Sleep apnea is identified by repetitive reduction or complete cessation of breathing during sleep. Sleep apnea affects cerebral hemodynamics and it is important to study this effect. Measuring cerebral blood flow during sleep is challenging due to the need to maintain a contact between the flow probe and the skull. It is hypothesized that there exists a relationship between the variations in the exhaled CO2 and Cerebral Blood Flow during sleep apnea. To test this hypothesis, the present study was conducted in two parts: simulated and nocturnal sleep study. 9 volunteer subjects (6 Male and 3 Female Age: 23.11±1.59 years BMI: 21.9±2.409kg/m2) participated in the simulated study and 10 volunteer subjects (9 Male and 1 Female Age: 50.2±7.48 years BMI: 31.541±4.56 kg/m2 AHI: 62.84±20.44) participated in a nocturnal sleep study. Analyzing full waveforms of cerebral blood flow velocity (CBFV) and exhaled CO2, the relationship between 4 metrics from CBFV and 2 metrics from exhaled CO2 were investigated. Although one metric pair showed statistically significant and relatively high correlation (ρ= 0.68 p=7.96×10-7) during the simulated study, the same was not observed during the nocturnal study. Therefore, the proposed hypothesis could not be proven.