Probing the arterial baroreflex: is there a ‘spontaneous’ baroreflex?

Diaz, Tulio; Taylor, J. Andrew

doi:10.1007/s10286-006-0352-5

Cited by 36 publications

(41 citation statements)

References 43 publications

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“…Our findings indicate greater baroreflex sensitivity at this time compared with the morning and so are somewhat contradictory; however, it is important to acknowledge that the use of steady-state l-noradrenaline infusions as a means to assess dynamic baroreflex sensitivity has been questioned. 35 Studies using spontaneous baroreflex indices have consistently shown that the highest sensitivities occur during the night, with reduced sensitivities in the morning after waking. 10,12,13,33 However, the variations during the daytime have not been consistent between studies.…”

Section: Comparison With Previous Studiesmentioning

confidence: 99%

Diurnal Variation in the Mechanical and Neural Components of the Baroreflex

et al. 2011

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Abstract-Diminished baroreflex sensitivity in the morning negatively influences morning coronary blood flow and blood pressure control in hypertensive patients. Our aim was to determine the contribution of the mechanical and neural components of the cardiac baroreflex to diurnal variation in blood pressure control. In 12 healthy participants, we used the modified Oxford method to quantify baroreflex sensitivity for rising (G up ) and falling (G down ) pressures in the morning (7:00 AM) and afternoon (4:00 PM). Beat-to-beat blood pressure, R-R intervals, and carotid artery diameter measurements were recorded. Integrated sensitivity was determined by plotting R-R intervals against systolic blood pressure. The mechanical component was carotid artery diameter plotted against systolic blood pressure, and the neural component was R-R intervals plotted against carotid artery diameter. Linear mixed models were used to compare the integrated, mechanical, and neural sensitivities between morning and afternoon. We found significant diurnal variation in integrated sensitivity, with an attenuated response in the morning (G up ϭ13.0Ϯ0.6; G down ϭ6.3Ϯ0.4 ms/mm Hg) when compared with the afternoon (G up ϭ15.1Ϯ0.6; G down ϭ12.6Ϯ0.4 ms/mm Hg). For rising pressures, the diminished integrated sensitivity in the morning was caused by a reduction in mechanical sensitivity, whereas for falling pressures it was caused by a reduction in neural sensitivity. Our findings explicate the mechanisms underlying diurnal variation in baroreflex function. Pharmacological and lifestyle interventions targeted specifically at the diminished component of the cardiac baroreflex in the morning may lead to better management of hypertension. (Hypertension. 2011;58:51-56.)Key Words: circadian rhythms Ⅲ baroreflex Ⅲ blood pressure Ⅲ heart rate Ⅲ carotid artery B lood pressure (BP) exhibits a circadian rhythm, with the lowest pressures occurring during nocturnal sleep and a rapid "morning surge" after waking. 1 BP is most reactive to a given level of physical activity in the morning, 2 and risk of orthostatic intolerance is also greater at this time compared with the afternoon. 3 In a number of prospective studies (reviewed by Kario 4 ), the morning surge in BP has been found to be an independent risk factor for cardiovascular and cerebrovascular events, which also peak between 6:00 AM and 12:00 PM. 5,6 There is a wealth of evidence that BP control varies significantly over a 24-hour period, with studies in the frequency domain indicating the presence of a circadian rhythm in sympathovagal balance. 7,8 However, investigations directed at unraveling the autonomic mechanisms governing these time-of-day differences are lacking.The arterial baroreflex control of vagal neural outflow is quantified by the responses in R-R interval to changes in systolic BP. 9 Previous studies have identified diurnal variation in baroreflex sensitivity in both normotensive and hypertensive people, with reduced sensitivities after waking compared with during sleep. 10 -13 Moreover,...

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Section: Comparison With Previous Studiesmentioning

confidence: 99%

Diurnal Variation in the Mechanical and Neural Components of the Baroreflex

et al. 2011

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“…However, spontaneous short-term fluctuations in RR interval are not intimately and always linked to those in BP via the baroreflex, and thus simple observation of arterial BP and heart period alone may not reveal the extent of arterial baroreflex involvement [30,31]. If baroreflex function is to be assessed with the fewest and safest assumptions, the input to the system should be driven externally to create large and apparent responses.…”

Section: Calculation Of the Baroreflex Gainmentioning

confidence: 99%

Squatting test: a dynamic postural manoeuvre to study baroreflex sensitivity

Scheen

Philips

2011

Clin Auton Res

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“…Indeed, the magnitude of the stimulation necessary to evoke a clearly driven response might be so important as to make impracticable the recognition of any activity due to the presence of feedback. For example, the large pressure change induced by the administration of a vasoactive drug necessary to evoke an evident heart rate variation during the assessment of baroreflex sensitivity [9] prevents any possibility to disentangle the reflex modification of arterial pressure provoked by the drug-induced heart rate variation [10]. Finally, there are systems that cannot be stimulated for ethical reasons without any evident therapeutic indication (e.g.…”

Section: Introductionmentioning

confidence: 99%

Cardiovascular control and time domain Granger causality: insights from selective autonomic blockade

Porta

Castiglioni

Rienzo

et al. 2013

Phil. Trans. R. Soc. A.

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We studied causal relations among heart period (HP), systolic arterial pressure (SAP) and respiration (R) according to the definition of Granger causality in the time domain. Autonomic pharmacological challenges were used to alter the complexity of cardiovascular control. Atropine (AT), propranolol and clonidine (CL) were administered to block muscarinic receptors, β-adrenergic receptors and centrally sympathetic outflow, respectively. We found that: (i) at baseline, HP and SAP interacted in a closed loop with a dominant causal direction from HP to SAP; (ii) pharmacological blockades did not alter the bidirectional closed-loop interactions between HP and SAP, but AT reduced the dominance of the causal direction from HP to SAP; (iii) at baseline, bidirectional interactions between HP and R were frequently found; (iv) the closed-loop relation between HP and R was unmodified by the administration of drugs; (v) at baseline, unidirectional interactions from R to SAP were often found; and (vi) while AT induced frequently an uncoupling between R and SAP, CL favoured bidirectional interactions. These results prove that time domain measures of Granger causality can contribute to the description of cardiovascular control by suggesting the temporal direction of the interactions and by separating different causality schemes (e.g. closed loop versus unidirectional relations).

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Probing the arterial baroreflex: is there a ‘spontaneous’ baroreflex?

Cited by 36 publications

References 43 publications

Diurnal Variation in the Mechanical and Neural Components of the Baroreflex

Diurnal Variation in the Mechanical and Neural Components of the Baroreflex

Squatting test: a dynamic postural manoeuvre to study baroreflex sensitivity

Cardiovascular control and time domain Granger causality: insights from selective autonomic blockade

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