The Effect And Mechanism Of Remote Ischemic Preconditioning On Dynamic Cerebral Autoregulation In Healthy Adults

Part One Study on The Rhythm of Dynamic Cerebral Autoregulation During the Daytime(8 AM to 8 PM)in Healthy AdultsBackground and objective: Many functions of the human body possess a daily rhythm,disruptions of which often lead to disease.Dynamic cerebral autoregulation(d CA)stabilizes the cerebral blood flow to prompt normal neural function.However,whether d CA is stable across the day remains unknown.This study aimed to investigate the daily rhythm of d CA.Participants and Methods: Fifty-one healthy adults were recruited and received six d CA measurements per individual that were conducted at predefined time points: 8:00,9:00,11:00,14:00,17:00,and 20:00.DCA was evaluated by a servo-controlled plethysmograph and transcranial Doppler ultrasound.The continuous arterial blood pressure(ABP)was measured non-invasively using a servo-controlled plethysmograph(Finometer Model 1,FMS,Netherlands)at the middle finger.Simultaneously,two 2 MHz transcranial Doppler probes were placed over the temporal windows to monitor in real-time the bilateral middle cerebral arteries at a depth of 45 to 60 mm.the probes were fixed with a customized head frame to make sure cerebral blood flow velocity(CBFV)was continuously and stably measured.CBFV and continuous ABP were recorded simultaneously from each subject for 10 minutes.All data were recorded for further assessment and analysis.Data of ABP and CBFV were acquired using MATLAB(Math Works,Inc.,US).The dynamic relationship between ABP and CBFV was analyzed by Transfer Function Analysis(TFA).Phase difference(PD),gain,and coherence function within a 0.06 to 0.12 Hz frequency range were then derived from TFA to evaluate d CA.Repeated measurement analysis of variance was performed for comparing differences in observed values at different time points.Results: The current study enrolled 51 healthy adults(38.294 ± 13.279 years,40females).DCA was measured in each subject for six times according to the preset procedure.The coherence of all records was over 0.40.From 8:00 to 20:00,the PD was not significantly changed within 12 hours(P = 0.233).ABP including systolic blood pressure(SBP),diastolic blood pressure(DBP),and mean arterial pressure(MAP)was statistically significant at different time points(P < 0.001).Heart rate remained stable during the whole 12 hours in a day(P = 0.052).The results of female or male independent analysis and whole subject analysis were consistent.Conclusions: The rhythm of dCA keep steady during the 8 AM to 8 PM interval in healthy adults,and it is not influenced by the fluctuations of ABP.For evaluating d CA,one random measurement of d CA is reliable.Part Two Study on The Changes in Dynamic Cerebral Autoregulation after Remote Ischemic ConditioningBackground and objective: RIPC,defined as brief transient episodes of ischemia-reperfusion applied in distant tissues or organs,renders remote tissues and organs resistant to a subsequent prolonged ischemia insult.Studies of cardiovascular diseases have repeatedly shown that RIPC could significantly reduce the infarct size after myocardial ischemia in both animals and human patients.Recently,several animal and clinical studies demonstrated a similar beneficial role of RIPC during cerebral ischemia-reperfusion injury and cerebral small-vessel disease.It has been shown that RIPC activates both neuronal signals and humoral factors to confer its protective effects on remote tissues and organs,but the underlying mechanisms,especially in the brain,remain unclear.d CA is a unique function of the cerebrovasculature and is critical to the regulation of cerebral hemodynamics.d CA predicts the occurrence and prognosis of cerebrovascular disease in clinic.Previous studies showed that RIPC can regulate several vasoactive cytokines,which may affect d CA.Nevertheless,it remains unknown whether RIPC can regulate d CA in humans.The study aimed to determine the effect of RIPC on d CA in healthy adults.Participants and Methods: The study was intended to recruited fifty healthy adults(age from 18 to 70,males and females,Asian).A self-controlled interventional study was conducted.Serial measurements of d CA were performed at 7 time points(7:00,9:00,11:00,14:00,17:00,and 20:00,and 8:00 on the next day)without or with RIPC,carried out at 7:20–8:00.d CA was evaluated by a servo-controlled plethysmograph and transcranial Doppler ultrasound.The continuous ABP was measured non-invasively using a servo-controlled plethysmograph(Finometer Model 1,FMS,Netherlands)at the middle finger.Simultaneously,two 2 MHz transcranial Doppler probes were placed over the temporal windows to monitor in real-time the bilateral middle cerebral arteries at a depth of 45 to 60 mm.the probes were fixed with a customized head frame to make sure CBFV was continuously and stably measured.CBFV and continuous ABP were recorded simultaneously from each subject for 10 minutes.All data were recorded for further assessment and analysis.Data of ABP and CBFV were acquired using MATLAB(Math Works,Inc.,US).The dynamic relationship between ABP and CBFV was analyzed by TFA.PD,gain,and coherence function within a 0.06 to 0.12 Hz frequency range were then derived from TFA to evaluate d CA.A paired t-test was used to compare the difference between the two groups if they were in normal distributions.Alternatively,the Wilcoxon signed-rank test was used if the data distribution was not normal.Categorical variables were described as absolute values and percentages.To compare PD,gain,mean arterial pressure,and heart rate between RIPC and different time points,a mixed linear model for repeated measurements was used.Both of the two factors(RIPC and time)that included in the mixed linear model were considered to be the factor of repeated measurement.Results: Fifty-eight healthy adult volunteers were assessed for eligibility,and 8volunteers who did not meet the inclusion criteria or decline to participate were excluded.In the current study,we enrolled 50 healthy adults(34.54 ± 12.01 years,22 males,44%,all Asian).Data from 2 participants were excluded due to low coherence.Thus,the study included 48 participants in total for statistical analysis.The mixed linear model identified the highly significant effects of intervention(P = 0.0006)and time points(P = 0.0024)on phase difference,but did not identify the interaction effect of them(P = 0.4836).In comparison with the PD values at the same time points on the control-day and the RIPC-day,the PD was not significantly altered within 3 h following RIPC.However,the PD value significantly increased starting from 6 h after RIPC,and the increase was sustained for at least 18 h until 24 h after RIPC.The gain did not significantly differ between the control-day and the RIPC-day across all study time points.Conclusions: Overall,our results suggested that RIPC improves dCA from at least 6h to 24 h after RIPC in healthy adults.Our study provides evidence of RIPC inducing neuroprotection and a new approach to improve the cerebrovascular function in terms of d CA.Part Three Study on The Changes of Neuroprotective cytokines and Inflammation-related Cytokines after Remote Ischemic PreconditioningBackground and objective: RIPC,defined as brief transient episodes of ischemia-reperfusion applied in distant tissues or organs,renders remote tissues and organs resistant to a subsequent prolonged ischemia insult.Studies of cardiovascular diseases have repeatedly shown that RIPC could significantly reduce the infarct size after myocardial ischemia in both animals and human patients.Recently,several animal and clinical studies demonstrated a similar beneficial role of RIPC during cerebral ischemia-reperfusion injury and cerebral small-vessel disease.It has been shown that RIPC activates both neuronal signals and humoral factors to confer its protective effects on remote tissues and organs,but the underlying mechanisms,especially in the brain,remain unclear.Previous studies showed that RIPC can regulate several vasoactive blood cytokines,such as adenosine,bradykinin,nitric oxide or nitrite,etc.Moreover,recent studies have shown that RIPC may have neuroprotective and inflammation regulatory functions in animal models.However,whether neuroprotective and inflammation-related cytokines are regulated by RIPC in humans are unknown.The study aimed to assess the effect of RIPC on 30 cytokines in venous blood,including 5 neuroprotective cytokines and 25 inflammation-related cytokines and try to demonstrate that RIPC can differentially regulate a series of neuroprotective and inflammation-related cytokines in the blood.Participants and Methods: Fifty healthy adult volunteers(age from 18 to 70,males and females,Asian)were included in the present study in January 2017 to July 2017.A self-controlled interventional study was conducted.Venous blood samples were collected at baseline and 1 hour after RIPC,and blood cytokines including 5neuroprotective factors and 25 inflammation-related cytokines,were measured using a quantitative protein chip.Five neuroprotective factors included brain-derived neurotrophic factor(BDNF),glial cell line-derived neurotrophic factor(GDNF),β-nerve growth factor(β-NGF),ciliary neurotrophic factor(CNTF),and vascular endothelial growth factor-A(VEGF-A,which is also a potent vasoactive factor).(2)Twenty-five inflammation-related cytokines included interleukin-1α(IL-1α),interleukin-1β(IL-1β),interleukin-4(IL-4),interleukin-6(IL-6),interleukin-8(IL-8),interleukin-10(IL-10),interleukin-18(IL-18),interferon-γ(IFN-γ),monocyte chemotactic protein-1(MCP-1),macrophage inflammatory protein-1β(MIP-1β),matrix metalloproteinase-2(MMP-2),matrix metalloproteinase-3(MMP-3),matrix metalloproteinase-9(MMP-9),tissue inhibitor of metalloproteinases-1(TIMP-1),tumor necrosis factor-α(TNF-α),transforming growth factor-β1(TGF-β1),C-reactive protein(CRP),granulocyte-macrophage colony-stimulating factor(GM-CSF),eotaxin(EOT),eotaxin-2(EOT-2),eotaxin-3(EOT-3),Adiponectin,tumor necrosis factor receptor superfamily member 6(Fas),leukemia inhibitory factor(LIF),thymus and activation-regulated chemokine(TARC).Multiple cytokines were compared between baseline and 1 h after RIPC,so Bonferroni correction for multiple comparison between groups was applied.The adjusted P value was obtained by multiplying the crude P value by the number of multiple comparisons(six times).Results: One hour after RIPC,VEGF-A and GDNF in venous blood serum increased significantly compared to the baseline levels(P=0.0006,P<0.0001).The levels of TGF-β1,LIF,MMP-9,and TIMP-1 were significantly higher than the baseline levels of these cytokines(P=0.0030,P=0.0372,P < 0.0001,P < 0.0001).In contrast,the level of MCP-1 was significantly lower than the baseline level(P=0.0234).Conclusions: RIPC also plays neuroprotective and inflammation regulatory roles in humans by altering various cytokines.Our study provides evidence of RIPC inducing neuroprotection and a new approach to improve the cerebrovascular function.