The goal of this clinical study is to learn how different head-of-bed positions affect lung movement during breathing in healthy adults. Researchers want to understand whether raising the head of the bed changes how the lungs move, which may help guide patient positioning in emergency and intensive care settings.

The main questions this study aims to answer are:

Does lung movement change when the head of the bed is positioned at zero, twenty, or forty degrees?

Are there differences in lung movement between the right and left lungs?

Are there differences between the upper (apical) and lower (basal) parts of the lungs?

Participants will be healthy adult volunteers between eighteen and sixty years of age. Each participant will lie on a bed in three different positions: flat, with the head raised to twenty degrees, and with the head raised to forty degrees.

During each position, researchers will use bedside lung ultrasound, a painless and non-invasive imaging method, to measure lung movement at four areas of the chest. No medications, injections, or invasive procedures will be used.

This study may help health care providers better understand how body position affects breathing and support safer and more effective positioning of patients with breathing problems.

This is a prospective, low-risk, non-drug interventional clinical study designed to evaluate the effect of head-of-bed elevation on lung sliding movement in healthy adult volunteers. Lung sliding is a dynamic ultrasound finding that reflects the movement between the visceral and parietal pleura during respiration and provides information about lung aeration and respiratory mechanics.

The primary objective of the study is to quantitatively assess changes in lung sliding amplitude across three standardized head-of-bed positions: zero degrees (supine), twenty degrees, and forty degrees. Measurements will be obtained using bedside lung ultrasonography at four predefined anatomical locations: right apical, right basal, left apical, and left basal lung regions.

Secondary objectives include evaluating potential differences in lung sliding between the right and left lungs, comparing apical and basal lung regions, and assessing whether positional changes have region-specific effects on lung movement.

The study population will consist of thirty-one healthy adult volunteers aged eighteen to sixty years. Individuals with known respiratory disease, significant cardiopulmonary conditions, pregnancy, prior thoracic surgery, or inability to tolerate position changes will be excluded. All participants will provide written informed consent prior to enrollment.

Each participant will undergo lung ultrasound measurements in all three positions in a repeated-measures design. Lung sliding will be recorded using high-frequency linear ultrasound probes. Quantitative assessment will be performed using M-mode imaging, measuring pleural line displacement in millimeters. Mean values will be calculated for each position and anatomical region.

No investigational drugs, medical devices, or invasive procedures will be used. The only intervention is controlled head-of-bed positioning. The study is considered minimal risk. Potential discomfort related to short-term position changes, such as mild dizziness or transient shortness of breath, will be monitored, and measurements will be discontinued if symptoms occur.

Data will be analyzed using repeated measures statistical methods to compare lung sliding values across positions and regions. The findings are expected to improve understanding of the positional sensitivity of lung ultrasound measurements and may contribute to evidence-based recommendations for patient positioning in emergency and critical care settings.

Inclusion Criteria:

• Healthy adult volunteers aged eighteen to sixty years.
• No history of acute or chronic respiratory disease.
• Body mass index between eighteen point five and twenty-nine point nine kilograms per square meter.
• Ability to understand the study procedures and provide written informed consent.
• No skin lesions or wounds at the chest wall that would interfere with lung ultrasound examination.

Exclusion Criteria:

• History of respiratory system diseases, including asthma, chronic obstructive pulmonary disease, bronchiectasis, pneumonia, or tuberculosis.
• Presence of chest wall deformities (such as kyphoscoliosis or pectus deformities) or history of thoracic surgery.
• Inability to tolerate position changes during the study, including development of dizziness, syncope, or shortness of breath.
• Pregnancy or breastfeeding.
• Known significant cardiac, neurological, or metabolic disease.
• Known allergy to ultrasound gel or latex.

Individual participant data will not be shared because this study involves a small sample of healthy volunteers and collects detailed physiological measurements that could increase the risk of re-identification, even after de-identification. The study protocol and informed consent do not include provisions for public sharing of individual-level data. Only aggregated and anonymized results will be reported.