The ®rst group (n 11) consisted of patients with progressive external ophthalmoplegia as the main symptom (PEO group). The defect in mitochondrial DNA analysis was multiple deletions. In the second group (n 5), the defect was a point mutation at codon 3243. Three patients in this group had major or minor clinical symptoms of MELAS syndrome (MELAS group). The third group (n 3) consisted of patients with a de®ciency of muscle phosphorylase enzyme (McArdle group). In the control group (n 15), no defects were found. During a maximum graded exercise test with a bicycle ergometer, ECG and ventilatory gases were monitored continuously and blood pressure and blood lactate samples were taken each increment of 20 W.The mean maximum working capacity was reduced in the MELAS and McArdle groups. The mean external working ef®ciency (W max /VO 2max ) was 17.1% in the MELAS group, 16.3% in the McArdle group, 21.4% in the PEO group and 22% in the control group. The mean maximum oxygen consumption (VO 2max , ml A1 kg A1 ) was 21.8 in the McArdle group (59% of reference value), 23.5 in the MELAS group (80%), 25.9 in the PEO group (72%) and 25.4 (83%) in the control group. The subjects in the MELAS group were smaller than the others. The mean respiratory quotient (RQ) reached 0.77 in the McArdle group, 1.02 in the PEO group, 0.99 in the MELAS group and 1.03 in the control group. In the McArdle group, blood lactate levels did not increase. Heart rate increased more intensively in the McArdle group. The ventilatory equivalent for CO 2 was higher in the MELAS and McArdle groups. The anaerobic threshold was lowest in the MELAS group.The changes in ventilatory gases and blood lactate in the McArdle group re¯ect the inability of these subjects to use glycogen as a fuel during exercise. The hyperkinetic circulatory adjustment in the McArdle group is in concordance with other studies. In more severe mitochondrial myopathies (MELAS), a typical feature is a more pronounced lactate production and an early anaerobic threshold. In addition, the external working capacity is reduced. The multiple deletions in mitochondrial DNA often affect only a small number of muscle cells. Although the small eyemoving muscles may exhibit symptoms, the large skeletal muscles maintain their working capacity. A graded exercise test with ventilatory gas analyses (spiroergometry) is a useful tool in evaluating the disorders of muscle metabolism.The pathophysiological mechanisms leading and maintaining essential hypertension have still not been established. There is clear evidence that autonomic nervous function is involved in the development of elevated blood pressure. Arterial baroreceptor re¯ex regulation has been shown to be reset and blunted in hypertension. If autonomic dysfunction is the maintaining mechanism in long-lasting essential hypertension, the level of autonomic control would be expected to differ in essential and secondary hypertension. The aim of this study was to examine how different types and severity of hypertension are associated with autonomic...

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