Oscillations in mean arterial blood pressure in conscious dogs.

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Abstract
Oscillations in mean arterial blood pressure (MABP) in 1.5 h were observed in conscious male dogs with pressure transducers implanted in the aortas. Cardiac output (CO) was measured with an electromagnetic flow probe implanted about the ascending aorta; 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 4 variables (MABP, TPR, CO and HR) to determine significant oscillations at the frequency of the MABP oscillation. Cross-spectral calculations produced phase relationships among the variables. TPR and CO were oscillating at the same frequency as MABP. TPR lagged MABP by 63.degree. but the phase angle for CO and MABP was not significantly different from zero. CO must be producing the MABP oscillations; the TPR oscillations arose as a reaction to the MABP or CO changes. HR was oscillating in phase with CO; probably CO fluctuations were induced in part by HR changes and the sympathetic nervous system was driving the heart. Chronic dietary Na changes did not alter the power spectra for MABP. The renin-angiotensin system (RAS) was not responsible for the oscillations; the oscillations were not acting as a signal to the RAS during Na-deficient states, a condition known to stimulate the RAS.