The physiologically relevant information regarding systemic blood pressure encoded in the carotid sinus baroreceptor discharge pattern.

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Abstract
The objective was to find what kind of information regarding systemic blood pressure is transduced by baroreceptors in vivo and how this information is coded in the receptor discharge. Carotid sinus pressure, ECG and receptor action potentials were recorded for 52 single fiber carotid sinus receptors found in 20 decerebrated unanesthetized cats. The inflation and gradual deflation of an intraaortic catheter tip balloon manipulated the blood pressure in the carotid sinus in a way as to define the full in vivo stimulus-response curve for each receptor. Correlation coefficients were computed between stimulus and response variables for several points on the response curve of each receptor and for every possible combination of stimulus and response variables defined. Stimulus variables were systolic, diastolic, mean, pulse pressures and peak positive dP/dt [change in pressure with time]. Response variables were average discharge rate, peak instantaneous frequency and average burst frequency. For every fiber in the sample only the correlations between systolic, diastolic and mean pressure vs. average discharge rate were consistently high and positive. All other correlations were numerically low and/or negative. In vivo baroreceptors signal mainly pressure level (systolic, diastolic or mean) as opposed to pulse pressure or dP/dt, and the average discharge rate is their best index of information content.