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Background: Feeding interventions for preterm infants aim to reduce the physiologic stress of feeding to promote growth. Heart rate variability (HRV) is a potential noninvasive measure of physiologic stress that may be useful for evaluating efficacy of feeding interventions.Purpose: To evaluate whether HRV is a sensitive measure of physiologic stress compared with standard physiologic outcomes in the context of a feeding intervention study.Methods: This was a secondary analysis of a within-subjects, cross-over design study comparing usual care feeding with a gentle, coregulated (CoReg) feeding approach in 14 infants born less than 35 weeks' postmenstrual age. HRV indices were calculated from electrocardiogram data and compared with standard physiologic outcomes, including oxygen saturation (Spo2), respiratory rate (RR), apnea, heart rate (HR), and bradycardia. Data were analyzed using linear mixed modeling.Results: Infants fed using the CoReg approach had fewer apneic events and higher RR, suggesting they were able to breathe more during feeding. No statistically significant differences were found in SpO2, HR, bradycardia, or high frequency power (the most commonly reported measure of HRV). Infants fed using the usual care approach had significantly higher SD12, a measure of HRV indicating randomness in the HR, which is a potential indicator of elevated stress.Implications For Practice: SD12 was more sensitive to stress than SpO2, HR, and bradycardia. The utility of HRV as a measure of feeding outcomes in clinical practice needs further exploration.Implications For Research: Further exploration of HRV as an intervention outcome measure is needed, particularly evaluating nonlinear indices, such as SD12. [ABSTRACT FROM AUTHOR]