The hypoxic challenge test in preterm infants with or without bronchopulmonary dysplasia: a test for pulmonary and pulmonary vascular function?

Preterm birth is a risk factor for respiratory and cardiovascular complications
later in life and this risk is even more pronounced in children with
bronchopulmonary dysplasia.
Currently, there is a lack of feasible function tests to investigate pulmonary
and pulmonary vascular function in infants after preterm birth. This is however
the best age to start treatment, prevention and follow-up, since most problems
(such as hypoxic incidents) occur in the early life years.
The hypoxic challenge test is a test that challenges ventilation, diffusion and
pulmonary vasoreactivity. Therefore, we hypothesize that in preterm born
children with or without bronchopulmonary dysplasia, the hypoxic challenge test
is actually a function test for the pulmonary and pulmonary vascular system.
When combined with echocardiography, pulmonary hemodynamics can be evaluated.
Children who do not pass the hypoxic challenge test have an impaired
cardiopulmonary function.

The primary objective is to assess the hypoxic challenge test, combined with
echocardiography, as a function test for the pulmonary and pulmonary vascular
system in preterm born children with and without bronchopulmonary dysplasia.
Secondary objectives are the rate of success or failure of the test in preterm
born children (with or without BPD), relation of the HCT outcome with right
ventricular function. For children with severe BPD: the difference between
children who fail and do not fail the HCT, in polysomnography outcomes and
chest CT scores.

This is a prospective observational two-year pilot study in preterm born
children (<32 weeks of gestational age) at six months corrected age. The
children will undergo a hypoxic challenge test in a body plethysmograph. The
test is preceded by a cardiac ultrasound to determine structural abnormalities,
pulmonary vascular resistance and right ventricular function. Immediately after
the hypoxic challenge test, additional echocardiographic images will be
obtained to determine pulmonary vascular reactivity and right ventricular
function to hypoxia.

The burden and risks associated with participation are very low. No extra
visits to the hospital are required; the standard outpatient clinic contact
will be prolonged by around 60 minutes. Both the HCT as well as the cardiac
ultrasound are non-invasive tests and carry no risk (cardiac ultrasound) or a
risk of a sh6rt desaturation (HCT) to a lowest value of 85%, which has no
clinical consequences.