Spectral analysis of cardiovascular responses in POTS

The inability to remain upright without orthostatic hypotension is the typical disabling symptom of Postural Orthostatic Tachycardia Syndrome (POTS), attributed either to the central hyperadrenergic outflow or to the compensatory mechanism after legs and splanchnic blood vessels denervation. To verify this second hypothesis we analyzed the neural autonomic responses to different conditions. 10 patients with POTS and 10 controls were investigated with power spectral analysis of the blood pressure and heart rate variability, in resting condition and during a period of 30 min of head – up tilt test to 60°. The difference between the two conditions was tested using the Wilcoxon signed rank test. No evidence of sympathetic cholinergic and adrenergic failure was found. The most significant and common finding of patients with POTS was a marked increase of the LF/HF ratio in the power spectrum of the R–R interval in the head – up tilt compared to the reduced values in supine. We did not find an exaggerated pressure response to the Valsalva manoeuvre, but a redistribution of blood flow, due to regional autonomic denervation, was excluded by the preserved increase of blood pressure response during the same test.