Filling characteristics of the left ventricle in newborn lambs.
Velvis, Harm, H. Sidney Klopfenstein.
Department of Pediatrics, Cardiology Section (HV) and Department of
Internal Medicine, Cardiology Section (HSK), Bowman Gray School of
Medicine, Wake Forest University, Winston-Salem, NC 27157
APStracts 2:0265H, 1995.
An integral component of increased cardiac performance in the
immediate newborn period is an increased rate of left ventricular
(LV) filling. To determine the factors that facilitate increased LV
filling in newborns, we compared filling characteristics in
chronically instrumented awake newborn (7 +/- 2 d) and older lambs
(55 +/- 5 d). The studies were performed 4 +/- 2 d after surgery,
during which pressure transducers, dimension crystals, a flow
transducer, and vascular occluders were placed. Newborn lambs had an
increased cardiac index (247 +/- 40 vs 127 +/- 48 ml/kg/min;
p<0.01), due to an increased heart rate (223 +/- 24 vs 120 +/- 9
bpm; p<0.01), and despite a similar stroke volume index (1.1 +/-
0.1 vs 1.1 +/- 0.5 ml/kg; NS). In newborn lambs, indexed mean LV
filling rates were more than two-fold higher (10.5 +/- 2.5 vs 4.6 +/-
1.7 ml/kg/sec; p<0.01) and a much greater percentage of filling
occurred in the first 35 msec after mitral valve opening (52 +/- 7 vs
23 +/- 8 %; p<0.01). In newborn lambs, early diastolic filling
was facilitated by more rapid LV relaxation (tau: 17.2 +/- 2.2 vs
23.3 +/- 1.2 msec; p<0.01) and a higher LA pressure at the time
of mitral valve opening (11.6 +/- 2.4 vs 7.2 +/- 3.2 mmHg;
p<0.05). LV filling in newborn lambs also occurred at the
expense of a higher mean LA pressure (8.4 +/- 2.4 vs 5.1 +/- 2.6
mmHg; p<0.05). These findings improve our understanding of LV
diastolic function in newborns.
Received 18 April 1995; accepted in final form 20 June 1995.
APS Manuscript Number H368-5.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 11 July 1995.