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Trial registered on ANZCTR

Registration number
Ethics application status
Date submitted
Date registered
Date last updated
Date data sharing statement initially provided
Type of registration
Prospectively registered

Titles & IDs
Public title
Breathing control and vein function in hypertension
Scientific title
Peripheral chemoreflex regulation of sympathetic outflow and venous function using pyridoxine supplements in human hypertension
Secondary ID [1] 302046 0
nil known
Universal Trial Number (UTN)
Trial acronym
Linked study record

Health condition
Health condition(s) or problem(s) studied:
Hypertension 318645 0
Condition category
Condition code
Cardiovascular 316658 316658 0 0

Study type
Description of intervention(s) / exposure
Daily oral pyridoxine supplement (5 mg·kg-1·day-1) will be taken in pill form for 4 weeks. Adherence of intervention will be confirmed with drug tablet return and laboratory tests.
Intervention code [1] 318353 0
Treatment: Drugs
Comparator / control treatment
Placebo (microcellulose) pill
Control group

Primary outcome [1] 324786 0
Breathing response to 5 min hypoxia (i.e., peripheral chemoreflex) will be assess using a heated pneumotach attached to a mouth piece. Participants will be exposed to a gas mixture containing 10% O2 in nitrogen during this assessment
Timepoint [1] 324786 0
At baseline and at 4 weeks follow-up
Primary outcome [2] 324787 0
Blood pressure control. Brachial blood pressure will be measured with a clinically validated automated sphygmomanometer (Omron), using a cuff wrapped around the upper arm. Beat-to-beat BP will be measured using finger photoplethysmography, using a small lightweight cuff wrapped around the finger.
Timepoint [2] 324787 0
Baseline and at 4 week follow-up
Secondary outcome [1] 385746 0
Venous compliance will be quantified using high-resolution Doppler ultrasound (uSmart 3300, Terason) coupled with automated edge detection and wall tracking of arterial images. Lower limb vein diameter will measured during progressive thigh cuff inflation and deflation
Timepoint [1] 385746 0
Baseline and 4 week follow up
Secondary outcome [2] 387003 0
Muscle sympathetic nerve activity (SNA), Muscle SNA will be measured using a small, sterile wire (unipolar tungsten microelectrodes, tip measuring 1-5 um) inserted near the fibular head on the outside of the leg using published techniques.
Timepoint [2] 387003 0
Baseline Baseline and 4 week follow up

Key inclusion criteria
-Patients with essential hypertension (At least Stage 2 hypertension; untreated office SBP greater or equal to 140 mmHg or DBP greater or equal to 90 mmHg);
-Men and women;
-Aged over 18 years;
-Body mass index <35 kg/m2
Minimum age
18 Years
Maximum age
85 Years
Both males and females
Can healthy volunteers participate?
Key exclusion criteria
-Significant arrhythmias (e.g., atrial fibrillation, previous VT / significant ventricular ectopy)
-Hemodynamically significant valvular heart disease (e.g., stenosis, mechanical valve replacement)
-Severe left ventricular systolic dysfunction
-Recent acute coronary syndrome (<12 months) (e.g., MI, angioplasty, unstable angina)
-Previous coronary artery bypass surgery
-Secondary causes of hypertension (e.g., phaeochromocytoma)
-Recent stroke/TIA (<12 months)
-Current smoker
-Body mass index <18 kg/m2.
-Current pregnancy
-Current user of recreational drugs
-Current abuser of alcohol
-Inability to fully or appropriately provide consent (e.g., language issue, reading capability)
-Underlying medical conditions, which in the opinion of the Investigator place the participant at unacceptably high risk for participating in the study.

Study design
Purpose of the study
Allocation to intervention
Randomised controlled trial
Procedure for enrolling a subject and allocating the treatment (allocation concealment procedures)
Methods used to generate the sequence in which subjects will be randomised (sequence generation)
Masking / blinding
Blinded (masking used)
Who is / are masked / blinded?
The people receiving the treatment/s
The people administering the treatment/s
The people assessing the outcomes
The people analysing the results/data
Intervention assignment
Other design features
Phase 4
Type of endpoint(s)
Statistical methods / analysis

Recruitment status
Not yet recruiting
Date of first participant enrolment
Date of last participant enrolment
Date of last data collection
Sample size
Accrual to date
Recruitment outside Australia
Country [1] 22856 0
New Zealand
State/province [1] 22856 0

Funding & Sponsors
Funding source category [1] 306468 0
Name [1] 306468 0
University of Auckland
Address [1] 306468 0
85 Park Road, Grafton
Auckland 1010
Country [1] 306468 0
New Zealand
Primary sponsor type
University of Auckland
85 Park Road, Grafton
Auckland 1010
New Zealand
Secondary sponsor category [1] 306995 0
Name [1] 306995 0
Address [1] 306995 0
Country [1] 306995 0

Ethics approval
Ethics application status
Ethics committee name [1] 306676 0
Northern A Health and Disability Ethics Committe
Ethics committee address [1] 306676 0
133 Molesworth Street
Wellington 6011
Ethics committee country [1] 306676 0
New Zealand
Date submitted for ethics approval [1] 306676 0
Approval date [1] 306676 0
Ethics approval number [1] 306676 0

Brief summary
High blood pressure (hypertension) affects one in three people, and remarkably ~50% of treated patients remain hypertensive. We need to better understand the mechanisms regulating blood pressure in hypertensive patients if new therapies are to be devised.

Current treatments target the heart and arterial resistance, but the ‘forgotten’ venous circulation has been largely neglected. We hypothesize that high levels of sympathetic activity in hypertension result in profound constriction of the veins, and that ameliorating this may be an effective way to help control arterial pressure.

Our extensive work in hypertensive animal models indicates that the carotid bodies develop tonicity and heightened reflex sensitivity due to excessive ATP bioavailability acting via purinergic (P2) receptors, which drive sympathetic outflows. We wish to determine whether a non-selective P2 receptor blocker reduces peripheral chemoreflex sensitivity, sympathetic activity, venous tone and blood pressure in humans with hypertension.

This project will provide novel mechanistic insights into carotid chemoreflex regulation and the neural control of the venous circulation. Translating insights from our animal models of hypertension into the human setting will lay the groundwork for future studies, potentially leading to a paradigm shift in the future treatment of hypertension.
Trial website
Trial related presentations / publications
Public notes

Principal investigator
Name 104634 0
A/Prof James Fisher
Address 104634 0
University of Auckland
85 Park Road, Grafton
Auckland 1023
Country 104634 0
New Zealand
Phone 104634 0
Fax 104634 0
Email 104634 0
Contact person for public queries
Name 104635 0
Dr Mickey Fan
Address 104635 0
University of Auckland
85 Park Road, Grafton
Auckland 1023
Country 104635 0
New Zealand
Phone 104635 0
Fax 104635 0
Email 104635 0
Contact person for scientific queries
Name 104636 0
A/Prof James Fisher
Address 104636 0
University of Auckland
85 Park Road, Grafton
Auckland 1023
Country 104636 0
New Zealand
Phone 104636 0
Fax 104636 0
Email 104636 0

Data sharing statement
Will individual participant data (IPD) for this trial be available (including data dictionaries)?
What data in particular will be shared?
Basic de-identified participant characteristics, resting blood pressure values
When will data be available (start and end dates)?
start date: 01/10/2022
end date: 01/10/2024
Available to whom?
Researchers whom have directly requested
Available for what types of analyses?
How or where can data be obtained?
Direct email contact (
What supporting documents are/will be available?
Study protocol
Ethical approval
How or where can supporting documents be obtained?
Type [1] 9347 0
Study protocol
Citation [1] 9347 0
Link [1] 9347 0
Email [1] 9347 0
Other [1] 9347 0
Type [2] 9348 0
Ethical approval
Citation [2] 9348 0
Link [2] 9348 0
Email [2] 9348 0
Other [2] 9348 0
Summary results
No Results