Background: Newborn mammals suffering from moderate hypoxia during or after\r\nbirth are able to compensate a transitory lack of oxygen by adapting their vital\r\nfunctions. Exposure to hypoxia leads to an increase in the sympathetic tone causing\r\ncardio-respiratory response, peripheral vasoconstriction and vasodilatation in\r\nprivileged organs like the heart and brain. However, there is only limited information\r\navailable about the time and intensity changes of the underlying complex processes\r\ncontrolled by the autonomic nervous system.\r\nMethods: In this study an animal model involving seven piglets was used to\r\nexamine an induced state of circulatory redistribution caused by moderate oxygen\r\ndeficit. In addition to the main focus on the complex dynamics occurring during\r\nsustained normocapnic hypoxia, the development of autonomic regulation after\r\ninduced reoxygenation had been analysed. For this purpose, we first introduced a\r\nnew algorithm to prove stationary conditions in short-term time series. Then we\r\ninvestigated a multitude of indices from heart rate and blood pressure variability and\r\nfrom bivariate interactions, also analysing respiration signals, to quantify the\r\ncomplexity of vegetative oscillations influenced by hypoxia.\r\nResults: The results demonstrated that normocapnic hypoxia causes an initial\r\nincrease in cardiovascular complexity and variability, which decreases during\r\nmoderate hypoxia lasting one hour (p < 0.004). After reoxygenation, cardiovascular\r\ncomplexity parameters returned to pre-hypoxic values (p < 0.003), however not\r\nrespiratory-related complexity parameters.\r\nConclusions: In conclusion, indices from linear and nonlinear dynamics reflect\r\nconsiderable temporal changes of complexity in autonomous cardio-respiratory\r\nregulation due to normocapnic hypoxia shortly after birth. These findings might be\r\nsuitable for non-invasive clinical monitoring of hypoxia-induced changes of\r\nautonomic regulation in newborn humans.
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