[Study on the changes of cardiac reserve function during normal vaginal delivery].

Objective: To investigate the trend of cardiac reserve function during the normal labor.

Methods: Sixty-three cases were chosen randomly from hospitalized maternal women in the First Affiliated Hospital of Chongqing Medical University from 2010 June to December (six months). The digital technique of heart sound signal processing was used to analyze cardiac reserve function parameters including the heart rate (HR), the ratio of the amplitude of the first heart sound to the second heart sound (S1/S2) and the ratio of diastolic to systolic duration (D/S) of pregnant women.

Results: (1) Comparisons of cardiac reserve function between uterine contractions and relaxations during labor: 1) Latent phase of labor (cervix dilation < 3 cm):HR was (87.3 ± 14.0) beats/min in uterine contractions and (82.8 ± 12.5) beats/min in uterine relaxations, the ratio of D/S was 1.14 ± 0.27 in uterine contractions and 1.21 ± 0.22 in uterine relaxations, the comparisons of the above two were statistically significant, P < 0.05; But the ratio of S1/S2 was 2.19 ± 0.82 in uterine contractions and 2.28 ± 0.81 in uterine relaxations, the comparison was not statistically significant, P > 0.05. 2) During early active stage of labor (cervix dilation 3 - 6 cm):HR was (89.3 ± 15.4) beats/min in uterine contractions and (83.1 ± 13.5) beats/min in uterine relaxations, the ratio of D/S was 1.09 ± 0.30 in uterine contractions and 1.20 ± 0.27 in uterine relaxations, the comparisons of the above two were statistically significant, (P < 0.05); But the ratio of S1/S2 was 2.42 ± 1.08 in uterine contractions and 2.29 ± 0.83 in uterine relaxations, the comparison was not statistically significant (P > 0.05); 3) During late active stage of labor (cervix dilation 6 - 10 cm), HR was (95.4 ± 18.7) beats/min in uterine contractions and (86.2 ± 15.6) beats/min in uterine relaxations, the ratio of D/S was 1.01 ± 0.25 in uterine contractions and 1.18 ± 0.25 in uterine relaxations, the comparisons of the above two were statistically significant, (P < 0.05); But the ratio of S1/S2 was 2.61 ± 1.26 in uterine contractions and 2.67 ± 1.19 in uterine relaxations, the comparison was not statistically significant (P > 0.05). 4) The second stage of labor (cervical dilation ≥ 10 cm):HR was (109.4 ± 19.7) beats/min in uterine contractions and (93.5 ± 16.7) beats/min in uterine relaxations, the ratio of D/S was 0.89 ± 0.23 in uterine contractions and 1.14 ± 0.26 in uterine relaxations, the ratio of S1/S2 was 3.66 ± 1.37 in uterine contractions and (2.81 ± 1.07) in uterine relaxations, the comparisons of all were statistically significant (P < 0.05). (2) Comparison of cardiac reserve function in uterine relaxations of each stage of labor: 1) Maternal heart rate gradually increased from latent stage of labor to the second stage of labor, and decreased postpartum, the comparison was statistically significant (P < 0.05); 2) The ratio of S1/S2 of maternal gradually increased from latent stage of labor to the second stage of labor, and decreased postpartum, the comparison was statistically significant (P < 0.05); 3) The ratio of D/S gradually decreased from latency to the second stage of labor, and increased postpartum, the comparison was statistically significant (P < 0.05). (3) Comparison of cardiac reserve function in uterine contractions of each stage of labor: 1) Maternal heart rate gradually decreased from latent stage of labor to the second stage of labor, the comparison was statistically significant (P < 0.05); 2) The ratio of S1/S2 of maternal gradually increased from latent stage of labor to the second stage of labor, the comparison was statistically significant (P < 0.05); 3) The ratio of D/S gradually decreased from latency to the second stage of labor, the comparison was statistically significant (P < 0.05).

Conclusions: The maternal cardiac reserve function decreased in uterine contractions than relaxation during labor; With the progress of labor, the maternal cardiac reserve function declined, especially in the second stage of labor, and recovered in postpartum stage.