HRV parameter | Number of studies included | Number of subjects included | Combined estimate (95% CI) | p Value for Cochran Q-statistics | I2 degree of heterogeneity (%) |
LF | |||||
All | 14 | 7172 | −1.66 (−2.58 to −0.74) | 0.02 | 45.0 |
Excluding occupational studies | 12 | 7152 | −2.05 (−3.21 to −0.88) | 0.0175 | 48.8 |
Excluding studies with long-term ECG measurements | 9 | 6949 | −1.73 (−2.73 to −0.73) | 0.4618 | 0.0 |
Excluding groups with patients suffering from cardiovascular disease | 16 groups | 7154 | −1.71 (−2.74 to −0.68) | 0.0178 | 47.7 |
Excluding studies with a cross-sectional design | 11 | 427 | −1.51 (−2.4 to −0.68) | 0.0246 | 48.7 |
Excluding studies with PM10 measurements | 11 | 924 | −1.48 (−2.35 to −0.61) | 0.0373 | 44.4 |
Excluding studies with a low quality score | 8 | 6532 | −2.49 (−4.36 to −0.62) | 0.0121 | 57.4 |
HF | |||||
All | 16 | 7356 | −2.44 (−3.76 to −1.12) | <0.0001 | 66.7 |
Excluding occupational studies | 14 | 7336 | −3.17 (−4.92 to −1.41) | <0.0001 | 70.1 |
Excluding studies with long-term ECG measurements | 10 | 7087 | −1.75 (−3.20 to −0.29) | 0.0005 | 62.3 |
Excluding groups with patients suffering from cardiovascular disease | 16 groups | 7140 | −2.84 (−4.32 to −1.36) | 0.0001 | 66.1 |
Excluding studies with a cross-sectional design | 13 | 611 | −1.93 (−3.12 to −0.73) | 0.0003 | 63.4 |
Excluding studies with PM10 measurements | 14 | 1108 | −2.04 (−3.26 to −0.82) | 0.0002 | 63.9 |
Excluding studies with a low quality score | 9 | 6585 | −5.74 (−8.82 to −2.66) | <0.0001 | 71.8 |
SDNN | |||||
All | 21 | 13 521 | −0.12 (−0.22 to −0.03) | <0.0001 | 74.0 |
Excluding occupational studies | 18 | 13 468 | −1.25 (−1.81 to −0.68) | <0.0001 | 76.1 |
Excluding studies with long-term ECG measurements | 11 | 13 167 | −0.73 (−1.17 to −0.29) | 0.0006 | 60.7 |
Excluding studies with short-term ECG measurements | 8 | 354 | −1.39 (−2.37 to −0.41) | <0.0001 | 84.5 |
Excluding groups with patients suffering from cardiovascular disease | 19 groups | 13 286 | −0.08 (−0.17 to 0.004) | <0.0001 | 74.5 |
Excluding studies with a cross-sectional design | 18 | 6210 | −0.11 (−0.21 to −0.02) | <0.0001 | 75.6 |
Excluding studies with PM10 measurements | 17 | 6595 | −0.07 (−0.14 to 0.005) | <0.0001 | 69.2 |
Excluding studies with a low quality score | 12 | 12 666 | −0.05 (−0.13 to 0.02) | <0.0001 | 73.6 |
rMSSD | |||||
All | 16 | 11 437 | −2.18 (−3.33 to −1.03) | 0.0007 | 57.8 |
Excluding occupational studies | |||||
Excluding studies with long-term ECG measurements | 8 | 11 033 | −3.21 (−4.66 to −1.76) | 0.1386 | 31.5 |
Excluding studies with short-term ECG measurements | 8 | 404 | −1.07 (−2.75 to 0.6) | 0.0013 | 70.4 |
Excluding groups with patients suffering from cardiovascular disease | 14 groups | 11 256 | −2.78 (−4.03 to −1.52) | 0.022 | 48.3 |
Excluding studies with a cross-sectional design | 15 | 5972 | −2.29 (−3.56 to −1.02) | 0.0004 | 60.0 |
Excluding studies with PM10 measurements | 15 | 11 349 | −1.86 (−2.96 to −0.76) | 0.0051 | 51.5 |
Excluding studies with a low quality score | 9 | 11 293 | −1.89 (−3.08 to −0.71) | 0.0643 | 40.4 |
HF, high frequency; HRV, heart rate variability; LF, low frequency; PM10, particulate matter with aerodynamic diameter of 10 μm or less; rMSSD, square root of the mean squared difference of successive normal to normal intervals; SDNN, SD of normal to normal intervals.