Clinical trial NCT05525416: Sex Differences in Sympathetic Vascular Reactivity at High Altitude
Official title: Sex Differences in Sympathetic Vascular Reactivity at High Altitude
Study type: INTERVENTIONAL
Overall status: COMPLETED
Phase: NA
Conditions: Vasodilation
Vasoconstriction
Lead sponsor: University of Alberta
Sponsor class: OTHER
First posted: 2022-09-01
Enrollment: 17
Sex: ALL
Minimum age (years): 18
Maximum age (years): 45
Standard ages: ADULT
Accepts healthy volunteers: yes
Allocation: NON_RANDOMIZED
Intervention model: CROSSOVER
Intervention model description: Participants will partake in both arms of the study, which include: 1) low altitude and 2) high altitude assessments.
Primary purpose: BASIC_SCIENCE

Brief summary: This study aims to investigate sex differences in blood pressure control associated with exposure to acute hypoxia (low oxygen), and short term acclimatization to hypoxia at high altitude.

Detailed description: About 200 million people worldwide live at high altitudes and millions of others travel to high altitude every year for work or pleasure. At high altitude participants are exposed to a lower than normal level of oxygen, also known as hypoxia. This causes stress to the human body, which will adapt in order to maintain adequate oxygen delivery to its tissues. One of these adaptations is an increase in activity of participants' sympathetic nervous system ("fight or flight" response). Sympathetic nerve activity affects the size of participants' blood vessels, which in turn will affect blood pressure. Men and women regulate their blood pressure in different ways; for example, women tend to have lower blood pressure and sympathetic nerve activity than men. Women also appear to have less constriction of their blood vessels in response to stress. This may be in part because estrogen causes blood vessels to dilate. It may also be due to differences in the receptors which are activated by the sympathetic nervous system. These receptors are called alpha and beta receptors and respond to sympathetic nerve activity in opposite directions. Women represent 50% of the population living at and travelling to high altitude, therefore, it is important to understand the differences in how men and women respond to low oxygen.

The main purpose of this study is to examine the differences between men and women in the sympathetic nervous system control of blood vessels during exposure to low oxygen. To study this question, the investigators will test how blood vessels respond to stressors in both men and women. Participants will be recruited at the Canadian sites, and the investigators will test them while they breathe low oxygen for a short amount of time at low altitude. The investigators will also perform assessments on the same participants during a two week stay at high altitude at White Mountain, CA, which is at an altitude of 3,800m. These data will have implications in the basic understanding of differences between male and female physiology. Specifically, to males and females living or travelling to high altitude.

Eligibility criteria: Inclusion Criteria:

* Between ages of 18-50
* No medical history of cardiovascular, respiratory, nervous system, or metabolic disease
* Females must be pre-menopausal

Exclusion Criteria:

* Any known cardiovascular, respiratory, nervous system, or metabolic disease (however, participants with controlled arterial hypertension will not be excluded)
* Having travelled above 2,000m within 1 month of testing at low and high altitude
* Females who are pregnant, confirmed by a pregnancy test
* Females who are post-menopausal
* Participants that are classified as obese (body mass index \> 30kg⋅m²)
* Participants who are current daily smokers
* Those with a known allergy to sulfites
* Participants taking monoamine oxidase (MAO) inhibitors or tricyclic antidepressants or other medications that have contraindications with the study drugs
* Participants who are still within the washout period from participating in other studies involving drugs.

Primary outcomes:
measure: Change in systolic, diastolic, and mean arterial blood pressure
timeFrame: 3 minutes
measure: Change in arterial blood flow
timeFrame: 1 hour 30 minutes
measure: Change in vascular conductance
timeFrame: 20 minutes
measure: Cold pressor test
timeFrame: 3 minutes
measure: Propranolol
timeFrame: 2 hours
measure: Phentolamine
timeFrame: 1 hour
Secondary outcomes:
Other outcomes:
Locations:
city: Edmonton
country: Canada
facility: University of Alberta
state: Alberta
city: Kelowna
country: Canada
facility: University of British Columbia - Okanagan
state: British Columbia
Study officials:
affiliation: University of Alberta
name: Sean van Diepen, MD, MSc
role: PRINCIPAL_INVESTIGATOR
affiliation: University of Alberta
name: Craig D Steinback, PhD
role: PRINCIPAL_INVESTIGATOR
References:
citation: Hart EC, Charkoudian N, Wallin BG, Curry TB, Eisenach JH, Joyner MJ. Sex differences in sympathetic neural-hemodynamic balance: implications for human blood pressure regulation. Hypertension. 2009 Mar;53(3):571-6. doi: 10.1161/HYPERTENSIONAHA.108.126391. Epub 2009 Jan 26.
citation: Mazzeo RS, Child A, Butterfield GE, Mawson JT, Zamudio S, Moore LG. Catecholamine response during 12 days of high-altitude exposure (4, 300 m) in women. J Appl Physiol (1985). 1998 Apr;84(4):1151-7. doi: 10.1152/jappl.1998.84.4.1151.
citation: Purdy GM, James MA, Rees JL, Ondrus P, Keess JL, Day TA, Steinback CD. Spleen reactivity during incremental ascent to altitude. J Appl Physiol (1985). 2019 Jan 1;126(1):152-159. doi: 10.1152/japplphysiol.00753.2018. Epub 2018 Nov 21.
citation: Usselman CW, Gimon TI, Nielson CA, Luchyshyn TA, Coverdale NS, Van Uum SH, Shoemaker JK. Menstrual cycle and sex effects on sympathetic responses to acute chemoreflex stress. Am J Physiol Heart Circ Physiol. 2015 Mar 15;308(6):H664-71. doi: 10.1152/ajpheart.00345.2014. Epub 2014 Dec 19.