Cardiac responses to exercise distinguish postural orthostatic tachycardia syndrome variants

Hyperventilation during rest and exercise in orthostatic intolerance and Spiky-Leaky Syndrome

Background

Orthostatic intolerance, with or without postural orthostatic tachycardia syndrome (POTS), is collectively referred to as orthostatic intolerance dysautonomia syndromes (OIDS). This condition often presents with daytime hyperventilation, which is considered to be secondary to sympathetic hyperactivity. This hyperventilation appears to be a key characteristic in a newly described subset of patients with OIDS who also exhibit craniocervical instability, mast cell activation syndrome (MCAS), hypermobility spectrum disorder (HSD), and the phenomenon of alternating intracranial hypertension with hypotension due to cerebrospinal fluid (CSF) leaks, collectively termed Spiky-Leaky Syndrome (SLS).

Methods

We performed a retrospective review of clinical metabolic exercise data in young patients with SLS, comparing them to matched patients with OIDS and healthy controls (CTL). We assessed metabolic parameters at rest, at the anaerobic threshold (AT), and at maximal oxygen consumption (VO2max). The parameters included end-tidal CO2 (ETCO2), end-tidal O2 (ETO2), peak oxygen pulse, total work performed, and peak oxygen uptake efficiency slope (OUESp).

Results

Of 323 reviewed exercise stress tests, 44 were conducted on patients with SLS, 210 on those with OIDS, and 53 on healthy controls. VO2max, AT, peak oxygen pulse, total work performed, and OUESp were all significantly reduced in patients with OIDS and were further reduced in those with SLS. ETCO2 levels were notably lower at rest, at the time of the anaerobic threshold, and at the time of maximal oxygen uptake in the OIDS group, and even more so in the SLS group. These lower levels of ETCO2 persisted throughout exercise. In contrast, ETO2 demonstrated a similarly strong but opposite trend.

Conclusion

Compared to the control group, patients with OIDS-and especially those with SLS-exhibited reduced metabolic parameters, particularly a decrease in peak oxygen pulse and ETCO2 levels during both rest and exercise. These findings suggest a reduction in ventricular preload and chronic daytime hyperventilation. These exercise parameters may serve as markers for POTS physiology and sympathetic hyperactivity, both of which could play a role in the pathophysiology of SLS.

Effects of different postures on the hemodynamics and cardiovascular autonomic control responses to exercise in postural orthostatic tachycardia syndrome

PURPOSE

To assess the effects of two different body positions on the cardiovascular autonomic profile during a single bout of exercise in patients with postural orthostatic tachycardia syndrome (POTS).

METHODS

Thirteen patients with POTS and thirteen healthy controls (C) participated in the study. ECG, respiration, beat-by-beat arterial pressure and O2 consumption (VO2) were continuously recorded while on a cycle ergometer in supine and upright positions, before and during exercise (6 min, 50 Watts). Spectral analysis of RR intervals and systolic arterial pressure (SAP) variability provided indexes of cardiac sympathovagal interaction (LF/HF ratio), cardiac vagal modulation (HFRR, high-frequency component of RR variability, ~ 0.25 Hz), sympathetic vasomotor control (LFSAP, low-frequency component of SAP variability, 0.1 Hz) and baroreflex sensitivity (BRS, αLF).

RESULTS

While supine, patients with POTS showed lower HFRR and αLF, greater heart rate (HR), LF/HF and LFSAP, compared with C, suggesting cardiovascular sympathetic over-activity and reduced BRS. While sitting upright, POTS showed greater HR and reduced HFRR and αLF compared with C. During supine exercise, SAP, HR, LF/HF increased and HFRR and αLF decreased similarly in POTS and C. In POTS, upright sitting exercise was associated with slightly higherV ˙ O 2 , a greater increase in HR whereas LFSAP was lower than in C.

CONCLUSION

Upright exercise was associated with excessive enhancement of HR and a blunted increase of the sympathetic vasomotor control in POTS. Conversely, supine exercise-induced hemodynamic and autonomic changes similar in POTS and C, thus making supine exercise potentially more suitable for physical rehabilitation in POTS.

Arterial Baroreceptor Physiology: Differences Between Normal Subjects and Pediatric Patients with Postural Tachycardia and Neurocardiogenic Syncope

The arterial baroreceptor reflex in children and adolescents has not been well studied in the current literature with a lack of agreed upon normal values, particularly in postural orthostatic tachycardia syndrome (POTS) or neurocardiogenic syncope (NCS). We used the sequence method and head-up tilt test (HUTT) to evaluate baroreceptor function in 3 phases: baseline supine position for 10 min, head-up position at 70° for 30 min or until syncope, and post-tilt supine reposition for 10 min. We measured the number of baroreceptor events, baroreceptor effectiveness index (BEI), and the magnitude of sensitivity of the events at each phase of HUTT. We studied 198 individuals (49 normal subjects, 67 POTS, 82 NCS) with age ranges from 8 to 21 years. The data show a statistically significant decrease in slope and BEI in patients with POTS and NCS during the head-up phase, with an increase in activity in the lag 1 and 2 portions of all phases in patients with POTS. This study provides terminology to describe baroreceptor function and identifies the slope and BEI portions of the baroreceptor reflex as the most useful objective measures to differentiate pediatric patients with POTS and NCS from normal subjects.

Postural orthostatic tachycardia syndrome: A respiratory disorder?

Postural orthostatic tachycardia syndrome (POTS) is a disorder epitomized by the story of the blind men and the elephant. Patients may see primary care internists or pediatricians due to fatigue, be referred to neurologists for “spells”, to cardiologists for evaluation of pre-syncope or chest pain, to gastroenterologists for nausea or dyspepsia, and even pulmonologists for dyspnea. Adoption of a more systematic approach to their evaluation and better characterization of patients has led to greater understanding of comorbidities, hypotheses prompting mechanistic investigations, and pharmacologic trials. Recent work has implicated disordered sympathetic nervous system activation in response to central (thoracic) hypovolemia. It is this pathway that leads one zero in on a putative focal point from which many of the clinical manifestations can be explained – specifically the carotid body. Despite heterogeneity in etiopathogenesis of a POTS phenotype, we propose that aberrant activation and response of the carotid body represents one potential common pathway in evolution. To understand this postulate, one must jettison isolationist or reductionist ideas of chemoreceptor and baroreceptor functions of the carotid body or sinus, respectively, and consider their interaction and interdependence both locally and centrally where some of its efferents merge. Doing so enables one to connect the dots and appreciate origins of diverse manifestations of POTS, including dyspnea for which the concept of neuro-mechanical uncoupling is wanting, thereby expanding our construct of this symptom. This perspective expounds our premise that POTS has a prominent respiratory component.

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Dyspnea affects ~⅓ patients with postural orthostatic tachycardia syndrome (POTS).

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POTS is characterized by thoracic hypovolemia and compromised cephalad perfusion when upright.

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Carotid body and adjacent carotid sinus mediate chemo- and baro- reflexes, respectively.

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These are not independent and stimulation of either activates sympathetic discharge.

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We speculate that carotid body mediates hyperventilation and dyspnea in POTS.

High Submaximal Exercise Heart Rate Impacts Exercise Intolerance in the Postural Orthostatic Tachycardia Syndrome

PURPOSE

Exercise intolerance is a hallmark of the postural orthostatic tachycardia syndrome (POTS). However, no data are available on the implications of an exaggerated submaximal heart rate (HR) on exercise intolerance in patients. We investigated whether exaggerated HR responses occurring early on during incremental stress testing relate with increased odds of POTS and exercise intolerance.

METHODS

Clinical characteristics and stress test HRs were compared between adults with POTS achieving ≥85% predicted metabolic equivalents (METs) (EX-TL, n = 101; body mass index [BMI] 24 ± 5 kg·m; 95% women) or <85% (EX-INTL, n = 71; BMI 28 ± 7 kg·m; 79% women) and sedentary controls (n = 30; BMI 36 ± 3 kg·m; 87% women). Multivariate logistic regressions were performed to estimate ORs and the probability of POTS and exercise intolerance associated with exercise HRs.

RESULTS

Exercise tolerance was increased in EX-TL, but not in EX-INTL (10.0 ± 1.3 and 8.3 ± 1.5 METs vs 8.0 ± 1.6 METs, respectively) versus controls. Absolute peak HR was increased in EX-TL and EX-INTL versus controls (P < .01), whereas percent predicted did not differ. Exercise within the first-to-second stress stages was performed at exaggerated HRs (122 ± 17 bpm vs 103 ± 15 and 113 ± 15 bpm, P < .001) and percent HR reserve in EX-INTL versus controls and EX-TL (49% ± 12% vs 34% ± 11% and 41% ± 11%, P < .001), respectively. In multivariate analyses, peak HR was not significant, whereas increased submaximal HR (either variable) was associated with increased odds of EX-TL or EX-INTL. Lastly, odds of EX-INTL increased as METs decreased, whereas METs was not a predictor of EX-TL.

CONCLUSIONS

An exaggerated submaximal exercise HR is predictive of POTS and exercise intolerance, and this chronotropic phenotype is exacerbated in patients achieving <85% predicted METs.

Efficacy of β-Blockers on Postural Tachycardia Syndrome in Children and Adolescents: A Systematic Review and Meta-Analysis

Background: Postural tachycardia syndrome (POTS) is a severe health problem in children. Short-term β-blockers are recommended for pharmaceutical treatment. However, there have been contradictory data about its efficacy among pediatric patients. Methods and Results: Eight studies comparing β-blockers to conventional treatments for children with POTS were selected, where 497 cases of pediatric POTS were included. The efficacy of β-blockers was evaluated using the effective rate, the change of symptom score, the change of heart rate difference and adverse events. The results were stated as relative ratio (RR) and mean difference (MD) with a 95% confidence interval (95% CI). A random-effects meta-analysis for the effective rate indicated that β-blockers were more effective in treating pediatric POTS than controlled treatment (79.5 vs. 57.3%, RR = 1.50, 95%CI: 1.15-1.96, P < 0.05). A fixed-effects model analysis showed that β-blockers were more effective in lowering the symptom score and the heart rate increment during standing test than controlled treatment with a mean difference of 0.81 (95% CI: 0.44-1.18, P < 0.05) and 3.78 (95% CI: 2.10-5.46, P < 0.05), respectively. There were no reported severe adverse events in included studies. Conclusion: β-blockers are effective in treating POTS in children and adolescents, alleviating orthostatic intolerance, and improving hemodynamic abnormalities.

Activity and Exercise Intolerance After Concussion: Identification and Management of Postural Orthostatic Tachycardia Syndrome

Supplemental Digital Content is Available in the Text.

Background and Purpose:

Postural orthostatic tachycardia syndrome (POTS) is increasingly recognized as a complication affecting recovery from concussion. Individuals with POTS demonstrate refractory dizziness, lightheadedness, cognitive dysfunction, fatigue, headache, chronic pain, nausea and gastrointestinal dysmotility, activity and exercise intolerance, syncope, and tachycardia. Subtypes of POTS may include hypovolemia, hyperadrenergic states, autonomic neuropathy, and underlying autoimmunity, which may variably impact response to rehabilitation in varying ways. The subtle presentation of POTS postconcussion is often mistaken for underlying anxiety, conversion disorder, or lack of motivation for recovery. This article will present clinical features of POTS that may arise after concussion, and propose a role for physical therapists in the diagnosis and management of POTS during concussion recovery.

Summary of Key Points:

Data recorded and entered into a database during clinic visits from a large pediatric institution indicate that 11.4% of individuals diagnosed with POTS report onset of symptoms within 3 months of sustaining a concussion. Activation of the sympathetic nervous system can result in lightheadedness, shortness of breath, chest pain, tachycardia, palpitations on standing or with exertion, and activity and exercise intolerance. Identified comorbidities in people with POTS such as joint hypermobility and autoimmune disorders can further influence recovery.

Recommendations for Clinical Practice:

Physical therapists may identify signs and symptoms of POTS in a subset of individuals who remain refractory to typical interventions and who exhibit symptom exacerbation with orthostatic activity. Incorporation of an individualized POTS exercise program into current established concussion interventions may be useful, with emphasis on initial recumbent exercises and ongoing physical therapy assessment of exercise tolerance for dosing of activity intensity and duration.

Video Abstract available for more insights from the authors (see Supplemental Digital Content 1, available at: http://links.lww.com/JNPT/A211).

Postural Tachycardia Syndrome: Diagnosis and Management in Adolescents and Young Adults

Postural tachycardia syndrome (POTS) represents a common form of orthostatic intolerance that disproportionately affects young women from puberty through adulthood. Patients with POTS have day-to-day orthostatic symptoms with the hallmark feature of an excessive, sustained, and symptomatic rise in heart rate during orthostatic testing. Although considerable overlap exists, three subtypes of POTS have been described: neuropathic, hyperadrenergic, and hypovolemic forms. The wide spectrum of symptoms and comorbidities can make treatment particularly challenging. Volume expansion with fluid and salt, exercise, and education constitute a reasonable initial therapy for most patients. Several medicines are also available to treat orthostatic intolerance and the associated comorbidities. Defining the POTS subtypes clinically in each patient may help to guide medicine choices. A multidisciplinary approach to overall management of the patient with POTS is advised. This review highlights several aspects of POTS with a specific focus on adolescent and young adult patients. [Pediatr Ann. 2017;46(4):e145-e154.].

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.