Myocardial performance and baroreceptor reflexes in preterm neonates: An echocardiographic evaluation using the tilt-table test

The hemodynamic consequence of head-up position in preterm infants is not k nown, so we used the tilt-table test to assess changes in myocardial perfor mance and baroreceptor reflexes. Twenty-five preterm infants with gestation al age (GA) (mean SD) 31 +/- 2.9 weeks (range 25-35.5 weeks), birth weight of 1612 +/- 642 g (range 520-3260 g) were studied in supine, 30 degrees, an d 60 degrees head-up positions. GA had a significant effect on heart rate ( HR) (p = 0.007), systolic blood pressure (SBP) (p = 0.03), left ventricular (LV) cavity dimensions (p = 0.001), cardiac output (CO) (p = 0.001), LV ej ection time (LVETc) (p = 0.05), and end systolic wall stress (ESWS) (p = 0. 003). An inverse relationship was seen between velocity of circumferential fiber shortening (VcFs) and ESWS (slope b = -0.019 +/- 0.008, p = 0.003). R esults of tilt tests showed that at supine, 30 degrees, and 60 degrees, res pectively, HR was 162 +/- 10.5, 162 +/- 9, and 164 +/- 12 (p = NS); SBP (mm Hg) was 73 +/- 11, 72.5 +/- 9.5, and 78 +/- 10 (p = NS); CO (L/kg/min) was 0.4 +/- 0.16, 0.4 +/- 0.15, and 0.43 +/- 0.16 (p = NS); ESWS (g/cm(2)) was 38.7 +/- 8.3, 40.9 +/- 9.9, and 43.4 +/- 10.7 (p = NS); and VcFs (circ/sec) was 1.35 +/- 0.3, 1.28 +/- 0.4, and 1.26 +/- 0.2 (p = NS). LV filling patt ern as seen by early/late atrial Doppler flow velocity ratio did not change with tilt (p = NS). Myocardial performance improved with increasing GA. No significant differences in myocardial performance were found between basel ine and head-up tilt positions.