Longitudinal Evaluation of Pulmonary Function in Premature Infants

Abstract

Background:

Infants born premature have decreased pulmonary function compared to full-term infants. Longitudinal infant studies are needed to determine whether impaired pulmonary function following premature birth demonstrates catch-up growth. This study measured airway and parenchymal function in infants born premature at approximately 6 months and 1 year of age to assess growth and the effects of gestational age (GA) and sex.

Methods:

37 infants born premature participated in two study visits (V1 and V2) at Riley Hospital in Indianapolis, IN. While sleeping, forced expiratory maneuvers were preformed to measure airway function. DL_CO, diffusion capacity of the lung, and V_A, alveolar volume, were measured under conditions of room air. Z scores were calculated to compare infants born premature and full-term, adjusting for size, race, and sex.

Demographics:

The subjects consisted of 21 females and 16 males. There were 7 subjects born at 24 – 28 weeks, 6 at 29 – 31 weeks, and 24 at 32 – 36 weeks.

Pulmonary Testing Results:

Variable

Z Score

V1

V2

V2-V1

Male

Female

GA

DL_CO

-0.17

(-0.59, 0.26)

*-0.75

(-1.18, -0.31)

*-0.58

(-1.03, -0.12)

*-0.86

(-1.42, -0.30)

-0.05

(-0.53, 0.43)

*0.13

(0.001,0.28)

V_A

0.06

(-0.24, 0.45)

-0.24

(-0.70, 0.23)

-0.30

(-0.72 ,0.14)

-0.14

(-0.71, 0.43)

-0.04

(-0.53, 0.45)

0.09

(-0.05, 0.23)

FVC

*-0.38

(-0.60, -0.17)

**-1.05

(-1.36, -0.74)

**-0.67

(-0.98, -0.36)

**-0.71

(-1.04, -0.38)

**-0.72

(-1.01, -0.44)

0.07

(-0.01, 0.15)

FEF₅₀

**-0.88

(-1.15, -0.62)

**-1.36

(-1.63, -1.08)

*-0.47

(-0.80, -0.14)

**-1.12

(-1.44, -0.79)

**-1.12

(-1.40, -0.84)

**0.15

(0.07,0.23)

FEF₇₅

**-0.57

(-0.88, -0.26)

**-1.16

(-1.48, -0.83)

*-0.59

(-0.93, -0.24)

**-0.76

(-1.16, -0.35)

**-0.97

(-1.32, -0.62)

**0.21

(0.11,0.31)

* = p < 0.05    ** = p < 0.001

DL_CO was decreased in male subjects compared to female subjects and male full-term infants. V_A was not significantly different between subjects and full-term infants. Compared to full-term infants, subjects had decreased forced vital capacity (FVC) and forced expiratory flow at 50% and 75% vital capacity (FEF₅₀ and FEF₇₅). DL_CO, FVC, FEF₅₀, and FEF₇₅ exhibited a significant decrease in pulmonary function from V1 to V2 among subjects. Gestational age showed a positive relationship for DL_CO, FEF₅₀, and FEF₇₅.

Conclusion and Potential Impact:

The subjects did not exhibit catch-up growth, or an increase in z score from V1 to V2, in parenchymal and airway function for DL_CO, FVC, FEF₅₀, and FEF₇₅. Gestational age and sex were factors affecting pulmonary function. As premature infants are born with lower pulmonary function than full-term infants, it is important to understand how lungs continue to develop after release from the NICU.