Presumed Normal Hemodynamic Values of the Arteries in the Final Third Period of Gestation in Bitches

Background: Doppler ultrasonography enables the investigation of vascular blood flow indexes in gestational assessment, being able to detect vascular resistances that can affect fetal and maternal circulation, such as cases of placental insufficiency, associated with fetal cerebral oxygenation deficit and fetal distress. The study aims to assume hemodynamically normal values in the final third of gestation in bitches, of the umbilical, uteroplacental, middle cerebral and internal carotid arteries, correlating the obtained Doppler velocimetric indexes, for the assessment of the feto-placental circulation, and prediction of fetal viability indexes, fetal centralization and probable date of delivery.Materials, Methods & Results: Thirty healthy bitches were examined in the final third of gestation (40-60 days). These were evaluated by Doppler ultrasonography at 2 times (T): T1: between 40-50 days; T2: between 51-60 of gestation. At each time point, the peak systolic velocities (PSV) and end-diastolic velocities (EDV) used to obtain the pulsatility (IP) and resistivity (IR) indexes of the umbilical, uteroplacental, middle cerebral and internal carotid arteries of fetuses were evaluated. Also, the systole/diastole (S/D) ratio of these vessels was evaluated. The data obtained were subjected to analysis of variance and Tukey test, using a P value equal to 5%. A significant difference was observed between velocities and Doppler velocimetric indexes between the 2 phases of the gestational final third in all studied vessels. There was an increase in the values of PSV and EDV and a decrease in the indexes, as the probable date of delivery approached. The analysis of the umbilical cord IR showed an increase from P1 to P2 (P < 0.05), while the IP decreased at the same time. For all studied variables there was a statistically significant difference (P < 0.05). In the uteroplacental artery, similarly to the umbilical artery, the PSV and EDV values showed an increase between P1 and P2, while the S/D ratio decreased up to 60 days of gestation (P2). The IR and IP of these vessels decreased during the study interval in pregnant bitches. The studied variables showed a statistically significant difference when analyzed comparatively between P1 and P2 (P < 0.05). As for the middle cerebral artery and internal carotid artery, the PSV and EDV values increased until the end of pregnancy. Likewise, the Doppler velocimetric values and the S/D ratio decreased until the end of pregnancy (P2).Discussion: The hemodynamic values obtained for the umbilical artery and uterine artery were significantly different between 40 and 50 days of gestation (P1) and 50 and 60 days of gestation (P2), with a decrease in vascular resistance and an increase in velocities. It can be related to a greater association of maternal-fetal blood perfusion, due to the increased demand for the development of the fetus. The Middle Cerebral Artery (MCA) also showed changes between P1 and P2, with an increase in PSV and EDV in the final third of pregnancy, and the S/D ratio was reduced, differing significantly between P1 and P2. The systolic (PSV) and diastolic (EDV) flow velocities of the internal carotid artery increased progressively, while the IR, IP and the S/D ratio decreased, between the evaluated periods (P1 and P2), providing greater flow in canine fetuses, maintaining normal heart rate, indicating positive fetal viability. Keywords: Doppler, gestational ultrasound, bitches, fetal circulation, umbilical artery, internal carotid, fetal middle cerebral artery.