Table 2. Study eligibility criteria based on the PICO framework.

GAD-7: generalized anxiety disorder 7-item scale, HRV: heart rate variability, MBBS: bachelor of medicine, bachelor of surgery, MD: doctor of medicine, PICO: population, intervention, comparator, outcome (framework), PSS: perceived stress scale, RCTs: randomized controlled trials, STAI: state-trait anxiety inventory

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Category	Inclusion criteria	Exclusion criteria
Population (P)	Students enrolled in an undergraduate or graduate medical degree program from different healthcare disciplines (e.g., MBBS, nursing, dentistry), irrespective of year of study.	Practicing physicians or residents.
Intervention (I)	Structured pranayama (e.g., Kapalabhati, Bhramari, Nadi Shodhana, slow-paced pranayama) as the primary, stand-alone intervention. The practice could be supervised or unsupervised.	Multi-modal interventions where the effect of breathing exercises could not be isolated (e.g., yoga combining asana, pranayama, and meditation); non-yogic breathing techniques (e.g., Buteyko).
Comparator (C)	Active control (e.g., non-pranayama relaxation, physical exercise) or passive control (e.g., wait-list, no intervention, treatment as usual).	Not applicable
Outcomes (O)	Primary: Validated scales measuring self-reported anxiety (e.g., GAD-7, STAI) or perceived stress (e.g., PSS). Secondary: Objective or performance-based measures of cognition (e.g., attention, memory tests), HRV parameters.	Studies reporting only qualitative outcomes or physiological measures unrelated to the review's outcomes.
Study design	RCTs and non-randomized controlled intervention studies (e.g., quasi-experimental, pre-post).	Case reports, case series, narrative reviews, editorials, conference abstracts without full data, and protocols.