Near infrared spectroscopy and transcranial Doppler in monohemispheric stroke

We simultaneously performed near infrared spectroscopy (NIRS) and transcran ial Doppler (TCD) to evaluate the effects of hypercapnia as well as of sea Ip ischemia on the blood flow at two different depth levels within the brai n and of the scalp vessels. A decrease in the backscattered light intensity , meaning an increment of blood volume, was detected at the end of hypercap nia in all healthy subjects. This decrement was partly masked by ischemia i n the cutaneous vessels. In 2 patients with a mono-hemispheric lesion in th e middle cerebral artery (MCA) territory, an increase in NIRS response was found in the healthy hemisphere, while in the stroke side the CO2-induced c hanges were negligible. TCD data showed a similar increment of blood flow v elocity to the hypercapnia in both hemispheres, with no differences between the affected and normal side in 1 patient, whereas in the second one, no i ncrement was observed on the affected side, probably due to internal caroti d artery stenosis, The two methods nicely integrate: TCD main ly tests subc ortical changes in the MCA flow, while NIRS is exquisitely sensitive to cor tical arterioles and capillary blood flow modifications.