C108-13 Investigating the Physiological Variability in Xe Gas-exchange MRI Metrics Across the Menstrual Cycle in Healthy Women

Abstract Background Xenon gas-exchange MRI (Xe MRI) is increasingly used to characterize pulmonary physiology and monitor disease progression, such as asthma and cystic fibrosis. Pulmonary function is known to vary across the menstrual cycle, which may impact the diagnosis and management of pulmonary disorders in pre-menopausal women. However, normal cyclical variation in Xe MRI metrics remains uncharacterized. Understanding these patterns is essential for distinguishing physiological changes from pathology. We hypothesized that cyclical hormonal fluctuations may lead to phase-dependent variation in Xe MRI metrics across the menstrual cycle. Purpose To investigate variation in Xe MRI metrics across distinct phases of the menstrual cycle in healthy women. Methods Ten healthy women (mean age = 28±5 years; 6 on oral contraceptives) with regular cycles underwent Xe MRI, spirometry, diffusion-capacity testing, and hemoglobin (Hb) measurement during one menstrual cycle at menstrual (Cycle Day 3, CD3), ovulatory (CD14), and mid-luteal (CD21) phases. Xe MRI was performed during a ≤ 16-second 1L Xe gas breath-hold to generate images of alveolar ventilation, membrane-uptake (alveolar-capillary membrane 2σ of mean ventilation signal. Median values for each Xe MRI and PFT metrics were compared across the menstrual cycle using the Friedman test. Results VDP, RBC-transfer, and KCO each varied significantly across the menstrual cycle (all p 0.05). Median IQR VDP was higher at CD21 (1.2% 1.0–2.0) than CD3 (0.7% 0.5–0.8) and CD14 (0.6% 0.4–1.0); p = 0.027. Median RBC-transfer (a.u) decreased slightly at CD14 (3.43 × 10−3 3.0 × 10−3–4.55 × 10−3) compared to CD3 (3.81 × 10−3 3.20 × 10−3–4.70 × 10−3) and CD21 (4.20 × 10−3 3.1 × 10−3–4.65 × 10−3); p = 0.045 (Figure). Similarly, KCO decreased slightly at CD14 (CD14: 4.87 vs CD3: 5.29 vs CD21: 4.94 mL/min/mmHg/L; p = 0.049). Bonferroni-corrected post-hoc testing confirmed a significant VDP difference between CD14 and CD21 (p = 0.025); other pairwise comparisons were not significant. No significant differences were found in spirometry and Hb. Stratified by contraceptive use, non-oral contraceptive users (n = 4; 2 using progesterone intrauterine device; 2 using vaginal ring) demonstrated larger median %-increase from CD3 to CD21 in RBC-transfer (+17.5% 11 – 22.8) than oral contraceptive users (n = 6; −7.65% −15.6 – +4.4); p = 0.043, suggesting attenuated hormonal influence with contraceptive use. Conclusion Menstrual-cycle phase may influence Xe gas-exchange MRI. To better understand and distinguish cyclical variability from pathological Xe MRI changes in disease states, these preliminary findings warrant investigation in a larger cohort, with additional considerations for contraceptive types and use. This abstract is funded by: Cincinnati Children’s Research Foundation