RESUMO
OBJECTIVE: Because fetal respiratory movements increase left ventricular compliance, we hypothesized that the left atrial shortening fraction increases during fetal respiratory motions. METHODS: A group of 26 normal fetuses with gestational ages between 28 and 38 weeks were assessed in a prospective cross-sectional study. Left atrial telesystolic and presystolic diameters were measured during apnea and after five consecutive respiratory movements. Left atrial shortening fraction was obtained by the ratio: [maximal left atrium diameter (telesystolic) - minimal left atrium diameter (presystolic)]/maximal left atrium diameter (telesystolic). The mean of three measurements were considered. Two-tailed Student's t-test was used. RESULTS: Mean gestational age was (mean ± SD) 30.7 ± 2.8 weeks. Mean left atrial telesystolic diameter in apnea was 10.6 ± 0.7 mm and during respiratory movements it was 10.5 ± 1.1 mm (p = 0.98). Presystolic left atrial diameter was 5.2 ± 0.1 mm in apnea and 4.4 ± 1.3 mm during respiratory movements (p < 0.001). Left atrial shortening fraction was 0.50 ± 0.05 in apnea and 0.58 ± 0.13 during respiratory movements (p < 0.001). CONCLUSION: Left atrial shortening fraction is higher during respiratory movements as a result of increased left ventricular compliance and consequent optimization of left atrial functional status.
