CO2 Rebreathing in nOH: A Proof-of-Concept Pilot Study

NCT ID: NCT05908760

Last Updated: 2024-05-09

Basic Information

• Recruitment Status: RECRUITING
• Clinical Phase: NA
• Total Enrollment: 28 participants
• Study Classification: INTERVENTIONAL
• Study Start Date: 2024-05-05
• Study Completion Date: 2028-12-31

Brief Summary

Neurogenic orthostatic hypotension (nOH) is a chronic condition associated with increased cardiovascular risk and reduced quality of life. On standing, patients with nOH experience a large reduction in blood pressure (BP; at least ≥20/10mmHg, but often much more), which is often accompanied by debilitating symptoms and syncope. A previous study (unpublished) showed that hypercapnia significantly increases standing BP in patients with nOH. Human bodies naturally produce and exhale CO2. Rebreathe devices offer a simple, cost-effective technology to increase arterial CO2. In brief, rebreathe devices work by capturing expired CO2, which is then re-inhaled. The net effect is a transient increase in CO2. A CO2 rebreathing device may offer a novel hemodynamic therapy for patients with nOH.

This is a pilot, proof-of-concept study to evaluate a CO2 rebreather to improve blood pressure and orthostatic tolerance in patients with nOH. The hypothesis is that a rebreather will increase CO2 sufficiently enough to improve BP in patients with nOH.

Male and female patients (n=28) will be asked to complete two randomized 70° head-up tilt (HUT) tests breathing either room air or using a CO2 rebreather. Hemodynamics (BP, heart rate, stroke volume, brain blood flow) and orthostatic symptoms will be assessed throughout. Breath-by-breath data will include O2, CO2, respiration rate and tidal volume.

The primary outcome measure will be the magnitude of the BP response (ΔBP = HUT - Supine) during Room Air vs. Hypercapnia. The primary outcome will be compared between room air and hypercapnia using a paired t-test.

Detailed Description

BACKGROUND: Neurogenic orthostatic hypotension (nOH) is a chronic condition associated with increased cardiovascular risk and reduced quality of life. On standing, patients with nOH experience a large reduction in blood pressure (BP; at least ≥20/10mmHg, but often much more), which is often accompanied by debilitating symptoms and syncope. nOH affects the elderly and patients with neurodegenerative diseases (e.g., Parkinson's disease, multiple system atrophy), neuropathies (e.g., diabetes), and neural injury (e.g., spinal cord injury).

In healthy controls, hypercapnia (i.e., high CO2) increases in sympathetic nerve activity and BP. Hypercapnia significantly increases supine and seated BP in patients with nOH, and a previous study (unpublished) showed that hypercapnia significantly increases standing BP in patients with nOH.

Human bodies naturally produce and exhale CO2. Rebreathe devices offer a simple, cost-effective technology to increase arterial CO2. In brief, rebreathe devices work by capturing expired CO2, which is then re-inhaled. The net effect is a transient increase in CO2. A CO2 rebreathing device may offer a novel hemodynamic therapy for patients with nOH.

OBJECTIVE: This is a pilot, proof-of-concept study to evaluate a CO2 rebreather to improve blood pressure and orthostatic tolerance in patients with nOH. The study hypothesis is that a rebreather will increase CO2 sufficiently enough to improve BP in patients with nOH.

METHODS: Male and female patients (n=28) will be recruited from the Calgary Autonomic Investigation and Management Clinic.

STUDY PROCEDURE Informed Consent: The informed consent will be sent by email to the patients in advance. The investigators will give each patient a chance to ask questions about the protocol and have these questions answered to their satisfaction. Written informed consent will be documented prior to engaging in study-related procedures.

Holding Pre-Existing Medications: Participants will be asked to hold their clinical medications on the day of the study testing, if possible, but this will not be mandatory. The investigators will make note of the medications used by each participant at the time of the study.

Study Day: Participants will be instrumented at least 2h post-prandial on an empty bladder. Participants will be asked to abstain from alcohol, caffeine, and exercise for a period of 12 hours prior to testing. Participants will be allowed to drink water on the morning of study. Upon lab arrival, a description of the study will be given and written informed consent will be attained if the individual chooses to participate in the study. A member of the research team will ask participants about current medications and other disorders they many have as part of the study inclusion/exclusion criteria. The investigators will also review all other inclusion/exclusion criteria for the study. All study equipment will be introduced to the participant, and then the investigators will begin to prepare for the study.

Participants will be asked to lie supine on the tilt table during instrumentation. Following instrumentation, the study will begin with a 10-minute baseline in the supine position. During this period, the investigators will track blood pressure, heart rate, brain blood flow velocity, fluid shifts, and respiratory pattern using the following equipment:

• Finger and arm blood pressure cuffs
• Skin electrodes to measure heart rate and fluid shifts
• A Transcranial Doppler (TCD) which will use a band around the head, with an ultrasound-like probe at the left and/or right temple
• Pulse oximeter on the finger to measure oxygen saturation
• Participants will be fitted with a mouthpiece to breathing into. The mouthpiece will be connected to a breathing bag that will capture the CO2 exhaled. The mouthpiece will also be connected to a tube that will measure respiratory rate, respiratory depth, CO2 and O2.

Following instrumentation, participants will complete up to two 70° head-up tilt (HUT) tests while breathing either normal room air or while breathing with the rebreather. Each HUT will last a maximum of 5 minutes, and when participants are not upright, the participants will be in the supine position. Participants will be asked to breathe with the rebreather until the measured CO2 increases between 5-10mmHg. Once CO2 is increased, HUT will begin. Participants will continue to breathe with the rebreather until the end of HUT.

The two HUT tests will be randomized and will consist of:

1. HUT with Room Air

2. HUT with ETCO2 levels increased 5-10mmHg above normal levels

The primary outcome measure will be the magnitude of the BP response (ΔBP = HUT - Supine) during Room Air vs. Hypercapnia. The primary outcome will be compared between room air and hypercapnia using a paired t-test.

Conditions

Neurogenic Orthostatic Hypotension; Autonomic Failure

Study Design

• Allocation Method: RANDOMIZED
• Intervention Model: CROSSOVER
• Primary Study Purpose: TREATMENT
• Blinding Strategy: NONE

Study Groups

CO2 Rebreathing

Participants will breathe with the rebreather in the supine position until CO2 levels increase between 5-10mmHg. Once CO2 levels are increased, participants will be tilted upright, and will continue to breathe with the rebreather during a 5-min HUT test

Group Type: EXPERIMENTAL

CO2 ReHaler

Intervention Type: DEVICE

The ReHaler captures expired CO2, which is then re-inhaled. The net effect is a transient increase in CO2.

Room Air

Participants will breathe room air in the supine position and during a 5-min HUT test

Group Type: NO_INTERVENTION

No interventions assigned to this group

Interventions

CO2 ReHaler

The ReHaler captures expired CO2, which is then re-inhaled. The net effect is a transient increase in CO2.

Intervention Type: DEVICE

Eligibility Criteria

Inclusion Criteria

• Age ≥18 years
• Male and Female
• Physician diagnosis of Neurogenic Orthostatic Hypotension
• Non-smokers.
• Able and willing to provide informed consent.
• Ability to travel to Libin Cardiovascular Institute Autonomic Testing Lab at the University of Calgary, Calgary, AB.

Exclusion Criteria

• Medical therapies or medications which could interfere with testing of autonomic function
• Pregnant or breast-feeding females
• Subjects with chronic heart failure or severe pulmonary disease who are unable to climb one flight of stairs due to shortness of breath.
• Presence of failure of other organ systems or systemic illness that can affect autonomic function or the participant's ability to cooperate. These include dementia, alcohol and/or drug abuse, cerebrovascular disease, kidney or liver disease, surgical procedures where the nerves of the sympathetic nervous system have been cut.
• Other factors which in the investigator's opinion would prevent the participant from completing the protocol, including poor compliance during previous studies.

• Minimum Eligible Age: 18 Years
• Maximum Eligible Age: 100 Years
• Eligible Sex: ALL
• Accepts Healthy Volunteers: No

Sponsors

University of Calgary

OTHER

Sponsor Role: lead

Responsible Party

Dr. Satish Raj

Professor

Responsibility Role: PRINCIPAL_INVESTIGATOR

Principal Investigators

Satish R Raj, MD

Role: PRINCIPAL_INVESTIGATOR

University of Calgary

Locations

University of Calgary

Calgary, Alberta, Canada

Site Status: RECRUITING

Countries

Canada

Central Contacts

Jacquie Baker, PhD

Role: CONTACT

autonomic.research@ucalgary.ca

4032107629

Tanya Siddiqui, MD

Role: CONTACT

autonomic.research@ucalgary.ca

4032107629

Facility Contacts

Satish R Raj, MD

Role: primary

autonomic.research@ucalgary.ca

403-210-6152

Robert S Sheldon, MD, PhD

Role: backup

autonomic.research@ucalgary.ca

403-220-8191

References

Freeman R, Abuzinadah AR, Gibbons C, Jones P, Miglis MG, Sinn DI. Orthostatic Hypotension: JACC State-of-the-Art Review. J Am Coll Cardiol. 2018 Sep 11;72(11):1294-1309. doi: 10.1016/j.jacc.2018.05.079.

Reference Type: BACKGROUND

PMID: 30190008 (View on PubMed)

Morgan BJ, Crabtree DC, Palta M, Skatrud JB. Combined hypoxia and hypercapnia evokes long-lasting sympathetic activation in humans. J Appl Physiol (1985). 1995 Jul;79(1):205-13. doi: 10.1152/jappl.1995.79.1.205.

Reference Type: BACKGROUND

PMID: 7559221 (View on PubMed)

Freeman R, Wieling W, Axelrod FB, Benditt DG, Benarroch E, Biaggioni I, Cheshire WP, Chelimsky T, Cortelli P, Gibbons CH, Goldstein DS, Hainsworth R, Hilz MJ, Jacob G, Kaufmann H, Jordan J, Lipsitz LA, Levine BD, Low PA, Mathias C, Raj SR, Robertson D, Sandroni P, Schatz I, Schondorff R, Stewart JM, van Dijk JG. Consensus statement on the definition of orthostatic hypotension, neurally mediated syncope and the postural tachycardia syndrome. Clin Auton Res. 2011 Apr;21(2):69-72. doi: 10.1007/s10286-011-0119-5. No abstract available.

Reference Type: BACKGROUND

PMID: 21431947 (View on PubMed)

Shoemaker JK, Vovk A, Cunningham DA. Peripheral chemoreceptor contributions to sympathetic and cardiovascular responses during hypercapnia. Can J Physiol Pharmacol. 2002 Dec;80(12):1136-44. doi: 10.1139/y02-148.

Reference Type: BACKGROUND

PMID: 12564639 (View on PubMed)

Fuglsang CH, Johansen T, Kaila K, Kasch H, Bach FW. Treatment of acute migraine by a partial rebreathing device: A randomized controlled pilot study. Cephalalgia. 2018 Sep;38(10):1632-1643. doi: 10.1177/0333102418797285. Epub 2018 Aug 22.

Reference Type: BACKGROUND

PMID: 30134739 (View on PubMed)

Other Identifiers

REB23-0791

Identifier Type: -

Identifier Source: org_study_id