Vasodilation, Vasoconstriction
Conditions
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.
Interventions
Series of three incremental bolus injections to observe α1-adrenoreceptor mediated vasoconstriction.
OTHERCold 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.
OTHERIsocapnic Acute Hypoxia
During low altitude assessment, participants will be exposed to isocapnic hypoxia equivalent to 3,800m to assess responses to acute exposure.
OTHERHyperoxia
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.
Sponsors
University of Alberta
Study design
Allocation
NON_RANDOMIZED
Intervention model
CROSSOVER
Primary purpose
BASIC_SCIENCE
Masking
NONE
Masking description
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.
Intervention model description
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.
Eligibility
Sex/Gender
ALL
Age
18 Years to 50 Years
Healthy volunteers
Yes
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
Design outcomes
Primary
| Measure | Time frame | Description |
|---|---|---|
| Change in blood pressure | 18 minutes | Phenylephrine sensitivity |
| Change in arterial blood flow | 18 minutes | Phenylephrine sensitivity |
| Cold pressor test reactivity | 4 minutes | — |
Countries
Canada
Outcome results
None listed