Ventilation-perfusion heterogeneity measured by the multiple inert gas elimination technique is minimally affected by intermittent breathing of 100% O2.

Ann R Elliott,Peter D Wagner,Jeremy E Orr,Beni Pazár,Abhilash S Kizhakke Puliyakote,Rui C Sá,Susan R Hopkins,Vincent Tedjasaputra,G Kim Prisk,Harrieth Wagner

doi:10.14814/phy2.14488

Ann R Elliott, Peter D Wagner + Show 8 more

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https://doi.org/10.14814/phy2.14488

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Journal: Physiological Reports	Publication Date: Jul 1, 2020
Citations: 4	License type: CC BY 4.0

Affiliation: University of California, San Diego

Abstract

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 FIO2‐dependent manner. Specific ventilation imaging data are acquired during five wash‐in/wash‐out cycles of breathing 21% O2 alternating with 100% O2 over ~20 min. This technique assumes that alternating FIO2 does not affect V˙A/Q˙ heterogeneity, but this is unproven. We tested the hypothesis that alternating FIO2 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.

Highlights

Many lung diseases are characterized by an increase in ventilation–perfusion (V A∕Q ) mismatch, which impairs pulmonary gas exchange
We evaluated the effect of an emulated specific ventilation imaging (SVI) oxygen consumption (O2) breathing protocol on V A∕Qheterogeneity in nine subjects with a clinical diagnosis of COPD
V O2 and respiratory exchange ratio were not calculated at the end of the emulated SVI (eSVI) because O2 consumption cannot be accurately measured during 100% O2 breathing

Summary

Introduction

Many lung diseases are characterized by an increase in ventilation–perfusion (V A∕Q ) mismatch, which impairs pulmonary gas exchange. Our laboratory has developed a proton magnetic resonance imaging (MRI) technique, to measure regional ventilation-perfusion mismatch, which combines specific ventilation imaging (SVI) with proton density (Holverda et al, 2011; Theilmann et al, 2009) and perfusion (Bolar et al, 2006) images to give regional V A∕Qratios (Henderson et al, 2013; Sá et al, 2017). Oxygen is paramagnetic; by breathing 100% O2 and using an appropriate magnetic resonance sequence, inhaled O2 is used as an MRI contrast agent (Sá et al, 2010, 2014). By analyzing the time course of the change in MR signal intensity on a voxel by voxel basis, a specific ventilation map is constructed (Sá et al, 2010, 2014), and combined with density and perfusion measures

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