Evaluation of Cognitive and Biochemical Brain Status in Patients after Carotid Endarterectomy

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LIST OF ABBREVIATIONS

ACAS — asymptomatic carotid atherosclerosis study

ACST-1 — asymptomatic carotid surgery trial

BDNF — brain derived neurotrophic factor

CEA — carotid endarterectomy

EDP — end diastolic pressure

ECST — European Carotid Surgery Trial

FAB — frontal assessment battery

ICA — internal carotid artery

MMSE — Mini Mental State Examination

MoCA-test — Montreal Cognitive Assessment

NASCET — North American Symptomatic Carotid Endarterectomy Trial

NIHSS — National Institutes of Health Stroke Scale

NSE — neuron specific enolase

RI — resistance index

TILB — temporary intraluminal bypass

VACS — Veterans Affairs Cooperative Study

INTRODUCTION

At the moment, surgical revascularization of the carotid system (carotid endarterectomy (CEA) or stenting of the carotid arteries)), if indicated, is the main method of both primary and secondary prevention of undesirable cerebral ischemic events associated with the degradation of an atherosclerotic plaque. Large studies, such as the North American Symptomatic Carotid Endarterectomy Trial (NASCET), the European Carotid Surgery Trial (ECST), the Veterans Affairs Cooperative Study (VACS), the Asymptomatic Carotid Atherosclerosis Study (ACAS) and the Asymptomatic Carotid Surgery Trial (ACST-1), show the leading role of CEA in the prevention of cerebrovascular catastrophes [1–5]. Nevertheless, in these studies, the role of changes in the cognitive status of the patient in the early and long-term postoperative period have not been investigated. Also of great importance is evaluation of predictors of changes in neuropsychic functions in this group of patients [6]. Taking into account a significant number of strokes occurring in the group patients of the working age, this is increasingly important for the socialization and return of the patient to work. Early cognitive and psychoemotional changes have been studied, although not widely, but, nevertheless, they are described in the literature as a postoperative cognitive dysfunction, and reflect short-term processes of restructuring cerebral hemodynamics in response to an increase in the cerebral blood flow [7–9].

The data about the long-term postoperative period and the status of the cerebral functions are ambiguous [10]. In a large meta-analysis including 31 studies and 2059 patients, it is stated that 64% of patients had no changes in the cognitive functions in the long-term period after carotid interventions, 24% of patients had improvements in several tests, 1.8% had impairment in all domains, and 1.5% had improvement [11].

Biochemical markers of cerebral damage are also of great importance for an objective assessment of the degree of ischemic and reperfusion damage to both neurons and glia [12–14].

Among the basic markers, of importance are 3 brain proteins [15–17]:

1. S100b protein is considered specific to cerebral tissue, as it is a component of different cells (Schwann cells, astrocytes). Since this protein is present in a large number of nerve cells, it should also be considered as an indirect sign of damage to the blood-brain barrier, because in this case it appears in the peripheral blood.
2. Neuron specific enolase (NSE) is present in almost all cells including granular cells, Purkinje cells, projection, sensory and autonomic neurons, etc. Appearance of NSE in the systemic circulation evidences damage to neurons and increase in the permeability of the blood-brain barrier.
3. Brain derived neurotrophic factor (BDNF) is widely expressed in the central nervous system and can have a strong influence on the development, morphology, synaptic plasticity and cerebral functions. Besides, it plays a role in the processes, such as neuronal maturation, synapse formation and synaptic plasticity. Its increase reflects the processes of restoring functions of nervous tissue in damages of different genesis.

The aim of this study to evaluate biochemical cerebral parameters, cognitive status of patients and their interrelation in the early and long-term periods after carotid endarterectomy.

MATERIALS AND METHODS

An open perspective study was conducted in the period from October 2021 to December 2022 on the base of the cardiovascular surgery department of Ryazan Regional Clinical Hospital. The study was approved by the Local Ethics Committee of Ryazan State Medical University (Protocol No. 3 of October 11, 2021). All the patients signed the informed consent to participate in the study.

Sixty patients were included and divided into two groups:

• Group A — 30 ‘symptomatic’ patients with a hemodynamically significant lesion of the internal carotid artery (ICA) and a history of an acute cerebrovascular accident (ischemic stroke, transient ischemic attack, retinal embolism), who underwent CEA.
• Group B — 30 ‘asymptomatic’ patients with a hemodynamically significant lesion of the ICA, but with no history of cerebral vascular accidents, who underwent CEA.

Both groups of patents were comparable in age and comorbid pathology, as well as in the technique of intervention. All the patients underwent CEA.

Inclusion criterion: hemodynamically significant lesion of the ICA. For verification, all the patients underwent preoperative US of brachiocephalic arteries. For the patients of group A, the indication for the intervention was ICA stenosis from 50% (with unstable atherosclerotic plaque), or 60% (with no signs of instability) to 99% (NASCET criterion), for group B patients — stenosis from 70% to 99%. Three patients of group A (10%) and 2 patients of group B (6%) had contralateral stenosis of the ICA more than 70%.

 

Table 1. Clinical and Demographic Characteristics of Studied Groups

Parameters	Group А, ‘symptomatic’ patients	Group B, ‘asymptomatic’ patients	p
n	30	30	–
Age, M ± m, лет	66.7 ± 8.2	68.2 ± 7.1	–
Number of men, n (%)	21 (70)	20 (66)	–
Essential hypertension, n (%)	28 (93)	26 (86)	0.424
Coronary heart disease, n (%)	11 (36)	15 (50)	0.123
Postinfarction cardiosclerosis, n (%)	4 (13)	6 (20)	0.302
Type 2 diabetes mellitus, n (%)	7 (23)	6 (20)	0.155

Note: р — significance level in comparison between groups A and B

 

Exclusion criteria: acute cerebrovascular accident (stroke or transient ischemic attack) in the early postoperative period, refusal of the patients from participation in further examination, identification of oncological disease irrespective of localization, and death of a patient.

A standard protocol of preoperative examination included general clinical examination and laboratory tests, examination by a therapist, neurologist, ophthalmologist, ultrasound examination of the extracranial sections of the brachiocephalic arteries (linear sensor 7 MHz–13 MHz; GE Vivid S5, USA), magnetic resonance imaging of the brain (SIEMENS MAGNETOM Symphony, Germany), in some cases, CT angiography of the aortic arch arteries to clarify the treatment tactics (Siemens Somatom Go Up, Germany).

The CEA technique (classic or eversion) was chosen based on the preferences of the operating surgeon, the extension of the atherosclerotic plaque to the internal and common carotid arteries, as well as the level of the carotid bifurcation. The types of surgical interventions and the angiological status are presented in Table 2.

 

Table 2. General Characteristics of Performed Interventions

Intervention	Group А, ‘symptomatic’ patients	Group B, ‘asymptomatic’  patients	p
n	30	30	–
Carotid endarterectomy, n (%)	Classic — 14 (46) Eversion — 16 (54)	Classic — 14 (46) Eversion — 16 (54)	0.519 0.457
Transient intraluminal bypass, n (%)	6 (20)	7 (23%)	0.378

 

A temporary intraluminal bypass (TILB) was used in patients whose cerebral reserve did not permit surgical intervention with prolonged clamping of the carotid arteries. Retrograde pressure was measured in the ICA, the criterion for installing TILB was retrograde pressure in the ICA below 45 mm Hg. Also, in some clinical situations, surgeons used an intraluminal bypass preventatively.

All patients were given a standard anesthetic support. Premedication included sedatives, antihistamines and M-cholinolytic drugs. Intraoperatively, total combined anesthesia was applied with use of fentanyl, inhalation anesthetic (nitric oxide), and oxygen.

The overall follow-up period was 6 months. All the patients underwent control examinations in the following periods:

• Before intervention;
• 1 day after intervention;
• 1 month after intervention;
• 6 months after intervention.

On the examination, the patients underwent:

1. Testing using cognitive status assessment scales:

• Mini Mental State Examination (MMSE) in five basic positions: orientation, memory, perception, attention, speech. Periods: before the intervention, after 1 day, 1 month, 6 months;
• Frontal Assessment Battery (FAB). Evaluation of the following parameters: conceptualization, verbal fluency, dynamic praxis, simple choice reaction, complicated choice reaction, and the study of grasping reflexes. Periods: before surgery, after 1 month, 6 months;
• Montreal Cognitive Assessment (MoCA). Evaluation of the following parameters: visual-constructive/executive skills, naming, memory, attention, speech, abstraction, delayed reproduction, orientation. Periods: before surgery, after 1 month, 6 months;
• National Institutes of Health Stroke Scale (NIHSS) — for symptomatic patients in the period before the intervention and after 6 months;

2. Assessment of markers of cerebral cellular dysfunction in the peripheral blood:

• S100b protein;
• neuron specific enolase (NSE);
• brain derived neurotrophic factor (BDNF).

Blood was taken in fasting condition. Next, the blood was centrifuged at 3000 revolutions per minute for 10 minutes, the obtained serum was used to determine the level of biochemical parameters. S100b protein was determined using SEA567Hu ELISA Kit for S100 Calcium Binding Protein B (S100B) (Korea); NSE — using SEA537Hu ELISA Kit for Enolase, Neuron Specific (NSE) (Korea) kits; BDNF — using SEA011Hu ELISA Kit for Brain Derived Neurotrophic Factor (BDNF) (Korea). The enzyme immunoassay was used (Stat Fax 3200, USA) with two control measurements of one sample;

3. Ultrasound examination to evaluate:

• the degree of ICA restenosis;
• end diastolic pressure (EDP) in ICA;
• resistance index in ICA.

On the 1^st day, testing was performed only on the MMSE scale to identify postoperative cognitive dysfunction, evaluate the predictivity of this scale, and also to avoid the effect of 'memorization' on other neuropsychic scales. All patients were tested in the daytime by the same specialist, the testing time did not exceed 30 minutes to reduce the risk of the exhaustion.

The statistical analysis was performed using Statistica 10.0 (Stat Soft Inc., USA), Excel (Microsoft, USA) program. The data distribution was performed using Shapiro–Wilk test (level: p > 0.05). In case of distribution of data different from normal, nonparametric statistical methods were used for further processing of the results obtained. Spearman's correlation coefficient was used to assess the interrelation of the studied parameters. Wilcoxon criterion was used to assess the statistical significance of intra-group differences (in symptomatic or asymptomatic patients in different follow-up periods). The intergroup differences (between groups A and B) were assessed using Mann–Whitney test. The critical significance level (p) was assumed to be < 0.05.

RESULTS

Cognitive and biochemical status in group A (symptomatic patients).

Cognitive testing in different periods before and after surgery showed improvement of the cognitive status of this group of patients on MMSE scale (p = 0.001) and MoCA-test (p = 0.09) by the 6th month relative to the initial data; on FAB scale relative to the data after 1 month (p = 0.01, Figure 1). At the same time, a decrease in the level of neurological deficit on NIHSS was noted (p = 0.01). On the whole, the increment was 1 point on MMSE, 2.5 points on MoCA and 1 point on FAB, but there was 1.5 point reduction on NIHSS scale, which reflects improvement of the cognitive status in this group of patients after surgical intervention.

 

Fig. 1. Dynamics of cognitive testing on MMSE, MoCa, FAB and NIHSS scales in group A in different periods relative to the intervention.

Notes: FAB — frontal assessment battery, MoCA-test — Montreal Cognitive Assessment, MMSE — Mini Mental State Examination, NIHSS — National Institutes of Health Stroke Scale; * — р < 0.05 — statistically significant differences relative to the initial level.

 

To note, there were no significant differences in the MMSE scores in patients on the first day after the intervention as a reflection of cerebral hyperperfusion syndrome or postoperative cognitive deficit. There was neither correlation between neuropsychic testing and ICA clamping time.

Comparing the parameters of cognitive status and the ultrasound data, it was noted that 6 months after surgery, the ultrasound data showed an inverse correlation between the MMSE score and the resistance index (RI; r = -0.675; p = 0.005; Figure 2A) and a direct correlation between the FAB score and EDP in ICA (r = +0.912; p = 0.005; Figure 2B). EDP parameters in ICA and RI reflect the state of intracerebral arteries and arterioles and, according to the data obtained, directly correlate with changes in the cognitive status of patients.

 

Fig. 2. Results of correlation analysis: A — correlation relationship between MMSE score and resistance index in the internal carotid artery in 6 months after the intervention, B — correlation relationship between FAB score and the end diastolic pressure in the internal carotid artery in 6 months after the intervention.

Notes: EDP — end diastolic pressure, FAB — frontal assessment battery, MMSE — Mini Mental State Examination.

 

In the course of the study, we examined the dynamics of changes in biochemical parameters (BDNF, 100b, NSE; Figure 3). It was found that in patients of group A, 6 months after surgery, the BDNF neuro-adaptation marker increased (p = 0.01) against the background statistically insignificant change in the NSE (p = 0.18) and S100b (p = 0.18) cerebral damage parameters compared to the initial values. It is also necessary to note a 16-fold increase in BDNF from the 1st day to the 6th month (p = 0.01). During the restoration of cerebral perfusion with an increase in the blood flow in the intracranial region, the neurons located on the border with the infarction zone, undergo restructure and release neurotrophic factors that enhance interneuronal interactions. To this end, the markers of cerebral damage did not show any statistically significant changes, which reflects an insignificant reperfusion damage to the brain tissue in a sharp increase in the intracranial blood flow.

The correlation analysis revealed a direct relationship between the initial levels of S100b and NSE (r = +0.834, p = 0.005) and their values in 6 months (r = +0.561, p = 0.005) after surgical intervention. These proteins are markers of damage to the brain tissue and reflect the degree of breakage of the integrity of both white and gray matter cells as such and of the blood-brain barrier.

 

Fig. 3. Dynamics of biochemical parameters of the brain tissue (protein S100b, pg/ml; NSE, ng/ml; BDNF, pg/ml of plasma) within the first six months after the intervention in patients of group A.

Notes: BDNF — brain derived neurotrophic factor, NSE — neuron specific enolase.

 

The analysis of interrelations between the level of proteins associated with changes in the perfusion status of the brain and cognitive testing, did not reveal any statistical relationships.

Cognitive and biochemical status in group B (asymptomatic patients).

The data of the analysis of the studied parameters in asymptomatic patients are given in Figure 4. By the 6th month, no statistically significant improvement or worsening of the cognitive status were identified on the FAB, MMSE, NIHSS scales, MoCA test showed an improvement on average by 2 points (p = 0.03).

Correlation analysis revealed a direct relationship between FAB scale and MoCA test before the intervention (r = +0.555; p = 0.005) and 1 month after (r = +0.566; p = 0.005).

It is also important to note that, like in the group of asymptomatic patients, there were no reliable differences in the cognitive status of patients on the first day after the intervention as a reflection of reperfusion syndrome.

 

Fig. 4. Dynamics of cognitive testing on the MMSE, MoCa, FAB и NIHSS scales in group B in different periods relative to the surgical intervention.

Notes: : MoCA-test — Montreal Cognitive Assessment, MMSE — Mini Mental State Examination; * — р < 0.05 — statistically significant differences compared to the initial level.

 

Considering the biochemical parameters, it was found that in 6 months after surgery, the S100b (p = 0.01) and NSE (p = 0.02) markers increased twice, and BDNF protein increased 1.5 times from the initial values (p = 0.005). As for NSE marker, it increased 4-fold by the 6th month relative to the values on the 1st day after the intervention (p = 0.005; Figure 5). These changes are rather ambiguous, S100b and NSE are markers of damage and appear in the peripheral blood only in case of disorders of the blood-brain barrier, which can be associated or not associated with damage to neurons. As for BDNF, it is a parameter of the restoration of the functions of neurons and glia. In our opinion, the detected changes should be considered as processes occurring in parallel, including damage due to chronic cerebral ischemia and restoration with replacement of the lost functions of a number of nerve cells.

 

Fig. 5. Dynamics of biochemical parameters of the cerebral tissue (protein S100b, pg/ml; NSE, ng/ml; BDNF, pg/ml of plasma).

Notes: BDNF — brain derived neurotrophic factor, NSE — neuron specific enolase.

 

Subsequently, a direct correlation was established between the initial levels of the following proteins: S100b and NSE (r = +0.838; p = 0.005), S100b and BDNF (r = +0.592; p = 0.005), NSE and BDNF (r = +0.577; p = 0.005); on the 1st day after the intervention: NSE and BDNF (r = +0.620; p = 0.005); after 6 months: NSE and BDNF (r = +0.752; p = 0.005).

In group B patients, the ultrasound data 6 months after surgery were not associated with either neuropsychic status or biochemical parameters.

When analyzing the studied parameters in groups A and B, a difference was revealed only between the initial levels of BDNF marker. In group A patients, the level of this protein was three times lower than in group B patients (p = 0.04). This may probably be due to the depletion of the cerebral reserve aimed at restoring interneuronal interactions and replacing the lost functions of some neurons lost after a past cerebrovascular accident.

We also conducted an intra-group analysis of the studied parameters, depending on the type of surgical intervention performed. When comparing classic and eversion CEA, a difference on the FAB scale was revealed before surgery (p = 0.04), after 1 (p = 0.04) and 6 months (p = 0.01) in group B patients. At the same time, the average score with the classic method was lower and was 15 in all periods, and with eversion method — 17. In our opinion, these data are quite ambiguous due to a small sample size and the influence of the CEA type on only one scale of assessment of cognitive status.

In group A, neither type of CEA, nor the clamping time had any reliable effect on the cognitive and biochemical cerebral status.

DISCUSSION

Considering a group of patients with a history of cerebrovascular accident, we found a reliable improvement of the cognitive status on all the studied scales (MMSE, FAB, MoCA-test, NIHSS) in the long-term period. It is difficult to say whether this is associated with the period of restoration of cerebral circulation after a cerebrovascular accident or with improvement of perfusion after CEA. Similar data were obtained by C. Baracchini, et al. (2012). They evidence improvement of the cognitive status in patients above 65 with an acute cerebrovascular accident in history and a significant lesion of the carotid artery, who underwent CEA. Patients with symptomatic stenoses showed a significant improvement of the average parameters of cognitive functions on MMSE and MoCA tests in 3 and 12 months, respectively [18]. Besides, in such patients, a relationship between neurophychic testing and ultrasound data should be noted: EDP and RI. Ultrasound parameters reflect a degree of brain perfusion directly related to the performed intervention. Similar data are reflected in the work of А. Nakamizo, et al. (2020), where the interrelation was shown between EDP and pulsation index in the common carotid artery and the level of neuropsychic status of patients after CEA [19].

In the group of patients without a previous acute cerebral ischemia, the neuropsychological testing data did not show much dynamics, only the MoCA scale scores significantly increased by the 6th month after the intervention. At the same time, the markers of cerebral damage (S100b and NSE protein) and of adaptation (BDNF protein) were higher by the 6th month. This cohort of patients had an inverse tendency compared to symptomatic patients. The noted changes may reflect restructure of the brain tissue in response to reperfusion with the intact white and gray matter.

In our study it was found that the groups of patients initially differed only in the level of BDNF protein, with the lower level in symptomatic patients. It is important to note the role of this protein in such processes as neuron maturation, synapse formation and synaptic plasticity [20]. Such changes may reflect the mechanisms of compensation and redistribution of functions between neurons due to formation of new interneuronal connections. Studies have shown that in chronic cerebral ischemia including that associated with stenoses of brachiocephalic arteries, the level of BDNF decreases, which correlates with impairment of cognitive functions, and in case of traumatic head injury it increases in the long-term period as a factor of regression of cognitive disorders [21, 22].

The limitations of the study include a small sample size, a short follow-up period after surgery, as well as the scales used (they are validated for assessing dementia, but not for determining postoperative cognitive deficits after CEA). In our opinion, it is necessary to continue this work and expand it by introducing a control group of patients and increasing the follow-up periods.

CONCLUSIONS

1. In symptomatic patients, carotid endarterectomy leads to a comprehensive improvement of the cognitive status evaluated on the scales (MMSE, FAB, MoCA-test, NIHSS) in the long-term postoperative period, and in asymptomatic patients — only to a partial improvement (on MoCA scale).
2. The degree of improvement of the neuropsychic status of patients with a history of an acute cerebrovascular accident directly depends on the level of the end diastolic pressure and resistance index in the internal carotid artery on the side of the intervention.
3. No reliable relationship was found between the biochemical status of the brain (the level of S100b, NSE and BDNF proteins) and cognitive functions.

ADDITIONALLY

Funding. The study was carried out within the framework of the grant of the President of the Russian Federation No. MD-922.2022.3.

Conflict of interests. The authors declare no conflicts of interests.

Contribution of authors: R. E. Kalinin — final approval of the article; I. A. Suchkov — checking the critical intellectual content of the work; A. S. Pshennikov — analysis and interpretation of data, concept and design of study; R. A. Zorin — conducting neuropsychological testing, analysis and interpretation of results; N. A. Solyanik — collecting material, conducting the main stages of the study, analysis and interpretation of data, writing the text; A. A. Nikiforov — collecting material, conducting biochemical studies, analyzing the results; E. A. Klimentova — analysis and interpretation of clinical data; I. V. Vezenova — conducting and interpreting ultrasound data; G. A. Leonov — analysis and interpretation of the results of neuropsychological testing; A. O. Burshinov — analysis and interpretation of data. The authors confirm the correspondence of their authorship to the ICMJE International Criteria. All authors made a substantial contribution to the conception of the work, acquisition, analysis, interpretation of data for the work, drafting and revising the work, final approval of the version to be published and agree to be accountable for all aspects of the work.

Финансирование. Исследование выполнено в рамках гранта Президента РФ № МД-922.2022.3.

Конфликт интересов. Авторы заявляют об отсутствии конфликта интересов.

Вклад авторов: Калинин Р. Е. — окончательное утверждение рукописи; Сучков И. А. — проверка критически важного интеллектуального содержания работы; Пшенников А. С. ― анализ и интерпретация данных, разработка концепции и дизайна; Зорин Р. А. — проведение нейропсихического тестирования, анализ и интерпретация результатов; Соляник Н. А. — забор материала, проведение основных этапов исследования, анализ и интерпретация данных, написание статьи; Никифоров А. А. — забор материала, проведение биохимических исследований, анализ результатов; Климентова Э. А. — анализ и интерпретация клинических данных; Везенова И. В. — проведение и интерпретация данных ультразвукового исследования; Леонов Г. А. — анализ и интерпретация результатов нейропсихического тестирования; Буршинов А. О. — анализ и интерпретация данных. Все авторы подтверждают соответствие своего авторства международным критериям ICMJE (все авторы внесли существенный вклад в разработку концепции, проведение исследования и подготовку статьи, прочли и одобрили финальную версию перед публикацией).

About the authors

Roman E. Kalinin

Ryazan State Medical University

Email: kalinin-re@yandex.ru
ORCID iD: 0000-0002-0817-9573
SPIN-code: 5009-2318

MD, Dr. Sci. (Med.), Professor

Russian Federation, Ryazan

Igor’ A. Suchkov

Ryazan State Medical University

Email: suchkov_med@mail.ru
ORCID iD: 0000-0002-1292-5452
SPIN-code: 6473-8662

MD, Dr. Sci. (Med.), Professor

Russian Federation, Ryazan

Aleksandr S. Pshennikov

Ryazan State Medical University

Email: pshennikov1610@rambler.ru
ORCID iD: 0000-0002-1687-332X
SPIN-code: 3962-7057

MD, Dr. Sci. (Med.), Associate Professor

Russian Federation, Ryazan

Roman A. Zorin

Ryazan State Medical University

Email: zorin.ra30091980@mail.ru
ORCID iD: 0000-0003-4310-8786
SPIN-code: 5210-5747

MD, Dr. Sci. (Med.), Associate Professor

Russian Federation, Ryazan

Nikita A. Solyanik

Ryazan State Medical University

Author for correspondence.
Email: solianik.nikita@gmail.com
ORCID iD: 0000-0002-4667-3513
SPIN-code: 3258-5210

MD, Cardiovascular Surgeon; Postgraduate Student of the Department of Cardiovascular, X-ray Endovascular Surgery and Radiation Diagnostics

Russian Federation, Ryazan

Aleksandr A. Nikiforov

Ryazan State Medical University

Email: a.nikiforov@rzgmu.ru
ORCID iD: 0000-0003-0866-9705
SPIN-code: 8366-5282

MD, Cand. Sci. (Med.), Associate Professor

Russian Federation, Ryazan

Emma A. Klimentova

Ryazan State Medical University

Email: klimentowa.emma@yandex.ru
ORCID iD: 0000-0003-4855-9068
SPIN-code: 5629-9835

MD, Dr. Sci. (Med.)

Russian Federation, Ryazan

Irina V. Vezenova

Ryazan Regional Clinical Hospital

Email: irina-vz@mail.ru
ORCID iD: 0009-0002-4410-3821
Russian Federation, Ryazan

Gennadiy A. Leonov

Ryazan State Medical University

Email: genady.leonov1956@gmail.com
ORCID iD: 0000-0001-5780-1675
SPIN-code: 5115-3996

MD, Dr. Sci. (Med.), Associate Professor

Russian Federation, Ryazan

Aleksandr O. Burshinov

Ryazan State Medical University

Email: baomz@mail.ru
ORCID iD: 0000-0002-6951-0290
SPIN-code: 8792-9686

MD, Dr. Sci. (Med.), Associate Professor

Russian Federation, Ryazan

References

Supplementary files