Water drinking improves orthostatic tolerance in patients with posturally related syncope

A protocol to simultaneously examine cardiorespiratory, cerebrovascular and neurophysiological responses inside a hypobaric chamber

We describe a protocol to examine neurophysiological (electroencephalography, EEG), cerebrovascular (ultrasound assessments of middle cerebral artery blood velocity, MCAv) and cardiorespiratory (blood pressure, oxygen saturation, end-tidal gases, respiratory rate) responses inside a hypobaric chamber. This procedure aims to standardize the methodology in experiments conducted within a hypobaric chamber such as comparing normobaric and hypobaric hypoxia. This is important because current understanding of relationships between neurophysiological activity, and cerebrovascular and cardiorespiratory responses under varying environmental conditions remains limited. This procedure combines simultaneous neurophysiological, cardiorespiratory and cerebrovascular evaluations, allowing a comprehensive understanding of electro-neurophysiological activity. Our protocol requires an hour and a half of equipment setup, 1-1.5 hours of participant set-up, and 30 minutes of experimental data collection. Since multiple simultaneous physiological recordings, including EEG in this environment, can be fraught with pitfalls, we also provide practical considerations for experimental design and recording setup. Advanced knowledge of hypobaric chamber operation is required, alongside expertise in EEG and transcranial Doppler ultrasonography. Following our procedure one will acquire simultaneous recordings of neurophysiological, cerebrovascular and cardiorespiratory data.

Syncope in the Emergency Department: A Practical Approach

Syncope is a common condition encountered in the emergency department (ED), accounting for about 0.6-3% of all ED visits. Despite its high frequency, a widely accepted management strategy for patients with syncope in the ED is still missing. Since syncope can be the presenting condition of many diseases, both severe and benign, most research efforts have focused on strategies to obtain a definitive etiologic diagnosis. Nevertheless, in everyday clinical practice, a definitive diagnosis is rarely reached after the first evaluation. It is thus troublesome to aid clinicians' reasoning by simply focusing on differential diagnoses. With the current review, we would like to propose a management strategy that guides clinicians both in the identification of conditions that warrant immediate treatment and in the management of patients for whom a diagnosis is not immediately reached, differentiating those that can be safely discharged from those that should be admitted to the hospital or monitored before a final decision. We propose the mnemonic acronym RED-SOS: Recognize syncope; Exclude life-threatening conditions; Diagnose; Stratify the risk of adverse events; Observe; decide on the Setting of care. Based on this acronym, in the different sections of the review, we discuss all the elements that clinicians should consider when assessing patients with syncope.

Evaluation of stroke volume estimation during orthostatic stress: the utility of Modelflow

Advanced blood pressure monitoring devices contain algorithms that permit estimation of stroke volume (SV). Modelflow (Finapres Medical Systems) is one common method to non-invasively estimate beat-to-beat SV. However, Modelflow accuracy during profound reductions in SV is unclear. We aimed to compare SV estimation by Modelflow and echocardiography, at rest and during orthostatic challenge. We tested 13 individuals (age 24 ± 2 years; 7 female) using combined head-up tilt and graded lower body negative pressure, continued until presyncope. SV was derived by both Modelflow and echocardiography on multiple occasions while supine, during orthostatic stress, and at presyncope. SV index (SVI) was determined by normalising SV for body surface area. Bias and limits of agreement were determined using Bland-Altman analyses. Two one-sided tests (TOST) examined equivalency. Across all timepoints, Modelflow estimates of SV (73.2 ± 1.6 ml) were strongly correlated with echocardiography estimates (66.1 ± 1.3 ml) (r = 0.56, P  < 0.001) with a bias of +7.1 ± 21.1 ml. Bias across all timepoints was further improved when SV was indexed (+3.6 ± 12.0 ml.m -2 ). Likewise, when assessing responses relative to baseline, Modelflow estimates of SV (-23.4 ± 1.4%) were strongly correlated with echocardiography estimates (-19.2 ± 1.3%) (r = 0.76, P  < 0.001), with minimal bias (-4.2 ± 13.1%). TOST testing revealed equivalency to within 15% of the clinical standard for SV and SVI, both expressed as absolute values and relative to baseline. Modelflow can be used to track changes in SV during profound orthostatic stress, with accuracy enhanced with correction relative to baseline values or body size. These data support the use of Modelflow estimates of SV for autonomic function testing.

Risk factors for reflex syncope in the British Army

INTRODUCTION

Reflex syncope in the UK Armed Forces is reportedly higher than comparable militaries and civilian populations and is significantly more common in soldiers who take part in State Ceremonial and Public Duties (SCPD) compared with other British Army service personnel (SP). This study aimed to investigate individual susceptibility factors for syncope in soldiers who regularly take part in SCPD.

METHODS

A retrospective cohort study was performed in 200 soldiers who perform SCPD. A questionnaire was undertaken reviewing soldiers' medical history and circumstances of any fainting episodes. A consented review of participants' electronic primary healthcare medical record was also performed. Participants were divided into two groups (syncope, n=80; control, n=120) based on whether they had previously fainted.

RESULTS

In the syncope group orthostasis (61%) and heat (35%) were the most common precipitating factors. The most common interventions used by soldiers were to maintain hydration (59%) and purposeful movements (predominantly 'toe wiggling'; 55%). 30% of participants who had previously fainted did not seek definitive medical attention. A history of migraines/headaches was found to increase the risk of reflex syncope (OR 8.880, 1.214-218.8), while a history of antihistamine prescription (OR 0.07144, 0.003671-0.4236), non-white ethnicity (OR 0.03401, 0.0007419-0.3972) and male sex (OR 0.2640, 0.08891-0.6915) were protective.

CONCLUSION

This is the first study, in the British Army, to describe, categorise and establish potential risk factors for reflex syncope. Orthostatic-mediated reflex syncope is the most common cause in soldiers who regularly perform SCPD and this is further exacerbated by heat exposure. Soldiers do not use evidence-based methods to avoid reflex syncope. These data could be used to target interventions for SP who have previously fainted or to prevent fainting during SCPD.

Hemodynamic Effects of the Osmopressor Response: A Systematic Review and Meta-Analysis

Background Rapidly consuming water may offer practical orthostatic hypotension therapy. However, its efficacy across disorders remains uncertain. This study aims to assess the impact of rapid 350- to 500-mL water intake on systolic and diastolic blood pressure (BP) and heart rate (HR) through a systematic review and meta-analysis. Methods and Results We systematically reviewed MEDLINE and Embase up to June 2023, including randomized controlled trials and prospective cohort studies. Using random-effects meta-analysis, we calculated pooled mean differences (MDs) for maximum hemodynamic effects of rapid 350- to 500-mL water bolus consumption. Participants with orthostatic hypotension experienced increased systolic BP (MD, 24.18 [95% CI, 15.48-32.88]) and diastolic BP (MD, 11.98 [95% CI, 8.87-15.09]) with decreased HR (MD, -3.46 [95% CI, -5.21 to -1.71]). Similar results were observed in multiple system atrophy and pure autonomic failure subgroup analysis. Healthy participants showed modest increases in systolic BP (MD, 2.33 [95% CI, 1.02-3.64]) and diastolic BP (MD, 2.73 [95% CI, 1.15-4.30]), but HR changes were not significant (MD, -2.06 [95% CI, -5.25 to 1.13]). Water had no significant hemodynamic effects in patients with seated or supine postural tachycardia syndrome, although standing effects were unassessed. Our data do not exclude water's potential standing effect in postural tachycardia syndrome. Conclusions In patients with orthostatic hypotension, rapid water intake elevated short-term systolic BP and diastolic BP, with mild HR reduction when seated or supine. Healthy participants exhibited similar but milder effects. However, patients with postural tachycardia syndrome did not experience these changes in seated or supine positions. Further research is needed to evaluate the promising impact of rapid water ingestion on patients with postural tachycardia syndrome in a standing position, which was not addressed in our study.

The effect of water temperature on orthostatic tolerance: a randomised crossover trial

Purpose

Bolus water drinking, at room temperature, has been shown to improve orthostatic tolerance (OT), probably via sympathetic activation; however, it is not clear whether the temperature of the water bolus modifies the effect on OT or the cardiovascular responses to orthostatic stress. The aim of this study was to assess whether differing water temperature of the water bolus would alter time to presyncope and/or cardiovascular parameters during incremental orthostatic stress.

Methods

Fourteen participants underwent three head-up tilt (HUT) tests with graded lower body negative pressure (LBNP) continued until presyncope. Fifteen minutes prior to each HUT, participants drank a 500 mL bolus of water which was randomised, in single-blind crossover fashion, to either room temperature water (20 °C) (ROOM), ice-cold water (0–3 °C) (COLD) or warm water (45 °C) (WARM). Cardiovascular parameters were monitored continuously.

Results

There was no significant difference in OT in the COLD (33 ± 3 min; p = 0.3321) and WARM (32 ± 3 min; p = 0.6764) conditions in comparison to the ROOM condition (31 ± 3 min). During the HUT tests, heart rate and cardiac output were significantly reduced (p < 0.0073), with significantly increased systolic blood pressure, stroke volume, cerebral blood flow velocity and total peripheral resistance (p < 0.0054), in the COLD compared to ROOM conditions.

Conclusions

In healthy controls, bolus cold water drinking results in favourable orthostatic cardiovascular responses during HUT/LBNP without significantly altering OT. Using a cold water bolus may result in additional benefits in patients with orthostatic intolerance above those conferred by bolus water at room temperature (by ameliorating orthostatic tachycardia and enhancing vascular resistance responses). Further research in patients with orthostatic intolerance is warranted.

Oral and intravenous hydration in the treatment of orthostatic hypotension and postural tachycardia syndrome

Hydration with water and salt is the mainstay of treatment for autonomic nervous system disorders that impair orthostatic tolerance. The goal is to expand intravascular volume to compensate for the downward displacement of blood volume that occurs when standing and thereby sustain cerebral perfusion and restore quality of life. Despite strong consensus recommendations for salt supplementation as standard treatment of these disorders, published evidence of benefit is relatively weak, and no randomized clinical trials have occurred. This review summarizes the physiological rationale for hydration and evaluates the literature on oral and intravenous hydration in the treatment of neurogenic orthostatic hypotension, postural tachycardia syndrome, and recurrent vasovagal syncope. We conclude that oral salt replacement is indicated for treatment of neurogenic orthostatic hypotension because these patients have excessive renal sodium excretion, and for treatment of chronic orthostatic intolerance because these patients are often hypovolemic. As not all patients are able to tolerate sufficient oral hydration, there is also a role for intravenous volume-loading in severe cases of postural tachycardia syndrome. We offer guidance, based on review of the literature and the clinical judgment of a cardiologist and neurologist with experience treating autonomic disorders, regarding the option of ongoing intravenous hydration for treatment of severe, refractory cases of postural tachycardia syndrome.

Intermittent Calf Compression Delays the Onset of Presyncope in Young Healthy Individuals

Orthostatic fluid shifts reduce the effective circulating volume and thus contribute to syncope susceptibility. Recurrent syncope has a devastating impact on quality of life and is challenging to manage effectively. To blunt orthostatic fluid shifts, static calf compression garments are often prescribed to patients with syncope, but have questionable efficacy. Intermittent calf compression, which mimics the skeletal muscle pump to minimize pooling and filtration, holds promise for the management of syncope. We aimed to evaluate the effectiveness of intermittent calf compression for increasing orthostatic tolerance (OT; time to presyncope). We conducted a randomized single-blind crossover study, in which participants (n = 21) underwent three graded 60° head-up-tilt tests to presyncope with combined lower body negative pressure on separate days. Low frequency intermittent calf compression (ICLF; 4 s on and 11 s off) at 0-30 and 0-60 mmHg was applied during two tests and compared to a placebo condition where the garment was fitted, but no compression applied. We measured continuous leg circumference changes (strain gauge plethysmography), cardiovascular responses (finger plethysmography; Finometer Pro), end tidal gases (nasal cannula), and cerebral blood flow velocity (CBFv, transcranial Doppler). The 0-60 mmHg ICLF increased OT (33 ± 2.2 min) compared to both placebo (26 ± 2.4 min; p < 0.001) and 0-30 mmHg ICLF (25 ± 2.7 min; p < 0.001). Throughout testing 0-60 mmHg ICLF reduced orthostatic fluid shifts compared to both placebo and 0-30 mmHg ICLF (p < 0.001), with an associated improvement in stroke volume (p < 0.001), allowing blood pressure to be maintained at a reduced heart rate (p < 0.001). In addition, CBFv was higher with 0-60 mmHg ICLF than 0-30 mmHg ICLF and placebo (p < 0.001). Intermittent calf compression is a promising novel intervention for the management of orthostatic intolerance, which may provide affected individuals renewed independence and improved quality of life.

Autonomic function test in progressive lacunar infarction

OBJECTIVE

Neurological progression is a major problem in managing the patients with acute lacunar infarction. The purpose of this was to investigate whether autonomic dysfunction is associated with neurological progression in patients with acute lacunar infarction.

MATERIALS AND METHODS

The study comprised 60 patients with acute lacunar infarction. All enrolled subjects underwent autonomic function tests including the 30° head-up tilt test, Valsalva test, heart rate response to deep breathing, and sympathetic skin response. The primary endpoint is the neurological progression, and the secondary endpoint is the 3-month outcome.

RESULTS

Increased initial National Institute of Health stroke scale (NIHSS), decreased time to admission from onset, decreased rise of heart rate in the 30° head-up tilt test, abnormal blood pressure response in the Valsalva test, and decreased rise of systolic blood pressure in stage IV of the Valsalva test are associated with neurological progression of acute lacunar infarction; an abnormal blood pressure response in the Valsalva test is significant in logistic regression analysis of neurological progression. Advanced age, increased initial NIHSS and modified Rankin scale, decreased expiration/inspiration ratio of heart rate to deep breathing, decreased rise of systolic blood pressure in stage IV of the Valsalva test, and neurological progression were associated with an unfavorable 3-month outcome; neurological progression was significant in logistic regression analysis of 3-month outcome.

CONCLUSIONS

An abnormal blood pressure change in the Valsalva test is associated with neurological progression in patients with acute lacunar infarction, and neurological progression can induce an unfavorable 3-month outcome.

Evaluating the efficacy of an active compression brace on orthostatic cardiovascular responses

Orthostatic intolerance, one of the principle causes of syncope, can occur secondary to concomitant venous pooling and enhanced capillary filtration. We aimed to evaluate a prototype portable calf active compression brace (ACB) designed to improve orthostatic haemodynamic control. Fourteen healthy volunteers participated in a randomized, placebo controlled, cross-over, double-blind study. Testing consisted of head-upright tilting and walking on a treadmill conducted on two consecutive days with a pair of ACBs wrapped around both calves. The ACB was actuated on one test day, but not on the other (placebo). Wearability, comfort, and ambulatory use of the ACB were assessed using questionnaires. The average calf pressure exerted by the ACB was 46.3±2.2 mmHg and the actuation pressure was 20.7±1.7 mmHg. When considering the differences between ACB actuation and placebo during tilt after supine rest there were trends for a larger stroke volume (+5.20±2.34%, p = 0.05) and lower heart rate (-5.12±2.41%, p = 0.06) with ACB actuation, with no effect on systolic arterial pressure (+4.86±3.41%, p = 0.18). The decrease in stroke volume after ten minutes of tilting was positively correlated with the height:calf circumference (r = 0.464; p = 0.029; n = 22; both conditions combined). The increase in heart rate after ten minutes of tilting was negatively correlated with the height:calf circumference (r = -0.485; p = 0.022; n = 22; both conditions combined) and was positively correlated with the average calf circumference (r = 0.539; p = 0.009; n = 22; both conditions combined). Participants reported good ACB wearability and comfort during ambulatory use. These data verify that the ACB increased stroke volume during tilting in healthy controls. Active calf compression garments may be a viable option for the management of orthostatic intolerance.

Cerebral autoregulation and symptoms of orthostatic hypotension in familial dysautonomia

Familial dysautonomia is an inherited autonomic disorder with afferent baroreflex failure. We questioned why despite low blood pressure standing, surprisingly few familial dysautonomia patients complain of symptomatic hypotension or have syncope. Using transcranial Doppler ultrasonography of the middle cerebral artery, we measured flow velocity (mean, peak systolic, and diastolic), area under the curve, pulsatility index, and height of the dictrotic notch in 25 patients with familial dysautonomia and 15 controls. In patients, changing from sitting to a standing position, decreased BP from 124 ± 4/64 ± 3 to 82 ± 3/37 ± 2 mmHg (p < 0.0001, for both). Despite low BP, all patients denied orthostatic symptoms. Middle cerebral artery velocity fell minimally, and the magnitude of the reductions were similar to those observed in healthy controls, in whom BP upright did not fall. While standing, patients had a greater fall in cerebrovascular resistance (p < 0.0001), an increase in pulsatility (p < 0.0001), and a deepening of the dicrotic notch (p = 0.0010), findings all consistent with low cerebrovascular resistance. No significant changes occurred in controls. Patients born with baroreflex deafferentation retain the ability to buffer wide fluctuations in BP and auto-regulate cerebral blood flow. This explains how they can tolerate extremely low BPs standing that would otherwise induce syncope.

The recommendations of a consensus panel for the screening, diagnosis, and treatment of neurogenic orthostatic hypotension and associated supine hypertension

Neurogenic orthostatic hypotension (nOH) is common in patients with neurodegenerative disorders such as Parkinson’s disease, multiple system atrophy, pure autonomic failure, dementia with Lewy bodies, and peripheral neuropathies including amyloid or diabetic neuropathy. Due to the frequency of nOH in the aging population, clinicians need to be well informed about its diagnosis and management. To date, studies of nOH have used different outcome measures and various methods of diagnosis, thereby preventing the generation of evidence-based guidelines to direct clinicians towards ‘best practices’ when treating patients with nOH and associated supine hypertension. To address these issues, the American Autonomic Society and the National Parkinson Foundation initiated a project to develop a statement of recommendations beginning with a consensus panel meeting in Boston on November 7, 2015, with continued communications and contributions to the recommendations through October of 2016. This paper summarizes the panel members’ discussions held during the initial meeting along with continued deliberations among the panel members and provides essential recommendations based upon best available evidence as well as expert opinion for the (1) screening, (2) diagnosis, (3) treatment of nOH, and (4) diagnosis and treatment of associated supine hypertension.

Sexual dimorphism in the osmopressor response following water ingestion

Compared with men, women exhibit a greater magnitude of increase in resting blood pressure after drinking a single water bolus of 500 ml. Accordingly, our study provides direct evidence of sexual dimorphism in the haemodynamic response to water intake.

There is conflicting evidence as to whether water drinking elicits a pressor response in healthy young adults. The inclusion of a variable number of women may have contributed to the discrepancies found in past research. Thus, we aimed at exploring whether the osmopressor response follows a sexually dimorphic pattern. In a randomized fashion, 31 healthy adults (16 men; 15 women, aged 18–40 years) ingested 50 and 500 ml of water before completing a resting protocol on two separate days. Arterial blood pressure, heart rate and spectral heart rate variability were measured in the seated position at pre- and post-25 min of water ingestion. Women responded to 500 ml of water with a greater proportion of change in diastolic and mean arterial pressure (MAP) (P<0.05). Conversely, the percent change in systolic blood pressure (SBP) and heart rate was not different between sexes after 500 ml of water. Overall, women demonstrated lower blood pressure, but higher resting heart rate compared with men (P<0.05). In contrast, heart rate variability was similar between sexes before and after ingesting either volume of water. There was a bradycardic effect of water and, irrespectively of sex; this was accompanied by increased high frequency power (HF) (P<0.05). We conclude that women display a greater magnitude of pressor response than men post-water ingestion. Accordingly, we provide direct evidence of sexual dimorphism in the haemodynamic response to water intake in young healthy adults.

INGESTÃO DE ÁGUA NO SISTEMA NERVOSO AUTÔNOMO: UMA REVISÃO SISTEMÁTICA E META-ANÁLISE

RESUMO Verificar, por meio de uma revisão sistemática, o efeito da ingestão de água (IA) no sistema nervoso autônomo (SNA) e variáveis hemodinâmicas em indivíduos adultos. Foram analisados estudos publicados entre 2000 e 2015, tendo como referência a base de dados Medline via Pubmed, sendo utilizado na construção da frase de pesquisa o MeSH. Foram estabelecidos os seguintes critérios de inclusão: ensaios clínicos controlados e randomizados (ECCR) realizados em humanos, na língua inglesa. Como critério de exclusão: intervenções pouco claras, mal descritas ou inadequadas e na forma de resumos. Utilizou-se as seguintes variáveis para a seleção dos estudos: frequência cardíaca (FC), pressão arterial (PA), componente de alta frequência (AF) e resistência vascular periférica (RVP). Foi usada a sistematização PRISMA para a elaboração desta revisão e a realização de uma meta-análise com o objetivo de evidenciar matematicamente os resultados da frequência cardíaca após a ingestão de água em sete estudos que avaliaram esta variável. Fizeram parte desta revisão 10 ECCR envolvendo 246 indivíduos com idade entre 19 a 64 anos, sendo que 34,55% do sexo masculino. A maioria dos ECCR analisados apresentou alterações após a IA. As alterações comumente observadas foram: diminuição da FC (estatisticamente significativa p < 0,001), aumento da AF e RVP. Contudo, em relação à PA, os resultados demonstraram-se conflitantes, com estudos que evidenciaram aumento e outros que não observaram diferença significativa. Esta revisão evidencia os efeitos da IA no SNA, em especial na FC, AF e RVP, não obstante em relação às alterações hemodinâmicas expressas pela PA permanece ainda um óbice em relação à comunidade científica.

Tilt testing with combined lower body negative pressure: a "gold standard" for measuring orthostatic tolerance

Orthostatic tolerance (OT) refers to the ability to maintain cardiovascular stability when upright, against the hydrostatic effects of gravity, and hence to maintain cerebral perfusion and prevent syncope (fainting). Various techniques are available to assess OT and the effects of gravitational stress upon the circulation, typically by reproducing a presyncopal event (near-fainting episode) in a controlled laboratory environment. The time and/or degree of stress required to provoke this response provides the measure of OT. Any technique used to determine OT should: enable distinction between patients with orthostatic intolerance (of various causes) and asymptomatic control subjects; be highly reproducible, enabling evaluation of therapeutic interventions; avoid invasive procedures, which are known to impair OT(1). In the late 1980s head-upright tilt testing was first utilized for diagnosing syncope(2). Since then it has been used to assess OT in patients with syncope of unknown cause, as well as in healthy subjects to study postural cardiovascular reflexes(2-6). Tilting protocols comprise three categories: passive tilt; passive tilt accompanied by pharmacological provocation; and passive tilt with combined lower body negative pressure (LBNP). However, the effects of tilt testing (and other orthostatic stress testing modalities) are often poorly reproducible, with low sensitivity and specificity to diagnose orthostatic intolerance(7). Typically, a passive tilt includes 20-60 min of orthostatic stress continued until the onset of presyncope in patients(2-6). However, the main drawback of this procedure is its inability to invoke presyncope in all individuals undergoing the test, and corresponding low sensitivity(8,9). Thus, different methods were explored to increase the orthostatic stress and improve sensitivity. Pharmacological provocation has been used to increase the orthostatic challenge, for example using isoprenaline(4,7,10,11) or sublingual nitrate(12,13). However, the main drawback of these approaches are increases in sensitivity at the cost of unacceptable decreases in specificity(10,14), with a high positive response rate immediately after administration(15). Furthermore, invasive procedures associated with some pharmacological provocations greatly increase the false positive rate(1). Another approach is to combine passive tilt testing with LBNP, providing a stronger orthostatic stress without invasive procedures or drug side-effects, using the technique pioneered by Professor Roger Hainsworth in the 1990s(16-18). This approach provokes presyncope in almost all subjects (allowing for symptom recognition in patients with syncope), while discriminating between patients with syncope and healthy controls, with a specificity of 92%, sensitivity of 85%, and repeatability of 1.1±0.6 min(16,17). This allows not only diagnosis and pathophysiological assessment(19-22), but also the evaluation of treatments for orthostatic intolerance due to its high repeatability(23-30). For these reasons, we argue this should be the "gold standard" for orthostatic stress testing, and accordingly this will be the method described in this paper.

Chronotropic and pressor effects of water ingestion at rest and in response to incremental dynamic exercise

Ingestion of water attenuates the chronotropic response to submaximal exercise. However, it is not known whether this effect is equally manifested during dynamic exercise below and above the ventilatory threshold (VT). We explored the effects of water ingestion on the heart rate response to an incremental cycle-ergometer protocol. In a randomized fashion, 19 healthy adults (10 men and nine women, age 20.9 ± 1.8 years) ingested 50 and 500 ml of water before completing a cycle-ergometer protocol on two separate days. The heart rate and oxygen uptake ( ) responses to water ingestion were analysed both at rest and during exercise performed below and above the VT. The effects of water intake on brachial blood pressure were measured only at rest. Resting mean arterial pressure increased and resting heart rate decreased, but only after 500 ml of water (P < 0.05). Compared with that seen after 50 ml of water, the 500 ml volume elicited an overall decrease in submaximal heart rate (P < 0.05). In contrast, drinking 500 ml of water did not affect submaximal . The participants' maximal heart rate, maximal and VT were similar between conditions. Our results therefore indicate that, owing to its effects on submaximal heart rate over a broad spectrum of intensities, the drinking of water should be recognized as a potential confounder in cardiovascular exercise studies. However, by showing no differences between conditions for submaximal , they also suggest that the magnitude of heart rate reduction after drinking 500 ml of water may be of minimal physiological significance for exercise cardiorespiratory capacity.

Non-pharmacological management of orthostatic hypotension in the older patient

Orthostatic hypotension (OH) occurs in up to 30% of community-dwelling older people. Its presence confers a greater risk of incident co-morbid disease and all-cause mortality. As per guidelines, first-line treatment should consist of non-pharmacological therapies. Effective lifestyle modification advice includes the avoidance of rapid postural changes and large meals. Physical counter-manoeuvres, when comprehensively described, effectively abate symptom progression. Patients should drink 1.5 to 2 litres of water daily, though reports suggest only half of older people comply with this regime. Moderate salt consumption is advised, though with caution as supine hypertension often co-exists. Compression hosiery benefits older people and, contrary to popular opinion, is well tolerated. Potential, future therapies include impedance threshold devices. Older patients with OH frequently have co-morbid disease such that a pharmacological approach is ill-advised. They respond well to non-pharmacological therapies and these should form the primary therapeutic approach.

Are compression stockings an effective treatment for orthostatic presyncope?

Background

Syncope, or fainting, affects approximately 6.2% of the population, and is associated with significant comorbidity. Many syncopal events occur secondary to excessive venous pooling and capillary filtration in the lower limbs when upright. As such, a common approach to the management of syncope is the use of compression stockings. However, research confirming their efficacy is lacking. We aimed to investigate the effect of graded calf compression stockings on orthostatic tolerance.

Methodology/Principal Findings

We evaluated orthostatic tolerance (OT) and haemodynamic control in 15 healthy volunteers wearing graded calf compression stockings compared to two placebo stockings in a randomized, cross-over, double-blind fashion. OT (time to presyncope, min) was determined using combined head-upright tilting and lower body negative pressure applied until presyncope. Throughout testing we continuously monitored beat-to-beat blood pressures, heart rate, stroke volume and cardiac output (finger plethysmography), cerebral and forearm blood flow velocities (Doppler ultrasound) and breath-by-breath end tidal gases. There were no significant differences in OT between compression stocking (26.0±2.3 min) and calf (29.3±2.4 min) or ankle (27.6±3.1 min) placebo conditions. Cardiovascular, cerebral and respiratory responses were similar in all conditions. The efficacy of compression stockings was related to anthropometric parameters, and could be predicted by a model based on the subject's calf circumference and shoe size (r = 0.780, p = 0.004).

Conclusions/Significance

These data question the use of calf compression stockings for orthostatic intolerance and highlight the need for individualised therapy accounting for anthropometric variables when considering treatment with compression stockings.

Liver afferents contribute to water drinking-induced sympathetic activation in human subjects: a clinical trial

Water drinking acutely increases sympathetic activity in human subjects. In animals, the response appears to be mediated through transient receptor potential channel TRPV4 activation on osmosensitive hepatic spinal afferents, described as osmopressor response. We hypothesized that hepatic denervation attenuates water drinking-induced sympathetic activation. We studied 20 liver transplant recipients (44±2.6 years, 1.2±0.1 years post transplant) as model of hepatic denervation and 20 kidney transplant recipients (43±2.6 years, 0.8±0.1 years post transplant) as immunosuppressive drug matched control group. Before and after 500 ml water ingestion, we obtained venous blood samples for catecholamine analysis. We also monitored brachial and finger blood pressure, ECG, and thoracic bioimpedance. Plasma norepinephrine concentration had changed by 0.01±0.07 nmol/l in liver and by 0.21±0.07 nmol/l in kidney transplant recipients (p<0.05 between groups) after 30–40 minutes of water drinking. While blood pressure and systemic vascular resistance increased in both groups, the responses tended to be attenuated in liver transplant recipients. Our findings support the idea that osmosensitive hepatic afferents are involved in water drinking-induced sympathetic activation in human subjects.

The effect of sleeping with the head of the bed elevated six inches on elderly patients with orthostatic hypotension: an open randomised controlled trial

BACKGROUND

the evidence for 6-inch tilt sleeping-head-up (SHU), a common therapy for the treatment of orthostatic hypotension (OH) in older people, is unavailable.

OBJECTIVE

to investigate the effects of 6-inch SHU for 6 weeks in community-living patients with chronic OH.

DESIGN

open labelled randomised controlled trial.

METHODS

one hundred patients aged ≥60 with chronic OH were randomised into SHU or control groups. Primary outcome measures were mean arterial pressure (MAP) and symptoms. Repeated measures of orthostatic haemodynamic parameters (systolic blood pressure, diastolic blood pressure, MAP, heart rate, percentage change of Modelflow parameters), weight, frequency of dizziness, 24-h urinary sodium and volume, 24-h ambulatory blood pressure (24-ABPM) and presence of ankle oedema were collected at baseline and at 6 weeks.

RESULTS

symptoms improved, to a similar extent, in both groups. There were no differences in MAP or other haemodynamic parameters, weight, urinary volume or 24-ABPM between SHU and controls. SHU were more likely to have leg oedema.

CONCLUSIONS

these findings suggested that SHU at 6 inches has no additional effects on symptoms or haemodynamic parameters at 6 weeks than existing non-pharmacological measures in older patients with OH. Its use in this group should therefore be discouraged.

Acute fluid ingestion in the treatment of orthostatic intolerance - important implications for daily practice

BACKGROUND

Rapid water ingestion improves orthostatic intolerance (OI) in multiple system atrophy (MSA) and postural tachycardia syndrome (PoTS). We compared haemodynamic changes after water and clear soup intake, the latter being a common treatment strategy for OI in daily practice.

METHODS

Seven MSA and seven PoTS patients underwent head-up tilt (HUT) without fluid intake and 30 min after drinking 450 ml of water and clear soup, respectively. All patients suffered from moderate to severe OI because of neurogenic orthostatic hypotension (OH) and excessive orthostatic heart rate (HR) increase, respectively. Beat-to-beat cardiovascular indices were measured non-invasively.

RESULTS

In MSA, HUT had to be terminated prematurely in 2/7 patients after water, but in 6/7 after clear soup. At 3 min of HUT, there was an increase in blood pressure of 15.7(8.2)/8.3(2.3) mmHg after water, but a decrease of 11.6(18.9)/8.1(9.2) mmHg after clear soup (P < 0.05). In PoTS, HUT could always be completed for 10 min, but OI subjectively improved after both water and clear soup. The attenuation of excessive orthostatic HR increase did not differ significantly after water and clear soup drinking.

CONCLUSIONS

In MSA, clear soup cannot substitute water for eliciting a pressor effect, but even worsens OI after rapid ingestion. In PoTS, acute water and clear soup intake both result in improvement of OI. These findings cannot solely be explained by difference in osmolarity but may reflect some degree of superimposed postprandial hypotension in widespread autonomic failure in MSA compared to the mild and limited autonomic dysfunction in PoTS.

The osmopressor response to water drinking

Water drinking elicits profound pressor responses in patients with impaired baroreflex function and in sinoaortic-denervated mice. Healthy subjects show more subtle changes in heart rate and blood pressure with water drinking. The water-induced pressor response appears to be mediated through sympathetic nervous system activation at the spinal level. Indeed, water drinking raises resting energy expenditure in normal weight and obese subjects. The stimulus setting off the response is hypoosmolarity rather than water temperature or gastrointestinal stretch. Studies in mice suggest that this osmopressor response may involve transient receptor potential vanniloid 4 (Trpv4) receptors. However, the (nerve) cell population serving as peripheral osmosensors and the exact transduction mechanisms are still unknown. The osmopressor response can be exploited in the treatment of orthostatic and postprandial hypotension in patients with severe autonomic failure. Furthermore, the osmopressor response acutely improves orthostatic tolerance in healthy subjects and in patients with neurally mediated syncope. The phenomenon should be recognized as an important confounder in cardiovascular and metabolic studies.

Diurnal variation in time to presyncope and associated circulatory changes during a controlled orthostatic challenge

Epidemiological data indicate that the risk of neurally mediated syncope is substantially higher in the morning. Syncope is precipitated by cerebral hypoperfusion, yet no chronobiological experiment has been undertaken to examine whether the major circulatory factors, which influence perfusion, show diurnal variation during a controlled orthostatic challenge. Therefore, we examined the diurnal variation in orthostatic tolerance and circulatory function measured at baseline and at presyncope. In a repeated-measures experiment, conducted at 0600 and 1600, 17 normotensive volunteers, aged 26 ± 4 yr (mean ± SD), rested supine at baseline and then underwent a 60° head-up tilt with 5-min incremental stages of lower body negative pressure until standardized symptoms of presyncope were apparent. Pretest hydration status was similar at both times of day. Continuous beat-to-beat measurements of cerebral blood flow velocity, blood pressure, heart rate, stroke volume, cardiac output, and end-tidal Pco2 were obtained. At baseline, mean cerebral blood flow velocity was 9 ± 2 cm/s (15%) lower in the morning than the afternoon ( P < 0.0001). The mean time to presyncope was shorter in the morning than in the afternoon (27.2 ± 10.5 min vs. 33.1 ± 7.9 min; 95% CI: 0.4 to 11.4 min, P = 0.01). All measurements made at presyncope did not show diurnal variation ( P > 0.05), but the changes over time (from baseline to presyncope time) in arterial blood pressure, estimated peripheral vascular resistance, and α-index baroreflex sensitivity were greater during the morning tests ( P < 0.05). These data indicate that tolerance to an incremental orthostatic challenge is markedly reduced in the morning due to diurnal variations in the time-based decline in blood pressure and the initial cerebral blood flow velocity “reserve” rather than the circulatory status at eventual presyncope. Such information may be used to help identify individuals who are particularly prone to orthostatic intolerance in the morning.

Dissociation Following Traumatic Stress

We postulate that the cascade “Freeze-Flight-Fight-Fright-Flag-Faint” is a coherent sequence of six fear responses that escalate as a function of defense possibilities and proximity to danger during life-threat. The actual sequence of trauma-related response dispositions acted out in an extremely dangerous situation therefore depends on the appraisal of the threat by the organism in relation to her/his own power to act (e.g., age and gender) as well as the perceived characteristics of threat and perpetrator. These reaction patterns provide optimal adaption for particular stages of imminence. Subsequent to the traumatic threats, portions of the experience may be replayed. The actual individual cascade of defense stages a survivor has gone through during the traumatic event will repeat itself every time the fear network, which has evolved peritraumatically, is activated again (i.e., through internal or external triggers or, e.g., during exposure therapy).When a parasympathetically dominated ‘‘shut-down’’ was the prominent peri-traumatic response during the traumatic incident, comparable dissociative responses may dominate responding to subsequently experienced threat and may also reappear when the traumatic memory is reactivated. Repeated experience of traumatic stress forms a fear network that can become pathologically detached from contextual cues such as time and location of the danger, a condition which manifests itself as posttraumatic stress disorder (PTSD). Intrusions, for example, can therefore be understood as repetitive displays of fragments of the event, which would then, depending on the dominant physiological response during the threat, elicit a corresponding combination of hyperarousal and dissociation. We suggest that trauma treatment must therefore differentiate between patients on two dimensions: those with peritraumatic sympathetic activation versus those who went down the whole defense cascade, which leads to parasympathetic dominance during the trauma and a corresponding replay of physiological and dissociative responding, when reminded. The differential management of dissociative stages (“fright” and “faint”) has important treatment implications.

Evidence for unloading arterial baroreceptors during low levels of lower body negative pressure in humans

Low levels (i.e., </=20 mmHg) of lower body negative pressure (LBNP) have been utilized to unload "selectively" cardiopulmonary baroreceptors in humans, since steady-state mean arterial pressure and heart rate (HR) have been found unchanged at such levels. However, transient reductions in blood pressure (BP), followed by reflex compensation, may occur without detection, which could unload arterial baroreceptors. The purposes of this study were to test the hypothesis that the arterial baroreflex is engaged even during low levels of LBNP and to determine the time course of changes in hemodynamics. Fourteen healthy individuals (age range 20-54 yr) were studied. BP (Portapres and Suntech), HR (ECG), pulmonary capillary wedge pressure (PCWP) or pulmonary artery diastolic pressure (PDP) and right atrial pressure (RAP) (Swan-Ganz catheter) and hemodynamics (Modelflow) were recorded continuously at baseline and -15- and -30-mmHg LBNP for 6 min each. Application of -15-mmHg LBNP resulted in rapid and sustained falls in RAP and PCWP or PDP, progressive decreases in cardiac output and stroke volume, followed subsequently by transient reductions in both systolic and diastolic BP, which were then restored through the arterial baroreflex feedback mechanism after approximately 15 heartbeats. Additional studies were performed in five subjects using even lower levels of LBNP, and this transient reduction in BP was observed in three at -5- and in all at -10-mmHg LBNP. The delay for left ventricular stroke volume to fall at -15-mmHg LBNP was about 10 cardiac cycles. An increase in systemic vascular resistance was detectable after 20 heartbeats during -15-mmHg LBNP. Steady-state BP and HR remained unchanged during mild LBNP. However, BP decreased, while HR increased, at -30-mmHg LBNP. These results suggest that arterial baroreceptors are consistently unloaded during low levels (i.e., -10 and -15 mmHg) of LBNP in humans. Thus "selective" unloading of cardiopulmonary baroreceptors cannot be presumed to occur during these levels of mild LBNP.

Vasodilation in vasovagal syncope and the effect of water ingestion

Abnormal (increased, but also decreased) vasodilative responses have been observed in patients with vasovagal syncope (VVS). The objective was to assess reactive vasodilation in supine patients with VVS and its relation to severity of the syndrome. Reactive vasodilation was also assessed after a simple therapeutic intervention (water drinking). Thirty-four patients were studied, all with recurrent VVS and a recent positive head-up tilt test result. Seventeen matched healthy subjects served as controls. Venous occlusion plethysmography was used to assess forearm blood flow (FBF) and forearm vascular resistance resistance (1) at rest and (2) during reactive hyperemia. Clinical severity of the syndrome was related to the intensity and duration of the vasodilative reflex. The same plethysmographic measurements were repeated 60 minutes after drinking 500 ml of water. Before water drinking, no difference was observed between groups in baseline measurements. However, duration of hyperemia was longer in patients (p <0.05) and was related to the duration of the previous positive tilt test (r = -0.69, p <0.05) and total number of each patient's symptomatic vasovagal episodes (r = 0.49, p <0.05). After water ingestion, baseline FBF decreased in patients (p <0.05) and remained stable in controls. In patients, duration of hyperemia decreased to normal values. Hyperemic FBF remained similar between groups. In conclusion, increased reactive vasodilative reflexes were observed in patients with VVS. They seemed to be of significant pathophysiologic significance. Water drinking can normalize them for >or=60 minutes.

Increased hydration alone does not improve orthostatic tolerance in patients with neurocardiogenic syncope

In patients with neurocardiogenic syncope, the beneficial effects of increased daily fluid intake, without an accompanying high dose of salt, are unknown. Our aim was to (1) determine whether plasma volume was low in patients with recurrent neurocardiogenic syncope, and (2) determine how recommendation about increased daily fluid intake, without an accompanying high dose of sodium, effects plasma volume and if this potential therapy improves orthostatic tolerance. Eighty-six patients with neurocardiogenic syncope were recruited in a prospective randomized open study. After an initial head-up tilt test, patients were randomly assigned to either the hydration supplementation group (1500 ml of water + 1500 mg of NaCl/day) or the no treatment (control) group. After ten days a second head-up tilt test was performed. Plasma volume, osmolality, and total body water were measured at baseline, and heart rate, arterial blood pressure, and cardiac transthoracic impedance were monitored during tilting. Hydration treatment did not affect the number of positive tilt tests (52% initial day, 54% after treatment, NS). In both groups, the overall number of positive tilt tests decreased between the initial and final head-up tilt test. There was no association between low plasma volume and positive tilt test. Patients with the lowest plasma volume were equally distributed in both positive and negative tilt response groups. An increased daily intake of fluid, without an accompanying high dose of salt, had no measurable beneficial effect on tolerance to head-up tilting in patients with neurocardiogenic syncope. Moreover in this patient group there was no association between a low plasma volume and a reduced tolerance to orthostatic stress.

Effects of daily water drinking on orthostatic and postprandial hypotension in patients with multiple system atrophy

OBJECTIVE

It has been demonstrated that the increased blood pressure (BP) caused by a single dose of water alleviates orthostatic hypotension (OH) and postprandial hypotension (PPH) in patients with autonomic failure (AF). The aim of this study was to evaluate the practical effect of daily water drinking on OH and PPH in the morning when patients with AF are usually most affected.

METHODS

In five patients with multiple system atrophy (MSA) characterized by intractable OH and PPH, we measured seated, standing and postprandial BP in the morning without and with ingestion of 350 ml tap water at 07.30 hours for seven successive days. The changes from the basal BP level at 07.30 hours (DeltaBP) were assessed as an index of the effect of water drinking.

RESULTS

Water drinking elicited a rapid pressor response in all patients. The DeltaBP during sitting, standing and after a meal following water drinking (day 1 and day 7) was significantly higher than without water drinking (day 0). The effects of reducing OH and PPH on day 7 were equivalent to those on day 1. No adverse effects associated with daily water drinking were observed, except later diuresis, which occurred in one patient.

CONCLUSIONS

Daily water drinking demonstrated constant pressor effects in the morning with no severe adverse effects in MSA patients. This finding suggests that water drinking should be tried as a practical measure to prevent or reduce OH and PPH.

Hypohydration and prior heat stress exacerbates decreases in cerebral blood flow velocity during standing

Hypohydration is associated with orthostatic intolerance; however, little is known about cerebrovascular mechanisms responsible. This study examined whether hypohydration reduces cerebral blood flow velocity (CBFV) in response to an orthostatic challenge. Eight subjects completed four orthostatic challenges (temperate conditions) twice before (Pre-EU and Pre-Hyp) and following recovery from passive heat stress ( approximately 3 h at 45 degrees C, 50% relative humidity, 1 m/s air speed) with (Post-EU) or without (Post-Hyp) fluid replacement of sweat losses (-3% body mass loss). Measurements included CBFV, mean arterial pressure (MAP), heart rate (HR), end-tidal CO(2), and core and skin temperatures. Test sessions included being seated (20 min) followed by standing (60 s) then resitting (60 s) with metronomic breathing (15 breaths/min). CBFV and MAP responses to standing were similar during Pre-EU and Pre-Hyp. Standing Post-Hyp exacerbated the magnitude (-28.0 +/- 1.4% of baseline) and duration (9.0 +/- 1.6 s) of CBFV reductions and increased cerebrovascular resistance (CVR) compared with Post-EU (-20.0 +/- 2.1% and 6.6 +/- 0.9 s). Standing Post-EU also resulted in a reduction in CBFV, and a smaller decrease in CVR compared with Pre-EU. MAP decreases were similar for Post-EU (-18 +/- 4 mmHg) and Post-Hyp (-21 +/- 5 mmHg) from seated to standing. These data demonstrate that despite similar MAP decreases, hypohydration, and prior heat stress (despite apparent recovery) produce greater CBFV reduction when standing. These observations suggest that hypohydration and prior heat stress are associated with greater reductions in CBFV with greater CVR, which likely contribute to orthostatic intolerance.

Salt wasting, hypotension, polydipsia, and hyponatremia and the level of spinal cord injury

STUDY DESIGN

Case control.

OBJECTIVE

To test the reported correlation of hypotension, polydipsia, and hyponatremia with higher levels of spinal cord injury (SCI).

SETTING

A Veterans Administration Hospital, USA.

METHODS

The records of men who were paralyzed owing to trauma at any spinal cord level with motor complete lesions (ASIA A or B) and who received an annual physical and laboratory examination were reviewed for age, duration of paralysis, level of paralysis, blood pressure (BP), serum sodium, and 24 h urinary volume, creatinine, and sodium. Creatinine clearance and fractional excretion of sodium (FcNa) were calculated. Spearman rank-order correlations (r (s)) were carried out.

RESULTS

Patients were aged 25 to 88 years, median 56 years, paralyzed 2-61 years, median 26 years, with levels of paralysis ranging from C2 to L4, median T4, n=111. From lower to higher levels of paralysis FcNa increased (0.4-7.3%), mean BP diminished (132-66 mmHg), urine volume increased (600-5400 ml), and serum sodium was reduced (148-129 mEq/l) - r (s)=0.29, 0.49, -0.22, and 0.23, respectively. Increasing 24 h urinary volumes correlated with lower serum sodium concentrations but higher creatinine clearance, r (s)=-0.28, 0.24. Increasing 24 h urinary sodium improved creatinine clearance, r (s)=0.37. P-values ranged from <0.05 to <0.001.

CONCLUSION

Higher levels of SCI correlate with reduced sodium conservation, hypotension, polydipsia, and hyponatremia. Greater water intake raises creatinine clearance but lowers serum sodium. Greater salt intake increases creatinine clearance.