Table 1.

Characteristics of included studies.

Study	Study design	Duration	Country	Population	Intervention type	Key findings
Chung et al [26], 2021	Pilot study	8 weeks	United States	Adults with a GAD-2a score ≥3 and PHQ-2b score ≤4 aged 24-47 years (N=14)	Assessed the feasibility of an HRVBc wearable device and remote stress management coach to reduce anxiety	Anxiety scores and depression scores decreased over the 8-week intervention**
Crivelli et al [27], 2018	Pretesting study	2 weeks	Italy	Adult professionals with no history of psychiatric or neurological disease (N=16), mean age 44.4 years	To test the training of Vipasyana meditation and technology-mediated mental training for stress management in people who were at risk of stress (which involved real-time acoustic feedback via an app based on changes in the physiological signature of the participant’s mindset)	Significant decrease to perceived stress scores*, situational anxiety**, and anger and fatigue**
Jaramillo-Quintanar et al [28], 2020	Pretesting study	1 session	Mexico	Children with high stress levels (N=29), mean age 8.7 years	To test the feasibility of i-CARE, which measures HRd and blood oxygenation, and provides visual and auditory biofeedback to learn to regulate symptoms of anxiety	Results demonstrate that i-CARE is effective at inducing relaxation in children with high stress (no P value reported)
Kizakevich et al [29], 2019	Pilot study	1 year	United States	Adults with a military background (N=328)	To test the effectiveness of 4 different resilience training techniques each with or without HRVe biofeedback for people with a risk of stress; continuous acquisition of HRV data enables analysis of physiological response to stress and breathing training	No conclusions on the results of effectiveness could be drawn from the data
Millings et al [30], 2015	RCTf	4 weeks	United Kingdom	University students with >14 on the PSS-10g and <19 on the Beck Depression Inventory (N=92), mean age 23.7 years	Stress management program and a prototype wearable sensor kit comprising of and ECGh and EEGi sensor; compared stress management program alone, program and sensor, or no intervention groups	Significant reductions in levels of stress in those in the program alone condition*; however, sensors impeded the effectiveness of the program potentially due to technical issues
Nguyen et al [31], 2021	RCT	4 training sessions	Canada	Children and adolescents with ASDj aged 8-18 years (N=28)	Use of anxiety meter and breathing techniques; on the fourth visit participants were randomized to receive feedback on anxiety level or no feedback while completing a stress-eliciting task	The anxiety meter improved awareness of anxiety states, which lead to increased likelihood of initiating calming strategies under stress**
Ponzo et al [32], 2020	RCT	4 weeks	United Kingdom	University students aged 18-25 years with score >14 (stress) or >7 (anxiety) on DASSk (N=262)	Biobase program, mobile app comprising psychoeducational content, mood tracking via EMAl, and in-the-moment exercises for stress and anxiety (eg, relaxation); real-time sensor data presented to user via app dashboard	Well-being increased and anxiety decreased during intervention and was sustained 2 weeks after the intervention**
Shruthi et al [33], 2021	Pilot study	2 months	India	Students (N=50), mean age 19 years	Wristband to treat anxiety that provided acupressure to the H7 point on the wrist crease when completing a stressful task vs group wearing Fitbit-like band	Intervention group had lower levels of anxiety compared to the active control group (note, no P values reported)
Serino et al [34], 2014	Pilot study	120 seconds or more on the app exercises	Italy	App users (N=68)	App that teaches guided relaxation, 3D biofeedback training, and stress self-tracking to help control respiration rate and therefore HR	The stress management exercises along with the app led to a significant decrease in perceived psychological stress**
Smith et al [35], 2020	RCT	4 weeks	United States	Adults who work in knowledgeable occupations (N=215), mean age 33.2 years	App for stress and anxiety that delivers mindfulness-based breathing from MBSRm and Spire Stone to measure subjective emotional state changes; both provide biofeedback about physiological state; the app provided push notifications	Participants in the treatment group experienced 15.8% fewer negative instances of stress**, 13% fewer instances of distressing symptoms, and 28.2%* fewer days feeling anxious compared to waitlist control**
Winslow et al [36], 2016	RCT	8-10 weeks	United States	Veterans (N=16), mean age 39.8 years; self-reported anger and stress	In-person CBTn + sensor and mobile app; alerted the user through the app when stress was detected and presented with prompts or reminders to engage with stress mitigation techniques	High attrition; significant reduction in anxiety and stress observed between intervention and control*; no difference in depression

^aGAD-2: Generalized Anxiety Disorder 2-item.

^bPHQ-2: Patient Health Questionnaire–2.

^cHRVB: heart rate variability biofeedback.

^dHR: heart rate.

^eHRV: heart rate variability.

^fRCT: randomized controlled trial.

^gPSS-10: Perceived Stress Scale.

^hECG: electrocardiogram.

ⁱEEG: electroencephalogram.

^jASD: autism spectrum disorder.

^kDASS: Depression Anxiety Stress Scales.

^lEMA: ecological momentary assessment.

^mMBSR: mindfulness-based stress reduction.

ⁿCBT: cognitive behavioral therapy.

*P<.05, **P<.01