Increased lung volume in infants and toddlers at high compared to low altitude

Abstract

Children and adults residing at high altitude (HA) compared to low altitude (LA) have larger lung volumes; however, it is unknown whether this response to chronic hypoxia begins early in life. Our objective was to determine whether infants and toddlers at HA have larger lung volumes compared to infants and toddlers at LA. Oxygen saturation (SaO2 ), functional residual capacity (FRC), as well as serum levels of vascular endothelial growth factor (VEGF) and erythropoietin (EPO) were measured in infants and toddlers from HA (N = 50; 3,440 m) and LA (N = 35; 440 m). There were no significant differences in somatic size for HA and LA subjects; however, HA subjects had significantly lower SaO2 (88.5% vs. 96.7%; P < 0.0001). Subjects at HA had significantly greater FRC compared to subjects at LA (group mean: 209 and 157 ml; P < 0.0001), adjusting for body length. Male infants at HA had a significantly greater FRC compared to males at LA (57 ml; P-value < 0.001); however, the increase in FRC for females at HA compared to LA was not significant (20 ml; P-value = 0.101). VEGF and EPO were significantly higher for subjects at HA compared to LA with no gender differences. In summary, infants and toddlers at HA have lower oxygen saturations, higher serum levels of VEGF and EPO, and higher FRC compared to subjects at LA; however, chronic hypoxia appears to generate a more robust response in lung growth in male compared to female infants early in life.

Keywords: chronic hypoxia; erythropoietin; functional residual capacity; oxygen saturation; vascular endothelial growth factor.

Fig. 1

Functional residual capacity (FRC) for infants and toddlers versus body length (cm) for males and females at high altitude (HA) and low altitude (LA). FRC adjusted for body length was significantly greater for infants and toddlers at HA compared to LA (P < 0.0001). When analyzed by gender, males at HA had significantly greater lung volumes compared to males at LA (P < 0.0001), as well as females at HA (P < 0.021). However, there were no significant differences in lung volumes for females at HA compared to females at LA (P = 0.1008), nor females at LA versus males at LA (P = 0.4109).

Fig. 2

Comparison of vascular endothelial growth factor (VEGF) and erythropoietin (EPO) for infants and toddlers at high altitude (HA; black bars) compared to low altitude (LA; grey bars) for males and females. A: Serum levels of log VEGF were significantly higher for infants and toddlers at HA compared to LA. The effect of HA was present for both males and females analyzed separately, while there were no significant differences between males and females at HA or LA. B: Serum levels of log EPO were significantly higher for infants and toddlers at HA compared to LA. The effect of HA was present for males, while the difference for females approached statistical significance (P = 0.06). There were no significant differences between males and females at either HA or LA.