.615±0.126). Therefore, the suggested piezoelectric-based sensory system has been validated as an effective means of categorizing stress and relaxation based on heart rate signals.
ABSTRAK: Tekanan mempunyai pelbagai kesan terhadap reaksi fisiologi manusia dan satu daripadanya adalah kadar denyut jantung (HR). Kaedah biasa bagi mengetahui HR adalah melalui elektrokardiogram (ECG) dan fotofetismogram (PPG). Elektrod ECG perlu dipasang pada dada di mana boleh menyebabkan ketidakselesaan dan tidak praktikal dalam kehidupan seharian, manakala isyarat PPG diketahui mengandungi lebih banyak bunyi berbanding ECG. Oleh itu, kajian ini bertujuan mengkaji kecekapan ystem deria berdasarkan piezoeletrik bagi mengukur HR dan menggunakan isyarat ini bagi membezakan keadaan tertekan atau tenang melalui cara analisis ystemic. Bagi mencapai tujuan ini, dua aktiviti dijalankan. Pertama eksperimen melibatkan pengumpulan dan analisis isyarat piezoeletrik bagi mengukur kadar nadi (bpm) dan membandingkan HR daripada PPG. Eksperimen kedua, HR berdasarkan piezoelektrik dikira dari 20 subjek (lelaki dan ystemic, berumur antara 20 dan 25) dalam keadaan tenang dan tertekan. Keadaan tertekan dibuat melalui dua ystemi: Ujian Stroop Patah Warna dan Ujian Rentang Digit. Analisis ystemic mendedahkan hubungkait yang kuat antara kadar denyut jantung (HR) berdasarkan piezoeletrik dan bacaan oksimeter (r(12) = 0.993, p < 0.001), walaupun bacaan tidak benar-benar serupa. Tambahan, penemuan ini menunjukkan terdapat kesan penting terhadap tahap mental (tertekan dan tenang) pada bacaan denyut jantung (HR) berdasarkan piezoeletrik (p<0.05). Dengan mengaplikasi keadaan reka bentuk subjek, dapatan menunjukkan bacaan piezoeletrik meningkat ystem keadaan tertekan (Mean±SD = 72.395±0.097) dan kurang ystem keadaan tenang (Mean±SD = 71.615±0.126). Oleh itu, ystem deria berdasarkan piezoeletrik telah diuji berkesan dalam mengkategori keadaan tertekan dan tenang berdasarkan isyarat denyut jantung.