| Dysfunction of the autonomic nervous system (ANS) has been linked to cardiovascular disease, stroke, sleep apnea, hypertension, and type 2 diabetes. The early identification of impairment in ANS function could effectively reduce the associated mortality and morbidity. As most of aforementioned disorders are intertwined, a screening tool with reasonable sensitivity and specificity would represent an important clinical advancement. In this report, we present methods for noninvasive assessment of cardiovascular autonomic dysfunction resulting from chronic exposure to sleep disordered-breathing (SDB) and impaired glucose metabolism (IGM), based on spectral indices derived from heart rate variability (HRV) and pulse transit time (PTT) variability (PTTV). HRV and PTTV are easily derived from the electrocardiogram (ECG) and photo-plethysmography (PLETH), both measurements being largely available in all clinical settings and relatively cheap.;The present study consists of two distinctive phases, which are discussed in sequence in this report. In phase I of the study, HRV indices and a new baroreflex sensitivity (BRS) measure BRSPTT were calculated from overnight polysomnography (PSG) and compared across four quadrants of disorder conditions: non-SDB-non-IGM, isolated SDB, isolated IGM, and mixed SDB+IGM. Sleep/wake stage, which has been previously identified as an important modulating factor, was adjusted by a novel weighted-sum method. In phase II of the study, to further unravel the tangled SDB-IGM effects among patients with mixed SDB and IGM, stage-specific BRSPTT were derived from PSGs of patients who went through a 2-month period of continuous positive airway pressure (CPAP) therapy. The association between BRSPTT and IGM, before and after CPAP treatment, was assessed using a fixed effects mixed model. |
