The effects of three models of airway disease on tidal breathing flow-volume loops of thoroughbred horses

Effects of a 15° Variation in Poll Flexion during Riding on the Respiratory Systems and Behaviour of High-Level Dressage and Show-Jumping Horses

From previous studies, the International Society for Equitation Science has advised that further research be conducted on the physiological/psychological effects of less-exacerbated poll flexion angles. We aimed to evaluate the effects of two riding poll flexion positions with a difference of only 15° on the respiratory systems and behaviour of horses through an evaluation of dynamic airway collapse via over-ground endoscopy, the pharyngeal diameter, pleural pressure, arterial oxygenation and lactate, HR/RR, and the occurrence of conflict behaviours. Twenty high-level dressage and twenty show-jumping horses underwent a 40 min ridden test at a ground angle of 85°; 3 weeks later, they underwent a ridden test at a 100° ground angle (the angle between the ground and the line from the forehead to the muzzle) and in a cross-over design. Using a mixed model for repeated measures, Wilcoxon/Friedman tests were carried out according to the experimental design and/or error normality. For both groups, at 100°, conflict behaviours and upper airway tract abnormalities were significantly more frequent, and the pleural pressure was higher, and the pharyngeal diameter was lower. At 85°, relaxation behaviours were significantly more frequent. Lactate was significantly higher at 100° only in the dressage horses. Compared to the first test at 85°, the HR/RR were significantly lower at the beginning of the second test (at 100°) but higher at the end. The significant differences identified in these dressage and show-jumping horses support the idea that an increase of just 15° in riding poll flexion can have negative effects on the respiratory system and behaviour of a horse and therefore on its welfare.

Can bronchoconstriction and bronchodilatation in horses be detected using electrical impedance tomography?

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.

Evaluation of histamine-provoked changes in airflow using electrical impedance tomography in horses

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 (InF_global ) and expiratory (ExF_global ) 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, InF_global and ExF_global at subsequent concentrations were indexed to baseline (y_i  = C_i /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 ExF_global , 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.

Physiology of equine performance and associated tests of function

This review addresses the physiology of performance horses in the context of functional tests aimed at assisting clinicians in the search for explanations of the individual's limitations, actual or perceived as below expectation. The intention is to assist clinicians who are faced frequently by owners or trainers seeking explanations for poor performance; and for research workers as a basis on which to proceed in their search for new methodologies, particularly those that can be applied in the field as for treadmill exercise. The review sets out fundamental physiological pathways, the entailment of which may represent a limiting factor to performance, while taking into account the individual's status, including anamnesis and the possibility of actual disease being present. Tests that assess the possible roles of several body systems, as causes of limited performance, are discussed. These systems include pulmonary, cardiovascular and neuromuscular systems. The evaluation of anaerobic and aerobic energy pathways is also discussed. Emphasis is given to the assessment of pulmonary ventilation by techniques such as spirometry and ergospirometry. These techniques are considered to be of particular potential for further development.

Effect of dorsal displacement of the soft palate on ventilation and airflow during high-intensity exercise

Dorsal displacement of the soft palate (DDSP) is one of the most common obstructive conditions of the upper respiratory tract in the racehorse. The present study was conducted to determine the effects of intermittent dorsal displacement of the soft palate (DDSP) on ventilation and respiratory airflow during high intensity exercise. Videoendoscopic recordings were made of the nasopharynx and larynx simultaneously with measurements of airflow and respiratory gas exchange, during high-speed treadmill exercise in 9 horses with confirmed intermittent DDSP admitted for clinical investigation of poor racing performance. In all horses, DDSP resulted in a reduction in minute ventilation (VE) (P<0.001), associated with a decrease in tidal volume (VT) (P<0.01) with no change in breathing frequency (f) and a reduction in oxygen consumption (VO2) (P<0.01). Further, DDSP resulted in reduction of expiratory flow parameters, including peak expiratory flow (PEF), EF50, EF25 and EF125 (P<0.01), with no alteration of inspiratory flow. These results confirm that naturally-occurring intermittent DDSP creates a flow-limiting expiratory obstruction. The associated impairment of athletic performance is probably caused, at least in part, by the accompanying decrease of oxygen uptake.