Light-headedness and defective cardiovascular reflexes after neck radiotherapy.
METHODS: We investigated the possibility of carotid baroreflex dysfunction as the cause of cerebral insufficiency in head and neck cancer patients treated with neck radiotherapy. Three patients cured with radiation therapy were evaluated for light-headedness and syncope. Orthostatic blood pressure, heart rate responses to esmolol and atropine, and baroreceptor sensitivity to amyl nitrite and phenylephrine were measured. The results were compared with measurements in six normal control subjects. RESULTS: All three patients had intact sympathetic and parasympathetic cardiac innervation. Nevertheless, their heart rate responses to amyl-nitrite-induced hypotension and phenylephrine hypertension were only one-third normal (P = 0.013), indicating poor baroreceptor function. Upon standing, diastolic pressure of control participants increased but that of the three patients decreased by 3 mmHg. After inhalation of amyl nitrite their systolic and diastolic blood pressures decreased by 70+/-9 and 28+/-2 mmHg, much more than the control participants' decrease of 33+/-5 and 17+/-3 mmHg (P = 0.006, P = 0.02). CONCLUSION: The baroreflex is the most important mechanism for short-term blood pressure homeostasis. Patients with transient light-headedness or syncope after radiotherapy to the neck may have baroreceptor damage. This defect is unlikely to be apparent on routine cardiovascular testing. However, testing with a rapidly acting hypotensive stimulus can reveal gross deficits in the regulation of heart rate and blood pressure.
Shapiro
MH
University of California, San Diego, Division of Nephrology and Hypertension, San Diego, California, USA.
Ruiz-Ramon
P
Fainman
C
Ziegler
MG