A novel pharmacological approach to determining parasympathetic heart rate reserve in human subjects

Severe cardiac parasympathetic dysfunction can be diagnosed using bedside tests, such as a Valsalva maneuver. However, the tests that are in use are of limited value in detecting and quantifying an early impairment in cardiac parasympathetic function. We showed that α-2-adrenoreceptor stimulation with clonidine combined with pharmacological baroreceptor loading unmasks impaired parasympathetic heart rate reserve before overt changes in heart rate regulation occur. The methodology could be utilized to monitor the progression of autonomic nervous system disease in studies carried out to test neuroprotective strategies.