Circuit Breathing Exercise on Smoking Cessation Among Youth E-Cigarette Users

A randomized crossover study will include 20 male and female e-cigarette users aged 15-25 years. Each participant will undergo three breathing conditions: circuit breathing, diaphragmatic breathing, and normal breathing, with a washout period of at least one week between sessions. The study will evaluate the acute effects of each breathing condition on nicotine withdrawal symptoms, e-cigarette dependence, physiological variables (resting heart rate and blood pressure), peak nasal inspiratory flow (PNIF), and fractional exhaled nitric oxide (FeNO).

• Circuit breathing (Other): The circuit breathing intervention consists of five stations: paper suction using a straw, blowing a toy pinwheel, incentive spirometry, balloon blowing, and weighted diaphragmatic breathing. Participants will rest for 1 minute between stations.
• Diaphragmatic Breathing (Other): The diaphragmatic breathing exercise will consist of inhaling through the nose for 4 seconds and exhaling through the nose for 6 seconds, continuously for 10 minutes per set. Participants will rest for 1 minute between sets and complete a total of 3 sets.
• Normal Breathing Condition (Other): Participants will breathe normally through the nose without deliberately controlling the rate, rhythm, or depth of breathing. Breathing will remain at each participant's natural pace for approximately 30 minutes.

Primary outcomes

• E-cigarette Dependence [Baseline for demographic data.]: E-cigarette dependence will be assessed using the Penn State Electronic Cigarette Dependence Index, adapted by Sornsenee et al. (2025). The questionnaire consists of 10 items, with a maximum total score of 20. Scores are interpreted as follows: 0-3 indicates no e-cigarette dependence, 4-8 indicates low dependence, 9-12 indicates moderate dependence, and 13 or higher indicates high dependence.
• Nicotine Withdrawal Symptoms [Immediately before and immediately after each breathing intervention session.]: Nicotine withdrawal symptoms will be assessed using the Thai version of the Minnesota Nicotine Withdrawal Scale-Revised (MNWS) (Hughes \& Hatsukami, 2008), translated by Sirirat Kanokururot and Sunida Preechawong (2010). This self-report questionnaire measures the perceived severity of nicotine withdrawal symptoms. It consists of 9 items rated on a 5-point scale ranging from 0 (no symptoms) to 4 (severe symptoms). The total score ranges from 0 to 36, with a score of 0 indicating no nicotine withdrawal symptoms and a score of 36 indicating the most severe nicotine withdrawal symptoms.

Secondary outcomes

• Fractional Exhaled Nitric Oxide (FeNO) [Immediately before and immediately after each breathing intervention session.]: FeNO will be measured using a device equipped with a bacterial filter and mouthpiece. Participants will place their lips around the mouthpiece and exhale into the device for 6 seconds while maintaining the indicator ball within the designated range. Results will be recorded in parts per million (ppm).
• Peak Nasal Inspiratory Flow (PNIF) [Immediately before and immediately after each breathing intervention session.]: Peak nasal inspiratory flow will be measured using a peak nasal inspiratory flow meter. Participants will perform the breathing maneuver according to the study procedure, and the measurement will be recorded in liters per second (L/s).

Sex: All, ages: 15 Years to 25 Years, accepts healthy volunteers

Inclusion Criteria:

* Male or female aged 15-25 years.
* Regular e-cigarette use for at least six months and current e-cigarette use, defined as use on at least one day per week or at least 10 puffs per day during the past 30 days.
* Not regularly physically active, defined as exercising fewer than two times per week during the preceding six months.
* Able to understand instructions, communicate effectively, and cooperate with the research procedures.
* No history of cardiovascular disease or respiratory disease, such as asthma or chronic obstructive pulmonary disease.
* No uncontrolled hypertension. Participants with controlled hypertension must have resting blood pressure ≤140/90 mmHg.
* Able to move independently without assistance or assistive devices.
* Willing to participate and provide informed consent.
* For participants younger than 18 years, consent from a parent or legally authorized representative is required.

Exclusion Criteria:

* Development of an illness, injury, or other circumstance that prevents continued participation.
* Withdrawal of consent or unwillingness to continue participation.
* Current use of illicit drugs or other tobacco/nicotine products, including conventional cigarettes, shisha/hookah, roll-your-own tobacco, or other nicotine-containing products.