Pulmonary Gas Exchange and Exercise Capacity in Adults Born Preterm

Abstract

Rationale: Preterm birth, and its often-required medical interventions, can result in respiratory and gas exchange deficits into childhood. However, the long-term sequelae into adulthood are not well understood.

Objectives: To determine exercise capacity and pulmonary gas exchange efficiency during exercise in adult survivors of preterm birth.

Methods: Preterm (n = 14), very low birth weight (<1,500 g) adults (20-23 yr) and term-born, age-matched control subjects (n = 16) performed incremental exercise on a cycle ergometer to volitional exhaustion while breathing one of two oxygen concentrations: normoxia (fraction of inspired oxygen, 0.21) or hypoxia (fraction of inspired oxygen, 0.12).

Measurements and main results: Ventilation, mixed expired gases, arterial blood gases, power output, and oxygen consumption were measured during rest and exercise. We calculated the alveolar-to-arterial oxygen difference to determine pulmonary gas exchange efficiency. Preterm subjects had lower power output at volitional exhaustion than did control subjects in normoxia (150 ± 10 vs. 180 ± 10 W; P = 0.01), despite similar normoxic oxygen consumption. However, during hypoxic exercise, there was no difference in power output at volitional exhaustion between the two groups (116 ± 10 vs. 135 ± 10 W; P = 0.11). Preterm subjects also exhibited a more acidotic, acid-base balance throughout exercise compared with control subjects. In contrast to other studies, adults born preterm, as a group developed a wider alveolar-to-arterial oxygen difference and lower PaO2 than did control subjects during normoxic but not hypoxic exercise.

Conclusions: This study demonstrates that pulmonary gas exchange efficiency is lower in some adult survivors of preterm birth during exercise compared with control subjects. The gas exchange inefficiency, when present, is accompanied by low arterial blood oxygen tension. Preterm subjects also exhibit reduced power output. Overall, our findings suggest potential long-term consequences of extreme preterm birth and very low birth weight on cardiopulmonary function.

Keywords: alveolar–arterial oxygen difference; prematurity; pulmonary gas exchange.

Figures

Figure 1.

Power output at volitional exhaustion in control subjects (red columns) and preterm subjects (black columns) breathing one of two oxygen concentrations (normoxia: FiO2 = 0.21; hypoxia: FiO2 = 0.12) while exercising on a cycling ergometer. FiO2 = fraction of inspired oxygen. Shown are means (adjusted for sex) and SE.

Figure 2.

Metabolic parameters during graded normoxic and hypoxic exercise. Shown are (A and B) respiratory quotient (R; R = V.o2/V.co2), (C and D) pH, (E and F) bicarbonate (HCO3–), (G and H) base excess of the extracellular fluid (BEecf), and (I and J) body temperature throughout (A, C, E, G, and I) normoxic and (B, D, F, H, and J) hypoxic progressive exercise (plotted as the percent maximal wattage at volitional exhaustion) in control adults (CTL; red triangles) and preterm adults (PT; open circles). Values are plotted for each individual throughout exercise.

Figure 3.

Arterial blood gases, pulmonary gas exchange efficiency, and its components during normoxic and hypoxic exercise. Shown are (A and B) alveolar oxygen tension (PaO2), (C and D) PaO2, (E and F) PaCO2, (G and H) oxygen saturation as measured by pulse oximetry (SpO2), and (I and J) pulmonary gas exchange efficiency (a–aDo2) throughout (A, C, E, G, and I) normoxic and (B, D, F, H, and J) hypoxic progressive exercise (plotted as increasing percent maximal wattage at volitional exhaustion) in control adults (CTL; red triangles) and preterm adults (PT; open circles). Values are plotted for each individual throughout exercise.