![]() ![]() The history and the physical examination are the most important features in helping distinguish between them. Distinguishing between potentialĬough may have many potential inciting causes. Might some dogs cough, not due to presence of pulmonary oedema, but due to the effects of left atrial enlargement as a result of mitral regurgitation compressing the bronchi (and thus exciting mechanoreceptor-mediated coughing)? One study specifically examining this failed to show an association between left atrial enlargement and bronchial collapse, and many dogs with bronchial collapse and left atrial enlargement have collapse (Singh et al., 2012) that is not just confined to the left-sided bronchi, suggesting more wide-spread bronchomalacia ( Figure 1). The dog had stage B2 mitral valve disease (cardiac enlargement but no congestive heart failure) and the cough was caused by generalised bronchomalacia and bronchial collapse ![]() Studies have shown that the presence of congestive heart failure is not significantly associated with coughing in dogs with MMVD, but that radiographic evidence of airway disease and left atrial enlargement is (Ferasin et al., 2013).įIGURE 1 Right lateral thoracic radiograph of a dog presenting with cough and a heart murmur. When patients with such murmurs present with cough, clinicians are presented with a diagnostic dilemma as to how relevant the finding of a heart murmur typical of MMVD may be. Thus, the typical busy small animal clinician will encounter many dogs with heart murmurs consistent with MMVD who will not be (and might never be within their lifetimes) in congestive heart failure. However, mitral valve disease is typically characterised by a very long pre-clinical period, and only a minority of patients with asymptomatic MMVD in most longitudinal studies progress to a point where symptoms of congestive heart failure develop. In one study, 24% of dogs aged nine to 12, and 37% of dogs aged 13 and over, were found to have murmurs consistent with MMVD (Detweiler and Patterson, 1965) and in some breeds, notably the Cavalier King Charles spaniel, prevalence in dogs older than eight years of age may become very high indeed. Heart murmurs consistent with MMVD may be identified in 3.54% of all dogs examined in UK first opinion clinics (Mattin et al., 2015), and the prevalence of heart murmurs in dogs, especially in small breed dogs, increases with age. The most common acquired cardiac disease associated with development of pulmonary oedema is myxomatous mitral valve disease (MMVD). However, in the majority of dogs with pulmonary oedema causing alveolar flooding, cough receptor excitation would not be an expected feature, with tachypnoea/hyperpnoea (‘breathlessness’) being a more consistent feature. ![]() The main cause of coughing therefore tends to be pathologies that either perform a mechanical or chemical irritant effect within the airways, though cough may also occur with parenchymal and pleural space disorders.Ĭardiogenic pulmonary oedema is often cited as a cause of cough, and indeed in those dogs presenting with fulminating pulmonary oedema with accumulation of large amounts of pink-tinged oedema fluid within larger airways, this may be a prominent clinical feature. Pulmonary C-fibres are considered sparse in small animal species. These receptors are primarily found in the large and transitional airways and are predominantly sensitive to mechanical stimulation, but also to chemical stimuli. The initiating cause of coughing is the activation of sensory receptors, which may be rapidly adapting (stretch) receptors (RARs) and augmented by bronchial C-fibres.
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