Cristy Secombe

Objective: Data from two-plane electrical impedance tomography (EIT) can be reconstructed into various slices of functional lung images, allowing for more complete visualisation and assessment of lung physiology in health and disease. The aim of this study was to confirm the ability of 3d EIT to visualise normal lung anatomy and physiology at rest and during increased ventilation (represented by rebreathing).

Approach: Two-plane EIT data, using two electrode planes 20cm apart, were collected in 20 standing sedate horses at baseline (resting) conditions, and during rebreathing. EIT data were reconstructed into 3d EIT whereby tidal impedance variation (TIV), ventilated area, and right-left and ventral-dorsal centres of ventilation (CoVRL and CoVVD, respectively) were calculated in cranial, middle and caudal slices of lung, from data collected using the two planes of electrodes.

Main results: There was a significant interaction of time and slice for TIV (p < 0.0001) with TIV increasing during rebreathing in both caudal and middle slices. The ratio of right to left ventilated area was higher in the cranial slice, in comparison to the caudal slice (p = 0.0002). There were significant effects of time and slice on CoVVD whereby the cranial slice was more ventrally distributed than the caudal slice (p < 0.0009 for the interaction).

Significance: The distribution of ventilation in the three slices corresponds with topographical anatomy of the equine lung. This study confirms that 3d EIT can accurately represent lung anatomy and changes in ventilation distribution during rebreathing in standing sedate horses.

Background
The natural progression of equine glandular gastric disease (EGGD) in the absence of treatment has not yet been described in the literature, nor has the prevalence in a teaching herd population been reported.

Objectives
The aims of this study were to determine the prevalence of disease in a teaching population over the study period (2019–2021) and to observe the changes over time in disease severity of naturally occurring diseases (not experimentally induced) without medical intervention.

Methods
Twenty-one horses underwent an initial gastroscopy and a repeat gastroscopy between 14 and 731 days later. Gastroscopy data were graded quantitatively and described qualitatively. Prevalence and 95% confidence intervals (CI) were calculated. The changes over time were determined by comparing initial and repeat gastroscopies.

Results
The prevalence from initial, repeat and total number of gastroscopies was 62% (95% CI: 40.8–79.3), 71% (95% CI: 50.0–86.2) and 67% (95% CI: 51.6–79), respectively. The changes over time included worsening of disease in 29% of horses (95% CI: 13.8–50.0), improvement of disease to a lower grade in 24% (95% CI: 10.6–45.1), no change in grade in 38% (95% CI: 20.8–59.1), and complete resolution of disease to grade 0 in 10% (95% CI: 2.7–28.9).

Main limitations
Limitations included a maximum of two gastroscopies per horse given COVID-19 restrictions on data collection, and highly varied interval times between initial and repeat gastroscopies.

Conclusion
In conclusion, there is a high prevalence of disease in this teaching herd. The changes over time in naturally occurring diseases without medical intervention might include worsening, improvement, no change or resolution of disease.
Main limitations

Limitations included a maximum of two gastroscopies per horse given COVID-19 restrictions on data collection, and highly varied interval times between initial and repeat gastroscopies.

Conclusion
In conclusion, there is a high prevalence of disease in this teaching herd. The changes over time in naturally occurring diseases without medical intervention might include worsening, improvement, no change or resolution of disease.

The provision of veterinary services is essential to deliver animal health and welfare outcomes, but over the last several decades demand for veterinary services in animal production systems has broadly declined in Australia. Reduced demand is closely related to a decline in the size of the production animal veterinary workforce, and there is evidence that the percentage of veterinarians participating in the delivery of veterinary services to animal production systems has lessened. Reduced demand for veterinary services in the production animal sector is likely to be attributed to several factors, including challenges around widespread adoption of preventive veterinary services, improved self‐efficacy of producers through advancement of knowledge, and potential concern by producers over the role of veterinarians in production animal systems. Declining veterinary engagement results in increased risk at both the individual farm level (diminished expertise to deliver reactive and proactive veterinary services) and at a population level (increased biosecurity risk and risk to social licence to operate). The current environment and the community trust in the profession should be seen as an opportunity to develop and implement a strategy to halt and reverse the decline in demand for production animal veterinary services. Such a strategy will require significant and sustained collaboration between the veterinary profession, Industry and government.

Electrical impedance tomography (EIT) is a non-invasive real-time non-ionising imaging modality that has many applications. Since the first recorded use in 1978, the technology has become more widely used especially in human adult and neonatal critical care monitoring. Recently, there has been an increase in research on thoracic EIT in veterinary medicine. Real-time imaging of the thorax allows evaluation of ventilation distribution in anesthetised and conscious animals. As the technology becomes recognised in the veterinary community there is a need to standardize approaches to data collection, analysis, interpretation and nomenclature, ensuring comparison and repeatability between researchers and studies. A group of nineteen veterinarians and two biomedical engineers experienced in veterinary EIT were consulted and contributed to the preparation of this statement. The aim of this consensus is to provide an introduction to this imaging modality, to highlight clinical relevance and to include recommendations on how to effectively use thoracic EIT in veterinary species. Based on this, the consensus statement aims to address the need for a streamlined approach to veterinary thoracic EIT and includes: an introduction to the use of EIT in veterinary species, the technical background to creation of the functional images, a consensus from all contributing authors on the practical application and use of the technology, descriptions and interpretation of current available variables including appropriate statistical analysis, nomenclature recommended for consistency and future developments in thoracic EIT. The information provided in this consensus statement may benefit researchers and clinicians working within the field of veterinary thoracic EIT. We endeavor to inform future users of the benefits of this imaging modality and provide opportunities to further explore applications of this technology with regards to perfusion imaging and pathology diagnosis.

We identified and isolated a novel Hendra virus (HeV) variant not detected by routine testing from a horse in Queensland, Australia, that died from acute illness with signs consistent with HeV infection. Using whole-genome sequencing and phylogenetic analysis, we determined the variant had ≈83% nt identity with prototypic HeV. In silico and in vitro comparisons of the receptor-binding protein with prototypic HeV support that the human monoclonal antibody m102.4 used for postexposure prophylaxis and current equine vaccine will be effective against this variant. An updated quantitative PCR developed for routine surveillance resulted in subsequent case detection. Genetic sequence consistency with virus detected in grey-headed flying foxes suggests the variant circulates at least among this species. Studies are needed to determine infection kinetics, pathogenicity, reservoir-species associations, viral-host coevolution, and spillover dynamics for this virus. Surveillance and biosecurity practices should be updated to acknowledge HeV spillover risk across all regions frequented by flying foxes.

Electrical impedance tomography (EIT) provides clinically useful lung images; however, it would be an advantage to extract additional cardiovascular information from the data. The aim of this study was to evaluate if cardiac-related changes measured by EIT can be used to measure pulse rate (PR) under physiological as well as high and low blood pressure states in anaesthetised horses. Electrical impedance tomography data and PR from seven horses anaesthetised in dorsal recumbency were recorded over 1 min during mechanical ventilation and 1 min of apnoea. Data were collected at four measurement time points; before and during intravenous administration of nitroprusside and phenylephrine, respectively. Nine pixels, estimated to represent the heart, were chosen from the EIT image. A novel algorithm detected peaks of impedance change for these pixels over 10 s intervals. Concurrent PR measured using an invasive blood pressure trace, was recorded every 10 s. EIT- and pulse-rate data were compared using Bland-Altman assessment for multiple measurements on each horse. Overall, 288 paired datasets from six of seven horses were available for analysis. There was excellent agreement for baseline measurements, as well as during hypertension and hypotension, with a bias of −0.26 and lower and upper limit of agreement at −2.22 (95% confidence intervals [CI], −2.89 to −1.86) and 1.69 (95% CI, 1.34–2.36) beats per min, respectively. EIT can be used to evaluate PR using cardiac-related impedance changes. More work is required to determine bias that might occur in anaesthetised horses in other recumbencies or clinical situations.

Background Left-sided cardiac volume overload (LCVO) can cause fluid accumulation in lung tissue changing the distribution of ventilation, which can be evaluated by electrical impedance tomography (EIT). Objectives To describe and compare EIT variables in horses with naturally occurring compensated and decompensated LCVO and compare them to a healthy cohort. Animals Fourteen adult horses, including university teaching horses and clinical cases (healthy: 8; LCVO: 4 compensated, 2 decompensated). Methods In this prospective cohort study, EIT was used in standing, unsedated horses and analyzed for conventional variables, ventilated right (VAR) and left (VAL) lung area, linear-plane distribution variables (avg-max VΔZLine, VΔZLine), global peak flows, inhomogeneity factor, and estimated tidal volume. Horses with decompensated LCVO were assessed before and after administration of furosemide. Variables for healthy and LCVO-affected horses were compared using a Mann-Whitney test or unpaired t-test and observations from compensated and decompensated horses are reported. Results Compared to the healthy horses, the LCVO cohort had significantly less VAL (mean difference 3.02; 95% confidence interval .77-5.2; P = .02), more VAR (−1.13; −2.18 to −.08; P = .04), smaller avg-max VΔZLLine (2.54; 1.07-4.00; P = .003) and VΔZLLine (median difference 5.40; 1.71-9.09; P = .01). Observation of EIT alterations were reflected by clinical signs in horses with decompensated LCVO and after administration of furosemide. Conclusions and Clinical Importance EIT measurements of ventilation distribution showed less ventilation in the left lung of horses with LCVO and might be useful as an objective assessment of the ventilation effects of cardiogenic pulmonary disease in horses.

Background Electrical impedance tomography (EIT) generates images of the lungs based on impedance change and was able to detect changes in airflow after histamine challenge in horses. Objectives To confirm that EIT can detect histamine‐provoked changes in airflow and subsequent drug‐induced bronchodilatation. Novel EIT flow variables were developed and examined for changes in airflow. Methods Bronchoconstriction was induced using stepwise histamine bronchoprovocation in 17 healthy sedated horses. The EIT variables were recorded at baseline, after saline nebulization (control), at the histamine concentration causing bronchoconstriction (Cmax) and 2 and 10 minutes after albuterol (salbutamol) administration. Peak global inspiratory (PIFEIT) and peak expiratory EIT (PEFEIT) flow, slope of the global expiratory flow‐volume curve (FVslope), steepest FVslope over all pixels in the lung field, total impedance change (surrogate for tidal volume; VTEIT) and intercept on the expiratory FV curve normalized to VTEIT (FVintercept/VTEIT) were indexed to baseline and analyzed for a difference from the control, at Cmax, 2 and 10 minutes after albuterol. Multiple linear regression explored the explanation of the variance of Δflow, a validated variable to evaluate bronchoconstriction using all EIT variables. Results At Cmax, PIFEIT, PEFEIT, and FVslope significantly increased whereas FVintercept/VT decreased. All variables returned to baseline 10 minutes after albuterol. The VTEIT did not change. Multivariable investigation suggested 51% of Δflow variance was explained by a combination of PIFEIT and PEFEIT. Conclusions and Clinical Importance Changes in airflow during histamine challenge and subsequent albuterol administration could be detected by various EIT flow volume variables.

Paraoxonase-1 (PON-1) activity is a new inflammatory and oxidative marker. Technical effects and biological factors could affect the accuracy of PON-1 activity measurement. We investigated the effects of storage at different temperatures, repeated freeze–thaw cycles, interferences from hemolytic, lipemic, and icteric samples, and seasonal effects on PON-1 activity in horses. We evaluated 2 substrates with an automated spectrophotometer. Ten equine serum samples were stored under different conditions. Although storage at room (21°C) or refrigeration (4°C) temperature induced a statistically significant decrease (p < 0.05) in PON-1 activity, this is not diagnostically relevant. PON-1 activity in frozen samples (−20°C) was stable for short-term storage; diagnostically significant (p < 0.01) fluctuations were observed after 1 mo. Four repeated freeze–thaw cycles were assessed, and all cycles affected PON-1 activity (p < 0.01); however, this was diagnostically significant only after the 4th cycle. Hemolysis induced an overestimation of PON-1 activity; lipemia and hyperbilirubinemia did not change PON-1 activity. Thirty-four horses were sampled monthly for 1 y, and PON-1 activity was higher in autumn (p < 0.05) and winter (p < 0.05) than in spring and summer.

Background Electrical impedance tomography (EIT) generates thoracic impedance images of the lungs and has been used to assess ventilation in horses. This technique may have application in the detection of changes in airflow associated with equine asthma. Objectives The objective was to determine if histamine‐induced airflow changes observed with flowmetric plethysmography (Δflow) could also be explained using global and regional respiratory gas flow signals calculated from EIT signals. Study design Experimental in vivo study. Methods Six horses, sedated using detomidine were fitted with a thoracic EIT belt and flowmetric plethysmography hardware. Saline (baseline = BL) and increasing concentrations of histamine (C1‐4) were nebulised into the face mask until a change in breathing pattern was clinically confirmed and Δflow increased greater or equal to 50%. After nebulisation Δflow and EIT images were recorded over 3 minutes and peak global inspiratory (InFglobal) and expiratory (ExFglobal) flow as well as peak regional expiratory and inspiratory flow for the dorsal and the ventral area of the right and left lungs were evaluated. Delta flow, InFglobal and ExFglobal at subsequent concentrations were indexed to baseline (yi = Ci/BL−1). Indexed and nonindexed variables were evaluated for a difference from baseline at sequential histamine doses (time). Multiple linear regression assessment of variance in delta flow was also investigated. Results Consistent with histamine‐provoked increases in Δflow, the global flow indices increased significantly. A significant increase in regional inspiratory flow was seen in the right and left ventral lung and dorsal right lung. Multiple regression revealed that the variance in ExFglobal, and right and left ventral expiratory flow best explained the variance in Δflow (r2 = .82). Main limitations Low number of horses and horses were healthy. Conclusions Standardised changes in airflow during histamine challenge could be detected using EIT gas flow variables.