垂体后叶素联合催产素对腹腔镜下子宫肌瘤剔除术患者循环系统的影响及止血效果

目的:研究垂体后叶素联合催产素对腹腔镜下子宫肌瘤剔除术患者循环系统的影响及止血效果。方法:收集本院2011年10月至2013年10月进行腹腔镜下子宫肌瘤剔除术的75例子宫肌瘤患者,采用简单随机分组的方法将研究样本序贯分为A组(垂体后叶素组)、B组(催产素组)、C组(垂体后叶素联合催产素组)三组,各25例。比较各组循环系统和止血效果指标是否有变化及差异。结果:三组之间收缩压、舒张压、心率差异有统计学意义(P0.05),不同时间的收缩压、舒张压、心率差异有统计学意义(P0.05),收缩压、舒张压、心率分组与时间之间有交互作用(P0.05)。A组较B组低血压、心动过速及出血量更少,B组较A组高血压、心动过缓更少,差异均有统计学意义(P0.05);C组较A组高血压、心动过缓更少,差异有统计学意义(P0.05);C组较B组低血压、心动过速及出血量更少,差异有统计学意义(P0.05)。结论:腹腔镜下子宫肌瘤剔除术患者联合应用垂体后叶素与催产素后循环波动小,止血效果好,值得在临床上推广应用。     

Comparative effects on blood pressure and heart rate of dynorphin A(1–13) in anterior hypothalamic area, posterior hypothalamic area, nucleus tractus solitarius, and lateral cerebral ventricle in the rat

The objective of this study was to explore the effects of the endogenous opioid peptide dynorphin A(1–13) on the CNS regulation of blood pressure and heart rate. Wistar rats, anesthetized with pentobarbital and halothane, received dynorphin A(1–13) microinjected into the anterior hypothalamus area (AHA), the posterior hypothalamic area (PHA), the nucleus tractus solitarius (NTS), or the lateral cerebral ventricle (ICV). Dynorphin A(1–13), 20 (12 nmol) or 30 μg ICV, produced significant (p < 0.05) reductions in blood pressure and heart rate. Naloxone, 50 μg/kg ICV, completely prevented the blood pressure response and significantly (p < 0.05) blunted the heart rate response to the highest dynorphin concentration, 30 μg ICV (18 nmol). Dynorphin A(1–13), 5 μg, in the NTS significantly (p < 0.05) decreased systolic and diastolic blood pressure and heart rate with the response being evident 10 min and persisting for 30 min after injection. In contrast, the same dose of dynorphin A(1–13) in the AHA produced an immediate, marked, and significant (p < 0.05) decrease in systolic and diastolic blood pressure and heart rate that attained its maximum 1–3 min and returned rapidly towards baseline levels. Dynorphin A(1–13), 5 or 10 μg in the posterior hypothalamic area, was not associated with any change in blood pressure or heart rate. Injection of the diluent at any site was not associated with any changes in blood pressure or heart rate. The maximum change in blood pressure with dynorphin was greater in the AHA than NTS, and the maximum change in heart rate was greater in the NTS than AHA. These data indicate a potential role for dynorphin as a modulator of the CNS regulation of blood pressure and cardiac rate, and this is mediated in part through different areas in the brain that maybe localized to the anterior hypothalamic area and nucleus tractus solitarius but not the posterior hypothalamic area.     

Effects of intracerebroventricularly injected glucagon-like peptide-1 on cardiovascular parameters; role of central cholinergic system and vasopressin

We aimed to investigate the effects of intracerebroventricularly (i.c.v.) injected glucagon-like peptide-1 (GLP-1) on blood pressure and heart rate, and whether central cholinergic system and vasopressinergic system play roles in these effects. Male Wistar albino rats were used throughout the experiments. Blood pressures and heart rates were observed before and for 30 min following drug injections. i.c.v. GLP-1 (100, 500 and 1000 ng/10 microl) caused a dose-dependent increase in both blood pressure and heart rate. Nicotinic receptor antagonist mecamylamine (25 microg/10 microl, i.c.v.) and muscarinic receptor antagonist atropine (5 microg/10 microl, i.c.v.) prevented the stimulating effect of GLP-1 on blood pressure. The effect of GLP-1 on heart rate was blocked only by mecamylamine. The V1 receptor antagonist of vasopressin (B-mercapto B, B-cyclopentamethylenepropionyl, O-Me-Tyr,Arg)-vasopressin (10 microg/kg), that was applied intraarterially, only prevented the effect of GLP-1 on blood pressure, but did not show any effect on heart rate. Our data indicate that i.c.v. GLP-1 increases blood pressure and heart rate, and stimulation of central nicotinic and partially muscarinic receptors and vasopressinergic system play a role in the effects of i.c.v. GLP-1 on blood pressure. The effect of GLP-1 on heart rate may be partially due to stimulation of central nicotinic receptors.     

A STUDY OF THE CIRCULATION,BLOOD PRESSURE,AND RESPIRATION OF SHARKS

The average branchial blood pressure in sand sharks was 32 mm. of mercury. The highest recorded in a resting animal was 43 mm. The average dorsal or systemic pressure was 23.3 mm.; highest 30 mm. The ratio of branchial to systemic pressure is about 3 to 2. The pressure in both systems keeps up well under trauma; but under experimental conditions, with or without manipulation of viscera, slowly falls after several hours. It rises with muscular effort, and a long rise usually follows stoppage of struggling. It rises when sodium carbonate is injected. The adrenalin curve resembles that in a mammal. Spontaneous rises and falls not attributable to the heart occur. Light in some animals increases blood pressure. It is suspected that these fishes have a vasomotor apparatus. The heart rate except after trauma is practically always the same as the respiration rate, and there is some reason for believing that the heart rate is determined by the respiration rate. When not in step with respiration, the heart is slower and often in a simple ratio with respiration. The heart is inhibited by all sorts of stimuli applied practically anywhere (except to the liver?). This effect is abolished by atropin. Respiration is faster in small animals and averages 24 per minute. Respiration slowly decreases in strength with little change in rate. Usually respiration ceases long before the heart stops.     

The Effects of a Therapy Dog on the Blood Pressure and Heart Rate of Older Residents in a Nursing Home

The aim of the present project was to investigate whether repeated visits by a therapy dog to nursing homes might affect the older residents’ systolic blood pressure and heart rate. A secondary aim was to investigate and compare effects (differences in responses) in older people with high and normal systolic blood pressure. The project consisted of two consecutive studies; the dog study (two researchers and a therapy dog with a handler visited the residents at three nursing homes, n = 13), and the control study (the two researchers alone visited the residents at three different nursing homes, n = 13). The studies were divided into three periods; period 1 (weeks 1–2), period 2 (weeks 3–4), and period 3 (weeks 5–6) and included two visits per week. The dog and her handler visited during periods 2 and 3 in the dog study. Participants’ heart rate and blood pressure were measured at 0 and 20 minutes at each visit. The data were analyzed using Friedman's two- way analysis of Variance by Rank with post-hoc analysis using Wilcoxon signed-rank tests with a Bonferroni correction, and also with the Mann-Whitney U test for independent samples. In the dog study, participants’ heart rate decreased significantly (p = 0.006) from period 1 to period 3. Participants with an initial systolic blood pressure ≥ 130 mmHg had a significant decrease in both systolic blood pressure (p = 0.009) and heart rate (p = 0.009). In the control study, participants’ heart rate and systolic blood pressure did not change significantly. The participants in the dog study had a significantly lower systolic blood pressure during period 3 (p = 0.016) compared with those in the control study. In conclusion, repeated visits by a therapy dog–handler team decreased the older adults’ heart rate, and for those with high initial systolic blood pressure, blood pressure also decreased. In addition, systolic blood pressure decreased significantly in the dog group when compared with the control group.     

Blood pressure and heart rate determination by radiotelemetry in mice

Mice are not commonly used in cardiovascular physiology, especially in space physiology because of methodological problems. The initial studies that have monitored arterial pressure and heart rate in mice used the tail cuff plethysmography method or classical catheterization techniques with a catheter liable to an external pressure transducer. But for long term arterial pressure measurements the studies have been facilitated by the development of radiotelemetry. This is a less constraining method as classical one allowing to monitor in continuous in freely moving animal blood pressure, heart rate and temperature. This technique allows to record these parameters thank to an implanted transmitter without physical connection with the monitoring system. The aim of this work was to valid the use of the radiotelemetry in mice to evaluate arterial blood pressure and heart rate during different stress conditions (but only control data are described in this paper).     

Femoral Arterial and Venous Catheterization for Blood Sampling,Drug Administration and Conscious Blood Pressure and Heart Rate Measurements

In multiple fields of study, access to the circulatory system in laboratory studies is necessary. Pharmacological studies in rats using chronically implanted catheters permit a researcher to effectively and humanely administer substances, perform repeated blood sampling and assists in conscious direct measurements of blood pressure and heart rate. Once the catheter is implanted long-term sampling is possible. Patency and catheter life depends on multiple factors including the lock solution used, flushing regimen and catheter material. This video will demonstrate the methodology of femoral artery and venous catheterization of the rat. In addition the video will demonstrate the use of the femoral venous and arterial catheters for blood sampling, drug administration and use of the arterial catheter in taking measurements of blood pressure and heart rate in a conscious freely-moving rat. A tether and harness attached to a swivel system will allow the animal to be housed and have samples taken by the researcher with minimal disruption to the animal. To maintain patency of the catheter, careful daily maintenance of the catheter is required using lock solution (100 U/ml heparinized saline), machine-ground blunt tip syringe needles and the use of syringe filters to minimize potential contamination. With careful aseptic surgical techniques, proper catheter materials and careful catheter maintenance techniques, it is possible to sustain patent catheters and healthy animals for long periods of time (several weeks).     

Effects of Amlodipine on Orcadian Rhythms in Blood Pressure,Heart Rate,and Motility: A Telemetric Study in Rats

In male Wistar rats [light (L): 07:00–19:00 h, dark (D): 19:00–07:00 h], the effects of the calcium channel blocker amlodipine (1, 3, 10 mg/kg i.p.) on blood pressure, heart rate, and motor activity were studied by telemetric monitoring. Amlodipine was injected either at 07:00 h or at 19:00 h. Systolic and diastolic blood pressure were dose-dependently decreased with more pronounced effects in the dark span, ED₅₀ values in D were about seven times lower than in L. In contrast, the dose-dependent increase in heart rate was more pronounced in L than in D. No significant effects of amlodipine were found on motor activity. The study gives evidence for a circadian phase-dependency in the cardiovascular effects amlodipine in rats.     

Circadian and short-term regulation of blood pressure and heart rate in transgenic mice with cardiac overexpression of the beta1-adrenoceptor

Congestive heart failure is associated with a loss of circadian and short-term variability in blood pressure and heart rate. In order to assess the contribution of elevated cardiac sympathetic activity to the disturbed cardiovascular regulation, we monitored blood pressure and heart rate in mice with cardiac overexpression of the β₁-adrenoceptor prior to the development of overt heart failure. Telemetry transmitters for continuous monitoring of blood pressure and heart rate were implanted in 8 to 9-week-old wildtype and transgenic mice, derived from crosses of heterozygous transgenic (line β₁TG4) and wildtype mice. Cardiovascular circadian patterns were analyzed under baseline conditions and during treatment with propranolol (500 mg/L in drinking water). Short-term variability was assessed by spectral analysis of beat-to-beat data sampled for 30 min at four circadian times. Transgenic β₁TG4 mice showed an increase in 24 h heart rate, while blood pressure was not different from wildtype controls. Circadian patterns in blood pressure and heart were preserved in β₁TG4 mice. Addition of propranolol to the animals' drinking water led to a reduction in heart rate and its 24 h variation in both strains of mice. Short-term variability in blood pressure was not different between wildtype and β₁TG4 mice, but heart rate variability in the transgenic animals showed a rightward shift of the high-frequency component in the nocturnal activity period, suggesting an increase in respiratory frequency. In conclusion, the present study shows that both the circadian and the short-term regulation of blood pressure and heart rate are largely preserved in young, nonfailing β₁-transgenic mice. This finding suggests that the loss of blood pressure and heart rate variability observed in human congestive heart failure cannot be attributed solely to sympathetic overactivity but reflects the loss of adrenergic responsiveness to changes in the activity of the autonomic nervous system.     

Contribution of social isolation, restraint, and hindlimb unloading to changes in hemodynamic parameters and motion activity in rats

The most accepted animal model for simulation of the physiological and morphological consequences of microgravity on the cardiovascular system is one of head-down hindlimb unloading. Experimental conditions surrounding this model include not only head-down tilting of rats, but also social and restraint stresses that have their own influences on cardiovascular system function. Here, we studied levels of spontaneous locomotor activity, blood pressure, and heart rate during 14 days under the following experimental conditions: cage control, social isolation in standard rat housing, social isolation in special cages for hindlimb unloading, horizontal attachment (restraint), and head-down hindlimb unloading. General activity and hemodynamic parameters were continuously monitored in conscious rats by telemetry. Heart rate and blood pressure were both evaluated during treadmill running to reveal cardiovascular deconditioning development as a result of unloading. The main findings of our work are that: social isolation and restraint induced persistent physical inactivity, while unloading in rats resulted in initial inactivity followed by normalization and increased locomotion after one week. Moreover, 14 days of hindlimb unloading showed significant elevation of blood pressure and slight elevation of heart rate. Hemodynamic changes in isolated and restrained rats largely reproduced the trends observed during unloading. Finally, we detected no augmentation of tachycardia during moderate exercise in rats after 14 days of unloading. Thus, we concluded that both social isolation and restraint, as an integral part of the model conditions, contribute essentially to cardiovascular reactions during head-down hindlimb unloading, compared to the little changes in the hydrostatic gradient.     

Integration of autonomic and local mechanisms in regulating cardiovascular responses to heating and cooling in a reptile (<Emphasis Type="Italic">Crocodylus porosus</Emphasis>)

Reptiles change heart rate and blood flow patterns in response to heating and cooling, thereby decreasing the behavioural cost of thermoregulation. We tested the hypothesis that locally produced vasoactive substances, nitric oxide and prostaglandins, mediate the cardiovascular response of reptiles to heat. Heart rate and blood pressure were measured in eight crocodiles (Crocodylus porosus) during heating and cooling and while sequentially inhibiting nitric-oxide synthase and cyclooxygenase enzymes. Heart rate and blood pressure were significantly higher during heating than during cooling in all treatments. Power spectral density of heart rate and blood pressure increased significantly during heating and cooling compared to the preceding period of thermal equilibrium. Spectral density of heart rate in the high frequency band (0.19–0.70 Hz) was significantly greater during cooling in the saline treatment compared to when nitric-oxide synthase and cyclooxygenase enzymes were inhibited. Cross spectral analysis showed that changes in blood pressure preceded heart rate changes at low frequencies (<0.1 Hz) only. We conclude that the autonomic nervous system controls heart rate independently from blood pressure at higher frequencies while blood pressure changes determine heart rate at lower frequencies. Nitric oxide and prostaglandins do not control the characteristic heart rate hysteresis response to heat in C. porosus, although nitric oxide was important in buffering blood pressure against changes in heart rate during cooling, and inhibition caused a compensatory decrease in parasympathetic stimulation of the heart.     

Hypotensive activity of TCV-116, a newly developed angiotensin II receptor antagonist, in spontaneously hypertensive rats.

TCV-116, a recently developed angiotensin II (Ang II) receptor antagonist, was administered orally (1 mg/kg per day) to 10-week-old spontaneously hypertensive rats (SHR) for 2 weeks. Blood pressure and plasma components of the renin-angiotensin-aldosterone system were determined in these rats. TCV-116 produced a marked reduction in blood pressure without altering heart rate. Whereas plasma renin concentration (PRC), angiotensin I (Ang I) and angiotensin II (Ang II) all were significantly increased, plasma aldosterone was decreased by approximately 70% compared with control animals. These results not only indicate therapeutic efficacy of this agent in the chronic treatment of human hypertension, but support also the concept that the renin-angiotensin system plays an important role in the control of blood pressure in this animal model of human essential hypertension.     

The effects of posture on blood pressure and heart rate in the three-toed sloth, Bradypus tridactylus

1. In unanesthetized, minimally restrained three-toed sloths, Bradypus tridactylus, the mean arterial pressure was 125/85 mmHg and the heart rate was 83.6 beats/min. There was no significant difference between these parameters whether the animal was erect or supine in the experimental chair. 2. Animals without any restraint had a mean blood pressure of 133/87 mmHg and a heart rate of 78.1 beats/min. There was no significant difference between these parameters whether the animal was seated or suspended from a horizontal bar and there was no significant difference between the minimally restrained and the unrestrained animals. 3. Tilting from the erect to the supine position produced large increases in blood pressure parameters, 37% in systolic and 21% in diastolic, reaching the maximum effect in a mean time of 38 sec. Tilting from the supine to the erect position caused even greater increases in pressure, 43% and 38% respectively, and reaching the maximum also in a mean time of 38 sec. 4. Tilting initially increased the heart rate, in going from erect to supine by 21% in 16 sec and from supine to erect by 23% in 20 sec. 5. In going from erect to supine there was a reflex bradycardia later, 15% below control level with a maximum at 40 sec, and to a lesser degree in going from supine to erect, 9% with maximum at 50 sec.     

Anti‐hypertensive treatment preserves appetite suppression while preventing cardiovascular adverse effects of tesofensine in rats

Objective:

Tesofensine is a novel triple monoamine reuptake inhibitor which is in development for the treatment of obesity. Preclinical and clinical data suggest that appetite suppression is an important mechanism by which tesofensine exerts its robust weight reducing effect. Notably, the strong hypophagic response to tesofensine treatment is demonstrated to be linked to central stimulation of noradrenergic and dopaminergic neurotransmission. The sympathomimetic mode of action of tesofensine may also associate with the elevated heart rate and blood pressure observed in clinical settings, and we therefore sought experimentally to address this issue.

Design and Methods:

The anorexigenic and cardiovascular effects of tesofensine were studied simultaneously in telemetrized conscious rats in a combined real‐time food intake and cardiovascular telemetry monitoring system.

Results:

Acute administration of tesofensine caused a dose‐dependent hypophagic effect as well as increased heart rate and blood pressure. Interestingly, combined treatment with metoprolol (b₁ adrenoceptor blocker, 10‐20 mg/kg, p.o.) fully prevented the cardiovascular sympathetic effects of tesofensine while leaving the robust inhibitory efficacy on food intake unaffected. Similarly, the angiotensin AT₁ receptor antagonist telmisartan (1.0‐3.0 mg/kg, p.o.) did not interfere with the anti‐obesity effects of tesofensine, however, telmisartan only partially reversed the increase in systolic blood pressure and had no effect on the elevated heart rate induced by tesofensine.

Conclusion:

These data suggests that tesofensine causes elevations in heart rate and blood pressure by increasing sympathetic activity, and that different adrenoceptor subtypes may be responsible for the anti‐obesity and cardiovascular effects of tesofensine.     

Digital heart rate monitor derived from the arterial pressure pulse

This monitor displays heart rate without the need for electrical contact with the experimental animal. The device uses a quartz pressure transducer connected to an arterial catheter and has a full scale accuracy of ± 3 beats min⁻¹; its range is 0–400 beats min⁻¹. There is an output voltage proportional to heart rate and internal calibration facilities are provided at 60 and 360 beats min⁻¹.     

Dynamical systems analysis of arterial blood pressure signals in relation to heart rate fluctuations in chick embryos

We attempted a new approach based on a modern dynamical system theory to reconstruct the arterial blood pressure signals in relation to heart rate fluctuations of developing chick embryos. The dynamical systems approach in general is to model a phenomenon that is presented by a single time series record and approximate the dynamical property (e.g. heart rate fluctuations) of a system based only on information contained in a single-variable (arterial blood pressure) of the system. The time-series data of the arterial blood pressure was reconstructed in 3-dimensional space to draw characteristic orbits. Since the reconstructed orbits of the blood pressure should retain information contained in the pressure signals, we attempted to derive instantaneous heart rate (IHR) from the reconstructed orbits. The derived IHR presenting HR fluctuations coincided well with the IHR obtained conventionally from the peak-to-peak time intervals of the maximum blood pressure. Movements of the reconstructed orbits of the arterial blood pressure in 3-dimensional space reflected HR fluctuations (i.e. transient decelerations and accelerations).     

A central link between angiotensinergic and cholinergic systems; role of vasopressin

Participation of central cholinergic system in the effects of intracerebroventricular (i.c.v.) injection of angiotensin II (Ang II) on blood pressure and heart rate was studied in conscious, freely moving rats. Ang II dose-dependently increased blood pressure and decreased heart rate. Both atropine and mecamylamine (i.c.v.) pretreatments prevented the cardiovascular effects of Ang II. Pretreatment with a vasopressin V1 antagonist also prevented the cardiovascular responses to Ang II. Our data suggest that the central pressor effect of Ang II is mediated in part by central acetylcholine via both muscarinic and nicotinic receptors, and vasopressin participates in this effect through V1 receptors.     

Effect of PGD2, PGE2, PGF2α and PGI2 on blood pressure,heart rate and plasma catecholamine responses to spinal cord stimulation in the rat

The following experiments were designed in order to examine the inter-relationships of various prostaglandins (PG's) and the adrenergic nervous system, in conjunction with blood pressure and heart rate responses, $\text{in vivo}$. Stimulation of the entire spinal cord (50v, 0.3–3 Hz, 1.0 msec) of the pithed rat increased blood pressure, heart rate and plasma epinephrine (EPI) and norepinephrine (NE) concentration (radioenzymatic-thin layer chromatographic assay). Infusion of PGE₂(10–30 μg/kg. min, i.v.) suppressed blood pressure and heart rate responses to spinal cord stimulation while plasma EPI (but not NE) was augmented over levels found in control animals. PGI₂ (0.03–3.0 μg/kg. min, i.v.) suppressed the blood pressure response to spinal cord stimulation without any effect on heart rate or the plasma catecholamine levels. PGE₂ and PGF_2α(10–30 μg/kg. min, i.v.) did not change the blood pressure, heart rate or plasma EPI and NE responses to the spinal cord stimulation although PGF_2α disclosed an overall vasopressor effect during the pre-stimulation period. At the pre-stimulation period it was also observed that PGE₂, PGF_2α and PGI₂, had a positive chronotropic effect on the heart rate, the cardiac accelerating effect of PGE₂ was not abolished by propanolol. These $\text{in vivo}$ studies suggest that in the rat, PGE₂ and PGI₂ modulate sympathetic responses, primarily by interaction with the post-synaptic elements — PGE₂ on both blood vessels and the heart and PGI₂ by acting principally on blood vessels.     

Factors affecting the heart activity and blood pressure of the swan mussel Anodonta cygnea.

1. The rate of heart beat increased with temperature and was three times as high in the active as in the inactive animal. 2. The rate of shell valve movement rose and the rate of heart beat fell when the foot was extended. 3. The rates of heart beat and shell valve movement decreased when the water was saturated with carbon dioxide. This heart response remained when the visceral ganglion was destroyed. 4. Ventricular contraction occurred simultaneously over the shole chamber. The passage of blood into the posterior aorta could be restricted by the protuberances on its wall. 5. Pericardial cavity pressure rose by about 5 cm H2O at shell valve adduction and 0-25--0-6 cm H2O at ventricular diastole. 6. Pulse pressure changes of 0-25--0-6 cm H2O occurred in the auricle and 1--3 cm H2O in the ventricle and anterior aorta.     

EVOLUTION OF CARDIOVASCULAR BARORECEPTOR CONTROL

During animal evolution the circulatory system has shown a progressive modification in structure, function and short-term control. Short-term circulatory control has evolved from the limitation of a rising blood pressure via a reflex bradycardia to bidirectional control of blood pressure by appropriate reflex changes in heart rate, vascular resistance and impedance. Relevant experimental data ranges from extensive in mammals to nugatory in invertebrates. Baroreceptor research in intervening animal groups is varied, being particularly sparse in birds. This research is reviewed. There are few interspecies comparisons of baroreceptor physiology. Available data is complicated by variation in the techniques employed for assessing baroreceptor function. In non-mammalian research the correlation of heart rate changes to pharmacologically induced changes in blood pressure predominate. In mammalian baroreceptor research methods based upon the ability of discrete baroreceptor sites to effect changes in the peripheral vasculature are more prevalent. All methods are susceptible to modification by other experimental variables, particularly the anaesthetic state of the animal. Available evidence shows a consistent response of a decreasing heart rate to baroreceptor loading throughout the vertebrates, with a progressive increase in the ability of the baroreceptors to change peripheral vascular resistance. These findings are consistent with the known, progressive trend from cholinergic to adrenergic control of the vascular system during evolution. Known baroreceptor sites appear to be located so as to protect the end-organ or-organs primarily at risk from inappropriate blood pressure changes; namely the gill vasculature in the fish, pulmonary circulation in the Amphibia and Reptilia, and the brain and heart in higher animal groups. It is postulated that the carotid sinus baroreceptors have developed in the Mammalia as a second functional baroreceptor site to provide extra protection against hypoperfusion of vital organs, particularly the heart and brain. In humans the dynamic aspects of cardiovascular carotid sinus control, particularly of skeletal muscle flow and integration with cardiopulmonary baroreceptors, may represent a specific response to the adoption of an upright stance. Extremes of environmental stress encountered in contemporary life may exceed the limitation of baroreceptor function in humans, as, for example, during gravitational loading particularly following periods of weightlessness and modification by endurance training.