Uterine haemodynamic, vascularization and blood pressure changes along the oestrous cycle in bitches

Characterization of the bitch's reproductive physiology is of utmost importance for the development of new reproductive techniques and the diagnosis of reproductive diseases. In this respect, uterine B-mode ultrasonography has been employed in several studies; however, the focus on haemodynamic changes along the oestrous cycle is yet to be described. Thus, the aim of this study was to characterize haemodynamic changes (uterine vascularization, systemic arterial blood pressure and heart rate) throughout the oestrous cycle in bitches. For this purpose, ten Golden Retriever bitches were evaluated during an entire oestrous cycle, twice during each stage of the cycle. Uterine artery blood flow, velocity wave forms, haemodynamic parameters and vascularization were analysed by Doppler ultrasonography. Furthermore, uterine diameter, arterial blood pressure and heart rate were measured. Uterine artery pulsatility index at early prooestrus was significantly lower in comparison with early oestrus, mid- and late anoestrus. Uterine artery resistance index was higher at early oestrus when compared to late oestrus and uterine diameter was significantly higher during late prooestrus. Furthermore, mean arterial blood pressure was lower and heart rate was higher during late prooestrus in comparison with the other oestrous cycle stages. In conclusion, haemodynamic changes in the uterine artery, uterine diameter, systemic blood pressure and heart rate occur during the canine oestrous cycle. Specifically, there is an increase in uterine artery perfusion, uterine diameter and mean arterial blood pressure during prooestrus, while uterine blood flow diminishes during oestrus and anoestrus.