HEART-RATE POWER SPECTRUM AND PLASMA-CATECHOLAMINE LEVELS AFTER POSTURAL CHANGE AND COLD PRESSER TEST

During stress, low-frequency (0.01-0.15 Hz) heart rate power and plasm a catecholamine levels increase in response to increased sympathetic e fferent activity. To test the hypothesis that low-frequency heart rate power, a measure of sympathetic control of heart rate, directly corre lates with plasma catecholamine concentrations during periods of incre ased sympathetic tone, we compared heart rate power spectral measures with antecubital vein norepinephrine, epinephrine, and dopamine concen trations during postural change and after cold presser testing. We ana lyzed absolute levels and changes in mean heart rate, respiratory rate , blood pressure, heart rate power spectra, and concentration of norep inephrine, epinephrine, and dopamine in 14 healthy volunteers (seven f emale/seven male) after postural change and in six (three female/three male) during cold presser testing. Postural change from supine to sta nding position resulted in increased heart rate [61 +/- 8 versus 83 +/ - 11 (SD) bpm, p < 0.05], diastolic (68 +/- 7 versus 77 +/- 6 mm Hg, p < 0.05) and mean blood pressures (84 +/- 6 versus 91 +/- 9 mm Hg, p < 0.05), norepinephrine con centration (2.09 +/- 1.11 versus 3.23 +/- 1 .62 nmol/L, p < 0.05), and low-frequency heart rate power (7.55 +/- 5. 63 versus 33.79 +/- 23.55 bpm(2), p < 0.05). High-frequency heart rate power, a measure of parasympathetic control of heart rate, decreased with standing (5.38 +/-: 4.22 versus 2.94 +/- 2.69 bpm(2), p < 0.05). Diastolic (66 +/- 7 versus 81 +/- 9 mm Hg, p < 0.05) and mean (83 +/- 9 versus 97 +/- 11 mm Hg, p < 0.05) blood pressures and norepinephrine concentration (1.21 +/- 0.40 versus 1.77 +/- 0.79 nmol/L, p < 0.05) i ncreased with cold presser testing. We found no correlation between ab solute levels or changes in low-frequency heart rate power and norepin ephrine, epinephrine, or dopamine concentration. Thus, we conclude tha t low-frequency heart rate power and plasma catecholamines are signifi cantly affected by physiologic changes but are likely regulated by dif ferent areas within the sympathetic nervous system.