Assessment of the impact of 10-day intermittent hypoxia on the autonomic control measured by heart rate variability.

PURPOSE: The purpose of this study is to establish the alterations in the activity of the autonomic nervous system (ANS) via heart rate variability (HRV) in subjects exposed to 1 h of exogenous hypoxia for 10 consecutive days. METHODS: Twelve healthy non-smoker males at mean age of 29.8 ± 7.4 (mean ± SD) breathed hypoxic air delivered through hypoxicator (FiО2 = 12.3% ± 1.5%) for 1 h in 10 consecutive days. Pulse oximetry and electrocardiography were monitored during the visit and HRV was calculated for the entire 1-h hypoxic period. RESULTS: Comparing the last hypoxic visit to the first, subjects had higher standard deviation of normal-to-normal interbeat intervals (SDNNs) (65.7 ± 32.5 vs. 81.1 ± 32.0 ms, p = 0.013) and root mean square of successive R-R interval difference (RMSSD) (58.1 ± 30.9 vs. 76.5 ± 34.6 ms, p = 0.029) as well as higher lnTotal power (8.1 ± 1.1 vs. 8.5 ± 0.9 ms2, p = 0.015) and high frequency (lnHF) (6.8 ± 1.3 vs. 7.5 ± 1.2 ms2, p = 0.05) and lower LF/HF (2.4 ± 1.4 vs. 1.5 ± 1.0, p = 0.026). Changes in saturation (87.0 ± 7.1 vs. 90.8 ± 5.0%, p = 0.039) and heart rate (67.1 ± 8.9 vs. 62.5 ± 6.0 beats/min, p = 0.040) were also observed. CONCLUSIONS: Intermittent hypoxic training consisting of 1-h hypoxic exposure for 10 consecutive days could diminish the effects of acute exogenous hypoxia on the ANS characterized by an increased autonomic control (SDNN and total power) with augmentation of the parasympathetic nervous system activity (increased RMSSD and HF and decreased LF/HF). Therefore, it could be applied as a pre-acclimatization technique aiming at an increase in the autonomic control and oxygen saturation in subjects with upcoming sojourn to high altitude.

A patient with a severe chronic airway obstruction and preserved exercise capacity (a case report).

We report a patient with chronic obstructive pulmonary disease (COPD) in whom severe lung function disorders are combined with completely preserved exercise capacity. We assessed the exercise capacity of a 44-year-old man (height 155 cm, BMI 19.6 kg.m-2, FEV1%pred. = 30.9%, FRC%pred. = 158%, KCO%pred. = 46.2%, PaO2 = 64.0 mmHg, Medical Research Council Dyspnea scale = 1, Baseline Dyspnea Index = 10) by the 6-minute walking distance test (6MWD) and the symptom-limited cardiopulmonary exercise test (CPET) on a treadmill using the Bruce protocol. The patient was able to walk 667 meters in the test and achieved peak relative oxygen consumption (VO2/kg) of 21.9 mL.min-1.kg-1. We attribute the preserved exercise capacity of the patient to the combined beneficial effect of the following factors: 1. Efficient extraction of the hemoglobin-transported oxygen from the alveoli (P50 = 3.10 kPa). 2. Optimal right ventricle remodelling with mild hypertrophy, without dilatation and congestion. 3. Hypoxic normoxemia without polyglobulia, resulting in good rheologic properties of blood. 4. A preserved locomotory activity of the patient. Such a combination of severe lung function disorders with mildly pronounced dyspnea and preserved exercise capacity supports the concept that the function profile of COPD patients is multidimensional and therefore such patients should have a complete assessment of their disability condition.