For an investigation, patients with post-acute sequela of COVID-19 (PASC) were subjected to head-up tilt table (HUTT) testing to look for orthostatic intolerance (OI), which might indicate autonomic dysfunction.

A prospective, observational study was conducted on individuals with PASC who complained of poor exertional tolerance, tachycardia with minor activity or positional shift, and palpitations. Pregnancy, pre-PASC autonomic dysfunction/syncope, or another possible reason for PASC symptoms were all excluded. HUTT was performed on all subjects.

The study comprised 24 participants with the identified PASC symptoms. HUTT was done 5.8+3.5 months after the beginning of symptoms. On HUTT, 23 of 24 patients reported OI, with 4 having POTS, 15 having POI after nitroglycerin, 3 having neurocardiogenic syncope, and 1 having orthostatic hypotension. Patients with POI reported much earlier improvement of symptoms than those with postural orthostatic tachycardia syndrome (POTS). 

The prospective study of HUTT in individuals with PASC found OI of HUTT in virtually all cases, indicating autonomic dysfunction. POI patients may be further down the road to clinical recovery than POTS patients.