Abstract

Changes in scalp and cortical blood flow induced by voluntary hyperventilation are investigated by near-infrared diffusing-wave spectroscopy. The temporal intensity autocorrelation function g⁽²⁾(τ) of multiply scattered light is recorded from the forehead of subjects during hyperventilation. Blood flow within the sampled tissue volume is estimated by the mean decay rate of g⁽²⁾(τ). Data measured from six subjects show that the pattern of the hemodynamic response during 50 s hyperventilation is rather complicated: within the first 10 s, in three subjects an initial increase in blood flow is observed; from 10 s to 20 s, the mean blood flow is smaller than its baseline value for all six subjects; for the duration from 20 s to 30 s, the blood flow increases again. However, after 30 s the change is not consistent across subjects. Further study on one of these subjects by using two receivers probing the blood flow in the cortex and in the superficial layers simultaneously, reveals that during hyperventilation, the direction of change in blood flow within the scalp is opposite to the one in the brain. This helps to understand the complicated hemodynamic response observed in our measurements.

© 2009 OSA/SPIE