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

University of Alberta

Status: Completed

Conditions: Vasodilation; Vasoconstriction

Treatments: Drug: Phenylephrine Hydrochloride; Other: Cold Pressor Test; Other: Isocapnic Acute Hypoxia; Other: Hyperoxia

Study type: Interventional

Funder types: Other

Identifiers

NCT05001048

Pro00088122

Details and patient eligibility

About

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.

Full 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.

Enrollment: 14 patients

Sex: All

Ages: 18 to 50 years old

Volunteers: Accepts Healthy Volunteers

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

Trial design

Primary purpose: Basic Science

Allocation: Non-Randomized

Interventional model: Crossover Assignment

Masking: None (Open label)

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14 participants in 3 patient groups

Low Altitude

Experimental group

Description:

Participants will be assessed at an altitude of \<1050m.

Treatment:

Other: Isocapnic Acute Hypoxia

Other: Cold Pressor Test

Drug: Phenylephrine Hydrochloride

Early Acclimatization to High Altitude

Experimental group

Description:

Participants will be assessed on day 2 or 3 of a high-altitude expedition at 3,800m.

Treatment:

Other: Cold Pressor Test

Other: Hyperoxia

Drug: Phenylephrine Hydrochloride

Late Acclimatization to High Altitude

Experimental group

Description:

Participants will be assessed on day 9 or 10 of a high-altitude expedition at 3,800m.

Treatment:

Other: Cold Pressor Test

Other: Hyperoxia

Drug: Phenylephrine Hydrochloride