Impaired respiratory sinus arrhythmia with paradoxically normal Valsalva ratio indicates combined cardiovagal and peripheral adrenergic failure

Combined reductions of the heart rate responses to deep breathing (HR_DB) and the Valsalva ratio (VR) are used as a standard test of cardiovagal function. We observed that some patients had marked reduction of HR_DB with a paradoxically normal VR. The mechanism of this paradox was evaluated. We found that these patients had evidence of peripheral adrenergic and postganglionic sudomotor impairment, including an excessive fall in blood pressure on upright tilt. Since VR depends on heart rate responses to blood pressure excursions, we evaluated the phases of the Valsalva manoeuvre and the ensuing heart rate responses in these patients and compared the responses to patients with generalized autonomic failure (Group II) and controls (Group III). Group I patients when compared with controls, had a larger phase II fall in blood pressure and normal phase IV resulting in a significantly enhanced baroreflex stimulus. These patients had a normal heart rate increment but 75% failed to develop reflex bradycardia. We conclude that the paradoxical VR is due to the exaggerated blood pressure swing due in turn to adrenergic failure. When both HR_DB and VR are reduced as in Group II, there may be the additional impairment of cardiac adrenergic failure.