Neurovascular Dysregulation and Acute Exercise Intolerance in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: A Randomized, Placebo-Controlled Trial of Pyridostigmine.

BACKGROUND: Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is characterized by intractable fatigue, postexertional malaise, and orthostatic intolerance, but its pathophysiology is poorly understood. Pharmacologic cholinergic stimulation was used to test the hypothesis that neurovascular dysregulation underlies exercise intolerance in ME/CFS. RESEARCH QUESTION: Does neurovascular dysregulation contribute to exercise intolerance in ME/CFS, and can its treatment improve exercise capacity? STUDY DESIGN AND METHODS: Forty-five subjects with ME/CFS were enrolled in a single-center, randomized, double-blind, placebo-controlled trial. Subjects were assigned in a 1:1 ratio to receive a 60-mg dose of oral pyridostigmine or placebo after an invasive cardiopulmonary exercise test (iCPET). A second iCPET was performed 50 min later. The primary end point was the difference in peak exercise oxygen uptake (Vo2). Secondary end points included exercise pulmonary and systemic hemodynamics and gas exchange. RESULTS: Twenty-three subjects were assigned to receive pyridostigmine and 22 to receive placebo. The peak Vo2 increased after pyridostigmine but decreased after placebo (13.3 ± 13.4 mL/min vs -40.2 ± 21.3 mL/min; P < .05). The treatment effect of pyridostigmine was 53.6 mL/min (95% CI, -105.2 to -2.0). Peak vs rest Vo2 (25.9 ± 15.3 mL/min vs -60.8 ± 25.6 mL/min; P < .01), cardiac output (-0.2 ± 0.6 L/min vs -1.9 ± 0.6 L/min; P < .05), and right atrial pressure (1.0 ± 0.5 mm Hg vs -0.6 ± 0.5 mm Hg; P < .05) were greater in the pyridostigmine group compared with placebo. INTERPRETATION: Pyridostigmine improves peak Vo2 in ME/CFS by increasing cardiac output and right ventricular filling pressures. Worsening peak exercise Vo2, cardiac output, and right atrial pressure following placebo may signal the onset of postexertional malaise. We suggest that treatable neurovascular dysregulation underlies acute exercise intolerance in ME/CFS. CLINICAL TRIAL REGISTRATION: ClinicalTrials.gov; No.: NCT03674541; URL: www. CLINICALTRIALS: gov.

The Role of Exercise Testing in Pulmonary Vascular Disease: Diagnosis and Management.

Exercise intolerance is the dominant symptom of pulmonary hypertension (PH). The gold standard for the estimation of exercise capacity is a cycle ergometer incremental cardiopulmonary exercise test (CPET). The main clinical variables generated by a CPET are peak oxygen uptake (Vo2peak), ventilatory equivalents for carbon dioxide (VE/Vco2), systolic blood pressure, oxygen (O2) pulse, and chronotropic responses. PH is associated with hyperventilation at rest and at exercise, and an increase in physiologic dead space. Maximal cardiac output depends on right ventricular function and critically determines a PH patient's exercise capacity. Dynamic arterial O2 desaturation can also depress the Vo2peak.