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Blood clots could be the cause of post-Covid brain fog
Blood clots could be the cause of the debilitating brain fogs experienced by people after a Covid infection, Oxford University has suggested.
Around 1.9 million people in Britain say they are still experiencing Long Covid, with around 37 per cent complaining that they have difficulty concentrating.
A new study by Oxford University has found that people who were hospitalized with Covid and went on to have cognitive problems had high levels of two proteins that make the blood clot.
It suggests that excess clotting during a Covid infection may have caused long-term damage that can still be felt more than two years later.
Experts said blood clots could cause a lack of blood supply to the brain or cause fatigue, both of which can cause cognitive problems.
Although the team did not study infected people who were not hospitilized, they said the findings could still apply, and warned that patients in hospital were often treated with anticoagulants, unlike those managing the condition at home.
Dr Max Taquet, a National Institute for Health and Care Research (NIHR) senior research fellow at the University of Oxford, said: “The results support the hypothesis that blood clots are a cause of post-Covid cognitive problems.”
The team looked at blood tests from 1,837 people who had been hospitalized with Covid and also suffered serious and persistent problems with thinking, concentration and memory.
Their memory was assessed at six and 12 months after hospitalization using both a formal test and by asking them their own subjective view about their memory.
‘Concentration-induced fatigue’
Dr Simon Retford, of the University of Central Lancashire, a participant in the study, said: “Since my illness I have been plagued by brain fog, concentration-induced fatigue, poor vocabulary, poor memory.
“I am unable to process the amount and scale of work that I would previously have done ‘stood on my head’.”
Tests showed that patients with “brain fog” had high levels of a protein called fibrinogen and raised levels of a protein fragment called D-dimer - both of which are involved in clotting.
Experts believe that fibrinogen may be directly acting on the brain and its blood vessels, whereas D-dimer often reflects blood clots in the lungs, which would mean brain problems are down to a lack of oxygen.
Prof Chris Brightling, NIHR Senior Investigator and Clinical Professor in Respiratory Medicine, at the University of Leicester, said: “One of the things we have been surprised about is the failure of recovery.
“I am disappointed that a number of people are still having persistent problems more than two years on from the pandemic.”
Explaining what might be causing the clotting, Prof Brightling added: “We know that Covid-19 leads to an inflammatory response and activates the lining of the blood vessels and it seems the combination of those is much more profound in Covid-19 than other infections.
“We think this not only leads to the activation of the immune system but also auto-immune activation where the body starts to fight itself.”
"First piece of the jigsaw’
The team are hoping that in the future doctors will be able to spot which Covid-19 patients are most at risk of long-term problems so that they can be treated early.
Prof Paul Harrison, from the University of Oxford, who supervised the study, said: “Identifying predictors and possible mechanisms is a key step in understanding post-Covid brain fog. This study provides some significant clues.”
“We are not saying it is only the cause of the cognitive problems and there may well be others. This is very much the first piece of the jigsaw. “
The research was published in the journal Nature Medicine.
注释：
debilitate: v
表示" 使 ... 衰弱"，means "make weak"，如：The patient had been so debilitate by the fever that he lacked the strength to sit up. 这病人因发烧而一直很虚弱，以至于连坐起来的力气都没有。
anticoagulant: n
表示" 抗凝血剂"，如：Anticoagulant is an effective treatment. 抗凝治疗有效。
plague: v
表示" 折磨；烦扰"，means " annoy (especially with repeated requests or questions)"，如：Plague came in the wake of earthquake. 地震之后紧跟着就是瘟疫。
fibrinogen: n
表示" 纤维蛋白原"，如：Fibrinogen of high cholesterol set is original to ascend occupy 80%. 高胆固醇组纤维蛋白原增高者占80%25。
dimer: n
表示" 二聚物"，如：Dye dimer is effective form of energy transfer, too. 染料二聚体也是能量转移的有效形式。
inflammatory: adj
表示" 煽动性的；发炎的；炎症的"，means "characterized or caused by inflammation"，如：He gave a inflammatory address to the audience. 他对听众发表了煽动性的讲话。Some inflammatory mediators also can stimulate mucin secretion.一些炎症介质也可以刺激粘蛋白的分泌。
中文简要说明：
新冠肺炎祸延世间已4年多，不时听闻有人染疫痊愈后仍受「脑雾」所苦，常感疲倦、忘东忘西、注意力不集中。英国牛津大学（Oxford University）最新研究显示，染疫后「脑子不好使」可能肇因于血栓。研究成果已发表于《自然医学》（Nature Medicine）期刊。
综合英国广播公司、英国《独立报》周四（8/31）报导，这项研究发现，染疫住院出现认知能力后遗症的患者，体内2种与凝血有关的蛋白质含量偏高，影响脑部、肺部。感染病毒期间凝血过量可能导致长期损伤，而且可能持续超过2年。
专家表示，血栓会引起大脑供血量不足或引发疲劳，两者都可能导致认知能力问题，染疫但未住院者不在研究对象之列仍同样适用。16%长新冠患者在染疫恢复后至少半年内思维、注意力、记忆力有困难，轻度患者也可能出现问题。英国约190万人自述处于长新冠（Long Covid）状态，37%注意力难以集中。
团队检视1837名曾因染疫住院且出现认知问题者的血检数据，他们住院后的6个月到12个月接受正规记忆力测试，并自主评估记忆力表现。检测显示，有脑雾者体内「纤维蛋白原」（fibrinogen）与「D-双合蛋白」（D-dimer）含量较高，两者均与凝血有关。「纤维蛋白原」可能直接作用于脑部与脑血管，「D-双合蛋白」往往与肺部血栓有关，这意味脑部状况恐是缺氧所致。
参与研究的英国中央兰开郡大学（University of Central Lancashire）研究人员瑞福（Simon Retford），2020年10月确诊，曾昏迷2周。他虽已恢复6到7成，自认仍如龟速且难以启动的计算机：「我自从染疫以来，一直苦于脑雾、注意力不集中引发的疲劳、语汇薄弱、记忆力变差。我现在能应付的工作量与规模已不比以往。」
中央兰开郡大学临床呼吸治疗学教授布莱特灵（Chris Brightling）说，这种损伤无法痊愈，令研究团队大感意外。他解释，新冠病毒（COVID-19）会引起发炎反应、激化血管内壁，两者合并后似乎使患者出现比其他感染更严重的状况：「这不仅激化免疫系统反应，也激化自体免疫，反过来攻击身体。」
指导这项研究的牛津大学教授哈里森（Paul Harrison）说，上述成果只是「整个拼图的第一片」，盼助医师辨识哪些患者长期后遗症风险最大，以及早治疗，这是关键步骤，但不代表血栓是唯一因素，仍待持续研究。
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