Positional Effects on Lung Ventilation and Perfusion in Obesity

Effects of Body Position on Ventilation and Perfusion Distribution in Obese and Non-Obese Healthy Volunteers Assessed by Electrical Impedance Tomography

Electrical Impedance Tomography (EIT) is a non-invasive, bedside monitoring tool that provides real-time information on regional ventilation and perfusion. In particular, EIT has the potential to guide individualized mechanical ventilation in obese patients by revealing how gravitational and positional factors alter regional lung behavior. Assessing the effects of different horizontal positions on both ventilation and perfusion may help optimize respiratory management strategies tailored to body habitus. By comparing obese and non-obese healthy participants across different positions, this study aims to provide novel insights into the postural effects on lung aeration and perfusion distribution, and to highlight the role of EIT in tailoring individualized ventilation strategies.

Study Overview

• Status: Completed
• Conditions: Ventilation Perfusion Mismatch; Obesity (Disorder); Perfusion; Ventilation Homogeneity; Electrical Impedance Tomography (EIT); Position Differences
• Intervention / Treatment: Other: Standardized body positioning

Detailed Description

This will be a observational, physiological study involving healthy volunteers divided into two groups: Obese group (BMI 30 - 40 kg/m²) and non-obese group (BMI 18.5 - 24.9 kg/m²). Each participant will serve as their own control across body positions. Baseline measurements will be obtained in upright sitting, followed by randomized order of supine, Trendelenburg (30°), prone, left lateral, and right lateral. Participants' demographic and anthropometric data, including height, weight, chest circumference, waist circumference, and hip circumference, will be recorded. Medical history, current medication use, smoking status, and cumulative smoking exposure (pack-years) will be documented.

Electrical Impedance Tomography (EIT) measurements will be performed using the Infivision ET1000 device. All study procedures will take place in a private room within the General Intensive Care Unit of Koç University Hospital, with privacy ensured throughout the protocol. After removal of upper body clothing, an appropriately sized EIT belt, selected according to chest circumference, will be positioned circumferentially around the thorax at the level of the axillae. A pulse oximetry probe will be applied, and continuous monitoring of heart rate and peripheral oxygen saturation will be maintained during all measurements.

Following a 5-minute stabilization period in the upright sitting position, baseline EIT measurements will be obtained. The following parameters will be recorded: percentage of ventral ventilation, percentage of dorsal ventilation, percentage of ventral perfusion, percentage of dorsal perfusion, Match Index (MI), Dead Space Index (DI), Shunt Index (SI), Global Inhomogeneity Index (GI), and Center of Ventilation (CoV). To minimize potential carry-over effects, the sequence of positions will be randomized individually for each participant. Randomization will be performed using computer-generated random sequences (randomizer.org), with predefined randomization sets created prior to study initiation.

Each position will be maintained for approximately 5 minutes. In each position, end-expiratory lung impedance difference (ΔEELI) will be measured using the upright sitting position as the reference. The total duration of the study protocol is expected to be approximately 30 minutes per participant. The study will be completed once all measurements have been obtained in all positions.

• Study Type: Observational
• Enrollment (Actual): 40

Contacts and Locations

Study Locations

• Turkey (Türkiye)
  • Istanbul, Turkey (Türkiye), 34010
    • Koç University Hospital

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult; Older Adult
• Accepts Healthy Volunteers: Yes

• Sampling Method: Non-Probability Sample

Study Population

Healthy non-obese and obese volunteers

Description

Inclusion Criteria:

-BMI between 18-25 kg/m² or 30-40 kg/m²

Exclusion Criteria:

• Individuals with a body mass index (BMI) between 25 and 30 kg/m²,
• Pregnancy
• Respiratory tract infection within the previous two weeks
• Anatomical abnormalities of the chest wall that may interfere with Electrical Impedance Tomography (EIT) measurements.

Study Plan

How is the study designed?

Number of groups / cohorts

2

Cohorts and Interventions

Group / Cohort	Intervention / Treatment
Non-obese group; Non-obese healthy individuals with BMI between 18.5 - 25 kg/m²	Other: Standardized body positioning; Standardized changes in body position (supine, Trendelenburg, prone, and lateral positions) performed solely for physiologic assessment of ventilation and perfusion using electrical impedance tomography. This does not constitute a therapeutic or preventive intervention.
Obese group; Obese healthy individuals with BMI between 30 - 40 kg/m²	Other: Standardized body positioning; Standardized changes in body position (supine, Trendelenburg, prone, and lateral positions) performed solely for physiologic assessment of ventilation and perfusion using electrical impedance tomography. This does not constitute a therapeutic or preventive intervention.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
MI	Match Index (MI, 0-100%): quantifying the spatial overlap of ventilation and perfusion distributions. MI values will be taken from the device's Match View. Change in Match Index (MI) between obese and non-obese participants across positions will be compared.	Periprocedural

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
VV %	Percentage of ventral ventilation across body positions.	Periprocedural
DV %	Percentage of dorsal ventilation across body positions.	Periprocedural
VP %	Percentage of ventral perfusion across body positions.	Periprocedural
DP %	Percentage of dorsal perfusion across body positions.	Periprocedural
DI %	Dead space index (DI), proportion (in %) of lung units (pixels or ROIs) that are ventilated but not perfused across body positions	Periprocedural
SI %	Shunt index (SI), proportion (in %) of lung units (pixels or ROIs) that are perfused but not ventilated across body positions	Periprocedural
GI	Global Inhomogeneity Index (0-100) quantifies how evenly ventilation is distributed across the lung regions. Higher values indicate more heterogeneous ventilation distribution across the lung cross-section.	Periprocedural
CoV	Center of ventilation (CoV) describes the center of mass of the ventilation distribution along the ventrodorsal axis (0-100, from ventral to dorsal). CoV <40% means more ventral ventilation while >50-55% means more dorsal ventilation.	Periprocedural
ΔEELI	ΔEELI represents the change in end-expiratory lung impedance measured by EIT between each body position and the upright sitting reference position, reflecting relative changes in end-expiratory lung volume associated with positioning.	Periprocedural
Heart rate	Heart rate per minute measured by pulse oximetry	Periprocedural
Oxygen saturation	Oxygen saturation measured by pulse oximetry	Periprocedural

Collaborators and Investigators

• Sponsor: Koç University
• Investigators: Study Director: Evren Şentürk, MD, Koç University School of Medicine

Publications and helpful links

General Publications

• De Jong A, Wrigge H, Hedenstierna G, Gattinoni L, Chiumello D, Frat JP, Ball L, Schetz M, Pickkers P, Jaber S. How to ventilate obese patients in the ICU. Intensive Care Med. 2020 Dec;46(12):2423-2435. doi: 10.1007/s00134-020-06286-x. Epub 2020 Oct 23.

Study record dates

Study Major Dates

• Study Start (Actual): December 1, 2025
• Primary Completion (Actual): March 5, 2026
• Study Completion (Actual): March 5, 2026

Study Registration Dates

• First Submitted: December 15, 2025
• First Submitted That Met QC Criteria: January 6, 2026
• First Posted (Actual): January 14, 2026

Study Record Updates

• Last Update Posted (Actual): April 15, 2026
• Last Update Submitted That Met QC Criteria: April 13, 2026
• Last Verified: December 1, 2025

More Information

Terms related to this study

• Keywords: obesity; electrical impedance tomography; ventilation perfusion; body positions
• Additional Relevant MeSH Terms: Nutrition Disorders; Overnutrition; Body Weight; Overweight; Pathological Conditions, Signs and Symptoms; Nutritional and Metabolic Diseases; Signs and Symptoms; Obesity
• Other Study ID Numbers: 2025.510.IRB2.232

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: YES
• IPD Plan Description: Data collected for the study, including de-identified individual participant data will be made available to other within 6 months after the publication of this trial, as will additional related documents (study protocol, statistical analysis plan and informed consent form), for academic purposes (e.g , meta-analyses) upon request to the corresponding author, and with a signed data access agreement.
• IPD Sharing Time Frame: 6 months after the publication
• IPD Sharing Access Criteria: Academic purposes
• IPD Sharing Supporting Information Type: STUDY_PROTOCOL; SAP; ICF; CSR

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No