Sex Differences in Sympathetic Activity and Vascular Reactivity During Acute and Chronic Hypoxia.

Vasodilation Clinical Trial

Official title:

Sex Differences in Sympathetic Activity and Vascular Reactivity During Acute and Chronic Hypoxia.

Clinical Trial Details — Status: Completed

Administrative data

• NCT number: NCT05001048
• Other study ID #: Pro00088122
• Status: Completed
• Phase: N/A
• Start date: August 4, 2019
• Est. completion date: September 9, 2022

Study information

• Verified date: October 2022
• Source: University of Alberta
• Contact: n/a
• Is FDA regulated: No
• Study type: Interventional

Clinical Trial 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.

Description:

About 200 million people worldwide live at high altitudes. Millions of others travel to high altitude every year for work or travel. The low oxygen (or hypoxia) experienced at high altitudes causes considerable physiological stress, and the body adapts in order to maintain adequate oxygen delivery to its tissues. One of these adaptations is an increase in the activity of the sympathetic nervous system. This system is responsible for the "fight or flight" response. Sympathetic activity regulates the size of the blood vessels, which will affect blood pressure. Previous studies suggest that males and females regulate their blood pressure in different ways. Females tend to have lower resting sympathetic activity, and less vasoconstriction in response to stressors than males. Blood pressure changes are also influenced by levels of sex hormones; for example, estrogen may cause opposing vasodilation. Therefore, it is important to understand the differences in how males and females respond to low oxygen. The main purpose of this study is to examine the differences between males and females in control of blood vessels during exposure to low oxygen. To study this question, we will test vasoreactivity to set physiological stressors in both males and females. Participants will be recruited at the Canadian sites, and we will test them while they breathe low oxygen for a short amount of time at low altitude. We 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.

Recruitment information / eligibility

• Status: Completed
• Enrollment: 14
• Est. completion date: September 9, 2022
• Est. primary completion date: December 7, 2021
• Accepts healthy volunteers: Accepts Healthy Volunteers
• Gender: All
• Age group: 18 Years to 50 Years

Eligibility

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)
• Have a history of smoking regularly in the last 6 months (but nicotine substitutes (patch, gum) not an exclusion criteria)
• Those with a known allergy to sulfites
• Participants taking monoamine oxidase (MAO) inhibitors or tricyclic antidepressants

Related Conditions & MeSH terms

• Hypoxia
• Vasoconstriction
• Vasodilation

Intervention

Drug:
• Phenylephrine Hydrochloride
Series of three incremental bolus injections to observe a1-adrenoreceptor mediated vasoconstriction.

Other:
• Cold Pressor Test
Standardized sympathetic stressor involving submersion of the hand in ice-cold water for 3-minutes, aiming to elicit endogenous neurotransmitter release and blood pressure increases.
• Isocapnic Acute Hypoxia
During low altitude assessment, participants will be exposed to isocapnic hypoxia equivalent to 3,800m to assess responses to acute exposure.
• Hyperoxia
During high altitude assessments, participants will breathe an oxygen concentration comparable to their end-tidal values at low altitude for the assessment of the influences of acclimatization.

Locations

Country	Name	City	State
Canada	Mount Royal University	Calgary	Alberta
Canada	University of Alberta	Edmonton	Alberta

Sponsors (1)

Lead Sponsor	Collaborator
University of Alberta

Country where clinical trial is conducted

Canada, 

References & Publications (4)

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. — View 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. — View 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. — View 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. — View Citation

Outcome

Type	Measure	Description	Time frame	Safety issue
Primary	Change in blood pressure	Phenylephrine sensitivity	18 minutes
Primary	Change in arterial blood flow	Phenylephrine sensitivity	18 minutes
Primary	Cold pressor test reactivity		4 minutes