## 4 Discussion  
Our present study evaluated the effects of low-dose dexamethasone therapy in premature neonates on cardiorespiratory function and physiology. Using standard and advanced echocardiographic techniques, we investigated the effects of steroids on cardiac performance and pulmonary vascular resistance. Our results show that there was a significant improvement in respiratory parameters with dexamethasone therapy, along with an improvement in right heart systolic performance. The longitudinal systolic function of the LV also improved, as indicated by increases in the LV S' and Septal S'. There was no significant reduction seen in the echocardiographic measures of PVR, and no change was seen in the LV wall thickness with the range of dexamethasone doses used in this cohort. Using echocardiography, we demonstrate the positive longitudinal changes to the markers of biventricular systolic heart function in extreme preterm neonates with dexamethasone therapy. Unlike previous studies, this is the first study to show an improvement in LV systolic function with dexamethasone therapy using load-independent technology such as TDI. The use of dexamethasone therapy in the management of CLD is based on the beneficial effects of steroids on the lungs. Steroids have been shown to improve lung function, reduce inflammation, increase antioxidant activity, and increase surfactant synthesis. In this study, we saw an improvement in the respiratory parameters of infants with the initiation of dexamethasone. This improvement was sustained 1-2 weeks post dexamethasone completion and was mainly seen in the form of reduced inflation pressure and oxygen requirements, subsequently suggesting an overall improvement in compliance and gas exchange. These findings are in keeping with other studies [2; 3; 4; 5; 6; 20]. Around 44% of the cohort was successfully extubated; however, the majority received a diagnosis of BPD. During the study period, two different dose regimes were used: a very-low-dose regime of a 0.35 mg/kg cumulative dose and a comparatively higher regimen of a 1.02 mg/kg cumulative dose. The latter dose was associated with a higher chance of extubation success. The latter dose is in keeping with the current recommendation by the CPS [8] and in line with the recently published network meta-analysis [5]. On examination of the RV indices, we found that dexamethasone therapy had a significant positive effect on right heart systolic performance, as measured by the RV FAC, TAPSE, and RV S' through TDI. There was a longitudinal reduction in the eccentricity index, suggesting a favorable transition from a pulmonary to systemic pressure relationship. Interestingly, we did not see any significant changes in the PAAT and PAAT: RVET ratio--a surrogate measure of PVR. With the improvement in PVR, we expect the PAAT: RVET ratio to increase. In our study, the PAAT: RVET ratio increased from 0.30 to 0.41 post dexamethasone therapy but was not statistically significant. [PERSON] et al. in 1994 [21] and more recently [PERSON] et al. in 2022 [22] demonstrated a reduction in PVR with the use of steroids. In the [PERSON] et al. study, 20 neonates who received dexamethasone therapy were observed to undergo an increase in the PAAT: RVET ratio after the initiation of dexamethasone, suggesting a decrease in pulmonary artery pressure; however, this change was not sustained and did not show a correlation with the improvement noted in the respiratory status. On the contrary, we did see a significant unit decrease in the eccentric index over time, which reflects a longitudinal reduction in pulmonary artery pressure. The lack of significant change in the PAAT: RVET ratio in our study could be due to the small sample size, two different dosing regimens making the assessment difficult, the inherent limitations of the measure to accurately reflect the actual state of PVR, technical limitations in the extreme preterm population, and/or shortcomings of the measurement, especially in the presence of a PDA.