Osteopontin and osteoprotegerin levels in type 2 diabetes and their association with cardiovascular autonomic function

AIMS

Osteopontin (OPN) and osteoprotegerin (OPG) are bone metabolism biomarkers potentially associated with nerve function. We evaluated the association of cardiovascular autonomic nerve function, OPN, and OPG in 50 individuals with type 2 diabetes mellitus (T2DM).

METHODS

RR-variation during deep breathing (i.e., mean circular resultant (MCR) and expiration/inspiration (E/I) ratio) was used to assess parasympathetic nerve function. Participants' demographics, HbA1c, 25-hydroxyvitamin D (25(OH)D), BMI, HOMA-IR, calcium, parathyroid hormone, creatinine, OPN, and OPG were determined.

RESULTS

Using stepwise multiple linear regression analysis with MCR or E/I ratio as the dependent variable, OPN was independently associated with reduced autonomic function. A previous report showed a significant association of cardiovascular autonomic function with age, 25(OH)D insufficiency, and the interaction of age×25(OH)D insufficiency. Here we report a novel association for OPN and its interaction with age indicating that for those who are younger, elevated OPN levels are related to a greater loss of autonomic function (MCR model R2=0.598, p<0.001; E/I model R2=0.594, p<0.001).

CONCLUSION

Our results suggest that OPN is associated with reduced parasympathetic function, particularly in younger individuals with T2DM. Further studies are needed to determine if OPN is neuroprotective, involved in the pathogenesis of autonomic dysfunction, or a bystander.

Estimation of parasympathetic nerve function during sleep in patients with obstructive sleep apnea by instantaneous time-frequency analysis

BACKGROUND AND OBJECTIVES

The pathophysiologic aspects of parasympathetic nerve (PN) function during sleep in patients with obstructive sleep apnea (OSA) studied by classical power spectrum analysis on heart rate variability (HRV) are highly controversial. The controversy is attributed to methodologic concerns, such as poor time resolution involved in power spectrum analysis. We aimed to establish the appropriate method for the investigation of PN function in OSA patients with apneas and hypopneas using instantaneous time-frequency analysis with complex demodulation (CD) and sufficient time resolution.

METHODS

A total of 30 patients with PSG-confirmed mild to severe OSA were recruited for the analysis of frequency spectra contained in R-R intervals (RRI) of overnight electrocardiograph (ECG) tracings. High-frequency (HF) domains ranging between 0.15 and 0.40 Hz were selected for analysis. Among these domains, the HF domain with the maximum instantaneous amplitude was defined as the main HF peak and was used as the surrogate marker of PN discharge. Based on density spectrum array (DSA) map for main HF peak constructed with a time scale of 1s and a frequency resolution of 0.002 Hz (HF-DSA map), the shift in central frequency (CF) of main HF peak over time was continuously monitored. When the main HF peak with the same CF lasted for more than 20 s or 5 min on HF-DSA map, the PN function was considered to be stable or very stable. The measurements were then repeated after continuous positive airway pressure (CPAP) treatment.

RESULTS

The extent of PN-evoked modulation of RRI was enhanced in nonrapid eye movement (NREM) sleep, though the stability was reduced in both NREM and rapid eye movement (REM) sleep. These peculiar behaviors of PN function were reversed by CPAP treatment.

CONCLUSION

We found that instantaneous time-frequency analysis allowed estimation of transitional changes in PN function during sleep in OSA patients.