Calculation of threshold and saturation points of sigmoidal baroreflex function curves

2006 ◽  
Vol 291 (4) ◽  
pp. H2003-H2007 ◽  
Author(s):  
Lachlan M. McDowall ◽  
Roger A. L. Dampney
Keyword(s):  
Heart Rate ◽  
Sympathetic Nerve Activity ◽  
Gain Coefficient ◽  
Open Loop ◽  
Sigmoid Function ◽  
Input Output ◽  
Nerve Activity ◽  
Baroreflex Function ◽  
Range Difference ◽  
The Difference

The logistic sigmoid function curve provides an accurate description of the baroreflex input-output relationship and is the most commonly used equation for this purpose. The threshold (Thr) and saturation (Sat) values for the baroreflex are commonly defined as the values of mean arterial pressure (MAP) at which the reflexly controlled variable (e.g., heart rate or sympathetic nerve activity) is within 5% of the upper or lower plateau, respectively, of the sigmoid function. These values are referred to here as Thr5% and Sat5%. In many studies, Thr and Sat are calculated with the equations Thr = A3 − 2.0/ A2 and Sat = A3 + 2.0/ A2, where A3 is the value of MAP at the point where the reflexly controlled variable is at the midpoint of its range and A2 is the gain coefficient. Although it is commonly stated that the values of Thr and Sat calculated with these equations represent Thr5% and Sat5%, we show here that instead they are significantly greater and less than Thr5% and Sat5%, respectively. Furthermore, the operating range (difference between Thr and Sat) calculated with these equations is 32% less than the difference between Thr5% and Sat5%. We further show that the equations that provide correct values of Thr5% and Sat5% are Thr5% = A3 − 2.944/ A2 and Sat5% = A3 + 2.944/ A2. We propose that these be used as the standard equations for calculating threshold and saturation values when a logistic sigmoid function is used to model the open-loop baroreflex function curve.

High-cut characteristics of the baroreflex neural arc preserve baroreflex gain against pulsatile pressure

2002 ◽  
Vol 282 (3) ◽  
pp. H1149-H1156 ◽  
Author(s):  
Toru Kawada ◽  
Can Zheng ◽  
Yusuke Yanagiya ◽  
Kazunori Uemura ◽  
Tadayoshi Miyamoto ◽  
...  
Keyword(s):  
Heart Rate ◽  
Transfer Function ◽  
Sympathetic Nerve Activity ◽  
Dynamic Range ◽  
Open Loop ◽  
Loop Gain ◽  
Frequency Range ◽  
Nerve Activity ◽  
Pulsatile Pressure ◽  
Rate Frequency

A transfer function from baroreceptor pressure input to sympathetic nerve activity (SNA) shows derivative characteristics in the frequency range below 0.8 Hz in rabbits. These derivative characteristics contribute to a quick and stable arterial pressure (AP) regulation. However, if the derivative characteristics hold up to heart rate frequency, the pulsatile pressure input will yield a markedly augmented SNA signal. Such a signal would saturate the baroreflex signal transduction, thereby disabling the baroreflex regulation of AP. We hypothesized that the transfer gain at heart rate frequency would be much smaller than that predicted from extrapolating the derivative characteristics. In anesthetized rabbits ( n = 6), we estimated the neural arc transfer function in the frequency range up to 10 Hz. The transfer gain was lost at a rate of −20 dB/decade when the input frequency exceeded 0.8 Hz. A numerical simulation indicated that the high-cut characteristics above 0.8 Hz were effective to attenuate the pulsatile signal and preserve the open-loop gain when the baroreflex dynamic range was finite.

Baroreflex regulation of renal sympathetic nerve activity and heart rate in renal wrap hypertensive rats

2005 ◽  
Vol 288 (4) ◽  
pp. R856-R862 ◽  
Author(s):  
M. Vitela ◽  
M. Herrera-Rosales ◽  
J. R. Haywood ◽  
S. W. Mifflin
Keyword(s):  
Heart Rate ◽  
Sodium Nitroprusside ◽  
Sympathetic Nerve ◽  
Sympathetic Nerve Activity ◽  
Sigmoid Function ◽  
Nerve Activity ◽  
Renal Sympathetic Nerve Activity ◽  
Renal Sympathetic Nerve ◽  
The Right ◽  
Renal Sympathetic

Despite its usefulness as a nongenetic model of hypertension, little information is available regarding baroreflex function in the Grollman, renal wrap model of hypertension in the rat. Baroreflex regulation of renal sympathetic nerve activity (RSNA) and heart rate (HR) were studied in male, Sprague-Dawley rats hypertensive (HT) for 1 or 4–6 wk after unilateral nephrectomy and figure-8 ligature around the remaining kidney or normotensive (NT) after sham surgery. Rats were anesthetized with Inactin and RSNA, and HR was recorded during intravenous infusions of sodium nitroprusside or phenylephrine to lower or raise mean arterial pressure (MAP). Response curves were analyzed using a logistic sigmoid function. In 1- and 4-wk HT rats the midpoints of RSNA and HR reflex curves were shifted to the right ( P < 0.05). Comparing NT to 1- or 4-wk HT rats, the gain of RSNA-MAP curves was no different; however, gain was reduced in the HR-MAP curves at both 1 and 4 wk in HT rats ( P < 0.05). In anesthetized rats the HR range was small; therefore, MAP and HR were measured in conscious rats during intravenous injections of three doses of phenylephrine and three doses of sodium nitroprusside. Linear regressions revealed a reduced slope in both 1- and 4-wk HT rats compared with NT rats ( P < 0.05). The results indicate that baroreflex curves are shifted to the right, to higher pressures, in hypertension. After 1–4 wk of hypertension the gain of baroreflex regulation of RSNA is not altered; however, the gain of HR regulation is reduced.

Comparison of Transient Heart Rate Reduction Associated with Acupuncture Stimulation in Supine and Sitting Subjects

2003 ◽  
Vol 21 (4) ◽  
pp. 133-137 ◽  
Author(s):  
Kenji Imai ◽  
Hiroshi Kitakoji
Keyword(s):  
Heart Rate ◽  
Supine Position ◽  
Sympathetic Nerve Activity ◽  
Sitting Position ◽  
Heart Rate Reduction ◽  
Rate Reduction ◽  
Nerve Activity ◽  
The Difference ◽  
The Right ◽  
Stimulation Of

We investigated the difference in transient heart rate reduction associated with brief acupuncture in 20 healthy subjects at rest in a supine and in a sitting position. After the subjects had been at rest for about 20 minutes, acupuncture needling using the sparrow-pecking method, in which the needle is moved vertically lifting and thrusting, was performed for one minute at the Shousanli point on the right forearm (LI10). The procedure was carried out with the subjects in a supine position and in a sitting position. The position for stimulation of each subject, either supine or sitting, was selected at random, and on different days. The results showed that the average heart rate reduction associated with stimulation in supine subjects was 3.6±0.19 (mean ± standard error {SE}) beats per minute (bpm), while that for sitting subjects was about 7.0±1.07 (mean ± SE) bpm, indicating that stimulation reduces heart rate to a greater degree in subjects who are sitting (p<0.05, Mann-Whitney test). These results would be consistent with a mechanism involving reduced sympathetic drive to the heart, as sympathetic nerve activity has more influence on the heart rate in the sitting than in the supine position.

Changes in ovine renal sympathetic nerve activity and baroreflex function at birth

1994 ◽  
Vol 267 (5) ◽  
pp. H1824-H1832 ◽  
Author(s):  
J. L. Segar ◽  
J. E. Mazursky ◽  
J. E. Robillard
Keyword(s):  
Heart Rate ◽  
Sympathetic Nerve ◽  
Sympathetic Nerve Activity ◽  
Enzyme Inhibitor ◽  
Response Curves ◽  
Nerve Activity ◽  
Renal Sympathetic Nerve Activity ◽  
Renal Sympathetic Nerve ◽  
Baroreflex Function ◽  
Renal Sympathetic

The purposes of this study were to characterize the changes in renal sympathetic nerve activity (RSNA) and baroreflex function at birth in conscious sheep. One hour after delivery by cesarean section, RSNA increased by 239 +/- 24% compared with fetuses. The upper and lower plateau values of the baroreflex function curves for RSNA, expressed as the percent maximum achieved in the fetus, were greater (P < 0.05) at 1 h (260 +/- 41 and 142 +/- 40%) and 5 h of age (254 +/- 34 and 100 +/- 19%) than in fetuses (100 and 10 +/- 3%), respectively. Curve midpoint pressures also were higher (P < 0.05) at 1 h (62 +/- 3 mmHg) and 5 h (66 +/- 4 mmHg) than in fetuses (51 +/- 2 mmHg). No changes in the sensitivity (gain) of the RSNA response to baroreceptor stimulation were seen. The baroreflex response curves for heart rate showed similar increases in the curve midpoint pressures, while gain did not change. To determine whether the high circulating levels of angiotensin II (ANG II) in the newborn period contribute to the rise in RSNA or the resetting of the baroreflex toward higher pressures, the angiotensin-converting-enzyme inhibitor, enalaprilat, was administered to five lambs before delivery. No differences in the increase in RSNA after birth were detected between control and treated animals. The curve midpoint pressures of both the RSNA and heart rate baroreflex response curves were significantly less (P < 0.05) in the treated compared with control lambs.(ABSTRACT TRUNCATED AT 250 WORDS)

scholarly journals GABA in the paraventricular nucleus tonically suppresses baroreflex function: alterations during pregnancy

2011 ◽  
Vol 300 (6) ◽  
pp. R1452-R1458 ◽  
Author(s):  
Mollie C. Page ◽  
Priscila A. Cassaglia ◽  
Virginia L. Brooks
Keyword(s):  
Heart Rate ◽  
Paraventricular Nucleus ◽  
Sympathetic Nerve ◽  
Sympathetic Nerve Activity ◽  
Sympathetic Nerves ◽  
Gabaergic Inhibition ◽  
Nerve Activity ◽  
Pregnant Rats ◽  
Baroreflex Function

It is well established that GABAergic inputs to the paraventricular nucleus of the hypothalamus (PVN) tonically suppress heart rate and the activity of several sympathetic nerves. However, whether GABA similarly inhibits PVN control of baroreflex function has not been previously investigated. To test this hypothesis, it was determined whether microinjection of the GABAA antagonist, bicuculline, into the PVN enhances the baroreflex in anesthetized female virgin rats. In addition, because GABAergic inhibition of PVN preautonomic neurons is decreased during pregnancy, it was also determined whether the effects of PVN bicuculline administration on baroreflex function were less in pregnant animals. In virgin rats, PVN microinjection of bicuculline increased ( P < 0.05) baroreflex gain and maximum levels of heart rate (gain, from 1.6 ± 0.6 to 3.8 ± 1.3 bpm/mmHg; maximum, from 406 ± 18 to 475 ± 14 bpm) and of lumbar sympathetic nerve activity (gain from 2.6 ± 0.7 to 4.8 ± 1.6%/mmHg; maximum, 149 ± 32 to 273 ± 48%), indicating that PVN GABA normally suppresses baroreflex function. Pregnancy decreased heart rate baroreflex gain (pregnant, 0.9 ± 0.3 bpm/mmHg; virgin, 1.9 ± 0.2 bpm/mmHg; P < 0.05). Following PVN bicuculline administration in pregnant rats, smaller ( P < 0.01) increments in baroreflex gain (pregnant, 0.6 ± 0.1 bpm/mmHg; virgin, 2.4 ± 0.9 bpm/mmHg) and maximum (pregnant, 33 ± 7 bpm; virgin, 75 ± 12 bpm; P < 0.05) were produced. Collectively, these data suggest that the PVN normally inhibits the baroreflex via tonic GABAergic inputs and that this inhibition is less during pregnancy.

Ontogeny of baroreflex control of renal sympathetic nerve activity and heart rate

1992 ◽  
Vol 263 (6) ◽  
pp. H1819-H1826 ◽  
Author(s):  
J. L. Segar ◽  
G. Hajduczok ◽  
B. A. Smith ◽  
D. C. Merrill ◽  
J. E. Robillard
Keyword(s):  
Blood Pressure ◽  
Heart Rate ◽  
Arterial Blood Pressure ◽  
Sympathetic Nerve Activity ◽  
Nerve Activity ◽  
Renal Sympathetic Nerve Activity ◽  
Arterial Blood ◽  
Baroreflex Function ◽  
Baroreceptor Stimulation ◽  
Renal Sympathetic

The purpose of this study was to characterize the developmental changes in baroreflex function during fetal and postnatal life in sheep. Resting mean arterial blood pressure increased significantly from 55 +/- 2 mmHg in fetuses to 86 +/- 3 mmHg in newborn lambs and to 105 +/- 4 mmHg in 4- to 6-wk-old lambs. The sensitivity (gain) of the renal sympathetic nerve activity (RSNA) response to baroreceptor stimulation was greater (P < 0.05) in fetuses (-7.7 +/- 1.9%/mmHg) than in newborn (-2.9 +/- 0.1%/mmHg) and 4- to 6-wk-old lambs (-2.2 +/- 0.2%/mmHg). The threshold and saturation pressures for the baroreflex function curve were lower (P < 0.05) in fetuses (44 +/- 2 and 61 +/- 2 mmHg) than in newborn (59 +/- 4 and 106 +/- 5 mmHg) or 4- to 6-wk-old lambs (78 +/- 5 and 132 +/- 6 mmHg). Similar findings were observed when the heart rate response to baroreceptor stimulation was examined. Additional experiments were performed in newborn and 4- to 6-wk-old lambs to determine whether the rise in arterial blood pressure associated with postnatal maturation contributed to baroreflex resetting. Sustained elevation of arterial blood pressure by 15–20 mmHg for over 90 min did not reset the baroreflex function curve in either newborn or 4- to 6-wk-old lambs.(ABSTRACT TRUNCATED AT 250 WORDS)

Glucocorticoids modulate baroreflex control of renal sympathetic nerve activity

2001 ◽  
Vol 280 (5) ◽  
pp. R1440-R1449 ◽  
Author(s):  
Deborah A. Scheuer ◽  
Steven W. Mifflin
Keyword(s):  
Sympathetic Nerve ◽  
Sympathetic Nerve Activity ◽  
Gain Coefficient ◽  
Sprague Dawley ◽  
Nerve Activity ◽  
Baroreflex Control ◽  
Renal Sympathetic Nerve Activity ◽  
Renal Sympathetic Nerve ◽  
Baroreflex Function ◽  
Renal Sympathetic

Experiments were performed to determine the effects of glucocorticoids on arterial baroreceptor reflex control of renal sympathetic nerve activity (RSNA). Intravenous infusions of phenylephrine and nitroprusside were used to produce graded changes in arterial pressure (AP) in Inactin-anesthetized male Sprague-Dawley rats. Baroreflex control of RSNA was determined during a baseline period and 2 and 3 h after administration of the glucocorticoid type II receptor antagonist Mifepristone (30 mg/kg sc) or vehicle (oil). Corticosterone (cort) treatment (100 mg cort pellet sc for 2–3 wk) increased baseline AP from 115 ± 2 to 128 ± 1 mmHg. Cort treatment also decreased the gain coefficient and increased the midpoint of the baroreflex curve. Treatment of cort rats with Mifepristone decreased AP within 2 h and increased the gain coefficient and decreased the midpoint of the baroreflex function curve back toward values measured in control rats. Mifepristone altered the baroreflex function curve even when AP was maintained at baseline levels. Therefore, these data demonstrate for the first time that glucocorticoids can modulate baroreflex control of RSNA by a mechanism that is, in part, independent of changes in AP.

Effect of human galanin on the response of circulating catecholamines to hypoglycemia in man

1995 ◽  
Vol 133 (6) ◽  
pp. 723-728 ◽  
Author(s):  
Ettore C degli Uberti ◽  
Maria R Ambrosio ◽  
Marta Bondanelli ◽  
Giorgio Transforini ◽  
Alberto Valentini ◽  
...  
Keyword(s):  
Heart Rate ◽  
Healthy Subjects ◽  
Sympathetic Nerve Activity ◽  
Heart Rate Response ◽  
Statistical Significance ◽  
Inhibitory Effect ◽  
Amino Acid Residues ◽  
Nerve Activity ◽  
Receptor Stimulation

degli Uberti EC, Ambrosio MR, Bondanelli M, Trasforini G, Valentini A, Rossi R, Margutti A, Campo M. Effect of human galanin on the response of circulating catecholamines to hypoglycemia in man. Eur J Endocrinol 1995;133:723–8. ISSN 0804–4643 Human galanin (hGAL) is a neuropeptide with 30 amino acid residues that has been found in the peripheral and central nervous system, where it often co-exists with catecholamines. In order to clarify the possible role of hGAL in the regulation of sympathoadrenomedullary function, the effect of a 60 min infusion of hGAL (80 pmol·kg−1 · min−1) on plasma epinephrine and norepinephrine responses to insulin-induced hypoglycemia in nine healthy subjects was investigated. Human GAL administration significantly reduced both the release of basal norepinephrine and the response to insulin-induced hypoglycemia, whereas it attenuated the epinephrine response by 26%, with the hGAL-induced decrease in epinephrine release failing to achieve statistical significance. Human GAL significantly increased the heart rate in resting conditions and clearly exaggerated the heart rate response to insulin-induced hypoglycemia, whereas it had no effect on the blood pressure. We conclude that GAL receptor stimulation exerts an inhibitory effect on basal and insulin-induced hypoglycemia-stimulated release of norepinephrine. These findings provide further evidence that GAL may modulate sympathetic nerve activity in man but that it does not play an important role in the regulation of adrenal medullary function. Ettore C degli Uberti, Chair of Endocrinology, University of Ferrara, Via Savonarola 9, I-44100 Ferrara, Italy

Sign in / Sign up

Export Citation Format

Share Document