Anti-acetylcholine receptor (AChR) antibody titers, toxin binding blocking antibody, functional activity of serum on rat myotube cultures, IgG subclasses, and clinical data were studied in relation to the onset of neonatal myasthenia gravis (NMG) in 30 children of myasthenic mothers. Fourteen had NMG, including 4 atypical cases. Anti-AChR antibody titer was the best indication of NMG onset. NMG in a previous baby was also predictive. Pattern of IgG subclasses, presence of toxin-binding blocking antibodies, and serum functional activity were less predictive, but cast light on the mechanism of anti-AChR antibody pathogenicity.

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The effects of breathing normoxic helium or argon gas mixture on the local muscular metabolism during exercise were compared to those of room air in four healthy subjects. For this purpose, PO2, PCO2, pH, the concentrations of lactate (LA), glucose (Gl) haemoglobin (Hb) and K+ and osmolarity were repeatedly measured in efferent muscular venous blood during 12 min of rhythmic forearm exercise and 16 min of recovery. The time courses and magnitude of the changes in PCO2, pH, [Gl], [Hb], [K+] and osmolarity during exercise and recovery were similar for breathing both the helium and argon gas mixtures. The main finding was that during exercise, the [LA] curve reached a peak value significantly higher by 25% under normoxic helium than under room air or normoxic argon breathing. This rise in [LA] was accompanied by a slight reduction in muscular venous PO2, too small to signify muscular hypoxia. The possibility that this decline in PO2 might be due to a shift in muscular metabolism towards lipid oxidation was confirmed by the lower muscular respiratory quotient observed during helium breathing. However, such a shift did not explain why [LA] rose during this breathing. The probable explanation is that helium facilitates LA diffusion out of the myocytes.