Charlene Krueger

A Comparison of the General Linear Mixed Model and Repeated Measures ANOVA Using a Dataset with Multiple Missing Data Points

Longitudinal methods are the methods of choice for researchers who view their phenomena of interest as dynamic. Although statistical methods have remained largely fixed in a linear view of biology and behavior, more recent methods, such as the general linear mixed model (mixed model), can be used to analyze dynamic phenomena that are often of interest to nurses. Two strengths of the mixed model are (1) the ability to accommodate missing data points often encountered in longitudinal datasets and (2) the ability to model nonlinear, individual characteristics. The purpose of this article is to demonstrate the advantages of using the mixed model for analyzing nonlinear, longitudinal datasets with multiple missing data points by comparing the mixed model to the widely used repeated measures ANOVA using an experimental set of data. The decision-making steps in analyzing the data using both the mixed model and the repeated measures ANOVA are described.

Elevated sound levels within a busy NICU.

Purpose: Elevated sound levels in the NICU may contribute to undesirable physiologic and behavioral effects in preterm infants. This study describes sound levels in a busy NICU in the southeastern U.S. and compares the findings with recommended NICU noise level standards. Design: NICU sound levels were recorded continuously at nine different locations within the NICU. Hourly measurements of loudness equivalent (Leq) sound level, sound level exceeded 10 percent of the time (L10), and maximum sound level (Lmax) were determined. Sample: Sound levels were sampled from nine different locations within the NICU. Main Outcome Variable: Sound levels are described using the hourly, A-weighted Leq, L10, and Lmax. Results: The overall average hourly Leq (M = 60.44 dB, range = 55–68 dB), L10 (M = 59.26 dB, range = 55–66 dB), and Lmax (M = 78.39, range = 69–93 dB) were often above the recommended sound levels (hourly Leq <50 dB, L10 <55 dB, and 1-second Lmax <70 dB). In addition, certain times of day, such as 6–7 AM and 10 AM–12 noon, were noisier than other times of day.

Effect of early breast milk expression on milk volume and timing of lactogenesis stage II among mothers of very low birth weight infants: a pilot study

Objective:The purpose of this randomized pilot study was to collect preliminary data regarding the feasibility and effects of early initiation of milk expression on the onset of lactogenesis stage II and milk volume in mothers of very low birth weight (VLBW) infants.Study Design:Twenty women were randomized to initiate milk expression within 60 min (group 1) or 1 to 6 h (group 2) following delivery. Milk volume and timing of lactogenesis stage II was compared between groups using Wilcoxons rank sum tests.Result:Group 1 produced statistically significantly more milk than group 2 during the first 7 days (P=0.05) and at week 3 (P=0.01). Group 1 also demonstrated a significantly earlier lactogenesis stage II (P=0.03).Conclusion:Initiation of milk expression within 1 h following delivery increases milk volume and decreases time to lactogenesis stage II in mothers of VLBW infants.

Exposure to maternal voice in preterm infants: a review.

The mothers voice, along with other developmentally appropriate sensory events (ie, touch, light, smells), stimulates maturation of the sensory systems and helps shape normal fetal development. While vast changes in the neonatal intensive care unit have occurred over the last 2 decades, little research has addressed the loss of exposure to maternal voice for the preterm infant. To address this gap, we compared studies that directly investigated effects of exposure to maternal voice on preterm infants. Studies reviewed were conducted between 1972 and 2007. All presented recordings of maternal voice at sound levels above current recommendations, and few of the findings reached statistical significance. Some potentially positive developmental effects were indicated. Future study of the effects of exposure to maternal voice on preterm infants using recommended sound levels is needed.

Maternal voice and short-term outcomes in preterm infants.

This study explored effects of exposure to maternal voice on short-term outcomes in very low birth weight preterm infants cared for within an neonatal intensive care unit (NICU) without an ongoing program of developmental care. Using a comparative design, 53 infants born during their 27th to 28th postmenstrual week were sampled by convenience. Experimental groups were exposed to maternal voice during two developmental time periods. Group 1 listened to a recording of their mothers reciting a rhyme from 28 to 34 postmenstrual weeks. Group 2 waited 4 weeks and heard the recording from 32 to 34 weeks. The control group received routine care. The primary analysis of combined experimental groups compared to the control group revealed that the experimental infants experienced significantly fewer episodes of feeding intolerance and achieved full enteral feeds quicker compared to the control group. Further, in an analysis evaluating all three groups separately, it was noted that Group 1 experienced significantly fewer episodes of feeding intolerance compared to the control group. Study findings warrant further investigation of exposure to maternal voice and the developmental timing at which exposure is begun.

Neonatal intensive care unit sound levels before and after structural reconstruction.

PurposeThis study compared sound levels before and after structural reconstruction within an NICU. Study Design and MethodsUsing a descriptive design, sound level recordings (in decibels, A-weighted scale) of the Leq, L10, and Lmax were measured continuously for 8 hours (0600-1400) before and after reconstruction in an NICU located in north central Florida. ResultsLevels before reconstruction were Leq M = 60.44 dB, L10 M = 59.26 dB, and Lmax M = 78.39 dB. The average overall sound levels after reconstruction were Leq M = 56.4 dB, L10 M = 60.6 dB, and LmaxM = 90.6 dB. Although an approximate 4-decibel decrease in the Leq sound level after reconstruction was noted, a similar decrease in the L10 and Lmax did not occur. Furthermore, sound levels after reconstruction in the NICU still exceeded recommended levels (Leq < 50 dB, L10 < 55 dB, and Lmax < 70 dB). Clinical ImplicationsFindings from this study demonstrated the positive impact that reconstruction can have on sound levels (4 dB Leq decrease); however, additional interventions may be needed to meet the current standards for noise reduction in an NICU.

Safe Sound Exposure in the Fetus and Preterm Infant

Exposure to sound can have beneficial and harmful effects on the developing fetus and preterm infant. Although recommendations for safe exposure to sound have existed for more than three decades, reports indicate that these recommendations are not being followed. Recommendations are made to promote attention to the problem of unsafe exposure to sound in early development, and a multidisciplinary team, including representatives from disciplines beyond medicine and nursing, must redress safe exposure.

A Longitudinal Description of Heart Rate Variability in 28—34-Week-Old Preterm Infants

The purpose of this study was to longitudinally describe changes in heart rate variability (HRV) from 28 to 34 weeks postmenstrual age (PMA). A convenience sample of 31 low-risk preterm infants participated. HRV was quantified using a spectral analysis of heart periods and recorded during seven weekly test sessions from an electrocardiogram (ECG) signal. The total range of frequency components (0.04—2.0 Hz), high-frequency (HF) components (0.30—1.3 Hz), and ratio of low-to-high frequency (LF/HF) components (0.04—0.20/ 0.30—1.3 Hz) were measured. A mixed general linear model analysis revealed no significant change over weekly test sessions for the total, the high, and the ratio of LF/HF components. A significant interaction effect was, however, noted in the HF components for test session × gender (df = 1; F = 4.85; p = .030). With increasing age, the HF components for females increased or displayed a pattern of HRV indicative of a more mature autonomic nervous system (ANS). Study findings warrant further investigation of the impact of gender on normative descriptions of HRV.

Fetal Response to Live and Recorded Maternal Speech

The purpose of this study was to compare the fetal response to live and recorded maternal speech following a lengthy history of exposure to a passage spoken by the mother. Participants comprised a convenience sample of 21 pregnant women. The women recited an assigned passage (nursery rhyme) twice daily from 28 to 34 weeks’ gestational age (GA), and their fetuses were tested at 34 weeks’ GA. During testing, fetal heart rate and movement were measured in response to two different formats of the assigned passage: maternal live voicing and a recording of the mother speaking the passage. The fetal cardiac response varied depending upon the format; however, fetal movement did not. A minimal cardiac deceleration occurred in response to live voicing compared to a cardiac acceleration in response to the recorded format. This is the first study to show differences in the fetal cardiac response to a passage spoken live compared to a recording of the passage following a lengthy history of controlled fetal exposure to the multimodal characteristics of maternal speech. Given the differential response to a live voicing compared to a recorded format, future study that incorporates lengthier exposure to the multimodal characteristics of maternal speech may be warranted.