The aim of the study was to determine the dependence of changes in the electrical stability of the heart on the light-dark cycle (LD cycle) in disorders of pulmonary ventilation. The ventricular arrhythmia threshold (VAT) was measured in female Wistar rats (adaptation to the light regime 12:12 h, ketamine/xylazine anesthesia 100 mg/15 mg/kg, i.m., open
chest experiments). The conditions of the normal artificial ventilation and reoxygenation were VT = 1 ml/100 g, respiratory rate 40 breaths/min, hypoventilation VT = 0.5 ml/100 g, respiratory rate 20 breaths/min. The animals (n=11 light group; n=19 dark group) were subjected to 20 min hypoventilation followed by 20 min reoxygenation. The control
prehypoventilatory VAT differences were not found between the light (1.90
±0.84 mA) and dark (1.88±0.87 mA) part of the day. Artificial hypoventilation changed the VAT values in light and dark part of the day differently. While during the light period, the average VAT values in most animals (90.9 %) were significantly decreased (1.29±0.59 vs. 1.90±0.84 mA control, p<0.05), during the dark part these values showed either significant increase (63.2 %) (2.23±0.77 vs. 1.48±0.39 mA, p<0.005) or a slight non-significant decrease (36.8 %) (2.18±0.89 vs. 2.54±0.99 mA).
Reoxygenation returned the VAT values to the level before hypoventilation by an increase of the VAT (81.8 %) in the light part of day and by decrease of the VAT (68.4 %) in the dark part of the day. It is concluded that 1) in hypoventilation/reoxygenation model, the significant higher average VAT values are in the dark part of the day vs. the light one, 2) rat hearts are more resistant to systemic hypoxia and reoxygenation in the dark part of day, and 3) proarrhythmogenic effect of the systemic hypoxia is only seen in the light part of the day.
Obstructive sleep apnoea (OSA) has been associated with disturbances in energy metabolism and insulin resistance,nevertheless, the links between OSA severity, resting energy expenditure (REE) and insulin resistance (homeostasis model assessment, HOMA-IR) remained unexplored Therefore, we investigates the effects of OSA severity on REE, and relationships between REE and HOMA-IR in patients with OSA. Forty men[mean (SD) age 49.4 (11.4) years] underwent overnight polysomnography; REE was assessed using indirect calorimetry. REE adjusted for fat -free mass (FFM) was higher in patients with moderate-to severe OSA [n=24; body mass index (BMI) 31.1(2.7) kg.m-2; apnoea-hypopnoea index (AHI) ≥15 episodes.h-1] compared to participants with no clinically significant OSA(n=16; BMI 30.3 (2.2) kg.m-2; AHI<15 episodes.h-1) [median (interquartile range) 30.4 (26.1-31.3) versus 25.8 (24.6-27.3) kcal.kg-1.24 h-1, p=0.005)]. AHI and oxygen desaturation index(ODI) were directly related to REE/FFM (p=0.001; p<0.001, respectively) and to HOMA-IR (p<0.001 for both). In stepwise multiple linea models,REE/FFM was independently predicted by ODI (p<0.001) and age(p=0.028) (R2=0.346); HOMA-IR wasindependently predicted by ODI only (p<0.001,R2=0.457). In conclusion, male patients with moderate-to severe OSA haveincreased REE paralleled by impaired insulin sensitivity. Severity of nocturnal intermittent hypoxia reflected by ODI is an independent predictor of REE/FFM and HOMA-IR.