Baroreflex inhibition of the human sinus node: importance of stimulus intensity, duration, and rate of pressure change.

SUMMARYThe baroreceptor control of the sinus node was evaluated in 10 normotensive and 10 age-matched essential hypertensive subjects in whom ambulatory blood pressure was recorded intraarterially for 24 hours and scanned by a computer to identify the sequences of three or more consecutive beats hi which systolic blood pressure (SBP) and pulse interval (PI) progressively rose (+ PI/ + SBP) or fell ( -PI/ -SBP) in a linear fashion, according to a method validated in cats. In normotensive subjects, several hundred +PI/+SBP and -P I / -S B P sequences of 3 beats were found whereas the number of sequences of 4,5, and more than 5 beats showed a progressive drastic reduction. The mean slopes of + PI/ + SBP (7.6 ± 2.0 msec/mm Hg) and -P I / -SBP (6.4 ± 1.5 msec/mm Hg) sequences were similar, but in both instances there was a large scattering of the values around the mean (variation coefficients: 64.2 ± 4.7 and 62.6 ± 2.4%). The slopes decreased as a function of the sequence length and baseline heart rate and increased to a marked extent during the night as compared with daytime values. All sequences were more rare (-33.2% for +PI/ + SBP and -31.7% for -P I / -S B P ) and less steep in hypertensive subjects ( -4 0 . 3 and -3 6 . 2 % , respectively), who failed to show the marked nighttime increase in slope observed in normotensive subjects. To our knowledge, these observations provide the first description in humans of the baroreceptor-heart rate reflex in daily life. This reflex is characterized by marked within-subject variations hi sensitivity due in part to hemodynamic, temporal, and behavioral factors. All features of the baroreceptor-heart rate reflex are unpaired hi essential hypertension. (Hypertension 12: 214-222, 1988) KEY WORDS • baroreceptor reflexes • ambulatory blood pressure monitoring • hypertension sleep • humans • heart rate W E have previously reported 1 -2 that blood pressure in unanesthetized cats exhibits spontaneous rises or falls that are accompanied by linearly related increases or reductions in pulse interval (PI). We have also reported 12 that sinoaortic denervation abolishes these events, which therefore reflect baroreceptor modulation of the sinus node. We have concluded that evaluation of these events by computer analysis of intra-arterial blood pressure tracings represents a powerful tool for studying the baroreceptor-heart rate reflex in daily life.

show abstract

“…-' •*• ^ Whether it is the increased baroreceptor reflex sensitivity that causes a bradycardia or vice versa 22 cannot be clarified by our data.…”

contrasting

confidence: 44%

Evaluation of the baroreceptor-heart rate reflex by 24-hour intra-arterial blood pressure monitoring in humans.

et al. 1988

View full text Add to dashboard Cite

show abstract

“…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).…”

Section: Resultsmentioning

confidence: 99%

“…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.…”

Section: Protocolmentioning

confidence: 99%

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

Ferguson¹,

Abboud²,

Mark³

1985

J. Clin. Invest.

View full text Add to dashboard Cite

We studied the contribution of carotid vs. extracarotid baroreceptors in control of heart rate in normal humans. We measured heart interval (HI) and arterial pressure during steady-state infusion of phenylephrine (PE). PE increased mean arterial pressure (MAP) by 13±2 mmHg (mean±SEM; n = 10) and thus stimulated both carotid and aortic baroreceptors. Neck pressure (NP) was applied during PE infusion to counter the increase in transmural carotid sinus pressure, thus leaving only aortic baroreceptors stimulated by the increase in arterial pressure. PE infusion alone prolonged HI by 230±24 ms (P < 0.05). Application of NP attenuated the HI response to 65±22 ms above control (P < 0.05 vs. PE alone). During these steady-state increases in arterial pressure, elimination of the carotid baroreflex contribution reduced the HI prolongation by 41-70% in five subjects and by >93% in five subjects.We also measured the HI response to dynamic ramp elevation of systolic arterial pressure (SAP) using bolus administrations of PE. Baroreflex control was calculated from the slope of the regression correlating SAP to succeeding HI for PE alone (carotid and aortic baroreceptor activation) and for PE plus superimposed dynamic NP at levels equal to the increases in SAP (aortic baroreceptor activation). During PE alone, the baroreflex slope was 20.2±2.9 ms/mmHg (a = 10). During PE plus NP, the baroreflex slope was reduced by 30% to 14.1±2.8 ms/mmHg (P < 0.02 vs. during PE alone). Thus, during dynamic increases in arterial pressure, eliminating the carotid baroreflex contribution reduced the HI response by 30%.These studies indicate that extracarotid (presumably aortic) and carotid baroreflexes both participate in control of heart rate in humans. Extracarotid (aortic) baroreflexes appear to have the greater role in control of heart rate during dynamic increases in arterial pressure.

show abstract

“…Neck suction, 10-70 mm Hg, was applied for 0.6 seconds and timed to begin 0.75-0.85 seconds before the appearance of the next anticipated P wave, as described earlier. 9 During held expiration, the heart rate is nearly constant; therefore, the timing of the next anticipated P wave could be predicted accurately on the basis of the preceding P-P interval. Prolongation of the first P-P interval after the onset of the stimulus, from the preceding P-P interval, was plotted as a function of stimulus intensity.…”

Section: Equipmentmentioning

confidence: 99%

Carotid baroreflex function in young men with borderline blood pressure elevation.

Eckberg¹

1979

Circulation

Self Cite

View full text Add to dashboard Cite

Volunteers, ages 19-25 years, were recruited from 900 university students whose blood pressures were measured during registration. Blood pressures of each volunteer were measured two to four (average 2.85) times with subjects in the sitting position, after 10 minutes of rest. Weight, height and skin fold thickness, measured in the midline midway between the chin and the upper margin of the thyroid cartilage were also measured.

show abstract

Baroreflex inhibition of the human sinus node: importance of stimulus intensity, duration, and rate of pressure change.

Cited by 83 publications

References 11 publications

Evaluation of the baroreceptor-heart rate reflex by 24-hour intra-arterial blood pressure monitoring in humans.

Evaluation of the baroreceptor-heart rate reflex by 24-hour intra-arterial blood pressure monitoring in humans.

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

Carotid baroreflex function in young men with borderline blood pressure elevation.

Contact Info

Product

Resources

About