Carbon Monoxide's Headache Inducing Characteristics and Effects on the Cerebral Arteries and Blood Flow

To investigate headache score and accompanying symptoms during and after inhalation of carbon monoxide. With transcranial Doppler imaging, c-scan and laser speckle the investigators will investigate changes in blood flow velocity of the middle cerebral artery (MCA), diameter of the superficial temporal artery (STA), the radial artery and facial skin perfusion.