Spaceflight is characterized by unique physiological adaptations. Cardiovascular system response to the microgravity includes major changes. During spaceflight, body fluids are displaced in the cephalad direction due to changes in gravity, resulting in altered vascular dynamics and the redistribution of the blood circulation.

As the investigators approach crewed Moon and Mars missions and commercial spaceflights become more frequent, understanding the impact of space travel on women's health is crucial. Despite the known importance of these vascular dynamics in both clinical and research settings, there is limited information on the pelvic blood flow under microgravity. The aim of this project is to fill this gap by analyzing the impact of simulated microgravity on the perfusion of female reproductive organs using Doppler velocimetry. Head-down tilt (HDT) position is an established model in literature for simulated microgravity on Earth.

This prospective study will assess pelvic organ blood flow in the supine position after a period of acclimation as a control. After completing Doppler measurements in the supine position, the participant will be placed in the HDT position. Following a period of acclimation, Doppler measurements will be repeated on the same vessels.During both supine and simulated microgravity conditions, vital signs (i.e., blood pressure, heart rate, oxygen saturation) will be collected.

Cardiovascular system response to the microgravity includes major changes. During spaceflight, body fluids are displaced in the cephalad direction due to changes in gravity, resulting in altered vascular dynamics and the redistribution of the blood circulation. Redistribution of fluids triggers baroreceptor reflex and autonomic response initiates. Cardiovascular response to the microgravity environment is affected by gender. Women tend to lose more plasma volume and have less peripheral vascular resistance in response to microgravity analogue situations like bed rest.

Simulated microgravity leads to increased stiffness and remodeling of the aorta, a major vessel supplying blood to the abdomen, pelvis, and lower extremities. Pelvic organs are located in the lower abdomen and have rich blood supply through these major blood vessels and anastomosis. Mathematical modeling for microgravity showed a 6% mean flow rate variation in the last part of abdominal aorta. Furthermore, mean flow rate variations and resistance changed based on the branching arteries, such as internal iliac arteries. The uterine and ovarian arteries branch from the internal iliac arteries and abdominal aorta, respectively. Blood supply to an organ and tissue perfusion are vital for the proper functioning of the organs and tissues.

As the investigators approach crewed Moon and Mars missions and commercial spaceflights become more frequent, understanding the impact of space travel on women's health is crucial. Despite the known importance of these vascular dynamics in both clinical and research settings, there is limited information on the pelvic blood flow under microgravity. Our aim is to fill this gap by analyzing the impact of simulated microgravity on the perfusion of female reproductive organs using Doppler velocimetry. Head-down tilt (HDT) position is an established model in literature for simulated microgravity on Earth.

This prospective study will be conducted at Koç University Hospital. Adult women of reproductive age (18-44 years) undergoing abdominal ultrasound will be recruited. Participants will be selected from a cohort presenting for their well-woman visit; there will be no additional visits. Ultrasound and Doppler spectrometry evaluations will be carried out with convex and linear probes of the GE Loqic S8 device. The researchers will assess pelvic organ blood flow in the supine position after a period of acclimation as a control. After completing Doppler measurements in the supine position, the participant will be placed in the HDT position. Following a period of acclimation, Doppler measurements will be repeated on the same vessels. During both supine and simulated microgravity conditions, vital signs (i.e., blood pressure, heart rate, oxygen saturation) will be collected. Pre- and post-HDT Doppler measurements will be compared and analyzed.

Inclusion Criteria:

• 18-44 years old healthy female individuals

Exclusion Criteria:

• History of hysterectomy and/or oophorectomy
• Pregnancy
• Premature ovarian insufficiency
• Women with reproductive tract pathologies
• Cardiovascular diseases