Strong coincidence between slow wave sleep and low AHI is explainable by the high instability of slow wave sleep to obstructive apnea exposure.

It is well known that in patients with obstructive sleep apnea syndrome (OSAS) the apnea-hypopnea index (AHI) is significantly decreased during slow wave sleep (SWS). It used to be explained by the ability of SWS to stabilize the upper airways against collapse. Another explanation, which is the focus of the current study, is that it is just a result of high instability of SWS to obstructive apnea exposure, i.e. high susceptibility of SWS to transition into lighter sleep stages during exposure to obstructive apneas. A retrospective chart review was performed on 560 males who underwent an overnight polysomnography. Two hundred and eighty-seven patients were eligible for the study. They were divided into 3 groups according to different AHI level. All three groups had a higher SWS occurrence in the lateral position than in the supine position. A special fourth group of patients was created with severe OSAS in the supine position but with very mild OSAS in the lateral position. This group had, in the lateral position, (A) higher AHI in NREM sleep (4.1+/-3.1/h vs. 0.7+/-1.2/h, p<0.001) as well as (B) higher SWS occurrence (27.7+/-15.0 % vs. 21.4+/-16.2 % of NREM sleep, p<0.05), than the group with the lowest AHI in the study, i.e. AHI<5/h in NREM sleep. These data suggest that strong coincidence between SWS and low AHI is the result of the high instability of SWS to obstructive apnea exposure. The data also support the presence of SWS-rebound in OSAS patients in the lateral body position.

Environmental estrogen bisphenol A and autoimmunity.

Over the past few years, there has been evidence of the increasing prevalence of autoimmune diseases. Autoimmune diseases consist of many complex disorders of unknown etiology resulting in immune responses to self-antigens. The immune system, and its function, is under complex and integrated control and its disruption can be triggered by multiple factors. Autoimmunity development is influenced by multiple factors and is thought to be a result of interactions between genetic and environmental factors. Here, we review the role of a specific environmental factor, bisphenol A (BPA), in the pathogenesis of autoimmune diseases. BPA belongs to the group of environmental estrogens that have been identified as risk factors involved in the development of autoimmune diseases.

Does obstructive sleep apnea worsen during REM sleep?

Although it is thought that obstructive sleep apnea (OSA) is worse during rapid eye movement (REM) sleep than in non-REM (NREM) sleep there are some uncertainties, especially about apnoe-hypopnoe-index (AHI). Several studies found no significant difference in AHI between both sleep stages. However, REM sleep is associated more with side sleeping compared to NREM sleep, which suggests that body position is a possible confounding factor. The main purpose of this study was to compare the AHI in REM and NREM sleep in both supine and lateral body position. A retrospective study was performed on 422 consecutive patients who underwent an overnight polysomnography. Women had higher AHI in REM sleep than NREM sleep in both supine (46.05+/-26.26 vs. 23.91+/-30.96, P<0.01) and lateral (18.16+/-27.68 vs. 11.30+/-21.09, P<0.01) body position. Men had higher AHI in REM sleep than NREM sleep in lateral body position (28.94+/-28.44 vs. 23.58+/-27.31, P<0.01), however, they did not reach statistical significance in supine position (49.12+/-32.03 in REM sleep vs. 45.78+/-34.02 in NREM sleep, P=0.50). In conclusion, our data suggest that REM sleep is a contributing factor for OSA in women as well as in men, at least in lateral position.

Autonomic nervous system under ketamine/ xylazine and pentobarbital anaesthesia in a Wistar rat model: a chronobiological view.

The aim of the present study was to determine the effect of ketamine/ xylazine and pentobarbital anaesthesia on heart rate variability as a marker of autonomic nervous system activity. The experiments were performed in ketamine/ xylazine (10 mg/kg/15 mg/kg) and pentobarbital (40 mg/kg, i.p.) anaesthetized female Wistar rats, after adaptation to a light-dark cycle of 12 hours light: 12 hours dark. Heart rate variability parameters (RR interval, power VLF (very low frequency), power LF (low frequency), power HF (high frequency) and relative powers) were evaluated during spontaneous breathing as a function of the light-dark cycle (LD cycle). Significant LD differences were found in the duration of RR intervals in ketamine/xylazine compared with pentobarbital-anaesthetized rats. Correlation analysis revealed moderate dependency between the RR interval duration and HF and LF power parameters in ketamine/xylazine anaesthesia in both light and dark parts of the cycle. In pentobarbital-anaesthetized rats, correlation analysis demonstrated a moderate dependence between RR interval duration and HF and VLF power parameters, but only in the dark part of the LD cycle. Ketamine/xylazine anaesthesia increased parasympathetic activity, and suppressed sympathetic and baroreceptor activity independently of the light-dark cycle. LD differences in RR interval duration were not eliminated. Pentobarbital anaesthesia increased parasympathetic activity, decreased sympathetic and baroreceptor activity, and eliminated LD differences in RR interval duration.

Heart rate variability in hypertension caused by sleep disordered breathing and its modification by CPAP.

OBJECTIVES: 1) To analyze heart rate variability (HRV) changes, reflecting the sympathovagal balance with secondary hypertension caused by sleep disordered breathing (SDB), compared to healthy controls and essential hypertension without SDB; 2) to compare HRV changes between various degrees of SDB severity; and 3) to test the modification of HRV indices by continuous positive airway pressure (CPAP) in SDB patients. BACKGROUND: Differentiation of secondary hypertension caused by SDB from essential hypertension and healthy controls by ambulatory blood pressure measurement (ABPM) and its modification by CPAP, requires an analysis of HRV changes, as frequently used for the prediction of cardiovascular risk. METHODS: HRV changes were analyzed in 48 adults divided into six groups according to the apnoea/hypopnoea index (AHI), i.e. three groups with various degrees of SDB, a group with severe SDB after CPAP application, a group with essential hypertension without SDB, and a group of healthy controls. Night-time and daytime values of low frequency (LF) and high frequency (HF) bands and the LF/HF ratio were compared in the six groups. RESULTS: The night-time values of LF bands were higher in severe than in moderate and mild degrees of SDB, and the correlation of LF/HF ratio with AHI (r = 0.3511) suggests the gradual increase of sympathetic predominance with the severity of SDB. The high sympathetic activity substantially decreased after application of CPAP in severe SDB. CONCLUSION: The increased nocturnal values of the LF band and the LF/HF ratio, caused by frequent apnoea/ hypopnoea episodes, support the usefulness of HRV spectral analysis for the prediction of cardiovascular risk in patients with SDB (Tab. 1, Fig. 3, Ref. 36).

Chronophysiologic aspects of ECG changes during a systemic asphyxic episode and subsequent reoxygenation in an experimental rat model.

The aim of the study was to evaluate the effect of ventilatory manoeuvres on some ECG parameters as a function of the light-dark (LD) cycle in in vivo conditions. The PQ and QT intervals were measured in ketamine/xylazine-anaesthetized female Wistar rats (100 mg/15 mg/kg, i.m.) after adaptation to an LD cycle (12:12 h). The animals were exposed to a 2 min apneic episode and subsequent 20 min period of reoxygenation. Significant LD differences were found in the duration of the PQ interval (p < 0.001) after 30 and 60 sec., and in the QT interval after 90 (p < 0.01) and 120 sec. (p < 0.001), apneic episode. Reoxygenation restored the PQ and QT intervals with the preservation of LD differences from the pre-asphyxic period. It is concluded that although long-term asphyxia probably minimized LD differences in the duration of the PQ interval, the dispersion of refractory periods increases by the manner depending on LD cycle. Reoxygenation did not act proarrhythmogenicly and the followed parameters were recovered to the pre-asphyxic level (Fig. 5, Ref. 43).

[Chronobiology and practical medicine]. / Chronobiológia a praktická medicína.

In present time, to classify the healthy as potencional possibility of the organism to accept variable environment influences without the break of the biological important functions is not satisfactory. Examples from the different field of the clinical medicine refer to importance of the knowledge's of the circadian rhythmicity concerning many diseases, symptoms or significant remissions. Therefore, clinical trials considering the biological variability differ from the convectional studies by assumption that biology of patient is dynamic, that time of the diagnostic test running is significant and that drugs can influence safety and therapeutic effect in the dependence on the day-time. In paper, it is showed on some examples from the clinical practice that respection of the chronobiological principles may play the important role in the medical diagnostics as well as in therapy and may improve accuracy of the whatever functional examination. For terms, which are often used in the chronobiological texts, no suitable terms were available and therefore it was necessary to introduce the descriptive phrases, which would be accepted by specialists in the field. Many of the introduced terms are still unknown to many investigators and physicians who might benefit from the application of chronobiologic principles to their work.