Accidental falls

意外跌倒
  • 文章类型: Journal Article
    背景:主观不稳定或头晕,通常不会增加身体摇摆,在老年人中很常见。缺乏对此类症状的机械理解使得临床治疗困难。这里,我们探索了这种特发性头晕(ID)背后的机制,专注于姿势控制异常。
    方法:30名ID患者和30名年龄匹配的对照组站在移动平台上。平台振荡以不同的速度(从0到0.2m/s)随机传递。姿势控制的标记,包括客观摇摆(树干摇摆路径,通过连接到椎骨C7的传感器记录),步进响应,获得主观不稳定性和焦虑评分。MRI扫描可用于与28例患者和24例对照的脑小血管疾病水平相关。
    结果:我们观察到所有组的客观和主观不稳定性之间存在显着关系。患者的这种拟合斜率明显比对照组更陡,表明对于相同的身体摇摆,感知到的不稳定性更大。逐步线性回归表明,这种客观-主观不稳定关系的斜率最好地解释了对跌倒的担忧(跌倒功效量表-国际),临床身体功能(短身体机能电池)和,在某种程度上,通过脑小血管病的神经影像学标记。此外,患者的踩踏阈值降低,暗示过于谨慎的姿势反应。
    结论:对平衡控制中的不稳定性和细微损害的扭曲感知,包括异常和过于谨慎的步进响应,这是ID出现的基础。它似乎与姿势表现的变化有关,与脑小血管病相关的心理功能和姿势脑网络的破坏。
    BACKGROUND: Subjective unsteadiness or dizziness, usually without increase in body sway, is common in older people. The absence of mechanistic understanding of such symptoms renders clinical management difficult. Here, we explore the mechanisms behind such idiopathic dizziness (ID), focusing on postural control abnormalities.
    METHODS: Thirty patients with ID and 30 age-matched controls stood on a moving platform. Platform oscillations were randomly delivered at different velocities (from 0 to 0.2 m/s). Markers of postural control, including objective sway (trunk sway path, recorded via a sensor attached to vertebrae C7), stepping responses, subjective instability and anxiety ratings were obtained. MRI scans were available for correlations with levels of cerebral small vessel disease in 28 patients and 24 controls.
    RESULTS: We observed a significant relationship between objective and subjective instability in all groups. The slope of this fit was significantly steeper for patients than controls, indicating greater perceived instability for the same body sway. Stepwise linear regression showed that the slopes of this objective-subjective instability relationship were best explained by concerns about falling (Falls Efficacy Scale-International), clinical physical functioning (Short Physical Performance Battery) and, to some degree, by neuroimaging markers of cerebral small vessel disease. In addition, patients had a reduced stepping threshold, suggesting an overly cautious postural response.
    CONCLUSIONS: The distorted perception of instability and subtle impairments in balance control, including abnormal and overly cautious stepping responses, underlies the emergence of ID. It appears to relate to changes in postural performance, psychological functioning and disruption of postural brain networks associated with cerebral small vessel disease.
    导出

    更多引用

    收藏

    翻译标题摘要

    我要上传

    求助全文

  • 文章类型: Journal Article
    目的:通过比较有和没有舟骨骨折的患者在伸出的手跌倒后腕关节的放射学参数,研究解剖变异对舟骨骨折机制的影响。
    方法:对有舟骨骨折(第1组,n=169)和无舟骨骨折(第2组,n=188)患者的X线片进行横断面比较回顾性分析。测量形态测量数据,包括径向倾角(RI),径向高度(RH),尺骨方差(UV),腕高(CH)比,修订腕部高度(RCH)比率和桡骨远端手掌倾斜(PT)。使用受试者工作特征(ROC)曲线分析来评估每个变量的诊断性能,具有统计学上的显着差异。
    结果:平均RI和PT度以及RH长度在统计学上明显更高,与第2组相比,第1组的平均紫外线较低。在CH比率和RCH比率方面,两组之间没有差异。用ROC曲线分析,将比值比最高的截止值确定为RH(截止值=10.77mm,OR=21.886)。
    结论:尽管RI较高,RH,与非骨折组相比,舟骨骨折组的PT值和更多的尺骨负方差,ROC曲线分析显示,仅RH增加可被认为是伸展手跌倒后舟骨骨折的可能危险因素。
    背景:射线照片,危险因素,舟骨骨折,手腕形态。
    OBJECTIVE: To investigate the effects of anatomical variations on the mechanism of scaphoid fracture by comparing the radiologic parameters of the wrist of patients with and without scaphoid fracture after a fall on an outstretched hand.
    METHODS: Cross-sectional comparative retrospective analysis of radiographs of patients with (Group 1, n=169) and without scaphoid fracture (Group 2, n=188). Morphometric data were measured including radial inclination (RI), radial height (RH), ulnar variance (UV), carpal height (CH) ratio, revised carpal height (RCH) ratio and palmar tilt of the distal radius (PT). Receiver operating characteristics (ROC) curve analysis was used to assess the diagnostic performance for each variable with statistically significant difference.
    RESULTS: The mean RI and PT degrees and RH length were statistically significantly higher, and the mean UV was lower in Group 1 compared to Group 2. No difference was determined between the groups with respect to the CH ratio and RCH ratio. With ROC curve analysis, the cut-off value with the highest odds ratio was determined as RH (Cut-off value=10.77 mm, OR=21.886).
    CONCLUSIONS: Although higher RI, RH, PT values and more negative ulnar variance were observed in the scaphoid fracture group compared to the non-fracture group, ROC curve analysis showed that only increased RH can be considered as a possible risk factor for scaphoid fractures after fall on an outstretched hand.
    BACKGROUND: radiographs, risk factor, scaphoid fracture, wrist morphology.
    导出

    更多引用

    收藏

    翻译标题摘要

    我要上传

    求助全文

  • 文章类型: Journal Article
    老年人跌倒对全球公共卫生构成重大挑战,影响个人福祉和医疗保健系统。本文探讨了预防老年人跌倒的重要性以及护理在该领域的关键作用。它提供的统计数据表明老年人跌倒的患病率很高,强调它们对发病率的重大影响,死亡率和医疗费用。此外,它讨论了跌倒风险因素的多因素性质,包括与年龄相关的变化,慢性健康状况,药物使用,行动不便,感官缺陷和环境危害。护理干预包括全面评估,个性化护理计划,旨在降低跌倒风险和提高安全性的患者教育和宣传工作。通过解决导致跌倒的内在和外在因素,护士对提高老年人的生活质量和减轻与跌倒相关损伤相关的经济负担做出了重要贡献.
    Falls among older individuals pose a significant public health challenge globally, impacting both individual wellbeing and healthcare systems. This article examines the importance of falls prevention in older people and the pivotal role of nursing in this domain. It presents statistics indicating the high prevalence of falls among older adults, highlighting their substantial impact on morbidity, mortality and healthcare costs. Furthermore, it discusses the multifactorial nature of fall risk factors, including age-related changes, chronic health conditions, medication use, impaired mobility, sensory deficits and environmental hazards. Nursing interventions encompass comprehensive assessments, personalised care plans, patient education and advocacy efforts aimed at reducing fall risks and enhancing safety. By addressing intrinsic and extrinsic factors contributing to falls, nurses contribute significantly to improving the quality of life for older adults and reducing the economic burden associated with fall-related injuries.
    导出

    更多引用

    收藏

    翻译标题摘要

    我要上传

    求助全文

  • 文章类型: Journal Article
    随着日本人口的持续老龄化,需要医疗保健的老年人数量有所增加。证据表明,因急性护理而住院对老年人的健康结果有负面影响。虚弱的老年人往往患有多种因素的疾病,统称为“老年综合征”。“当患有这些病前疾病的人住院接受急性护理时,他们倾向于发展新的问题,如谵妄和新的功能损害。住院的不利后果包括丧失功能独立性和慢性残疾的风险。2019年,“医院相关并发症”(HACs)的新概念被提出来描述这些新问题。HAC包括五个条件:与医院相关的跌倒,谵妄,功能衰退,失禁,压力伤。这篇综述讨论了HAC在分类方面的重要问题,患病率,危险因素,预防,以及因急性护理住院的老年人的管理。必须进行强有力的预防和管理,以解决与HAC相关的严重后果和不断上升的医疗费用,多层面和多学科的方法是实现这一目标的关键。综合老年评估(CGA)是老年医学的基石,提供了涉及多学科和多维评估的整体方法。关于CGA和协调护理如何改善住院老年人的预后的大量证据正在积累。需要进一步研究以了解该人群中HAC的发生并制定有效的预防措施。
    As the Japanese population continues to age steadily, the number of older adults requiring healthcare has increased. Evidence demonstrates that hospitalization for acute care has a negative impact on the health outcomes of older adults. Frail older adults tend to have multifactorial conditions collectively known as \"geriatric syndromes.\" When those with these premorbid conditions are hospitalized for acute care, they tend to develop new problems such as delirium and new functional impairments. Adverse consequences of hospitalization include the risk of loss of functional independence and chronic disability. In 2019, the new concept of \"hospital-associated complications\" (HACs) was proposed to describe these new problems. HACs comprise five conditions: hospital-associated falls, delirium, functional decline, incontinence, and pressure injuries. This review discusses the important issues of HACs in relation to their classification, prevalence, risk factors, prevention, and management in older adults hospitalized for acute care. Robust prevention and management are imperative to address the serious consequences and escalating medical costs associated with HACs, and a multidimensional and multidisciplinary approach is key to achieving this goal. Comprehensive geriatric assessment (CGA) is the cornerstone of geriatric medicine and offers a holistic approach involving multidisciplinary and multidimensional assessments. Considerable evidence is accumulating regarding how CGA and coordinated care can improve the prognosis of hospitalized older adults. Further research is needed to understand the occurrence of HACs in this population and to develop effective preventive measures.
    导出

    更多引用

    收藏

    翻译标题摘要

    我要上传

       PDF(Pubmed)

  • 文章类型: Journal Article
    目的:虚弱是一种普遍的老年病,对老年人的健康有显著影响。本研究旨在调查65岁以上中国老年人的身体虚弱患病率,并评估其与老年不良结局的相关性。
    方法:本研究纳入江苏省20,724名年龄≥65岁的老年人,中国,利用随机的,分层,多级整群抽样方法。使用5项FRAIL量表评估虚弱。老年病结果,如日常生活活动的独立性(ADL),认知障碍,和频繁的跌倒事件(前一年发生四次或更多次),进行了评估。采用Logistic回归模型评估虚弱与老年结局之间的关联,结果以比值比(OR)和95%置信区间(CI)表示。
    结果:参与者的平均年龄为73.4±6.4岁。脆弱和脆弱的标准化患病率分别为35.2%和10.3%,分别。被认定为脆弱或脆弱的人往往生活在农村地区,教育水平较低,丧偶,收入较低,从事较少的体力活动。优先和虚弱与BADL(OR:9.62,95%CI:7.43-12.46;OR:29.25,95%CI:22.42-38.17)和IADL(OR:2.54,95%CI2.35-2.74;和OR:5.19,95%CI4.66-5.78)的局限性风险增加有关,认知障碍筛查阳性(OR:1.23,95%CI:1.16-1.31;和OR:1.72,95%CI:1.56-1.91),和频繁跌倒(上一年发生四次或更多次)(OR:3.38,95%CI:2.50-4.56;OR:8.37,95%CI:6.01-11.65)。在年轻年龄组中,虚弱与BADL和跌倒的局限性之间的关联更为明显(相互作用p<0.001)。
    结论:根据5项FRAIL量表,虚弱与BADLs和IADLs的局限性有关,认知障碍筛查阳性,以及最近居住在社区中的老年人的跌倒。筛查年轻年龄组的虚弱有可能防止身体功能下降和跌倒。
    OBJECTIVE: Frailty is a prevalent geriatric condition that significantly impacts the health of older adults. This study aimed to examine the prevalence of frailty among older Chinese adults aged ≥ 65 years and to assess its association with adverse geriatric outcomes.
    METHODS: This study included 20,724 older adults aged ≥ 65 years in Jiangsu Province, China, utilizing a random, stratified, multistage cluster sampling approach. Frailty was assessed using the 5-item FRAIL scale. Geriatric outcomes, such as independence in activities of daily living (ADL), cognitive impairment, and frequent fall events (occurring four or more times in the preceding year), were evaluated. Logistic regression models were employed to evaluate the association between frailty and geriatric outcomes, with results presented as odds ratios (ORs) and 95% confidence intervals (CIs).
    RESULTS: The mean age of the participants was 73.4 ± 6.4 years. The standardized prevalence of prefrailty and frailty was 35.2% and 10.3%, respectively. Individuals identified as prefrail or frail tended to live in rural areas, have lower educational levels, be widowed, have lower incomes, and engage in less physical activity. Prefrailty and frailty were associated with an increased risk of limitations in BADL (OR: 9.62, 95% CI: 7.43-12.46; and OR: 29.25, 95% CI: 22.42-38.17, respectively) and IADL (OR: 2.54, 95% CI 2.35-2.74; and OR: 5.19, 95% CI 4.66-5.78, respectively), positive cognitive impairment screening (OR: 1.23, 95% CI: 1.16-1.31; and OR: 1.72, 95% CI: 1.56-1.91, respectively), and frequent falls (occurring four or more times in the preceding year) (OR: 3.38, 95% CI: 2.50-4.56; and OR: 8.37, 95% CI: 6.01-11.65). The association between frailty and both limitations in BADL and falls was notably more pronounced among the younger age groups (p for interaction < 0.001).
    CONCLUSIONS: According to the 5-item FRAIL scale, frailty was associated with limitations in BADLs and IADLs, positive cognitive impairment screening, and recent falls among older adults living in the community. Screening for frailty in younger age groups has the potential to prevent declines in physical function and falls.
    导出

    更多引用

    收藏

    翻译标题摘要

    我要上传

       PDF(Pubmed)

  • 文章类型: Journal Article
    一名60多岁的男子在意外跌倒后出现左眼视力下降,鼻出血。经检查,他的左上眼睑被撕裂,左颞巩膜被刺穿,在局部麻醉下进行修复,然后由眼科医生出院,但继续抱怨疼痛和左鼻塞。鼻旁窦CT检查显示左眶内侧壁骨折,左侧筛骨嗜酸性粒细胞和蝶骨隔膜和前部的金属异物(FB)。为去除金属FB而进行的诊断性鼻内窥镜检查显示,塑料碎片嵌入鼻腔粘膜中,这是出乎意料的。因此,由于诊断困境,FB在两次中被删除。
    A man in his 60s presented with diminution of vision of the left eye with nasal bleeding after accidental fall. On examination his left upper eyelid was lacerated and left temporal sclera was punctured which was repaired under local anaesthesia after which he was discharged by ophthalmologists but continued to complain of pain and left nasal obstruction. A non-contrast CT of paranasal sinuses revealed fracture of medial wall of left orbit, left ethmoid haemosinus and a metallic foreign body (FB) in the septum and anterior face of sphenoid. Diagnostic nasal endoscopy performed to remove the metallic FB showed plastic splinters embedded in the mucosa of nasal cavity which was unexpected. Hence, the FB was removed in two sittings because of diagnostic dilemma.
    导出

    更多引用

    收藏

    翻译标题摘要

    我要上传

    求助全文

  • 文章类型: Journal Article
    瀑布是辅助生活设施(ALF)居民的重大经济负担和健康危害。然而,观察居民的能力有限,阻碍了对房间内居民与工作人员互动的理解。当前的研究旨在使用来自计算机视觉和员工位置跟踪的远程技术的数据来描述护士与住院医师的互动。
    在研究开始时,对在城市ALF工作的有215名居民的83名工作人员进行了培训。在32个住宅中安装了远程监控设备,并在170天内跟踪了员工和居民的互动。
    工作人员每天平均访问居民20.7次,持续时间短(平均=1.08分钟)。紧急警报响应时间平均为3.0分钟,与现场(平均=3.3分钟)响应相比,通过移动应用程序的响应时间更快(平均=2.7分钟)。
    通过更好地了解ALF中的员工活动模式,这项研究有可能改善ALF居民的跌倒预防和护理.[老年护理杂志,50(7)、7-11.].
    UNASSIGNED: Falls are a significant financial burden and health hazard for residents in assisted living facilities (ALFs). However, limited capacity to observe residents has hindered understanding of resident-staff interactions within rooms. The current study aimed to describe nurse-resident interactions using data from a remote technology combining computer vision and staff location tracking.
    UNASSIGNED: Eighty-three staff working at an urban ALF with 215 residents were trained at the initiation of the study. Remote surveillance devices were installed in 32 residences and staff and resident interactions were tracked over 170 days.
    UNASSIGNED: Staff visited residents an average of 20.7 times per day for short durations (mean = 1.08 minutes). Urgent alert response times averaged 3.0 minutes, with faster response times through the mobile application (mean = 2.7 minutes) compared to in-person (mean = 3.3 minutes) response.
    UNASSIGNED: By better understanding staff activity patterns in ALFs, this study has the potential to improve fall prevention and care for residents in ALFs. [Journal of Gerontological Nursing, 50(7), 7-11.].
    导出

    更多引用

    收藏

    翻译标题摘要

    我要上传

    求助全文

  • 文章类型: Journal Article
    关于老年人跌倒的社会因素的研究有限。这项研究评估了过去一年跌倒与社会参与之间的关系,儿童的支持,与孩子的关系,社会脆弱。
    参与者是来自SABE的17,687名社区居住的老年人(健康,幸福,和衰老,2015)哥伦比亚调查。协变量包括社会人口统计学特征,环境障碍,精神药物摄入量,视力问题,记忆丧失,多浊度,害怕跌倒。
    在多变量逻辑回归分析中,社交脆弱(与不虚弱)与较高的跌倒几率相关(OR=1.20;95%置信区间[CI],1.10-1.32)。参与组(OR=1.07;95%CI,1.03-1.11),帮助他人(OR=1.04;95%CI,1.02-1.06),或志愿服务(OR=1.09;95%CI,1.01-1.17)也与较高的跌倒几率相关.这些发现得到了部分解释,因为大多数团体参与者居住在城市,他们更容易受到环境障碍的影响。相比之下,接受帮助,感情,和来自儿童的陪伴(OR=0.95;95%CI,0.93-0.97)与较低的跌倒几率相关。此外,与不令人满意的关系相比,与儿童良好的关系与较低的跌倒几率相关(OR=0.75;95%CI,0.66-0.85).
    儿童的支持和与他们的良好关系与较少的跌倒有关;然而,社会脆弱和参与社会群体与更多的跌倒有关。
    UNASSIGNED: There is limited research on social factors related to falls among older adults. This study assessed the association between falls during the past year with social participation, children\'s support, relationship with children, and social frailty.
    UNASSIGNED: Participants were 17,687 community-dwelling older adults from the SABE (Health, Well-being, and Aging, 2015) Colombia survey. Covariates included sociodemographic characteristics, environmental barriers, psychotropic intake, vision problems, memory loss, multimorbidity, and fear of falling.
    UNASSIGNED: In multivariate logistic regression analyses, being socially frail (vs. no-frail) was associated with higher odds of falls (OR=1.20; 95% confidence interval [CI], 1.10-1.32). Participating in groups (OR=1.07; 95% CI, 1.03-1.11), helping others (OR=1.04; 95% CI, 1.02-1.06), or volunteering (OR=1.09; 95% CI, 1.01-1.17) were also associated with higher odds of falls. These findings were partly explained because most group participants reside in cities where they are more exposed to environmental barriers. In contrast, receiving help, affection, and company from children (OR=0.95; 95% CI, 0.93-0.97) was associated with lower fall odds than not receiving it. Moreover, having a good relationship with children was associated with lower odds of falls (OR=0.75; 95% CI, 0.66-0.85) compared to an unsatisfactory relationship.
    UNASSIGNED: Support from children and having a good relationship with them were associated with fewer falls; however, social frailty and participation in social groups were associated with more falls.
    导出

    更多引用

    收藏

    翻译标题摘要

    我要上传

    求助全文

  • 文章类型: Systematic Review
    背景:《世界跌倒预防和管理指南》推荐多因素跌倒风险评估和多领域干预措施。为了成功实施这些干预措施,重要的是要了解影响实施的决定因素。
    方法:在2021年12月3日对该系统综述进行了文献检索,并于2023年4月3日在五个数据库中进行了更新:PubMed(包括MEDLINE),EMBASE(通过Embase.com),Cochrane中央对照试验登记册(通过Cochrane图书馆),WebofScience核心合集和CINAHL(通过EBSCO)。如果研究报告了影响社区老年人实施多因素跌倒风险评估和/或多领域干预措施的决定因素,则包括研究。社论,意见文件,针对一个人群(如帕金森)的系统评价和研究被排除.两名研究人员独立筛选了标题上的文章,摘要和全文。基于敏感性分析评价质量。“实践决定因素综合综合清单”用于对决定因素进行分类。
    结果:纳入29项研究。决定因素分为障碍(n=40)和促进因素(n=35)。必要资源的可用性是报告最多的决定因素。其他通常报告的决定因素是知识,老年人和医疗保健专业人员的意图/信念和动机,将干预措施融入当前的实践,通信,团队和推荐流程以及财务(DIS)激励。
    结论:确定障碍和促进因素对于选择适合具体情况的实施策略至关重要,并提高多因素跌倒风险评估和/或多领域干预措施的吸收和有效性。
    BACKGROUND: Multifactorial falls risk assessment and multidomain interventions are recommended by the World guidelines for falls prevention and management. To successfully implement these interventions, it is important to understand determinants influencing the implementation.
    METHODS: A literature search was conducted for this systematic review on the 3 December 2021 and updated on the 3 April 2023 in five databases: PubMed (including MEDLINE), EMBASE (via Embase.com), Cochrane Central Register of Controlled Trials (via Cochrane Library), Web of Science Core Collection and CINAHL (via EBSCO). Studies were included if they reported on determinants influencing the implementation of a multifactorial falls risk assessment and/or multidomain interventions in community-dwelling older people. Editorials, opinion papers, systematic reviews and studies focusing on one population (e.g. Parkinson) were excluded. Two researchers independently screened the articles on title, abstract and full text. The quality was evaluated based on a sensitivity analysis. \'The Comprehensive Integrated Checklist of Determinants of practice\' was used to categorise the determinants.
    RESULTS: Twenty-nine studies were included. Determinants were classified as barriers (n = 40) and facilitators (n = 35). The availability of necessary resources is the most reported determinant. Other commonly reported determinants are knowledge, intention/beliefs and motivation at the levels of older people and healthcare professionals, fitting of the intervention into current practice, communication, team and referral processes and financial (dis)incentives.
    CONCLUSIONS: Mapping of the barriers and facilitators is essential to choose implementation strategies tailored to the context, and to enhance the uptake and effectiveness of a multifactorial falls risk assessment and/or multidomain interventions.
    导出

    更多引用

    收藏

    翻译标题摘要

    我要上传

    求助全文

  • 文章类型: Journal Article
    这篇综述文章评估了减少衰弱和痴呆住院老年人跌倒的策略的有效性和局限性。它探讨了现有的跌倒预防策略对急性容易跌倒和跌倒相关后果的队列的有效性。在MEDLINE进行了系统的文献检索,Embase,CINAHL,和PsycINFO,采用医学主题词(MeSH)确定2013年至2023年发表的关于患有痴呆和虚弱的住院老年人跌倒预防策略的研究.最初的643条记录被提炼成八篇文章,结构化跨学科床边回合(SIBR)作为一种值得注意的干预措施。SIBR通过促进改进的跨学科交流和护理计划,证明了跌倒的减少。然而,连续会议期间家庭参与的下降表明需要采取策略来维持家庭参与.研究结果提倡以患者为中心的干预措施,以解决该老年人群面临的认知和功能挑战。这篇综述提倡在医院环境中进行全面和包容性的研究,以改善虚弱的老年痴呆症患者的跌倒预防策略。
    This review article assesses the effectiveness and limitations of strategies to reduce falls among hospitalized older adults with frailty and dementia. It explores the efficacy of existing fall prevention strategies for a cohort that is acutely susceptible to falls and fall-related consequences. A systematic literature search was conducted across MEDLINE, Embase, CINAHL, and PsycINFO, employing Medical Subject Headings (MeSH) to identify studies on fall prevention strategies in hospitalized older adults with both dementia and frailty published from 2013 to 2023. The initial 643 records were distilled to eight articles, with Structured Interdisciplinary Bedside Rounds (SIBR) emerging as a notable intervention. SIBR demonstrated a reduction in falls by fostering improved interdisciplinary communication and care planning. However, a decline in family engagement during consecutive sessions suggests a need for strategies to sustain familial involvement. The findings advocate for patient-centered interventions that address the cognitive and functional challenges faced by this cohort of older adults. This review advocates for comprehensive and inclusive research in hospital environments to improve fall prevention strategies for frail older adults with dementia.
    导出

    更多引用

    收藏

    翻译标题摘要

    我要上传

       PDF(Pubmed)

公众号