Hemodynamic response of the frontal cortex elicited by intravenous thiamine propyldisulphide administration

The intravenous olfaction (IVO) test is a unique type of clinical olfactometry and is widely used in Japan. However, it is difficult to distinguish actual olfactory disturbance from feigned disturbance because the IVO test is a psychophysical test. To resolve this problem, we investigated the possibility of an objective IVO test assisted with near infrared spectroscopy (NIRS). IVO testing was performed according to the usual protocol with thiamine propyldisulphide (alinamin) administration. The relative oxy- and deoxyhemoglobin levels of the orbitofrontal area during olfactory stimulation by IVO test were measured by NIRS. Pairs of NIRS emitters and detectors were positioned on the bilateral frontal scalp. After administration of alinamin, oxyhemoglobin levels increased, though deoxyhemoglobin levels did not change. An increase in oxyhemoglobin levels was observed bilaterally. Administration of saline did not elicit any change in the oxy- or deoxyhemoglobin levels and concentration of the administered alinamin related increasing of the oxyhemoglobin level was observed. Oxyhemoglobin remained unchanged in anosmic subjects despite administration of alinamin. The latency of oxyhemoglobin increase on each side and smelling latency showed significant correlation. Latencies of oxyhemoglobin increases between the right and left sides also showed significant correlation. Oxyhemoglobin response appears to be linked to olfactory related response. NIRS is a useful technique for the development of an objective form of IVO testing.