The purpose of this study is to examine 1) effects of cutaneous electrical trigeminal nerve stimulation (eTNS) on respiratory control in healthy volunteers and 2) explore the potential of this approach to mitigate dyspnea in patients with chronic obstructive lung disease (COPD).

Arm1 - Healthy Volunteers

Inclusion Criteria:

• Adults aged 18-50 years
• BMI 18-30 kg/m²
• Ability to provide informed consent and complete study procedures in English

Exclusion Criteria:

• Current daytime respiratory impairment such as uncontrolled asthma, uncontrolled COPD, pneumonia, or interstitial lung disease
• Use of supplemental oxygen
• Pregnancy or breastfeeding
• Current use of acetazolamide, Sodium-glucose cotransporter-2 (SGLT2) inhibitors, or daily opioids
• History of claustrophobia or panic disorder
• Metallic implants in the craniofacial or cervical region that may interfere with electrode placement or electrical stimulation
• Implanted cardiac or neuroelectric device (e.g., pacemaker, implantable cardioverter-defibrillator (ICD), deep brain stimulator, vagus nerve stimulator, implanted drug pump)
• Open, broken, inflamed, infected, or healing skin lesions at or near facial electrode placement sites
• Resting heart rate <60 Beats Per Minute
• History of seizure disorder or epilepsy

Arm 2 -COPD

Inclusion Criteria:

• Adults aged 40-75 years
• Confirmed diagnosis of COPD by spirometry (post-bronchodilator Forced Expiratory Volume (FEV1) /Forced Vital Capacity (FVC) <0.70) or provider documentation in medical records
• Modified Medical Research Council (mMRC) dyspnea grade ≥2
• Stable COPD (no exacerbation requiring hospitalization, systemic corticosteroids, or antibiotic therapy within the preceding 6 weeks)
• On stable COPD therapy for at least 4 weeks prior to enrollment
• Ability to provide informed consent and complete questionnaires in English
• Resting Peripheral Capillary Oxygen Saturation (SpO₂) ≥88% on room air or prescribed supplemental oxygen

Exclusion Criteria:

• Unstable cardiovascular disease (e.g., unstable angina, decompensated heart failure, recent MI within 6 months, uncontrolled arrhythmia) or peripheral vascular disease
• Patients with cardiovascular disease, including chest pain, heart failure, and aortic stenosis
• Resting heart rate <60 BPM
• Implanted cardiac or neuroelectric device (e.g., pacemaker, ICD, deep brain stimulator, vagus nerve stimulator, implanted drug pump)
• Metallic implants in the craniofacial or cervical region that may interfere with electrode placement or stimulation
• Open, broken, inflamed, infected, or healing skin lesions at or near facial electrode placement sites
• Active trigeminal neuralgia or other cranial neuropathy
• History of seizure disorder or epilepsy
• Severe or uncontrolled psychiatric disorder (e.g., psychosis, severe untreated anxiety or panic disorder) that would impair the ability to participate
• Pregnancy or breastfeeding
• COPD exacerbation requiring hospitalization, systemic corticosteroids, or antibiotics within the preceding 3 months
• Musculoskeletal pain, injury, or any other condition that precludes the use of a stationary bike for Cardiopulmonary Exercise Test (CPET)
• Any condition that, in the opinion of the investigator, would compromise participant safety or data integrity