Caregivers' physiological responses during toddler vaccinations: associations with psychological and behavioral responses.

Objective: This study investigated biological, psychological, and behavioral aspects of caregivers' responses to toddlers' pain-related distress by measuring caregivers' high-frequency heart rate variability (HRV) responses during toddler vaccination pain and examining associations with caregivers' behavioral responses and psychological stress.

Methods: Participants included caregiver-toddler dyads (N = 194) from a longitudinal cohort-sequential study who were observed during toddlers' 12-, 18-, or 24-month routine vaccinations. Changes in caregiver HRV were analyzed using growth curve modeling. Conditional growth curve models examined associations between caregiver HRV and caregivers' concurrent behavior and psychological stress.

Results: The unconditional growth curve model indicated a slight linear decrease in caregiver HRV (i.e., vagal withdrawal) across the 3 min post-needle (unstandardized B = -0.06, p = .049). In conditional growth curve models, higher levels of parenting stress were associated with less vagal withdrawal during the post-needle period (standardized B = 0.47, unstandardized B = 0.02, p = .003). Caregivers' behavioral responses (i.e., use of soothing and distress-promoting behaviors), state anxiety, and general anxiety symptomology were not significantly associated with HRV responses.

Conclusions: Caregiver parasympathetic nervous system activity levels changed minimally from baseline to post-needle and decreased slightly across the post-needle period. Caregivers' self-reported parenting stress was associated with their parasympathetic responses to the procedure. Findings support an improved understanding of the mechanisms underlying caregivers' responses to children's pain-related distress in a naturalistic setting.