Table 1 HRV analysis under meditative condition
From: Nonlinear analysis of heart rate variability signals in meditative state: a review and perspective
Sl. no. | Authors (Year) | Database (subjects) | Nonlinear parameters | Observations/findings during meditation |
|---|---|---|---|---|
1 | Sarkar and Barat [10] (2008) | PhysioNet (8) | DFA, DEA, Recurrence and MSE analysis | DFA shows strong affect in long-range correlation, DEA exhibits regular repetitive oscillations of time series |
2 | Papasimakis and Pallikari [32] (2009) | PhysioNet (8) | DFA scale exponent and ShEn | DFA scale exponent decreases; decimated long-range correlation, standard deviation of ShEn decreases at higher scales indicating reduced variations in the correlations of HRV |
3 | Goswami et al. [13] (2010) | PhysioNet (12) and own (3) | Normalized ShEn | Normalized ShEn decreases for advanced meditators which indicates lower HRV dynamics. No statistical test found |
4 | Diosdado et al. [29] (2010) | PhysioNet (46) | Higuchi’s fractal dimension (HFD) | HFD graph possesses quasi-periodic components indicating reduced complexity. No statistical test found |
5 | Li et al. [26] (2011) | PhysioNet (26) | Base-scale entropy (BSEn) | BSEn* decreases, \(\pi \)-type probability distribution shows more certainty; indicates low complexity of HRV |
6 | Goswami et al. [33] (2011) | PhysioNet (12), own (3) | Second order difference plot (SODP) | Cluster formed by SODP rotates anticlockwise during meditation; indicates detachment from the external world. No statistical test found |
7 | Raghavendra and Dutt [24] (2011) | PhysioNet (12) | MED, CD, LLE and NLS | MED* and CD* decrease, whereas LLE* and NLS* increase; inducement of overwhelming calmness and significant alertness |
8 | Raghavendra and Dutt [12] (2011) | PhysioNet (12) | Fractal dimension | Significantly low fractal dimension*; increases for scales 1 to 7 and then becomes constant |
9 | Song et al. [12] (2013) | PhysioNet (8) | Multifractal detrended fluctuation analysis, singularity spectrum width | Significantly narrow singularity spectrum width indicating reduced dynamical complexity. No statistical test |
10 | Jiang et al. [30] (2013) | PhysioNet (12) | Visibility Graph method and P(k) | P(k) initially decreases (\(k\le 8\)) and then significantly increases (\(k>\)11). Long-range correlation is retained only at higher scales. No statistical test found |
11 | Goshvarpour and Goshvarpour [34] (2013) | PhysioNet (12) | Higher order spectral (HOS) analysis: Bispectrum estimation | Bispectrum amplitude increases during KYM and decreases significantly (\(p<0.05\)) during Chi meditation |
12 | Kamath [15] (2013) | PhysioNet (12) | CCTM and HFD | Significant increase in CCTM; indicates activation of PNS. |
13 | Goshvarpour and Goshvarpour [35] (2015) | PhysioNet (8) | SD1 (minor axis), SD2 (major axis), area under Poincaré plot | SD1/SD2* increase significantly; elliptical Poincaré becomes circular; indicates definite change in the psychological state |
14 | Bhaduri and Ghosh [28] (2017) | PhysioNet (12) | Multifractal-DFA and PSVG analysis | PSVG increases during Kundalini yoga and Chi meditation, indicates increase in the degree of complexity. No statistical test found |
15 | Alvarez-Ramirez [36] (2017) | PhysioNet (12) | Hurst exponent | Hurst exponent decreases; indicating uncorrelated HRV dynamics and destruction of long-range correlation. No statistical test found. |
16 | Goshvarpour and Goshvarpour [37] (2018) | PhysioNet (12) | Correlation entropy and Cauchy–Schwarz divergence | Correlation entropy* is the lowest and Cauchy–Schwarz divergence* is the highest (low SNS activity) |
17 | Yao et al. [38] (2018) | PhysioNet (26) | Entropy measures: KW, BS, PEn, and DSJE | All the entropies are significantly lesser. Lower dynamical complexity |
18 | Guo et al. [39] (2019) | Author’s own (70) | DFA scale exponents \(\alpha _1\) and \(\alpha _2\) | Significant increase in \(\alpha _1\) and \(\alpha _2\)*. Prevalent SNS activity is observed |
19 | Nasrolahzadeh et al. [40] (2019) | PhysioNet (8) | Graph index complexity (GIC) based on visibility graph | GIC values are significantly higher indicating higher complexity |
20 | Goshvarpour and Goshvarpour [27] (2019) | PhysioNet (12) | SD1, SD2, LZ complexity, LLE, SampEn, ShEn, ApEn, LogEn | SD1*** and SD2*** show large variations, LLE*** increases, LogEn*** increase but LZ*** complexity, SampEn***, ApEn***, and Shannon entropy*** decrease; indicates low complexity |
21 | Deka and Deka [41] (2020) | PhysioNet (12) | IncrEn | Decrease in IncrEn during meditation; however the difference is not statistically significant (\(p>0.05\)). |
22 | Goshvarpour and Goshvarpour [42] (2020) | PhysioNet (12) | Heart rate asymmetry (HRA) index | Significant increase in HRA index with the increase in lags of NN intervals |
23 | Rohila and Sharma [43] (2020) | PhysioNet (8) | Asymmetric spread index (ASI), Porta’s index (PI), Guzik’s index (GI), slope index (SI) and area index (AI) | Significant increase in ASI, PI and GI. Crossover of ASI is observed in some meditators. Overall dominant PNS activity |
24 | Deka and Deka [14] (2021) | PhysioNet (12) | EMD-based Energy ShEn (eShEn), Kurtosis, Skewness, DFA based short-term scale exponent (\(\alpha _1\)), multiscale PEn (MPE) | Significant decrease in eShEn***, MPE*** at lower scales (1,2,3,4) and \(\alpha _1\)***. However with the increase in scales, MPE increases during meditation providing a hint of higher underlying complexity |
25 | Goshvarpour and Goshvarpour [44] (2022) | PhysioNet (12) | Verhulst map-based measures: area, circumradius, inradius | Significant decrease in area, circumradius, and inradius during Chi meditation and significant increase in area, circumradius, and inradius during KYM |
26 | Deka and Deka [45] (2022) | PhysioNet (12) | Improved multiscale distribution entropy (ImDistEn) | Significant increase in ImDistEn over higher scales (>5) during Chi and KYM meditation as compared to before meditation |