The relation between lower limb pooling and blood flow during orthostasis in the postural orthostatic tachycardia syndrome of adolescents

Pediatric Postural Orthostatic Tachycardia Syndrome: Where We Stand

Postural orthostatic tachycardia syndrome (POTS), first described in 1992, remains an enigmatic, yet severely and variably debilitating, disorder. The pathophysiology of this syndrome is still not understood, and there remains no biomarker indicating the presence of POTS. Although research interest has increased in recent years, there are relatively fewer clinical and research studies addressing POTS in children and adolescents compared with adults. Yet, adolescence is when a large number of cases of POTS begin, even among adult patients who are subsequently studied. This article summarizes reported research in POTS, specifically in pediatric patients, including discussion of aspects of diagnostic criteria, risk factors and outcomes, neurohormonal and hemodynamic abnormalities, clinical assessment, and treatment. The goals of this review are increased recognition and acknowledgment of POTS among pediatric and adolescent providers, as well as to provide an understanding of reported abnormalities of homeostasis, such that symptomatic patients will be able to be recognized and appropriately managed, enabling them to return to their activities of daily living.

Leg pain in neuropathic postural tachycardia syndrome is associated with altered muscle membrane properties

Purpose

In neuropathic postural tachycardia syndrome, peripheral sympathetic dysfunction leads to excessive venous blood pooling during orthostasis. Up to 84% of patients report leg pain and weakness in the upright position. To explore possible pathophysiological processes underlying these symptoms, the present study examined muscle excitability depending on body position in patients with neuropathic postural tachycardia syndrome and healthy subjects.

Methods

In ten patients with neuropathic postural tachycardia syndrome and ten healthy subjects, muscle excitability measurements were performed repeatedly: in the supine position, during 10 min of head-up tilt and during 6 min thereafter. Additionally, lower leg circumference was measured and subjective leg pain levels were assessed.

Results

In patients with neuropathic postural tachycardia syndrome, muscle excitability was increased in the supine position, decreased progressively during tilt, continued to decrease after being returned to the supine position, and did not completely recover to baseline values after 6 min of supine rest. The reduction in muscle excitability during tilt was paralleled by an increase in lower leg circumference as well as leg pain levels. No such changes were observed in healthy subjects.

Conclusions

This study provides evidence for the occurrence of orthostatic changes in muscle excitability in patients with neuropathic postural tachycardia syndrome and that these may be associated with inadequate perfusion of the lower extremities. Insufficient perfusion as a consequence of blood stasis may cause misery perfusion of the muscles, which could explain the occurrence of orthostatic leg pain in neuropathic postural tachycardia syndrome.

Using the PEOP Model to Understand Barriers to Functioning in Postural Orthostatic Tachycardia Syndrome

Individuals with postural orthostatic tachycardia syndrome (POTS) experience many barriers that lead to decreased functioning and quality of life. At this time, there are limited resources regarding the functional impact of POTS on occupational performance. Therefore, this narrative review demonstrates how occupational therapy practitioners can conceptualize, categorize, and systematically organize their thinking around barriers individuals with POTS experience using the Person-Environment-Occupation-Performance (PEOP) model of practice.

Screening for Orthostatic Intolerance in Symptomatic Children Presenting for Concussion Care

Following concussion, children often experience nonspecific symptoms that overlap with those of other common pediatric conditions, including orthostatic intolerance (OI). The primary goal of this study was to evaluate OI in youth presenting for clinical care for concussion and reporting symptoms frequently observed in OI. Eighty-two of 114 patients aged 10 to 22 years endorsed symptoms based on 8 screening questions, and 24 of those 82 patients met criteria for OI based on an active standing test. No screening question generated clinically useful likelihood ratios for predicting OI. The prevalence of OI in this cohort is considerably higher than estimates in the general pediatric population, suggesting a link between concussion and OI. Future work is needed to evaluate the best method of testing for OI, the natural history of OI symptoms in youth with concussion, and the response to intervention in children with both concussion and OI.

Haemodynamic and cerebrovascular effects of intermittent lower-leg compression as countermeasure to orthostatic stress

NEW FINDINGS

What is the central question of this study? Does smartly timed intermittent compression of the lower legs alter cerebral blood velocity and oxygenation during acute orthostatic challenges? What is the main finding and its importance? Intermittent compression timed to the local diastolic phase increased the blood flux through the legs and heart after two different orthostatic stress tests. Cerebral blood velocity improved during the first minute of recovery, and indices of cerebral tissue oxygenation remained elevated for 2 min. These results provide promise for the use of lower-leg active compression as a therapeutic tool for individuals vulnerable to initial orthostatic hypotension and orthostatic stress.

ABSTRACT

Intermittent compression of the lower legs provides the possibility of improving orthostatic tolerance by actively promoting venous return and improving central haemodynamics. We tested the hypothesis that intermittent compression of 65 mmHg timed to occur only within the local diastolic phase of each cardiac cycle would attenuate the decrease in blood pressure and improve cerebral haemodynamics during the first minute of recovery from two different orthostatic stress tests. Fourteen subjects (seven female) performed four squat-to-stand transitions and four repeats of standing bilateral thigh-cuff occlusion and release (TCR), with intermittent compression of the lower legs applied in half of the trials. Blood flow in the superficial femoral artery, mean arterial pressure, Doppler ultrasound cardiac output, total peripheral resistance, middle cerebral artery blood velocity (MCAv) and cerebral tissue saturation index (TSI%) were monitored. With both orthostatic stress tests, there was a significant compression × time interaction for superficial femoral artery flow (P < 0.001). The hypotensive state was attenuated with intermittent compression despite decreased total peripheral resistance (squat-to-stand, compression × time interaction, P < 0.001; TCR, compression × time interaction, P = 0.002) as a consequence of elevated cardiac output in both tests (P < 0.001). Intermittent compression also increased MCAv (P = 0.001) and TSI% (P < 0.001) during the squat-to-stand transition and during TCR (MCAv and TSI%, compression × time interaction, P < 0.001). Intermittent compression of the lower legs during quiet standing after an active orthostatic challenge augmented local, central and cerebral haemodynamics, providing potential as a therapeutic tool for individuals vulnerable to orthostatic stress.

Clinical neurophysiology of postural tachycardia syndrome

Postural tachycardia syndrome (POTS) is one of several disorders of orthostatic intolerance (OI). It is defined by the development of symptoms of cerebral hypoperfusion or sympathetic activation and a sustained heart rate increment of 30 beats/min or more (40 beats/min for teenagers) within 10min of standing or head-up tilt in the absence of orthostatic hypotension; the standing heart rate is often 120 beats/min or higher. POTS is approximately five times more common in women than men. This heterogeneous syndrome is caused by several pathophysiologic mechanisms (limited autonomic neuropathy, hyperadrenergic state, hypovolemia, venous pooling, deconditioning), which are not mutually exclusive. Anxiety and somatic hypervigilance play significant roles in POTS. Common comorbidities include visceral pain and dysmotility, chronic fatigue and fibromyalgia, migraine, joint hypermobility, mitral valve prolapse, and inappropriate sinus tachycardia. Patients with suspected POTS should undergo comprehensive cardiac and neurologic examinations and autonomic and laboratory tests to determine the most likely pathophysiologic basis of OI. The objectives of POTS management are to (1) increase the time that patients can stand, perform daily activities, and exercise and (2) avoid syncope. Management involves nonpharmacologic (fluid and salt loading, physical countermaneuvers, compression garments, exercise training) and pharmacologic (β-blockers, pyridostigmine, fludrocortisone, midodrine) approaches.

Exercise and non-pharmacological treatment of POTS

Recent research has demonstrated that cardiovascular deconditioning (i.e., cardiac atrophy and hypovolemia) contributes significantly to the Postural Orthostatic Tachycardia Syndrome (POTS) and its functional disability. Therefore, physical reconditioning with exercise training and volume expansion via increased salt and fluid intake should be initiated early in the course of treatment for patients with POTS if possible. The use of horizontal exercise (e.g., rowing, swimming, recumbent bike, etc.) at the beginning is a critical strategy, allowing patients to exercise while avoiding the upright posture that elicits their POTS symptoms. As patients become increasingly fit, the duration and intensity of exercise should be progressively increased, and upright exercise can be gradually added as tolerated. Supervised training is preferable to maximize functional capacity. Other non-pharmacological interventions, which include: 1) chronic volume expansion via sleeping in the head-up position; 2) reduction in venous pooling during orthostasis by lower body compression garments extending at least to the xiphoid or with an abdominal binder; and 3) physical countermeasure maneuvers, such as squeezing a rubber ball, leg crossing, muscle pumping, squatting, negative-pressure breathing, etc., may also be effective in preventing orthostatic intolerance and managing acute clinical symptoms in POTS patients. However, randomized clinical trials are needed to evaluate the efficacies of these non-pharmacological treatments of POTS.

Postural tachycardia syndrome: current perspectives

Postural tachycardia syndrome (POTS) is the combination of an exaggerated heart rate response to standing, in association with symptoms of lightheadedness or pre-syncope that improve when recumbent. The condition is often associated with fatigue and brain fog, resulting in significant disruptions at a critical time of diagnosis in adolescence and young adulthood. The heterogeneity of the underlying pathophysiology and the variable response to therapeutic interventions make management of this condition challenging for both patients and physicians alike. Here, we aim to review the factors and mechanisms that may contribute to the symptoms and signs of POTS and to present our perspectives on the clinical approach toward the diagnosis and management of this complex syndrome.

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.

"Doesn't Anyone Believe How I Feel?": Postural Orthostatic Tachycardia Syndrome (POTS)

The school nurse is often the first person with whom a student may discuss untoward health symptoms and concerns. Being cognizant of the clinical features of postural orthostatic tachycardia syndrome (POTS) will help the nurse alleviate some of the student's anxiety. Due to misunderstandings and misconceptions about POTS, family and peers may disbelieve a student who is experiencing symptoms. Displaying compassion and support will help the student understand that someone does believe his or her symptoms. As the student's advocate, the school nurse will champion a plan for the student's health and safety in the academic environment.

Comorbidity of postural orthostatic tachycardia syndrome and chronic fatigue syndrome in an Australian cohort

OBJECTIVE

Patients with chronic fatigue syndrome (CFS) are frequently diagnosed with comorbid postural orthostatic tachycardia syndrome (POTS), suggesting a shared pathogenesis. The aim of this study was to examine the relationship between demographic characteristics, autonomic functioning and fatigue levels amongst CFS patients with and without comorbid POTS.

DESIGN AND SETTING

All patients presenting to the CFS Discovery Clinic between 2009 and 2012 completed a 20-min standing task as part of their initial assessment. Heart rate and pulse pressure were recorded at baseline, at 2-min intervals poststanding, at the end of the task and following a recovery period. Average heart rate and pulse pressure variability were calculated from this data. Age, gender, length of illness and self-reported fatigue scores were also recorded. POTS patients were diagnosed by an orthostatic increase in heart rate >30 beats per min, concomitant symptoms of orthostatic intolerance and no orthostatic hypotension. Differences in autonomic functioning between POTS and CFS patients were compared using independent samples t-tests, whilst logistic and linear regressions were performed to examine the contribution of autonomic functioning to task completion and perceived fatigue, respectively.

RESULTS

Comorbidity of CFS and POTS (CFS-POTS) was observed in 11% (33/306) of patients. CFS-POTS patients were significantly younger (P < 0.001), had a shorter length of illness (P = 0.034), experienced greater task difficulty (P = 0.002) and were able to stand for significantly shorter periods compared to the CFS-only patients (P < 0.001). CFS-POTS patients experienced significantly lower baseline diastolic blood pressure (P = 0.002), significantly higher heart rate and lower pulse pressures at each standing measurement. Early heart rate changes (P = 0.002) and overall heart rate change (P < 0.001) were significant predictors of completion status, whereas heart rate variability (P < 0.001) and female gender (P < 0.001) were significant predictors of increased perceived task difficulty.

CONCLUSIONS

Haemodynamic and demographic differences between CFS-POTS and CFS-only patients suggest that the former group reflects a distinct subgroup of the CFS population. The findings highlight the utility of screening younger patients with fatigue for POTS, and identified heart rate variability as an important marker of fatigue for CFS patients in general.

A review of orthostatic blood pressure regulation and its association with mood and cognition

AIMS

This paper will review literature that examines the psychological and neuropsychological correlates of orthostatic blood pressure regulation.

RESULTS

The pattern of change in systolic blood pressure in response to the shift from supine to upright posture reflects the adequacy of orthostatic regulation. Orthostatic integrity involves the skeletal muscle pump, neurovascular compensation, neurohumoral effects and cerebral flow regulation. Various physiological states and disease conditions may disrupt these mechanisms. Clinical and subclinical orthostatic hypotension has been associated with impaired cognitive function, decreased effort, reduced motivation and increased hopelessness as well as dementia, diabetes mellitus, and Parkinson's disease. Furthermore, inadequate blood pressure regulation in response to orthostasis has been linked to increased depression and anxiety as well as to intergenerational behavioral sequalae.

CONCLUSIONS

Identifying possible causes and consequences of subclinical and clinical OH are critical in improving quality of life for both children and older adults.

Acrocyanosis: the Flying Dutchman

Acrocyanosis is symmetric, painless, discoloration of different shades of blue in the distal parts of the body that is marked by symmetry, relative persistence of the skin color changes with aggravation by cold exposure, and frequent association with local hyperhidrosis of hands and feet. Described over a century ago and despite seeming familiarity, it remains a poorly understood condition that shares much in clinical presentation with other conditions characterized by skin color changes in the distal parts of the body. The diagnosis remains mostly clinical, and pathological mechanisms vary suggesting that acrocyanosis may not be a single entity. We performed an extensive literature review to summarize existing knowledge about the demographics, pathology, diagnosis, and treatment of this condition.

Orthostatic heart rate and blood pressure in adolescents: reference ranges

This descriptive population study of 307 public high school students, ages 15 to 17 years, was performed to establish reference ranges for orthostatic changes in heart rate and blood pressure in adolescents, and to identify influential variables. Noninvasive measurements of blood pressure and heart rate were obtained. Reference ranges for orthostatic heart rate change in this population at 2 minutes were -2 to +41 beats per minute and at 5 minutes were -1 to +48 beats per minute. Orthostatic blood pressure changes were within the adult range for 98% of adolescents tested. One-third of participants experienced orthostatic symptoms during testing. In conclusion, this study shows that orthostatic symptoms and large orthostatic heart rate changes occur in adolescents. This suggests that the current orthostatic heart rate criterion aiding the diagnosis of adult orthostatic intolerance syndromes is likely not appropriate for adolescents and should be reevaluated.

Delayed vasoconstrictor response to venous pooling in the calf is associated with high orthostatic tolerance to LBNP

Central blood volume loss to venous pooling in the lower extremities and vasoconstrictor response are commonly viewed as key factors to distinguish between individuals with high and low tolerance to orthostatic stress. In this study, we analyzed calf vasoconstriction as a function of venous pooling during simulated orthostatic stress. We hypothesized that high orthostatic tolerance (OT) would be associated with greater vasoconstrictor responses to venous pooling compared with low OT. Nineteen participants underwent continuous stepped lower body negative pressure at -10, -20, -30, -40, -50, and -60 mmHg each for 5 min or until exhibiting signs of presyncope. Ten participants completed the lower body negative pressure procedure without presyncope and were categorized with high OT; the remaining nine were categorized as having low OT. Near-infrared spectroscopy measurements of vasoconstriction (Hachiya T, Blaber A, Saito M. Acta Physiologica 193: 117-127, 2008) in calf muscles, along with heart rate (HR) responses for each participant, were evaluated in relation to calf blood volume, estimated by plethysmography. The slopes of this relationship between vasoconstriction and blood volume were not different between the high- and low-tolerance groups. However, the onset of vasoconstriction in the high-tolerance group was delayed. Greater HR increments in the low-tolerance group were also observed as a function of lower limb blood pooling. The delayed vasoconstriction and slower HR increments in the high-tolerance group to similar venous pooling in the low group may suggest a greater vascular reserve and possible delayed reduction in venous return.

Deciphering the sinus tachycardias

Sinus tachycardia is the most common rhythm disturbance encountered in clinical practice. Primary sinus tachycardia without an underlying secondary cause, despite often being associated with troublesome symptoms, is often neglected leading to multiple consultations and frustration on part of both the practitioner and the patient. The fact that primary sinus tachycardias are a heterogeneous group of disorders is seldom appreciated; hence, a firm diagnosis is rarely reached and management is haphazard. Furthermore, there may be prognostic implications for prolonged or recurrent sinus tachycardia, making it imperative that this group of arrhythmias receive adequate and appropriate attention. Normal sinus tachycardia (i.e., secondary), inappropriate sinus tachycardia, postural orthostatic tachycardia syndrome (POTS) and sinus node reentry tachycardia make up this group of arrhythmias. Their definitions, clinical features, diagnostic criteria, pathophysiologic mechanisms, and optimum management are discussed in this review.

Regional blood volume and peripheral blood flow in postural tachycardia syndrome

Variants of postural tachycardia syndrome (POTS) are associated with increased ["high-flow" POTS (HFP)], decreased ["low-flow" POTS (LFP)], and normal ["normal-flow" POTS (NFP)] blood flow measured in the lower extremities while subjects were in the supine position. We propose that postural tachycardia is related to thoracic hypovolemia during orthostasis but that the patterns of peripheral blood flow relate to different mechanisms for thoracic hypovolemia. We studied 37 POTS patients aged 14-21 yr: 14 LFP, 15 NFP, and 8 HFP patients and 12 healthy control subjects. Peripheral blood flow was measured in the supine position by venous occlusion strain-gauge plethysmography of the forearm and calf to subgroup patients. Using indocyanine green techniques, we showed decreased cardiac index (CI) and increased total peripheral resistance (TPR) in LFP, increased CI and decreased TPR in HFP, and unchanged CI and TPR in NFP while subjects were supine compared with control subjects. Blood volume tended to be decreased in LFP compared with control subjects. We used impedance plethysmography to assess regional blood volume redistribution during upright tilt. Thoracic blood volume decreased, whereas splanchnic, pelvic, and leg blood volumes increased, for all subjects during orthostasis but were markedly lower than control for all POTS groups. Splanchnic volume was increased in NFP and LFP. Pelvic blood volume was increased in HFP only. Calf volume was increased above control in HFP and LFP. The results support the hypothesis of (at least) three pathophysiologic variants of POTS distinguished by peripheral blood flow related to characteristic changes in regional circulations. The data demonstrate enhanced thoracic hypovolemia during upright tilt and confirm that POTS is related to inadequate cardiac venous return during orthostasis.

Microvascular filtration is increased in postural tachycardia syndrome

BACKGROUND

Postural tachycardia syndrome (POTS) is related to defective peripheral vasoconstriction of dependent extremities with redistributive hypovolemia.

METHODS AND RESULTS

To test whether enhanced microvascular filtration produces leg enlargement, we studied 12 patients 13 to 19 years of age with POTS and defective leg vasoconstriction and 13 age-matched healthy control subjects, with strain-gauge plethysmography used to measure venous pressure (Pv), forearm and calf blood flow, vascular capacitance, and the microvascular filtration coefficient (Kf). Measurements were made while the patient was supine and at steady state during upright tilt to 35 degrees. Supine Pv was not different in POTS, but upright leg Pv tended to be increased above control. Arm and leg peripheral arterial resistance was decreased in the supine and upright positions in patients with POTS compared with control subjects (P=0.01, upright legs). Supine Kf was not significantly increased in the forearm in patients with POTS but was increased in the calf (9.3+/-2.2 versus 5.7+/-2.4 [10(-3)] mL/100 mL per minute per mm Hg, P=0.04), correlating with calf blood flow (rs=0.84, P=0.002). Kf was invariant with orthostasis. The hydraulic contribution to upright filtered flow at 35 degrees tilt, the product of Kf and Pv, was approximately twice that of control (0.41+/-0.09 versus 0.19+/-0.04 mL/100 mL per minute, P=0.04).

CONCLUSIONS

Increased microvascular filtration accounts for enhanced leg swelling in patients with POTS with increased arterial blood flow.

Sinus tachyarrhythmias and the specific bradycardic agents: a marriage made in heaven?

A relatively novel group of drugs that inhibit the funny current in the sinus node pacemaker cells, the so-called specific bradycardic agents, are likely to play a significant role in the management of a wide range of cardiovascular disorders, including the sinus tachyarrhythmias. This comprehensive review initially provides an insight into these agents, their historical background, and their mechanism of action. It then discusses the differential diagnosis of the sinus tachyarrhythmias (normal sinus tachycardia, inappropriate sinus tachycardia, postural orthostatic tachycardia syndrome, and sinus node reentry tachycardia), elaborates on their pathophysiologic basis, and provides up-to-date evidence-based information on their optimum management. The specific bradycardic agents, by the very nature of their mode of action, may prove ideal therapies for the management of the sinus tachyarrhythmias, and this is explored at every stage.

Limb venous compliance in patients with idiopathic orthostatic intolerance and postural tachycardia

Venous denervation and increased venous pooling may contribute to symptoms of orthostatic intolerance. We examined venous compliance in the calf and forearm in 11 orthostatic-intolerant patients and 15 age-matched controls over a range of pressures, during basal conditions and sympathetic excitation. Occlusion cuffs placed around the upper arm and thigh were inflated to 60 mmHg and deflated to 10 mmHg over 1 min. Limb volume was measured continuously with a mercury-in-Silastic strain gauge. Compliance was calculated as the numerical derivative of the pressure-volume curve. The pressure-volume relationship in the upper and lower extremities in the basal and sympathetically activated state was significantly lower in the orthostatic-intolerant patients (all P < 0.05). Sympathoexcitation lowered the pressure-volume relationship in the lower extremity in patients (P < 0.001) and controls (P < 0.01). Venous compliance was significantly less in patients in the lower extremity in the basal state over a range of pressures (P < 0.05). Venous compliance was less in patients compared with controls in the upper (P < 0.005) and lower extremities (P < 0.01) in the sympathetically activated state, but there were no differences at individual pressure levels. Sympathetic activation did not change venous compliance in the upper and lower extremity in patients and controls. Patients with orthostatic intolerance have reduced venous compliance in the lower extremity. Reduced compliance may limit the dynamic response to orthostatic change and thereby contribute to symptoms of orthostatic intolerance in this population group.

Transient orthostatic hypotension is common in adolescents

OBJECTIVES

We hypothesized that transient hypotension associated with the symptom of lightheadedness with standing is a common phenomenon in healthy adolescents but may be mistaken for orthostatic intolerance.

STUDY DESIGN

We studied 23 healthy adolescents, combining upright tilt to 70 degrees and to 35 degrees (in 12 patients) with continuous heart rate and blood pressure (BP) measurements. We measured peripheral blood flow and venous pressure in the arms and legs by using venous plethysmography.

RESULTS

Healthy subjects with normal vasoconstrictive responses to sustained upright tilt uniformly have a transient fall in BP during 70 degrees upright tilt that varies from almost undetectable to large decreases in BP easily exceeding the 20-mm Hg threshold for orthostatic hypotension. Large decreases are associated with short-lived symptoms of lightheadedness and are most marked in those with the largest calf blood flow. The higher the flow, the lower the BP falls. There is appropriate reflex tachycardia.

CONCLUSIONS

We conclude that transient orthostatic hypotension is common in many healthy adolescents, especially after prolonged recumbency, and is related to dependent vascular tone.

Orthostatic hypotension in pediatrics

Transient orthostatic hypotension is a common experience of many healthy adolescents and is the expected outcome of relatively dilated-dependent vascular tone. These children may experience brief symptoms of orthostatic intolerance when standing up rapidly, but they have no chronic symptoms or diseases. However, persistent orthostatic hypotension and chronic symptoms of orthostatic intolerance indicate postural tachycardia syndrome.