Why Low Lung Volumes are BAD

In previous tutorials I discussed the problem of ventilation perfusion mismatch, intrapulmonary shunt and physiologic dead space. I explained how different injuries to the lung (the 6 s approach - slimy, soggy, sticky etc.) resulted in poorly aerated airways and atelectasis. Before moving on to a discussion about CPAP/PEEP we need to explore the problem of low lung volumes. Although the lungs can hold up to 6L of air - in reality most of the time there is 2-2.5L in the alvoli. This is the resting lung volume that is found at end expiration and results when the tendency for the chest wall to spring outwards is balanced by the tendency for the lungs to collapse inwards. That resting lung volume is established by negative pleural pressure and it represents the expiratory reserve volume and residual volume - together the functional residual capacity (FRC). FRC is the lung capacity in which most oxygenation takes place, in which lung compliance is highest, airway resistance lowest and pulmonary vascular resistance optimal. Loss of FRC ("low lung volumes") - results in hypoxemia, increased work of breathing, autopeep and pulmonary hypertension. During the tutorial I elaborate on lung volumes - how they are affected by position and age, how airway closure becomes a major issue as we get older - particularly in the supine position, and I introduce the volume pressure curve which is essential for understanding dynamic respiratory system compliance. @ccmtutorials www.ccmtutorials.org Description 00:10 Introduction 00:30 Review of Previous Tutorial 01:15 Contents of This Tutorial 01:30 Clinical Scenario - Peadar 01:55 Lung Volumes and Capacities 05:00 Lung Lobe Volumes and Changes With Position 12:23 Ventilation Perfusion and FRC 16:30 Why the Respiratory Cycle Matters and Why FRC and Oxygenation are linked. 19:54 Airway Closure and its Impact on FRC 21:45 Closing Volume and Closing Capacity and Age 23:00 "Phasic Shunting" - V/Q Mismatch During the Respiratory Cycle 24:40 Venous Admixture and Age 25:38 FRC and Patient Position 28:00 The Volume-Pressure Curve 28:50 Dynamic Compliance 31:00 Volume Pressure Relationships at Normal FRC 31:40 Dynamic Airway Collapse During Expiration 35:48 Volume Pressure Relationships at Low FRC 37:46 Pulmonary Vascular Resistance and FRC 38:30 Summary - What We Know About FRC 39:40 Why Low Lung Volumes are BAD (Low FRC) 40:00 Clinical Scenario Revisited 41:10 Review of This Tutorial 41:45 Preview of Next Tutorial