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Gas Transfer and Pulmonary Blood Flow at Rest and during Exercise in Adults 21 Years after Preterm Birth

¹ Division of Respiratory Medicine, Hospital for Sick Children, Toronto, Canada; ² Department of Paediatric Respiratory Medicine, Royal Brompton Hospital, London, United Kingdom

Correspondence and requests for reprints should be addressed to Indra Narang, M.D., B.Med.Sci., M.B.B.Ch., F.R.C.P.Ch., Division of Respiratory Medicine, Hospital for Sick Children, 555 University Avenue, Toronto, ON M5G 1X8, Canada. E-mail: indra.narang{at}sickkids.ca

Rationale: After preterm birth, limited data exist in adulthood regarding alveolar–capillary growth and exercise capacity. Gas transfer at rest through exercise is a noninvasive measure of alveolar–capillary development.

Objectives: To determine exercise capacity and gas transfer at rest and during exercise in ex-preterm adults.

Methods: Ex-preterm subjects (n = 60; median gestation, 31.5 wk) recruited at birth underwent exercise testing at 21 years of age and were contemporaneously compared with 50 healthy control subjects.

Measurements and Main Results: Subjects exercised on a cycle ergometer, and measurements of heart rate (HR), FRC, effective pulmonary blood flow (peff), stroke volume (SV), DL_CO, O₂, arteriovenous oxygen difference (AVO), transit time (TT), respiratory rate (Rf), CO₂, E, VT, and respiratory quotient (RQ) were made using a respiratory mass spectrometer. In the index study group and control subjects, the median DL_CO (mmol/min/kPa/m²) at rest was 4.33 (95% confidence interval [CI], 4.18–4.62) and 4.75 (95% CI, 4.50–5.10), respectively (P = 0.01), and the median peff (L/min/m²) at rest was 3.26 (95% CI, 3.16–3.49) and 3.59 (95% CI, 3.43–3.81), respectively (P = 0.04). peff and DL_CO values normalized during exercise but were reduced and lower than controls after a recovery period. No significant differences were found in exercise capacity between the groups.

Conclusions: The data suggest a long-term effect of premature delivery on resting cardiac output and gas transfer, not due to abnormal cardiac or pulmonary function and with no evidence of exercise limitation.

Key Words: exercise capacity • transfer factor • prematurity

AT A GLANCE COMMENTARY Scientific Knowledge on the Subject Preterm birth is associated with an interruption of alveolar–capillary development, but the long-term consequences of this are not well understood. What This Study Adds to the Field This study shows that ex-preterm subjects in adulthood have reduced gas transfer and effective pulmonary blood flow at rest, which normalize during exercise with no impairment of exercise capacity when compared with control subjects.