The autonomic nervous system controls the smooth muscles of the internal organs, the cardiovascular system and the secretory function of the glands and plays a major role in the processes of adaptation. Heart rate variability is a non-invasive and easily applicable method for the assessment of its activity. The following review describes the origin, parameters and characteristics of this method and its potential for evaluation of the changes of the autonomic nervous system activity in different physiological and pathological conditions such as exogenous hypoxia, physical exercise and sleep. The application of heart rate variability in daily clinical practice would be beneficial for the diagnostics, the outcome prognosis and the assessment of the effect of treatment in various diseases.

Background-A suboptimal haematological status has often been recorded in athletes involved in intensive physical activity. There have even been reports of "sports anaemia" associated with intensive physical exercise. However, studies on the eVect of diVerent types of exercise practiced over a long period of time on the red blood cell variables in pubescent athletes are very few. Aim-To assess the basic red blood cell variables in highly trained pubescent athletes from diVerent sports and to compare the results with those for a control untrained group. Sex related diVerences in these variables were also assessed. Methods

Zjistit dynamiku autonomního nervového systému (ANS) pomocí variability srdeční frekvence (heart rate variability, HRV) během akutní expozice normobarické hypoxii a po ní, k níž dochází během jednoho sezení podle protokolu intermitentního hypoxického tréninku. Materiál a metody: Čtyřiadvacet zdravých mužů ve věku 28,0 ± 7,2 (průměr ± SD) vdechovalo po dobu jedné hodiny hypoxický vzduch (inspirační koncentrace kyslíku [FiO 2 ] 12,3 ± 1,5 %) z hypoxického generátoru (Al-tiPro 8850 Summit+, Altitude Tech, Kanada). Před expozicí hypoxii, během ní a po ní se provádělo vyšetření pulsní oxymetrií a měřila se variabilita HRV. Výsledky: Na konci hypoxického sezení vykazovali všichni hodnocení jedinci vyšší nízkou frekvenci (lnLF) (6,9 ± 1,1 ms² vs. 7,5 ± 1,1 ms²; p = 0,042), LF/HF (1,5 ± 0,8 vs. 3,3 ± 2,8; p = 0,007) a směrodatnou odchylku 2 na Poincarého mapě (SD2) (92,8 ± 140,0 ms vs. 120,2 ± 54,2 ms; p = 0,005) i nárůst celkové síly (7,7 ± 1,1 ms² vs. 8,1 ± 1,2 ms²; p = 0,032) a směrodatné odchylky intervalu mezi dvěma normálními tepy (SDNN) (57,3 ± 31,0 ms vs. 72,3 ± 41,1 ms; p = 0,024), avšak nižší entropii vzorku (SampEn) (1,6 ± 0,2 vs. 1,4 ± 0,2; p = 0,010). Bezprostředně po expozici hypoxii se snížila hodnota LF/HF (3,3 ± 2,8 vs. 2,2 ± 1,8; p = 0,001) při současném významném zvýšení lnHF (6,6 ± 1,4 ms² vs. 7,1 ± 1,3 ms²; p = 0,020). Závěr: Akutní normobarická hypoxie jako součást jednoho sezení v rámci tréninkového protokolu intermitentní hypoxie vede ke změnám aktivity ANS. Během expozice hypoxii převažuje tonus sympatiku a okamžitě po zrušení účinku hypoxií indukovaného faktoru dochází k nárůstu tonu parasympatiku.

Continuous positive airway pressure (CPAP) improves autonomic activity in patients with chronic heart failure (CHF) and central sleep apnoea (CSA), but its effect on heart rate variability (HRV) during therapy has not been reported. We hypothesized that CPAP may decrease HRV, despite its beneficial effects on sympathetic overactivation, due to the expected stabilization of breathing. Sixty-seven CHF patients underwent polysomnography (PSG). Ten of them presented with CSA (age 66.1±8.5 years, apnoea-hypopnea index [AHI]=57.6±23.3, central AHI [cAHI]=41.6±24.6 [mean±SD]) and were subjected to a second PSG with manual CPAP titration. Beat-to-beat heart intervals for a 6-hour period of sleep were extracted from each recording and HRV was analysed. CPAP significantly reduced AHI (AHI=23.1±18.3 P=.004). Standard deviation of normal-normal interbeat interval (SDNN) (61.5±29.0 vs 49.5±19.3 ms, P=.021), root mean square of successive differences (RMSSD) (21.8±9.2 vs 16.4±7.1 ms, P=.042), total power (lnTP=7.8±1.1 vs 7.4±0.8 ms , P=.037), low frequency power (lnLF=5.5±1.5 vs 5.0±1.4 ms , P=.003) and high frequency power (lnHF=4.6±1.0 vs 4.0±1.0 ms , P=.024) were decreased. There was a strong correlation between the decrease in AHI and the decrease in lnHF (Spearman's ρ=.782). CPAP leads to a decrease in spectral and time domain parameters of HRV during therapy in CHF patients with CSA. These changes are best explained by the effect which CPAP-influenced breathing pattern and lowered AHI exert on HRV.

No abstract