Humming is probably more effective than speech for improving mothers' cardiorespiratory function and infants' self-regulation. We intend to understand the effects of (1) maternal humming vs. speech on preterm infants' physiological parameters, (2) maternal humming vs. speech on mothers' physiological parameters, and (3) humming melodic contours and the process of the lengthening of the final note on preterm infants' physiological parameters. This study was designed as a single-group repeated measures study, using microanalytical methodology (ELAN software version 4.9.4), with a protocol (silent baseline/speech, humming/silence/humming, or speech/silence) applied to preterm dyads (N = 36). Audio and video observations were recorded. Infants' and mothers' heart rates (HR) and O2 saturations were observed once a minute. The proportion of O2 saturation relative to HR (Prop. O2 saturation/HR) was estimated for both partners during the protocol. We found that the infants' HR mean was significantly lower during humming (p = 0.028), while a significantly higher Prop. O2 saturation/HR ratio was recorded during humming for infants (p = 0.027) and mothers (p = 0.029). The duration of sinusoidal contours, together with the lengthening of the final note, predicts infants' Prop. O2 saturation/HR ratio. Musical features of humming seem to improve the physiological stability of preterm infants during kangaroo care.
Keywords: kangaroo care; maternal humming; melodic contours; physiological parameters; preterm dyads.