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Oxygen delivery and carbon dioxide removal being critical to cell survival, mammals have developed collateral vascular and ventilation systems to ensure tissue viability. Collateral ventilation, defined as ventilation of alveoli via pathways that bypass normal airways, is present in humans and many other species. The presence of collateral ventilation can be beneficial in certain disease states, whereas its relative absence can predispose to other diseases. These well defined anatomical pathways contribute little to ventilation in normal humans, but modulate ventilation perfusion imbalance in a variety of diseases, including obstructive diseases, such as asthma and emphysema. These pathways can be affected by pharmaceuticals and inhaled gas compositions. The middle lobe and lingula, constrained by their isolated, segmental anatomy, have reduced collateral ventilation, which predisposes them to disease. Recently, attempts to improve the quality of life of patients with emphysema, by performing nonsurgical lung volume reduction via use of endobronchial valves, have led to mixed results, because the role of collateral ventilation in the success or failure of the procedure was not initially appreciated. This review describes the anatomical pathways of collateral ventilation, their physiology and relationship to disease states, their modulatory effects on gas exchange, treatment considerations, and their effect on diagnostic procedures.

Pandemic influenza or other crises causing mass respiratory failure could easily overwhelm current North American critical care capacity. This threat has generated large-scale federal, state, and local efforts to prepare for a public health disaster. Few, however, have systematically engaged the public regarding which values are most important in guiding decisions about how to allocate scarce healthcare resources during such crises.The aims of this pilot study were (1) to test whether deliberative democratic methods could be used to promote engaged discussion about complex, ethically challenging healthcare-related policy issues and (2) to develop specific deliberative democratic procedures that could ultimately be used in a statewide process to inform a Maryland framework for allocating scarce healthcare resources during disasters. Using collaboratively developed focus group materials and multiple metrics for assessing outcomes, we held 5-hour pilot community meetings with a combined total of 68 community members in two locations in Maryland. The key outcomes used to assess the project were (1) the comprehensibility of the background materials and ethical principles, (2) the salience of the ethical principles, (3) the perceived usefulness of the discussions, (4) the degree to which participants' opinions evolved as a result of the discussions, and (5) the quality of participant engagement.Most participants were thoughtful, reflective, and invested in this pilot policy-informing process. Throughout the pilot process, changes were made to background materials, the verbal introduction, and pre- and post-surveys. Importantly, by holding pilot meetings in two distinct communities (an affluent suburb and inner city neighborhood), we discerned that participants' ethical reflections were framed in large part by their place-based life experiences.This pilot process, coupled with extensive feedback from participants, yielded a refined methodology suitable for wider-scale use and underscored the need for involvement of diverse communities in a statewide engagement process on this critical policy issue.