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Background Orthostatic intolerance (OI) markedly impairs activities of daily living in patients with myalgic encephalomyelitis (ME) or chronic fatigue syndrome. OI is surmised to be a cardiovascular symptom correlated with cerebral hypo-perfusion and exaggerated sympathetic activation. Postural instability or disequilibrium may be part of the etiology of OI. Methods The study comprised 72 patients with ME (18 men, 54 women; mean age, 37 ± 10 years) who underwent neurological examinations and the 10 min standing test. We quantified disequilibrium (instability upon standing with feet together and eyes shut), ability to complete the 10 min standing test, and postural orthostatic tachycardia (POT) during the test. Results Disequilibrium was detected in 23/72 (32%) patients and POT in 16 (22%). Nineteen (26%) patients failed to complete the 10 min standing test; disequilibrium was significantly more common in the 19- patient subgroup than in the 53-patient test-completing subgroup (89% vs. 11%, p, Highlights • Most patients with chronic fatigue syndrome suffers from orthostatic intolerance (OI). • OI significantly restricts daily functional capacity. • Circulatory and autonomic nervous dysregulation is not the sole cause of OI. • Disequilibrium should be recognized as the important cause of OI. • Disequilibrium is more influential cause of OI than postural orthostatic tachycardia.

A 24-year-old male with a history of dizziness and syncope presented to the emergency department via ambulance for the fourth time in 36 hours. His medical history is significant for postural orthostatic tachycardia and factitious disorder. Upon examination in the emergency department, the patient appeared somnolent and displayed shallow, short breaths with occasional apnea. There was a concern for possible opioid overdose prompting admission to the medical intensive care unit. Laboratory testing demonstrated hypercapnic respiratory failure and a negative urine drug screen. Though the patient’s symptoms resolved upon administration of naloxone he denied ingestion of any substances that would contribute to his condition. Previous medical issues had been attributed to misuse of medications prescribed to the patient and loperamide was discovered in his belongings. Testing confirmed the presence of loperamide at supratherapeutic concentrations in his serum.

Perturbations and dysfunction of the autonomic nervous system can lead to a variety of clinical syndromes with multiple manifestations including loss of appropriate homeostatic blood pressure control, syncope, tachycardia or bradycardia, and in some cases cardiomyopathy, cardiac arrest, and sudden cardiac death. Treatment of cardiac autonomic disorders requires an understanding of the underlying heart/brain pathophysiology. However, current theories regarding the genesis of multiple syndromes such as recurrent unprovoked vasovagal syncope, postural orthostatic tachycardia, and partial dysautonomia syndromes are inadequate and further investigation and research are required.

Postural Orthostatic Tachycardia Syndrome (POTS) is a condition characterized by orthostatic tachycardia and associated intolerance. Common types are due to deconditioning. Less common types are neuropathic and hyperadrenergic POTS. Underlying hypovolemia and deconditioning are common in all types. The natural history is that of improving function, although symptoms tend to persist. Management consists of volume expansion (salt and fluids) and exercise. Drug treatment is helpful in the short term, although its value long term is unproven.

Publisher Summary This chapter describes postural tachycardia syndrome (POTS) is a syndrome of orthostatic tachycardia associated with symptoms of cerebral hypoperfusion and autonomic activation. POTS is best considered a condition rather than a disease so that the same patient may or may not fulfill criteria at different times. There is considerable heterogeneity. Some of the disparate reports likely relate to different phenotypes, with different underlying mechanisms. Onset of POTS was often postviral and peripheral autonomic denervation was manifest as loss of sweating on QSART and thermoregulatory sweat test distally. Adrenergic denervation was evident from loss of vasoconstrictor reflexes during the Valsalva maneuver. A variety of approaches have been used to alleviate symptoms in POTS. All patients need volume expansion and a high salt or high fluid regimen. Certain drugs appear to be beneficial, at least temporarily. The most widely used drugs are midodrine, propranolol, and fludrocortisone. Other measures used include body stockings and physical counter maneuvers. Medications that are commonly used include beta-blockers, midodrine, and fludrocortisones.

Publisher Summary This chapter focuses on mechanisms of postural tachycardia syndrome (POTS). Norepinephrine is the primary neurotransmitter among postganglionic neurons in the sympathetic nervous system, and plasma norepinephrine can provide a crude biochemical estimate of sympathetic nervous system activity. There are some cases of POTS in which the primary underlying problem seems to be excessive sympathetic discharge. The norepinephrine transporter (NET) is a presynaptic transporter in sympathetic neurons that is important for the clearance of synaptic norepinephrine. A specific genetic abnormality has been identified in a kindred with hyperadrenergic POTS. Some patients with POTS have coexistent mast cell activation disorder (MCAD). These patients often present with episodic flushing. Around episodes, they will have abnormal increases in urinary methylhistamine. Some POTS patients have a form of dysautonomia, with preferential denervation of sympathetic nerves innvervating the lower limbs. The rennin–angiotensin–aldosterone system plays a key role in the neurohormonal regulation of plasma volume in humans and may be a part of the problem in POTS.

Publisher Summary The idiopathic hypovolemia is a definite syndrome characterized by orthostatic intolerance, disabling orthostatic tachycardia, and episodes of paroxysmal supine hypertension. Orthostatic intolerance is one of the most common symptoms in patients with chronic idiopathic hypovolemia. However, in contrast with other types of orthostatic intolerance, these patients frequently have episodic clinical manifestations suggestive of adrenergic hyperactivity even in the supine resting posture. Marked reduction of pulse pressure may occur in patients with hypovolemia because of the increase of diastolic blood pressure and the accompanying reduction of systolic blood pressure secondary to the reduction of cardiac output. Patients with severe idiopathic hypovolemia typically have normal baroreceptor reflexes and normal response of the autonomic nervous system (ANS) to the Valsalva maneuver, cold pressor test, and hyperventilation. This syndrome is important to recognize because its normal clinical picture may lead to delays in diagnosis and use of appropriate therapy. Favorable clinical response has been observed when patients are treated with blood volume expansion, either alone or in combination with clonidine therapy.