Pulmonary gas exchange correlated to clinical signs and lung pathology in horses with chronic bronchiolitis

Abstract

Summary Eight horses (mean weight 438 kg) with chronic obstructive pulmonary disease (COPD) were studied for clinical signs, ventilation/perfusion relationships (V̇A/Q̇) and lung morphology. Four horses were killed and necropsied after the study. In horses with COPD, minute ventilation was almost twice as high as normal, whereas PaO2 was significantly decreased. Cardiac output was normal, but pulmonary artery pressure and pulmonary vascular resistance were significantly increased. The V̇A/Q̇ distribution was abnormal with an increased scatter of V̇A/Q̇ ratios. However, shunt (V̇A/Q̇=0) was increased in one horse only. Ventilation of dead space and high V̇A/Q̇ regions (V̇A/Q̇>10) were increased markedly and comprised 74 per cent of minute ventilation. On lung biopsy, all horses showed chronic bronchiolitis with epithelial hyperplasia and metaplasia. Diffuse acinar hyperinflation also was evident at necropsy. There was a significant inverse correlation between the respiratory rate and the fractional ventilation of normal V̇A/Q̇ regions. Also, there was a significant agreement between the extent of bronchiolar epithelial hyperplasia in necropsy specimens of lungs and the degree of ventilation of high V̇A/Q̇ regions and dead space. The findings suggest that hyperinflation of the lung due to obstructed airways may be the common denominator of increased ventilation of high V̇A/Q̇ regions and dead space ventilation and of elevated pulmonary artery pressure in horses with COPD from chronic bronchiolitis.

Evaluation of a Thoracoscopic Technique Using Ligating Loops to Obtain Large Lung Biopsies in Standing Healthy and Heaves‐Affected Horses

“…32 Heaves-affected horses in crisis, also had a significant decrease in PaO 2 at baseline and during surgery compared with their baseline and surgical values when in remission. This finding is consistent with respiratory modifications related to the horses' condition, 5 where pulmonary exchange is not optimal and administration of intranasal O 2 could improve gas exchange 33 and increase tolerance to surgery. Six of 22 horses, including 4 heaves-affected horses, required intranasal O 2 administration (15 L/min) to increase PaO 2 and these horses subsequently maintained respiratory rate and PaO 2 within normal limits during surgery.…”

“…7 Despite these complications, biopsies were histologically representative of tissue and horse disease, including heaves also known as recurrent airway obstruction (RAO). 4,5,8 Thoracoscopic anatomy in standing horses, for diagnostic and therapeutic purposes, has been described. [10][11][12][13] Thoracoscopic lung biopsy technique using biopsy forceps has been used in several species 14,15 including horses 13 with harvested samples being representative of the patient's condition.…”

Pulmonary Blood Flow

“…Pulmonary hypertension has been identified in RAO-affected horses (Dixon 1978, Littlejohn & Bowles 1980, Nyman et al 1991a, Benamou et al 1998. Human patients may also develop pulmonary hypertension secondary to hypoventilation via the HPV mechanism.…”

Exercise‐induced pulmonary perfusion redistribution in heaves

“…Clinical signs that include expiratory dyspnoea and chronic cough are generally associated with exercise intolerance (Robinson et al 1996). In animals clinically affected by heaves, pulmonary artery hypertension has been reported under resting conditions (Dixon 1978;Nyman et al 1991). When kept in a low dust environment for weeks, 'heavey' horses enter in clinical remission therefore showing clinical, respiratory, haemodynamic and blood gas parameters similar to healthy animals (Robinson et al 1996;Vandenput et al 1997).…”