Assessment Of Olfactory Responses In Patients With Disorders Of Consciousness And Its Application In Prediction

Objective:Severe brain injuries may cause varying kinds of disorders of consciousness(DoC).Clinical evaluation of consciousness is mostly dependent on DoC patients’behavioral responses.However,there is no consensus on whether olfactory stimuli can be used for the evaluation of consciousness.The purpose of this study is to evaluate the olfactory responses of different stimuli in patients with DoC and analyze the prognostic value,meanwhile to explore the behavioral and electroencephalogram(EEG)characteristics.Methods:The olfactory responses of pleasant,unpleasant and blank stimuli were evaluated in DoC patients and resting-state EEG and olfactory task-related EEG were collected.We observed the olfactory response occurrence rate of DoC patients with different levels of consciousness under different olfactory stimuli,and compared the difference of whole-brain level relative power at rest between patients with presence of olfactory response and absence of olfactory response,as well as the changes of weighted Phase-Lag Index(wPLI)after olfactory stimuli.EEG data of healthy subjects were also collected as controls.The DoC patients with or without olfactory response were followed up three months later.The disability rating scale was used to assess the recovery of function and the Coma Recovery Scale-Revised scale was used to assess the recovery of consciousness.Results:A total of 28 DoC patients(13 with VS/UWS and 15 with MCS)were included in this study.A total of 16(57%)had olfactory responses(ORES group)and 12(43%)had no olfactory response(N-ORES group).The results found that(1)compared to blank stimulus,odorant stimulation can effectively induce DoC patients’ olfactory response(pleasant stimulus:χ2=14.275,P=0.007;unpleasant stimulus:χ2=9.524,P=0.001);(2)31%(4/13)of VS/UWS patients and 80%(12/15)of MCS patients have olfactory responses.A positive relationship was found between the presence of olfactory responses and level of consciousness(χ2=6.892,P=0.020);(3)With respect to prognosis after three months’ follow-up,31%(5/16)of ORES patients and 8%(1/12)of N-ORES patients had improved their function.62.5%(10/16)of ORES patients and 16.7%(2/12)of N-ORES patients had returned to a higher level of consciousness.ORES patients had more consciousness recovery rate than the N-ORES patients(χ2=5.882,P=0.023).However,the relationship between olfactory response and functional improvement was not significant(χ2=2.139,P=0.196);(4)ORES patients showed higher alpha relative power than N-ORES patients in resting-state EEG(P=0.030);(5)For olfactory EEG,N-ORES patients showed higher theta functional connectivity than ORES patients after pleasant stimuli(P=0.029).Conclusions:Olfactory response can be used to assess consciousness and predict consciousness recovery in patients with DoC.The brain function between DoC patients with and without olfactory response at rest-state EEG and olfactory tasked-related EEG were different.The changes of theta functional connection under pleasant stimuli may be the neural correlates of olfactory responses in DoC patients.