Comparison of electrical impedance tomography and spirometry-based measures of airflow in healthy adult horses

David P Byrne; Ben Keeshan; Giselle Hosgood; Andy Adler; Martina Mosing

doi:10.3389/fphys.2023.1164646

Comparison of electrical impedance tomography and spirometry-based measures of airflow in healthy adult horses

Front Physiol. 2023 Jul 5:14:1164646. doi: 10.3389/fphys.2023.1164646. eCollection 2023.

Authors

David P Byrne¹, Ben Keeshan², Giselle Hosgood¹, Andy Adler², Martina Mosing³

Affiliations

¹ School of Veterinary Medicine, Murdoch University, Perth, WA, Australia.
² Department of Systems and Computer Engineering, Carleton University, Ottawa, ON, Canada.
³ Anaesthesiology and Perioperative Intensive Care, Department for Companion Animals and Horses, University of Veterinary Medicine, Vienna, Austria.

Abstract

Electrical impedance tomography (EIT) is a non-invasive diagnostic tool for evaluating lung function. The objective of this study was to compare respiratory flow variables calculated from thoracic EIT measurements with corresponding spirometry variables. Ten healthy research horses were sedated and instrumented with spirometry via facemask and a single-plane EIT electrode belt around the thorax. Horses were exposed to sequentially increasing volumes of apparatus dead space between 1,000 and 8,500 mL, in 5-7 steps, to induce carbon dioxide rebreathing, until clinical hyperpnea or a tidal volume of 150% baseline was reached. A 2-min stabilization period followed by 2 minutes of data collection occurred at each timepoint. Peak inspiratory and expiratory flow, inspiratory and expiratory time, and expiratory nadir flow, defined as the lowest expiratory flow between the deceleration of flow of the first passive phase of expiration and the acceleration of flow of the second active phase of expiration were evaluated with EIT and spirometry. Breathing pattern was assessed based on the total impedance curve. Bland-Altman analysis was used to evaluate the agreement where perfect agreement was indicated by a ratio of EIT:spirometry of 1.0. The mean ratio (bias; expressed as a percentage difference from perfect agreement) and the 95% confidence interval of the bias are reported. There was good agreement between EIT-derived and spirometry-derived peak inspiratory [-15% (-46-32)] and expiratory [10% (-32-20)] flows and inspiratory [-6% (-25-18)] and expiratory [5% (-9-20)] times. Agreement for nadir flows was poor [-22% (-87-369)]. Sedated horses intermittently exhibited Cheyne-Stokes variant respiration, and a breath pattern with incomplete expiration in between breaths (crown-like breaths). Electrical impedance tomography can quantify airflow changes over increasing tidal volumes and changing breathing pattern when compared with spirometry in standing sedated horses.

Keywords: asthma; equine; expiratory; inspiratory; peak flow; plethysmography.

Grants and funding

Funding was provided by Murdoch University.