Rheoencephalography: A non-invasive method for neuromonitoring.

In neurocritical care, the gold standard method is intracranial pressure (ICP) monitoring for the patient's lifesaving. Since it is an invasive method, it is desirable to use an alternative, noninvasive technique. The computerized real-time invasive cerebral blood flow (CBF) autoregulation (AR) monitoring calculates the status of CBF AR, called the pressure reactivity index (PRx). Studies documented that the electrical impedance of the head (Rheoencephalography - REG) can detect the status of CBF AR (REGx) and ICP noninvasively. We aimed to test REG to reflect ICP and CBF AR. For nineteen healthy subjects we recorded bipolar bifrontal and bitemporal REG derivations and arm bioimpedance pulses with a 200 Hz sampling rate. The challenges were a 30-second breath-holding and head-down-tilt (HDT - Trendelenburg) position. Data were stored and processed offline. REG pulse wave morphology and REGx were calculated. The most relevant finding was the significant morphological change of the REG pulse waveform (2nd peak increase) during the HDT position. Breath-holding caused REG amplitude increase, but it was not significant. REGx in male and female group averages have similar trends during HDT by indicating the active status of CBF AR. The morphological change of REG pulse wave during HDT position was identical to ICP waveform change during increased ICP, reflecting decreased intracranial compliance. A correlation study between ICP and REG was initiated in neurocritical care patients. The noninvasive REG monitoring would also be useful in space research as well as in military medicine during the transport of wounded service members as well as for fighter pilots to indicate the loss of CBF and consciousness.

Comparative study of the effect of bilastine and cetirizine on cognitive functions at ground level and at an altitude of 4,000 m simulated in hypobaric chamber: a randomized, double-blind, placebo-controlled, cross-over study.

INTRODUCTION: Antihistamines are easily accessible and cover the vast majority of the medical therapy of allergic rhinitis. However, their systemic administration may more frequently associate with their well-known side-effect, sedation, which is a serious problem in persons in safety-critical jobs such as aviation. We have a poor understanding whether a non-sedative antihistamine has an impact on vigilance when hypobaric hypoxia occurs during flight. METHODS: In this randomized, placebo-controlled, double-blind, cross-over study the effect of 20 mg bilastine was compared to 10 mg cetirizine and to placebo (20 mg pyridoxine) in 33 individuals at ground level and at 4,000 m altitude simulated in hypobaric chamber. Levels of vigilance, ultrashort memory, combined distributive attention, monotony tolerance and peripheral blood oxygen saturation (SpO2) were assessed. RESULTS: Bilastine did not impair the tested abilities in comparison with the control groups either at ground level or hypobaric hypoxia. Administration of cetirizine increased the number of errors at ground level. At the simulated altitude, already impaired results were additionally demonstrated with regards to the distributive attention test. CONCLUSIONS: From the two examined antihistamines, bilastine should be the preferred medication for by individuals who require constant attention and are exposed to hypobaric hypoxia.

Short-term hypobaric hypoxia enhances visual contrast sensitivity.

The effect of hypoxia on early visual functions remains a controversial area of research. To explore this question, we measured static and dynamic visual contrast sensitivity in 14 healthy volunteers at a simulated altitude of 5500 m. In comparison with the baseline condition (mean arterial oxygen saturation: 98.4%), contrast sensitivity significantly increased after 5, 10 and 15 min of hypoxic exposure (saturation: 82.9%, 77.0%, 74.3%, respectively). After 10 min, this enhancement was markedly pronounced under dynamic conditions. Returning to the baseline altitude (saturation: 97.7%), contrast sensitivity recovered, mostly at the lower spatial frequencies. There was a significant negative relationship between arterial oxygen saturation and contrast sensitivity values at low and medium spatial frequencies (0.5-4.8 c/deg). These results suggest that early visual processing may be enhanced during short-term hypoxic challenge.