Cerebral Blood Flow Response to Different Breathing Patterns During Inspiratory Pressure Threshold Loading

Introduction: Regulation of cerebral blood flow (CBF) is vital for ensuring blood supply to cerebral tissue, and studies have shown that CBF increases to match the demands of whole-body exercise. Additionally, studies have shown that an inspiratory muscle metaboreflex induced by fatiguing inspiratory work causes a decrease in blood flow to limbs and splanchnic organs, presumably redirecting blood flow to the activated inspiratory muscles. However, it is unknown if the metaboreflex response is greater when targeting the diaphragm during inspiration as opposed to using all inspiratory muscles. We aimed to determine if middle cerebral artery velocity (MCAv), a surrogate for global CBF, was affected by inspiratory muscle metaboreflex, and if so, if MCAv is affected differently when targeting diaphragmatic pressure (PTL-diaphragm; PTL di ) vs targeting mouth pressure (PTL-mouth; PTL mo ). We hypothesized that MCAv will be preserved with fatiguing inspiratory work, in both PTL di and PTL mo breathing patterns. Methods: We studied 11 (5 females) participants without any cardiorespiratory, metabolic, or musculoskeletal diseases (36±9 yrs, FEV 1 /FVC: 100±8%predicted). Each participant had gastric and esophageal balloon catheters placed to measure respiratory pressures. Blood pressure was continuously recorded via finger photoplethysmography. Transcranial doppler ultrasound continuously recorded MCAv. Participants performed breathing trials through a custom-built inspiratory pressure loading (IPTL) device, designed to open when negative pressure was generated. Each trial was comprised of 15 breaths/minute, with each breath consisting of 70% inspiration and 30% expiration. Trial 1 involved 5 minutes of PTL mo targeting 60% of their maximal inspiratory pressure, and trial 2 consisted of 5 minutes of PTL di targeting 60% transdiaphragmatic pressure. CO 2 was administered during IPTL to avoid hypocapnia. Cerebrovascular conductance index (CVCi) was calculated from MCAv. A paired t-test compared the 2 trials, deltas are calculated from end task to baseline, and data are reported as mean±SD. Results: The transdiaphragmatic pressures (PTP di ) between the two trials were different (PTL mo : 5,051±2,620, PTL di : 7,082±2,200 cmH 2 O·s/min; p=0.009). The change inMAP were not different between trials (PTL mo : 8±4, PTL di : 13±9 ΔmmHg; p=0.10). There was no difference in the change in MCAv (PTL mo : 10.07±21.51, PTL di : 9.66±22.10 Δcm/s; p=0.96) or CVCi (PTL mo : 0.03±0.23, PTL di : -0.01±0.17 Δcm/s/mmHg; p=0.55) between the two trials. Conclusion: These findings suggest that the inspiratory muscle metaboreflex does not impair CBF regulation during IPTL; this is true regardless of inspiratory muscle recruitment. Further work should focus on continuing the breathing exercises until exhaustion. NIH (HL139854); NSERC (PDF-577750-2023) This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.