Modulation of human swallowing behaviour by thermal and chemical stimulation in health and after brain injury

Few data support thermal or chemical stimulation as therapy for neurogenic dysphagia. Our aims were to explore the behavioural effects of thermal (cold) and chemical (citrus) modalities on water swallowing in health (n = 65, mean age 45 years, 44 females) and acute stroke (n = 22, mean age 67 years, eight females). Multiple randomized timed 50-mL swallowing tests were performed for each of four water conditions: (a) room temperature (RT), (b) cold (CD), (c) citrus (CT) and (d) combined cold and citrus (CD + CT). The inter-swallow interval (ISI), swallowing volume velocity (speed), and volume per swallow (capacity) were measured. In health, compared to RT, only CD + CT slowed the speed (12.3 +/- 0.5 vs 10.3 +/- 0.5 mL s(-1), P < 0.03) and decreased the capacity (16.4 +/- 0.9 vs 14.6 +/- 0.7 mL per swallow, P < 0.02) of swallowing. ISI was unaffected, except by CD + CT in healthy young subjects (<60 years) where it was reduced (1.44 +/- 0.02 vs 1.30 +/- 0.02 s, P < 0.02). Despite smaller volumes ingested by stroke patients, CD + CT, compared to RT, again slowed both the speed (3.8 +/- 0.4 vs 4.5 +/- 0.5 mL s(-1), P < 0.03) and capacity (7.6 +/- 0.7 vs 8.5 +/- 0.7 mL per swallow, P < 0.03) of swallowing but had no effect on ISI. We conclude that combined thermal and chemical modification of water consistently alters swallowing behaviour in health and after cerebral injury. These findings have relevance in the management of neurogenic swallowing problems.