Pulmonary 129Xe Magnetic Resonance Gas-exchange Abnormalities in Moderate-Severe Asthma

Abstract

BACKGROUND: Asthma is recognized as an inflammatory disease of the airways, but inflammation may also affect the parenchyma and pulmonary vasculature. Hyperpolarized ¹²⁹Xe MRI and MR spectroscopy (MRS) provide a way to quantify the transfer of gas from the airways through the alveolar membrane and its binding to hemoglobin in the red blood cells (RBC) of the pulmonary microvasculature. The vast majority of ¹²⁹Xe MRS studies have investigated interstitial lung disease and the ratio of ¹²⁹Xe binding to the RBC and ¹²⁹Xe present in the alveolar membrane, (RBC:membrane) which is a surrogate of oxygen gas-transfer to the blood. We wondered if ¹²⁹Xe RBC:membrane would differ in asthma patients as compared to healthy volunteers because of recent work showing abnormally diminished pulmonary vascular small-vessel structure in severe- asthma. RESEARCH QUESTION: Do ¹²⁹Xe MRI gas-transfer measurements differ significantly in patients with moderate-severe asthma? STUDY DESIGN AND METHODS: In this retrospective study, healthy (NCT02484885) and asthma (NCT04651777; NCT02351141) participants were evaluated who provided written informed consent. RESULTS: Thirty-one participants with asthma (mean age=55 years ± 18; 22 females) and 32 healthy volunteers (mean age=31 years ± 14; 12 females) with ¹²⁹Xe MRS were evaluated. FEV1, VDP and DLCO/KCO were significantly different in asthma compared to healthy participants. Age-corrected 1RBC:membrane was significantly different in moderate-severe asthma (0.32±0.09) as compared to healthy participants (0.47±0.12, P=.01). RBC:membrane was significantly related to pulse-oximetry hemoglobin estimates (ρ=.29; P=.04) and DLCO (ρ=.71; P<.001). Significant relationships between ¹²⁹Xe RBC:membrane and age were observed in healthy (ρ=-.55; P=.002) and asthma participants (ρ=-0.49; P=.006), adjusted for sex. A significant ANCOVA model also revealed the influence of age (P=.002), sex (P<.001), hemoglobin (P=.003) and asthma status (P=.02) on RBC:membrane. INTERPRETATION: ¹²⁹Xe RBC:membrane values were significantly different in moderate-severe asthma compared to healthy volunteers and were explained by age, sex, hemoglobin, and asthma status.