Orientation and motion-specific visual cortex responses in infants born preterm.

Orientation-specific cortical responses develop earlier in infancy than motion-specific responses. The maturation of orientation-reversal and direction-reversal visual evoked potentials was evaluated in 17 healthy, low risk, preterm infants (born <32 weeks gestation), compared with a group of 26 infants born at term. Both groups were studied at a corrected age of 2-4 months. The age function and magnitude of the orientation-reversal responses was similar in the two groups. Direction-reversal responses across the age range, however, were smaller in the preterm infants, suggesting a delayed maturation of motion processing. Reasons for the vulnerability of motion processing are discussed; the results may reflect anomalies of white matter development in preterm infants that are undetected by ultrasonography.

The variable component of lateral body sway during walking in young and older humans.

INTRODUCTION: Because sideways falls are common in elderly persons, we devised a method to measure variable lateral movements of the thorax with respect to foot position during normal walking. METHODS: Movements of the ankles and shoulders were measured during walking a distance of 9 m. Two age groups were studied: young (n = 17, 6 male, mean age 27.3 years) and older (n = 21, 13 male, mean age 72.7 years) people. During walking, the path followed in the horizontal plane by the midpoint between the two shoulders was compared to the line connecting successive positions of the ankles during stance. Lateral deviations between these two paths were divided into a regular component (average of about 30 strides) and a variable component (the difference between the deviation during each stride and the average). Lateral sway was also observed while standing with eyes open for 1 minute. RESULTS: The older group had more lateral movement during walking in the variable component (p =.006) and a nonsignificant trend (p =.054) in the same direction in the regular component. Eight of the older participants had a value for the variable component greater than the 95% confidence limit for the young participants. Only two of the older participants had a standing sway outside the confidence limit for the young participants. The variable component was associated with variability in stride width. DISCUSSION: The variable component of lateral sway during walking provides good discrimination between age groups, as does variability in step width. It remains to be seen whether these variables are different in fallers and nonfallers.

Venous obstruction in healthy limbs: a model for chronic compartment syndrome?

PURPOSE: Chronic exertional compartment syndrome (CECS) in the anterior tibial (AT) compartment is generally believed to be the result of reduced venous blood flow caused by restrictive compartments and increased intramuscular pressures. If this is so, then restricting venous flow in the muscles of healthy subjects during exercise should mimic CECS. METHODS: This hypothesis was tested in 10 control subjects (aged 19-41 yr, five males) with and without external venous occlusion induced by a sphygmomanometer cuff fitted just below the knee and inflated to 80 mm Hg. Twenty CECS patients (20-39 yr, 16 males) were studied without external occlusion. Subjects performed intermittent, isometric maximal voluntary contractions (MVC) of the AT for 20 min (1.6-s contractions, 0.5 duty cycle). MVC, tetanic force (2 s at 50 Hz), muscle thickness (ultrasound imaging), and pain were measured during exercise and 10 min of recovery. RESULTS: Venous occlusion in the controls induced greater pain, fatigue, and increase in muscle thickness (P < 0.01). Initially the patients fatigued more slowly than the occluded controls, but at the end of exercise, the fatigue and pain were similar in these two groups. The controls showed a greater increase in muscle size (P = 0.01). Recovery was similar in all three groups, although the size of the patients' muscles recovered rather more slowly. CONCLUSION: External venous occlusion of the AT muscles in control subjects induces changes very similar to those of CECS patients, although the different time courses indicate that different processes are involved. The AT compartment of CECS patients is capable of distension.

Chronic exertional compartment syndrome: muscle changes with isometric exercise.

UNLABELLED: Chronic exertional compartment syndrome (CECS) is a well-documented cause of lower leg pain in active individuals. The pathophysiology is unclear, although it is generally believed to be associated with increased intramuscular pressure, but there is very little information about muscle function in relation to the onset of pain. PURPOSE: To investigate strength, fatigue, and recovery of the anterior tibial muscles in CECS patients and healthy subjects during an isometric exercise protocol. METHODS: Twenty patients and 22 control subjects (mean age 27.6 yr and 33.0 yr, respectively) performed a 20-min isometric exercise protocol consisting of intermittent maximal voluntary contractions (MVC). Central fatigue was evaluated by comparing changes in electrically stimulated (2 s at 50 Hz) and voluntary contraction force before and during the exercise, and then throughout 10 min of recovery. Muscle size was measured by ultrasonography. Pain and cardiovascular parameters were also examined. RESULTS: The absolute MVC forces were similar, but MVC:body mass of the patients was lower (P < 0.05) as was the ratio of MVC to muscle cross-sectional area (P < 0.01). The extent of central and peripheral fatigue was similar in the two groups. The patients reported significantly higher levels of pain during exercise (P < 0.05 at 4 min) and after the first minute of recovery (P < 0.001). An 8% increase in muscle size after exercise was observed for both groups. There were no differences in the cardiovascular responses of the two groups. CONCLUSIONS: CECS patients were somewhat weaker than normal but fatigued at a similar rate during isometric exercise. Patients reported higher pain than controls despite comparable changes in muscle size, suggesting that abnormally tight fascia are not the main cause of CECS symptoms.