Autonomic function tests

Sympathetic function

Blood pressure response to: Head-up tilt or upright posture.

Cold pressor test: the systolic and diastolic blood pressures rise by 10-20 mm Hg with the immersion of one hand in cold water, when blood pressure is measured at 30 seconds and 1 minute. Mental stress.

Isometric exercise, e.g. handgrip. Plasma noradrenaline levels in response to head-up tilt or upright posture.

Parasympathetic function:

Beat-to-beat variation in heart rate with deep breathing (respiratory sinus arrhythmia). This can be achieved by R-R interval variability assessment (expiratory: inspiratory ratio). Power spectral analysis of continuous electrocardiographic (ECG) recordings allows determination of heart rate variability.

Sudomotor function

Galvanic skin-resistance test; Thermoregulatory sweat tests;

Quantitative sudomotor axon reflex test, which involves ionotophoresis of acetylcholine.

Autonomic function testing u n

Valsalva manoeuvre |

This entails forcible expiration against resistance, through a closed glottis. This c is mimicked by heavy lifting or straining activities. A normal cardiovascular g response involves:

Phase I: increased intrathoracic pressure with pressure on the aorta leading to a small sudden increase in arterial blood pressure.

Phase II: reduced venous return to the heart and reduced cardiac output, leading to a reduction in systolic and diastolic blood pressures and in pulse pressure.

Phase III: return to normal of the intrathoracic pressure, with a sudden transient fall in arterial blood pressure.

Phase IV: rebound and overshoot in systolic and diastolic blood pressures over the baseline level, with a compensatory reflex reduction in heart rate.

A normal response requires preserved baroreceptor reflexes, a functioning central control system, functioning efferent pathways to the heart and peripheral blood vessels and responsive effector organs.

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