Preterm infant weight gain is increased by massage therapy and exercise via different underlying mechanisms
Introduction
Prematurity is among the leading causes of infant morbidity [1]. Supplementary stimulation programs in the NICU including massage therapy (moderate pressure stroking) and exercise (passively moving the limbs into flexion and extension) can improve preterm infant development, including increased weight gain [2], [3]. Inasmuch as most preterm infant massage studies have combined tactile (massage) and kinesthetic (exercise) stimulation, it is unclear whether the tactile or the kinesthetic component is responsible for the increased weight gain observed in these studies.
Preterm infants receiving a combined tactile–kinesthetic stimulation protocol show increased weight gain [2], [4]. Similarly, studies utilizing either only kinesthetic stimulation [3], [5] or only tactile stimulation [6] have shown increased weight gain, suggesting that both the tactile and kinesthetic components are effective by themselves in promoting preterm infant weight gain.
A potential mechanism underlying preterm infant weight gain following tactile–kinesthetic stimulation may involve the stimulation of baroreceptors and mechanoreceptors leading to the activation of vagal afferent and efferent pathways involved in the parasympathetic control of the cardiovascular and gastro-intestinal systems [7], [8]. This mechanism is supported by studies revealing that a combined tactile/kinesthetic stimulation protocol elicits increases in cardiac vagal activity that are associated with increased gastric motility and preterm infant weight gain [7], [8], [9]. Tactile and kinesthetic stimulation may promote preterm infant weight gain via different underlying mechanisms. While preterm infant cardiac vagal activity has yet to be assessed independently for kinesthetic and tactile stimulation, studies with adults suggest that passive exercise, which is similar to the kinesthetic stimulation protocol used with preterm infants, inhibits cardiac vagal activity [10], [11], while moderate pressure massage therapy, which is analogous to the tactile stimulation protocol used with preterm infants, increases cardiac vagal activity [12]. The aim of this study was to compare the effects of the tactile and the kinesthetic stimulation protocols on preterm infant weight gain while exploring cardiac vagal activity as a potential underlying mechanism.
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Participants
Following institutional review board approval and parental informed consent, medically stable preterm neonates were recruited from a neonatal intensive care unit. Preterm infants were considered eligible for recruitment if: a) their gestational age (GA) at birth was between 28 and 32 weeks; b) their birth weight was between 800 and 1400 g; c) their NICU stay at study entry was 15–60 days; and d) their weight at study entry was between 1000 and 1500 g. Preterm infants were excluded if: a) they had
Results
Maternal and neonatal demographic and study entry characteristics did not differ between groups (Table 1). Group (Tactile vs Kinesthetic) × Time (Baseline/Post Treatment) repeated measures analyses of variance conducted on study outcome variables revealed the following: a) Weight Gain (g/day): a significant main effect for time, F (1, 28) = 9.95; p < .005; η2 = .26, but no Group by Time interaction or main effect for Group, suggesting a significant increase in weight gain for both the tactile and
Discussion
Preterm infants who received three, 10-min sessions of either tactile or kinesthetic stimulation per day, exhibited greater weight gain during the 5-day treatment period than during baseline. These findings are consistent with research documenting that both kinesthetic [3], [5] and tactile stimulation [6] are effective for promoting weight gain in preterm infants. In the present study, weight gain did not differ between infants who received tactile and kinesthetic stimulation. To our knowledge,
Conflict of interest
There was no conflict of interest, real or perceived for any of the authors and the aforementioned sponsors did not influence in any way the (1) study design; (2) the collection, analysis, and interpretation of data; (3) the writing of the report; and (4) the decision to submit the paper for publication.
Acknowledgments
We thank the mothers and neonates who participated in this study and the Jackson Memorial NICU nurses and neonatologists, research assistants and massage therapists for their help with this study. This research was supported by NIH Senior Research Scientist Awards (MH00331 and AT001585) and an NCCAM Research Grant (AT00370) to Tiffany Field, an NCCAM Research Supplement (AT00370-02S1) to Miguel Diego and funding from Johnson and Johnson Pediatric Institute to the Touch Research Institute.
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