180 research outputs found

    Blood pressure drop prediction by using HRV measurements in orthostatic hypotension

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    Orthostatic Hypotension is defined as a reduction of systolic and diastolic blood pressure within 3 minutes of standing, and may cause dizziness and loss of balance. Orthostatic Hypotension has been considered an important risk factor for falls since 1960. This paper presents a model to predict the systolic blood pressure drop due to orthostatic hypotension, relying on heart rate variability measurements extracted from 5 minute ECGs recorded before standing. This model was developed and validated with the leave-one-out cross-validation technique involving 10 healthy subjects, and finally tested with an additional 5 healthy subjects, whose data were not used during the training and cross-validation process. The results show that the model predicts correctly the systolic blood pressure drop in 80 % of all experiments, with an error rate below the measurement error of a sphygmomanometer digital device

    Measurement of Autonomic Function in Renal Disease and Diabetes

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    Renal disease and diabetes lead to dysautonomia resulting in consequences ranging from gastroparesis to sudden death. New technologies to detect dysautonomia, such as 24-hr heart rate variability, are being evaluated and compared to traditional evoked tests. These advances have, however, lead to a lack of standardization in testing batteries, procedures, and reporting formats. This series of 3 studies psychometrically assessed measures of autonomic function (AF) and explored relationships among objective and subjective measures in healthy adults and uremic patients. Participants underwent evoked tests that included change in heart rate with deep breathing and Valsalva. In addition, measures of 24-hr HRV (time-domain: SDNN, SDANN, RMSSD; frequency-domain: total power, low and high frequency) and symptomatology were obtained. Study 1 examined the development and psychometric testing of the Autonomic Symptom Checklist (ASC), an instrument designed to assess autonomic symptomatology, with uremic patients (n=244) and healthy adults (n=34). Findings showed the ASC was able to differentiate among healthy and uremic patients with and without diabetes. Test-retest reliability was moderate to high for most categories. Study 2 established normal, borderline, and abnormal AF values and determined if these values could distinguish healthy (n=158) from uremic adults (n=363). Abnormal values were established at the 2.3 quantile of healthy adults. Uremic patients, especially those with diabetes, had much poorer values than healthy adults. The influence of age and gender on AF measures was attenuated in uremic as compared to healthy adults. Study 3 examined relationships among and the clinical utility of evoked tests, 24- hr HRV, and the ASC. Data were obtained from pre (n=130) and post (n=55) kidney and kidney-pancreas transplant recipients (n=130), and healthy adults (n=22). The frequency of abnormal values was used to identify the most sensitive measure. Measures of 24-hr HRV were more sensitive than evoked measures, with frequency measures being most sensitive. In conclusion, this series of studies established reliability and validity for the ASC, referent values for AF tests, devised a scoring system for AF tests, and found 24-hr HRV measures more sensitive than evoked measures

    Central and Peripheral Chemoreflex Function in the Supine and Upright Postures in Women throughout the Menstrual Cycle with a Comparison to Men

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    The primary purpose of the study was to examine sex differences and menstrual cycle time-points on chemoreflex function during supine and 70o upright (HUT) positions during: 1) normoxia, 2) hypercapnia (5% CO2), or 3) hyperoxia (100% O2). Women were tested during the early-follicular phase (EF; days 2-5) and the mid-luteal phase (ML; days 18-24). Compared to baseline, men and women had lower cardiac output index (Qi), mean arterial pressure (MAP), cerebrovascular resistance index, and respiratory rate during HUT. In response to hypercapnia during HUT (compared to supine), men had an augmented increase in MAP, while all groups had an augmented increase in ventilation suggesting sexually dimorphic interactions between the baroreflex and central chemoreflex. In response to hyperoxia during HUT, men and women displayed an attenuated increase of total peripheral resistance index and an attenuated decrease of Qi suggesting upright posture activated peripheral chemoreceptors

    Resting Heart Rate Variability Is Associated With Subsequent Orthostatic Hypotension: Comparison Between Healthy Older People and Patients With Rapid Eye Movement Sleep Behavior Disorder.

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    Background:Orthostatic hypotension (OH) caused by autonomic dysfunction is a common symptom in older people and patients with idiopathic rapid eye movement sleep behavior disorder (iRBD). The orthostatic challenge test is a standard autonomic function test that measures a decrease of blood pressure during a postural change from supine to standing positions. Although previous studies have reported that changes in heart rate variability (HRV) are associated with autonomic dysfunction, no study has investigated the relationship between HRV before standing and the occurrence of OH in an orthostatic challenge test. This study aims to examine the connection between HRV in the supine position and the occurrence of OH in an orthostatic challenge test.Methods:We measured the electrocardiograms of patients with iRBD and healthy older people during an orthostatic challenge test, in which the supine and standing positions were held for 15 min, respectively. The subjects were divided into three groups: healthy controls (HC), OH-negative iRBD [OH (–) iRBD], and OH-positive iRBD [OH (+) iRBD]. HRV measured in the supine position during the test were calculated by time-domain analysis and Poincaré plots to evaluate the autonomic dysfunction.Results:Forty-two HC, 12 OH (–) iRBD, and nine OH (+) iRBD subjects were included. HRV indices in the OH (–) and the OH (+) iRBD groups were significantly smaller than those in the HC group. The multivariate logistic regression analysis for OH identification for the iRBD groups showed the model whose inputs were the HRV indices, i.e., standard deviation 2 (SD2) and the percentage of adjacent intervals that varied by more than 50 ms (pNN50), had a receiver operating characteristic curve with area under the curve of 0.840, the sensitivity to OH (+) of 1.000, and the specificity to OH (–) of 0.583 (p = 0.023).Conclusions:This study showed the possibility that short-term HRV indices in the supine position would predict subsequent OH in iRBD patients. Our results are of clinical importance in terms of showing the possibility that OH can be predicted using only HRV in the supine position without an orthostatic challenge test, which would improve the efficiency and safety of testing

    Reflex syncope : an integrative physiological approach

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    Síncope, a forma mais comum de perda temporária de consciência é responsável por até 5% das idas aos serviços de emergência e até 3% dos internamentos hospitalares. É um problema médico frequente, com múltiplos gatilhos, incapacitante, potencialmente perigoso e desafiante em termos diagnósticos e terapêuticos. Assim, é necessária uma anamnese detalhada para primeiro estabelecer a natureza da perda de consciência, mas, após o diagnóstico, as medidas terapêuticas existentes são pouco eficazes. Embora a fisiopatologia da síncope vasovagal ainda não tenha sido completamente esclarecida, alguns mecanismos subjacentes foram já desvendados. Em última análise, a síncope depende de uma falha transitória na perfusão cerebral pelo que qualquer factor que afecte a circulação sanguínea cerebral pode determinar a ocorrência de síncope. Assim, o objectivo do presente estudo é caracterizar o impacto hemodinâmico e autonómico nos mecanismos subjacentes à síncope reflexa, para melhorar o diagnóstico, o prognóstico e a qualidade de vida dos doentes e dos seus cuidadores. Para isso, desenhámos e implementámos novas ferramentas matemáticas e computacionais que permitem uma avaliação autonómica e hemodinâmica integrada, de forma a aprofundar a compreensão do seu envolvimento nos mecanismos de síncope reflexa. Além disso, refinando a precisão do diagnóstico, a sensibilidade e a especificidade do teste de mesa de inclinação (“tilt test”), estabelecemos uma ferramenta preditiva do episódio iminente de síncope. Isso permitiu-nos estabelecer alternativas de tratamento eficazes e personalizadas para os doentes refractários às opções convencionais, sob a forma de um programa de treino de ortostatismo (“tilt training”), contribuindo para o aumento da sua qualidade de vida e para a redução dos custos directos e indirectos da sua assistência médica. Assim, num estudo verdadeiramente multidisciplinar envolvendo doentes com síncope reflexa refractária à terapêutica, conseguimos demonstrar uma assincronia funcional das respostas reflexas autonómicas e hemodinâmicas, expressas por um desajuste temporal entre o débito cardíaco e as adaptações de resistência total periférica, uma resposta baroreflexa atrasada e um desequilíbrio incremental do tónus autonómico que, em conjunto, poderão resultar de uma disfunção do sistema nervoso autónomo que se traduz por uma reserva simpática diminuída. Igualmente, desenhámos, testámos e implementámos uma plataforma computacional e respectivo software associado - a plataforma FisioSinal –incluindo novas formas, mais dinâmicas, de avaliação integrada autonómica e hemodinâmica, que levaram ao desenvolvimento de algoritmos preditivos para a estratificação de doentes com síncope. Além disso, na aplicação dessas ferramentas, comprovámos a eficácia de um tratamento não invasivo, não disruptivo e integrado, focado na neuromodulação das variáveis autonómicas e cardiovasculares envolvidas nos mecanismos de síncope. Esta terapêutica complementar levou a um aumento substancial da qualidade de vida dos doentes e à abolição dos eventos sincopais na grande maioria dos doentes envolvidos. Em conclusão, o nosso trabalho contribuiu para preencher a lacuna entre a melhor informação científica disponível e sua aplicação na prática clínica, sustentando-se nos três pilares da medicina translacional: investigação básica, clínica e comunidade.Syncope, the most common form of transient loss of consciousness, accounts for up to 5% of emergency room visits and up to 3% of hospital admissions. It is a frequent medical problem with multiple triggers, potentially dangerous, incapacitating, and challenging to diagnose. Therefore, a detailed clinical history is needed first to establish the nature of the loss of consciousness. However, after diagnosis, the therapeutic measures available are still very poor. Although the exact pathophysiology of vasovagal syncope remains to be clarified, some underlying mechanisms have been unveiled, dependent not only on the cause of syncope but also on age and various other factors that affect clinical presentation. Ultimately, syncope depends on a failure of the circulation to perfuse the brain, so any factor affecting blood circulation may determine syncope occurrence. Thus, the purpose of the present study is to understand the impact of the hemodynamic and autonomic functions on reflex syncope mechanisms to improve patients diagnose, prognosis and general quality of life. Bearing that in mind, we designed and implemented new mathematical and computational tools for autonomic and hemodynamic evaluation, in order to deepen the understanding of their involvement in reflex syncope mechanisms. Furthermore, by refining the diagnostic accuracy, sensitivity and specificity of the head-up tilt-table test, we established a predictive tool for the impending syncopal episode. This allowed us to establish effective and personalised treatment alternatives to patient’s refractory to conventional options, contributing to their increase in the quality of life and a reduction of health care and associated costs. In accordance, in a truly multidisciplinary study involving reflex syncope patients, we were able to show an elemental functional asynchrony of hemodynamic and autonomic reflex responses, expressed through a temporal mismatch between cardiac output and total peripheral resistance adaptations, a deferred baroreflex response and an unbalanced, but incremental, autonomic tone, all contributing to autonomic dysfunction, translated into a decreased sympathetic reserve. Through the design, testing and implementation of a computational platform and the associated software - FisioSinal platform -, we developed novel and dynamic ways of autonomic and hemodynamic evaluation, whose data lead to the development of predictive algorithms for syncope patients’risk stratification. Furthermore, through the application of these tools, we showed the effectiveness of a non-invasive, non-disruptive and integrated treatment, focusing on neuromodulation of the autonomic and cardiovascular variables involved in the syncope mechanisms, leading to a substantial increase of quality of life and the abolishment of syncopal events in a vast majority of the enrolled patients. In conclusion, our work contributed to fill the gap between the best available scientific information and its application in the clinical practice by tackling the three pillars of translational medicine: bench-side, bedside and community

    Cardiac Autonomic Dysfunction and Incidence of Atrial Fibrillation

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    Cardiac autonomic perturbations frequently antecede onset of paroxysmal atrial fibrillation (AF). Interventions that influence autonomic inputs to myocardium may prevent AF. However, whether low heart rate or heart rate variability (HRV), which are noninvasive measures of cardiac autonomic dysfunction, are associated with AF incidence is unclear

    Short-Term Fasting and Autonomic Control

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    Obesity is a chronic metabolic disorder associated with increased risk of cardiovascular disease. Evidence suggests that chronic intermittent fasting improves cardiometabolic health and reduces arterial blood pressure. However, the mechanisms underlying the reductions in blood pressure and improved cardiovascular health observed from chronic fasting studies remain unclear. The autonomic nervous system has a central role in the regulation of blood pressure and is essential for cardiovascular homeostasis. We conducted a study to investigate how acute fasting influences autonomic control of blood pressure at rest and during stress. Twenty-five young, healthy, normal weight, normotensive participants were tested twice, once in the fed state (3 hours postprandial) and again in the fasted state (24 hours postprandial). Aim 1 of the study was to determine the influence of an acute fast on hemodynamics, peripheral neural activity, and cardiovascular control at rest. To fulfill this aim we measured 24-hour ambulatory blood pressure for both conditions leading up to an autonomic function test. During the autonomic function test, we controlled breathing at 0.25 Hz and measured blood pressure, heart rate, muscle sympathetic nerve activity, and forearm blood flow for 10 minutes. Fasting reduced overall ambulatory blood pressure and heart rate compared to the fed condition. From the autonomic test we measured enhanced vagal modulation of the heart through 1) increased R-R interval and heart rate variability measured via spectral analysis; 2) Increased spontaneous (rest) and dynamic (Valsalva Maneuver) cardiovagal baroreflex sensitivity indicating enhanced reflexive vagal activation. Fasting did not alter peripheral sympathetic activity or blood pressure during the autonomic test. However, forearm vascular resistance and stroke volume were increased during the fasting condition. Aim 2 investigated if fasting influenced cardiovascular and neural reactivity to a mental stressor (5 min mental arithmetic). Fasting did not augment neural or cardiovascular reactivity to a mental stress challenge. Aim 3 investigated if fasting reduced orthostatic tolerance to intense lower body negative pressure (LBNP). LBNP was applied in a stepwise manner until participants became presyncopal. Fasting reduced the duration of negative pressure participants could tolerate before presyncope occurred. The reduced tolerance to central hypovolemia seems to have been caused by an impaired ability to increase peripheral resistance as measured from the forearm. This dissertation provides novel insight into how systemic energy balance influences autonomic regulation of blood pressure. Specifically, that fasting reduces 24-hour ambulatory blood pressure, increases vagal modulation of the heart, and enhances cardiovagal baroreflex sensitivity
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