The Response of Intraocular Pressure to Systemic Hypercapnia and Hyperoxia

Study Description

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Study Description Study Design Groups and Cohorts Outcome Measures Eligibility Criteria Contacts and Locations More Information

Brief Summary:

The purpose of this study is to determine how intraocular pressure responds to changes in the levels of carbon dioxide or oxygen that a healthy individual inspires.

Condition or disease	Intervention/treatment
Intraocular Pressure	Device: RespirAct

Detailed Description:

In response to changes in the composition of inhaled gases, blood vessels will dilate or constrict. As a result, hypercapnia or hyperoxia may affect the production and drainage of aqueous humour in the anterior chamber of the eye. The balance between the production and drainage of the aqueous humour determines the intraocular pressure. As this system is hydrodynamic, it is expected that any increase or decrease in the production of aqueous humour due to dilation or constriction of the capillaries within the ciliary body will be compensated by increased or decreased drainage at the trabecular meshwork. Therefore intraocular pressure is not expected to show a response to hypercapnia or hyperoxia, but this supposition needs to be tested in a stably controlled manner of inducing inhaled gas provocations. This study will measure the intraocular pressure at varying levels of hypercapnia and hyperoxia using a sequential rebreathing circuit and automated gas blender. This will allow the precise targeting and stable control of end-tidal partial pressure values of carbon dioxide and oxygen.

In this study, intraocular pressure will be measured at seven different inhaled gas stages. The seven stages are as follows:

1. Baseline, measured in eye A (PETCO2=38mmHg and PETO2=100mmHg)
2. 10% hypercapnic increase, measured in eye A (PETCO2=42mmHg and PETO2=100mmHg)
3. 20% hypercapnic increase, measured in eye A (PETCO2=46mmHg and PETO2=100mmHg)
4. Baseline, measured in both eyes (PETCO2=38mmHg and PETO2=100mmHg)
5. 250% hyperoxic increase, measured in eye B (PETCO2=38mmHg and PETO2=250mmHg)
6. 500% hyperoxic increase, measured in eye B (PETCO2=38mmHg and PETO2=500mmHg)
7. Baseline, measured in eye B (PETCO2=38mmHg and PETO2=100mmHg)

Study Design

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Study Type :	Observational
Estimated Enrollment :	14 participants
Observational Model:	Case-Only
Time Perspective:	Cross-Sectional
Official Title:	The Response of Intraocular Pressure to Systemic Hypercapnia and Hyperoxia
Study Start Date :	August 2011
Estimated Primary Completion Date :	September 2011
Estimated Study Completion Date :	September 2011

Groups and Cohorts

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Intervention Details:

Device: RespirAct

Participants will breathe through a mask connected to a sequential rebreathing circuit and gas blender. The following seven gas stages will be targeted for about 10 minutes each:

1. Baseline, measured in eye A (PETCO2=38mmHg and PETO2=100mmHg)
2. 10% hypercapnic increase, measured in eye A (PETCO2=42mmHg and PETO2=100mmHg)
3. 20% hypercapnic increase, measured in eye A (PETCO2=46mmHg and PETO2=100mmHg)
4. Baseline, measured in both eyes (PETCO2=38mmHg and PETO2=100mmHg)
5. 250% hyperoxic increase, measured in eye B (PETCO2=38mmHg and PETO2=250mmHg)
6. 500% hyperoxic increase, measured in eye B (PETCO2=38mmHg and PETO2=500mmHg)
7. Baseline, measured in eye B (PETCO2=38mmHg and PETO2=100mmHg)
Other Name: Inhaled gas provocations

Outcome Measures

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Study Description Study Design Groups and Cohorts Outcome Measures Eligibility Criteria Contacts and Locations More Information

Primary Outcome Measures :

1. Intraocular pressure [ Time Frame: Intraocular pressure will be measured during the study visit, ten minutes into each of the seven inhaled gas provocation stages ]
   Intraocular pressure will be measured using Goldmann applanation tonometry.

Secondary Outcome Measures :

1. Retinal blood flow [ Time Frame: Retinal blood flow will be measured during the second (optional) study visit, ten minutes into each of the seven inhaled gas provocation stages ]
   Retinal blood flow will be measured using the Canon Laser Blood Flowmeter in a subset of participants asked to return for a second visit. This will demonstrate that retinal blood flow behaves as the study claims that it does.

Eligibility Criteria

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Study Description Study Design Groups and Cohorts Outcome Measures Eligibility Criteria Contacts and Locations More Information

Ages Eligible for Study:	18 Years to 30 Years (Adult)
Sexes Eligible for Study:	All
Accepts Healthy Volunteers:	Yes
Sampling Method:	Non-Probability Sample

Study Population

Healthy young individuals (age 18-30)

Criteria

Inclusion Criteria:

• Age range 18-30 years old
• Visual acuity of 20/20 or better

Exclusion Criteria:

• Refractive error >±6.00 DS and/or ± 2.00 DC
• History or presence of ocular disease
• Family history of diabetes or glaucoma
• History of intraocular or refractive surgery
• Nursing or pregnant women
• History of clinically diagnosed endocrine disease
• History of vascular disease, cardiovascular disease, or any treated respiratory disorders (seasonal asthma excluded from this so long as subject not taking Rx at the time)
• History of systemic hypertension
• Habitual smoking
• Use of medications that affect blood flow

Contacts and Locations

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Study Description Study Design Groups and Cohorts Outcome Measures Eligibility Criteria Contacts and Locations More Information

Contacts

Contact: Alanna Adleman, BSc	416-603-5694	aadleman@uhnresearch.ca
Contact: Tien Wong, BSc	416-603-5694	twong@uhnresearch.ca

Locations

Canada, Ontario
Toronto Western Hospital	Not yet recruiting
Toronto, Ontario, Canada
Contact: Alanna Adleman, BSc 416-603-5694 aadleman@uhnresearch.ca
Contact: Tien Wong, BSc 416-603-5694 twong@uhnresearch.ca
Principal Investigator: Christopher Hudson, PhD
Sub-Investigator: Joseph Fisher, FRCPC, MD
Sub-Investigator: Richard Cheng, BSc

Sponsors and Collaborators

University of Toronto

University Health Network, Toronto

Thornhill Research

Investigators

Principal Investigator:	Christopher Hudson, PhD	University of Toronto

More Information

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Study Description Study Design Groups and Cohorts Outcome Measures Eligibility Criteria Contacts and Locations More Information

Publications:

Hosking SL, Harris A, Chung HS, Jonescu-Cuypers CP, Kagemann L, Roff Hilton EJ, Garzozi H. Ocular haemodynamic responses to induced hypercapnia and hyperoxia in glaucoma. Br J Ophthalmol. 2004 Mar;88(3):406-11.

Slessarev M, Han J, Mardimae A, Prisman E, Preiss D, Volgyesi G, Ansel C, Duffin J, Fisher JA. Prospective targeting and control of end-tidal CO2 and O2 concentrations. J Physiol. 2007 Jun 15;581(Pt 3):1207-19. Epub 2007 Apr 19.

Responsible Party:	Dr. Christopher Hudson, University of Toronto, University of Waterloo, and Toronto Western Research Institute
ClinicalTrials.gov Identifier:	NCT01325285 History of Changes
Other Study ID Numbers:	10-0655
First Posted:	March 29, 2011
Last Update Posted:	August 18, 2011
Last Verified:	November 2010

Keywords provided by University of Toronto:

Intraocular pressure; Hypercapnia; Hyperoxia; Rebreathing circuit

Additional relevant MeSH terms:

Hypercapnia; Hyperoxia; Signs and Symptoms, Respiratory; Signs and Symptoms