Variability of Cardiovascular and Plasma Noradrenaline Responses to Sustained Isometric Contraction in Normal Human Subjects

Abstract

1. Eight healthy adult males underwent three sustained isometric contractions at 30% of maximal voluntary contraction for 3 min, within a 9 day period. 2. The study focuses on the inter-individual and day-to-day intra-individual variability of cardiovascular and plasma noradrenaline responses to sustained isometric contraction. 3. The results of this study indicate that inter-individual variability is generally greater than intra-individual variability. Diastolic blood pressure was the most sensitive as well as the least variable cardiovascular parameter measured. 4. The variability of plasma noradrenaline levels in both the basal and the stimulated state was high. The present study suggests that it is preferable to determine the 'true' noradrenaline peak after the release of handgrip, as this is associated with a lower variability than the plasma noradrenaline peak taken at the time of the release of handgrip.

Methods of investigation for cardiac autonomic dysfunction in human research studies

“…Plasma DHPG may be a more sensitive marker of overall sympathetic innervation than supine plasma norepinephrine 40, and simultaneous measurement of norepinephrine and DHPG yields more information than measurement of either alone. Catecholamine assessment in diabetes showed in general lower than normal responses to postural changes 41, exercise 42, 43, hypoglycaemia 44, and CARTs 45–47. A subnormal orthostatic increment in plasma norepinephrine is a specific but not sensitive index of baroreflex–sympathoneural failure or sympathetic noradrenergic denervation.…”