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Bird, Jordan Douglas

University of British Columbia

Current understanding of diaphragm blood flow (Q̇DIA) is almost exclusively informed by animal models with no viable method of routinely interrogating Q̇DIA in humans. We aimed to assess the feasibility, validity, and reliability of contrast-enhanced ultrasound (CEUS) as a means of quantifying Q̇DIA within the medial costal diaphragm of humans during graded inspiratory pressure threshold loading (ITL). We hypothesized that 1) Q̇DIA would linearly increase with respiratory muscle work and 2) that there would be good test-retest reliability and inter-observer reliability of CEUS as a measure of Q̇DIA. Quantitative CEUS perfusion imaging of the medial diaphragm was performed in sixteen healthy participants (10M/6F; Age 28±5 yrs; BMI 22.8 ± 2.0 kg/m2) at the 8-10th right intercostal space. Respiratory muscle work was modulated by four 5-minute bouts of ITL (baseline, stage 1, stage 2, stage 3). Nasogastric balloon catheters were used to collect transdiaphragmatic pressures and calculate diaphragmatic work. CEUS was performed during a constant-rate intravenous infusion of lipid-stabilized microbubbles during the last two minutes of each level of ITL. CEUS images were acquired after a destruction-replenishment sequence and time-intensity data was measured from regions of interest placed over the diaphragm to determine Q̇DIA. %MIP for baseline (BL), stage 1 (S1), stage 2 (S2), and stage 3 (S3) were 0.7 ± 0.4, 9.3 ± 0.4, 17.6 ± 0.4, and 25.2 ± 0.4%, respectively. Q̇DIA significantly increased with ITL (3.1 ± 3.1 vs, 6.9 ± 3.6 vs, 11.0 ± 4.9 vs, 13.5 ± 5.4 AU·s-1) at BL, S1, S2, and S3 (all P < 0.01). There was a reproducible linear relationship between Q̇DIA and diaphragmatic work from day-to-day. There was good-to-excellent test-retest (ICC = 0.86 [0.77, 0.92]; P < 0.0001) and inter-observer (ICC = 0.93 [0.90, 0.95]; P < 0.0001) reliability for Q̇DIA. Mean differences with 95% limits of agreements for Q̇DIA were 0.6 ± 6.1 AU·s⁻¹ and 0.1 ± 4.4 AU·s⁻¹ for test-retest and inter-observer reliability, respectively. These data demonstrate that CEUS-derived measurements of Q̇DIA have valid physiological underpinnings and are reliable day-to-day and observer-to-observer. CEUS appears to be a viable and minimally invasive method of assessing Q̇DIA in health humans.

Text

2024-09-01

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/85987

Health and Exercise Sciences

University of British Columbia

UBCO

http://creativecommons.org/licenses/by-nc-nd/4.0/