Autonomic function testing: Compliance and consequences

The deep breathing test (DB) and Valsalva maneuver (VM) are used to detect autonomic dysfunction. The VM induces sympathetically mediated changes in blood pressure (phase II late, phase IV, and recovery time) and both tests induce vagally mediated heart rate changes. There is limited information on effects of key variables, compliance with testing and the effects of non-compliance This study has twin goals of evaluating compliance with standard instructions and the effects of changes in key variables. We also evaluated the effect of position on the VM.

Forty healthy males performed DB at air exchange volumes of 50, 80, and 100% of vital lung capacity (VLC). The VM was performed at 40 and 30mmHg expiratory pressure for 15 and 10s in sitting and supine position, respectively.

Participants performed DB at lower volumes than intended and were not able to maintain 100% VLC for the duration of the test. The DB heart rate response decreased 6.3beats/min per liter below VLC. During the VM, subjects blew at lower pressures than instructed. The VM responses were significantly larger with longer expiration durations, higher expiratory pressures and when performed sitting. Performing the VM at 40mmHg for 10s in supine position increased the odds ratio of experiencing flat-top responses.

The ability of subjects to strictly comply with methodological guidelines significantly improves results. Recording of both test parameters and ensuing results is suggested.