Table 3. Predictors of HRV difference after controlling for age, BMI, exercise level, SOWS score, BDI score, current methadone dose and substance Q scores by multiple linear regression analysis.

	△HF		△LF%		△LF/HF
R2	0.147		0.324		0.441
	β	p value	β	p value	β	p value
Age	0.004	0.983	−0.088	0.590	−0.029	0.854
BMI	0.078	0.674	−0.108	0.522	−0.089	0.595
Exercise level	−0.095	−0.595	0.333	0.045*	0.200	0.200
SOWS score	0.063	0.725	0.094	0.567	0.083	0.586
BDI score	0.118	0.512	−0.171	0.295	−0.108	0.492
Current methadone dose	0.004	0.983	−0.243	0.168	−0.337	0.039*
Heroin Q score	0.040	0.833	−0.246	0.157	−0.233	0.174
Alcohol Q score	0.287	0.111	−0.281	0.086	−0.331	0.037*
Cigarette Q score	−0.108	0.546	−0.002	0.991	0.096	0.560
Tranquilizer Q score	−0.104	0.563	−0.044	0.786	−0.094	0.538
Borderline index	−0.383	0.037*	0.465	0.007*	0.448	0.009*

^* p<0.05,

^** p<0.001.

HRV, heart rate variability; BMI, body mass index; SOWS, Subjective Opiate Withdrawal Scale; BDI, Beck Depression Inventory; Q score, estimated consumption amount score; HF, high frequency power of HRV, LF, low frequency power of HRV, LF%, normalized low frequency power of HRV.