The simple act of chewing triggers a state of arousal with a sudden increase in blood pressure, according to a study published today in Experimental Physiology. This response was observed in patients with familial dysautonomia (FD; a developmental disorder affecting the autonomic nervous system. Under normal circumstances, the baroreflex regulates blood pressure changes by controlling the diameter of the blood vessels and by varying the heart rate. This process relies on special sensory (afferent) nerves that transmit blood pressure information to the brain to restrain the autonomic nerves from further increasing the blood pressure. Patients with FD have afferent baroreflex failure as they are born without these blood pressure sensing nerves and their blood pressure is thus wildly erratic and surges uncontrollably.
The researchers measured blood pressure and heart rate changes to chewing, swallowing and expanding the stomach with a gastrostomy tube feed in FD patients. They compared their responses to those observed in a different group of patients with impairment of the sympathetic nerves due to chronic autonomic failure (who lack the nerves responsible for raising blood pressure) and a control group with no autonomic dysfunction.
In the absence of sensory baroreceptor nerves, eating and chewing gum triggered a big increase in blood pressure and heart rate, as well as sweating and flushing of the skin in patients with FD, but not in patients with chronic autonomic failure or control groups. Expanding the stomach didn't cause any signs or symptoms.
Dr Lucy Norcliffe-Kaufman, Dysautonomia Center, New York University School of Medicine an author of the study explained,
'This arousal response when eating may have served an evolutionary advantage especially at times when food was scarce, allowing humans to be ready to fight to defend a precious biological commodity. Such a response would be mediated by certain areas in the brain (the cortex and the limbic system), and these responses are well known to be exaggerated in patients with no afferent baroreceptor signaling.'
She adds,
'The findings help us to better understand why patients with familial dysautonomia have high blood pressure when eating. We didn't know why newborns with FD become sweaty and mottled when attempting to bottle-feed, or why teenagers with the disease get noticeably flushed, sweaty and breathless while eating a sandwich. This can all be triggered by chewing, and occurs independently of swallowing or mechanical distention of the stomach. It's important to be able to tell patients that this is a transient response and will go back to normal.'
Dysautonomia is an umbrella term for medical conditions causing a malfunction of the autonomic nervous system and thus lead to problems regulating "automatic" body functions such as heart rate, blood pressure, digestion etc..
Afferent Baroreflex Failure is a rare disorder characterised by change of blood pressure with episodes high blood pressure. rarediseasesnetwork.org/ARDCRC/patients/learnmore/baroreflex/.
Patients with familial dysautonomia and afferent baroreflex failure have a genetic mutation that affects the development of the IXth and Xth cranial nerves. These patients lack incoming information from the arterial baroreceptors to the CNS and fail to restrain sympathetic outflow.