Table 2.

Autonomic parameters for drug-free comparison subjects (n = 21) and participants with a history of METH dependence (n = 17) during the 5 minute rest period. SampEn tolerance level r for determining RR sequence matches was set at 10% (0.1) of the standard deviation of the data set. Data are represented as means ± S.E.M. Asterisks indicate significant group differences

Parameter	Comparison	METH-Dependent	Effect Size (r)
Time Domain
HR (beats/min)	64.0 ± 2.1	70.8 ± 2.4†	0.32
SDNN (ms)	69.5 ± 6.9	56.0 ± 5.7	0.23
RMSSD (ms)	54.6 ± 8.3	31.0 ± 4.3*	0.37
pNN50 (%)	0.28 ± 0.05	0.09 ± 0.03*	0.39
Frequency Domain
HFn	0.40 ± 0.04	0.21 ± 0.03**	0.51
LFn	0.53 ± 0.04	0.65 ± 0.03*	0.36
LF/HF ratio	2.0 ± 0.36	4.10 ± 0.64**	0.46
Nonlinear Analysis
entropy h	0.35 ± 0.01	0.30 ± 0.01**	0.46
SampEn (m = 1)	0.21 ± 0.05	0.09 ± 0.03†	0.30
SampEn (m = 2)	0.19 ± 0.04	0.09 ± 0.02*	0.31
SampEn (m = 3)	0.16 ± 0.04	0.08 ± 0.02†	0.31

^*p < 0.05

^**p < 0.01.

^†indicates a trend towards a group effect (p < 0.1).