Abstract
[Porpose] It is reported that in neonatal period, the pulmonary vagal reflex may promote the oscillations of PP interval from after 1 month postnatal. However, the modulability of the atrioventricular (AV) conduction (PR interval) by respiratory vagal input is unclear in the low-birth-weight infants (LBWI). We attempted to evaluate what correlation and change of PP interval and PR interval variabilities in 0 day and 1month of age. [Methods] Sixteen preterm, LBWI (mean gestational age 33±1 weeks, mean birth weight 1380±110g) were evaluated. ECG, respiratory wave (RW) were recorded using the polygraph system. The frequency domain analysis of PP, PR interval and RW were carried out by FFT method. Power spectrum density was obtained from four frequency regions; low (LF:0.036∼0.146 Hz), high (HF:0.146∼0.390 Hz), total (TF:0.036∼2.000 Hz) and respiratory frequency (RSA). We compared the ratio (LF/HF, RSA/TF) of each intervals between 0 day and 1 month of age. Statistical analysis was performed. [Results] LF/HF of PP decreased in 1 month from day-old 0. Contrary, RSA/HF of PP significantly increased. LF/HF of PR also significantly increased in 1 month from day-old 0, whereas RSA/HF of PR remained statistically. [Conclusion] It is suggested that AV nodal conduction was dominated by non-respiratory related vagus nerve activity, and controlled by an autonomic regulation independent of sinus node after postnatal 1 month. [Jpn J Physiol 55 Suppl:S88 (2005)]
