Structural equation modeling of parasympathetic and sympathetic response to traffic air pollution in a repeated measures study

Table 1 Summary statistics for heart rate variability (HRV) and 24-hr moving average ambient air pollutant measures (November 2000 to December 2009)

	Average	Median	SD	5%	95%	IQR
Air pollution measure
BC (μg/m³)	0.83	0.73	0.43	0.31	1.62	0.55
CO (ppm)	0.43	0.40	0.26	0.11	0.92	0.31
NO (ppm)	0.02	0.01	0.02	0.01	0.06	0.01
NO₂ (ppm)	0.02	0.02	0.01	0.01	0.03	0.01
HRV measure^a
ln(SDNN)	3.7	3.6	0.8	2.6	5.2	1.0
ln(r-MSSD)	3.5	3.2	1.1	2.1	5.6	1.5
ln(HF)	4.9	4.6	2.0	2.2	8.8	2.7
ln(LF)	4.8	4.6	1.6	2.6	8.0	2.0
ln(LF/HF)	−0.1	0.0	1.1	−2.0	1.7	1.5

^alog transformed HRV measures; SDNN, 5-min SD of normal-to-normal intervals; r-MSSD, square root of the mean squared differences of successive normal-to-normal intervals; HF, high-fequency HRV; LF, low-frequency HRV; LF/HF, ratio of LF and HF.