Decreased skeletal muscle pump activity in patients with postural tachycardia syndrome and low peripheral blood flow

Navigating Complexity in Postural Orthostatic Tachycardia Syndrome

Postural Orthostatic Tachycardia Syndrome (POTS) affects up to 1% of the US population, predominantly women, and is characterized by a complex, elusive etiology and heterogeneous phenotypes. This review delves into the intricate physiology and etiology of POTS, decoding the roles of the sinoatrial node, the autonomic nervous system, fluid dynamics, and the interplay between the immune and endocrine systems. It further examines key contributing factors such as dysautonomia, thoracic hypovolemia, autonomic neuropathies, sympathetic denervation, autoimmune responses, and associations with conditions such as small-fiber neuropathy and mast cell activation syndrome. Given the numerous mysteries surrounding POTS, we also cautiously bring attention to sinoatrial node and myocardial function, particularly in how the heart responds to stress despite exhibiting a normal cardiac phenotype at rest. The potential of genomic research in elucidating the underlying mechanisms of POTS is emphasized, suggesting this as a valuable approach that is likely to improve our understanding of the genetic underpinnings of POTS. The review introduces a tentative classification system for the etiological factors in POTS, which seeks to capture the condition's diverse aspects by categorizing various etiological factors and acknowledging co-occurring conditions. This classification, while aiming to enhance understanding and optimize treatment targets, is presented as a preliminary model needing further study and refinement. This review underscores the ongoing need for research to unravel the complexities of POTS and to develop targeted therapies that can improve patient outcomes.

Autonomic nervous system and postural control regulation during orthostatic test as putative markers of physical resilience among community-dwelling older adults

INTRODUCTION

We examined whether autonomic nervous system (ANS) and postural control regulation during orthostatic test reflect physical resilience by studying their associations with maximal walking speed and mortality.

METHODS

The participants were community-dwelling Finnish men (n = 303) and women (n = 386) aged 75, 80, and 85 years at baseline. Systolic and diastolic blood pressure (BP), heart rate, heart rate variability (HRV), respiratory rate, and postural sway were obtained using a digital sphygmomanometer, a single-channel ECG, and thigh- and chest-worn accelerometers. Linear and Cox regression models were used to estimate the associations of the physiological indices with maximal 10-m walking speed and 5-year mortality separately for sexes.

RESULTS

Better maintenance of BP under orthostatic stress was associated with faster walking speed in women and lower mortality hazard in men. Greater HRV in terms of low frequency power and lower respiration rate in supine position and smaller orthostatic changes in these were associated with faster walking speed especially in women. Less postural sway after standing up was associated with faster walking speed in women (-0.057, SE 0.022, p = 0.011) and more postural sway with increased mortality hazard in men (HR 1.71, 95 % CI 1.20-2.43) even after controlling for BP responses.

CONCLUSIONS

In addition to ANS regulation at rest and under stress, adaptation of postural control system to orthostasis may be used in quantifying older adults' physical resilience. Wearable sensors capturing stimulus-response patterns and natural fluctuations of body functions may provide opportunities to monitor and incorporate different subsystems' resilience also in free-living conditions.

Atrial electromechanical delay in post-COVID-19 postural orthostatic tachycardia: Innocent bystander or pathologic factor

BACKGROUND

Post-COVID-19 syndrome represents a wide range of ongoing symptoms that persist beyond weeks or even months, after recovery from the acute phase. Postural orthostatic tachycardia (POT) is one of these symptoms with a poorly recognized underlying pathophysiology.

PURPOSE

We aimed to investigate atrial electromechanical delay (AEMD), demonstrated by electrocardiographic P wave dispersion (PWD) and tissue Doppler echocardiography (TDE) in patients with POST-COVID-19 POT (PCPOT).

METHODS

94 post-COVID-19 patients were enrolled and classified into two groups; PCPOT group, 34 (36.1%) patients, and normal heart rate (NR group), 60 (63.9%) patients. 31.9% of them were males and 68.1% were females, with a mean age of 35 ± 9 years. Both groups were compared in terms of PWD and AEMD.

RESULTS

As compared to the NR group, the PCPOT group showed a significant increase in PWD (49 ± 6 versus 25.6 ± 7.8, p < 0.001), higher CRP (37 ± 9 versus 30 ± 6, p = 0.04), prolonged left-atrial EMD, right-atrial EMD and inter-atrial EMD at (p = 0.006, 0.001, 0.002 respectively). Multivariate logistic regression analysis revealed that P wave dispersion (β 0.505, CI (0.224-1.138), p = 0.023), PA lateral (β 0.357, CI (0.214-0.697), p = 0.005), PA septal (β 0.651, CI. (0.325-0.861), p = 0.021), and intra-left atrial EMD (β 0.535, CI (0.353-1.346) p < 0.012) were independent predictors of PCPOT.

CONCLUSION

Atrial heterogenicity in the form of prolonged AEMD and PWD seems to be a reasonable underlying pathophysiology of PCPOT. This could provide a new concern during the management and novel pharmacological approaches in these patients.

Predicting Therapeutic Efficacy of Pharmacological Treatments in Children with Postural Orthostatic Tachycardia Syndrome: A Mini-Review

Postural orthostatic tachycardia syndrome (POTS) is common in children, with an excessive increment in heart rate when moving from the supine to upright position. It has significant negative impacts on the daily life of pediatric patients. The pathogenesis of POTS includes peripheral vascular dysfunction, central hypovolemia, abnormal autonomic function, a high-adrenergic state, impaired skeletal-muscle pump function, the abnormal release of vasoactive factors, and autoimmune abnormalities. Therefore, the empirical use of pharmacological treatments has limited therapeutic efficacy due to the diversity of its mechanisms. A crucial aspect of managing POTS is the selection of appropriate treatment targeting the specific pathogenesis. This review summarizes the commonly used pharmacological interventions, with a focus on their predictive indicators for treatment response. Factors such as heart rate variability, plasma biomarkers, and cardiac-function parameters are discussed as potential predictors of therapeutic efficacy, enabling the implementation of individualized treatment to improve therapeutic effectiveness. This review consolidates the current knowledge on POTS, encompassing its clinical characteristics, epidemiological patterns, underlying pathogenic mechanisms, and predictive indicators for treatment response. Further research is warranted to enhance the understanding of POTS and facilitate the development of more effective therapeutic approaches for this challenging syndrome.

Relationship between sarcopenia and orthostatic blood pressure recovery in older falls clinic attendees

PURPOSE

Sarcopenia and delayed orthostatic blood pressure (BP) recovery are two disorders increasingly associated with adverse clinical outcomes in older adults. There may exist a pathophysiological link between the two via the skeletal muscle pump of the lower limbs. Previously in a large population-based study, we found an association between probable sarcopenia and orthostatic BP recovery. Here, we sought to determine the association between confirmed sarcopenia and orthostatic BP recovery in falls clinic attendees aged 50 years or over.

METHODS

One hundred and nine recruited patients (mean age 70 years, 58% women) underwent an active stand with non-invasive beat-to-beat haemodynamic monitoring. Hand grip strength and five-chair stands time were measured, and bioelectrical impedance analysis was performed. They were then classified as robust, probable sarcopenic or sarcopenic as per the European Working Group on Sarcopenia in Older People guidelines. Mixed effects models with linear splines were used to model the effect of sarcopenia status on orthostatic BP recovery, whilst controlling for potential confounders.

RESULTS

Probable sarcopenia was identified in 32% of the sample and sarcopenia in 15%. Both probable and confirmed sarcopenia were independently associated with an attenuated rate of recovery of both systolic and diastolic BP in the 10-20 s period after standing. Attenuation was larger for confirmed than probable sarcopenia (systolic BP β - 0.85 and - 0.59, respectively, P < 0.01; diastolic BP β - 0.65, - 0.45, P < 0.001).

CONCLUSION

Sarcopenia was independently associated with slower BP recovery during the early post-stand period. The potentially modifiable effect of the skeletal muscle pump in orthostatic haemodynamics requires further study.

The Effect of Cardiac Mass and Venous Return in Children with Postural Orthostatic Tachycardia Syndrome: A Prospective, Observational Study

Low left ventricular mass index (LVMI) is thought to limit exercise tolerance in adult patients with postural orthostatic tachycardia syndrome (POTS). This finding has not been studied in children. We evaluated the effect of LVMI and hemodynamics at baseline and during exercise in POTS versus controls. POTS and control subjects aged 12-18 years were prospectively enrolled. POTS patients underwent autonomic studies. An echocardiogram was performed on all patients at baseline and during exercise. LVMI, venous return from inferior vena cava (IVC-VTI), left ventricular dimension, and cardiac output were assessed at baseline and during exercise. Generalized linear modeling with mixed effects was used to perform repeated measures testing between POTS and controls. Eighteen POTS patients (14 female, aged 15.4 ± 1.4 years) and nine control subjects (six female, aged 15.0 ± 1.3 years; p = 0.44) were enrolled. At baseline, LVMI was similar in both groups. During exercise, IVC-VTI, left ventricular end-diastolic dimension and volume, and stroke volume were lower in POTS patients. Peak heart rate was higher in POTS patients, but cardiac output was similar in both groups. Exercise time was higher in the control group (11.4 ± 2.7 min vs 9.2 ± 2.1, p = 0.024). Lower venous return resulted in smaller cardiac dimension and stroke volume during exercise. Higher heart rate in POTS may compensate to achieve similar cardiac output compared with control subjects. Lower ventricular filling and earlier time to peak heart rate may explain lower exercise capacity in pediatric POTS.

Exaggerated postural sway improves orthostatic cardiovascular and cerebrovascular control

Introduction

Healthy individuals with poor cardiovascular control, but who do not experience syncope (fainting), adopt an innate strategy of increased leg movement in the form of postural sway that is thought to counter orthostatic (gravitational) stress on the cardiovascular system. However, the direct effect of sway on cardiovascular hemodynamics and cerebral perfusion is unknown. If sway produces meaningful cardiovascular responses, it could be exploited clinically to prevent an imminent faint.

Methods

Twenty healthy adults were instrumented with cardiovascular (finger plethysmography, echocardiography, electrocardiogram) and cerebrovascular (transcranial Doppler) monitoring. Following supine rest, participants performed a baseline stand (BL) on a force platform, followed by three trials of exaggerated sway (anterior-posterior, AP; mediolateral, ML; square, SQ) in a randomized order.

Results

All exaggerated postural sway conditions improved systolic arterial pressure (SAP, p = 0.001) responses, while blunting orthostatic reductions in stroke volume (SV, p < 0.01) and cerebral blood flow (CBFv, p < 0.05) compared to BL. Markers of sympathetic activation (power of low-frequency oscillations in SAP, p < 0.001) and maximum transvalvular flow velocity (p < 0.001) were reduced during exaggerated sway conditions. Responses were dose-dependent, with improvements in SAP (p < 0.001), SV (p < 0.001) and CBFv (p = 0.009) all positively correlated with total sway path length. Coherence between postural movements and SAP (p < 0.001), SV (p < 0.001) and CBFv (p = 0.003) also improved during exaggerated sway.

Discussion

Exaggerated sway improves cardiovascular and cerebrovascular control and may supplement cardiovascular reflex responses to orthostatic stress. This movement provides a simple means to boost orthostatic cardiovascular control for individuals with syncope, or those with occupations that require prolonged motionless standing.

Counter pressure maneuvers for syncope prevention: A semi-systematic review and meta-analysis

Physical counter pressure maneuvers (CPM) are movements that are recommended to delay or prevent syncope (fainting) by recruiting the skeletal muscle pump to augment cardiovascular control. However, these recommendations are largely based on theoretical benefit, with limited data evaluating the efficacy of CPM to prevent syncope in the real-world setting. We conducted a semi-systematic literature review and meta-analysis to assess CPM efficacy, identify literature gaps, and highlight future research needs. Articles were identified through a literature search (PubMed, April 2022) of peer-reviewed publications evaluating the use of counter pressure or other lower body maneuvers to prevent syncope. Two team members independently screened records for inclusion and extracted data. From 476 unique records identified by the search, 45 met inclusion criteria. Articles considered various syncopal conditions (vasovagal = 12, orthostatic hypotension = 8, postural orthostatic tachycardia syndrome = 1, familial dysautonomia = 2, spinal cord injury = 1, blood donation = 10, healthy controls = 11). Maneuvers assessed included hand gripping, leg fidgeting, stepping, tiptoeing, marching, calf raises, postural sway, tensing (upper, lower, whole body), leg crossing, squatting, “crash” position, and bending foreword. CPM were assessed in laboratory-based studies (N = 28), the community setting (N = 4), both laboratory and community settings (N = 3), and during blood donation (N = 10). CPM improved standing systolic blood pressure (+ 14.8 ± 0.6 mmHg, p < 0.001) and heart rate (+ 1.4 ± 0.5 bpm, p = 0.006), however, responses of total peripheral resistance, stroke volume, or cerebral blood flow were not widely documented. Most patients experienced symptom improvement following CPM use (laboratory: 60 ± 4%, community: 72 ± 9%). The most prominent barrier to employing CPM in daily living was the inability to recognize an impending faint. Patterns of postural sway may also recruit the skeletal muscle pump to enhance cardiovascular control, and its potential as a discrete, proactive CPM needs further evaluation. Physical CPM were successful in improving syncopal symptoms and producing cardiovascular responses that may bolster against syncope; however, practical limitations may restrict applicability for use in daily living.

Biomarkers and Hemodynamic Parameters in the Diagnosis and Treatment of Children with Postural Tachycardia Syndrome and Vasovagal Syncope

In children, vasovagal syncope and postural tachycardia syndrome constitute the major types of orthostatic intolerance. The clinical characteristics of postural tachycardia syndrome and vasovagal syncope are similar but their treatments differ. Therefore, their differential diagnosis is important to guide the correct treatment. Therapeutic methods vary in patients with the same diagnosis because of different pathomechanisms. Hence, in patients with vasovagal syncope or postural tachycardia syndrome, routine treatments have an unsatisfactory efficacy. However, biomarkers could increase the therapeutic efficacy significantly, allowing for an accurate and detailed assessment of patients and leading to improved therapeutic effects. In the present review, we aimed to summarize the current state of research into biomarkers for distinguishing the diagnosis of pediatric vasovagal syncope from that of postural tachycardia syndrome. We also discuss the biomarkers that predict treatment outcomes during personalized therapy for each subtype.

Predictive Value of Heart Rate and Blood Pressure on the Prognosis of Postural Tachycardia Syndrome in Children

Background

To investigate the predictive value of heart rate (HR) and blood pressure (BP) on the prognosis of postural tachycardia syndrome (POTS) in children.

Materials and Methods

53 cases of children aged 5 to 15 years who visited in the Pediatric Syncope Specialist Clinic of The Second Xiangya Hospital of Central South University for unexplained syncope or syncope precursor were diagnosed with POTS by head-up tilt test (HUTT) as the POTS group. 38 healthy children aged 5 to 16 years who underwent physical examination at the Child Health Care Clinic of the hospital in the same period were matched as controls (control group). The children with POTS were followed up after 3 months of treatment and were divided into good prognosis group (40 cases) and poor prognosis group (13 cases) according to the results of HUTT re-examination and whether the symptoms improved or not. HR and BP indicators were collected from each group at baseline and during HUTT.

Results

There were 91 research subjects, of which 45 are males, with a mean age of 11.52 ± 2.13 years. (1) HR at 5 and 10 min (HR 5 and HR 10, respectively), HR difference at 5 and 10 min (HRD 5 and HRD 10, respectively), and HR and BP product at 5 and 10 min (RPP 5 and RPP 10, respectively) were greater in the POTS group than in the control group (P < 0.01). (2) HR 5, HR 10, HRD 5, HRD 10, and RPP 10 in children with POTS were smaller in the good prognosis group than the poor prognosis group (P < 0.01). (3) The area under curve was 0.925 on the four combined indicators (HR 5, HR 10, HRD 5, and HRD 10), predicting a good prognosis of POTS, sensitivity of 99.99%, and specificity of 75.00%.

Conclusions

HR 5, HR 10, HRD 5, HRD 10, and RPP 10 and the four combined indicators (HR 5, HR 10, HRD 5, and HRD 10) had predictive value for the POTS prognosis in children. The predictive value of the four combined indicators for the POTS prognosis was better than that of the single HR 5, HRD 5, and RPP 10.

Orthostatic intolerance: a frailty marker for older adults

PURPOSE

Frailty, orthostatic blood pressure changes (OBPC), and orthostatic intolerance syndrome (OIS) are common in geriatric patients. However, the results of the studies evaluating the relationship between these entities are discordant. We aimed to investigate the association between frailty and OIS with or without OBPC.

METHODS

Comprehensive geriatric assessment (CGA), frailty assessment, OBPC evaluations in the active-standing test (1st, 3rd, 5th, and 10th min), OIS investigation both in history before the test (self-reported OIS) and emerged during the active-standing test, and sarcopenia assessment via BIA and handgrip strength (HGS) were performed in 102 geriatric outpatients.

RESULTS

Patients were divided into three categories according to their frailty status (non-frail, prefrail, and frail) by Modified Fried Frailty Index (FFI) and Clinical Frailty Scale (CFS). Prevalence of self-reported OIS and OIS during the test were statistically higher in the frail group assessed by both frailty scales (P value: 0.001 for CFS, P value < 0.0001 for FFI, and P value: 0.001 for CFS, P value: 0.007 for FFI, respectively). Logistic regression analysis showed that OIS significantly increased frailty assessed both by FFI and CFS, when adjusted for age, sex, comorbidities, CGA, and sarcopenia (For FFI, OR: 19.37; 95% CI: 2.38-157.14; P value: 0.006 and for CFS OR: 4.32; 95% CI: 1.184-11.47; P value: 0.003, respectively).

CONCLUSION

To the best of our knowledge, this is the first study defining OIS as symptoms both self-reported and provoked during the test, and showed a strong correlation between OIS and frailty. OIS may be defined as a multifactorial and independent marker for frailty, regardless of OBPC. Further prospective investigations are warranted to support the relationships between OIS and frailty.

Baseline Corrected QT Interval Dispersion Is Useful to Predict Effectiveness of Metoprolol on Pediatric Postural Tachycardia Syndrome

OBJECTIVES

The study was designed to explore the role of baseline-corrected QT interval dispersion (QTcd) in predicting the effectiveness of metoprolol on pediatric postural tachycardia syndrome (POTS).

METHODS

There were two groups in the study, the discovery group and the validation group. The children with POTS in the discovery group were treated with oral metoprolol, with the completed necessary medical records, head-up tilt test (HUTT), blood chemistry, and 12-lead ECG before treatment at the pediatrics of Peking University First Hospital, China. According to whether the symptom score (SS) was reduced by more than 2 points after administration with oral metoprolol as compared with that before treatment, the children with POTS were separated into responders and non-responders. The demographic characteristics, hemodynamic indicators, and the QTcd of the two groups were compared, and the estimate of the baseline QTcd in predicting the treatment response to metoprolol was tested through a receiver operating characteristic (ROC) analysis. Other 24 children suffering from POTS who were, administrated with metoprolol at the pediatrics of Peking University First Hospital were included in the validation group. The sensitivity, specificity, and accuracy of the baseline QTcd in the prediction of the effectiveness of metoprolol on POTS were validated in children.

RESULTS

The pre-treatment baseline QTcd in responders treated with metoprolol was longer than that of the non-responders in the discovery group [(66.3 ± 20.3) ms vs. (45.7 ± 19.9) ms, p = 0.001]. The baseline QTcd was negatively correlated with SS after metoprolol treatment (r = -0.406, p = 0.003). The cut-off value of baseline QTcd for the prediction of the effectiveness of metoprolol on pediatric POTS was 47.9 ms, yielding a sensitivity of 78.9% and a specificity of 83.3%, respectively. The validation group showed that the sensitivity, specificity, and accuracy of the baseline QTcd ≥ 47.9 ms before treatment for estimating the effectiveness of metoprolol on POTS in children were 73.7, 80.0, and 75.0%, respectively.

CONCLUSION

Baseline QTcd is effective for predicting the effectiveness of metoprolol on pediatric POTS.

Impaired Endothelial Function in Patients With Postural Tachycardia Syndrome

The purpose of this study is to evaluate endothelial function in postural tachycardia syndrome (PoTS), a poorly understood chronic condition characterized by a state of consistent orthostatic tachycardia (delta heart rate ≥30 beats per minute) upon standing without orthostatic hypotension. Nineteen patients with PoTS and 9 healthy controls were studied after 3 days of a fixed, caffeine-free, normal sodium (150 milliequivalents/day) diet. All participants underwent autonomic function testing, including sinus arrhythmia, valsalva maneuver, hyperventilation, cold pressor, handgrip, and a standing test with catecholamine measurements, followed by endothelial function testing. We analyzed 3 measures of endothelial function: percent brachial flow-mediated dilation, digital pulsatile arterial tonometry, and postischemic percent leg blood flow. Flow-mediated dilation was significantly lower in patients with PoTS (6.23±3.54% for PoTS) than in healthy controls (10.6±4.37% for controls versus, P=0.014). PoTS and controls had similar digital pulsatile arterial tonometry (1.93±0.40 arbitrary units for controls versus 2.13±0.63 arbitrary units for PoTS). PoTS had similar but suggestive percent leg blood flow to controls (313±158% for PoTS versus 468±236% for controls, P=0.098). Patients with PoTS have significantly reduced flow-mediated dilation compared with healthy controls, suggesting that PoTS is characterized by endothelial dysfunction in conduit arteries. Registration: URL: https://www.clinicaltrials.gov. Unique identifier: NCT01308099.

Postural Tachycardia Syndrome in Children and Adolescents: Pathophysiology and Clinical Management

Postural tachycardia syndrome (POTS), characterized by chronic (≥6 months) orthostatic intolerance symptoms with a sustained and excessive heart rate increase while standing without postural hypotension, is common in children and adolescents. Despite the unclear pathogenesis of POTS, the present opinion is that POTS is a heterogeneous and multifactorial disorder that includes altered central blood volume, abnormal autonomic reflexes, "hyperadrenergic" status, damaged skeletal muscle pump activity, abnormal local vascular tension and vasoactive factor release, mast cell activation, iron insufficiency, and autoimmune dysfunction. A number of pediatric POTS patients are affected by more than one of these pathophysiological mechanisms. Therefore, individualized treatment strategies are initiated in the management of POTS, including basal non-pharmacological approaches (e.g., health education, the avoidance of triggers, exercise, or supplementation with water and salt) and special pharmacological therapies (e.g., oral rehydration salts, midodrine hydrochloride, and metoprolol). As such, the recent progress in the pathogenesis, management strategies, and therapeutic response predictors of pediatric POTS are reviewed here.

Modulation of left ventricular diastolic filling during exercise in persons with cervical motor incomplete spinal cord injury

PURPOSE

To characterize left ventricular diastolic function during an exertional challenge in adults with incomplete cervical spinal cord Injury (icSCI).

METHODS

In this cross-sectional study, a two-group convenience sample was used to compare left ventricular LV diastolic performance during a 5-10 W·min-1 incremental arm ergometer exercise protocol, using bioimpedance cardiography. Subjects were eight males with cervical incomplete spinal cord injury (icSCI; C5-C7: age 39 ± 14 years) versus eight able-bodied males (CON: age 38 ± 13 years). Left ventricular (LV) diastolic indices included end-diastolic volume (EDV) and early diastolic filling ratio (EDFR). LV ejection time (LVET), inotropic index (dZ/dT2) and stroke volume (SV) were compared between the groups at peak exercise, and maximum workload for the icSCI group (isomax).

RESULTS

EDV (at peak exercise:131.4 ± 7.3 vs 188.78 ± 9.4, p < 0.001; at isomax: 131.4 ± 7.3 vs 169 ± 23, p = 0.0009) and EDFR (at peak exercise 73 ± 14% vs 119 ± 11%, p = 0.006; at isomax 94 ± 10; p = 0.009) were significantly reduced in icSCI compared to CON, respectively. Significant differences in LVET (icSCI: 273 ± 48 vs CON: 305 ± 68; p = 0.1) and dZ/dT2 (icSCI: 0.64 ± 0.11 vs CON: 0.85 ± 0.31; p = 0.1) were not observed at isomax, despite a significant decrease in SV in the subjects with icSCI (77.1 ± 6.05 mL vs 105.8 ± 9.2 mL, p < 0.00) CONCLUSION: Left ventricular filling was impaired in the subjects with icSCI as evidenced at both peak exercise and isomax. It is likely that restrictions on the skeletal muscle pump mechanized the impairment but increased left ventricular wall stiffness could not be excluded as a mediator.

Comparison of Autonomic Control of Blood Pressure During Standing and Artificial Gravity Induced via Short-Arm Human Centrifuge

Autonomic control of blood pressure is essential toward maintenance of cerebral perfusion during standing, failure of which could lead to fainting. Long-term exposure to microgravity deteriorates autonomic control of blood pressure. Consequently, astronauts experience orthostatic intolerance on their return to gravitational environment. Ground-based studies suggest sporadic training in artificial hypergravity can mitigate spaceflight deconditioning. In this regard, short-arm human centrifuge (SAHC), capable of creating artificial hypergravity of different g-loads, provides an auspicious training tool. Here, we compare autonomic control of blood pressure during centrifugation creating 1-g and 2-g at feet with standing in natural gravity. Continuous blood pressure was acquired simultaneously from 13 healthy participants during supine baseline, standing, supine recovery, centrifugation of 1-g, and 2-g, from which heart rate (RR) and systolic blood pressure (SBP) were derived. The autonomic blood pressure regulation was assessed via spectral analysis of RR and SBP, spontaneous baroreflex sensitivity, and non-linear heart rate and blood pressure causality (RR↔SBP). While majority of these blood pressure regulatory indices were significantly different (p < 0.05) during standing and 2-g centrifugation compared to baseline, no change (p > 0.05) was observed in the same indices during 2-g centrifugation compared to standing. The findings of the study highlight the capability of artificial gravity (2-g at feet) created via SAHC toward evoking blood pressure regulatory controls analogous to standing, therefore, a potential utility toward mitigating deleterious effects of microgravity on cardiovascular performance and minimizing post-flight orthostatic intolerance in astronauts.

Pediatric Disorders of Orthostatic Intolerance

Orthostatic intolerance (OI), having difficulty tolerating an upright posture because of symptoms or signs that abate when returned to supine, is common in pediatrics. For example, ∼40% of people faint during their lives, half of whom faint during adolescence, and the peak age for first faint is 15 years. Because of this, we describe the most common forms of OI in pediatrics and distinguish between chronic and acute OI. These common forms of OI include initial orthostatic hypotension (which is a frequently seen benign condition in youngsters), true orthostatic hypotension (both neurogenic and nonneurogenic), vasovagal syncope, and postural tachycardia syndrome. We also describe the influences of chronic bed rest and rapid weight loss as aggravating factors and causes of OI. Presenting signs and symptoms are discussed as well as patient evaluation and testing modalities. Putative causes of OI, such as gravitational and exercise deconditioning, immune-mediated disease, mast cell activation, and central hypovolemia, are described as well as frequent comorbidities, such as joint hypermobility, anxiety, and gastrointestinal issues. The medical management of OI is considered, which includes both nonpharmacologic and pharmacologic approaches. Finally, we discuss the prognosis and long-term implications of OI and indicate future directions for research and patient management.

Pathogenesis and Individualized Treatment for Postural Tachycardia Syndrome in Children

Objective:

Postural tachycardia syndrome (POTS) is one of the major causes of orthostatic intolerance in children. We systematically reviewed the pathogenesis and the progress of individualized treatment for POTS in children.

Data Sources:

The data analyzed in this review are mainly from articles included in PubMed and EMBASE.

Study Selection:

The original articles and critical reviews about POTS were selected for this review.

Results:

Studies have shown that POTS might be related to several factors including hypovolemia, high catecholamine status, abnormal local vascular tension, and decreased skeletal muscle pump activity. In addition to exercise training, the first-line treatments mainly include oral rehydration salts, beta-adrenoreceptor blockers, and alpha-adrenoreceptor agonists. However, reports about the effectiveness of various treatments are diverse. By analyzing the patient's physiological indexes and biomarkers before the treatment, the efficacy of medication could be well predicted.

Conclusions:

The pathogenesis of POTS is multifactorial, including hypovolemia, abnormal catecholamine state, and vascular dysfunction. Biomarker-directed individualized treatment is an important strategy for the management of POTS children.

Recent advances in the understanding of the mechanisms underlying postural tachycardia syndrome in children: practical implications for treatment

Postural tachycardia syndrome is defined by a heart rate increment of 40 beats/minute (bpm) (or a heart rate that exceeds 125 bpm) within 10 minutes of change from the supine position to an upright position in the absence of obvious orthostatic hypotension. There are multiple pathophysiological mechanisms that underlie postural tachycardia syndrome, including peripheral denervation, β-receptor supersensitivity, hypovolaemia, and impaired muscle pump. Some children afflicted with postural orthostatic tachycardia syndrome and hypovolaemic dysregulation have been found to have perturbed renin-angiotensin-aldosterone profile, disturbed vascular endothelial function, and abnormal vasodilation. The hyperadrenergic state in some postural tachycardia syndrome patients is likely a driver for orthostatic tachycardia. Other mechanisms include the presence of treatable autonomic neuropathies. An understanding of these pathophysiological mechanisms might be helpful for the effective treatment of postural tachycardia syndrome.

Baroreflex Sensitivity Predicts Short-Term Outcome of Postural Tachycardia Syndrome in Children

Objective

The study was designed to examine if baroreflex sensitivity (BRS) could predict the short-term outcome of postural tachycardia syndrome (POTS) in children.

Methods

Seventy-seven children subjects were included in the study. Among them, 45 children were in the POTS group and another 32 healthy children were in the control group. A ninety-day clinical follow-up was conducted and the symptom score before and after the follow-up was calculated for POTS patients by using POTS score system. Hemodynamics and continuous BRS monitoring were recorded by Finapres Medical System-FMS (FinometerPRO, FMS Company, Netherlands). According to the symptom score change during follow-up period, POTS patients were further divided into subgroup A (n = 24) with symptom score decreased by at least two points and subgroup B (n = 21) with symptom score decreased by less than two points. The predictive value of BRS in the short-term outcome of POTS in children was analyzed using receiver-operating characteristic (ROC) curve.

Results

BRS of POTS children was significantly higher than that of the healthy children (18.76±9.96 ms/mmHg vs 10±5.42 ms/mmHg, P<0.01). It was higher in subgroup B than that of subgroup A (24.7±9.9 ms/mmHg vs 13.5±6.6 ms/mmHg, P <0.01). BRS was positively correlated with HR change in POTS Group (r = 0.304, P <0.05). Area under curve (AUC) was 0.855 (95% of confidence interval 0.735–0.975), and BRS of 17.01 ms/mmHg as a cut-off value yielded the predictive sensitivity of 85.7% and specificity of 87.5%.

Conclusions

BRS is a useful index to predict the short-term outcome of POTS in children.

Orthostatic cardiovascular profile of subjective well-being

Previous clinical and elderly population studies have found that affective well-being can be assessed by clino-orthostatic cardiovascular reactivity. This study explored this relationship in a young healthy sample, and with respect to cognitive appraisals of well-being. Four successive readings of blood pressure (BP) and heart rate (HR) after lying down (clinostatic probe) followed by four successive readings after standing up (orthostatic probe) were obtained from 52 healthy students along with questionnaire-reported well-being. Analyses indicated that a deeper drop of systolic BP (SBP) and mean arterial (MAP) pressure during supine was related to higher positive mood, but higher and more stable orthostatic MAP and HR response were related to lower negative mood. A higher diastolic BP while standing upright and lower SBP in general were associated with higher optimism and higher global life satisfaction, respectively. The findings confirm previous results and indicate that cognitive appraisals of well-being are also related to BP regulation.

Cardiac responses to exercise distinguish postural orthostatic tachycardia syndrome variants

We previously showed that one‐third of adolescents with postural orthostatic tachycardia syndrome (POTS) have hyperkinetic circulation. In a subsequent cohort, we compare participants with POTS grouped according to cardiac output (Q˙) versus oxygen uptake (V˙O2) function, whose circulatory response to exercise lay at the lower end of this distribution. We hypothesized that such grouping determines the circulatory response to incremental‐protocol, upright, cycle ergometry by whatever blend of flow and resistance adjustments best maintains normal blood pressure. We reviewed data on 209 POTS participants aged 10–19 years (73% female) grouped as follows: Q˙−V˙O2 < 3.20 L·min⁻¹ per L·min⁻¹ were designated low Q˙ or hypokinetic variant (N = 31); normal‐Q˙ had slopes between 3.21 and 7.97; hyperkinetic participants had Q˙−V˙O2 slope >8 L·min⁻¹ per L·min⁻¹ (N = 32). Heart rate response to exercise was virtually identical in each group. Mean stroke volume (SV) rose normally in the hyperkinetic group (51 ± 38%); less in the normal Q˙ group (22 ± 27%); but was flat in the low Q˙ group (−7 ± 16%). Mean arterial pressure was similar at rest while systemic vascular conductance was flat from rest to exercise in the hypokinetic group, and by comparison rose more steeply in the normal Q˙ (P < 0.001) and in the hyperkinetic (P = 0.02) groups. In conclusion, we identified a variant of POTS with a hypokinetic circulation maintained by a vasoconstricted state. We speculate that they cannot muster preload to augment exercise SV due to profound thoracic hypovolemia, and must resort to vasoconstriction in order to maintain perfusion pressure within working muscle.

Body Mass Index (BMI) is Associated with the Therapeutic Response to Oral Rehydration Solution in Children with Postural Tachycardia Syndrome

We aimed to explore whether the body mass index (BMI) was associated with the therapeutic response to oral rehydration solution (ORS) in children with postural tachycardia syndrome (POTS). Fifty-four children diagnosed as having POTS were included in this study. Fifty-six healthy children served as the controls. Children with POTS were treated with ORS, and their treatment response was evaluated. The baseline BMI was obtained by measuring the height and weight. The Pearson correlation was made between the baseline BMI and change in heart rate from supine to upright (ΔHR) and between baseline BMI and symptom score change (post-treatment vs. pre-treatment) in the POTS group. The value of BMI in predicting the therapeutic response to ORS was assessed by analyses of the receiver operating characteristic (ROC) curve. The BMI in the POTS group was significantly lower than that in the control group (18.22 ± 3.23 vs. 20.62 ± 3.05 kg/m(2), p < 0.01). There were no statistical differences between responders and non-responders in symptom scores before treatment (p > 0.05), but symptom score was lower in responders than that in non-responders (1.52 ± 0.95 vs. 2.32 ± 1.22, p < 0.01) after treatment. The BMI in responders to ORS was significantly lower than that of non-responders (16.32 ± 2.28 vs. 20.43 ± 2.74 kg/m(2), p < 0.01). The BMI was correlated negatively with ΔHR in the POTS group (n = 54, r = -0.766, p < 0.01) and with the decrease in symptom scores after treatment in POTS patients (n = 54, r = -0.28, p < 0.05). ROC curve revealed the area under the curve to be 92.3 % (95 % confidence interval 0.829-0.996). A cutoff value of the BMI of 18.02 kg/m(2) had high sensitivity (92 %) and high specificity (82.8 %) for predicting the effect of ORS treatment for POTS. BMI is associated with the therapeutic response to ORS in children with POTS.

Total peripheral vascular resistance, cardiac output, and plasma C-type natriuretic Peptide level in children with postural tachycardia syndrome

OBJECTIVE

To investigate the total peripheral vascular resistance (TPVR), cardiac output (CO), and plasma C-type natriuretic peptide (CNP) levels in children with postural tachycardia syndrome (POTS) during supine, upright, and return to supine.

STUDY DESIGN

Twenty-nine children with POTS, aged 12 ± 3 years, were recruited, and 32 healthy children, aged 11 ± 2 years, served as controls. Heart rate (HR), blood pressure, TPVR, and CO were continuously monitored with Finapres Medical System, and plasma CNP levels were detected with Sandwich immunoluminescence assay.

RESULTS

In children with POTS, upright TPVR and CO were significantly lower than those in supine position, and they rose again when they returned to supine position. However, in healthy control patients, both TPVR and CO did not change during supine, upright, and supine again positions. Also, in the supine position, there was no significant difference in TPVR and CO between POTS children and control subjects (P > .05). When upright, however, TPVR and CO in children with POTS were significantly lower than those of controls. Plasma CNP levels were significantly greater in children with POTS than that of controls (32.8 ± 9.7 vs 24.2 ± 8.4 [pg/mL], P < .01), and symptom scores and ΔHR positively correlated with plasma CNP levels in children with POTS (symptom scores: r = 0.490, P < .01; ΔHR: r = 0.508, P < .001), but CO negatively correlated with plasma CNP levels (r = -0.446, P < .01).

CONCLUSION

Reduced TPVR and CO associated with the elevated plasma CNP might be involved in the pathogenesis of POTS.

Effects of diaphragmatic contraction on lower limb venous return and central hemodynamic parameters contrasting healthy subjects versus heart failure patients at rest and during exercise

The main objective was to assess the effects of abdominal breathing (AB) versus subject's own breathing on femoral venous blood flow (Q_fv) and their repercussions on central hemodynamics at rest and during exercise contrasting healthy subjects versus heart failure (HF) patients. We measured esophageal and gastric pressure (P_GA), Q_fv and parameters of central hemodynamics in eight healthy subjects and nine HF patients, under four conditions: subject's own breathing and AB (∆P_GA ≥ 6 cmH₂O) at rest and during knee extension exercises (15% of 1 repetition maximum) until exhaustion. Q_fv and parameters of central hemodynamics [stroke volume (SV), cardiac output (CO)] were measured using Doppler ultrasound and impedance cardiography, respectively. At rest, healthy subjects Q_fv, SV, and CO were higher during AB than subject's breathing (0.11 ± 0.02 vs. 0.06 ± 0.00 L·min⁻¹, 58.7 ± 3.4 vs. 50.1 ± 4.1 mL and 4.4 ± 0.2 vs. 3.8 ± 0.1 L·min⁻¹, respectively, P ≤ 0.05). ∆SV correlated with ∆P_GA during AB (r = 0.89, P ≤ 0.05). This same pattern of findings induced by AB was observed during exercise (SV: 71.1 ± 4.1 vs. 65.5 ± 4.1 mL and CO: 6.3 ± 0.4 vs. 5.2 ± 0.4 L·min⁻¹; P ≤ 0.05); however, Q_fv did not reach statistical significance. The HF group tended to increase their Q_fv during AB (0.09 ± 0.01 vs. 0.07 ± 0.03 L·min⁻¹, P = 0.09). On the other hand, unlike the healthy subjects, AB did not improve SV or CO neither at rest nor during exercise (P > 0.05). In healthy subjects, abdominal pump modulated venous return improved SV and CO at rest and during exercise. In HF patients, with elevated right atrial and vena caval system pressures, these findings were not observed.

Circulatory function of the diaphragm produces an increase in circulatory output. Moreover, the peripheral muscle contraction produces greater venous blood return due to increased blood expulsion. In this study, we focused on the effects of diaphragm contraction at rest and during knee extension exercise on venous return and central hemodynamics in healthy subjects and heart failure patients. These results help us understand the mechanisms of abdominal pump modulation on venous return in healthy subjects and under conditions of elevated pressure of the right atrium and the vena cava.

The Association of Calf Circumference with Resting Pulse Rate in Community-dwelling Healthy Elderly Women -Pilot Study-

[Purpose] High resting blood pressure and heart rate are associated with the risk of cardiovascular events. In patients with decreasing amounts of slow twitch muscle fiber, hypertension may develop and resting heart rate may increase. Measurement of the amount of slow twitch muscle fiber and capillary density using muscle biopsy is inconvenient and expensive. Therefore, a better screening test is required to determine these parameters for prevention of cardiovascular events. In this study, relationships among calf circumference, resting blood pressure, and pulse rate in the soleus muscle were investigated. [Subjects] Healthy elderly women (n= 19, 61–84 years of age) living in the community were the subjects of this study. [Methods] Blood pressure was measured using an automatic hemodynamometer on the left arm. The calf circumference was measured, and pulse rate was measured on the left radial artery for 1 min by palpation. [Results] No correlations were observed between calf circumference, resting systolic or diastolic pressure, pulse pressure, or mean blood pressure. However, an inverse correlation was observed between calf circumference and resting pulse rate. [Conclusion] Calf circumference measurement may be used as a screening test for resting pulse rate. This test may be useful for the prevention of cardiovascular events.

Ventilation and respiratory mechanics

During dynamic exercise, the healthy pulmonary system faces several major challenges, including decreases in mixed venous oxygen content and increases in mixed venous carbon dioxide. As such, the ventilatory demand is increased, while the rising cardiac output means that blood will have considerably less time in the pulmonary capillaries to accomplish gas exchange. Blood gas homeostasis must be accomplished by precise regulation of alveolar ventilation via medullary neural networks and sensory reflex mechanisms. It is equally important that cardiovascular and pulmonary system responses to exercise be precisely matched to the increase in metabolic requirements, and that the substantial gas transport needs of both respiratory and locomotor muscles be considered. Our article addresses each of these topics with emphasis on the healthy, young adult exercising in normoxia. We review recent evidence concerning how exercise hyperpnea influences sympathetic vasoconstrictor outflow and the effect this might have on the ability to perform muscular work. We also review sex-based differences in lung mechanics.

Influence of wearing an unstable shoe on thigh and leg muscle activity and venous response in upright standing

PURPOSE

To quantify the effect of unstable shoe wearing on muscle activity and haemodynamic response during standing.

METHODS

Thirty volunteers were divided into 2 groups: the experimental group wore an unstable shoe for 8 weeks, while the control group used a conventional shoe for the same period. Muscle activity of the medial gastrocnemius, tibialis anterior, rectus femoris and biceps femoris and venous circulation were assessed in quiet standing with the unstable shoe and barefoot.

RESULTS

In the first measurement there was an increase in medial gastrocnemius activity in all volunteers while wearing the unstable shoe. On the other hand, after wearing the unstable shoe for eight weeks these differences were not verified. Venous return increased in subjects wearing the unstable shoe before and after training.

CONCLUSIONS

The unstable shoe produced changes in electromyographic characteristics which were advantageous for venous circulation even after training accommodation by the neuromuscular system.

Effects of lower-leg rhythmic cuff inflation on cardiovascular autonomic responses during quiet standing in healthy subjects

To determine the effects of muscle pump function on cardiac autonomic activity in response to quiet standing, we simulated the muscle pump effect by rhythmic lower-leg cuff inflation (RCI) with four cuff pressures of 0 (sham), 40, 80, and 120 mmHg at 5 cycles/min. The R-R interval (RRI) and beat-to-beat blood pressure (BP) were acquired in healthy subjects (6 males and 5 females, aged 21-24 yr). From the continuous BP measurement, stroke volume (SV) was calculated by a pulse-contour method. Using spectral and cross-spectral analysis, RRI and systolic BP variability as well as the gain of spontaneous cardiac baroreflex sensitivity (sBRS) were estimated for the low- and high-frequency (HF) bands. Compared with the sham condition, RCI with cuff pressures of 80 and 120 mmHg led to increases in the mean RRI (P < 0.01) and HF power of RRI fluctuation (P < 0.05 for 80 mmHg and P < 0.01 for 120 mmHg) during quiet standing. Reduction in SV during standing was suppressed, and the sBRS of the HF band for standing were increased by RCI for either cuff pressure (P < 0.05 for 80 mmHg and P < 0.01 for 120 mmHg). However, at 40 mmHg RCI, these remained unchanged. These results suggest that, during standing, RCI of the lower leg increases cardiac vagal outflow when the cuff pressure is raised enough to oppose the hydrostatic-induced venous pressure in the calf.

Flow-mediated vasodilation and endothelium function in children with postural orthostatic tachycardia syndrome

The study was designed to explore flow-mediated vasodilation (FMD) and endothelium function in children with postural orthostatic tachycardia syndrome (POTS). The patient group consisted of 46 children 12 +/- 3 years of age who were diagnosed with POTS from June 2008 to January 2009 by head-up test or head-up tilt test at Peking University First Hospital. Twenty healthy children 12 +/- 4 years of age were selected for the control group. Plasma concentrations of nitric oxide (NO) and activity of NO synthase (NOS) were determined in the patient and control groups. FMD of each participant's brachial artery was measured using color Doppler vascular ultrasound and a comparison of FMDs and plasma NO and NOS activities between the 2 groups was done using independent t test. No significant differences were found between the POTS and control groups in age, sex ratio, height, body weight, baseline blood pressure, heart rate, and baseline brachial artery diameter. Patients in the POTS group had larger FMD (10.8 +/- 4.4%) than children in the control group (5.7 +/- 2.2%), and this difference was significant (p <0.01). Plasma NO and NOS levels were significantly higher in the POTS group than in the control group (NO 74 +/- 19 micromol/L in POTS group vs 62 +/- 6 micromol/L in control group, p <0.01; NOS 21 +/- 3 U/mL in POTS group vs 15 +/- 1 U/mL in control group, p <0.01). In addition, there was a significant correlation between FMD and the NOS activity. In conclusion, augmented FMD and abnormal function of vascular endothelium may play an important role in POTS in children.

Cardiac origins of the postural orthostatic tachycardia syndrome

OBJECTIVES

The purpose of this study was to test the hypothesis that a small heart coupled with reduced blood volume contributes to the postural orthostatic tachycardia syndrome (POTS) and that exercise training improves this syndrome.

BACKGROUND

Patients with POTS have marked increases in heart rate during orthostasis. However, the underlying mechanisms are unknown and the effective therapy is uncertain.

METHODS

Twenty-seven POTS patients underwent autonomic function tests, cardiac magnetic resonance imaging, and blood volume measurements. Twenty-five of them participated in a 3-month specially designed exercise training program with 19 completing the program; these patients were re-evaluated after training. Results were compared with those of 16 healthy controls.

RESULTS

Upright heart rate and total peripheral resistance were greater, whereas stroke volume and cardiac output were smaller in patients than in controls. Baroreflex function was similar between groups. Left ventricular mass (median [25th, 75th percentiles], 1.26 g/kg [1.12, 1.37 g/kg] vs. 1.45 g/kg [1.34, 1.57 g/kg]; p < 0.01) and blood volume (60 ml/kg [54, 64 ml/kg] vs. 71 ml/kg [65, 78 ml/kg]; p < 0.01) were smaller in patients than in controls. Exercise training increased left ventricular mass and blood volume by approximately 12% and approximately 7% and decreased upright heart rate by 9 beats/min [1, 17 beats/min]. Ten of 19 patients no longer met POTS criteria after training, whereas patient quality of life assessed by the 36-item Short-Form Health Survey was improved in all patients after training.

CONCLUSIONS

Autonomic function was intact in POTS patients. The marked tachycardia during orthostasis was attributable to a small heart coupled with reduced blood volume. Exercise training improved or even cured this syndrome in most patients. It seems reasonable to offer POTS a new name based on its underlying pathophysiology, the "Grinch syndrome," because in this famous children's book by Dr. Seuss, the main character had a heart that was "two sizes too small."

Peripheral vascular adaptation and orthostatic tolerance in Fontan physiology

BACKGROUND

The Fontan circulation is critically dependent on elevated venous pressures to sustain effective venous return. We hypothesized that chronically increased systemic venous pressures lead to adaptive changes in regional and peripheral vessels to maintain cardiac output, especially when patients are upright.

METHODS AND RESULTS

Nine post-Fontan procedure patients (aged 13 to 24 years) and 6 age- and sex-matched controls were compared with techniques to measure circulatory responses (peripheral and compartmental blood flow, venous capacity, and microvascular filtration). Parameters studied included strain-gauge plethysmography measures of peripheral circulatory function, regional blood volume distribution by impedance plethysmography, and head-up tilt testing. Important differences between Fontan patients and controls were seen in several vascular compartments: (1) Calf capacitance was lower (median, 3.5 versus 5.5 mL/100 mL tissue; P=0.005), and resting venous pressure was higher (13.0 versus 10.5 mm Hg; P=0.004); (2) higher leg arterial resistance was observed (32.1 versus 22.2; P=0.03); (3) microvascular filtration pressures and threshold for edema were elevated; and (4) with head-up tilt testing, splanchnic flow was not reduced in Fontan patients versus controls (fractional change, +4% versus -32%; P=0.004), and splanchnic arterial resistance did not increase as expected (fractional change, +8% versus +79%; P=0.003).

CONCLUSIONS

Reduced venous compliance and increased filtration thresholds may act as adaptive mechanisms in maintaining venous return in Fontan circulation. Well-compensated Fontan subjects demonstrate superior orthostatic tolerance resulting from decreased compartmental fluid shifts in response to head-up tilt and higher vascular resistance. This results from increased venous stiffness and decreased splanchnic capacitance and may also be an adaptive mechanism to maintain venous return in these patients while standing.

Japanese clinical guidelines for juvenile orthostatic dysregulation version 1

This clinical practice guideline provides recommendations for the assessment, diagnosis and treatment of school-aged children and juveniles with orthostatic dysregulation (OD), usually named orthostatic intolerance in USA and Europe. This guideline is intended for use by primary care clinicians working in primary care settings. The guideline contains the following recommendations for diagnosis of OD: (i) initial evaluation composed of including and excluding criteria, the assessment of no evidence of other disease including cardiac disease and so on; (ii) a new orthostatic test to determine four different subsets: instantaneous orthostatic hypotension, postural tachycardia syndrome, neurally mediated syncope and delayed orthostatic hypotension; (iii) evaluation of severity; and (iv) judgment of psychosocial background with the use of rating scales. The guideline also contains the following recommendations for treatment of OD on the basis of the result of an orthostatic test in addition to psychosocial assessment: (i) guidance and education for parents and children; (ii) non-pharmacological treatments; (iii) contact with school personnel; (iv) use of adrenoceptor stimulants and other medications; (v) strategies of psychosocial intervention; and (vi) psychotherapy. This clinical practice guideline is not intended as a sole source of guidance in the evaluation of children with OD. Rather, it is designed to assist primary care clinicians by providing a framework for decision making of diagnosis and treatments.

The postural tachycardia syndrome

Postural tachycardia syndrome (POTS) is a disorder of unknown etiology, and patients with this condition exhibit orthostatic intolerance (OI) and excessive tachycardia. Excessive tachycardia with POTS has been defined as a rapid (within 10 minutes) increase in heart rate by more than 30 beats per minute or a heart rate that exceeds 120 beats per minute. Patients with POTS can experience difficulty with daily routines such as housework, shopping, eating, and attending work or school. The possibility exists that all forms of OI, including POTS, result from central hypovolemia even without tachycardia. The clinical findings of POTS are observed in an increasing number of patients who are usually female and aged 15 to 50 years. Adults with POTS do not have hypotension, whereas children may exhibit hypotension. Many patients with POTS are intolerant of exercise. "Idiopathic" POTS must be distinguished from other conditions that can reduce venous return to the heart and produce similar signs and symptoms such as dehydration, anemia, or hyperthyroidism. Therapies for POTS are directed at relieving the central hypovolemia or at compensating for the circulatory dysfunctions that may cause this disorder. Treatments have resulted in varying degrees of success and are often used in combination with each other.

Left ventricular function during arm exercise: influence of leg cycling and lower body positive pressure

The purpose of this study was to characterize left ventricular (LV) diastolic filling and systolic performance during graded arm exercise and to examine the effects of lower body positive pressure (LBPP) or concomitant leg exercise as means to enhance LV preload in aerobically trained individuals. Subjects were eight men with a mean age (+/-SE) of 26.8 +/- 1.2 yr. Peak exercise testing was first performed for both legs [maximal oxygen uptake (Vo(2)) = 4.21 +/- 0.19 l/min] and arms (2.56 +/- 0.16 l/min). On a separate occasion, LV filling and ejection parameters were acquired using non-imaging scintography using in vivo red blood cell labeling with technetium 99(m) first during leg exercise performed in succession for 2 min at increasing grades to peak effort. Graded arm exercise (at 30, 60, 80, and 100% peak Vo(2)) was performed during three randomly assigned conditions: control (no intervention), with concurrent leg cycling (at a constant 15% leg maximal Vo(2)) or with 60 mmHg of LBPP using an Anti G suit. Peak leg exercise LV ejection fraction was higher than arm exercise (60.9 +/- 1.7% vs. 55.9 +/- 2.7%; P < 0.05) as was peak LV end-diastolic volume was reported as % of resting value (110.3 +/- 4.4% vs. 97 +/- 3.7%; P < 0.05) and peak filling rate (end-diastolic volume/s; 6.4 +/- 0.28% vs. 5.2 +/- 0.25%). Concomitant use of either low-intensity leg exercise or LBPP during arm exercise failed to significantly increase LV filling or ejection parameters. These observations suggest that perturbations in preload fail to overcome the inherent hemodynamic conditions present during arm exercise that attenuate LV performance.