Syndrome X and hyperventilation

Cardiovascular syndromes X, endothelial dysfunction and insulin resistance

Cardiac Syndrome X (microvascular angina) and the more recently described metabolic Syndrome X (an epidemiological association between insulin resistance and atheroma, dyslipidaemia, and hypertension) may have more in common than the chance of their common sobriquet, in view of evidence that microvascular angina too is characterised by insulin resistance and endothelial dysfunction. The implications are discussed.

Hyperventilation test in syndrome X

The hyperventilation (HV) test has been extensively used in different forms of coronary artery disease. The purpose of this work was to investigate the response to HV in patients with syndrome X and compare HV with exercise (EX) test. The authors studied 20 patients with syndrome X (angina, a positive EX test, and normal coronary angiogram) and 20 healthy subjects who underwent HV and EX tests. In 7 patients, all women, angina and electrocardiographic (ECG) changes occurred during HV but in none of the controls. Patients with syndrome X and controls had a similar rate-pressure product (RPP) at rest and achieved a similar RPP with HV. The RPP achieved with HV in patients with syndrome X without ECG changes was significantly lower, 121.8 +/-29.1(mean +/-SD), than what was achieved by those with changes, 167.9 +/-42.9, P < 0.01. In patients with an abnormal response to HV the RPP at which angina and ECG changes occurred was similar to that where similar changes were observed during EX. There was a significant correlation of the RPPs between the two tests, r=0.82, P < 0.02. In contrast, in patients in whom no angina or ECG changes occurred, the RPP they achieved with HV was significantly lower than the anginal threshold during EX 204 +/- 47.4, P < 0.0001. In conclusion, a significant proportion of patients with syndrome X, mainly women, who achieve a high RPP with HV, develop angina and ECG changes during overbreathing. The close relation between EX and HV RPPs where these changes occur suggests an increased myocardial oxygen demand as the most likely underlying mechanism for this behavior.

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 VO2) in patients with MA, the anaerobic threshold was reduced (41.6 +/- 5.82; P < 0.02) although still within accepted normal limits. Maximal (symptom limited) oxygen consumption, as a percentage of predicted, was reduced 60.73 +/- 16.51 compared to 87.21 +/- 5.2 (P < 0.003). The ventilatory response (VE/VCO2 l l-1 CO2 output) was significantly increased in the MA patients compared to controls (35.9 +/- 8.01 and 27.5 +/- 3.08, respectively; P < 0.02).(ABSTRACT TRUNCATED AT 250 WORDS)