Entrainment of respiration to rocking in premature infants: coherence analysis.

Vestibular influences on breathing pattern were investigated in 18 premature infants in the neonatal intensive care nursery. Respiratory abdominal movements were recorded while the babies were manually rocked at varying rates between 30 and 60 cycles/min (cpm). Coherence spectra were estimated between the respiratory and rocker signals, and their magnitudes were evaluated at the rocking frequency, with coherence spectra > 0.85 indicative of strong entrainment to rocking. At least one incident of entrainment was seen in 15 of 18 infants, with 2:1 ratios (2 breaths/rocker cycle) occurring at rocking frequencies of 30-40 cpm (8 of 18 subjects) and 1:1 entrainment at rates of 42-50 cpm (5 of 18 subjects). More complex synchronization was observed in three infants, with patterns consisting of alternans between 2:1 and 3:2 ratios (5:3 entrainment). Infants > 35 wk postconceptional age exhibited greater coherence to rocking than infants < 35 wk (P < 0.01), indicating a maturational change in the reflex may occur. Results show that the natural stimulation of rocking a newborn provides a phasic input to its respiratory pattern generator that is capable of resetting the system's oscillation and entraining its rhythm.