Early detection of pulmonary dysfunction in the horse - an introduction

Abstract

2 SummaryEquine pulmonary function testing has long focused on horses with clinical signs of recurrent airway obstruction (RAO). The most widely used method is based on esophageal balloon pressure and pneumotachograph measurements. The disadvantages of this traditional pulmonary function test are its invasiveness, considerable cost and lack of sensitivity: airway obstruction can only be detected and measured, once it has become relatively severe and is clinically apparent. Volumetric capnography, on the other hand, is an effort-independent method of pulmonary function testing, which promises superior characteristics and performance. The goal of the work was to validate this method by the use of ultrasonic spirometry and capnography in the awake, spontaneous breathing horse. Recurrent airway obstruction (RAO), also known as heaves, is a form of the syndrome known as equine chronic obstructive pulmonary disease (COPD) and is a hypersensitivity to the dust, molds, mites and spores in the environment of a susceptible horse (Marti et al. 1991; Halliwell et al. 1993). It is now clear that equine 'heaves' is characterized by reversible airway constriction that is due to bronchospasm apart from mucous swelling and secretion. In this regard, it more closely resembles human asthma than human COPD, which is a progressive disease with little reversibility that is usually related to smoking.Recurrent airway obstruction plays a crucial role in equine medicine. In a study of Swiss and German horses, in which the diagnosis was based on abnormal lung sounds, and the presence of airway secretions containing neutrophils, the incidence of lower airway disease was 54 %, respectively 52 % (Bracher et al. 1991, Herholz 1993.The main lesion of RAO in horses is bronchiolitis characterized by diffuse epithelial hyperplasia, mucus plugging of airways and neutrophilic, lymphocytic and plasmacytic infiltrates and hypertrophy of bronchiolar musculature (Thurlbeck and Lowell 1964; Gerber 1973, Robinson et al. 1996. In many instances the onset of disease is insidious and the owner is unaware of exactly when clinical signs started (Herholz 1993).Clinical signs range from intolerance to exercise in the performance horse to expiratory dyspnoea, chronic purulent nasal discharge, cough and weight loss in the chronic respiratory patient.From a functional point of view, respiratory diseases exert their main deleterious effect through factors that alter ventilation to perfusion (VA/Q) ratios throughout the lung. The VA/Q matching of the lung is known to be vital to ensure efficient gas exchange and oxygenation of all body systems. A widening of the range of VA/Q ratios is associated with an increase in the number of alveoli which are either overventilated or underventilated with respect to their perfusion and diffusion capacity. The differences may be evenly distributed throughout the lung or confined to individual lobes and segments. VA/Q disturbances may occur long before clinical manifestations of respiratory disease appear.Objective quantification...

Equine Asthma: Current Understanding and Future Directions

“…With a significantly impaired expiratory airflow, part of the air that reaches the alveoli remains trapped. This leads horses with severe EA in exacerbation to breath at increasing lung volumes [functional residual capacity (102)] in the attempt to maintain airway patency, which causes lung hyperinflation and enlarged fields of thoracic auscultation (103).…”

Recurrent airway obstruction: A review

“…However, despite providing an objective measure of airway mechanics, these traditional methods have the disadvantages of being relatively expensive and invasive, necessitating the measurement of either intraoesophageal or intrapleural pressures. Furthermore, the sensitivity of these methods is relatively poor as changes consistent with the presence of airway obstruction are generally evident only when relatively severe and often clinically apparent . Consequently, alternative more sensitive methods have been evaluated in recent years.…”