“In adults, obesity is associated with increased oxygen cost of breathing, and weight loss is effective in reducing the oxygen cost of breathing; however, there have been no reports on the effects of obesity in oxygen cost in children,” explains Dharini M. Bhammar, PhD, MBBS. “It’s important to study this topic, since the findings could offer important mechanistic information on the effects of obesity on exertional dyspnea, exercise tolerance, and exercise performance in children with obesity.”
For a study published in Respiratory Physiology & Neurobiology, Dr. Bhammar and Tony G. Babb, PhD, examined the effects of obesity on the oxygen cost of breathing in children using the eucapnic voluntary hyperpnea (EVH) technique. Children aged 10 and 11, with and without obesity, underwent EVH trials at two levels of ventilation for assessing the oxygen cost of breathing and a dual energy x-ray absorptiometry scan. The slope of the relationship between whole body oxygen uptake and minute ventilation provides a measure of the oxygen cost for each liter of minute ventilation, notes Dr. Bhammar.
Resting Oxygen Uptake Higher in Children With Obesity
“We found that the oxygen cost of breathing did not differ between children, with and without obesity,” Dr. Bhammar says. “However, resting oxygen uptake was significantly higher in children with obesity when compared with children without obesity. Furthermore, chest mass explained 85% of the variance in resting oxygen update in children with obesity. These findings suggest that reduced chest wall compliance and increased work of breathing in children with obesity could explain the higher resting metabolic costs of obesity.” The researchers further observed that obesity was associated with increased metabolic costs that are present at rest and remain increased during periods of increased ventilatory demand (Table). “Obesity is linked with altered respiratory mechanics in children,” Dr. Bhammar says. “Children with obesity breathe at lower lung volumes when compared with children without obesity, which means that they have limited expiratory reserve volumes. As a result, children with obesity are unable to decrease their end-expiratory lung volumes during times of higher ventilatory demand, which could predispose them to ventilatory constraints.”
When children with obesity exercise, Dr. Bhammar explains, the elevated resting costs are superimposed on the ventilatory demands of exercise, even though the oxygen cost for each additional liter of minute ventilation may not be increased. “These observations offer insight into respiratory mechanisms for dyspnea in this population, which is useful for pediatricians and pulmonologists who routinely assess children with obesity experiencing exertional dyspnea,” she says.
Lifestyle Modification & Pulmonary Rehabilitation
Dr. Bhammar notes that physiological studies such as her and Dr. Babb’s offer clinicians mechanistic insights into how obesity could lead to dyspnea in children. “These studies also fit into the broader context of dyspnea evaluation, because they imply that respiratory diagnoses like asthma may not always be the predominant cause of dyspnea in children with obesity,” she adds. “For children with obesity who may be resistant to traditional treatments, exercise testing can reveal the extent of ventilatory constraints that are due to obesity and even help rule out cardiac or other respiratory diagnoses for exertional dyspnea.”
Future studies with larger sample sizes are needed to improve understanding of the physiological mechanisms that contribute to respiratory symptoms in children with obesity, according to Dr. Bhammar. “Additional research in this area should also focus on delineating the contribution of obesity in exertional dyspnea genesis and empirically testing treatment options such as pulmonary rehabilitation or lifestyle modifications. This is especially important for children with obesity who experience exertional dyspnea and are consequently avoiding physical activity, but who are unresponsive to traditional treatment options.”