RESULTS
Demographics and Clinical Characteristics :
Of the 598 subjects in the registry who were older than five years of
age, 88 (14.7%) patients performed adequate pulmonary function testing
at a clinic visit between the ages of five and seven years old and thus
were included in the study population. The study population was 45.5%
female and had an average gestational age of 26.8 ± 2.9 weeks. 63.6% of
subjects identified as non-white race/ethnicity. The mean median
household income was $63,000 ± $180,800, and 62.5% had public
insurance. 14.5% of subjects reported second hand smoke exposure, and
64.5% reported a family history of asthma. A total of 38 patients
(43.2%) required supplemental oxygen at the time of discharge from the
NICU with an average amount of 0.35 ± 0.27 liters per minute.
Seventy-eight (88.6%) patients had data available that allowed them to
be classified according to the severity of their BPD with 11.5% with
chronic lung disease of prematurity (no BPD), 7.7% with mild BPD,
33.3% with moderate BPD, and 47.4% with severe BPD. Of the study
population, 34.1% had a gastrostomy tube placed, 22.7% underwent
Nissen fundoplication, and 18.2% had pulmonary hypertension. In terms
of growth parameters, subjects had an average birthweight of 980 ± 518
grams with a percentile of 41 ± 25 corrected for gestational age. At two
years of age, subjects had an average weight percentile for age of 30%
± 31%, an average height percentile for age of 24% ± 26%, and an
average BMI percentile for age of 49% ± 31%. The study population had
an average FEV1 of 84.5% predicted ± 22.7% and an
average FVC of 94.2% predicted ± 26.5%. See Table 1 for
additional demographic characteristics of the study population.
Additional analysis illustrated that the study population was not
significantly different from the entire registry population in terms of
demographic characteristics, clinical characteristics, or growth
parameters (Supplemental Table 1 ).
Predictors of Forced Expiratory Volume in 1 second
(FEV1) :
On average, the study population had a FEV1 % predicted
of 84.5% ± 22.7%. Of the demographic characteristics included, in
univariate regression analysis, only higher median household income (2.9
+/- 1.4, p=0.044) was significantly associated with an improvement in
FEV1% predicted. There was no significant association
between sex (p=0.55), gestational age (p=0.54), race/ethnicity (p=0.1),
use of public insurance (p=0.36), secondhand smoke exposure (p=0.74),
and family history of asthma (p=0.99) and FEV1%
predicted at six years of age. The need for supplemental oxygen at the
time of NICU discharge (-11 ± 5.1, p=0.035) and a greater amount of
oxygen required at discharge (-23.7 ± 9.9, p=0.02), the presence of
gastrostomy tube (-14.5 ± 5.2, p=0.007), history of Nissen
fundoplication (-19.6 ± 5.6, p=0.001), and higher weight percentile at
two years of age (p=0.026) were all associated with significantly lower
FEV1% predicted at six years of age. However, there was
no significant association between a diagnosis of severe BPD (p=0.051),
presence of pulmonary hypertension (p=0.44), personal diagnosis of
reactive airway disease or asthma in childhood (p=0.61), or prescription
for inhaled corticosteroid (p=0.92) and FEV1% predicted
at age 6. Weight percentile at age two was shown to be negatively
associated with FEV1% predicted at age six (-0.2 ± 0.1,
p=0.026) but no association was seen between birth weight percentile
(p=0.63), height percentile for age at age two (p=0.07), or BMI
percentile for age at age two (p=0.10) and FEV1%
predicted.
Multivariate analysis was performed using the variables found to have
association with FEV1% predicted in univariate
analysis. After adjusting for severity of BPD, a positive association
was seen between median household income (2.6 ± 1.3, p=0.04) with
FEV1% predicted whereas a negative association was
noted between Nissen fundoplication (-17.9 ± 6.2, p=0.005) and weight
percentile for age at age 2 (-0.2 ± 0.1, p=0.011) and
FEV1% predicted. Severe BPD was adjusted for in the
model but was not found to be significant (-5.3 ± 5.5, p=0.34).
Predictors of Forced Vital Capacity (FVC) :
On average, the study population had a FVC% predicted of 94.2% ±
26.5%. In univariate regression none of the demographic characteristics
were shown to have a significant association with FVC% predicted
including sex (p=0.55), gestational age (p=0.54), race/ethnicity
(p=0.1), median household income (p=0.25), use of public insurance
(p=0.36), secondhand smoke exposure (p=0.74), and family history of
asthma (p=0.99).
In terms of clinical characteristics, a requirement for supplemental
oxygen at the time of discharge from the NICU (-14 ± 5.4, p=0.012) and
the amount of oxygen required (-36.7 ± 10.2, p=0.001) were both found to
be negatively associated with FVC% predicted at six years of age.
Additionally, the presence of a gastrostomy tube (-12.5 ± 5.7, p=0.031)
and Nissen fundoplication (-19.7 ± 6.1, p=0.002) were also found to be
negatively associated with FVC% predicted.
No significant association was seen between FVC% predicted at six years
of age and severity of BPD (p=0.08), pulmonary hypertension (p=0.17),
personal diagnosis of reactive airway disease or asthma (p=0.28), or
prescription for inhaled corticosteroids (p=0.57). A significant
negative association was found between weight percentile for age at two
years of age (-0.2 ± 0.1, p=0.016) and FVC% predicted at six years of
age but no significant association was seen with the other growth
parameters analyzed including birth weight percentile (p=0.86), height
percentile for age at age two (p=0.11), and BMI percentile for age at
age two (p=0.12) and FVC% predicted.
Multivariate analysis was performed using the variables found in
univariate analysis to have an association with FVC% predicted. The
amount of oxygen required at the time of discharge from the NICU (-26.7
± 10.8, p=0.016), the presence of Nissen fundoplication (-14.9 ± 6.8,
p=0.031), and weight percentile for age at age 2 (-0.2 ± 0.1, p=0.005)
were found to be negatively associated with FVC% predicted at six years
of age. Severe BPD was adjusted for in the multivariate model but was
not found to have a significant association with FVC% predicted (0.2 ±
6.1, p=0.98).