Hyperventilation Effects on Bodily Self-Consciousness

NCT07769710 | Not Yet Recruiting

• 2 other identifiers: HYPERSELF-2026-013852026-01385
• Study Type: interventional
• Target: 35
• Locations: 1 country
• Sites: 1

Brief Summary

This study examines how voluntary fast, deep breathing (hyperventilation) affects the way healthy adults perceive their own body. Participants wear a virtual-reality (VR) headset and see a virtual body; a glowing halo around it either pulses exactly in time with their own breathing or is time-shifted. During the study, breathing, heart activity, blood-oxygen level, the carbon-dioxide content of exhaled air, and brain activity (EEG, measured non-invasively from the scalp) are recorded continuously, and participants complete questionnaires about their experience. The aim is to understand whether and how altered breathing changes the interplay between what people see and what they feel inside their body, and thereby the sense of being located within one's own body. The study uses a 2×2 within-subjects design crossing Breathing (normal vs. hyperventilation) with Visual synchrony (synchronous vs. asynchronous), with the asynchronous and normal-breathing conditions serving as within-subject controls. No medication is administered and no medical device is being tested; the instruments used serve only for monitoring and measurement. Participation involves a screening visit (including a short, \~5-minute guided-hyperventilation tolerance test) and an experimental visit.

Conditions

Bodily Self-Consciousness; Interoception; Healthy Volunteers

Keywords

hyperventilation; bodily self-consciousness; full-body illusion; respiratory-visual synchrony; interoception; virtual reality; EEG; heartbeat-evoked potential; altered states of consciousness; breathwork

Outcome Measures

Primary Outcomes (1)

• Mean Rating of Perceived Breathing Location in the Virtual Body: Bodily Self-Consciousness Questionnaire Item 1 (BSC-Q1)

  Self-reported agreement with the statement "It seemed as if I was feeling my respiration in the virtual body", item 1 of the Bodily Self-Consciousness Questionnaire (BSC-Q). Rated on a 7-point Likert scale from -3 (totally disagree) to +3 (totally agree); minimum -3, maximum +3. Higher scores indicate that the participant's own breathing is felt more strongly to be located in the virtual body (a stronger illusion). This is a mechanistic outcome; neither a higher nor a lower score is a better or worse clinical outcome. Rated after each of the 6 virtual reality (VR) exposures (2 normal-breathing exposures, 4 hyperventilation cycles); the two hyperventilation cycles at each synchrony level are averaged within participant. Reported as the mean rating in each of the 4 conditions (Synchronous/Asynchronous x Normal breathing/Hyperventilation). Primary analysis: the Synchrony x Breathing interaction in a within-subjects linear mixed-effects model.

  Experimental visit (single visit, approximately 188 minutes); rated after each of the 6 VR exposures

Secondary Outcomes (15)

• Mean Drift in Perceived Self-Location Toward the Virtual Body, Measured With the Mental Imagery Task (MIT)

  Experimental visit (single visit, approximately 188 minutes); measured after each of the 6 VR exposures, each baseline-corrected against a matched breathing-state pre-test

• Mean Rating of Perceived Breathing Synchrony With the Virtual Body: Bodily Self-Consciousness Questionnaire Item 2 (BSC-Q2)

  Experimental visit (single visit, approximately 188 minutes); rated after each of the 6 VR exposures

• Mean Rating of Self-Identification With the Virtual Body: Bodily Self-Consciousness Questionnaire Item 3 (BSC-Q3)

  Experimental visit (single visit, approximately 188 minutes); rated after each of the 6 VR exposures

• Mean Rating of Being Located Outside the Physical Body: Bodily Self-Consciousness Questionnaire Item 4 (BSC-Q4)

  Experimental visit (single visit, approximately 188 minutes); rated after each of the 6 VR exposures

• Mean Rating of Separation From the Physical Body: Bodily Self-Consciousness Questionnaire Item 5 (BSC-Q5)

  Experimental visit (single visit, approximately 188 minutes); rated after each of the 6 VR exposures

Study Arms (2)

Sequence A: synchronous-first (normal-breathing block)

EXPERIMENTAL

Sequence A: synchronous-first (normal-breathing block): Randomised sequence group A. Participants complete all four cells of the 2x2 design in a single experimental visit: the normal-breathing block first (fixed order), then the hyperventilation block. In the normal-breathing block this group receives the SYNCHRONOUS respiratory-visual VR exposure first and the asynchronous exposure second. In the hyperventilation block the participant is separately allocated, from the same pre-generated permuted-block randomisation list, one of six balanced sequences comprising two synchronous and two asynchronous VR exposures; the list is balanced on the first-exposure condition. The interventions received are identical to those in Sequence B, and only the order of the synchronous and asynchronous VR exposures differs. Open label.

Other: Voluntary hyperventilation (guided paced breathing); Other: Normal spontaneous breathing (within-subject control); Other: Synchronous respiratory-visual VR feedback; Other: Asynchronous respiratory-visual VR feedback

Sequence B: asynchronous-first (normal-breathing block)

EXPERIMENTAL

Randomised sequence group B. Participants complete all four cells of the 2x2 design in a single experimental visit: the normal-breathing block first (fixed order), then the hyperventilation block. In the normal-breathing block this group receives the ASYNCHRONOUS respiratory-visual VR exposure first and the synchronous exposure second. In the hyperventilation block the participant is separately allocated, from the same pre-generated permuted-block randomisation list, one of six balanced sequences comprising two synchronous and two asynchronous VR exposures; the list is balanced on the first-exposure condition. The interventions received are identical to those in Sequence A, and only the order of the synchronous and asynchronous VR exposures differs. Open label.

Other: Voluntary hyperventilation (guided paced breathing); Other: Normal spontaneous breathing (within-subject control); Other: Synchronous respiratory-visual VR feedback; Other: Asynchronous respiratory-visual VR feedback

Interventions

Voluntary hyperventilation (guided paced breathing) OTHER

Participants breathe deeper and faster than normal, maintaining continuous cyclic breathing without pauses between inhalation and exhalation, paced by a pre-recorded standardised voice guide in German or English with background music. The hyperventilation block comprises four cycles, each with a 10-minute guided paced-hyperventilation induction, a 2-minute VR exposure and a 3-minute post-exposure stack (BSC-Q, Mental Imagery Task, distress NRS); cycle 1 additionally includes a 2-minute hyperventilation-state Mental Imagery Task pre-test between the induction and the VR exposure. A 5-minute sustained-hyperventilation resting-state EEG window is collected between cycles 2 and 3, with the voice guide replaced by a soft drum pacing tone. Cumulative hyperventilation is approximately 45 minutes, followed by a single supervised recovery. EtCO2, SpO2, heart rate and heart rate variability (ECG) are monitored continuously under the protocol's tiered stop criteria.

Sequence A: synchronous-first (normal-breathing block); Sequence B: asynchronous-first (normal-breathing block)

Normal spontaneous breathing (within-subject control) OTHER

Within-subject control condition for the Breathing factor. Participants breathe at their natural spontaneous rate while receiving audio guidance from the same pre-recorded standardised voice guide and background music used in the hyperventilation condition, so that the auditory environment is held constant across conditions and only the breathing instruction differs. Delivered as two 8-minute normal-breathing cycles (3 minutes spontaneous breathing in VR, a 2-minute VR exposure, and a 3-minute post-exposure stack of BSC-Q, Mental Imagery Task and distress NRS), one with synchronous and one with asynchronous respiratory-visual feedback, seated in the experimental chair wearing the head-mounted display.

Sequence A: synchronous-first (normal-breathing block); Sequence B: asynchronous-first (normal-breathing block)

Synchronous respiratory-visual VR feedback OTHER

Respiratory-visual VR paradigm delivering contingent feedback; this is the measurement method through which bodily self-consciousness is assessed. Seated participants wear a head-mounted display showing a first-person view of a three-dimensional virtual body positioned about 2 metres in front of the viewpoint and seen from behind. A respiratory belt at the level of the umbilicus drives, in real time, a luminous halo surrounding the virtual body: the halo becomes increasingly visible during inspiration, reaches maximum luminosity at peak inspiration and fades during expiration, in synchrony with the participant's actual breathing. Each exposure lasts 2 minutes (120 seconds). Each participant receives one synchronous exposure in the normal-breathing block and two in the hyperventilation block.

Sequence A: synchronous-first (normal-breathing block); Sequence B: asynchronous-first (normal-breathing block)

Asynchronous respiratory-visual VR feedback OTHER

Respiratory-visual VR paradigm delivering non-contingent feedback; the control level of the Synchrony factor. Setup is identical to the synchronous condition (seated, head-mounted display, virtual body about 2 metres in front seen from behind, respiratory belt at the umbilicus), except that the halo modulation is phase-shifted and frequency-adjusted to 80% or 120% of the measured breathing frequency, so that the visual feedback never corresponds to the participant's respiratory state. Each exposure lasts 2 minutes (120 seconds). Each participant receives one asynchronous exposure in the normal-breathing block and two in the hyperventilation block.

Sequence A: synchronous-first (normal-breathing block); Sequence B: asynchronous-first (normal-breathing block)

Eligibility Criteria

• Age: 18 Years - 55 Years
• Sex: all
• Healthy Volunteers: Yes
• Age Groups: Adult (18-64)

You may qualify if:

• Healthy adult aged 18-55 years
• Able to provide written informed consent
• Normal or corrected-to-normal vision
• Sufficient German or English to follow instructions and complete questionnaires
• Tolerates the \~5-minute VR-guided hyperventilation test at screening

You may not qualify if:

• Cardiovascular or cerebrovascular disease posing a risk during hyperventilation (e.g., myocardial infarction or stroke within 12 months, significant/unstable cardiac disease, heart failure, uncontrolled/severe hypertension, aneurysm, Moyamoya)
• Respiratory disease (asthma, COPD, restrictive lung disease, pulmonary fibrosis, recent severe lung infection, dyspnoea at rest)
• Haematological disease (sickle cell disease or trait, severe anaemia)
• Neurological disease (epilepsy or seizures, severe/recurrent migraine, neurodegenerative disorder)
• Psychiatric disorder (panic or severe anxiety disorder, psychosis or schizophrenia, severe bipolar disorder, acute major depression, acute addiction)
• Metabolic disease (Type 1 or poorly controlled Type 2 diabetes, BMI \> 35)
• Pregnancy (confirmed by urine test at screening) or planned pregnancy during the study period
• Medication affecting respiration or brain function
• Physical inability to cooperate or to remain seated for the \~188-minute experimental visit
• Insufficient understanding of study procedures and risks
• Intolerable reaction to the hyperventilation tolerance test at screening

Sponsors & Collaborators

• University of Fribourg: lead

Study Sites (1)

University of Fribourg, Molecular Psychiatry Laboratory, (at Réseau fribourgeois de santé mentale, RFSM/FNPG)

Villars-sur-Glâne, 1752, Switzerland

Location

MeSH Terms

Conditions

Hyperventilation

Condition Hierarchy (Ancestors)

Respiration Disorders; Respiratory Tract Diseases; Signs and Symptoms, Respiratory; Signs and Symptoms; Pathological Conditions, Signs and Symptoms

Study Officials

• Gregor Hasler, Prof. Dr. med.

  University of Fribourg

  PRINCIPAL INVESTIGATOR

Central Study Contacts

Parsa Yousefi, Mas

CONTACT

+41 26 308 16 03; parsa.yousefi@unifr.ch

Study Design

• Study Type: interventional
• Phase: not applicable
• Allocation: RANDOMIZED
• Masking: NONE
• Purpose: BASIC SCIENCE
• Intervention Model: CROSSOVER
• Sponsor Type: OTHER
• Responsible Party: SPONSOR

Model Details: Within-subjects 2x2 factorial crossover. Factors: Breathing condition (normal vs. hyperventilation) x respiratory-visual VR synchrony (synchronous vs. asynchronous). All participants complete all four cells in one experimental visit. NOT randomised: block order is fixed; the normal-breathing block always precedes the hyperventilation block, for safety and physiological reasons. RANDOMISED: within each block the order of the synchronous and asynchronous VR exposures is allocated from a computer-generated permuted-block list prepared before enrolment and held centrally (normal-breathing block: 1 synchronous + 1 asynchronous exposure, block size 2; hyperventilation block: one of six balanced sequences of 2 synchronous + 2 asynchronous exposures). Both lists are balanced on the first-exposure condition. The two arms are the randomised sequence groups; they receive identical interventions and differ only in exposure order. Open label.

Study Record Dates

• First Submitted: July 14, 2026
• First Posted: August 18, 2026
• Study Start: September 1, 2026
• Primary Completion (Estimated): July 31, 2027
• Study Completion (Estimated): July 31, 2027
• Last Updated: August 18, 2026

Record last verified: 2026-08

Data Sharing

• IPD Sharing: Will not share

Locations

CH (1)