Oscillations in mean arterial blood pressure in conscious dogs.

Oscillations in mean arterial blood pressure (MABP) with periods near 1.5 hours were observed in conscious male dogs with pressure transducers implanted in their aortas.Cardiac output (CO) was measured with an electromagnetic flow probe implanted about the ascending aorta, and total peripheral resistance (TPR) was calculated as the ratio of MABP to CO. Heart rate (HR) was measured with a cardiotachometer.Coherence functions were calculated among the four variables (MABP, TPR, CO, and HR) to determine significant oscillations at the frequency of the MABP oscillation.Crossspectral calculations produced phase relationships among the variables.TPR and CO were both oscillating at the same frequency as MABP.However, TPR lagged MABP by 63 degrees, whereas the phase angle for CO and MABP was not significantly different from zero.We concluded that CO must be producing the MABP oscillations, and that the TPR oscillations arose as a reaction to the MABP or CO changes.HR was oscillating in phase with CO, indicating that CO fluctuations were induced in part by HR changes and that the sympathetic nervous system was probably driving the heart.In further experiments, chronic dietary sodium changes did not alter the power spectra for MABP.Thus, the renin-angiotensin system (RAS) was not responsible for the oscillations; conversely, the oscillations were not acting as a signal to the RAS during sodium-deficient states, a condition known to stimulate the RAS.Circ Res 44; 692-700, 1979 CARDIOVASCULAR periodicities have been known since man first felt his pulse, but the heart beat and circadian rhythms are the only frequencies that have attracted much attention.Rhythms lying between these two extremes have been reported for a number of physiological variables (Kleitman, 1963;Krieger et al., 1971;Lenfant, 1967;Ookhtens et al., 1974;Yamaji et al., 1972), but not for the circulation.We speculated, from very general considerations, that flows and pressures might fluctuate periodically at an intermediate frequency (Marsh, 1973), and the major purpose of this paper is to report observations of such oscillations in mean arterial blood pressure (MABP), cardiac output (CO), heart rate (HR), and total peripheral resistance (TPR) in conscious dogs.The period length is 1.5 hours.An important unresolved question in the area of fluid volume regulation is the identification of the signal that triggers reiim release when extracellular fluid volume is depleted, as during dietary NaCl restriction.Arterial blood pressure governs renin release, at least in part, but MABP remains normal over a wide range of renin secretion rates (Davis and Freeman, 1976).We therefore speculated that a blood pressure signal that varied in the frequency