Warfighters are frequently exposed to environments and life-support systems that increase breathing resistance and the work of breathing (WOB), such as aircraft on-board oxygen generation systems and underwater breathing apparatuses. Elevated WOB then increases the perception of breathing difficulty (dyspnea) and has been associated with impaired cognitive performance, including slower reaction time and reduced accuracy during attention-demanding tasks. These effects are particularly concerning in operational settings that require rapid decision-making and precise motor responses.

Despite growing recognition of this issue, critical gaps remain regarding strategies to mitigate the perceptual and cognitive consequences of elevated inspiratory resistance, especially under realistic operational stressors. The objective of this experiment is to determine whether modifying the sensory perception of breathing alters breathing perception and cognitive performance during inspiratory resistance. Auditory feedback of ventilation will be manipulated (normal, reduced, or amplified) to assess whether altering breathing-related sensory input affects breathing perception and cognitive performance without changing mechanical load.

In some instances, reducing inspiratory resistive loads (e.g., OBOGs, SCUBA) for Warfighters may not be feasible, but understanding how breathing perception is affected by resistance is essential. Auditory feedback of ventilation significantly influences breathing awareness, and as the WOB increases, this perception intensifies due to enhanced auditory input. This heightened awareness can distract and tax cognitive processing. Recent studies indicate that auditory distractions, like music during exercise, can lessen dyspnea and respiratory and whole-body discomfort in healthy individuals and those with chronic obstructive pulmonary disease. This effect may stem from reduced auditory feedback or improved emotional states linked to music. However, a key knowledge gap exists: it is unclear whether reducing auditory feedback of ventilation during increased inspiratory resistance affects breathing perception and cognitive function. The study will assess the impact of different auditory feedback of ventilation conditions (normal, eliminated via noise distraction, and amplified) on cognitive function under high inspiratory resistance. It's hypothesized that reducing auditory feedback of ventilation will not alter the WOB but will decrease breathing perception and enhance cognitive performance compared to standard or amplified feedback.

Participants will complete two study visits: a screening/familiarization visit (Study Day 0) followed by one experimental visit (Study Day 1). Participants will be instructed to avoid caffeine, alcohol, stimulant medication, pain/anti-inflammatory medication, cannabis and cannabis related products, and vigorous exercise for at least 24 hours prior to experimental visits. On Study Day 0, participants will complete a short familiarization breathing task in which they will breathe for 10 minutes through an 8-10mm hole at the end of a customized device, generating a pre-determined inspiratory resistance of 6-9.5 centimeters of water per liter per second (cmH2O/L/s). During the breathing task, cerebral vascular, cardiovascular and autonomic activity responses will be measured. Every 5 minutes during the breathing test, participants will be asked to rate breathing intensity and unpleasantness, and perform an inspiratory capacity maneuver. Cognitive assessments will be administered every 10 minutes. After the breathing task, participants will complete lung and respiratory muscle function tests.

Prior to Study Day 1 (the experimental visit), participants will be randomized to the order in which they are exposed to the interventional conditions (ambient/normal auditory feedback, enhanced auditory feedback, or removed auditory feedback with replacement of a self-selected music playlist). Upon arrival, an esophageal balloon will be placed to measure the pressure around the heart and lungs. Participants will then complete three full-length breathing tasks, in which they inspire against a predetermined resistive load for 60 minutes, with auditory conditions in the order of randomization. Biometric monitoring, cognitive tasks and participant ratings during the breathing tasks will be completed with the same frequency as Study Day 0. A 1-hour rest period will be observed between the breathing tasks.

Inclusion Criteria:

• Between the ages of 18-40 years old.
• English speaking and reading.
• Self-reported weekly activity of at least 120 minutes/week of high intensity exercise for the previous 2 years.
• Normal pulmonary function assessed by a resting forced expiratory volume in 1 second over forced vital capacity (FEV1/FVC) > 75% of predicted.
• Normal cognitive function assessed using the Montreal cognitive function test [18].
• Body mass index (BMI) ≤ 35 kg/m2.
• Females with a regular menstrual cycle that ranges from 21-35 days (eumenorrhea)

Exclusion Criteria:

• History of smoking or recreational smoking, cardiovascular disease, renal disease, pulmonary disease (including asthma or exercise-induced asthma), neurological disease, and metabolic disease.
• Are pregnant or could possibly be pregnant by self-report.
• Are color blind.
• Known allergy or hypersensitivity latex.
• Take selective serotonin reuptake inhibitors, stimulant medication, antibiotics, and chronically consume pain medication (Aleve, Tylenol, etc.).
• Resting blood pressure of > 130mmHg systolic or 90 mmHg diastolic and/or resting pulse rate of > 100 bpm.
• Females with irregular menstrual cycles (oligomenorrhea) that ranges from 36-90 days, and females with the absence of a menstrual cycle (amenorrhea).
• Taking birth control for the sole purpose of period cessation (eg., Mirena IUD)

The plan to share individual participant data (IPD) is still unknown. However, if other researchers request IPD, we will evaluate that request and determine to share IPD.