Table 2

Sensitivity analysis

HRV parameterNumber of studies includedNumber of subjects includedCombined estimate (95% CI)p Value for Cochran Q-statisticsI2 degree of heterogeneity (%)
LF
 All147172−1.66 (−2.58 to −0.74)0.0245.0
 Excluding occupational studies127152−2.05 (−3.21 to −0.88)0.017548.8
 Excluding studies with long-term ECG measurements96949−1.73 (−2.73 to −0.73)0.46180.0
 Excluding groups with patients suffering from cardiovascular disease16 groups7154−1.71 (−2.74 to −0.68)0.017847.7
 Excluding studies with a cross-sectional design11427−1.51 (−2.4 to −0.68)0.024648.7
 Excluding studies with PM10 measurements11924−1.48 (−2.35 to −0.61)0.037344.4
 Excluding studies with a low quality score86532−2.49 (−4.36 to −0.62)0.012157.4
HF
 All167356−2.44 (−3.76 to −1.12)<0.000166.7
 Excluding occupational studies147336−3.17 (−4.92 to −1.41)<0.000170.1
 Excluding studies with long-term ECG measurements107087−1.75 (−3.20 to −0.29)0.000562.3
 Excluding groups with patients suffering from cardiovascular disease16 groups7140−2.84 (−4.32 to −1.36)0.000166.1
 Excluding studies with a cross-sectional design13611−1.93 (−3.12 to −0.73)0.000363.4
 Excluding studies with PM10 measurements141108−2.04 (−3.26 to −0.82)0.000263.9
 Excluding studies with a low quality score96585−5.74 (−8.82 to −2.66)<0.000171.8
SDNN
 All2113 521−0.12 (−0.22 to −0.03)<0.000174.0
 Excluding occupational studies1813 468−1.25 (−1.81 to −0.68)<0.000176.1
 Excluding studies with long-term ECG measurements1113 167−0.73 (−1.17 to −0.29)0.000660.7
 Excluding studies with short-term ECG measurements8354−1.39 (−2.37 to −0.41)<0.000184.5
 Excluding groups with patients suffering from cardiovascular disease19 groups13 286−0.08 (−0.17 to 0.004)<0.000174.5
 Excluding studies with a cross-sectional design186210−0.11 (−0.21 to −0.02)<0.000175.6
 Excluding studies with PM10 measurements176595−0.07 (−0.14 to 0.005)<0.000169.2
 Excluding studies with a low quality score1212 666−0.05 (−0.13 to 0.02)<0.000173.6
rMSSD
 All1611 437−2.18 (−3.33 to −1.03)0.000757.8
 Excluding occupational studies
 Excluding studies with long-term ECG measurements811 033−3.21 (−4.66 to −1.76)0.138631.5
 Excluding studies with short-term ECG measurements8404−1.07 (−2.75 to 0.6)0.001370.4
 Excluding groups with patients suffering from cardiovascular disease14 groups11 256−2.78 (−4.03 to −1.52)0.02248.3
 Excluding studies with a cross-sectional design155972−2.29 (−3.56 to −1.02)0.000460.0
 Excluding studies with PM10 measurements1511 349−1.86 (−2.96 to −0.76)0.005151.5
 Excluding studies with a low quality score911 293−1.89 (−3.08 to −0.71)0.064340.4
  • 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.