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

Not Applicable

Completed

• Conditions: Vasodilation; Vasoconstriction
• Interventions: Drug: Phenylephrine Hydrochloride; Other: Cold Pressor Test; Other: Isocapnic Acute Hypoxia; Other: Hyperoxia

• Registration Number: NCT05001048
• Lead Sponsor: University of Alberta

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. 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.

Study Timeline

• Study Start: 2019-08-04
• Study First Submitted: 2021-08-04
• Study First Submitted QC: 2021-08-10
• Study First Posted: 2021-08-11
• Primary Completion: 2021-12-07
• Study Completion: 2022-09-09
• Status Verified: 2022-10
• Last Update Submitted: 2022-10-27
• Last Update Posted: 2022-10-31

Recruitment & Eligibility

• Status: COMPLETED
• Sex: All
• Target Recruitment: 14

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

Study & Design

• Study Type: INTERVENTIONAL
• Study Design: CROSSOVER

Arm && Interventions

Group	Intervention	Description
Low Altitude	Phenylephrine Hydrochloride	Participants will be assessed at an altitude of \<1050m.
Low Altitude	Cold Pressor Test	Participants will be assessed at an altitude of \<1050m.
Low Altitude	Isocapnic Acute Hypoxia	Participants will be assessed at an altitude of \<1050m.
Early Acclimatization to High Altitude	Phenylephrine Hydrochloride	Participants will be assessed on day 2 or 3 of a high-altitude expedition at 3,800m.
Early Acclimatization to High Altitude	Cold Pressor Test	Participants will be assessed on day 2 or 3 of a high-altitude expedition at 3,800m.
Early Acclimatization to High Altitude	Hyperoxia	Participants will be assessed on day 2 or 3 of a high-altitude expedition at 3,800m.
Late Acclimatization to High Altitude	Phenylephrine Hydrochloride	Participants will be assessed on day 9 or 10 of a high-altitude expedition at 3,800m.
Late Acclimatization to High Altitude	Cold Pressor Test	Participants will be assessed on day 9 or 10 of a high-altitude expedition at 3,800m.
Late Acclimatization to High Altitude	Hyperoxia	Participants will be assessed on day 9 or 10 of a high-altitude expedition at 3,800m.

Primary Outcome Measures

Name	Time	Method
Change in blood pressure	18 minutes	Phenylephrine sensitivity
Change in arterial blood flow	18 minutes	Phenylephrine sensitivity
Cold pressor test reactivity	4 minutes

Trial Locations

Locations (2)

University of Alberta; 🇨🇦 Edmonton, Alberta, Canada

Mount Royal University; 🇨🇦 Calgary, Alberta, Canada