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NCT Number: NCT07285031

Histamines and Central Hemodynamics

When we exercise, more blood flow goes to our muscles, challenging our blood vessels. Following exercise, blood flow remains elevated and seems to be the reason for many of the positive cardiovascular benefits that occur with exercise. When the actions of histamine, a molecule primarily known for its role in allergies, are blocked, there is an attenuated blood flow response following exercise. However, this effect has never been studied in the blood vessels that supply our lungs. The purpose of this study is to examine the effects of histamines on pulmonary hemodynamics following exercise.

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Key information

Conditions

Histamine Behavior Exercise Motor Activity

Age range

19 year–39 year

Sex eligibility

All sexes

Study type

Interventional

Phase

Not applicable

Primary location

University of British Columbia

Kelowna, British Columbia, V1V2L2, Canada

Location status: Recruiting

Location contact

Neil Eves, PhD

CONTACT

[email protected]

(250) 807-9676

Who can participate

Healthy volunteers accepted: Yes

Only the study team can determine whether someone qualifies for participation.

Inclusion criteria

  • Age: 19 - 39.
  • Willing to visit the lab on 3 separate occasions.

Exclusion criteria

  • Previously diagnosed heart condition,
  • Previously diagnosed lung condition (including asthma),
  • Previously diagnosed metabolic condition,
  • Currently smokers (cigarettes, electronic cigarettes, cannabis) or who have smoked within the last 3 months,
  • Resting blood pressure >140/90 mmHg,
  • Unable to obtain appropriate quality ultrasound images of the heart.,
  • Individuals without tricuspid regurgitation at rest to allow assessment of the primary outcome,
  • Pregnant or trying to become pregnant,
  • Breastfeeding,
  • Chronically take antihistamines (i.e. daily),
  • History of adverse reactions to antihistamines,
  • Never taken antihistamines previously,
  • Currently taking any medications (including oral contraceptives).

Treatment and study plan

Diphenhydramine hydrochloride

Drug

H1 receptor antagonist: 50mg Diphenhydramine Hydrochloride

Placebo

Other

Placebo

Exercise Bout

Other

Participants will complete a total of three 5-minute high intensity exercise intervals, interspersed with 5-minute lower intensity exercise bouts (4 total), for a total of 35 minutes.

Primary outcomes

  1. Systolic pulmonary artery pressure

    Time frame: Pre-exercise and 10, 20, and 30-minutes post-exercise.

    The difference in systolic pulmonary artery pressure (measured as tricuspid regurgitation velocity using echocardiography) between the H1 blockade condition and the placebo condition.

Secondary outcomes

  1. Tricuspid annular plane systolic displacement

    Time frame: Pre-exercise and 0, 10, 20, 30, 45, and 60 minutes post-exercise.

    The difference in tricuspid annular plane systolic displacement between the H1 receptor blockade condition and the placebo condition.

  2. Right ventricular stroke volume

    Time frame: Pre-exercise and 0, 10, 20, 30, 45, and 60-minutes post-exercise.

    The difference in right ventricular stroke volume (measured using pulsed wave velocity of the right ventricular outflow tract velocity time integral) between the H1 receptor blockade condition and the placebo condition.

  3. Femoral artery blood flow

    Time frame: Pre-exercise and 0, 10, 20, 30, 45, and 60-minutes post-exercise.

    The difference in femoral artery blood flow between the H1 receptor blockade condition and the placebo condition.

  4. Mean arterial systemic pressure

    Time frame: Pre-exercise and 0, 10, 20, 30, 45, and 60-minutes post-exercise.

    The difference in mean arterial systemic pressure between the H1 receptor blockade condition and the placebo condition.

Study contacts

Contact information is provided by the study sponsor or research team.

Cassidy Williams, BHK

CONTACT

[email protected]

(250) 807-9676

Neil Eves, PhD

CONTACT

[email protected]

(250) 807-9676

Sponsors and collaborators

Lead sponsor

University of British Columbia

Other

Registry information

Official study title

The Role of Histamines on Central Hemodynamics

Important dates

Study start
2025
Primary completion
2026
Study completion
2026
First posted
Dec 16, 2025
Registry last updated
Dec 23, 2025

OpenTrials presents study information sourced from ClinicalTrials.gov. The official registry record should be consulted for the latest information.

View the official ClinicalTrials.gov record (opens in a new tab)

This listing is for discovery and informational purposes only. It is not medical advice, does not guarantee that a study is recruiting, and does not determine eligibility. Contact the study team and a qualified healthcare professional when considering participation.

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