Reproducibility of laboratory tests evaluating neural cardiovascular regulation in man

In 31 normotensive and hypertensive subjects with continuous intra-arterial blood pressure (BP) and heart rate (HR) monitoring, we examined the short term reproducibility of the haemodynamic responses to a number of tests commonly employed in studies on neural cardiovascular regulation: (1) hand-grip exercise and cold pressor tests that increase BP and HR through central and reflex mechanisms; (2) bolus injections of phenylephrine and trinitroglycerine that reflexly reduce and increase HR through stimulation and inhibition of arterial baroreceptors; (3) negative and positive pressure alterations within a neck chamber that reflexly reduce and increase BP through stimulation and inhibition of carotid baroreceptors. Each test was standardized and repeated at 30 min intervals six times in each subject. In the group as a whole the BP and HR responses to hand-grip showed a variability (mean variation coefficient, VC) of 22 and 25% respectively. BP and HR responses to cold pressor test showed a VC of 17 and 44% and HR responses to trinitroglycerine showed a VC of 28%. HR responses to phenylephrine were slightly less (19%) and BP responses to neck chamber considerably less variable (14 and 10%). The variability of the responses was not related to basal BP or HR or to the time sequence of the tests. Thus, tests commonly employed for studying neural cardiovascular control in man have a limited short-term reproducibility. This implies that caution should be used in interpreting results obtained by a single performance of any given test, and in comparing results in different states or groups such as normotensive and hypertensive subjects, unless a relatively large number of responses is available.