Pathophysiology of Hypoventilation in Obesity and Effects of Bariatric Intervention (PHOEBI)

  • End date
    Jul 23, 2023
  • participants needed
  • sponsor
    Guy's and St Thomas' NHS Foundation Trust
Updated on 12 February 2022
bariatric surgery
gastric bypass
weight control
obesity treatment
Accepts healthy volunteers


Breathing is impacted by obesity. Early changes are characterised by significant breathing abnormalities during sleep (a condition called sleep disordered breathing, the most common of which is obstructive sleep apnoea). As the breathing changes worsen in severity, it may result in a rise in carbon dioxide levels during daytime causing a condition called obesity hypoventilation syndrome (OHS). The current treatment for obesity related breathing changes include supportive breathing therapy at night, optimisation of associated medical conditions and weight loss.

Weight management is an important part of obesity treatment. Weight loss strategies such as life-style modification do not always work. Weight loss surgery (bariatric surgery) has been shown to be an effective weight management intervention with long-term results. This study aims to understand breathing changes that occurs due to obesity and their resolution after weight loss surgery. The investigators are aiming to recruit participants with sleep disordered breathing who are currently awaiting bariatric surgery. In particular, the investigators are interested in comparing breathing changes in participants with OHS, who have abnormal regulation of their carbon dioxide levels, and participants with sleep disordered breathing with normal CO2 regulation.

Participants will be recruited through outpatient clinics for sleep disordered breathing. The participants will undergo comprehensive breathing assessments on enrolment including an overnight sleep study. Participants will undergo further daytime breathing assessments before and after their bariatric surgery. End of study will be 6 months after surgery - participants will have a final comprehensive breathing assessment including an overnight sleep study to review resolution of their breathing changes. Depending on the wait list time for the bariatric surgery, it is anticipated that participants will be enrolled in the study for 2 years.

Condition Obesity Hypoventilation Syndrome (OHS)
Treatment Bariatric Surgery
Clinical Study IdentifierNCT04025528
SponsorGuy's and St Thomas' NHS Foundation Trust
Last Modified on12 February 2022


Yes No Not Sure

Inclusion Criteria

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

Exclusion Criteria

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
Chronic pain syndrome on high dose opioid medications
Treatment for drug or alcohol addiction
Cognitive impairment that would prevent informed consent
Need for long-term renal replacement therapy
Patients who undergo bariatric intervention with gastric balloon or gastric band
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