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.
To investigate headache score and accompanying symptoms during and after inhalation of carbon monoxide.