The Autonomic Physiology Facility focuses on quantitative autonomic reflex studies. Available to researchers are a series of studies/tests that investigate the severity and distribution of autonomic failure by non-invasively evaluating cardiovagal, sudomotor and cardiovascular adrenergic function. These studies comprise:
- Quantitative sudomotor axon reflex test (QSART)
- Heart rate response to deep breathing and the Valsalva maneuver
- Beat-to-beat blood pressure (BP) and heart rate responses to the Valsalva maneuver
- Head-up tilt (HUT)
QSART evaluates the function of the postganglionic sympathetic sudomotor axon. The patient is supine and rested. The stimulus is acetylcholine, which is iontophoresed into one compartment of a multicompartmental sweat cell and the evoked sweat response is recorded from a central compartment. The stimulus compartment surrounds the central compartment, separated by an air gap. The test is done simultaneously over a forearm site and three leg sites. This test was invented at Mayo and provides quantitative and reproducible results.
Tests of cardiovagal function are done with the patient supine. Heart rate and respiration are continuously recorded. Heart rate response to deep breathing is followed by the performance of the Valsalva maneuver. The subject blows into a bugle and maintains a column of mercury pressure of 40 mm Hg for 15 seconds. Cardiovagal function is evaluated by interpreting the heart rate response to these maneuvers.
Tests of cardiovascular adrenergic function are evaluated by continuously recording the beat-to-beat BP and heart rate responses to the Valsalva maneuver and HUT. A series of maneuvers are done to generate two reproducible responses. The BP and heart period response to the phases of the Valsalva maneuver can be used to evaluate the vagal and adrenergic components of the baroreflex. The subject is tilted using a motorized tilt-table for a variable duration, usually 5-10 minutes.
From an evaluation of cardiovagal, sudomotor and adrenergic functions, we can correct for the effects of age and gender, and generate a composite autonomic severity score (CASS). The program is capable of significant data reduction — including evaluation in the frequency domain and the calculation of baroreflex sensitivity.
The close interactions between the Autonomic Physiology Facility and the Autonomic and Microneurography Laboratory results in a unique situation — studies that require more sophisticated techniques have these needs met within the latter laboratory. A significant role of leadership of both facilities is to act as a resource to investigators — especially inexperienced investigators — in need of autonomic research support.
Some additional autonomic approaches include:
- Research sudomotor studies
- Microneurographic recordings of sympathetic and somatic C fibers
- Plethysmography recordings of veins and capillaries
- Whole body heating and cooling studies
- Transcranial and laser Doppler recordings to study cerebral autoregulation
- Evaluation of chemo-receptor sensitivity
- Signal analysis of autonomic signals