Paul R. Swyer

Diet, fat accretion, and growth in premature infants

To compare the growth and accumulation of protein, fat, and carbohydrate in the formula-fed premature infant and in the fetus of a similar postconceptional age, we performed 22 metabolic studies in 13 infants of very low birth weight (1155 +/- 39 g [mean +/- S.E.]). Measurements combining nutritional balance and indirect calorimetry demonstrated the deposition rates of protein and fat. We found that the formula-fed, very-low-birth-weight infant who gained weight comparably to the fetus retained the same amount of protein (1.92 +/- 0.1 g per kilogram of body weight per day) but accumulated fat at a rate of 5.4 +/- 0.3 g per kilogram per day - about three times that in the fetus, as confirmed by increased skin-fold thickness. How this change in body composition affects the future growth of formula-fed premature infants, and how body composition is altered by other dietary regimens such as the provision of human milk, remain to be determined.

Validation of Doubly Labeled Water for Assessing Energy Expenditure in Infants

ABSTRACT: Previous studies show that the doubly labeled water method is accurate for measuring energy expenditure in the adult human. To validate this method in infants, carbon dioxide production rate and energy expenditure were measured for 5 to 6 days by doubly labeled water (DLW) and periodic open circuit respiratory gas exchange (RGE) in 10 blinded studies in nine infants following abdominal surgery. Infants were maintained on consistant oral or parenteral nutrition prior to and during study. This avoided diet-related changes in baseline isotopic enrichment of body water which could theoretically contribute to significant errors in calculation of carbon dioxide production rate. For DLW, insensible water loss was assumed to be proportional to respiratory volume and body surface area, where the former was predicted from carbon dioxide production rate. Insensible water loss thus calculated averaged 18% of water turnover. Rates of carbon dioxide production measured by DLW were not significantly different from that of RGE (10.4 ± 1.1 and 10.5 ± 0.9 1/kg/day, mean ± SD, respectively). Energy expenditure was calculated using respiratory quotients from dietary intake (DLW:DIET) and RGE (DLW:RGE) data. There was no significant difference between energy expenditure determined by DLW (DLW:DIET and DLW:RGE) and that measured by RGE (58.5 ± 6.1, 56.8 ± 6.1, and 57.3 ± 5.1 kcal/kg/day, mean ± SD, respectively). Rate of carbon dioxide production, DLW:diet, and DLW:RGE calculated by DLW differed from corresponding RGE values by - 0.9 ± 6.2, -1.1 ± 6.1, and 1.6 ± 6.2%, mean ± SD, respectively. These findings demonstrate the validity of the doubly labeled water method for determining energy expenditure in infants without concurrent water balance studies.

Influence of postnatal age, energy intake, and weight gain on energy metabolism in the very low-birth-weight infant.

The relative importance and interrelationship of postnatal age, energy intake, and weight gain on metabolic rate is evaluated in 28 studies in 13 formula-fed very low-birth-weight AGA infants. The relationships between metabolic rate, energy intake, weight gain, and age all follow a similar pattern, increasing in the first two weeks of life and subsequently stabilizing. Significant linear correlations are demonstrated between metabolic rate and both energy intake (r = 0.88, P less than 0.001) and weight gain (r = 0.86, P less than 0.001). For each gram of weight gain, 0.67 kcal (2.8 kj) are expended in addition to the maintenance energy requirement of 51 kcal/kg/day. The increase in metabolic rate in the early postnatal period appears to be a consequence of the energy cost of tissue synthesis. Changes in metabolic rate with postnatal age are modulated by increasing energy intake and weight gain.

Iatrogenic rickets in low-birth-weight infants

This report describes 4 premature infants, all with very low birth weights, whodeveloped nutritional rickets in a neonatal unit of a pediatric hospital. All infants were fed a proprietary milk formula containing vitamin D but no vitamin supplement. Because of their small size, the amount of formula ingested was small, resulting in a low daily vitamin D intake. A comparable group of infants who received a daily vitamin D supplement of 400 I.U. in addition to the enriched formula did not develop rickets. It is concluded that the rickets developed because the vitamin D intake was inadequate.

Metabolic Consequences of Intrauterine Growth Retardation in Very Low Birthweight Infants

Summary: By the combination of energy and macronutrient balances, continuous open circuit computerized indirect calorimetry, and anthropometry, we have compared small for gestational age (SGA) and appropriate for gestational age (AGA) very low birthweight infants with respect to metabolizable energy intake (mean ± SE: 125.9 ± 2.5 versus 130.4 ± 3.5 kcal/kg·day), energy expenditure (67.4 ± 1.3 versus 62.6 ± 0.9 kcal/kg·day), storage of energy and macronutrients and growth. Fourteen studies in six SGA infants (gestational age, 33.1 ± 0.3 weeks; birthweight, 1120 ± 30 g) and 22 studies in 13 AGA infants (gestational age, 29.3 ± 0.4 weeks; birthweight, 1155 ± 40 g) were performed. The SGA infants had a lower absorption of fat (68.7 ± 3.2 versus 79.7 ± 1.7%) and protein (69.1 ± 3.2 versus 83.4 ± 1.5%) and hence increased (P > 0.001) energy loss in excreta (29.9 ± 2.8 versus 18.2 ± 1.5 kcal/kg·day). The significant hypermetabolism of SGA infants by 4.8 kcal/kg·day was associated with an increased fat oxidation. Despite lower energy storage, SGA infants were gaining weight (19.4 ± 0.9 g/kg·day), length (1.25 ± 0.14 cm/week), and head circumference (1.16 ± 0.9 cm/week) at higher rates than the AGA group. The energy storage per g weight gain was lower (P > 0.001) in the SGA group (3.0 ± 0.14 versus 4.26 ± 0.26 kcal) reflecting higher water, lower fat (22.2 ± 1.8 versus 33.8 ± 2.5%; P > 0.001) and lower protein (7.7 ± 0.5 versus 12.5 ± 0.8%; P > 0.001) contents of weight gain in the SGA group.

Ventilation and ventilatory mechanics in the newborn: Methods and results in 15 resting infants

Summary A method is described for the study of the mechanics of respiration in the newborn by measuring simultaneously the pressure in the esophagus and the air flow rate. Figures are given for 15 normal newborn infants for tidal and minute volumes, lung compliance, airway resistance, air flow rates, and the mechanical work of breathing.

Fatty acid accretion in fetal and neonatal liver: Implications for fatty acid requirements

The fatty acid content of liver was determined during the last trimester of infant growth and first 4 months of life in order to estimate fatty acid levels of developing liver and to assess minimal fatty acid requirements for tissue synthesis. Accretion rates were computed by regression analysis on fatty acid determinants of total liver lipid extracts from infants of varying developmental ages. During the last trimester of liver growth, accretion of most fatty acids paralleled increases in liver weight with the exception of C18:3, omega-3. This fatty acid remained at consistently low levels during the last trimester and represented less than 10% of total omega-3 fatty acids present in liver, even though significant accretion of longer chain omega-3 homologues occurred during the final trimester. For the term infants studied, significant increase in liver weight did not occur during the early weeks of life. However, liver levels of major fatty acids declined during the first five weeks of life apparently reflecting mobilization of saturated, omega-9 and omega-3 fatty acids from liver. During the first four months of life C18:2, omega-6 and total omega-6 fatty acid content of liver increased about 3.5- and 2-fold, respectively. After the initial 5 week lag net accretion of other fatty acid components also occurred in the developing liver. These developmental changes in fatty acid components of liver are quantitatively relevant to estimating the magnitude of the potential essential fatty acid reserve that may be present in liver of the developing human neonate.

Intermittent positive pressure respiration as a treatment in severe respiratory distress syndrome.

Since the initial work of Donald and Lord (1953) and Donald, Kerr, and MacDonald (1958), there have been several reported survivals ofinfants with the respiratory distress syndrome (RDS) treated by assisted ventilation (Benson, Celander, Haglund, Nilsson, Paulsen, and Renck, 1958; Stahlman, Young, and Payne, 1962; Delivoria-Papadopoulos and Swyer, 1963; Heese, Wittmann, and Malan, 1963). Previous work in our unit (Delivoria-Papadopoulos and Swyer, 1964) demonstrated the possibility of reversing at least temporarily the biochemical changes of terminal asphyxia in patients dying with RDS. The purpose of this study was to gain further information regarding criteria for initiating assisted ventilation and its technique in relation to the clinical features and course of the disease.

Quality of growth in premature infants fed their own mothers' milk

With the renewed interest in the feeding of human milk to preterm infants, we have evaluated the partition of energy metabolism and of macronutrient utilization and accretion in growing very low birth weight infants fed their own mothers milk. Fifteen studies combining macronutrient balance, computerized continuous open-circuit indirect calorimetry, and anthropometric measurements were performed in 11 growing, very low birth weight (less than 1.300 gm) preterm infants. The mean milk intake of 172 ml/kg/day provided a gross energy intake of 111 kcal/kg/day. Energy losses in excreta were 11 kcal/kg/day, and the metabolic energy expenditure was 56 kcal/kg/day. The remainder (44 kcal/kg/day) represented the energy stored in the components of new tissue. The infants were gaining weight (15.3 g/kg/day), length (0.98 cm/wk), and head circumference (0.76 cm/wk) at rates approximating intrauterine growth rates. The metabolic energy expenditure was derived from the oxidation (mean +/- SE) of carbohydrate, 9.5 +/- 0.7 gm/kg/day; fat, 1.63 +/- 0.34 gm/kg/day; and protein, 0.68 +/- 0.07 gm/kg/day. The stored energy comprised 2.98 +/- 0.86 gm/kg/day as carbohydrate, 2.25 +/- 0.54 gm/kg/day as fat, and 1.97 +/- 0.1 gm/kg/day as protein. The accretion rates of fat and protein, as well as the composition of the weight gain (fat, 16.6 +/- 4.1%; protein, 13.4 +/- 0.5%), were similar to those reported for the fetus of comparable gestational age.

Relation between heart rate and energy expenditure in the newborn.

Summary: This study defines the relationship between heart rate and metabolic rate in newborn infants and evaluates the accuracy of prediction of metabolic rate from heart rate. Continuous measurements of oxygen uptake, CO2 production, respiratory quotient, and cumulative heart rate were performed using computerized, open-circuit indirect calorimetry and on-line electrocardiogram monitoring over periods of 1 to 24 hr (mean 4.5 hr). Metabolic rate was calculated from the individual oxygen uptake and respiratory quotient. Thirty-five studies were performed in 16 infants (birthweight 0.75 to 3.1 kg; gestational age, 26 to 42 wk; mean ± S.D. age at study, 26.5 ± 15.7 days; study weight, 1.78 ± 0.5 kg). Metabolic rate (cal/kg · min) and heart rate (beats/min) were compared minute by minute (8269 measurements) and showed a close third degree polynomial relationship for heart rates of 110 to 230/min (y = −0.0000291x3 + 0.01685x2 − 2.93x + 197; r = 0.99; P < 0.001); however, at heart rates above 140 beats/min, a linear relationship was found (r = 0.997; P < 0.001). From cumulated heart rate measurements, factors defining metabolic rate per heart beat were also determined: for each beat 51.8 ± 6.8 μl of oxygen/kg are consumed and 0.258 ± 0.03 cal/kg (1.1 J/kg) are expended. Despite the wide variation in birthweight, gestational age, method of feeding, and clinical characteristics, there was a remarkable consistency in the heart rate-metabolic rate relationships.A further 10 studies were performed in a similar group of infants to assess the predictive value of the previously defined relationships and showed a mean percentage deviation of 5.7 ± 4% from the measured value.We conclude that in the varied group of newborns studied, heart rate correlates closely with metabolic rate and that cumulative heart rate measurements enable the estimation of metabolic rate in newborn infants. This provides a method of monitoring energy expenditure and caloric requirements over long periods.Speculation: The “heart rate-metabolic rate” relationship defined in this paper, could offer a simple method of estimating energy expenditure and, hence, energy requirements for newborn infants.