Fluid and hemodynamic management in hemodialysis patients: challenges and opportunities / Manejo hídrico e hemodinâmico em pacientes em hemodiálise: desafios e oportunidades

Abstract Fluid volume and hemodynamic management in hemodialysis patients is an essential component of dialysis adequacy. Restoring salt and water homeostasis in hemodialysis patients has been a permanent quest by nephrologists summarized by the 'dry weight' probing approach. Although this clinical approach has been associated with benefits on cardiovascular outcome, it is now challenged by recent studies showing that intensity or aggressiveness to remove fluid during intermittent dialysis is associated with cardiovascular stress and potential organ damage. A more precise approach is required to improve cardiovascular outcome in this high-risk population. Fluid status assessment and monitoring rely on four components: clinical assessment, non-invasive instrumental tools (e.g., US, bioimpedance, blood volume monitoring), cardiac biomarkers (e.g. natriuretic peptides), and algorithm and sodium modeling to estimate mass transfer. Optimal management of fluid and sodium imbalance in dialysis patients consist in adjusting salt and fluid removal by dialysis (ultrafiltration, dialysate sodium) and by restricting salt intake and fluid gain between dialysis sessions. Modern technology using biosensors and feedback control tools embarked on dialysis machine, with sophisticated analytics will provide direct handling of sodium and water in a more precise and personalized way. It is envisaged in the near future that these tools will support physician decision making with high potential of improving cardiovascular outcome.

Resumo O volume de fluidos e o controle hemodinâmico em pacientes em hemodiálise é um componente essencial da adequação da diálise. A restauração da homeostase do sal e da água em pacientes em hemodiálise tem sido uma busca constante por parte dos nefrologistas, no que condiz à abordagem do "peso seco. Embora essa abordagem clínica tenha sido associada a benefícios no desfecho cardiovascular, recentemente tem sido questionada por estudos que mostram que a intensidade ou agressividade para remover fluidos durante a diálise intermitente está associada a estresse cardiovascular e dano potencial a órgãos.para remover fluidos durante a diálise intermitente está associada a estresse cardiovascular e dano potencial a órgãos. Uma abordagem mais precisa é necessária para melhorar o desfecho cardiovascular nessa população de alto risco. A avaliação e monitorização do estado hídrico baseiam-se em quatro componentes: avaliação clínica, ferramentas instrumentais não invasivas (por exemplo, US, bioimpedância, monitorização do volume sanguíneo), biomarcadores cardíacos (e.g. peptídeos natriuréticos), algoritmos e modelagem de sódio para estimar a transferência de massa. O manejo otimizado do desequilíbrio hídrico e de sódio em pacientes dialíticos consiste em ajustar a remoção de sal e líquido por diálise (ultrafiltração, dialisato de sódio), e restringir a ingestão de sal e o ganho de líquido entre as sessões de diálise. Tecnologia moderna que utiliza biosensores e ferramentas de controle de feedback, hoje parte da máquina de diálise, com análises sofisticadas, proporcionam o manejo direto sobre o sódio e a água de uma maneira mais precisa e personalizada. Prevê-se no futuro próximo que essas ferramentas poderão auxiliar na tomada de decisão do médico, com alto potencial para melhorar o resultado cardiovascular.

Impact of exercise training and detraining after myocardial infarction: a literature review

Despite the advances in the treatment and prevention, myocardial infarction (MI) remains the leading causeof morbidity and mortality worldwide. Different degrees of ventricular dysfunction, changes in hemodynamicand molecular mechanisms, as well as neurohumoral derangements, are substantially associated with increasedmortality rate in MI patients. Cardiovascular, metabolic and autonomic benefits of acute and chronic exercise training (ET) have led many researchers to suggest ET as an important tool in the management of coronary artery disease and after MI. Regarding cardiovascular rehabilitation, several factors, such as illness, injury, travel, vacation or even rehabilitation program discharge may often interfere with the ET process, leading toa disruption in physical activity patterns by either decreasing training level or frequency or interrupting thetraining program altogether. Thus, it is necessary to identify the impact of ET after MI, as well as the possibleconsequences of such disruption in infarcted individuals.

Microgravity-induced cardiovascular deconditioning: mechanisms and countermeasures / 中国应用生理学杂志

It has been demonstrated that individuals exposed to actual or simulated microgravity often experience cardiovascular dysfunctions when returning to Earth. The underlying mechanisms of orthostatic intolerance and countermeasure treatment are still poorly understood. In this paper, the progress in the mechanism of cardiovascular deconditioning from the view of vascular remodeling, increased venous compliance in the lower limbs, cellular proliferation and differentiation, and cell signaling pathway was reviewed. Meanwhile, an overview of the countermeasures including exercise, lower body negative pressure, thigh cuffs, traditional Chinese herb medicine and artificial gravity was presented.

Exercise training and detraining modify the morphological and mechanical properties of single cardiac myocytes obtained from spontaneously hypertensive rats

We determined the effects of exercise training and detraining on the morphological and mechanical properties of left ventricular myocytes in 4-month-old spontaneously hypertensive rats (SHR) randomly divided into the following groups: sedentary for 8 weeks (SED-8), sedentary for 12 weeks (SED-12), treadmill-running trained for 8 weeks (TRA, 16 m/min, 60 min/day, 5 days/week), and treadmill-running trained for 8 weeks followed by 4 weeks of detraining (DET). At sacrifice, left ventricular myocytes were isolated enzymatically, and resting cell length, width, and cell shortening after stimulation at a frequency of 1 Hz (~25°C) were measured. Cell length was greater in TRA than in SED-8 (161.30 ± 1.01 vs 156.10 ± 1.02 μm, P < 0.05, 667 vs 618 cells, respectively) and remained larger after detraining. Cell width and volume were unaffected by either exercise training or detraining. Cell length to width ratio was higher in TRA than in SED-8 (8.50 ± 0.08 vs 8.22 ± 0.10, P < 0.05) and was maintained after detraining. Exercise training did not affect cell shortening, which was unchanged with detraining. TRA cells exhibited higher maximum velocity of shortening than SED-8 (102.01 ± 4.50 vs 82.01 ± 5.30 μm/s, P < 0.05, 70 cells per group), with almost complete regression after detraining. The maximum velocity of relengthening was higher in TRA cells than in SED-8 (88.20 ± 4.01 vs70.01 ± 4.80 μm/s, P < 0.05), returning to sedentary values with detraining. Therefore, exercise training affected left ventricle remodeling in SHR towards eccentric hypertrophy, which remained after detraining. It also improved single left ventricular myocyte contractile function, which was reversed by detraining.

The Effects of Regular Walking Exercise on Metabolic Syndrome, Cardiovascular Risk Factors, and Depressive Symptoms in the Elderly with Diabetic Mellitus

PURPOSE: This study aimed to estimate the effects of a regular walking exercise program on metabolic syndrome, cardiovascular risk factors, and depressive symptoms among the elderly with diabetic mellitus (DM) based on the Theory of Reasoned Action (TRA). METHODS: This study has randomized and stratified experimental design with experimental and control groups. We developed a regular walking exercise program suitable for the elderly with DM based on the guidance of AAHPERD. The experimental group participated in the regular walking exercise program, which contains walking exercise 3 times a week and 50 minutes each time for 3 months and education on controlling diet and preventing complications once a week and 20 minutes each time for 4 weeks. Post-test was conducted after 3 months to estimate metabolic syndrome, cardiovascular risk factors, and depressive symptoms. RESULTS: The regular walking exercise program was effective for decreasing the waist size, the level of fasting blood glucose (FBG) and triglyceride (TG), cardiovascular risk factors and the severity of depressive symptoms among the elderly with DM. CONCLUSION: The incidence of complications would be decreased by applying a regular walking exercise program.

Impaired but reversible vascular reactivity in a rat model of microgravity / 대한마취과학회지

BACKGROUND: The hindlimb unweighting (HLU) rat model mimics cardiovascular deconditioning following microgravity or human bed rest, particularly for the development of orthostatic intolerance. We have examined vascular responses to alpha1 adrenergic and non-alpha1 adrenergic agonists in vitro. We have also explored the reversibility of the contractile abnormalities observed. METHODS: Dose-response curves were generated to phenylephrine (PE) and norepinephrine (NE) (10(-9) to 10(-4) M), U46619 (U4) (10(-10) to 10(-6) M) at one-half log order intervals in controls (n = 6), HLU (n = 6), or recovered rats (n = 6). EC(50)s and maximal responses (E(max)) were calculated by nonlinear logistic regression analysis with PRIZM software (Graphpad, Mountain View, CA). RESULTS: Simulated microgravity results in attenuated contractile responses to both alpha1 adrenergic and non-alpha1 adrenergic agonists, but the impaired contractile phenomenon reverses with time. CONCLUSIONS: The decreased vascular reactivity after microgravity and prolonged bed rest could cause attenuated baroreflex function and produce orthostatic intolerance, but that problem resolved with time.

Impaired but reversible vascular reactivity in a rat model of microgravity / 대한마취과학회지

BACKGROUND: The hindlimb unweighting (HLU) rat model mimics cardiovascular deconditioning following microgravity or human bed rest, particularly for the development of orthostatic intolerance. We have examined vascular responses to alpha1 adrenergic and non-alpha1 adrenergic agonists in vitro. We have also explored the reversibility of the contractile abnormalities observed. METHODS: Dose-response curves were generated to phenylephrine (PE) and norepinephrine (NE) (10(-9) to 10(-4) M), U46619 (U4) (10(-10) to 10(-6) M) at one-half log order intervals in controls (n = 6), HLU (n = 6), or recovered rats (n = 6). EC(50)s and maximal responses (E(max)) were calculated by nonlinear logistic regression analysis with PRIZM software (Graphpad, Mountain View, CA). RESULTS: Simulated microgravity results in attenuated contractile responses to both alpha1 adrenergic and non-alpha1 adrenergic agonists, but the impaired contractile phenomenon reverses with time. CONCLUSIONS: The decreased vascular reactivity after microgravity and prolonged bed rest could cause attenuated baroreflex function and produce orthostatic intolerance, but that problem resolved with time.

The changes of cardiovascular response to orthostatic stress caused by hypovolemia induced by weightlessness: a simulation study / 生物医学工程学杂志

We introduced the method of computer simulation in the studies of gravitational physiology. Based on work of Melchior (1994), we developed a mathematical model that can be used to stimulate cardiovascular responses to orthostatic stress (lower body negative pressure, LBNP). The model includes 7 sub-models: the redistribution of blood, the filling of left ventricle, left ventricle working, peripheral circulation, control of heart rate (HR), control of peripheral resistance and control of venous tone. Then we simulated the changes of blood pressure (BP) and heart rate during lower body negative pressure, and the results agreed well with the results of our human experiment. By using the developed model, we also simulated the effects of hypovolemia on the BP, HR and shock index during orthostatic stress. The simulation results indicate that the cardiovascular responses to orthostatic stress change significantly when the decrease of blood volume is more than 15% of the total blood volume. However, if the amount of the decrease of blood volume is less than 5% of the total blood volume, HR and BP could be maintained in normal range by the regulation of baroreflex during LBNP. Our simulation results suggest that hypovolemia may be the main cause of orthostatic intolerance induced by weightlessness.

Efeitos do destreinamento físico sobre a "performance" do atleta: uma revisäo das alteraçöes cardiovasculares e músculo-esqueléticas / Effects of physical detraining on athlete performance: a review about skeletal muscle and cardiovascular changes

As adaptaçöes cardiovasculares e metabólicas adquiridas com o treinamento físico de "endurance" podem ser revertidas quando o atleta é submetido a um período de inatividade física, devido ao reajuste dos sistemas corporais às alteraçöes dos estímulos fisiológicos induzidos pelo treinamento físico. Reduçöes significantes do consumo máximo de oxigênio (VO2max) parecem ocorrer dentro de duas a quatro semanas de destreinamento físico, provocando um grande declínio da "performance" do atleta em esportes de "endurance". A queda inicial do VO2max está associada à reduçäo do débito cardíaco consequente da reduçäo significante da diferença artério-venosa máxima de oxigênio contribuindo também para a reduçäo do VO2max. Se a condiçäo física elevada de um atleta pode ser obtida após alguns anos seguidos de eventualidades que impeçam a continuidade da preparaçäo física do atleta näo resultem em prejuízos na sua "performance". Sendo assim, esta revisäo tem como objetivo descrever o curso temporal e a magnitude de perda das adaptaçöes fisiológicas adquiridas com o treinamento físico, bem como os mecanismos envolvidos nas mesmas

Exercise in the treatment of type 2 diabetes

Unlike the type 1, type 2 diabetes benefits from an improvement in glycaemic control, because of the effect of exercise on insulin sensitivity. The level of improvement is comparable to that achieved with pharmacological agents. This is significant where cost is a major consideration. These positive effects of exercise are maintained only if exercise is sustained. The effect of a single bout of exercise lasts from 12-48 hours, so exercise should be performed at least every other day or preferably every day. Improvement in glycaemic control with exercise is not related to level of fitness so everyone can benefit, as long as glycogen depletion is achieved, with results from moderately intense exercise for a reasonable duration of time. Even more important than glycaemic control is the benefit of reducing the risk of developing coronary events. Cardiovascular abnormalities are commonly seen in diabetes especially in those persons with type 2 and this is all related to the state of insulin resistance. Exercise also reduces the progression of metabolic abnormalities from mild to more severe forms of diabetes mellitus. The exercise prescription must consider socioeconomic and personal factors in addition to scientific criteria of exercise intensity. The current trend is to recommend a combination of modest, high-volume resistance training and aerobic training. Diabetes have a lower VO2max than normal individuals and so should not be placed on the same programmes. Flexibility is advised. For example, although the exercise period may be an hour long, little rest periods at intervals will not undo the metabolic benefits.