An introduction to ventilatory modes and monitoring, including a novel application of electrical impedance tomography: With a focus on respiratory mechanics and physiology in cattle

Olivia A Brabant

Ventilation is key to life, coupled with perfusion it is the mainstay of homeostasis. As veterinarians we study the complexities of ventilation with the aim of understanding the physiological process in order to be able to define normal and abnormal. Research into respiratory mechanics using spirometry devices has largely been limited to more manageable species such as dogs, cats and more recently horses. Knowledge and experience in cattle is deficient. Improving knowledge of respiratory mechanics is the foundation for further research into novel applications of technology designed to improve disease detection in cattle. Cattle are an important global commodity as a food source and product for trade with the dairy and beef industries being valued at $871 and $897.5 billion US in 2021, respectively (Shahbandeh, 2019, Shahbandeh, 2022). With consumption increasing and many countries reliant on the cattle industry for food and trade, efficient production is fundamental. Respiratory disease is the single greatest health risk to cattle in both the dairy and beef sectors. It is estimated to cost the feedlot industry $40 AUS million in Australia and $800-$900 US million in the United States of America annually (CSIRO, 2023, Spadaro, 2022). Cattle health and welfare with a focus on zoonotic Tuberculosis has been highlighted as an area of global concern, with investments into disease reduction and eradication being amongst the global targets set by the World Health Organisation (WHO, 2018). To achieve these targets research into new technologies to monitor lung function and combat disease are needed. Electrical impedance tomography (EIT) allows non-invasive, radiation free, real-time imaging of the lung, providing a visual representation of ventilation, where an electrode belt is placed around the thorax of the patient and a small current is emitted and registered by the electrodes. The recorded signals are impedance changes that are reconstructed to provide a cross section through the thorax of ventilation and perfusion, visible as real-time moving images. First described in 1978 by Henderson and Webster, EIT was used for thoracic measurements in human medicine (Henderson and Webster, 1978). Electrical impedance tomography has since developed into perfusion, brain/neural, mammary tissue and gastric emptying monitoring (Frerichs et al., 2017, Adler and Holder, 2021a, Cherepenin V et al., 2001, Kim et al., 1983, Avill et al., 1987). More recently, this imaging modality has migrated into the veterinary field (Schramel et al., 2012, Mosing et al., 2018a, Meira et al., 2018, Mosing et al., 2018b). The real-time ability to monitor ventilation lends itself to ventilation monitoring in cattle without the need for chemical restraint or large and inaccessible equipment, such as computed tomography (CT) or magnetic resonance imaging (MRI). There is scope with this imaging modality to develop novel applications that could be clinically useful for diagnosis of pathologies within the lung. The objectives of this thesis were to provide an anatomically correct finite element model allowing accurate analysis of the data, validate the use of EIT in cattle, improve the robustness of the electrode belt design to obtain measurements, and expand the current knowledge to explore the possibility of pathology diagnosis for respiratory disease in cattle...

An introduction to ventilatory modes and monitoring, including a novel application of electrical impedance tomography: With a focus on respiratory mechanics and physiology in cattle

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