Comparison of Methods for Eliciting the Baroreceptor‐heart Rate Reflex in Conscious Rabbits

Abstract

1. Two methods were used for altering blood pressure in conscious rabbits by up to & 30 mmHg from the resting level in order to characterize the baroreceptor-heart rate reflex. These were to inflate descending aortic or inferior vena caval cuffs, or to give brief intravenous infusions of phenylephrine or glycerol trinitrate. The relation of change in blood pressure to change in heart interval was examined, both during the initial 'ramp' changes of these variables and when they had reached a 'steady-state'.2. Both methods allowed the construction of 'steady-state' sigmoid stimulusresponse curves whose parameters were reproducible within animals, and which were attended by a relatively small variance between animals. The inflatablecuff method gave a higher average value for maximum gain than the vasoactive drug method (10.0 u 5.4 ms/mmHg) and a narrower pressure range between the threshold and saturation points of the response, but values for the other parameters were similar. Corresponding parameters obtained by the two methods correlated closely.3. After denervating all arterial baroreceptors except one carotid sinus, 'steady-state' maximum gain by cuff-inflation was reduced to 3.1 ms/mmHg, and to 2.6 ms/mmHg by the vasoactive drug method. The heart interval range between upper and lower plateau levels was reduced, but the pressure range between threshold and saturation points was widened, with both methods. 4. During the initial 'ramp' changes of blood pressure the sensitivity of the reflex was described by the slope of the linear regression of heart interval on 'mean blood pressure. The slopes obtained by aortic cuff inflation, and by infusion of either vasoactive drug, correlated positively with 'steady-state' maximum gain. However, the reproducibility of the 'ramp' method was inferior to that of the 'steady-state' method with respect to reflex sensitivity, and other parameters of the stimulus-response relation cannot be estimated. I. B. Faris et al.5. Complete baroreceptor denervation virtually eliminated heart rate changes over the range of blood pressures usually employed. However, when blood pressure was increased by more than 40 mmHg a profound reflex bradycardia and hypopnoea were then evoked.

Relative contribution of aortic and carotid baroreflexes to heart rate control in man during steady state and dynamic increases in arterial pressure.

“…Thus, in the doses employed, PE does not appear to sensitize arterial baroreceptors to graded levels of NP. In addition, Faris et al (18) showed comparable baroreceptor-heart rate reflex responses in rabbits when assessed by either injecting PE intravenously or by inflating descending aortic cuffs to induce elevation of arterial pressure.…”

“…Figure 6. Baroreflex slope during bolus PE alone and during bolus PE with superimposed dynamic NP (subjects 1 [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. The slope of the arterial baroreflex control of HI during PE bolus plus superimposed dynamic NP application (aortic baroreflex activation alone) was reduced by 30% over that during bolus PE alone (aortic and carotid baroreflex activation).…”

“…Because of study design, in the experiments with ramp increase in arterial pressure (subjects 1 [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] we attempted to match with dynamic application of NP the beat-by-beat change in SAP following PE bolus administration. Fortunately, we achieved nearly perfect correlation of NP to ASAP (r = 0.996, P < 0.001), and the increase in NP averaged 1.12 times the increase in SAP (assumes 92% transmission).…”

“…There was a 2-min rest period between each level of NP. The subjects were then given gradually increasing doses of intra- Subjects [11][12][13][14][15][16][17][18][19][20] (dynamic protocol). In each of these subjects, bolus injections of PE were administered in 150-300-,ug doses (205±22, mean±SE) and each R-R interval (HI), beginning with the rise ofarterial pressure, was plotted as a function of the preceding SAP.…”

A Simple Method for Generating a Blood Pressure‐Unit Activity Relationship for Central Cardiovascular Neurons in the Rat

“…1C and D). To avoid stimulation of ventricular receptors (Faris et al 1980) and losing the cell, the pressure rise induced by the inflation of the balloon was in the 20-40 mmHg range. In our experiments, after more than five inflations in each rat, the balloon was delivering the expected rise in pressure.…”