Cerebral circulation time is defined as the difference between the time to peak of the cavernous sinus segment of the internal carotid artery and the Trolard vein, which is easily obtained in digital subtraction angiography and is closely associated with hemodynamics. Cerebral circulation time can be used to evaluate the outcome of acute ischemic stroke, especially in patients receiving endovascular treatment. This article reviews the evaluation methods of cerebral circulation time and its clinical significance in patients with acute ischemic stroke.

Objective:To explore the risk factors associated with the clinical progression of COVID-19 infection in kidney transplant(KT)recipients during the spread of Omicron variant and evaluate the effectiveness of anti-RNA virus agents in blocking the clinical progression of COVID-19 in these recipients.Methods:Retrospective analysis was conducted for the clinical data on COVID-19 infection in 232 KT recipients followed up from December 4, 2022 to January 31, 2023 at Department of Renal Transplantation, Organ Transplantation Center, Beijing Tsinghua Changgung Hospital.Inclusion criteria were age ≥18 years and stable kidney function without renal replacement therapy.The follow-up time was 30 days after COVID-19 infection.Based upon whether or not there was an infection of COVID-19, KT recipients were divided into two groups of infection(181 cases)and non-infection(51 cases). In infection group, recipients were further assigned into two sub-groups of disease progression(n=23)and stable(158 cases)according to whether or not there was a progression to severe disease.Various factors such as gender, age, body mass index(BMI), time after transplantation, underlying diseases(history of hypertension, diabetes mellitus, coronary heart disease & chronic lung disease), smoking history and dosing of anti-RNA virus agents were collected.Pearson χ2 test or Fisher's exact probability method was utilized for examining enumeration data while Mann-Whitney U test for measurement data.Univariate Logistic regression analysis was conducted and variables with P<0.05 were included into multifactorial Logistic regression analysis to identify independent risk factors for clinical progression of COVID-19 infection in KT recipients. Results:Among 232 KT recipients, infection rate of COVID-19 was 78.0%(181/232). The clinical classification was mild(112 cases), moderate(46 cases), severe(21 cases)and critical(n=2 cases). The severe rate was 12.7%(23/181). After infection with COVID-19, the proportion of KT recipients aged ≥65 years progressing from mild/moderate to severe was higher than those aged<65 years[38.5%(5/13)vs 10.7%(18/168)]. The difference was statistically significant( P=0.014); The proportion of diabetic KT recipients progressing from mild/moderate to severe was higher than those without diabetes[19.1%(13/68)vs 8.8%(10/113)]. The difference was statistically significant( P=0.045). Univariate Logistic analysis showed similar results.Age≥65 years( OR=5.21, 95% CI: 1.54-17.64, P=0.008)or diabetes mellitus( OR=2.44, 95% CI: 1.003-5.911, P=0.049)were the risk factors for COVID-19 infection recipients progressing from mild/moderate to severe disease.Multivariate Logistic analysis revealed that age ≥65 years( OR=4.03, 95% CI: 1.14-14.34, P=0.031)was an independent risk factor for COVID-19 infection recipients progressing from mild/moderate to severe.Among 181 cases of COVID-19 mild/medium infected patients, 18 cases received nimativir/ritonavir and 10 cases had azvudine for anti-RNA virus treatment.However, none of them progressed to severe; 153 cases did not use anti-RNA virus drugs and 23 cases(15.0%)progressed to severe disease and the difference was statistically significant( P=0.028). Among 23 severe cases, 14 cases received nirmatrelvir/ritonavir and 2 cases had azivudine for anti-RNA virus treatment.The former did not progress to critical disease while 1 case in the latter progressed to critical illness and death; 1/7 recipients not using anti-RNA virus agents progressed to critical illness and died while another 6 cases did not progress to critical illness. Conclusions:KT recipients aged ≥65 years or diabetes mellitus have a greater risk of progression from mild/moderate to severe disease after COVID-19 infection.Among them, age ≥65 years is an independent risk factor for patients with COVID-19 infection to progress from mild/moderate to severe.Antiviral treatment with nirmatrelvir/ritonavir or azivudine in KT recipients during mild/moderate stage of COVID-19 infection can significantly reduce the rate of severe disease.Treatment with Nirmatrelvir/Ritonavir is still effective in the severe stage.