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PHOEBIBreathing Changes in Obesity and Effects of Bariatric Surgery

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Study Aim

This observational study aims to explore how the degree of change in breathing patterns, specifically expiratory flow limitation, can differentiate between individuals with obesity who have normal carbon dioxide levels (eucapnic) and those with high carbon dioxide levels (hypercapnic), as well as the impact of bariatric surgery on these changes.

What is being collected

Data Collection

Collected from today forward - Prospective
Who is being recruted

Apnea+14

+ Hypoventilation

+ Nervous System Diseases

From 18 to 80 Years
+14 Eligibility Criteria
See all eligibility criteria
How is the trial designed

Case-Control

Comparing exposures between individuals with and without disease in order to identify potential risk factors.
Observational
Study Start: June 2019
See protocol details

Summary

Principal SponsorGuy's and St Thomas' NHS Foundation Trust
Study ContactMichael Cheng, MBBS
Last updated: January 28, 2026
Sourced from a government-validated database.Claim as a partner

Study start date: June 20, 2019

Actual date on which the first participant was enrolled.

Obesity can affect how a person breathes, leading to issues like sleep disordered breathing, a condition where breathing is abnormal during sleep, the most common form being obstructive sleep apnoea. If these breathing problems worsen, they can cause a rise in carbon dioxide levels during the day, leading to a condition called obesity hypoventilation syndrome (OHS). Current treatments include supportive breathing therapy at night, managing associated medical conditions, and weight loss. This study focuses on understanding how these breathing changes occur due to obesity and how they might improve after weight loss surgery. It specifically looks at individuals with sleep disordered breathing who are waiting for bariatric surgery, comparing those with OHS to those with normal carbon dioxide regulation. Participants in this study will be recruited from outpatient clinics for sleep disordered breathing. They will undergo comprehensive breathing assessments upon enrollment, including an overnight sleep study. Further daytime breathing assessments will be conducted before and after their bariatric surgery. The study will end 6 months after surgery, with a final comprehensive breathing assessment and overnight sleep study to review any improvements in their breathing. The primary outcomes of the study include measuring changes in expiratory flow limitation, which is the difficulty in exhaling air, at different positions. The study will explore whether these changes can differentiate between patients with normal and high carbon dioxide levels.

Official TitlePathophysiology of Hypoventilation in Obesity and Effects of Bariatric Intervention: PHOEBI Study
Principal SponsorGuy's and St Thomas' NHS Foundation Trust
Study ContactMichael Cheng, MBBS
Last updated: January 28, 2026
Sourced from a government-validated database.Claim as a partner

Protocol

This section provides details of the study plan, including how the study is designed and what the study is measuring.
Design Details

30 patients to be enrolled

Total number of participants that the clinical trial aims to recruit.

Case-Control

These studies compare people who have a disease (cases) with those who don't (controls). The goal is to look back at previous exposures or risk factors to identify what might have contributed to the disease.

Eligibility

Researchers look for people who fit a certain description, called eligibility criteria: person's general health condition or prior treatments.
Conditions
Criteria

Any sex

Biological sex of participants that are eligible to enroll.

From 18 to 80 Years

Range of ages for which participants are eligible to join.

Healthy volunteers allowed

If individuals who are healthy and do not have the condition being studied can participate.

Conditions

Pathology

ApneaHypoventilationNervous System DiseasesNutrition DisordersNutritional and Metabolic DiseasesObesityObesity Hypoventilation SyndromeRespiration DisordersRespiratory InsufficiencyRespiratory Tract DiseasesSleep Apnea SyndromesSleep Wake DisordersSleep Apnea, ObstructiveSleep Disorders, IntrinsicDyssomniasOvernutritionOverweight

Criteria

4 inclusion criteria required to participate
Patients 18 years or older

BMI > 40

Patients with significant sleep disordered breathing requiring treatment

Patient is being assessed for bariatric surgery for either gastric sleeve or gastric bypass surgery

10 exclusion criteria prevent from participating
Patients with decompensated hypercapnic respiratory failure (pH< 7.3)

Chronic hypercapnic respiratory failure due to a cause other than obesity such as neuromuscular, chest wall or airway disease

Unstable cardiac disease including coronary artery disease and heart failure

Significant co-morbid psychiatric disease requiring anti-psychotic medications

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Study Plan

Find out more about all the medication administered in this study, their detailed description and what they involve.
Study Objectives

Study Objectives

Primary Objectives

Secondary Objectives

Study Centers

These are the hospitals, clinics, or research facilities where the trial is being conducted. You can find the location closest to you and its status.

This study has 1 location

Recruiting

Guy's and St Thomas' NHS Trust

London, United KingdomOpen Guy's and St Thomas' NHS Trust in Google Maps
SuspendedOne Study Center