Human Cerebral Blood Flow Regulation (Gas Challenge)

  • End date
    May 25, 2026
  • participants needed
  • sponsor
    University of Wisconsin, Madison
Updated on 25 July 2022
Accepts healthy volunteers


This study tests basic differences in how men and women control brain (cerebral) blood flow (CBF), at rest and under stress. The stress is low oxygen or high carbon dioxide. The investigators hypothesize that sex differences per se, plus sex hormone differences, drive different signals in blood vessels that change the way CBF is regulated. The investigators will test these mechanisms with medicine infusions during stress, and measure CBF using state-of-the-art MRI approaches. Research confounding variables like aging and disease will be mitigated by comparing younger adults (18-40 years old).


Cerebrovascular disease is the third leading killer in the U.S., and contributes to decreased quality of life and increased long-term care spending. The risk of cerebrovascular disease is inversely associated with resting cerebral blood flow (CBF). Men exhibit a lower resting CBF and have twice the risk of cerebrovascular disease when compared to premenopausal women. The ability of cerebral vessels to respond to challenges is also inversely related to disease risk, and may be useful in identifying at-risk patients pre-clinically. However, these studies are often confounded by aging and/or comorbidities, and the associations provide little insight into physiologic mechanisms responsible for sexually dimorphic cerebrovascular disease risk. Conversely, animal studies use supraphysiologic levels of hormone treatment in primarily young animals, which limits the translational relevance of animal CBF mechanisms. While there is general agreement that estrogen is protective in healthy adults, the basic impact of sex, and physiologic fluctuations in sex hormones, on mechanisms of CBF control remains unclear.

The overall goal of this research program is to investigate the mechanisms which actively control cerebral blood flow (CBF) in humans, particularly how men and women differ in control mechanisms on a regional basis throughout the brain circulation. The investigators propose to study CBF control mechanisms in healthy younger (18-40 yrs) adult men and women. The overall hypothesis is that female sex and sex hormones contribute to larger stress-induced increases in CBF, due to greater prostanoid (COX) and nitric oxide (NOS) dilation.

A key technological innovation of this proposal derives from multi-mode, high-resolution, flow sensitive MRI to quantify CBF at macrovascular and microvascular levels, at rest, and in response to environmental challenges (stress test for the brain). Additionally, the research design allows for quantification of sex differences in two vascular control mechanisms across all brain regions. Preliminary data demonstrate: hypoxic cerebral vasodilation is 60-100% higher in women compared to men, COX inhibition reduces dilation in women but not men, NOS inhibition reduces vasodilation more in women. Those concepts will be tested in Aims 1-2 of the grant in this current proposal, covered in Phase 1 using technical innovative MRI and pharmacologic tools to test potential sex specific mechanisms of CBF control. The conceptual innovation is planned in Aim 3 of the grant (or Phase 2). Participants must complete Phase 1 studies to continue to Phase 2. Study procedures in Phase 1 and 2 are identical, but we conduct them twice: once in the context of sex hormone suppression, and a second time during a single hormone replacement (during suppression), to study the independent impact of testosterone (men) and estrogen (women) on CBF control mechanisms.

Substantial preliminary findings support these hypotheses, and integrated physiologic, pharmacologic, and MRI approaches are available to test them. This state-of-the-art approach will yield previously unattainable insight into not only maintaining basal CBF, but actively controlling it during physiologic demands for increased flow. These novel, high resolution, regionally-specific, sex-specific, and mechanism-specific findings will serve as a knowledge platform, for designing sex-specific CBF studies in high risk disease populations (e.g. diabetes, hypertension, Alzheimer's) which exhibit strong sex-specific etiology and important vascular contributions.

Three Specific Aims will be addressed in this study:

Aim 1: Test the hypothesis that healthy males exhibit reduced cerebral vasodilation compared to healthy females despite exhibiting similar vasodilation to hypercapnia.

  • Aim 1A: Vasodilation to hypoxia will be markedly lower in males, more so in anterior brain regions.
  • Aim 1B: Vasodilation to hypercapnia will be similar between sexes.

Aim 2: Test the hypothesis that acute inhibition of COX or NOS will reduce sex differences in hypoxia-mediated cerebral vasodilation.

  • Aim 2A: COX-mediates vasodilation primarily in females.
  • Aim 2B: NOS mediates vasodilation more in females than males.

Aim 3: Test the hypothesis that manipulating sex steroids can abolish or magnify sex differences in vasodilation.

  • Aim 3A: Short-term suppression of sex steroids will abolish sex differences in resting and hypoxic CBF via greater losses of COX- and NOS-mediated vasodilation in females than males.
  • Aim 3B: Short-term supplementation of unopposed testosterone in males will magnify sex differences by driving COX vasoconstriction (TXA2) and uncoupled NOS vasoconstriction.
  • Aim 3C: Short-term supplementation of unopposed estradiol in females will magnify sex differences via increased NOS and COX vasodilation.

Condition Cerebral Arterial Diseases
Treatment Ketorolac Tromethamine, L-NMMA, Ganirelix acetate, Testosterone Transdermal Product, Estradiol Topical, Estradiol Topical
Clinical Study IdentifierNCT04265053
SponsorUniversity of Wisconsin, Madison
Last Modified on25 July 2022


Yes No Not Sure

Inclusion Criteria

All participants will be healthy adults between 18-40 years old, matched for age and aerobic fitness
Participants will be non-hypertensive (<125/80mm Hg)
Participants will be non-obese (BMI 19-25 kg/m2)
Participants will have normal blood glucose (<100 g/dl)
Participants will have normal lipids (LDL cholesterol <130 mg/dl, triglycerides <150 mg/dl)
Women must have a natural regular menstrual cycle

Exclusion Criteria

Participants with a history of
peripheral vascular disease
hepatic disease
renal disease
hematologic disease
sleep apnea
Participants with current BP>130/85 mmHg
Regular smokers
Taking cardiovascular medications
Women who take hormonal birth control
Women who are pregnant or have polycystic ovarian syndrome [Hormonal birth control will not be allowed in women]
Contradictions to MRI
Clear my responses

How to participate?

Step 1 Connect with a study center
What happens next?
  • You can expect the study team to contact you via email or phone in the next few days.
  • Sign up as volunteer to help accelerate the development of new treatments and to get notified about similar trials.

You are contacting

Investigator Avatar

Primary Contact



Additional screening procedures may be conducted by the study team before you can be confirmed eligible to participate.

Learn more

If you are confirmed eligible after full screening, you will be required to understand and sign the informed consent if you decide to enroll in the study. Once enrolled you may be asked to make scheduled visits over a period of time.

Learn more

Complete your scheduled study participation activities and then you are done. You may receive summary of study results if provided by the sponsor.

Learn more

Similar trials to consider


Browse trials for

Not finding what you're looking for?

Every year hundreds of thousands of volunteers step forward to participate in research. Sign up as a volunteer and receive email notifications when clinical trials are posted in the medical category of interest to you.

Sign up as volunteer

user name

Added by • 



Reply by • Private

Lorem ipsum dolor sit amet consectetur, adipisicing elit. Ipsa vel nobis alias. Quae eveniet velit voluptate quo doloribus maxime et dicta in sequi, corporis quod. Ea, dolor eius? Dolore, vel!

  The passcode will expire in None.

No annotations made yet

Add a private note
  • abc Select a piece of text from the left.
  • Add notes visible only to you.
  • Send it to people through a passcode protected link.
Add a private note