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

Study Results

Results pending

The study team has not published outcome measurements, participant flow, or safety data for this trial yet. Check back later for updates.

Basic Information

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Recruitment Status

COMPLETED

Clinical Phase

NA

Total Enrollment

14 participants

Study Classification

INTERVENTIONAL

Study Start Date

2019-08-04

Study Completion Date

2022-09-09

Brief Summary

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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.

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Detailed Description

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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.

Conditions

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Vasodilation Vasoconstriction

Study Design

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Allocation Method

NON_RANDOMIZED

Intervention Model

CROSSOVER

Participants will partake in all three arms of the study, which include: 1) low altitude, 2) early acclimatization, and 3) late acclimatization to high altitude assessments.

Primary Study Purpose

BASIC_SCIENCE

Blinding Strategy

NONE

Due to the study design, masking is not possible. The time points and dosages of the study drug will be known to the participant. Further, due to the wash-out time of the acute hypoxia/hyperoxia interventions, these will always be completed second to the interventions breathing room air.

Study Groups

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Low Altitude

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

Group Type EXPERIMENTAL

Phenylephrine Hydrochloride

Intervention Type DRUG

Series of three incremental bolus injections to observe α1-adrenoreceptor mediated vasoconstriction.

Cold Pressor Test

Intervention Type OTHER

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

Intervention Type OTHER

During low altitude assessment, participants will be exposed to isocapnic hypoxia equivalent to 3,800m to assess responses to acute exposure.

Early Acclimatization to High Altitude

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

Group Type EXPERIMENTAL

Phenylephrine Hydrochloride

Intervention Type DRUG

Series of three incremental bolus injections to observe α1-adrenoreceptor mediated vasoconstriction.

Cold Pressor Test

Intervention Type OTHER

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.

Hyperoxia

Intervention Type OTHER

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.

Late Acclimatization to High Altitude

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

Group Type EXPERIMENTAL

Phenylephrine Hydrochloride

Intervention Type DRUG

Series of three incremental bolus injections to observe α1-adrenoreceptor mediated vasoconstriction.

Cold Pressor Test

Intervention Type OTHER

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.

Hyperoxia

Intervention Type OTHER

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.

Interventions

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Phenylephrine Hydrochloride

Series of three incremental bolus injections to observe α1-adrenoreceptor mediated vasoconstriction.

Intervention Type DRUG

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.

Intervention Type OTHER

Isocapnic Acute Hypoxia

During low altitude assessment, participants will be exposed to isocapnic hypoxia equivalent to 3,800m to assess responses to acute exposure.

Intervention Type OTHER

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.

Intervention Type OTHER

Other Intervention Names

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Neo-Synephrine

Eligibility Criteria

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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)
* Those with a known allergy to sulfites
* Participants taking monoamine oxidase (MAO) inhibitors or tricyclic antidepressants

Minimum Eligible Age

18 Years

Maximum Eligible Age

50 Years

Eligible Sex

ALL

Accepts Healthy Volunteers

Yes