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Cardiorespiratory costs of growth in low birth weight infants
K Schulze1, S Kashyap, R Ramakrishnan
1Department of Pediatrics, Columbia University College of Physicians and Surgeons, New York.
Insights
Infant growth requires energy for tissue building and cardiorespiratory work. Diet and weight gain influence heart rate in low birth weight infants, indicating energy expenditure during growth.
Area of Science:
- Physiology
- Nutritional Science
- Pediatrics
Background:
- Energy cost of growth involves tissue anabolism and cardiorespiratory work.
- Assessing cardiorespiratory work provides insights into energy expenditure during growth.
- Low birth weight infants present unique challenges for optimizing growth and energy utilization.
Purpose of the Study:
- To investigate the relationship between diet, weight gain, and cardiorespiratory parameters in low birth weight infants.
- To determine how nutritional intake and growth rates affect heart rate and respiratory frequency.
- To understand the energy expenditure associated with growth in vulnerable infant populations.
Main Methods:
- Studied 66 healthy low birth weight infants with controlled protein and energy intakes.
- Monitored weight gain rates ranging from 13.9 to 21.7 g/kg per day.
- Conducted bi-weekly 6-hour assessments of energy expenditure, heart rate, respiratory frequency, and sleep state.
Main Results:
- Age-adjusted heart rate during active sleep correlated with weight gain, nitrogen-energy ratio, and energy expenditure.
- Multiple regression analysis showed heart rate was significantly related to these three variables (r2 = 0.31).
- Dietary composition and growth rate are key determinants of cardiorespiratory effort in growing infants.
Conclusions:
- Cardiorespiratory work is a significant component of the energy cost of growth in infants.
- Nutritional strategies can modulate energy expenditure by influencing cardiorespiratory function.
- Monitoring heart rate provides a non-invasive method to assess metabolic and growth-related energy demands in neonates.
Abstract:
The energy cost of growth includes two components: the energy stored in new tissues and the energy expended in all energy requiring steps associated with nutrient intake and net tissue accretion. Most of the energy expended in growth is accounted for by the energy cost of tissue anabolism: peptide bonds, lipogenesis, substrate transport, etc. However, to the extent that additional work is required of the heart and lungs for growth-related increases in O2 and CO2 transport, increased energy is also expended in cardiorespiratory work. Indirect estimates of these costs can be gained by examining the effects of diet and weight gain on heart rate and respiratory frequency. We studied 66 healthy low birth weight infants, mean study weight = 2010 g, fed constant intakes of protein (2.25-3.9 g/kg per day) and energy (100-150 kcal/kg per day). These diets led to rates of weight gain ranging from 13.9 to 21.7 g/kg per day, among the diet groups. Bi-weekly 6-h assessments of energy expenditure, heart rate, respiratory frequency and state of sleep were made after full enteral intake was achieved. After adjustment of heart rate for the effect of postnatal age, heart rate during active sleep was related to weight gain (y = 0.97 x + 144, r2 = 0.15), nitrogen-energy ratio of the diet (y = 5.9 x + 139,2 r2 = 0.22), and energy expenditure (y = 0.53 x + 129, r2 = 0.13). Multiple regression analysis revealed that age-adjusted heart rate during active and quiet sleep was significantly related to a combination of the same three variables (r2 = 0.31).(ABSTRACT TRUNCATED AT 250 WORDS)