The aim of the study was to investigate the effect of mild cerebral hypoxia on haemoglobin oxygenation (HbO2), cerebrospinal fluid dynamics and cardiovascular physiology. To achieve this goal, four signals were recorded simultaneously: blood pressure, ECG, HbO2 from right hemisphere and changes of SAS width from left hemisphere. Signals were registered from 30 healthy, young participants (2 females and 28 males, BMI = 24.5 ± 2.3 kg/m2, age 30.8 ± 13.4 years). We analysed the recorded signals using wavelet transform (WT). We demonstrated for the first time that in healthy subjects exposed to mild poikilokapnic hypoxia that there were increases in very low frequency HbO2 oscillations (< 0.052 Hz) in prefrontal cortex. Additionally, SAS fluctuation diminishes in the whole frequency range which could be explained by brain oedema. Consequently the study provides insight into mechanisms governing brain response to a mild hypoxic challenge. Our study supports the notion that HbO2 and SAS width monitoring might be beneficial for patients with acute lung disease, including SARS-CoV-2.