Efficacy of Slow-Paced Breathing as a Just-in-Time Adaptive Intervention for Anxiety—A Randomized Controlled Study

Numerous studies have substantiated the efficacy of slow-paced breathing (SPB) in decreasing anxiety and increasing vagally-mediated heart rate variability (vmHRV). Given its effectiveness and simplicity, SPB is a promising candidate for a just-in-time adaptive intervention (JITAI). This study examined the efficacy of SPB, triggered by increased anxiety and perseverative cognition (PC), on reducing these symptoms and increasing vmHRV at macro, micro, and immediate levels. Eighty individuals with subclinical anxiety from the Flemish general population were randomized into experimental (EC) or passive control (CC) conditions. Anxiety symptoms were evaluated at baseline and after 15 days. Participants underwent a control period (CP; 6 days) and an intervention period (IP; 6 days), during which they reported momentary anxiety and PC via a mobile application while wearing a portable electrocardiogram. EC participants received SPB training between CP and IP and were prompted to use SPB exercises during IP when anxiety/PC increased. Analyses revealed a significant effect of SPB on reducing retrospectively reported anxiety (p < .05), but not on average daily-life anxiety and PC or vmHRV assessed throughout the IP. Micro-level analyses indicated that SPB was associated with a decrease in PC (p < .05) but not anxiety at the subsequent daily-life assessment. Anxiety and PC decreased substantially from immediately before to immediately after SPB (< 0.001). The effect of SPB on vmHRV remains inconclusive due to methodological concerns in measuring vmHRV in ambulatory settings. The results provide mixed evidence for the efficacy of SPB as a JITAI, indicating the need for replication studies to further evaluate its potential.