H-REFLEX

The H-reflex is present in both the upper extremity (median and ulnar) and lower extremity (with posterior tibial stimulation) in infancy. While the tibial H-reflex persists into adulthood, the upper extremity H-reflex responses are present in virtually all infants at birth and

become suppressed in most children over the course of the first year. Normal values for H-reflex latencies in children are shown in Table 6.7.

NEUROMUSCULAR TRANSMISSION

The NMJ shows less stability with repetitive nerve stimulation in normal newborns. At low rates of stimulation (1-2 Hz), no significant incremental or décrémentai changes in CMAP amplitude are observed (23). At higher

TABLE 6.5 NORMAL SNAP AMPLITUDES IN CHILDREN (nV)

MEDIAN (REF.)

ULNAR (REF.)

SURAL (REF.)

24-72 hours

6.76 ± 0.79 (D2-W) (12)

5.26 ± 0.57 (D5-W) (12)

5.29 ± 2.16 (6 cm) (12)

7 days-1 month

6.22 ± 1.30 (D2-W) (9) 4.86 ± 2.23 (D3-W) (10)

5.5 ± 3.1 (D5-W) (6)

9.12 ± 3.02 (4-8 cm) (9)

0-3 months

16.74 ± 1.47 (D2-W) (12)

7.83 ± 0.60 (D5-W) (12)

9.97 ± 1.24 (8 cm) (12)

4-6 months

17.72 ± 3.35 (D2-W) (12)

8.26 ± 1.00 (D5-W) (12)

13.58 ± 2.19 (8 cm) (12)

1-6 months

15.86 ± 5.18 (D2-W) (9) 10.66 ± 3.62 (D3-W) (13)

9.4 ± 3.2 (D5-W; 1-3 months) (6) 13.2 ± 3.23 (D5-W; 3-6 months) (6)

11.66 ± 3.57 (6-8 cm) (9)

6-12 months

16.00 ± 5.18 (D2-W) (9) 17.55 ± 1.70 (D2-W) (12) 9.00 ± 3.45 (D3-W) (13)

13.0 ± 5.6 (D5-W) (6) 10.87 ± 2.4 (D5-W)(12)

14.87 ± 4.67 (8 cm) (12)

1-2 years

24.00 ± 7.36 (D2-W) (9) 15.72 ± 4.50 (D3-W) (10)

16.3 ± 2.44 (D2-W) (6)

15.41 ± 9.98 (8-10 cm) (9)

1-3 years

19.51 ± 3.99 (D2-W) (12)

12.34 ± 2.1 (D5-W) (12)

18.02 ± 3.83 (8 cm) (12)

2-4 years

24.28 ± 5.49 (D2-W) (9) 12.02 ± 5.89 (D3-W) (10)

16.0 ± 3.6 (D5-W) (6)

23.27 ± 6.84 (8-10 cm) (9)

4-6 years

25.12 ± 5.22 (D2-W) (9) 19.78 ± 4.21 (D2-W) (12) 14.04 ± 5.99 (D3-W) (10)

14.2 ± 2.72 (D5-W) (6) 13.15 ± 3.6 (D5-W) (12)

22.66 ± 5.42 (8-10 cm) (9) 18.50 ± 3.89 (8 cm) (12)

6-14 years

26.72 ± 9.43 (9)

20.50 ± 3.49 (D2-W) (12)*

13.4 ± 4.2 (D5-W) (6) 14.30 ± 2.5 (D5-W) (12)*

26.75 ± 6.59 (9)

18.67 ± 4.39 (8 cm) (12)*

Data are presented as means ± standard deviation *Amplitudes determined from baseline to peak

Amplitudes are determined peak to peak from positive to negative peak of the SNAP unless otherwise noted

D-W = finger to wrist using ring electrodes with orthodromic stimulation

D2 = index finger for median; D3 = middle finger for median; D5 = fifth finger for ulnar

Sural nerve studies used antidromic stimulation with recording electrodes behind the lateral malleolus with stimulus delivered at 6 m to 14 cm above the malleolus as specified.

rates of stimulation (5-10 Hz), normal infants may show slight facilitation. Décrémentai responses averaging 24% have been reported at high rates of stimulation (20 Hz) in normal newborn infants. At 50 Hz stimulation, normal newborns may show decrements of the order of 50% (20). In general, décrémentai changes greater than 10% at low rates of stimulation (2-5 Hz) and facilitatory changes greater than 23% at high rates of stimulation (20-50 Hz) are felt to be significant in the post-term infant (24). Some authors have utilized high rates of stimulation of the order of 50 Hz for 10 seconds to document facilitation greater than 20% to 23% (at times, over 100% increments are observed) in infantile botulism (24-26).

microvolts to approximately 2,000 microvolts. Generally, MUAPs more than 1,000 microvolts in 0 to 3-year-old children are rare (27,28). In infants, MUAPs are usually biphasic or triphasic.

MOTOR UNIT DURATION

Infantile MUAPs are often shorter in duration. De Carmo (27) found newborn infants to exhibit durations 17% to 26% shorter than those seen in adults. Durations of MUAPs are often shorter than 5 msec in infants.

 
< Prev   CONTENTS   Next >