Ventilation Perfusion Mismatch

Acute respiratory distress syndrome (ARDS) is when a person's lungs become inflamed, which can be caused by infection, trauma, surgery, blood transfusion, or burn. ARDS often leads to a situation where the person cannot breathe independently and needs machines' help. Once the lungs are inflamed, the small air sacs responsible for exchanging gases (i.e., ventilation) and the blood flow in the lungs (i.e., perfusion) can be affected. In the past, most research focused on studying ventilation physiology and how to help people breathe with machines. Less was done on perfusion because it requires imaging techniques such as computed tomography with intravenous contrast and radiation. One treatment option for low oxygen levels is inhaled nitric oxide (iNO), a gas that can dilate the lung blood vessels and improve oxygenation; however, it is not always clear whether this treatment will work. Prone position has been used for several years in the care of ARDS patients and has been demonstrated to improve survival in more severe patients. It is not known how iNO and prone positioning interact in determining the distribution of pulmonary perfusion and whether their combine use can benefit ARDS patients. Electrical Impedance Tomography (EIT) is a bedside and accessible imaging technique that is radiation-free and non-invasive and can potentially detect changes in lung perfusion. EIT can perform multiple measurements; it is portable and accessible. This prospective interventional study aims to assess changes in regional blood perfusion in the lungs of patients with ARDS in response to iNO and to prone positioning utilizing EIT. The main questions it aims to answer are: 1. If EIT can measure lung regional perfusion response to an iNO challenge of 20ppm for 15 minutes. 2. If EIT can measure the lung regional perfusion responses to prone position, applied alone and in combination with iNO. 3. If EIT is comparable to dual-energy computed tomography (DECT), the gold-standard method, in the detection of changes in regional lung perfusion due to iNO. 4. If EIT can be an imaging marker to identify ARDS severity Participants will be divided into three cohorts: 1. Sub-Cohort 1 (n=60): Participants will be asked to be monitored by EIT before, during, and after the administration of iNO (20 ppm) for 15 minutes (OFF-ON-OFF) in the supine position 2. Sub-Cohort 2 (N=10): Participants will be asked to be monitored by EIT before and during the administration of iNO (20 ppm) for 15 minutes (OFF-ON) in both the supine and in the prone position. The same subjects will be monitored also with DECT in the supine position and then after 30 minutes in the prone position (without NO administration). 3. Sub-Cohort 3 (N=10): In this subset of Sub-Cohort 1, subjects will be asked to be monitored also with DECT (in addition to EIT) in the supine body position before iNO and after 15 minutes while receiving iNO.

In preterm infants \< 34 weeks' gestation at birth receiving respiratory support with invasive positive pressure ventilation, the positive end-expiratory pressure (PEEP) of best compliance will increase the cardiac output and improve oxygenation. This study may emphasize using point-of-care echocardiography along with electrical impedance tomography (EIT) to optimize ventilator settings in preterm infants. Infants will be randomized to a 4-hour crossover period of increasing and decreasing PEEP in random order from baseline to determine compliance, oxygenation, and cardiac hemodynamics at each step using echocardiography (ECHO) and EIT measurements. There will be a 15-minute washout period after changes prior to data collection.

This study aims to compare lung perfusion distribution between inspiratory breath-hold and expiratory breath-hold phases using the saline indicator method combined with electrical impedance tomography (EIT). A self-controlled crossover design will be used in which each participant undergoes both breath-hold conditions with standardized rapid intravenous saline injections. The primary objective is to evaluate changes in global and regional pulmonary perfusion under different lung volume states. The findings may improve understanding of perfusion redistribution with lung inflation and support optimized ventilatory strategies in clinical practice.

This study evaluates the effects of prone positioning on homogenization of ventilation.