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
