Hyperbaric Oxygen Therapy for PTSD: Threshold Effect for Sustained Symptom Improvement in a Biologically Based Treatment

Objective Emerging evidence suggests that hyperbaric oxygen therapy (HBOT) promotes neuroplasticity and alleviates symptoms in individuals with post‐traumatic stress disorder (PTSD). As a biologically based treatment, HBOT may demonstrate a threshold effect, wherein sufficient treatment leads to sustained symptom improvement, while insufficient treatment results in diminishing benefits. This study tested the threshold hypothesis reanalyzing the end of treatment and a 3‐month follow‐up symptoms scores of a randomized controlled trial (RCT) comparing HBOT to sham treatment in 56 male veterans with treatment‐resistant PTSD. Methods A post hoc analysis was conducted on data from the RCT. The elbow method identifies thresholds in the relationship between end‐of‐treatment improvement and follow‐up outcomes. Spearman's rank correlation was used to assess the relationship between changes in cluster‐specific symptoms and total CAPS scores at the end of treatment and at follow‐up evaluation. Results Participants achieving ≥ 35% improvement by the end of treatment demonstrated continued improvement at follow‐up ( p = 2e −6 ). Significant correlations were observed between changes in each of the symptom clusters and total CAPS scores, with the strongest correlation in intrusive symptoms (Cluster B, r = 0.74, p = 10e −4 and r = 0.80, p = 10e −4 ). Changes in avoidance (Cluster C, r = 0.70, p = 10e −4 ) at the end of treatment were the best predictors of follow‐up improvements. Conclusions A threshold effect is evident in HBOT treatment for PTSD, where ≥ 35% improvement posttreatment predicts continued gains. Symptom reduction beyond the threshold may serve as a target for HBOT when prescribed for PTSD. The suggested underlying physiological mechanisms, involving bistable circuit dynamics, justify evaluating potential threshold effect in other treatment modalities. Trial Registration : ClinicalTrial.gov identifier: NCT04518007