The Response of Intraocular Pressure to Systemic Hypercapnia and Hyperoxia

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.

Study Overview

• Status: Unknown
• Conditions: Intraocular Pressure
• Intervention / Treatment: 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 Type: Observational
• Enrollment (Anticipated): 14

Contacts and Locations

• Study Contact: Name: Alanna Adleman, BSc; Phone Number: 416-603-5694; Email: aadleman@uhnresearch.ca
• Study Contact Backup: Name: Tien Wong, BSc; Phone Number: 416-603-5694; Email: twong@uhnresearch.ca

Study Locations

• Canada
  • Ontario
    • Toronto, Ontario, Canada
      • Toronto Western Hospital
      • Contact: Alanna Adleman, BSc; Phone Number: 416-603-5694; Email: aadleman@uhnresearch.ca
      • Contact: Tien Wong, BSc; Phone Number: 416-603-5694; Email: twong@uhnresearch.ca
      • Sub-Investigator: Joseph Fisher, FRCPC, MD
      • Sub-Investigator: Richard Cheng, BSc

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: 18 years to 30 years (Adult)
• Accepts Healthy Volunteers: Yes
• Genders Eligible for Study: All

• Sampling Method: Non-Probability Sample

Study Population

Healthy young individuals (age 18-30)

Description

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

Study Plan

How is the study designed?

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Intraocular pressure	Intraocular pressure will be measured using Goldmann applanation tonometry.	Intraocular pressure will be measured during the study visit, ten minutes into each of the seven inhaled gas provocation stages

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Retinal blood flow	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.	Retinal blood flow will be measured during the second (optional) study visit, ten minutes into each of the seven inhaled gas provocation stages

Collaborators and Investigators

• Sponsor: University of Toronto
• Collaborators: University Health Network, Toronto; Thornhill Research

Publications and helpful links

General 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. doi: 10.1136/bjo.2002.008995.
• 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. doi: 10.1113/jphysiol.2007.129395. Epub 2007 Apr 19.

Study record dates

Study Major Dates

• Study Start: August 1, 2011
• Primary Completion (Anticipated): September 1, 2011
• Study Completion (Anticipated): September 1, 2011

Study Registration Dates

• First Submitted: February 15, 2011
• First Submitted That Met QC Criteria: March 28, 2011
• First Posted (Estimate): March 29, 2011

Study Record Updates

• Last Update Posted (Estimate): August 18, 2011
• Last Update Submitted That Met QC Criteria: August 17, 2011
• Last Verified: November 1, 2010

More Information

Terms related to this study

• Keywords: Intraocular pressure; Hypercapnia; Hyperoxia; Rebreathing circuit
• Additional Relevant MeSH Terms: Signs and Symptoms, Respiratory; Hypercapnia; Hyperoxia
• Other Study ID Numbers: 10-0655