Glutamate-induced fastigial pressor response in the dog

This study indicates that orthodromic pathways emanating from the fastigial nucleus are responsible for the pressor/tachycardia response observed with electrical stimulation of the nucleus. The fastigial presser response was obtained electrically using bipolar electrodes. l-glutamate, which activates only cell bodies, was then injected into the nucleus through the hollow electrode. A slowly-rising pressor response and vagal-mediated bradycardia resulted. On the basis of: (1) dye diffusion studies; (2) the time course of events and similarity to the electrical response;(3) comparison with direct injections into the fourth ventricle; and (4) glutamate injections into adjacent cerebellar tissue, it was concluded that the response emanated from the fastigial nucleus. Electrophysiological studies on cat spinal cord confirmed that the technique of injecting relatively large amounts of glutamate into nuclei activates cell bodies and not axons.     

Association of breathing movements to the variability of heart rate and blood pressure in foetal lambs

Heart rate (HR) variability and arterial blood pressure (BP) variability were analysed as functions of foetal breathing movements (FBMs) by means of power spectral analysis in seven foetal lambs during the third trimester of gestation. No evidence of FBM-related changes, either in mean HR, mean systolic or diastolic arterial pressures, were found. Mean arterial pulse pressure, HR variability, and BP variability increased during FBMs. The increase in BP variability occurred at frequencies higher than 0.35 Hz, i.e. those of FBMs. The increase in HR variability occurred at 0.07-1.0 Hz, i.e. at every frequency band except the lowest one. Thus, the increase in HR variability was not frequency-specifically related to FBMs. During FBMs the periodic variability of HR at frequencies > 0.35 Hz was only 10% of total HR variability. We suggest that the FBM-related changes of BP variability may be mediated by direct peripheral, hydraulic mechanisms. HR changes involve autonomic control systems: the vagal component of baroreflex seems to be relatively insensitive, whereas the very slow vasomotor component of HR variability is dominant.     

Periodic variations of blood pressure and heart rate in premature neonates

Laboratory of Experimental Brain Pathology and Department of Newborn and Premature Infants, Research Institute of Pediatrics, Academy of Medical Sciences of the USSR, Moscow. (Presented by Academician of the Academy of Medical Sciences of the USSR M. Ya. Studenikin.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 109, No. 3, pp. 217–219, March, 1990.     

Verylow frequency variability in arterial blood pressure and blood volume pulse

Several parameters of the cardiovascular system fluctuate spontaenously owing to the activity of the autonomic nervous system. In the study, the simultaneous very low frequency (VLF) fluctuations of the arterial blood pressure, the tissue blood content and the tissue blood volume pulse are investigated. The latter two parameters are derived from the baseline BL and the amplitude AM of the photoplethysmographic (PPG) signal, measured on the fingertips of 20 healthy male subjects: the changes in the PPG parameters AM and BV, defined by BV=const.-BL, are related to the change in the tissue blood volume pulse and the total tissue blood volume, respectively. The VLF fluctuations in BV and AM are directly correlated, those of AM preceding those of BV by 4–13 heart-beats. The VLF fluctuations in the systolic (SBP) and the diastolic (DBP) blood pressure are inversely correlated to those of AM and BV, those of AM preceding those of SBP and lagging behing those of DBP by about one heart-beat. For most subjects, the period P of the PPG pulse, which is equal to the cardiac cycle period, directly correlates with AM and BV and inversely correlates with DBP and SBP. On average, the fluctuations fluctuations in tissue blood volume, systolic blood volume pulse, diastolic and systolic blood pressure, and heart period, together with their interrelationship, can provide a better understanding of the autonomic nervous control of the peripheral circulation and a potential tool for the evaluation of its function.     

Changes in spontaneous and evoked release of transmitter induced by the crotoxin complex and its component phospholipase A2 at the frog neuromuscular junction.

The time course and characteristics of the changes induced by the action of the crotoxin complex and of its component phospholipase A₂ on transmission at the frog neuromuscular junction was studiedin vitro at single endplates using intracellular recording techniques. Both the crotoxin complex and phospholipase A₂ induced variable changes in spontaneous transmitter release in which bursts of miniature endplate potentials alternated with periods when the frequency of miniature endplate potentials was stable but their amplitudes were markedly heterogeneous. The bursts of miniature endplate potentials were of sudden onset and of a high initial frequency, and their duration and incidence were highly variable both at one endplate and between endplates. These changes in the frequency and amplitude of miniature potentials occurred both before and after the abolition of neurally evoked endplate potentials and in the presence of tetrodotoxin. At a late stage in crotoxin intoxication, potassium depolarization of the motor nerve terminals failed to increase spontaneous transmitter release. Both the crotoxin complex and phospholipase A₂ reduced the amplitude of endplate potentials although phospholipase A₂ was less effective. The course of depression of the quantal content of evoked transmitter release induced by the crotoxin complex was occasionally interrupted by a brief facilitation of response; these irregularities in the rate of depression were more clearly seen when endplate potentials were recorded at partially curarized endplates exposed to either the crotoxin complex or to phospholipase A₂. At the stage of abolition of endplate potentials an increase in the external concentration of Ca^{2 +} enabled the evoked response to be restored temporarily. The crotoxin complex and phospholipase A₂ had no effect on the input resistance of the sarcolemmal membrane, but raised the threshold stimulus required to initiate an action potential at concentrations which affected transmitter release. Crotapotin did not affect any of the measured parameters even at high concentrations.The diversity of changes observed in the properties of spontaneous and evoked transmitter release, suggests that the crotoxin complex and phospholipase A₂ may induce two kinds of alterations in the structure of the presynaptic membrane as a result of the action of phospholipase A₂, viz (a) the formation of transient instabilities with an increased Ca^{2 +} inflow and (b) prolonged disturbance of the calcium channel and/or the synchronized release of subunits at the active zone.     

The beat-to-beat blood pressure response to postural change in young and elderly healthy adult males

Heart rate and blood pressure were studied with the beat-to-beat tracking cuff system in two groups (n=20 per group) of healthy, unmedicated males, one between 60 and 75 years of age and the second between 18 and 29 years of age. The study confirms the previously reported blunted heart rate response to standing and the fact that, when blood pressure is recorded by conventional means, the response exhibited during orthostasis does not differ in healthy groups of young and elderly subjects. With the tracking cuff system, however, the elderly exhibited a smaller immediate systolic and diastolic drop in response to the change to upright posture and less variability in beat-to-beat blood pressure changes. The results have implications for cardiovascular studies, where age and posture can influence both blood pressure and heart rate.This research was supported by National Heart, Lung, and Blood Institute Research Grant HL-31184-05.     

Central apnoeas have significant effects on blood pressure and heart rate in children

Brief central apnoeas (CAs) during sleep are common in children and are not usually considered clinically significant unless associated with oxygen desaturation. CAs can occur spontaneously or following a movement or sigh. The aim of this study was to investigate acute cardiovascular changes associated with CAs in children. Beat‐by‐beat mean arterial pressure (MAP) and heart rate (HR) were analysed across CAs, and spontaneous and movement‐induced events were compared using two‐way analysis of variance with post hoc analyses. Fifty‐three children (28 male/25 female) aged 7–12 years referred for investigation of sleep‐disordered breathing (SDB) and 21 age‐matched healthy controls (8 male/13 female) were studied. Children underwent routine clinical polysomnography with continuous blood pressure (BP) recordings. Movement‐induced, but not spontaneous, CAs were more frequent in children with mild or moderate/severe obstructive sleep apnoea (OSA) compared with healthy controls (P < 0.05 for both). Movement‐induced CAs were associated with significantly larger MAP and HR changes across the event compared with spontaneous CAs. The percentage changes in MAP and HR between late‐event and post‐event were significantly greater for movement‐induced compared with spontaneous CAs (MAP 20.6 ± 2.3 versus 12.2 ± 1.8%, P < 0.01; HR 28.2 ± 2.6 versus 14.7 ± 2.5%, P < 0.001). This study demonstrates that movement‐induced CAs are more common in children with OSA, and are associated with significantly greater changes in HR and BP compared with spontaneous CAs. These data suggest that movement‐induced CAs should be considered when assessing the cardiovascular impact of SDB.     

Contribution of pH,diprotonated phosphate and potassium for the reflex increase in blood pressure during handgrip

The relative importance of pH, diprotonated phosphate (H₂PO₄^?) and potassium (K⁺) for the reflex increase in mean arterial pressure (MAP) during exercise was evaluated in seven subjects during rhythmic handgrip at 15 and 30% maximal voluntary contraction (MVC), followed by post-exercise muscle ischaemia (PEMI). During 15% MVC, MAP rose from 92 ± 1 to 103 ± 2 mmHg, [K⁺] from 4.1 ± 0.1 to 5.1 ± 0.1 mmol L^?1, while the intracellular (7.00 ± 0.01 to 6.80 ± 0.06) and venous pH fell (7.39 ± 0.01 to 7.30 ± 0.01) (P < 0.05). The intracellular [H₂PO₄^?] increased 8.4 ± 2 mmol kg^?1 and the venous [H₂PO₄^?] from 0.14 ± 0.01 to 0.16 ± 0.01 mmol L^?1 (P < 0.05). During PEMI, MAP remained elevated along with the intracellular [H₂PO₄^?] as well as a low intracellular and venous pH. However, venous [K⁺] and [H₂PO₄^?] returned to the level at rest. During 30% MVC handgrip, MAP rose to 130 ± 3 mmHg, [K⁺] to 5.8 ± 0.2 mmol L^?1, the intracellular and extracellular [H₂PO₄^?] by 20 ± 5 mmol kg^?1 and to 0.20 ± 0.02 mmol L^?1, respectively, while the intracellular (6.33 ± 0.06) and venous pH fell (7.23 ± 0.02) (P < 0.05). During post-exercise muscle ischaemia all variables remained close to the exercise levels. Analysis of each variable as a predictor of blood pressure indicated that only the intracellular pH and diprotonated phosphate were linked to the reflex elevation of blood pressure during handgrip.     

The effect of centrally administered TRH on blood pressure,heart rate and ventilation in rat

Different doses (3, 16, 80, 400 and 2000 ng per rat) of TRH or alternatively saline were infused into the lateral ventricle of urethane-ahaesthetized rats and blood pressure, heart rate, respiration rate and tidal volume were recorded. A dose of 3 ng TRH caused a significant elevation of blood pressure and heart rate, whereas 16 ng was needed for respiration rate to be elevated. There was no change in respiratory minute volume during the experiment. We conclude that TRH has profound physiological effects and that TRH, given centrally, is a potent hypertensive, chronotropic and tachypnoeic agent.     

Nitric oxide donors dose-dependently reduce heart rate in rats against the background of blood pressure drop

The effect of nitroglycerin in increasing doses (0.2-1.0 mg/kg) and sodium nitroprusside (1 mg/kg) on the heart rate, P-Q interval of ECG, and blood pressure was studied on 53 albino rats. NO donors nitroglycerin and sodium nitroprusside directly affected vascular endothelium (the maximum decrease in blood pressure was 28.5 and 57.0%, respectively) and produced a dose-dependent negative chronotropic effect (the maximum decrease in heart rate was 13.6 and 27.0%, respectively). These drugs also affected myocytes of the cardiac conduction system: P-Q interval increased by 16.0-29.7%.     

John Henryism and blood pressure in black college students

Previous research on John Henryism, a coping mechanism linked to hypertension in blacks, has focused almost exclusively on rural, low-socioeconomic status (SES), adult populations. Furthermore, these studies have not evaluated mediating influences of John Henryism except in terms of SES. The primary focus of the current investigation was to examine the influence of John Henryism on cardiovascular disease risk factors among a relatively healthy sample of 421 urban, black college students. A second component of the study was to determine the role of social support as a mediating influence on those with limited coping resources and high John Henryism scores. Approximately 30% of males and 9% of females had systolic blood pressures 140 mm Hg or diastolic blood pressures 90. Females had higher John Henryism scores than males. John Henryism was also correlated with social support in females. Gender-specific regression models revealed that John Henryism was not an independent predictor of blood pressure in black college students. The results are discussed in terms of apparent gender differences with regard to overall coping mechanisms in black students and possible explanations for the lack of a John Henryism-blood pressure relationship in this population.Dr. Adams-Campbell was supported by NIH Grants: HL07701 and HL39788.     

肥胖儿童血压及其与X线心脏大小的关系

目的：探讨不同判定标准下3～7岁单纯肥胖儿童高血压发生率,以及血压与心脏大小的相关性。方法：体质测量、血压测量、X线测量心脏大小,对有关数据的相关性进行统计学分析。结果：肥胖儿童血压及不同标准下高血压检出率显著地高于正常儿童。高血压肥胖儿童心脏大小10个指标均大于非高血压肥胖者。血压与心脏面积、心脏体积呈低～中度相关。结论：高血压肥胖儿童心脏向各个方向增大,与非高血压者有显著差异。血压与心脏体积指数关系不密切,血压升高,会引起心脏增大和受累。     

Diurnal changes of blood pressure,heart rate and body temperature during sleep in the rat

We have studied diurnal changes in mean arterial pressure (MAP), heart rate (HR) and body temperature (Tb) during wake (W), non-rapid eye movement sleep (NREMS) and REM sleep (REMS) in the rat. Although HR and Tb show a similar sinusoidal diurnal variation during all vigilance states, the diurnal profile for the MAP is vigilance-state dependent. During W, MAP values are higher during the dark phase, during NREMS, no significant diurnal change is seen, and during REMS, the MAP exhibits a reversed diurnal change, being higher during the light phase. The low frequency component (0.25–0.725 Hz) in the power spectral density of the blood pressure, an index of sympathetic activity, is also higher during the light phase than the dark phase in REMS. The present findings suggest that diurnal changes in MAP in the rat result from the wake rhythm, and that the mechanism for the diurnal control of MAP may be different from that for HR or Tb.     

Effects of 4-week administration of simvastatin in different doses on heart rate and blood pressure after metoprolol injection in normocholesterolaemic and normotensive rats

Introduction

Statins and β1-adrenergic antagonists are well established in cardiovascular events therapy and prevention. The previous study showed that statins might impact on β-adrenergic signalling and blood pressure in a dose-dependent manner. The aim of the study was to evaluate the impact of 4-week administration of simvastatin given at different doses on the heart rate and blood pressure after injection of metoprolol in rats.

Material and methods

The experiments were performed in normocholesterolaemic and normotensive Wistar rats. Rats received simvastatin in doses of 1, 10 and 20 mg/kg body weight (bw) for 4 weeks. The control group received 0.2% methylcellulose. For the further estimation of the heart rate and blood pressure, metoprolol at 5 mg/kg bw or 0.9% NaCl was injected intraperitoneally.

Results

Simvastatin at doses of 1, 10 and 20 mg/kg bw did not influence the heart rate or blood pressure as compared to the control group. Metoprolol injection statistically significantly decreased the heart rate (439.29±14.03 min⁻¹ vs. 374.41±13.32 min⁻¹; p<0.05). In rats receiving simvastatin during the 4-week period after metoprolol injection, heart rate and blood pressure (mean, systolic, diastolic) were similar as compared to the group receiving metoprolol alone.

Conclusions

Simvastatin administration during a 4-week period in different doses did not influence the heart rate or blood pressure after metoprolol injection in normocholesterolaemic and normotensive rats.     

Handgrip contraction induces a linear increase in arterial pressure by peripheral vasoconstriction,increased heart rate and a decrease in stroke volume

Aim: The hypothesis that isometric handgrip induces a progressive increase in arterial pressure and a linear increase in setpoint for arterial pressure control was tested. Methods: The continuous time course of changes in heart rate (HR), stroke volume (SV) and mean arterial pressure (MAP) was recorded during a 2-min handgrip contraction of 40% of maximal voluntary contraction force. Twice during the development of the handgrip-induced, gradual pressure increase of ∼25 mmHg, additional, transient changes in arterial pressure were mechanically induced. The subsequent baroreflex responses to these additional pressure changes were studied. The additional steep increase in arterial pressure (∼10 mmHg) was induced both after 70 and 100 s of handgrip contraction, by inflating bilateral thigh cuffs to suprasystolic pressure. Cuff pressure was released after 10 s, thus introducing a steep decrease in MAP. Results: During the development of the handgrip-induced pressure increase, HR increased, SV decreased, cardiac output (CO) increased slightly and total peripheral conductance (TPC = CO/MAP) increased (i.e. peripheral vasoconstriction). The circulatory responses to the additional, sudden increase and subsequent decrease in arterial pressure after 70 and 100 s perfectly adjusted arterial pressure back to the linear increase in MAP, indicating an effective baroreflex response. Conclusion: The increase in MAP which characterizes handgrip-induced pressure response can be regarded as a result of a gradual increase in the set point of the arterial baroreflexes, with no change in the time course and magnitude of the baroreflex responses to additional, induced changes in MAP.     

直立倾斜引起的心率和血压的耦合性变化分析

从动态和稳态两个视角,研究直立倾斜(HUT)引起体位改变前后以及不同速度改变体位过程中RR间期(RRI)与收缩压(SBP)间耦合性的变化。所用数据来自PhsioNet发布的体位变化所引起的生理响应数据库(PRCP),含有10位健康受试者(5男5女)在HUT过程中记录的连续心电和动脉血压信号。慢速体位变化(ST)和快速体位(RT)变化分别为在50和2 s之间从水平仰卧升至75°倾斜。提取逐拍RRI和SBP数据后,运用交叉时频分析和信息分解方法,结合时域和短时分形指数(α₁),进行RRI和SBP时间序列的联合分析。信息分解分析结果表明,所有的显著差异集中在压力反射导致心率变化的后向反馈回路(SBP→RRI),ST后心率的可预测性较平卧时显著增高(0.416±0.067 vs 0.626±0.127),压力反射支路的SBP-RRI耦合性升高。而在RRI→SBP方向,HUT对其几乎没有影响。ST和RT之前,所有的同类指标相比均无显著差异。ST和RT之后的稳态,虽然RRI无显著差异,但较之ST之后,RT之后RRI的变异系数显著升高(0.054±0.014 vs 0.074±0.027),α₁显著降低(1.45±0.25 vs 1.28±0.27)。同时,交叉时频分析结果揭示了ST和RT过程中自主神经不同的动态反应行为。研究证明了信息分解方法的有效性,可明确区分心率与血压相互作用时的前向反馈和后向反馈的主导因果方向,而且可反映HUT前后信号可预测性的变化。     

Blood pressure and heart rate response to static exercise in relation to electromyographic activity and force development

5 healthy men performed static knee extension (90° knee angle) with one leg for 5 min. In one series of experiments the force was held constant at 20% of the isometric maximal voluntary contraction. In the other the initial force development was also 20%, but the smoothed, rectified electromyographic activity, (SREMG) recorded after 5 s of contraction was kept constant. Heart rate (HR), arterial mean blood pressure (MBP) (measured 20 cm proximally to the elbow in a. brachialis), EMG (surface electrodes) from the lateral portion of m. quadriceps femoris, and force were continuously recorded. HR and MBP increased approximately 40% in the force-constant experiments and approximately 20% in the SREMG-constant experiments. The greatest increase occurred during the first two minutes of contraction. In the force-constant experiments SREMG doubled, with the most marked increases occurring during the very early and late parts of the contraction. SREMG correlated with both HR (r=0.85) and MBP (r=0.98). In the SREMG-constant experiments force declined quickly during the first minute and remained at about 12% MVC thereafter. The observed cardiovascular responses to static contraction can best be explained as the result of the combined action of central and peripheral drives, the central drive being related to the central activity for the recruitment of motor units, and the peripheral drive being mediated through chemoreceptors in the exercising muscles.