Ultradian rhythms of autonomic, cardiovascular, and neuroendocrine systems are related in humans

Autonomic, cardiovascular, and neuroendocrine activities were monitored for 5-6 h in 10 normal adult resting humans (8 males, 2 females). The nasal cycle, a measure of lateralized autonomic tone, was measured at 4 Hz. Impedance cardiography (BoMed NCCOM3) was used to measure cardiac output, thoracic fluid index, heart rate, ejection velocity index, stroke volume, and ventricular ejection time (averages of 12 heart beats). Systolic, diastolic, and mean arterial pressures were measured with an automated cuff at 7.5-min intervals. Separate blood samples were taken every 7.5 min simultaneously from both arms with the use of indwelling venous catheters. Assays for adrenocorticotropic hormone, luteinizing hormone, norepinephrine, epinephrine, and dopamine were performed on samples from each arm. Time-series analysis, using the fast orthogonal search method of Korenberg, was used to detect variance structure. Significant spectral periods were observed in five windows at 220-340, 170-215, 115-145, 70-100, and 40-65 min. The greatest spectral power was observed in the lower frequencies, but periods at 115-145, 70-100, and 40-65 min were common across variables. Significant correlation coefficients for linear regressions of all paired variables in each subject were observed in 38.87% of the comparisons (subject range, 18.05-48-9.70%) with r > 0.30. These results suggest that either a common oscillator (the hypothalamus) or mutually entrained oscillators regulate these systems.