Phase-Specific Changes in Vital Signs and Electrocardiogram Findings During Hyperbaric Oxygen Therapy in Hemodynamically Stable Patients: A Prospective Observational Study.

Background/Objectives: Physiological changes during hyperbaric oxygen therapy (HBOT) are not well characterized, particularly in non-emergent patients receiving HBOT as part of a repeated or maintenance treatment course, in whom understanding physiological responses during individual sessions is important for clinical monitoring. This study evaluated changes in vital signs and electrocardiographic (ECG) findings across the pre-compression, compression, maintenance, decompression, and post-treatment phases and evaluated clinical symptoms. Methods: This prospective observational study enrolled 50 hemodynamically stable non-emergent patients undergoing HBOT at a single tertiary center. Changes in vital signs and ECG findings were recorded across all phases. Repeated vital sign measurements were analyzed using linear mixed models; ECG abnormalities were assessed using generalized linear mixed models. Results: Heart rate decreased significantly across all HBOT phases compared with baseline. Blood pressure (BP) remained stable during compression and maintenance but increased significantly during decompression and post-treatment. Respiratory rate decreased during treatment and then returned to baseline. Oxygen saturation remained within normal ranges throughout all phases. Transient ECG rhythm abnormalities were observed in 10.0% of patients, primarily during compression and maintenance phases. One patient developed brief clinical symptoms accompanied by supraventricular tachycardia immediately after decompression, which resolved spontaneously without intervention. No significant oxygen toxicity or serious adverse events were observed. Conclusions: HBOT in hemodynamically stable non-emergent patients induces predictable, largely transient physiological changes and is well tolerated under standard protocols. Blood pressure elevation was most pronounced during decompression and the post-treatment phase, whereas transient ECG abnormalities were observed primarily during the compression and maintenance phases, with a single episode of supraventricular tachycardia occurring immediately after decompression. These findings provide foundational clinical data for understanding phase-specific physiological responses during HBOT and inform future studies in higher-risk patient populations.