Developmental changes in infant heart rate responses to head-up tilting.

AIM

Newborn infants produce significant heart rate responses to both head-up and head-down tilting: heart rate increases with head-up tilting and decreases with head-down tilting. However, previously we found that, at 2-4 mo of age, heart rate increases were no longer significant following slow head-up tilting. This study was designed to determine if 2-4-mo-old infants have significant increases in heart rate when tilted rapidly.

METHODS

Fifty-four infants were tested as newborns or at 2-4 mo of age. Heart rate was measured while infants were tilted to a 30 degrees head-up angle either slowly over a period of 30 s or rapidly in 5 s.

RESULTS

Newborns exhibited increases in heart rate using both tilt speeds; however, at 2-4 mo of age, heart rate did not change significantly using either speed of tilting.

CONCLUSION

There are significant early developmental changes in cardiac responses to hypotensive challenge. Newborns react like adults, mounting sustained increases in heart rate in response to head-up tilting, but at 2-4 mo of age sustained heart rate responses are no longer significant. Tilt tests may provide a standardized method for assessing autonomic competence during the period of maximum vulnerability to sudden infant death syndrome.