EFFECT OF TEMPERATURE ON SWALLOWING REFLEX IN ELDERLY PATIENTS WITH ASPIRATION PNEUMONIA

Abstract

To the Editor: Morbidity and mortality from aspiration pneumonia continues to be a major health problem in the elderly. A swallowing disorder such as delayed triggering of the swallowing reflex, an important respiratory defense mechanism, exists in patients with aspiration pneumonia.1 Although caregivers often adjust the viscosity of swallowed material to prevent fragile elderly from aspiration, they do not pay much attention to the temperature of meals, tending to serve meals at about room temperature to avoid injurious temperatures. However, the precise relationship between temperature and swallowing efficacy in elderly patients with impaired swallowing is not known. Therefore, we examined the effect of temperature of swallowed material on the swallowing reflex in the elderly patients with aspiration pneumonia. The elderly patients were recruited from institutionalized patients in a nursing home located near Sendai, Japan. The nursing home serves as a long-term care facility for older patients who are physically handicapped or suffer from mental deterioration. Thus, to a large extent, they are dependent on the service of caregivers for activities of daily living. Fourteen elderly nursing home poststroke patients with repeated episodes of aspiration pneumonia were studied. The patients fed themselves or needed help eating. Patients had neither feeding tube nor percutaneous endoscopic gastrostomy. Written informed consent was obtained from all subjects or their families. The swallowing reflex was provoked by a bolus injection of 1 mL of distilled water injected into the pharynx. A two-lumen indwelling catheter (7 Fr) was inserted up to the level of the uvula through a naris. One lumen was used to inject distilled water, and the other was to measure the temperature of the injected water at the larynx using a miniature thermocouple (MT-29/2, Physitemp, Clifton, NJ). The subjects were unaware of the actual injection. Swallowing was identified using submental electromyographic activity and visual observation of characteristic laryngeal movement. Electromyographic activity was recorded from surface electrodes on the chin. The swallowing reflex was evaluated using the latency of response, timed from the injection to the onset of swallowing.2 Distilled water at various temperatures (10–80°C) was injected in a double-blind and randomized manner at 2-minute intervals. The latency of swallowing reflex was plotted as a function of the temperature of injected water at the catheter outlet (Figure 1). The temperature-latency relationship was bell-shaped in the experimental range. At approximately body temperature (30–40°C), the latency of the swallowing reflex showed a maximal value in each subject (mean±standard error 14.7±2.7 s). Temperatures of 10°C to 20°C, 60°C to 70°C, and 70°C to 80°C induced a significantly shorter latency of swallowing reflex than that induced by a temperature of 30°C to 40°C (P<.05 using one-way analysis of variance with Scheffe as a post hoc test). There was no harmful effect or unpleasant feeling during and after the study in all patients. Relationship between temperatures of injected distilled water and latency of swallowing reflex in poststroke patients with repeated aspiration pneumonia. Each point shows the mean±standard error of latency within the temperature range indicated on the x-axis. *Significant differences from latency at a temperature of 30–40°C (P<.05). These data showed that temperatures above and below body temperature accelerated triggering of the swallowing reflex. Recently, several channels responsive to temperature sensing were identified as proteins of a transient receptor potential superfamily on sensory nerve terminals.3, 4 Simultaneous activations of these channels can strengthen sensory inputs from the pharynx and larynx.3, 4 Therefore, it might be better to serve meals at hot and cold temperatures rather than at room temperature in elderly patients at high risk for aspiration pneumonia. Recently, it was reported that the cortical excitability of swallowing is strongly correlated with the improvement of the swallowing function and highly depends on the frequency and intensity of the applied stimuli.5 The evidence supports the fundamental principle that every meal should be served as soon as cooked, especially in the elderly.