The Investigation Of The Therapeutic Effect And FMRI Mechanism Of The Transcutaneous Auricular Vagus Nerve Stimulation In Maintenance Hemodialysis Patients With Sleep Disorders

BackgroundPatients receiving maintenance hemodialysis(HD)frequently report insomnia complaints,accompanying with a variety of comorbidities such as irritability,immune suppression,anxiety,depression,cognitive impairment,etc,which may have a potentially great impact on their quality of life and even survival.Over the past decades,despite the fact that the current management including medication,behavioral cognitive therapy(CBT-i)and acupuncture has developed for MHDSD,it is still far from satisfactory.Generally,CBT-i is a safe and effective approach and is recommended as the first-line therapy for insomnia in the Western countries,but its high cost and the lack of sufficient professional therapists to implement it would be the main barriers to access to the needs of general population.Medications are generally short-term effective in improving symptoms with various side effects as well as psychological and physiological dependence.Therefore,it is necessary to seek other alternative treatments.Transcutaneous auricular vagus nerve stimulation(taVNS),as well as auricular acupressure(AA),as one of Chinese traditional auricular therapy,has been proved to be efficient for insomnia by previous studies.A growing body evidence has demonstrated that both taVNS and AA might exert therapeutic effect by irritating the auricular branch of the vagus nerve at the external ear.More importantly,compared with AA,taVNS seems to exhibit more advantageous properties such as explicit and controllable parameters which are beneficial for us to conduct high-quality qualitative researches.However,to date a head-to-head comparison of taVNS versus AA within a randomized clinical trial is still lacking.Moreover,the precise central mechanisms underlying its therapeutic effects remain unclear.Resting-state functional magnetic resonance imaging(rs-fMRI)is a non-invasive technique,which could detect the ongoing neuronal process at the "resting state" through measuring the spontaneous brain activity by low-frequency fluctuations in blood oxygen level-dependent(BOLD)signals,and consequently provide a new opportunity to investigate the functional abnormalities on several neurological disorders including insomnia.In addition,in the past several years,there has been a promising improvements of machine learning(ML)techniques in brain disease classification or prediction.The strength of ML algorithm is that it could detect hard-to-discern patterns from the large and complex data sets and is particularly well-suited to large fMRI data mining,especially in exploring neurological disease biomarkers for disease diagnosis and underlying therapeutic mechanisms.Therefore,the use of rs-fMRI method may advance our understanding of the spontaneous neural activities of the brain in MHDSD patients after intervention at group-level,while the combination with ML algorithm may provide multi-level information for disease classification,and may give better understanding of the mechanisms of MHDSD and corresponding therapeutic mechanism than single-level study.Study 1 Identification of discriminative biomarkers for patients on hemodialysis with insomnia:A fractional Amplitude of Low Frequency Fluctuation-based machine learning analysisObjectiveTo detect the spontaneous brain activity pattern in MHD patients with insomnia(HDWI)by using fractional fractional amplitude of low frequency fluctuation(fALFF)method and further identify brain regions showing altered fALFF as biomarkers to discriminate HDWI patients from those on hemodialysis but without insomnia(HDWoI)and healthy controls(HCs).Method30 HD subjects comorbid with insomnia(HDWI),30 HD subjects without insomnia(HDWoI),and 30 sex-,age-,education-matched healthy controls(HCs)were recruited between Mar 2021 and Aug 2022 from the Department of hemodialysis center,Guangdong Provincial Hospital of Chinese Medicine.Neuropsychological assessments including the pittsburgh sleep quality index(PSQI),the 20-item Self-Rating Anxiety Scale(SAS),the 20-item self-rating depression scale(SDS)and the short form 36 health survey questionnaire(SF-36)were performed in all subjects before the MRI scan on the day before HD treatment.Meanwhile,the rs-fMRI data as well as patients’ demographic data,was also collected and analyzed.We compared fALFF differences among HDWI subjects,HDWoI subjects and HCs,and extracted altered fALFF features for the subsequent discriminative analysis.Then by using such extracted features,we constructed a support vector machine(SVM)classifier to identify distinct biomarkers for HDWI.Results(1)Demographic and clinical measurementsA total of 84 subjects(HDWI=28,HDWol=28,HCs=28)were included for the last analysis.There were no significant differences in age,sex,and education among three groups(P>0.05).The PSQI total score,PSQI subscore,SDS score,SAS score and SF-36 score in HDWI subjects were significantly higher than HDWoI subjects and HCs,respectively(P<0.001).Furthermore,there were no significant difference in hemodialysis duration between HDWI group and HDWoI group.(2)rs-fMRI results①Analysis of ANOVA among the three groups revealed significant fALFF difference in multiple regions including the bilateral calcarine(CAL),bilateral middle occipital gyrus(MOG),bilateral precentral gyrus(PreCG),bilateral postcentral gyrus(PoCG),right lingual gyrus(LING),bilateral inferior inferior parietal lobule(IPL),left superior parietal(SPL),bilateral cerebellum,and right insula.②Compared with HCs,HDWI subjects exhibited signficant decreased fALFF value in the bilateral CAL/TMG,right MOG/PoCG/IPL/LING and left PoCG/PreCG while increased fALFF in the bilateral CAL and right insular.③Compared with HCs,HDWoI subjects exhibited significant decreased fALFF value in the bilateral CLA/MOG/PoCG/PreCG/TMG and left SPL while increased ALFF in the bilateral CAL and right insular.④Compared with HDWoI subjects,an opposite pattern of increased fALFF in the bilateral CAL/right MOG and decreased fALFF in the right cerebellum was observed in HDWI subjects.(3)Correlation analysisCorrelation analyses showed significant positive correlations of the fALFF values in the bilateral calcarine and the sleep efficiency subscore of PSQI(r=0.460,P=0.014)in HDWI subjects.We also observed significant negative correlation between the right cerebelum and the sleep quality subscore of PSQI in HDWI subjects(r=0.421,P=0.026).(4)Machine learning analysisUsing the fALFF values voxels in these two clusters as input features to construct the SVR model and we found that the top 78 meaningful features significantly contributed to the classifier with the best discriminative ability(accuracy=82.14%,sensitivity=85.7%,specificity=78.6%and AUC=0.8202,respectively).The permutation analysis conducted 5,000 times showed that the classifier with78 meaningful features was superior to the random classifiers(P<0.0002).ConclusionTo conclude,our study for the first time revealed that the HDWI patients exhibited abnormal fALFF in the right MOG,bilateral CAL and the right cerebellum compared to HDWoI,which mainly located in the visual and emotional/cognitive network,suggesting that these network could be identified as reliable markers in discriminating the insomniacs on hemodialysis from those non-insomniacs.Study 2 The efficacy and safety of transcutaneous auricular vagus nerve stimulation in hemodialysis patients with insomniaObjectiveIn this study,we aimed to evaluate the efficacy and safety of taVNS in the treatment of MHDSD compared with AA.Methods60 cases were randomly assigned into treatment group and control group for 4-week intervention.The clinical variables including demographic data,biochemical markers and outcome measurements before and after 4-week treatment were collected.Then we recorded the changes of PSQI score at 4 time endpoints(T0=baseline,T1=4 week,T2=8 week,T3=16 week and T4=24 week)after treatment and compared the dynamic therapeutic effects between two groups for MHDSD by using mixed linear effect model.Meanwhile,during the treatment and follow-up period,we also recorded the adverse event to evaluate the safety of taVNS and AA therapy.Results(1)The baseline clinical variables results56 MHDSD patients who completed 4-week treatment with complete clinical variables data were included in the final analysis,including 28 patients in the treatment group and 28 patients in the control group.The intra-group comparison results showed that:①there were no significant differences in baseline demographic characteristics(age,sex,height,weight,BMI and educational level)and disease data(age of dialysis,age of insomnia,use of sleeping pills and underlying diseases)between the two groups(P>0.05).②There were no significant differences in biochemical markers(serum creatinine,urea nitrogen,urea clearance index,serum calcium,serum chlorine,serum inorganic phosphorus,serum sodium,serum potassium,hemoglobin,blood glucose,serum albumin,parathyroid hormone,C-reactive protein,systolic/diastolic blood pressure fluctuation)between the two groups(P>0.05).(2)The results of outcome measurements of 4-week treatmentThe results showed that compared with pre-treatment(T0),the scores of PSQI,ISI,ESS,SAS,SDS,FS-14,MMSE and SF-36 at different time points were significantly different(P<0.001).We identified a significant time x group interaction effect on the primary outcome variables of PSQI score(P<0.05)except ISI,ESS,SAS,SDS,FS-14,MMSE and SF-36 scores(P>0.05).The results of intra-group comparison showed that after treatment,the mean scores of PSQI,ISI,ESS,SAS,SDS,FS-14 and MMSE in the treatment group and the control group were lower than that before,and the difference was statistically significant(P<0.001),and those indicators in the treatment group decreased more significantly than that in the control group(P<0.05).After intervention,SF-36 scores in both groups were higher than before,and the difference was statistically significant(P<0.001).(3)The follow-up resultsThe mixed linear model results showed that there were significant differences among different time end-point(Ftime=37.615,P<0.001),and there was significant time group interaction effect on the PSQI score(P<0.05).The results of intra-group and inter-group comparison showed that compared with pre-treatment(T0),the PSQI scores of the treatment group at each time point(4,8,16,24 weeks)was lower than pre-treatment,the difference was statistically significant(P<0.001).The PSQI scores of the control group at the time point of 4,8 and 16 week were significantly different(P<0.001),but there was no significant difference in PSQI scores at the time point of 24 week(P>0.05).(4)Adverse eventsThe most common side effect was skin irritation on the stimulation sites with a total of 9 participants from two groups(treatment group:4 of 30,13.3%;control group:5 of 30,16.7%)describing pruritus,mild burns,discomforts,numbness or pain.In the treatment group,1 of 30(3.3%)participants dropped out of the trial due to the poor tolerance to ear pain.Additionally,other adverse events including gastrointestinal reactions(1 of 30,3.3%)and blood pressure fluctuations(1 of 30,3.3%)were also observed in the treatment group.ConclusionCompared with AA group,the therapeutic effect of taVNS was more effective and safe,and the curative effect lasts more longer.Study 3 The exploration of the therapeutic mechanism of taVNS versus AA in the treatment of MHDSDObjectiveBased on the therapeutic effect of taVNS and AA,we aimed to investigate the changes of brain functional activity of MHSD patients after treatment by using rs-fMRI,and provide more objective evidence for the clinical application of taVNS.Methods40 MHDSD subjects were recruited and randomly allocated into taVNS group and AA group.The clinical variables including demographic data,biochemical markers,outcome measurements and rs-fMRI data before and after treatment were also collected.Then we compared the therapeutic effects and safety between two groups and further investigate the differences of spontaneous neural activities of the brain between two groups for MHDSD patients.Results(1)The baseline clinical variables results34 MHDSD patients who completed 4-week treatment with complete clinical variables data and fMRI data were included in the final analysis,including 18 patients in the treatment group and 16 patients in the control group.The intra-group comparison results showed that:①there were no significant differences in baseline demographic characteristics(age,sex,height,weight,BNI,educational level)and disease data(age of dialysis,age of insomnia,use of sleeping pills,and underlying diseases)between the two groups(P>0.05).②There were no significant differences in biochemical markers(serum creatinine,urea nitrogen,urea clearance index,serum calcium,serum chlorine,serum inorganic phosphorus,serum sodium,serum potassium,hemoglobin,blood glucose,serum albumin,parathyroid hormone,C-reactive protein,systolic/diastolic blood pressure fluctuation)between the two groups(P>0.05).③There was no significant difference in clinical measurements between the two groups,including PSQI,SDS,SAS and SF-36 scores(P>0.05).(2)The outcome measurement①After four weeks of treatment,there was no significant difference in PSQI scores between the two groups(P>0.05).However,there was significant difference of the PSQI score before and after treatment in both groups,and the PSQI score in the treatment group decreased more significantly than that in the control group(P<0.05).②There were no significant differences in SDS,SAS and SF-36 scores between two groups after 4 weeks of treatment(P>0.05);There was no significant difference in the difference of SDS,SAS and SF-36 scores in both groups before and after treatment(P>0.05).(3)rs-fMRI analysis results2x2 repeated measurement analysis of variance showed that after four weeks of treatment,the brain regions with interactive effects of fALFF between two groups mainly located in the right middle/suproccipital gyrus,left cuneus gyrus,and left cerebellar/lingual gyrus(voxel-wise P>0.001 uncorrected and cluster-level P<0.05 after 3dFWHMx and 3dClustSim).(4)Correlation analysisThere were significant positive correlations of the fALFF changes(pre-post)in the right middle/suproccipital gyrus with sleep quality changes(pre-post)(r=0.632,P=0.015)and the sleep disturbance(r=0.532,P=0.05).We also observed significant correlations of the fALFF changes(pre-post)in left cuneus gyrus with the sleep quality changes(pre-post)(r=0.581,P=0.029)and the SAS changes(pre-post)(r=0.579,P=0.03).Conclusion:To conclude,our findings revealed a previously unidentified mechanism by which taVNS would modulate the visual and emotional/cognitive network to achieve improvements for MHDSD patients.