Proton magnetic resonance (MR) imaging to quantify regional ventilation-perfusion ( V ˙ A / Q ˙ ) ratios combines specific ventilation imaging (SVI) and separate proton density and perfusion measures into a composite map. Specific ventilation imaging exploits the paramagnetic properties of O2 , which alters the local MR signal intensity, in an FI O2 -dependent manner. Specific ventilation imaging data are acquired during five wash-in/wash-out cycles of breathing 21% O2 alternating with 100% O2

more »

... ver ~20 min. This technique assumes that alternating FI O2 does not affect V ˙ A / Q ˙ heterogeneity, but this is unproven. We tested the hypothesis that alternating FI O2 exposure increases V ˙ A / Q ˙ mismatch in nine patients with abnormal pulmonary gas exchange and increased V ˙ A / Q ˙ mismatch using the multiple inert gas elimination technique (MIGET).The following data were acquired (a) breathing air (baseline), (b) breathing alternating air/100% O2 during an emulated-SVI protocol (eSVI), and (c) 20 min after ambient air breathing (recovery). MIGET heterogeneity indices of shunt, deadspace, ventilation versus V ˙ A / Q ˙ ratio, LogSD V ˙ , and perfusion versus V ˙ A / Q ˙ ratio, LogSD Q ˙ were calculated. LogSD V ˙ was not different between eSVI and baseline (1.04 ± 0.39 baseline, 1.05 ± 0.38 eSVI, p = .84); but was reduced compared to baseline during recovery (0.97 ± 0.39, p = .04). There was no significant difference in LogSD Q ˙ across conditions (0.81 ± 0.30 baseline, 0.79 ± 0.15 eSVI, 0.79 ± 0.20 recovery; p = .54); Deadspace was not significantly different (p = .54) but shunt showed a borderline increase during eSVI (1.0% ± 1.0 baseline, 2.6% ± 2.9 eSVI; p = .052) likely from altered hypoxic pulmonary vasoconstriction and/or absorption atelectasis. Intermittent breathing of 100% O2 does not substantially alter V ˙ A / Q ˙ matching and if SVI measurements are made after perfusion measurements, any potential effects will be minimized.