Cortes-Puentes, Gustavo A.

Body positioning exerts profound physiological effects in critically ill patients, influencing respiratory mechanics, ventilation-perfusion matching, hemodynamics, and overall clinical outcomes. Transitioning from an upright to a recumbent position alters thoracoabdominal pressure relationships, reduces ribcage contribution to tidal ventilation, and shifts ventilatory load to the diaphragm. These changes decrease functional residual capacity and promote airway closure in dependent lung regions, predisposing patients to atelectasis—an effect further amplified by intra-abdominal pathology or diaphragmatic weakness. Positioning also reshapes pulmonary perfusion and ventilation, which impact cardiopulmonary hemodynamics. These physiologic principles translate to important therapeutic applications across disease states. In ARDS, prone positioning improves oxygenation via a number of mechanisms, reduces ventilator-induced lung injury, and confers substantial mortality benefit. Prone position may also improve air flow distribution in COPD and enhance venous return in select cardiac physiologies. Conversely, conditions such as ascites, morbid obesity, and hepatopulmonary syndrome exemplify pathologic interactions between abdominal pressure, lung volumes, and posture, often requiring tailored positioning strategies to optimize respiratory performance. Overall, body positioning represents a potent, underutilized intervention in critical care. Understanding the mechanistic foundations of position-dependent changes in ventilation, perfusion, and pleural pressure can help clinicians strategically leverage positioning to improve patient outcomes across a spectrum of pulmonary and systemic illnesses.

Abstract Background: Tracheobronchomalacia (TBM) presents diagnostic challenges due to its nonspecific symptoms and variability in diagnostic methods. This study evaluates physician concordance in TBM diagnosis and phenotyping using chest computed tomography (CT) scans with dynamic expiratory views. Methods: We conducted a retrospective cross-sectional study at Mayo Clinic Rochester, analyzing 150 patients with dynamic expiratory CT scans. Three specialists—a thoracic radiologist, a bronchoscopist, and a pulmonologist—reviewed identical CT scans, blinded to prior interpretations. Inter-rater agreement was assessed using Fleiss's Kappa for TBM diagnosis and Cohen's Kappa for TBM phenotype classification into six categories: No TBM, Excessive Dynamic Airway Collapse (EDAC), Crescent Type, Circumferential Type, Saber-Sheath Type, and Mixed Type. Results: Among the 150 patients, 54 (36%) were diagnosed with TBM or EDAC. TBM was more prevalent in males, older individuals, and smokers. Agreement among specialists was substantial for TBM diagnosis (Fleiss’s Kappa = 0.61, p < 0.001) but moderate for phenotype classification (Fleiss’s Kappa = 0.52, p < 0.001). The highest concordance was between the thoracic radiologist and the pulmonologist (Cohen's Kappa = 0.68), while the lowest was between the bronchoscopist and other specialists. Conclusion: There is substantial agreement in TBM diagnosis using chest CT scans with dynamic expiratory views, but moderate variability in phenotyping. Standardizing criteria and integrating pulmonary function testing could enhance diagnostic consistency and clinical relevance.