Pulmonary dysfunction and reduced exercise capacity in patients with myelomeningocele.

OBJECTIVE: To evaluate pulmonary function and exercise capacity in children with myelomeningocele. STUDY DESIGN: Prospective evaluation in a randomly selected cohort of 12 subjects (10 to 17 years of age) with myelomeningocele and 12 control subjects matched for age, sex, and arm span. METHODS: Spirometry, lung volumes, maximum respiratory pressures, maximum oxygen expenditure during arm ergometry, and anaerobic threshold were measured. RESULTS: Mean total lung capacity and fractional lung volumes were significantly lower in case subjects than control subjects. Eleven subjects (92%) had a reduced forced vital capacity; seven (58%) had restrictive disease as evidenced by reductions in total lung capacity with normal or increased forced expiratory volume in 1 second/forced vital capacity ratio. Nine subjects (75%) had respiratory muscle weakness as evidenced by reduced maximum respiratory pressures or a low maximum voluntary ventilation. Exercise capacity was reduced as evidenced by a lower maximum oxygen consumption at peak exercise (13.8 +/- 4.8 vs 21.3 +/- 7.5 ml/min per kilogram of body weight; p < 0.02) and a lower anaerobic threshold (12.4 +/- 5.1 vs 17.3 +/- 4.2 ml/min per kilogram; p < 0.01) than the control group. Though the majority of subjects with myelomeningocele had a significant degree of restrictive disease, respiratory muscle weakness, or both, only one subject had pulmonary symptoms during exercise. CONCLUSIONS: Though most subjects with myelomeningocele had a significant degree of restrictive lung disease, respiratory muscle weakness, or both, exercise capacity was mostly limited by arm weakness. Skeletal muscle weakness may mask the symptoms of an underlying pulmonary abnormality, which may not be evident unless a pathologic cause of increased ventilation is present. Pulmonary function testing is suggested to screen for these abnormalities.

Intact alpha-actinin molecules are needed for both the assembly of actin into the tails and the locomotion of Listeria monocytogenes inside infected cells.

After the infectious bacterium, Listeria monocytogenes, is phagocytosed by a host cell, it leaves the lysosome and recruits the host cell's cytoskeletal proteins to assemble a stationary tail composed primarily of actin filaments cross-linked with alpha-actinin. The continual recruitment of contractile proteins to the interface between the bacterium and the tail accompanies the propulsion of the bacterium ahead of the elongating tail. When a bacterium contacts the host cell membrane, it pushes out the membrane into an undulating tubular structure or filopodium that envelops the bacterium at the tip with the tail of cytoskeletal proteins behind it. Previous work has demonstrated that alpha-actinin can be cleaved into two proteolytic fragments whose microinjection into cells interferes with stress fiber integrity. Microinjection of the 53 kD alpha-actinin fragment into cells infected with Listeria monocytogenes, induces the loss of tails from bacteria and causes the bacteria to become stationary. Infected cells that possess filopodia when injected with the 53 kD fragment lose their filopodia. These results indicate that intact alpha-actinin molecules play an important role in the intracellular motility of Listeria, presumably by stabilizing the actin fibers in the stationary tails that are required for the bacteria to move forward. Fluorescently labeled vinculin associated with the tails when it was injected into infected cells. Talin antibody staining indicated that this protein, also, is present in the tails. These observations suggest that the tails share properties of attachment plaques normally present in the host cells. This model would explain the ability of the bacterium (1) to move within the cytoplasm and (2) to push out the surface of the cell to form a filopodium. The attachment plaque proteins, alpha-actinin, talin, and vinculin, may bind and stabilize the actin filaments as they polymerize behind the bacteria and additionally could also enable the tails to bind to the cell membrane in the filopodia.