A Novel Smartphone App for the Measurement of Ultra-Short-Term and Short-Term Heart Rate Variability: Validity and Reliability Study

Author: Yung-Sheng Chen1, Wan-An Lu2, Jeffrey C Pagaduan3, Cheng-Deng Kuo4 5
1 Department of Exercise and Health Sciences, University of Taipei, Taipei, Taiwan.
2 Institute of Cultural Asset and Reinvention, Fo-Guang University, Yilan, Taiwan.
3 College of Health and Medicine, School of Health Sciences, University of Tasmania, Launceston, Australia.
4 Department of Medical Research, Taipei Veterans General Hospital, Taipei, Taiwan.
5 Tanyu Research Laboratory, Taipei, Taiwan.
Conference/Journal: JMIR Mhealth Uhealth
Date published: 2020 Jul 31
Other: Volume ID: 8 , Issue ID: 7 , Pages: e18761 , Special Notes: doi: 10.2196/18761. , Word Count: 405

PMID: 32735219 DOI: 10.2196/18761 Free article Abstract Background: Smartphone apps for heart rate variability (HRV) measurement have been extensively developed in the last decade. However, ultra-short-term HRV recordings taken by wearable devices have not been examined. Objective: The aims of this study were the following: (1) to compare the validity and reliability of ultra-short-term and short-term HRV time-domain and frequency-domain variables in a novel smartphone app, Pulse Express Pro (PEP), and (2) to determine the agreement of HRV assessments between an electrocardiogram (ECG) and PEP. Methods: In total, 60 healthy adults were recruited to participate in this study (mean age 22.3 years [SD 3.0 years], mean height 168.4 cm [SD 8.0 cm], mean body weight 64.2 kg [SD 11.5 kg]). A 5-minute resting HRV measurement was recorded via ECG and PEP in a sitting position. Standard deviation of normal R-R interval (SDNN), root mean square of successive R-R interval (RMSSD), proportion of NN50 divided by the total number of RR intervals (pNN50), normalized very-low-frequency power (nVLF), normalized low-frequency power (nLF), and normalized high-frequency power (nHF) were analyzed within 9 time segments of HRV recordings: 0-1 minute, 1-2 minutes, 2-3 minutes, 3-4 minutes, 4-5 minutes, 0-2 minutes, 0-3 minutes, 0-4 minutes, and 0-5 minutes (standard). Standardized differences (ES), intraclass correlation coefficients (ICC), and the Spearman product-moment correlation were used to compare the validity and reliability of each time segment to the standard measurement (0-5 minutes). Limits of agreement were assessed by using Bland-Altman plot analysis. Results: Compared to standard measures in both ECG and PEP, pNN50, SDNN, and RMSSD variables showed trivial ES (<0.2) and very large to nearly perfect ICC and Spearman correlation coefficient values in all time segments (>0.8). The nVLF, nLF, and nHF demonstrated a variation of ES (from trivial to small effects, 0.01-0.40), ICC (from moderate to nearly perfect, 0.39-0.96), and Spearman correlation coefficient values (from moderate to nearly perfect, 0.40-0.96). Furthermore, the Bland-Altman plots showed relatively narrow values of mean difference between the ECG and PEP after consecutive 1-minute recordings for SDNN, RMSSD, and pNN50. Acceptable limits of agreement were found after consecutive 3-minute recordings for nLF and nHF. Conclusions: Using the PEP app to facilitate a 1-minute ultra-short-term recording is suggested for time-domain HRV indices (SDNN, RMSSD, and pNN50) to interpret autonomic functions during stabilization. When using frequency-domain HRV indices (nLF and nHF) via the PEP app, a recording of at least 3 minutes is needed for accurate measurement. Keywords: autonomic nervous function; heart rate variability; limits of agreement; reproducibility; smartphone. ©Yung-Sheng Chen, Wan-An Lu, Jeffrey C Pagaduan, Cheng-Deng Kuo. Originally published in JMIR mHealth and uHealth (http://mhealth.jmir.org), 31.07.2020.