Approximately half of all healthy adults aspirate small amounts of oropharyngeal secretions during sleep. The low burden of virulent bacteria in normal pharyngeal secretions, together with forceful coughing, active ciliary transport, and normal humoral and cellular immune mechanisms, protect the airways from repeated clinical infection. However, defense of the airway is impaired in the elderly by decreased mucociliary clearance, alteration in respiratory mechanics, and, in some cases, concomitant illnesses that predispose to aspiration. Furthermore, normal aging is associated with impaired oro-pharyngeal deglutition. This has been attributed to an increased neural processing time (Tracy et al., 1989). Indeed, there is a high incidence of silent aspiration in elderly patients who develop pneumonia: 71% of patients with CAP vs. 10% of the control subjects (Kikuchi et al., 1994). Cough reflex sensitivity may also be altered in older subjects with recurrent pneumonia. Conversely, intensive oral care for one month has been shown to enhance cough reflex sensitivity, in a controlled randomized trial of older nursing home patients (Niimi et al., 2003; Watando et al., 2004).
As previously mentioned, aspiration pneumonia is a frequent complication of acute ischaemic stroke. Aspiration pneumonia was documented in 13.6% of 1455 patients during the three months following the acute event; associated risk factors were male gender, age, and diabetes; furthermore, pneumonia was associated with a higher mortality, and a lower functional status at three months (Barthel Index, Rankin scale) (Aslanyan et al., 2004). In a large study of 13440 patients with ischemic stroke, in-hospital mortality was 4.9%; pneumonia accounted for 31% of all deaths (Heuschmann et al., 2004).
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