Breathlessness in microvascular angina

In patients with microvascular angina (MA), there is some evidence from studies of plethysmography, that there are widespread microvascular abnormalities. In addition to exertional chest pain, all these patients complain of breathlessness, with no evidence of airways obstruction or resting left ventricular dysfunction. Progressive exercise testing was performed in 12 age and sex matched controls and 12 patients (three males), in whom the diagnosis of MA was established on the basis of exertional chest pain, abnormal thallium scans, and an attenuated myocardial flow response to a vasodilator challenge, with angiographically entirely normal epicardial vessels. Symptom limited exercise was performed with on line ventilation and expired gas analysis, measuring minute ventilation, oxygen consumption and carbon dioxide production and arterial blood gas values using a transcutaneous system. Anaerobic threshold was calculated by curve fitting a plot of oxygen consumption against carbon dioxide production. Compared to controls (49·7±7·3 sd % predicted maximum VO 2) in patients with MA, the anaerobic threshold was reduced (41·6±5·82; P