Table 2.

Correlations between participants’ characteristics and relative PIPR and nocturnal aMT6s (N = 45).

	Relative PIPR		Urine aMT6s
	r	p	r	p
Age	−0.199	0.191	-0.154	0.312
Male	−0.056	0.713	-0.332	0.028
BMI (kg/m2)	0.129	0.400	0.078	0.609
Relative PIPR			0.536	<0.001
aMT6s/Cr ratio	0.536	<0.001
Sleep variables
Insomnia severity index	−0.325	0.029	−0.250	0.097
Sleep duration (min)	0.019	0.904	−0.096	0.541
Sleep efficiency (%)	0.134	0.390	0.217	0.163
Sleep duration variability (min)	−0.142	0.364	−0.337	0.027
Mid-sleep time (hh:mm)	−0.136	0.384	−0.300	0.051
Rest-activity rhythm parameters
IV	−0.056	0.720	0.025	0.874
IS	0.006	0.970	0.099	0.528
M10-onset (h after midnight)	−0.001	0.994	−0.053	0.734
L5-onset (h after noon)	0.048	0.759	−0.209	0.179
RA	0.142	0.364	0.180	0.247
Sleep disordered breathing assessment
AHI	−0.281	0.079	−0.134	0.409
Neuropathy assessment
MNSI score	−0.585	<0.001	−0.609	<0.001
The LF/HF ratio	−0.060	0.715	−0.276	0.089
RMSSD	0.298	0.066	0.414	0.009

AHI = apnea hypopnea index, BMI = body mass index, IV = intradaily variability, IS = , interdaily stability, LF/HF ratio = low frequency/high-frequency ratio, MNSI = the Michigan Neuropathy Screening Instrument, RA = relative apmplitude, RMSSD = root mean square of the successive differences.