Network-Level Effects of Nitrous Oxide in the Human Brain

• Sponsor: University of Michigan (Other)
• Overall Status: Completed
• CT.gov ID: NCT03435055
• Collaborator: (none)
• Enrollment: 21
• Location: 1
• Arm: 1
• Actual Duration (Months): 26.7
• Patients Per Site Per Month: 0.8

Study Details

Study Description

Brief Summary

The purpose of this study is to understand how a commonly used drug, nitrous oxide, acts on the brain to reduce pain. Nitrous oxide is commonly used in anesthesiology but there is limited knowledge on how this drug affects functional networks in the brain.

Condition or Disease	Intervention/Treatment	Phase
Healthy	Drug: Nitrous Oxide Gas for Inhalation	Phase 4

Detailed Description

The objective of this study is to identify the network transformations that account for the analgesic effects of nitrous oxide. Our hypothesis is that analgesic doses of nitrous oxide increase network efficiency and disrupt normal pain processingOur approach is to administer subanesthetic nitrous oxide during the acquisition of fMRI (functional magnetic resonance imaging) and EEG (electroencephalogram).

Study Design

• Study Type: Interventional
• Actual Enrollment: 21 participants
• Allocation: N/A
• Intervention Model: Single Group Assignment
• Masking: None (Open Label)
• Primary Purpose: Basic Science
• Official Title: Network-Level Effects of Nitrous Oxide in the Human Brain
• Actual Study Start Date: Jul 21, 2017
• Actual Primary Completion Date: Oct 11, 2019
• Actual Study Completion Date: Oct 11, 2019

Arms and Interventions

Arm	Intervention/Treatment
Experimental: Nitrous Oxide - inhaled Each volunteer will participate in one scanning visit in which simultaneous functional magnetic resonance imaging (fMRI) and electroencephalogram (EEG) data will be collected wherein they receive placebo (20 minutes) followed by inhaled nitrous oxide at subanalgesic levels (35% inhaled concentration) over 40 minutes.	Drug: Nitrous Oxide Gas for Inhalation; Each volunteer will participate in one scanning visit in which simultaneous functional magnetic resonance imaging (fMRI) and electroencephalogram (EEG) data will be collected wherein they receive placebo (20 minutes) followed by inhaled nitrous oxide at subanesthetic levels (35% inhaled concentration) over 40 minutes.

Outcome Measures

Primary Outcome Measures

1. Functional Connectivity During Nitrous Oxide [Baseline to 50 minutes]

   Functional connectivity measures will be assessed at rest (baseline) and during sub anesthetic dose nitrous oxide (nitrous oxide). Seed-to-whole brain functional connectivity (Fisher's r-transformed z) will be measured from the left anterior insula, previously shown to be involved in pain and sensory processing. Paired t-test were conducted on subject specific beta maps to identify changes in connectivity associated with nitrous oxide in SPM12. The z-score descriptors represent the Fishers-r-to-z transformed. Here the z-score is a transformation of the Pearson's (r) correlation coefficient of the BOLD timeseries between two brain regions. Higher z-scores are associated with higher correlations in timeseries and correspond with higher functional connectivity between two brain regions.

2. Functional Connectivity Associated With Tonic Stimulus [Baseline to 50 minutes]

   Functional connectivity measures will be assessed at rest (baseline) and during a tonic cuff stimulus (6-minutes). Seed-to-whole brain functional connectivity (Fisher's r-transformed z) will be measured from the left anterior insula, previously shown to be involved in pain and sensory processing. Paired t-test were conducted on subject specific beta maps to identify changes in connectivity associated with nitrous oxide in SPM12. The z-score descriptors represent the Fishers-r-to-z transformed. Here the z-score is a transformation of the Pearson's (r) correlation coefficient of the BOLD timeseries between two brain regions. Higher z-scores are associated with higher correlations in timeseries and correspond with higher functional connectivity between two brain regions.

Secondary Outcome Measures

1. Tonic Stimulus Intensity During Nitrous Oxide [Baseline to 50 minutes]

   Participants will receive a tonic (6 minutes) pressure applied to the lower leg at baseline and under subanesthetic dose of nitrous oxide (35% inhaled concentration). Following each pressure stimulus, participants will rate the pain intensity of the tonic stimulus (0 ="no pain", 10= "worst pain imaginable", Visual Analog Scale, e.g pain intensity).

2. Spectral Power of Sub-anesthetic Dose of Nitrous Oxide [Baseline to 50 minutes]

   Brain imaging data were obtained from functional magnetic resonance imaging (fMRI) data recorded simultaneously with electroencephalography (EEG) data at baseline and under a sub-anesthetic dose of nitrous oxide. Spectral data were averaged from EEG data at all electrodes collected during the baseline and sub-anesthetic dose (35%) of nitrous oxide to observe changes in spectral power. The EEG power spectrum was divided into three frequency bands: Delta = 1-3 Hz; Theta = 4-7 Hz; and Alpha = 8 - 13 Hz

Eligibility Criteria

Criteria

• Ages Eligible for Study: 21 Years to 40 Years
• Sexes Eligible for Study: All
• Accepts Healthy Volunteers: Yes

Inclusion Criteria:

1. Body mass index <30

2. Must be right-handed

3. Must be capable of giving written informed consent

Exclusion Criteria:

1. History of obstructive sleep apnea;

2. History of a difficult airway with a previous anesthetic

3. Gastroesophageal reflux;

4. Hypertension or other cardiovascular abnormalities;

5. Pulmonary hypertension;

6. History of recreational drug use;

7. History of chronic alcohol abuse

8. Having any chronic medical illness involving pain;

9. History of major depression;

10. History of psychosis or bipolar disorder;

11. History of methylenetetrahydrofolate reductase deficiency;

12. History of a known hypersensitivity to ketamine, midazolam, Zofran, labetalol or glycopyrrolate

13. History of seizures or other neurologic disorders;

14. Pregnant or nursing mothers;

15. Tattoos on the head or neck region - all other tattoos are subject to determination by investigators;

16. Contraindications to neuroimaging methods;

17. Any impairment, activity or situation that in the judgment of the Study Coordinator or Principal Investigators would prevent satisfactory completion of the study protocol.

Contacts and Locations

Locations

	Site	City	State	Country	Postal Code
1	Michigan Medicine - University of Michigan	Ann Arbor	Michigan	United States	48109

Sponsors and Collaborators

• University of Michigan

Investigators

• Principal Investigator: Richard Harris, PhD, Associate Professor of Anesthesiology and Associate Professor of Internal Medicine

Study Documents (Full-Text)

• Study Protocol and Statistical Analysis Plan - Jul 23, 2020

More Information

Publications

None provided.

• Responsible Party: Richard Harris, Associate Professor of Anesthesiology and Associate Professor of Internal Medicine, University of Michigan
• ClinicalTrials.gov Identifier: NCT03435055
• Other Study ID Numbers: HUM00096321
• First Posted: Feb 15, 2018
• Last Update Posted: Nov 30, 2021
• Last Verified: Nov 1, 2021

• Individual Participant Data (IPD) Sharing Statement: No
• Plan to Share IPD: No
• Studies a U.S. FDA-regulated Drug Product: Yes
• Studies a U.S. FDA-regulated Device Product: No
• Product Manufactured in and Exported from the U.S.: No
• Additional relevant MeSH terms: Nitrous Oxide

Study Results

Participant Flow

Pre-assignment Detail	A total of 21 participants consented to participate but 2 participants did not participate in any part of the research.

Arm/Group Title	Nitrous Oxide - Inhaled
Arm/Group Description	Each volunteer will participate in one scanning visit in which simultaneous fMRI/EEG data will be collected wherein they receive placebo (20 minutes) followed by inhaled nitrous oxide at subanalgesic levels (35% inhaled concentration) over 30 minutes.
Period Title: Screening
STARTED	21
COMPLETED	19
NOT COMPLETED	2
Period Title: Screening
STARTED	19
COMPLETED	16
NOT COMPLETED	3

Baseline Characteristics

Arm/Group Title	Nitrous Oxide - Inhaled
Arm/Group Description	Each volunteer will participate in one scanning visit in which simultaneous fMRI/EEG data will be collected wherein they receive placebo (20 minutes) followed by inhaled nitrous oxide at subanalgesic levels (35% inhaled concentration) over 30 minutes.
Overall Participants	21
Age (years) [Mean (Full Range) ]
Mean (Full Range) [years]	25
Sex: Female, Male (Count of Participants)
Female	11 52.4%
Male	10 47.6%
Ethnicity (NIH/OMB) (Count of Participants)
Hispanic or Latino	0 0%
Not Hispanic or Latino	21 100%
Unknown or Not Reported	0 0%
Race (NIH/OMB) (Count of Participants)
American Indian or Alaska Native	0 0%
Asian	4 19%
Native Hawaiian or Other Pacific Islander	0 0%
Black or African American	2 9.5%
White	14 66.7%
More than one race	0 0%
Unknown or Not Reported	1 4.8%

Outcome Measures

1. Primary Outcome

Title	Functional Connectivity During Nitrous Oxide
Description	Functional connectivity measures will be assessed at rest (baseline) and during sub anesthetic dose nitrous oxide (nitrous oxide). Seed-to-whole brain functional connectivity (Fisher's r-transformed z) will be measured from the left anterior insula, previously shown to be involved in pain and sensory processing. Paired t-test were conducted on subject specific beta maps to identify changes in connectivity associated with nitrous oxide in SPM12. The z-score descriptors represent the Fishers-r-to-z transformed. Here the z-score is a transformation of the Pearson's (r) correlation coefficient of the BOLD timeseries between two brain regions. Higher z-scores are associated with higher correlations in timeseries and correspond with higher functional connectivity between two brain regions.
Time Frame	Baseline to 50 minutes

Outcome Measure Data

Analysis Population Description

Three participants had missing data because they did not complete the full scanning protocol.

Arm/Group Title	Pre-Nitrous	Nitrous Oxide - Subanesthetic Dose
Arm/Group Description	Each volunteer will participate in one scanning visit in which simultaneous fMRI/EEG data will be collected as they receive oxygen (20 minutes) followed Functional connectivity (Fisher's r to z transformed) between the left anterior insula and superior frontal gyrus were measured at baseline.	Each volunteer will participate in one scanning visit in which simultaneous fMRI/EEG data will be collected as they received subanesthetic dose of nitrous oxide at (35% inhaled concentration) over 30 minutes. Functional connectivity (z-score) between the left anterior insula and superior frontal gyrus were measured during administration of subanesthetic nitrous oxide.
Measure Participants	16	16
L superior frontal gyrus	0.1123 (0.0639)	0.0358 (0.0620)
R superior frontal gyrus	0.1492 (0.1179)	0.0394 (0.0950)

Statistical Analysis 1

Statistical Analysis Overview	Comparison Group Selection	Pre-Nitrous, Nitrous Oxide - Subanesthetic Dose
	Comments	Paired t-test were conducted on subject specific beta maps to identify changes in connectivity associated with nitrous oxide in SPM12. Hypothesis was that the results would be deemed significant at false discovery rate (FDR) cluster level corrected p < 0.05 derived from a voxel-wise uncorrected p-value < 0.001.
	Type of Statistical Test	Superiority
	Comments
Statistical Test of Hypothesis	p-Value	0.001
	Comments
	Method	t-test, 2 sided
	Comments

2. Primary Outcome

Title	Functional Connectivity Associated With Tonic Stimulus
Description	Functional connectivity measures will be assessed at rest (baseline) and during a tonic cuff stimulus (6-minutes). Seed-to-whole brain functional connectivity (Fisher's r-transformed z) will be measured from the left anterior insula, previously shown to be involved in pain and sensory processing. Paired t-test were conducted on subject specific beta maps to identify changes in connectivity associated with nitrous oxide in SPM12. The z-score descriptors represent the Fishers-r-to-z transformed. Here the z-score is a transformation of the Pearson's (r) correlation coefficient of the BOLD timeseries between two brain regions. Higher z-scores are associated with higher correlations in timeseries and correspond with higher functional connectivity between two brain regions.
Time Frame	Baseline to 50 minutes

Outcome Measure Data

Analysis Population Description

Number of participants scanned.

Arm/Group Title	Pre-Tonic Cuff	Tonic Cuff Stimulus
Arm/Group Description	Each volunteer will participate in one scanning visit in which simultaneous fMRI/EEG data will be collected as they receive oxygen (20 minutes) at rest and during a tonic cuff stimulus applied to the leg (6 minutes). Functional connectivity (Fisher's r to z score transformed) between the left anterior insula and the postcentral gyrus prior to (baseline) and during a tonic cuff stimulus.	Each volunteer will participate in one scanning visit in which simultaneous fMRI/EEG data will be collected while a tonic cuff stimulus was applied to the calf of the left leg (6 minutes). Functional connectivity (z score) was measured between the left anterior insula and the right postcentral gyrus from the fMRI data during the tonic cuff stimulus.
Measure Participants	19	19
Mean (Standard Deviation) [Z score]	-0.0509 (0.0822)	0.0486 (0.1001)

Statistical Analysis 1

Statistical Analysis Overview	Comparison Group Selection	Pre-Nitrous, Nitrous Oxide - Subanesthetic Dose
	Comments	Paired t-test were conducted on subject specific beta maps to identify changes in connectivity associated with nitrous oxide in SPM12. Hypothesis was that results would be deemed significant at false discovery rate (FDR) cluster level corrected p < 0.05 derived from a voxel-wise uncorrected p-value < 0.001.
	Type of Statistical Test	Superiority
	Comments
Statistical Test of Hypothesis	p-Value	0.006
	Comments
	Method	t-test, 2 sided
	Comments

3. Secondary Outcome

Title	Tonic Stimulus Intensity During Nitrous Oxide
Description	Participants will receive a tonic (6 minutes) pressure applied to the lower leg at baseline and under subanesthetic dose of nitrous oxide (35% inhaled concentration). Following each pressure stimulus, participants will rate the pain intensity of the tonic stimulus (0 ="no pain", 10= "worst pain imaginable", Visual Analog Scale, e.g pain intensity).
Time Frame	Baseline to 50 minutes

Outcome Measure Data

Analysis Population Description

Three participants had missing data because they did not complete the full scanning protocol.

Arm/Group Title	Pre-nitrous	Nitrous Oxide - 35% Inhaled Concentration
Arm/Group Description	Participants will receive a tonic (6 minutes) pressure applied to the lower leg prior to (baseline) and during administration of subanesthetic dose of nitrous oxide (35% inhaled concentration). Following each pressure stimulus, participants will rate the pain intensity of the tonic stimulus (0 = "no pain", 10= "worst pain imaginable", Visual Analog Scale, e.g pain intensity.	Participants will receive a tonic (6 minutes) pressure applied to the lower leg prior to (baseline) and during administration of subanesthetic dose of nitrous oxide (35% inhaled concentration). Following each pressure stimulus, participants will rate the pain intensity of the tonic stimulus (0 = "no pain", 10= "worst pain imaginable", Visual Analog Scale, e.g pain intensity.
Measure Participants	16	16
Mean (Standard Deviation) [score on a scale]	4.9688 (1.217)	2.500 (2.309)

Statistical Analysis 1

Statistical Analysis Overview	Comparison Group Selection	Pre-Nitrous, Nitrous Oxide - Subanesthetic Dose
	Comments	Paired-t tests were conducted to determine whether changes in stimulus intensity: post stimulus at baseline and under subanesthetic dose of nitrous oxide. Statistical tests were completed in SPSS 26 and determined by p < 0.05.
	Type of Statistical Test	Superiority
	Comments
Statistical Test of Hypothesis	p-Value	<0.01
	Comments
	Method	t-test, 2 sided
	Comments

4. Secondary Outcome

Title	Spectral Power of Sub-anesthetic Dose of Nitrous Oxide
Description	Brain imaging data were obtained from functional magnetic resonance imaging (fMRI) data recorded simultaneously with electroencephalography (EEG) data at baseline and under a sub-anesthetic dose of nitrous oxide. Spectral data were averaged from EEG data at all electrodes collected during the baseline and sub-anesthetic dose (35%) of nitrous oxide to observe changes in spectral power. The EEG power spectrum was divided into three frequency bands: Delta = 1-3 Hz; Theta = 4-7 Hz; and Alpha = 8 - 13 Hz
Time Frame	Baseline to 50 minutes

Outcome Measure Data

Analysis Population Description

[Not Specified]

Arm/Group Title	Pre-Nitrous	Nitrous Oxide - Subanesthetic Dose
Arm/Group Description	Each volunteer will participate in one scanning visit in which simultaneous fMRI/EEG data will be collected as they receive oxygen (20 minutes) followed	Each volunteer will participate in one scanning visit in which simultaneous fMRI/EEG data will be collected as they received subanesthetic dose of nitrous oxide at (35% inhaled concentration) over 30 minutes.
Measure Participants	16	16
Delta	13.31 (2.20)	14.65 (2.56)
Theta	11.88 (1.89)	12.80 (1.87)
Alpha	6.72 (1.92)	6.97 (2.05)

Statistical Analysis 1

Statistical Analysis Overview	Comparison Group Selection	Pre-Nitrous, Nitrous Oxide - Subanesthetic Dose
	Comments	Delta
	Type of Statistical Test	Other
	Comments	Paired T-test comparing baseline to nitrous
Statistical Test of Hypothesis	p-Value	0.0622
	Comments
	Method	Paired t-test
	Comments

Statistical Analysis 2

Statistical Analysis Overview	Comparison Group Selection	Pre-Nitrous, Nitrous Oxide - Subanesthetic Dose
	Comments	Theta
	Type of Statistical Test	Other
	Comments	Paired T-test comparing baseline to nitrous
Statistical Test of Hypothesis	p-Value	0.0292
	Comments
	Method	Paired t-test
	Comments

Statistical Analysis 3

Statistical Analysis Overview	Comparison Group Selection	Pre-Nitrous, Nitrous Oxide - Subanesthetic Dose
	Comments	Alpha comparison
	Type of Statistical Test	Other
	Comments	Paired T-test comparing baseline to nitrous
Statistical Test of Hypothesis	p-Value	0.5905
	Comments
	Method	Paired t-test
	Comments

Adverse Events

Time Frame	Adverse event data was collected for 24 hours.
Adverse Event Reporting Description	The definition of adverse event and/or serious adverse event does not differ from the clinicaltrials.gov definition.
Arm/Group Title	Nitrous Oxide - Inhaled
Arm/Group Description	Each volunteer will participate in one scanning visit in which simultaneous fMRI/EEG data will be collected wherein they receive placebo (20 minutes) followed by inhaled nitrous oxide at subanalgesic levels (35% inhaled concentration) over 30 minutes. A total of 21 participants consented to participate but 2 participants did not participate in any part of the research and thus no adverse events data could have been collected.
All Cause Mortality
	Nitrous Oxide - Inhaled
	Affected / at Risk (%)	# Events
Total	0/19 (0%)
Serious Adverse Events
	Nitrous Oxide - Inhaled
	Affected / at Risk (%)	# Events
Total	0/19 (0%)
Other (Not Including Serious) Adverse Events
	Nitrous Oxide - Inhaled
	Affected / at Risk (%)	# Events
Total	2/19 (10.5%)
General disorders
Tachycardia	1/19 (5.3%)	1
Emesis	1/19 (5.3%)	1

Limitations/Caveats

Data for the Spectral Power of Sub-anesthetic Dose of Nitrous Oxide outcome measure will be analyzed within the coming year and the ClinicalTrials.gov record will be updated at that time.

More Information

Certain Agreements

All Principal Investigators ARE employed by the organization sponsoring the study.

There is NOT an agreement between Principal Investigators and the Sponsor (or its agents) that restricts the PI's rights to discuss or publish trial results after the trial is completed.