Compatibility of pulse–pulse intervals with R–R intervals in assessing cardiac autonomic function and its relation to risks of atherosclerosis

OBJECTIVE: Heart rate variability (HRV) analysis using electrocardiographic R–R intervals (RRIs) in either a time or a frequency domain is a useful tool for assessing cardiac autonomic dysfunction in clinical research. For convenience, pulse–pulse intervals (PPIs) acquired by photoplethysmography have been used to assess HRV. However, the compatibility of PPI with RRI is controversial. MATERIALS AND METHODS: In this study, we investigated the compatibility of PPI with RRI in five groups of participants, including nonoverweight young individuals with a body mass index (BMI) <24 kg/m(2) (Group 1, n = 20, aged 18–40 years), overweight young individuals with a BMI ≥24 kg/m(2) (Group 2, n = 13, aged 21–38 years), nonoverweight upper middle-aged individuals with a BMI <24 kg/m(2) (Group 3, n = 21, aged 45–89 years), overweight upper middle-aged individuals with a BMI ≥24 kg/m(2) (Group 4, n = 14, aged 43–74 years), and diabetic patients with a BMI ≥24 kg/m(2) (Group 5, n = 19, aged 35–74 years). We then used cross-approximate entropy (CAE) to assess the compatibility between RRI and PPI and analyzed HRV in the time and frequency domains derived from PPR and RRI with traditional methods. RESULTS: The CAE values in Group 1 were significantly lower than those in Group 2 (1.68 ± 0.16 vs. 1.78 ± 0.15, P = 0.041), Group 3 (1.68 ± 0.16 vs. 2.05 ± 0.27, P < 0.001), Group 4 (1.68 ± 0.16 vs. 1.87 ± 0.23, P = 0.023), and Group 5 (1.68 ± 0.16 vs. 2.09 ± 0.23, P < 0.001). There were no significant differences in HRV acquired by PPI and RRI, except for proportion of pairs of adjacent NN intervals differing by more than 50 ms in the entire recording in Group 1. All HRVs derived from PPI were different from those acquired from RRI in the other groups. CONCLUSION: PPI may be an alternative parameter for effectively assessing cardiac autonomic function in nonoverweight healthy individuals. It should be used carefully in overweight, elderly, or diabetic individuals.