|Title:||Influence of inspired oxygen concentration on the assessment of language lateralization using Transcranial Doppler Sonography|
|Subject:||Hong Kong Polytechnic University -- Dissertations.|
Transcranial Doppler ultrasonography.
Brain -- Localization of functions.
Language and languages -- Physiological aspects.
Oxygen -- Physiological effect.
|Department:||Department of Health Technology and Informatics|
|Pages:||xvii, 98 leaves : ill. (some col.) ; 30 cm.|
|Abstract:||Assessment of language lateralization is essential in surgical planning, for the preservation of the language area and estimation of possible functional loss after surgery. Trancranial Doppler Sonography (TCD) is one of the techniques used in the assessment of language lateralization. Relative change of blood flow velocity (BFV) in the middle cerebral arteries (MCA) has been measured for the determination of language lateralization. Any non-neural factor such as increased inspired oxygen concentration may change the lateralization assessment result. Vasoconstrictive effect of oxygen causes the reduction of BFV, which is opposite to the increase of BFV under the influence of language stimuli. The purpose of this project was to investigate the effect of oxygen on BFV of the MCA, and to investigate the influence of increased inspired oxygen concentration on the result of language lateralization assessment. In order to study how the inspired oxygen concentration affects the language lateralization assessment, the project was divided into two studies. In Study One, the change of BFV in the MCA on both left and right sides was simultaneously recorded during 35% oxygen inhalation and during room air inhalation. We recruited 20 healthy subjects aged from 20 to 32 years (mean + S.D. = 24 + 2.9 years). All of them were native Chinese speakers. The BFV in bilateral MCA was measured simultaneously in each subject using TCD. During the TCD examination, subjects were asked to breath in 35% oxygen for 40 seconds and then room air for 40 seconds. This procedure was repeated 10 times. In the second part of the study, oxygen was applied into language lateralization assessment to investigate its influence. We included 50 Chinese volunteers: 25 males and 25 females aged from 20 to 38 years (mean +- S.D. = 23.9 +- 3.5 years). All of them were native Chinese speakers. A language task of recognizing Chinese synonyms was used in the language lateralization assessment. The BFV in bilateral MCA was measured simultaneously in each subject using TCD while they were performing the language task. The examination was performed separately during room air inhalation and during 35% oxygen inhalation. In the Study One, a reduction of BFV of was caused by inhalation of 35% oxygen (-7.76 +/- 5.54% for left MCA; -6.96 +/- 4.36% for right MCA), and restoration of BFV to the baseline level after inhalation of room air. Continuous TCD assessment found that the change in BFV during oxygen inhalation phase was not always decreased. Mean Latent period of 3.02 seconds and mean BFV increase of 2.48% - 2.90% above the baseline was demonstrated. In the Study Two, a significant difference of the BFV change in left and right MCA (p<0.001) was observed during room air inhalation. Left lateralization of language processing was identified in all the subjects (mean lateralization =1.61 towards left). When 35% oxygen concentration was inhaled, there was a significant reduction of BFV (p<0.001) in both left and right MCA. The difference in BFV between left and right MCA was not significant (p = 0.057). The degree of lateralization was reduced from 1.61 to 0.56 with the effect of 35% oxygen inhalation. In the present study, latent period of cerebral haemodynamic response to increased oxygen concentration was obtained in the continuous measurement of BFV in the left and right MCA. Before the vasoconstrictive effect of oxygen was reflected by reduction of BFV, there was a small increase of BFV suggesting that the effect of oxygen on MCA is faster in the distal portion than in the proximal portion. The changing pattern of BFV in oxygen inhalation is not always decreasing. These findings increase the understanding of the effect of oxygen on cerebral haemodynamics. It provides a reference of using oxygen in the assessment of cerebrovascular reactivity. At the same time, owing to the vasoconstrictive effect of oxygen, the result of language lateralization assessment was altered during the inhalation of 35% oxygen. The laterality index changed from 1.61 during room air inhalation to 0.56 during oxygen inhalation. This alerts the clinicians in interpretating the results of language lateralization assessment using TCD when oxygen is administered to the patient. Since the determination of hemispheric language lateralization using TCD depends on the corresponding hemodynamic changes, the effect of oxygen on such assessment using any techniques involving the measurement of haemodynamic changes should not be ignored.|
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