Kiyoko Ohira-Kist

Effects of quality of energy intake on growth and metabolic response of enterally fed low-birth-weight infants

Carbohydrate and fat may vary in their ability to support protein accretion and growth. If so, variations in the source of nonprotein energy might be used to therapeutic advantage in enterally fed low-birth-weight infants. To test the hypothesis that high-carbohydrate diets are more effective than isocaloric high-fat diets in promoting growth and protein accretion, low-birth-weight infants weighing 750–1600 g at birth were randomized in a double blind study to receive one of five formulas differing only in the quantity and quality of nonprotein energy. Groups 1, 2, and control received 130 kcal·kg−1·d−1 with 35, 65, and 50% of the nonprotein energy as carbohydrate. Groups 3 and 4 received energy intake of 155 kcal·kg−1·d−1 with 35 and 65% of the nonprotein energy as carbohydrate. Protein intake of all groups was 4 g·kg−1·d−1. Growth and metabolic responses were followed weekly, and macronutrient balances including 6-h indirect calorimetry were performed biweekly. Greater rates of weight gain and nitrogen retention were observed at high-carbohydrate intake compared with high-fat intake at both gross energy intakes. Greater rates of energy storage and an increase in skinfold thickness were observed in group 4 (high-energy high-carbohydrate diet) despite higher rates of energy expenditure. These data support the hypothesis that at isocaloric intakes, carbohydrate is more effective than fat in enhancing growth and protein accretion in enterally fed low-birth-weight infants. However, a diet with high-energy and high-carbohydrate content also results in increased fat deposition.

Body position, sleep states, and cardiorespiratory activity in developing low birth weight infants

The objective of this study was to determine the effects of body position (supine vs prone) on cardiorespiratory activity during quiet and active sleep in growing low birth weight (LBW) infants. The effect of postconceptional age on cardiorespiratory activity in the two positions was also evaluated. Fifty-one healthy, growing, appropriate for gestational age LBW infants (795-1600 g), ranging from 26-37 weeks in gestational age, were evaluated. All subjects were enrolled in an ongoing study of the effects of quality of dietary energy on the rate and composition of weight gain. Infants were randomly assigned to the supine or prone position for the first 3 h of the 6-h studies; the position was reversed for the second 3 h. Continuous recordings of cardiorespiratory activity were performed along with simultaneous minute by minute assignment of behavioral sleep state. Measurements of heart rate (HR), heart period variability (RR-SD), respiratory rate (f), and respiratory variability (fSD) were made each minute. Low birth weight infants had higher HR and f and lower RR-SD and fSD in the prone position compared to the supine position, during both quiet and active sleep. With increasing postconceptional age, positional differences in HR increased during quiet sleep and differences in RR-SD increased during both sleep states. These data demonstrate systematic differences in cardiorespiratory control related to body position during sleep. We speculate that such positional differences are due to variations in autonomic control, and may, in turn, contribute to variations in susceptibility to sudden infant death syndrome.

Maturational changes in heart rate and heart rate variability in low birth weight infants

To provide insight into the maturation of neural mechanisms responsible for variability in heart rate during quiet and active sleep, 6-hour continuous electrocardiographic recordings and simultaneous minute-by-minute behavioral activity state assignments were performed in 61 healthy, growing low birth weight infants. The infants weighed 795-1600 g at birth and ranged between 31-38 weeks in postconceptional age. During this age interval there was a decrease in heart rate during quiet sleep and an increase in both time domain and frequency domain measures of the variability in cardiac interbeat intervals. In quiet sleep, global variability, measured as SD of R-R intervals, increased in relation to age, as did higher frequency variability, measured as the square root of the mean of squared successive differences in R-R intervals. Developmental changes in the 0.5-2.0 Hz spectral power band of RR-interval variability, another measure of high frequency variability, paralleled the changes seen in the time domain measure. Evaluation of patterns of changes in the magnitude and direction of successive interbeat intervals provided evidence that the incidence of sustained accelerations or decelerations increased whereas the incidence of no change in consecutive RR-intervals decreased as infants matured. Among the various measures of heart rate variability, the incidence of sustained change and no change in successive interbeat intervals were most closely related to postconceptional age in both sleep states. The overall decrease in heart rate, increase in heart rate variability, and increase in the pattern of changes in interbeat interval with postconceptional age are consistent with the maturation of the autonomic cardio-regulatory activity from 31-38 weeks age.

Is the New Definition of Bronchopulmonary Dysplasia More Useful

OBJECTIVE:To determine the incidence of bronchopulmonary dysplasia (BPD) in low birth weight (LBW) infants <1251 g managed with early bubble nasal continuous positive airway pressure (NCPAP) and a gentle ventilation strategy using the newly proposed definition for BPD and the previous definitions.METHODS:Needs for supplemental oxygen and positive pressure (positive pressure ventilation or NCPAP) during initial hospitalization were evaluated in 266 inborn LBW infants (birth weight <1251 g). The data were categorized in three weight groups, <751, 751 to 1000 and 1001 to 1250 g and the incidence of BPD was computed in survivors based on oxygen need at 28 days, 36 weeks postmenstrual age (PMA) and the new severity of BPD criteria, that is, mild BPD: need for supplemental oxygen ≥28 days, but not at 36 weeks PMA; moderate BPD: need for supplemental oxygen ≥28 days and <30% at 36 weeks PMA and severe BPD: need for supplemental oxygen ≥28 days, and >30% at 36 weeks PMA and/or positive pressure at 36 weeks PMA. Further, BPD-associated comorbidities and short-term outcome data during hospitalization were compared among the groups, defined by severity of BPD.RESULTS:Among LBW infants <1251 g, the incidences of BPD at 28 days and 36 weeks PMA were 21.1 and 7.4% respectively. Using the newly defined criteria, the incidences of mild, moderate and severe BPD were 13.5, 4.8 and 2.6%, respectively. In total, 64.6% of these infants had mild BPD and 70.8% weighed <751 g at birth. Associated comorbidities correlated significantly with grades of underlying pulmonary disease. Also, significantly longer hospital stay, discharge at a higher PMA and lower growth velocity was observed with increasing grades of BPD.CONCLUSIONS:The new system for grading the severity of BPD offers a better description of underlying pulmonary disease and correlates with the infants maturity, growth and overall severity of illness. Whether it will have a role in predicting long-term outcome remains to be determined.

Effects of body position on thermal, cardiorespiratory and metabolic activity in low birth weight infants

BACKGROUND Low birth weight (LBW) infants sleeping prone are known to exhibit many physiological differences from those sleeping supine, including lower energy expenditure (heat production) and higher surface temperature. This apparent increase in heat storage suggests that heat loss may be inhibited in the prone position which, in turn, might influence cardiorespiratory activity. AIMS To determine the effects of body position (prone vs. supine) on absolute surface temperature profile (heat storage), central-peripheral (C-P) thermal gradients (vasomotor response), cardiorespiratory activity and metabolic gas exchange in growing LBW infants. METHODS Six-hour continuous recordings of absolute surface temperature profiles, cardiorespiratory activity and O2 and CO2 exchange, along with minute-to-minute assessment of behavioral sleep states were performed in 32 healthy growing LBW infants (birth weight 805-1590 g, gestational age 26-35 weeks and postconceptional age at study 33-38 weeks). Each infant was randomly assigned to the prone or supine position for the first 3 h of the study and then reversed for the second 3 h. Surface temperatures were recorded from 4 sites (forehead, flank, forearm and leg) and averaged each minute. Central (forehead and flank)-to-peripheral (forearm and leg) and forehead-to-environment (H-E) thermal gradients were calculated from the surface temperatures. Corresponding sleep states were aligned with minute averages obtained from the temperature and cardiorespiratory measurements. Data were then sorted for prone and supine positions during quiet (QS) and active sleep (AS) and compared using paired t-tests. RESULTS In the prone position during both AS and QS, infants had higher forehead, flank, forearm and leg surface temperatures, narrower C-P gradients, higher heart rates and respiratory frequency, and lower heart rate and respiratory variability. Despite similar environmental temperatures, the H-E gradient was higher in the prone position. In the prone position infants demonstrated lower O2 consumption and CO2 production and a higher respiratory quotient. CONCLUSIONS Despite thermoregulatory adjustments in cardiorespiratory function, infants sleeping prone have relatively higher body temperature. The cardiorespiratory responses to this modest increase in temperature indicate that thermal and metabolic control of cardiac and respiratory pumps seem to work in opposition. The consequences of any attendant changes in blood gas activity (e.g. hypocapnia and/or increased mixed venous oxygen concentration) due to this override of metabolic control remains speculative.

Postural differences in cardiac dynamics during quiet and active sleep in low birthweight infants

To study the effects of body position (supine versus prone) on changes in cardiac inter‐beat interval during quiet and active sleep, 6‐h continuous electrocardiographic recordings and simultaneous minute‐by‐minute behavioural activity state assignments were made in 61 healthy, growing, low birthweight infants. The infants weighed 795‐1600 g at birth and ranged between 30–38 wk in postconceptual age. Infants were randomly assigned to the supine or prone position for the first 3 h of each study; the position was reversed for the second 3 h. Higher heart rates and lower time and frequency domain measures of inter‐beat interval variability were observed in the prone position as compared to the supine position, during both quiet and active sleep. In addition, an analysis of consecutive increases and decreases in the instantaneous heart rate revealed a lower incidence of sustained accelerations or decelerations in the prone position. Although consistent findings concerning inter‐beat interval variability and sleeping position were obtained from all analytic techniques, the differences derived from analysis of consecutive inter‐beat changes were the most robust. These differences in multiple measures of cardiac rate and rhythm between prone and supine positions suggest that autonomic control of the heart is altered by body position, the net effect on heart rate being increased sympathetic dominance.

Interactions among peripheral perfusion, cardiac activity, oxygen saturation, thermal profile and body position in growing low birth weight infants.

Aims:  To investigate the correlation between the ‘perfusion index’ (PI) and other commonly used estimates of cutaneous blood flow [heart rate (HR), surface temperatures (ST) and central‐to‐peripheral thermal gradients (C‐P grad)] and to use this new non‐invasive tool to compare differences between prone and supine sleep position in low birth weight (LBW) infants.

Quality of Diet, Body Position, and Time after Feeding Influence Behavioral States in Low Birth Weight Infants

The effects of variations in carbohydrate and fat intake and body position on behavioral activity states were evaluated in 64 healthy, growing low birth weight infants (birth weight, 750–1600 g). The infants, enrolled in a prospective, randomized, double-blind, controlled study of effects of quality of dietary energy, were fed one of the five formulas. These formulas contained fixed intakes of protein (4 g/kg per day) but different intakes of carbohydrate (9.1 to 20.4 g/kg per day) and fat (4.3 to 9.5 g/kg per day). Six-hour daytime sleep studies were performed at 2-wk intervals from time of full enteral intake until discharge (mean postconceptional age at first study, 33.2 ± 1.8 wk). Infants were randomly assigned to the prone or supine position for the first 3-h postprandial period; the position was reversed during the second 3 h. Behavioral activity state, i.e. quiet sleep (QS), active sleep, indeterminate sleep, awake, or crying was coded each minute throughout the postprandial period. The overall incidence of QS was almost double in the prone position versus the supine (p < 0.0001). In contrast, the probability of being in either of the two wakeful states (awake and crying) was increased when infants were placed in supine position (p < 0.0001). Increased likelihood of being in QS while prone was found only during the 30 min after and before feeding in a 150-min prandial cycle. In contrast, increased amounts of awake and crying in supine position were observed throughout the feeding interval. As carbohydrate intake increased, time spent in QS in supine position increased (from 8.6% to 12.5%, p < 0.02), and a trend in the same direction was noted for the prone position (p = 0.06). However, during postprandial minutes 10–100, when QS is likely to be entrained by the nutrient intake, enhancement of QS was found in the prone position only (p < 0.02). Carbohydrate intake influences the total time spent and the distribution of behavioral activity states within the postprandial period in low birth weight infants. The effect of nutrient intake on sleep profile is dependent on body position and time after feed. Mechanistic hypotheses relating sudden infant death syndrome to sleeping position may need to take these observations into account.

The Effects of Prone vs Supine Body Position on Metabolic and Thermal Measurements in Growing Low Birth Weight (LBW) Infants † 1737

Objectives: To determine the effects of prone vs supine positioning on the metabolic gas exchange and surface temperature profile of healthy growing enterally nourished LBW infants.

Effects of Variations in Carbohydrate (CHO) Intake on Postprandial Gas Exchange, and Respiratory Frequency of Low Birth Weight (LBW) Infants

Effects of Variations in Carbohydrate (CHO) Intake on Postprandial Gas Exchange, and Respiratory Frequency of Low Birth Weight (LBW) Infants