Purpose: Preterm infants are at increased risk of systemic hypertension compared to term infants. Bronchopulmonary dysplasia (BPD) has been shown to be associated with hypertension in preterm infants albeit with no causation reported. BPD is characterized by abnormal pulmonary function tests (PFTs), specifically elevated passive respiratory resistance (Rrs), decreased passive respiratory compliance (Crs), and decreased functional residual capacity (FRC). There have been no studies comparing PFTs in very low birth weight (VLBW) infants with and without hypertension. We hypothesized that stable VLBW infants with hypertension will have altered PFTs. Patients and methods: Retrospective cohort study of infants <1500 g at birth (VLBW) who had PFTs performed near 34-36 weeks of corrected gestational age (CGA). We excluded infants with congenital anomalies, known hypertensive disorders or those at risk of medication-induced hypertension. Data obtained included PFT parameters (Rrs, Crs, FRC) and mean systolic blood pressure (SBP). Results: Fifty-nine VLBW infants were identified for analysis, 14 with and 45 without hypertension. Hypertensive and normotensive patients were similar in terms of mean gestational age (26.6 vs 27.4 weeks), mean CGA at PFTs (36.1 vs 34.6 weeks) and proportion of BPD (36% vs 36%). The Rrs was significantly higher in hypertensive versus normotensive patients [median Rrs of 0.080 (0.069, 0.090) versus 0.066 (0.054, 0.083) cmH 2 O/mL/s; p=0.04]. There was no difference in systolic blood pressure in the infants with and without BPD. Conclusion: In this cohort of contemporary VLBW infants, those with hypertension had increased Rrs. This finding warrants a prospective study with a larger sample size and longterm follow-up.
Plain language summaryPrior work has linked bronchopulmonary dysplasia (a chronic lung disease that is relatively common in the most premature of neonates) to systemic hypertension; however, this link has not been fully elucidated. To add to the limited fund of knowledge surrounding this association, our group compared objective pulmonary function test parameters of premature neonates with and those without systemic hypertension. The findings of our work demonstrate that there is commonly an increase in the airway resistance in those with systemic hypertension compared to those without. We speculate that since adequate vascular development within the lungs and kidneys promotes growth, there could be a common developmental issue within the lung and kidney causing the altered lung mechanics and elevated blood pressure, but this will require further study.