LAS CODE - professional
Long COVID syndrome frequently manifests with autonomic dysfunction, particularly through orthostatic intolerance and persistent fatigue. This study employed head-up tilt table testing (HUTT) to evaluate cardiovascular autonomic regulation in 39 Long COVID patients compared to 22 matched healthy controls. The standardized protocol consisted of 15 min supine rest, 20 min at 70° tilt, and 10 min recovery. We simultaneously analyzed continuous blood pressure (BP) and heart rate variability (HRV) parameters, including time-domain (RMSSD, pNN50) and frequency-domain (LFnor, HFnor, LF/HF ratio) measures. Key findings revealed significant autonomic dysregulation in Long COVID patients across all test phases. During supine rest, we observed marked parasympathetic withdrawal (RMSSD 30.4±3.2ms vs 35.9±4.1ms, p= 0.04; pNN50 12.7±2.1% vs 18.5±3.4%, p= 0.03). The tilt phase demonstrated blunted sympathetic response (LF/HF ratio 3.81±0.45 vs 5.91±0.62, p= 0.03) with paradoxical vagal predominance (HF power 31.1±4.2 vs 20.9±3.8 normalized units, p= 0.03). Post-tilt recovery showed sustained hemodynamic impairment, with significantly lower BP recovery (Δ(SBP-DBP)= -4.9 ± 2.1mmHg, p=0.04) and delayed autonomic normalization. These results characterize a distinct autonomic phenotype in Long COVID featuring: (1) baseline parasympathetic insufficiency, (2) orthostatic sympathetic failure, (3) maladaptive vagal rebound during stress, and (4) prolonged cardiovascular recovery. The observed 28% increase in BP variability during orthostasis correlated strongly with HRV abnormalities (r=0.72, p <0.01), suggesting combined baroreflex and central autonomic network dysfunction. Clinical implications highlight the diagnostic utility of combined BP-HRV analysis during HUTT for post-COVID dysautonomia evaluation. The identified pattern suggests potential therapeutic targets including graded orthostatic training and pharmacological autonomic modulation. Persistent recovery-phase abnormalities indicate chronic autonomic dysfunction requiring long-term monitoring, while future studies should link these measures to symptom severity and treatment outcomes.