Distribution of Ventilation, Respiratory Drive and Gas Exchange: Measurements and Monitoring

Study Overview
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Brief Summary
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Respiratory physiology involves a complex interplay of elements including control of breathing, respiratory drive, pulmonary mechanics, distribution of ventilation and gas exchange. Body position may also play an important role in respiratory mechanics. While effective methods exist for measuring these variables, they are typically measured in isolation rather than in combination. In pulmonary disease, decreasing mechanical stress and strain and optimizing transpulmonary pressure or the distending pressure across the lung, minimizing overdistention and collapse are central to clinical management. Obesity has a significant impact on pulmonary mechanics and is a risk factor for obstructive sleep apnea (OSA). However, our understanding of these elements is limited even in the general population. The investigators plan to use various validated methods to assess control of breathing, respiratory drive, distribution of ventilation and gas exchange to obtain a better understanding of underlying physiologic signatures in patients with and without obesity and the role of posture/position, with a secondary analysis comparing participants with and without obstructive sleep apnea.

Official Title
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Distribution of Ventilation, Respiratory Drive and Gas Exchange: Measurements and Monitoring

Conditions
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OSA, Pulmonary Disease, Respiratory System Abnormalities, Respiratory Failure

Intervention / Treatment
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* Other: Position change


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: 18 years or older Non-smokers Exclusion Criteria: <18 years old Significant history of pulmonary disease Chest wall, anatomical, physical abnormalities, skin integrity issues precluding placement of electrode belt in direct contact with skin Skin integrity issues precluding placement of nose clips, or transcutaneous carbon dioxide monitoring Inability to form a seal around a mouthpiece Known esophageal strictures, webs, or varices (if esophageal manometry to be included) Known platelet count < 100,000 (if esophageal manometry to be included) On therapeutic anticoagulation (if esophageal manometry to be included) Known multidrug resistant (MDR) pulmonary infection Non-English language speakers Chronic hypoxemic respiratory failure Confirmed or suspected intracranial bleed, stroke, edema Active implants (i.e. implantable electronic devices such as pacemakers, cardioverter defibrillators or neurostimulators) or if device compatibility is in doubt Pregnant or lactating patients as safety and efficacy for use of EIT in such cases has not been verified

Ages Eligible for Study
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Minimum Age: 18 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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Accepts Healthy Volunteers

Study Plan
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How is the study designed?
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Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| BMI>24.9 kg/m2<br> | Other: Position change<br>* Distribution of ventilation, respiratory drive, pulmonary mechanics and gas exchange will be measured in 3 unique positions: prone, head of bed (HOB) flat (i.e. 0 degrees) and HOB elevated (i.e. 30 degrees).<br>|
| BMI 18-24.9 kg/m2<br> | Other: Position change<br>* Distribution of ventilation, respiratory drive, pulmonary mechanics and gas exchange will be measured in 3 unique positions: prone, head of bed (HOB) flat (i.e. 0 degrees) and HOB elevated (i.e. 30 degrees).<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Distribution of ventilation | Change in regional ventilation distribution (ventral/dorsal) measured through electrical impedance tomography (EIT) | 3 hours | 
| Respiratory drive | Respiratory drive differences will be measured by mean desaturation (change from baseline percent oxygen saturation) following breath-hold maneuvers | 3 hours | 
| Respiratory drive | Respiratory drive differences will be assessed by the duration of maximal breath-hold (seconds) | 3 hours | 
| Respiratory drive | Respiratory drive will also be assessed by measurement of occlusion pressure (cm H2O) at 100 ms (P0.1) after the initiation of an inspiratory effort against a closed circuit. | 3 hours | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Pulmonary mechanics | Pulmonary mechanics will be measured by transpulmonary pressure (cmH2O)obtained from esophageal manometry (transpulmonary pressure= airway pressure- esophageal pressure) | 3 hours | 
| Dead space fraction | Dead space fraction will be calculated by partial pressure arterial/transcutaneous CO2 (PCO2) minus partial pressure of CO2 in mixed expired gas divided by the partial pressure of arterial/transcutaneous CO2 | 3 hours | 
| Ventilatory ratio | Ventilatory ratio will be calculated as measured minute ventilation multiplied by the measured partial pressure of PCO2 divided (transcutaneous) by the predicted minute ventilation based on ideal body weight multiplied by the ideal PaCO2 | 3 hours |