Effects of Hydrotherapy During Post-COVID-19 Rehabilitation

Patients recovering from Post-COVID Syndrome often experience persistent fatigue, autonomic dysregulation, microcirculatory disturbances, and low-grade inflammation, all of which may hinder their return to full function. Kneipp hydrotherapy-using cold water applications-can address these pathophysiological changes through several mechanisms:

Autonomic regulation: Cold stimuli trigger parasympathetic activation and improve sympathovagal balance, helping to stabilize heart rate variability and reduce symptoms of dysautonomia often seen in Post-COVID.

Enhanced microcirculation: Repeated vasoconstriction and reactive vasodilation promote endothelial function and tissue perfusion, which may alleviate muscle aches, dizziness, and fatigue by improving oxygen and nutrient delivery.

Anti-inflammatory effects: Hydrothermal stimuli have been shown to modulate cytokine profiles, increasing anti-inflammatory mediators and potentially dampening the persistent, low-grade inflammation implicated in Post-COVID pathophysiology.

Musculoskeletal recovery: Thermo-mechanical stimulation relaxes tense muscle fibers, reduces pain perception, and supports gradual increases in physical capacity, all of which are important for overcoming Post-COVID deconditioning.

Taken together, these effects suggest that adjunctive cold water hydrotherapy could accelerate functional recovery, reduce symptom burden, and enhance quality of life in Post-COVID rehabilitation.

Baseline Assessments:

At baseline, demographic data including sex, age, height, and weight will be collected. Participants will report their current main Post-COVID symptoms, which will be categorized into symptom clusters: Fatigue (A), Cognitive (B), and Somatic (C). Smoking history will be assessed, including smoking status (current, former, or never), number of cigarettes per day, years of smoking, and pack-years.

The time (in months) since the COVID-19 infection that led to Post-COVID syndrome will be documented, along with the number of COVID-19 vaccinations received at the time of infection. Employment status will be recorded, distinguishing between full-time or part-time employment, COVID-related work disability, retirement, unemployment, or disability pension.

Comorbidities will be documented across the following categories: cardiovascular, pulmonary, cerebrovascular, metabolic, musculoskeletal, psychiatric, and other conditions. The severity of the acute COVID-19 illness will be assessed using the WHO Clinical Progression Scale, including information on any hospital admission and length of stay (in days).

Pulmonary function testing at baseline (V1) will include FEV₁, FVC, FEV₁/FVC ratio, and total lung capacity (TLC), all expressed as percent predicted. Autonomic function will be evaluated using the Schellong test. Vascular status will be assessed by four-limb blood pressure measurement. Additionally, self-reported work ability and the number of Post-COVID-related sick leave days within the past 12 weeks will be recorded.

• Fatigue severity by Fatigue Severity Scale [Time frame: From baseline (Visit 1) to end of inpatient rehabilitation (3 weeks, Visit 2)]
• Sleep quality by Pittsburgh Sleep Quality Index [Time frame: From baseline (Visit 1) to end of inpatient rehabilitation (3 weeks, Visit 2)]
• Health status by EuroQol-5 Dimensions-5 Levels [Time frame: From baseline (Visit 1) to end of inpatient rehabilitation (3 weeks, Visit 2)]
• Autonomic function (heart rate variability by photoplethysmography) [Time frame: Daily during first 3 weeks of rehabilitation (Visit 1 to Visit 2)]
• Resting blood pressure (systolic and diastolic) [Time frame: Daily during first 3 weeks of rehabilitation (Visit 1 to Visit 2)]
• Post-COVID work-absence days [Time frame: From baseline (Visit 1) to 3 months (Visit 3) and to 6 months (Visit 4)]
• Long-term quality of life by Short Form-12 [Time frame: From baseline (Visit 1) to 3 months (Visit 3) and to 6 months (Visit 4)]
• Long-term fatigue by Fatigue Severity Scale [Time frame: From baseline (Visit 1) to 3 months (Visit 3) and to 6 months (Visit 4)]
• Adherence to hydrotherapy [Time frame: During the 3-week intervention phase (up to Visit 2) and over the 6-month follow-up period (to Visit 4)]
• Adverse events recording [Time frame: From start of intervention (Visit 1) through end of study (Visit 4, 6-month follow-up)]
• Long-term heart rate variability changes (HRV) [Time frame: From baseline (Visit 1) to 3 months (Visit 3) and to 6 months (Visit 4)]
• Post-exertional malaise severity [Time frame: From baseline (Visit 1) to 6-month (Visit 4) follow-up]