Abstract. Patients with a hereditary myopathy with paroxysmal myoglobinuria were studied in the chronic state of the disease. They were characterized by muscle contractions of fairly normal strength and quite good endurance in exercise with small muscle groups, but a poor physical performance in exercise of some duration with large muscle groups. Several facts indicate that it was not muscular weakness, but the circulatory capacity that was a main factor limiting the physical working capacity in exercise of some duration with large muscle groups. The oxygen uptake was largely normal in relation to the work performed. However, even light exercise on a bicycle ergometer caused tachycardia (approaching maximum heart rate), a high cardiac output (approaching, for the size of the individual, maximum values in the normal range) and an abundant blood flow through the exercising legs. Thus, there were no signs of insufficient heart function, but the utilization of the oxygen of the blood in the exercising limbs was low. The concentration of lactate, and particularly of pyruvate, in the blood, and the lactate and pyruvate production increased more than in the controls for the slight work performed. During exercise the lactate/pyruvate ratio decreased and the calculated “excess of lactate” was negative, while it increased in normal subjects. After exercise the excess lactate was higher in the patients than in the controls. This indicates an abnormal muscle metabolism, probably a decreased capacity for pyruvate oxidation. It is suggested that a metabolic disturbance caused an abnormally large production of metabolites in the working muscles, resulting in muscular vessel dilatation by a local humoral effect. The muscles acted almost like a‐v shunts and, as a consequence, the patients had a hyperkinetic circulation, i.e. a low O2 uptake in relation to cardiac output, a low a‐v O2 difference for mixed venous blood and for the venous blood of the exercising limbs.
Abstract. The respiratory mechanics have been studied in nine patients with myasthenia gravis in the untreated state. Comparisons have been made with the findings in healthy controls. Although the patients mainly had moderate myasthenia gravis the maximum respiratory pressures as expressions of the respiratory muscle strength were significantly decreased. Vital capacity, functional residual capacity, total lung capacity and the dynamic lung volumes were also diminished. No mean changes in lung resistance or lung compliance were shown to exist in the group. The relative mean value of maximum expiratory pressure (PEmax) (the observed value in per cent of the predicted normal mean value) was lower than any other relative lung function variable. Thus the maximum inspiratory force (P1max), of paramount importance for the ventilatory capacity, was systematically less decreased than PEmax. Even after consideration of the effect of decreased respiratory muscle strength vital capacity, total lung capacity and functional residual capacity were still diminished. It is suggested that decreased physical activity might diminish these static lung volumes via a low thoracic compliance. The results also suggested another volume‐pressure relationship between vital capacity and P1max, as is found in control cases with normal muscular strength. Otherwise similar functional relationships were at hand. The decreased values of dynamic lung volumes in comparison with those predicted only from anthropometric variables could only be explained to a minor extent by the direct influence of decreased respiratory muscle strength. The differences were mainly mediated via changes in the vital capacity, which is dependent on the respiratory force available.
Abstract. The effects of anticholinesterase, and subsequently sympathomimetics, on respiratory mechanics have been studied in ten patients, with moderate to rather severe myasthenia gravis, one of them being studied separately. A systematic increase in lung resistance was first shown to occur. The latter seemed to increase with larger doses of anticholinesterase while sympathomimetics gave a return to the initial values. Subsequently, increases in the maximum respiratory pressures (P1max and PEmax), the static lung volumes with maximum inspiration included and all dynamic lung volumes were found. Considering the basic disease, the increases in respiratory forces were thought of causal importance for the increased lung volumes. Using the functional relationships found in the untreated state this could also be shown for the change in the vital capacity. For the dynamic lung volumes the changes in the forced inspiratory (FIV1.0) and expiratory volume (FEV1.0) were primarily mediated by this dimensional effect i.e. increase in vital capacity. The increase in maximum voluntary ventilation (MVV) was, however, dependent on the dimensional effect to about the same extent as on a more direct muscular effect on the ventilatory forces. These changes are in principle in agreement with existing conditions in healthy controls. The successive deterioration of the disease in one patient and varying degrees of medication made it possible to instructively illustrate both these mechanical interrelationships and important implications for a simultaneous slight airway obstructive disease when administering anticholinesterase. Thus, the present results indicate that the clinical improvement in myasthenia gravis reported in other studies after ephedrine medication may to a significant extent be explained by its sympathomimetic action on the smooth bronchial muscles.
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