Pulmonary Host Defenses and Factors Predisposing to Lung Infection
Section snippets
Normal pulmonary defense mechanisms
The upper airway poses several barriers to microbial contamination of the lower respiratory tract. In addition to humidification, the tortuous anatomic arrangement of the nasal airways provides a filtering function of inspired air. Larger inspired particles impact in the anterior nasal passages and are removed by sneezing or nose blowing, or are deposited more distally and swept posteriorly by the ciliated epithelium to the nasopharynx to be cleared by swallowing or expectoration. The upper
Host related
Most episodes of bacterial pneumonia, whether community-acquired or nosocomial, are initiated by the introduction (via aspiration or otherwise) of oropharyngeal secretions into the lower respiratory tract. The secretions are heavily contaminated by the patient's oropharyngeal flora, which, in the hospitalized host with comorbidities, is subject to evolution from normal flora to a spectrum that contains more virulent pathogens than in the normal healthy host (Box 1). The most frequently
Summary
Multiple factors predispose the hospitalized host to pneumonia, particularly in the setting of the ICU. Some of these factors are intrinsic to the host or his or her associated comorbidities, and some are external environmental factors inherent in the therapeutic modalities employed in the hospital. Increased recognition of these risk factors will facilitate attempts at minimizing their effects and will lessen the incidence of nosocomial pneumonia.
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This work supported by National Institutes of Health grants AA11760 and AA09803, and La BOR HEF (2000-05)-06.