Table 1.
Methods to assess human autonomic cardiovascular regulation
| Vagal | Sympathetic | Ancillary data | Research utility | Clinical utility | |
|---|---|---|---|---|---|
| Heart rate (HR) at rest | Yes | Yes | + | ++ | |
| HR response to Valsalva's manoeuver | Yes | Yes | + | + | |
| HR variation: time domain | Yes | If with BP | Quantitation of spontaneous blood pressure (BP) → HR relationship to estimate arterial baroreflex regulation of sino-atrial deceleration (vagal) or acceleration (sympathetic) | ++ | +++ |
| HR variation: frequency domain | Yes | Yes | High-frequency spectral power reflects vagal HR modulation; spectral power at lower frequencies primarily sympathetic HR modulation; Concurrent BP → HR spectral power transfer function to estimate arterial baroreflex regulation of HR |
++ | + |
| HR responses to drug stimuli | Yes | Yes | Arterial baroreceptor stimulation by phenylephrine elicits immediate vagal response; unloading by vasodilators elicits reflex sympathetic response | +++ | ++ |
| HR response to mechanical stimuli | Yes | Yes | Responses to lower body negative or positive pressure primarily sympathetic; to negative or positive neck pressure primarily vagal | ++ | ? |
| BP variability | ? | ? | Time or frequency domain measures not specific to autonomic regulation; Principal utility when evaluated in conjunction with HRV spectrum |
? | ? |
| Arterial/venous norepinephrine (NE) | No | Yes | Global non-specific index | + | ++ |
| Urinary NE excretion | No | Yes | Global non-specific index | + | ++ |
| NE spillover to plasma | No | Yes | Total body or organ-specific (heart, kidney, limb muscle, brain) data | +++ | + |
| Sympathetic nerve recordings | No | Yes | Multi-unit or single-unit efferent muscle sympathetic nerve activity (MSNA); Sympathetic reflex response to baroreceptor, chemoreceptor, muscle mechano- and metabo-reflex and other reflex simulation or inhibition can be estimated in time domain; Concurrent BP → MSNA spectral power transfer function estimates arterial baroreflex efferent sympathetic regulation in frequency domain |
+++ | + |
| Sympathetic nerve imaging | No | Yes | Nuclear tracers or PET ligands to assess principally cardiac sympathetic innervation and NE uptake | ++ | ++ |