Inspiratory Pressure Threshold Loading: Effects on Inspiratory Pattern, Perception and Prefrontal Cortical Activity

Cognitive awareness of breathing can lead to behavioral ventilatory compensation, respiratory interoception and activation of brain regions associated with decision processes, including the dorsal prefrontal cortex (dPFC). The dPFC is a critical cortical region mediating executive functions and dPFC activity is modulated during increased breathing load. This study investigated load compensation and perception response to sustained breathing against inspiratory pressure threshold (PT) loads. We hypothesized that increasing magnitudes of PT loads require increasing time to valve opening resulting in; greater inspiratory motor drive, increased perception of breathing effort (INT), increased perception of unpleasantness (UPL) and increased dPFC oxygen consumption (OXY, a measure of increased neural activity). Functional near-infrared spectroscopy (fNIRS) was used to measure OXY changes in the dPFC. Healthy subjects were exposed to 5 cmH2O (LoPT) and 20 cmH2O (HiPT) inspiratory PT loads for 1 minute load-on and 1 minute load-off trials. A total of 8 trials for each load were presented, 4 INT trials and 4 UPL trials. Perception of inspiratory INT and UPL was rated with a 0-10 modified Borg scale. There was a significant PT magnitude dependent increase in valve opening duration (0.18±0.15 LoPT vs 0.57±0.17 HiPT) and pressure (-4.4±0.75 LoPT vs -21.3±2.2 HiPT, p<0.001). The pressure-time-product (PtP), a measure of inspiratory motor drive, significantly (p<0.001) increased with PT magnitude. A significant PT magnitude dependent increase in INT (2.8±1.3 vs 7.9±1.2, p<0.001) and UPL (1.9±1.4 vs 7.8±1.4, p<0.001) ratings occurred but perception ratings did not significantly change throughout the 1-minute trial. The average 1-minute trial OXY LoPT was significantly (p<0.02) less than HiPT. The right dPFC OXY did not significantly change between trial Breath 1 and Breath 10. The left dPFC OXY significantly (p<0.01) increased from trial Breath 1 to Breath 10. These results suggest increased PT load magnitude required greater inspiratory drive to breathe. Breathing against a HiPT load was perceived as highly effortful and unpleasant. Sustained breathing against PT loads progressively increased left dPFC neural activity. Supported by the University of Florida, College of Veterinary Medicine. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.