Oscillations of cerebrovascular resistance throughout the menstrual cycle in healthy women.
OBJECTIVES: Increased concentration of endogenous estrogen during a typical menstrual cycle has been shown to correlate with augmentation of blood flow through the internal carotid arteries (ICAs), which may be related to changes in vascular resistance within the brain. In this study we investigated the effects of endogenous estrogen and progesterone on cerebrovascular impedance in young healthy women. METHODS: The blood flow in the ICA and the common (CCA) and external (ECA) carotid arteries was studied with duplex Doppler sonography. The resistance index (RI) was determined and correlated with plasma 17beta-estradiol concentration in 14 young healthy women throughout their menstrual cycle. RESULTS: The concentration of 17beta-estradiol increased in the follicular phase of the cycle and reached a peak on day 14, whereas concentration of progesterone remained low. Along with an increase in estrogen concentration, the ICA RI had decreased from its initial level on average by 9.2% on day 13 and by 6.7% on day 14 (P < 0.05). In contrast, the trend of the ECA RI was to increase during the peak of estrogen concentration. There were no significant changes in the CCA RI or in the systolic blood pressure, heart rate, hematocrit and hemoglobin concentration through the menstrual cycle. CONCLUSIONS: Estrogen-related augmentation of blood flow through the ICA is caused mainly by decreased cerebrovascular impedance, as shown by a decrease in the ICA RI. These changes in RI suggest that estrogen influences cerebral impedance mainly by altering the resistance of cerebral microvasculature.