Reduced forearm α1-adrenergic vasoconstriction is associated with enhanced heart rate fluctuations in humans

2006 ◽  
Vol 100 (3) ◽  
pp. 792-799 ◽  
Author(s):  
Shizue Masuki ◽  
John H. Eisenach ◽  
Frank A. Dinenno ◽  
Michael J. Joyner
Keyword(s):  
Heart Rate ◽  
Arterial Pressure ◽  
Brachial Artery ◽  
Coefficient Of Variation ◽  
Pressure Fluctuations ◽  
Systolic Pressure ◽  
Systolic Arterial Pressure ◽  
Adrenergic Agonist ◽  
Arterial Blood ◽  
Young Subjects

In the present study, we assessed whether heart rate (HR) or arterial pressure fluctuations are enhanced in healthy young humans with reduced α-adrenergic vasoconstrictor responses and, if so, whether this occurs for both α1- and α2-adrenergic receptor-mediated vasoconstriction. Arterial pressure (brachial artery catheter) and HR (ECG) were monitored continuously, and α1- and α2-adrenergic responsiveness was determined by assessing the effects of brachial artery infusions of phenylephrine (α1-adrenergic agonist) and dexmedetomidine (α2-adrenergic agonist), respectively, on forearm blood flow (strain gauge plethysmography). α1-Adrenergic responsiveness varied markedly among the subjects ( n = 20) and was inversely correlated with coefficient of variation for HR ( R2 = 0.37, P < 0.01), whereas the responsiveness was not correlated with the coefficient of variation for either systolic or diastolic arterial pressure. α1-Adrenergic responsiveness was inversely and more strongly correlated with baroreflex sensitivity ( R2 = 0.62, P < 0.0001), determined from beat-to-beat changes in HR and systolic arterial pressure, than the coefficient of variation for HR. On the other hand, α2-adrenergic responsiveness was not correlated with any of the parameters determined above. These results suggest that, in healthy young subjects, the enhanced HR response to changes in systolic pressure helps maintain the stability of arterial blood pressure when α1-adrenergic responsiveness is reduced.

scholarly journals Blood pressure changes in dogs with babesiosis

2000 ◽  
Vol 71 (1) ◽  
Author(s):  
L.S. Jacobson ◽  
R.G. Lobetti ◽  
T. Vaughan-Scott
Keyword(s):  
Arterial Pressure ◽  
Systolic Pressure ◽  
Systolic Arterial Pressure ◽  
Significant Negative Correlation ◽  
Arterial Blood ◽  
Significant Relationships ◽  
Normal Mean ◽  
Blood Pressures ◽  
Pressure Changes ◽  
And Control

Systemic arterial blood pressures were measured in 30 dogs with acute babesiosis, 10 each with mild uncomplicated, severe uncomplicated and complicated disease. Ten healthy dogs were used as controls. Hypotension was defined as more than 3 standard deviations below the control mean. Normal mean pressures (±SD) were: systolic arterial pressure 151 (±11) mm Hg, diastolic arterial pressure 89 (±8) mm Hg and mean arterial pressure 107 (±10) mmHg. Hypotension was the most frequent abnormality, and increased strikingly in incidence as disease severity increased, with 5/10 dogs in the complicated group being hypotensive for systolic, diastolic and mean arterial pressures, compared with 2/10 in the severe uncomplicated group and 0/10 in the mild uncomplicated group. Systolic, diastolic and mean arterial pressures in the complicated group and severe uncomplicated group, and systolic pressure in the mild uncomplicated group, were significantly lower than in the controls. There were no significant relationships between arterial pressures and age, pulse rate, respiratory rate, temperature, mucous membrane colour or haematocrit. There was a significant negative correlation between arterial pressures and white cell and immature neutrophil counts. Arterial pressures differed significantly between dogs that were clinically collapsed and those that were not, but not between survivors and non-survivors. Pulse pressure (systolic - diastolic) was low in 7/10 complicated, 1/10 mild uncomplicated, and 1/10 severe uncomplicated cases, and differed significantly between the complicated and control groups. The high incidence of hypotension in clinically severe babesiosis has important implications for therapy.

Baroreceptor reflex control of heart rate in rats studied by induced and autogenic changes in arterial pressure

2005 ◽  
Vol 288 (5) ◽  
pp. H2422-H2430 ◽  
Author(s):  
Julia A. Moffitt ◽  
Angela J. Grippo ◽  
Alan Kim Johnson
Keyword(s):  
Blood Pressure ◽  
Heart Rate ◽  
Arterial Pressure ◽  
Arterial Blood Pressure ◽  
Surgical Stress ◽  
Pressure Fluctuations ◽  
Pulse Interval ◽  
Sprague Dawley ◽  
Arterial Blood ◽  
Sequence Method

The function of the arterial baroreflex has traditionally been assessed by measurement of reflex changes in heart rate (HR) or sympathetic nerve activity resulting from experimenter-induced manipulation of arterial blood pressure (the Oxford method, also termed the pharmacological method). However, logistical and flexibility limitations of this technique have promoted the development of new methods for assessing baroreflex function such as the evaluation of changes in spontaneous arterial pressure and HR. Although this new spontaneous method has been validated in dogs and humans, it has not been rigorously tested in rats. In the present study, the method of correlating spontaneous changes in systolic blood pressure and HR was evaluated in resting, normotensive Sprague-Dawley rats. This technique was found to be neither reliable nor valid under the conditions employed in the present protocol. We also tested a variation of the spontaneous method that evaluates particular sequences of data during which arterial pressure and pulse interval are changing in the same direction for at least three consecutive heartbeats (the sequence method). The sequence method did not provide extra reliability or validity over the spontaneous method. We conclude that due to the restricted range of variability obtained by measuring spontaneous blood pressure fluctuations, the spontaneous and sequence techniques do not provide data that are comparable to the traditional method of assessing HR changes triggered by arterial blood pressure increases and decreases induced by vasoactive drugs. However, it is possible that surgical stress obscured the relationship between blood pressure and HR, and therefore additional studies are needed to determine whether the spontaneous and sequence methods can be applied to rats during different behavioral states.

scholarly journals The Effects of Vibroacoustically Induced Microvibrations on Arterial Blood Pressure and Oxidative Stress in Rats

2014 ◽  
Vol 15 (2) ◽  
pp. 83-88
Author(s):  
Dusko Kornjaca ◽  
Vladimir Zivkovic ◽  
Nevena Barudzic ◽  
Vladimir Jakovljevic ◽  
Dragan Djuric
Keyword(s):  
Oxidative Stress ◽  
Arterial Pressure ◽  
Systolic Arterial Pressure ◽  
Control Group ◽  
Oxidative Stress Markers ◽  
Sound Waves ◽  
Initial Value ◽  
The Third ◽  
Stress Markers ◽  
Arterial Blood

ABSTRACT Vibroacoustics, a scientific field that has been intensively studied for the last thirty years, uses the properties of sound waves (infrasound, ultrasound, noise and music) to induce vibrations that, like a sound wave, may have both useful and harmful effects. Th e aim of this study was to examine the effects of vibroacoustically induced microvibrations on arterial blood pressure and markers of oxidative stress in the blood. Th e experiments were performed on Wistar male rats that had a 180-200 g body mass and were divided into control and experimental groups (6 rats in each). In the experimental group, microvibrations were induced using the Vitafon vibroacoustic apparatus (Vitafon, St. Petersburg, Russian Federation), which delivers sound waves of varying frequencies by a process called “phoning”. Up to 60 minutes of phoning time was delivered to the kidney and liver using 4 diff erent regimens that included a 5-minute stabilisation time; up to four 10-minute phoning regimens, with 5-minute breaks between each single regimen, at a 30 Hz-18000 kHz frequency range;, and 2.8 μm-12.3 μm microwave amplitudes. After the completion of a phoning regimen, animals were sacrificed and the oxidative stress markers were measured in blood samples (O2-, H2O2, nitrites, lipid peroxidation index, superoxide dismutase, catalase, and glutathione) and compared with the values of markers in the control group. Systolic arterial pressure was analysed after the acute application of up to four diff erent regimens of vibroacoustic microvibrations. Systolic arterial pressure decreased significantly during the administration of the second regimen in comparison to the control group. Systolic arterial pressure returned, almost completely, to the initial value after the administration of the third and fourth regimens. Th ere was no significant change in diastolic arterial pressure after the acute administration of up to four different regimens, although the pressure decreased slightly after the first and second regimens and returned to the initial value during the administration of the third and fourth regimens. Analysis of oxidative stress markers showed a statistically significant change in the catalase level. No statistically significant differences were found in the other oxidative stress markers analyzeanalysed. Further research is needed to clarify the physiological effects of low compared to high frequencies of vibroacoustically induced microvibrations and their possible therapeutic significance.

Exploring directionality in spontaneous heart period and systolic pressure variability interactions in humans: implications in the evaluation of baroreflex gain

2005 ◽  
Vol 288 (4) ◽  
pp. H1777-H1785 ◽  
Author(s):  
Giandomenico Nollo ◽  
Luca Faes ◽  
Alberto Porta ◽  
Renzo Antolini ◽  
Flavia Ravelli
Keyword(s):  
Spectral Analysis ◽  
Spectral Component ◽  
Systolic Pressure ◽  
Low Frequency ◽  
Systolic Arterial Pressure ◽  
Phase Lag ◽  
Healthy Humans ◽  
Head Up Tilt ◽  
Causal Approach ◽  
Young Subjects

Although in physiological conditions RR interval and systolic arterial pressure (SAP) are likely to interact in a closed loop, the traditional cross-spectral analysis cannot distinguish feedback (FB) from feedforward (FF) influences. In this study, a causal approach was applied for calculating the coherence from SAP to RR ( Ks-r) and from RR to SAP ( Kr-s) and the gain and phase of the baroreflex transfer function. The method was applied, compared with the noncausal one, to RR and SAP series taken from 15 healthy young subjects in the supine position and after passive head-up tilt. For the low frequency (0.04–0.15 Hz) spectral component, the enhanced FF coupling ( Kr-s = 0.59 ± 0.21, significant in 14 subjects) and the blunted FB coupling ( Ks-r = 0.17 ± 0.17, significant in 4 subjects) found at rest indicated the prevalence of nonbaroreflex mechanisms. The tilt maneuver recovered FB influences ( Ks-r = 0.47 ± 0.16, significant in 14 subjects), which were stronger than FF interactions ( Ks-r = 0.34 ± 0.19, significant in 9 subjects). At the respiratory frequency, the RR-SAP regulation was balanced at rest ( Ks-r = 0.30 ± 0.18 and Kr-s = 0.29 ± 0.20, significant in 11 and 8 subjects) and shifted toward FB mechanisms after tilt ( Ks-r = 0.35 ± 0.19 and Kr-s = 0.19 ± 0.11, significant in 14 and 8 subjects). The causal baroreflex gain estimates were always lower than the corresponding noncausal values and decreased significantly from rest to tilt in both frequency bands. The tilt-induced increase of the phase lag from SAP to RR suggested a shift from vagal to sympathetic modulation. Thus the importance of nonbaroreflex interactions pointed out the necessity of accounting for causality in the cross-spectral analysis of the interactions between cardiovascular variables in healthy humans.

Breathing through an inspiratory threshold device improves stroke volume during central hypovolemia in humans

2008 ◽  
Vol 104 (5) ◽  
pp. 1402-1409 ◽  
Author(s):  
Kathy L. Ryan ◽  
William H. Cooke ◽  
Caroline A. Rickards ◽  
Keith G. Lurie ◽  
Victor A. Convertino
Keyword(s):  
Cardiac Output ◽  
Arterial Pressure ◽  
Stroke Volume ◽  
Lower Body Negative Pressure ◽  
Systolic Arterial Pressure ◽  
Intrathoracic Pressure ◽  
Subsequent Increase ◽  
Arterial Blood ◽  
Threshold Device ◽  
Inspiratory Resistance

Inspiratory resistance induced by breathing through an impedance threshold device (ITD) reduces intrathoracic pressure and increases stroke volume (SV) in supine normovolemic humans. We hypothesized that breathing through an ITD would also be associated with a protection of SV and a subsequent increase in the tolerance to progressive central hypovolemia. Eight volunteers (5 men, 3 women) were instrumented to record ECG and beat-by-beat arterial pressure and SV (Finometer). Tolerance to progressive lower body negative pressure (LBNP) was assessed while subjects breathed against either 0 (sham ITD) or −7 cmH2O inspiratory resistance (active ITD); experiments were performed on separate days. Because the active ITD increased LBNP tolerance time from 2,014 ± 106 to 2,259 ± 138 s ( P = 0.006), data were analyzed (time and frequency domains) under both conditions at the time at which cardiovascular collapse occurred during the sham experiment to determine the mechanisms underlying this protective effect. At this time point, arterial blood pressure, SV, and cardiac output were higher ( P ≤ 0.005) when breathing on the active ITD rather than the sham ITD, whereas indirect indicators of autonomic activity (low- and high-frequency oscillations of the R-to-R interval) were not altered. ITD breathing did not alter the transfer function between systolic arterial pressure and R-to-R interval, indicating that integrated baroreflex sensitivity was similar between the two conditions. These data show that breathing against inspiratory resistance increases tolerance to progressive central hypovolemia by better maintaining SV, cardiac output, and arterial blood pressures via primarily mechanical rather than neural mechanisms.

Comparison of phenylephrine bolus and infusion methods in baroreflex measurements

1990 ◽  
Vol 69 (3) ◽  
pp. 962-967 ◽  
Author(s):  
J. T. Sullebarger ◽  
C. S. Liang ◽  
P. D. Woolf ◽  
A. E. Willick ◽  
J. F. Richeson
Keyword(s):  
Heart Rate ◽  
Arterial Pressure ◽  
Baroreflex Sensitivity ◽  
Heart Rate Response ◽  
Pressor Response ◽  
Plasma Catecholamines ◽  
Systolic Arterial Pressure ◽  
Normal Subjects ◽  
Vagus Nerves ◽  
Baroreflex Control

Phenylephrine (PE) bolus and infusion methods have both been used to measure baroreflex sensitivity in humans. To determine whether the two methods produce the same values of baroreceptor sensitivity, we administered intravenous PE by both bolus injection and graded infusion methods to 17 normal subjects. Baroreflex sensitivity was determined from the slope of the linear relationship between the cardiac cycle length (R-R interval) and systolic arterial pressure. Both methods produced similar peak increases in arterial pressure and reproducible results of baroreflex sensitivity in the same subjects, but baroreflex slopes measured by the infusion method (9.9 +/- 0.7 ms/mmHg) were significantly lower than those measured by the bolus method (22.5 +/- 1.8 ms/mmHg, P less than 0.0001). Pretreatment with atropine abolished the heart rate response to PE given by both methods, whereas plasma catecholamines were affected by neither method of PE administration. Naloxone pretreatment exaggerated the pressor response to PE and increased plasma beta-endorphin response to PE infusion but had no effect on baroreflex sensitivity. Thus our results indicate that 1) activation of the baroreflex by the PE bolus and infusion methods, although reproducible, is not equivalent, 2) baroreflex-induced heart rate response to a gradual increase in pressure is less than that seen with a rapid rise, 3) in both methods, heart rate response is mediated by the vagus nerves, and 4) neither the sympathetic nervous system nor the endogenous opiate system has a significant role in mediating the baroreflex control of heart rate to a hypertensive stimulus in normal subjects.

Ovine fetal adrenal gland and cardiovascular function

1988 ◽  
Vol 254 (4) ◽  
pp. R706-R710 ◽  
Author(s):  
N. D. Ray ◽  
C. S. Turner ◽  
N. M. Rawashdeh ◽  
J. C. Rose
Keyword(s):  
Heart Rate ◽  
Adrenal Gland ◽  
Arterial Pressure ◽  
Blood Volume ◽  
Cardiovascular Function ◽  
Late Gestation ◽  
Arterial Blood ◽  
Significant Difference ◽  
Ovine Fetus ◽  
Ovine Fetal

Given the necessity of the adrenal gland in maintaining cardiovascular function in adults of various species, these experiments were conducted to determine if fetal bilateral adrenalectomy results in altered resting heart rate, hypotension, and decreased basal blood volume as well as a diminished ability of the fetus to maintain arterial pressure and restore blood volume in response to hemorrhage. We studied heart rate, arterial blood pressure, and blood volume changes in response to hemorrhage of 20% of blood volume at 2%/min in seven adrenalectomized and six intact chronically cannulated unanesthetized lambs between 119 and 133 days of gestation. Blood volumes and percent restitution of shed volume were determined using 51Cr-tagged red blood cells and changes in hematocrit. There was no significant difference between groups in basal heart rate, mean arterial pressure, hematocrit, and blood volume. The two groups were similar to hemorrhage-induced changes in these and restitution of volume. Therefore, fetal adrenal glands are not necessary for basal cardiovascular function or regulation subsequent to moderate hemorrhage in the late gestation ovine fetus.

Analysis of heart rate-based control of arterial blood pressure

1996 ◽  
Vol 271 (2) ◽  
pp. H812-H822 ◽  
Author(s):  
W. C. Rose ◽  
J. S. Schwaber
Keyword(s):  
Blood Pressure ◽  
Heart Rate ◽  
Arterial Pressure ◽  
Stroke Volume ◽  
Vascular System ◽  
Reciprocal Relation ◽  
Arterial Baroreflex ◽  
Arterial Blood ◽  
Limited Effectiveness ◽  
Filling Time

Vagal control of the heart is the most rapidly responding limb of the arterial baroreflex. We created a mathematical model of the left heart and vascular system to evaluate the ability of heart rate to influence blood pressure. The results show that arterial pressure depends nonlinearly on rate and that changes in rate are of limited effectiveness, particularly when rate is increased above the basal level. A 10% change in heart rate from rest causes a change of only 2.4% in arterial pressure due to the reciprocal relation between heart rate and stroke volume; at higher rates, insufficient filling time causes stroke volume to fall. These findings agree well with published experimental data and challenge the idea that changes in heart rate alone can strongly and rapidly affect arterial pressure. Possible implications are that vagally mediated alterations in inotropic and dromotropic state, which are not included in this model, play important roles in the fast reflex control of blood pressure or that the vagal limb of the baroreflex is of rather limited effectiveness.

The Influence of Physical Activity on Arterial Pressure during Ambulatory Recordings in Man

1980 ◽  
Vol 58 (1) ◽  
pp. 115-117 ◽  
Author(s):  
D. B. Rowlands ◽  
T. J. Stallard ◽  
R. D. S. Watson ◽  
W. A. Littler
Keyword(s):  
Physical Activity ◽  
Blood Pressure ◽  
Heart Rate ◽  
Arterial Pressure ◽  
Ambulatory Blood Pressure ◽  
Physical Activities ◽  
Hypertensive Patients ◽  
Arterial Blood ◽  
Significant Difference ◽  
Hypotensive Therapy

1. Ambulatory blood pressure recordings were made over a 48 h period on six hypertensive patients. The conditions of study were standardized, particularly with regard to physical activity, and during one period of each day the patients were randomly allocated to be active or inactive. 2. Results show that blood pressure was highest during physical activity and lowest during sleep. There was no significant difference between the arterial pressures measured during the same physical activities carried out at the same time each day. However, during the same time on consecutive days when activity was randomized, there was a significant difference between the pressure recordings during physical activity compared with those during inactivity. Heart rate changes showed a similar trend during the randomized period. 3. Physical activity and sleep have a profound effect on continuous arterial blood pressure recordings and these are independent of time alone. These observations should be taken into account when using this ambulatory system to assess hypotensive therapy.

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