Heart rate power spectrum and plasma catecholamine levels after postural change and cold pressor test

During stress, low-frequency (0.01-0.15 Hz) heart rate power and plasma catecholamine levels increase in response to increased sympathetic efferent activity. To test the hypothesis that low-frequency heart rate power, a measure of sympathetic control of heart rate, directly correlates with plasma catecholamine concentrations during periods of increased sympathetic tone, we compared heart rate power spectral measures with antecubital vein norepinephrine, epinephrine, and dopamine concentrations during postural change and after cold pressor testing. We analyzed absolute levels and changes in mean heart rate, respiratory rate, blood pressure, heart rate power spectra, and concentration of norepinephrine, epinephrine, and dopamine in 14 healthy volunteers (seven female/seven male) after postural change and in six (three female/three male) during cold pressor testing. Postural change from supine to standing position resulted in increased heart rate [61 ± 8 versus 83+11 (SD) bpm, p < 0.05], diastolic (68 ± 7 versus 11 ± 6 mm Hg, p < 0.05) and mean blood pressures (84 ± 6 versus 91 ± 9 mm Hg, p < 0.05), norepinephrine concentration (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 bpm², 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 bpm², 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) increased with cold pressor testing. We found no correlation between absolute levels or changes in low-frequency heart rate power and norepinephrine, epinephrine, or dopamine concentration. Thus, we conclude that low-frequency heart rate power and plasma catecholamines are significantly affected by physiologic changes but arc likely regulated by different areas within the sympathetic nervous system.