Effects Of Sleep Reactivity On Sleep Structure,orderliness And Cortisol After Stress: A Preliminary Study In Healthy Young Adults

BackgroundIn recent years,the incidence of insomnia is gradually increasing and getting younger,but the pathogenesis of insomnia is still unclear.Studies have shown that people with high sleep reactivity（H-SR）are more likely to develop insomnia,and stress can also induce insomnia.Therefore,the premorbid characteristics of people with insomnia can help us understand the onset and development of insomnia.Evidence-based evidence suggests that polysomnography（PSG）shows decreased objective sleep quality,changes in the micro-structure and orderliness of the electroencephalogram,and increased cortisol secretion in patients with insomnia.Entropy is a nonlinear method to measure the orderliness of brain waves,while cortisol is associated with stress reactivity.The present study aimed to investigate the changes and links of SR and stress reactivity on the macro-structure and orderliness of sleep and cortisol levels in healthy young adults.MethodsSixty-two healthy young adults were recruited,with 32 in a stress group and30 in a control group.The general data of all participants were collected and tested with Pittsburgh Sleep Quality Index,Hamilton Depression Rating Scale-17,Hamilton Anxiety Scale-14 and The Ford Insomnia Response to Stress Test（FIRST）.Each group was further divided into H-SR and low sleep reactivity（L-SR）subgroups according to the FIRST≥16.All participants completed two nights of polysomnography in a sleep laboratory.Before conducting polysomnography on the second night,the stress group completed the Trier Social Stress Test and saliva was collected at four time points（-20min,+1min,+15min,+30min）.After completing all the tests,we analyze the PSG data,including total sleep time（TST）,the total duration of wakefulness after sleep onset（WASO）,sleep efficiency（SE）,sleep latency（SL）,rapid eye movement sleep latency（REM-L）,duration of REM sleep and non-REM（NREM）sleep stages 1,2,3（N1,N2,N3）,and their relative percentages of the total sleep time.REM density,approximate entropy（Ap En）,sample entropy（Samp En）,fuzzy entropy（Fuzz En）and multiscale entropy（MSE）are calculated.An enzyme-linked immunosorbent assay was performed to determine the cortisol levels.Results1.PSG:Compared with the healthy young adults without stress,the TST[F_（1,62）=14.130,P<0.001],N1[F_（1,62）=4.344,P=0.042],N2[H_（1,62）=6.915,P=0.009]and REM%[F_（1,60）=4.362,P=0.041]decreased,while SL[H_（1,62）=6.000,P=0.014],REM-L[H_（1,60）=4.011,P=0.045]and REM density[F_（1,58）=8.155,P=0.006]increased significantly in the healthy young adults with stress.Compared with healthy young adults with L-SR,the TST[F_（1,62）=18.383,P<0.001],SE[H_（1,62）=22.805,P<0.001],N1%[F_（1,62）=9.709,P=0.003],N2[H_（1,62）=9.116,P=0.003]and REM%[F_（1,60）=4.566,P=0.037]decreased,while WASO[H_（1,62）=22.523,P<0.001],SL[H_（1,62）=4.760,P=0.029]and REM-L[H_（1,60）=4.854,P=0.028]increased significantly in healthy young adults with H-SR.The duration of REM sleep was affected by the interaction of stress×SR[F_（1,60）=4.811,P=0.032].2.Entropy:Compared with the unstressed healthy young adults,the Ap En[F_（1,62）=6.733,P=0.012],Samp En[F_（1,62）=5.338,P=0.024],Fuzz En[H_（1,62）=4.447,P=0.035]and MSE[F_（1,54）=8.834,P=0.005]during wakefulness;Ap En[F_（1,62）=5.805,P=0.019],Samp En[F_（1,62）=6.148,P=0.016],Fuzz En[H_（1,62）=4.805,P=0.028]and MSE[F_（1,54）=11.929,P=0.001]during N1 sleep;and MSE[H_（1,54）=3.901,P=0.048]during N2 sleep increased significantly in the stressed healthy young adults.Compared with the healthy young adults with L-SR,the Ap En[F_（1,62）=15.993,P<0.001],Samp En[F_（1,62）=7.981,P=0.006],Fuzz En[H_（1,62）=3.913,P=0.048]and MSE[F_（1,54）=13.797,P<0.001]during wakefulness;Ap En[F_（1,62）=4.276,P=0.043]and MSE[F_（1,54）=6.822,P=0.012]during N1 sleep;and in Ap En[F_（1,62）=4.222,P=0.044],Samp En[H_（1,62）=4.728,P=0.030],Fuzz En[H_（1,62）=4.061,P=0.044]and MSE[H_（1,54）=9.830,P=0.002]during N2 sleep increased significantly in healthy young adults with H-SR.3.Cortisol:Cortisol levels in H-SR and L-SR stress groups had a significant main effect of time[F_（1,31）=4.480,P<0.05].There was a significant difference between the two groups（P<0.05）.ConclusionsN1,N2 and REM sleep are more likely to be affected,while N3 sleep is relatively stable.Stress can damage the sleep of healthy young adults,especially those with H-SR.The cortisol response of healthy young adults with H-SR was stronger than that of L-SR after stress.