The Role of Heliox in Respiratory Control

Increases in the WOB intensify the sensory and emotional perceptions of dyspnea, at least partly due to heightened conscious awareness of breathing. Recent data indicate that elevated WOB, and likely breathing perception, can impair cognitive function. This impairment is likely caused by negative affective sensations resulting from the increased WOB, which distracts from central information processing during complex reaction-time tasks. Additionally, both reaction time and accuracy worsen when greater loads are placed on the inspiratory muscles. However, several key knowledge gaps remain that are pertinent to Warfighters that experience elevated inspiratory resistance. This study will investigate whether reducing the WOB during inspiratory resistance can lower breathing perception and restore cognitive function.

Heliox lowers the resistive WOB and muscle load because of its low density and viscosity, allowing for higher ventilation rates than room air by reducing turbulent flow in the airways. Therefore, breathing heliox, which will lower the WOB, under high inspiratory resistance will provide critical insights into whether reducing the WOB can improve cognitive function. It's hypothesized that using heliox will decrease the WOB, lower perceived breathing effort, and improve cognitive function compared to breathing normal density air with elevated inspiratory resistance.

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 every10 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 (room air or heliox). Upon arrival, an esophageal balloon will be placed to measure the pressure around the heart and lungs. Participants will then complete two full-length breathing tasks, in which they inspire against a predetermined resistive load for 60 minutes, while breathing under the assigned 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.