Cardiovascular control from cardiac and pulmonary vascular receptors.

What is the topic of this review? The purpose of this review is to summarize present knowledge of the function of the afferent nerves arising from the heart and the coronary and pulmonary arteries. Although there is abundant evidence that atrial receptor stimulation influences heart rate and urine flow, with little or no effect elsewhere, and that ventricular receptors are strongly excited only by chemical stimuli, there is still the erroneous belief that they act as a homogeneous group causing cardiovascular depression. What advances does it highlight? Coronary receptors deserve to be recognized as a potentially important additional group of baroreceptors.

Reflexes from pulmonary arterial baroreceptors in dogs: interaction with carotid sinus baroreceptors.

In contrast to the reflex vasodilatation occurring in response to stimulation of baroreceptors in the aortic arch, carotid sinuses and coronary arteries, stimulation of receptors in the wall of pulmonary arteries results in reflex systemic vasoconstriction. It is rare for interventions to activate only one reflexogenic region, therefore we investigated how these two types of reflexes interact. In anaesthetized dogs connected to cardiopulmonary bypass, reflexogenic areas of the carotid sinuses, aortic arch and coronary arteries and the pulmonary artery were subjected to independently controlled pressures.

Carotid baroreflex testing using the neck collar device.

A neck chamber device for stimulation of carotid sinus baroreceptors by changing carotid transmural pressure was first described in 1957 by Ernsting and Parry and, with several modifications, has been extensively used in a number of physiological and clinical studies. This article outlines the evolution of neck chamber devices and describes some of the advantages and limitations of the technique. We also describe the responses in healthy subjects and the changes observed in patients with some disorders affecting the autonomic nervous system.

Head-up sleeping improves orthostatic tolerance in patients with syncope.

Objectives: This study was designed to examine the effect of head-up sleeping as a treatment for vasovagal syncope in otherwise healthy patients. Treatment for syncope is difficult. Pharmacological treatments have potential side effects and, although other non-pharmacological treatments such as salt and fluid loading often help, in some cases they may be ineffective or unsuitable.

Adaptation and mal-adaptation to ambient hypoxia; Andean, Ethiopian and Himalayan patterns.

The study of the biology of evolution has been confined to laboratories and model organisms. However, controlled laboratory conditions are unlikely to model variations in environments that influence selection in wild populations. Thus, the study of "fitness" for survival and the genetics that influence this are best carried out in the field and in matching environments.

Cerebrovascular responses to hypoxia and hypocapnia in Ethiopian high altitude dwellers.

Background And Purpose: Cerebrovascular responses to hypoxia and hypocapnia in Peruvian altitude dwellers are impaired. This could contribute to the high incidence of altitude-related illness in Andeans. Ethiopian high altitude dwellers may show a different pattern of adaptation to high altitude.

Enhanced vascular responses to hypocapnia in neurally mediated syncope.

Objective: The susceptibility to suffer neurally mediated syncope and loss of consciousness varies markedly. In addition to vasodilatation and bradycardia, hyperventilation precedes loss of consciousness. The resultant hypocapnia causes cerebral vasoconstriction and peripheral vasodilatation.

Cardiovascular adjustments for life at high altitude.

The effects of hypobaric hypoxia in visitors depend not only on the actual elevation but also on the rate of ascent. There are increases in sympathetic activity resulting in increases in systemic vascular resistance, blood pressure and heart rate. Pulmonary vasoconstriction leads to pulmonary hypertension, particularly during exercise.

Daytime variability in carotid baroreflex function in healthy human subjects.

Variability of blood pressure is limited by arterial baroreceptors, yet blood pressure still shows circadian changes. This study was undertaken to examine if the responses to the carotid baroreflex also change throughout the day. Responses of cardiac interval (RR), mean arterial pressure (MAP) and vascular resistance (VR) to carotid baroreflex stimulation and inhibition using pressures and suction applied to a neck chamber, were measured in 14 healthy, normotensive subjects.

The autonomic nervous system at high altitude.

The effects of hypobaric hypoxia in visitors depend not only on the actual elevation but also on the rate of ascent. Sympathetic activity increases and there are increases in blood pressure and heart rate. Pulmonary vasoconstriction leads to pulmonary hypertension, particularly during exercise.

Autonomic regulation during orthostatic stress in highlanders: comparison with sea-level residents.

This report is a comparison of orthostatic tolerance and autonomic function in three groups of high-altitude dwellers: Andeans with and without chronic mountain sickness (CMS) and healthy Ethiopians. Results are compared with those from healthy sea-level residents. The aim was to determine whether different high-altitude populations adapted differently to the prevailing hypobaric hypoxia.

Cerebral vasodilatation to exogenous NO is a measure of fitness for life at altitude.

Background And Purpose: Andean highlanders, unlike Ethiopians, develop chronic mountain sickness (CMS), a maladaptation to their native land. Ambient hypoxia induces NO-mediated vasodilatation. Fitness for life at altitude might be revealed by cerebrovascular responses to NO.

Carotid baroreflex regulation of vascular resistance in high-altitude Andean natives with and without chronic mountain sickness.

We investigated carotid baroreflex control of vascular resistance in two groups of high-altitude natives: healthy subjects (HA) and a group with chronic mountain sickness (CMS), a maladaptation condition characterized by high haematocrit values and symptoms attributable to chronic hypoxia. Eleven HA controls and 11 CMS patients underwent baroreflex testing, using the neck collar method in which the pressure distending the carotid baroreceptors was changed by applying pressures of -40 to +60 mmHg to the chamber. Responses of forearm vascular resistance were assessed from changes in the quotient of blood pressure divided by brachial artery blood velocity.

Phase of the menstrual cycle does not affect orthostatic tolerance in healthy women.

Women of child-bearing age have a lower orthostatic tolerance (OT) than older women or men, and women suffering from frequent syncopal episodes often comment that their symptoms occur at certain times of the menstrual cycle. However, it is not known whether, in asymptomatic women, OT varies at different phases of the menstrual cycle. We studied 8 healthy asymptomatic women aged 26.

Water drinking improves orthostatic tolerance in patients with posturally related syncope.

Water drinking improves OT (orthostatic tolerance) in healthy volunteers; however, responses to water in patients with PRS (posturally related syncope) are unknown. Therefore the aim of the present study was to examine whether water would improve OT in patients with PRS. In a randomized controlled cross-over fashion, nine patients with PRS ingested 500 ml and 50 ml (control) of water 15 min before tilting on two separate days.

Increased postural sway in control subjects with poor orthostatic tolerance.

Objectives: This study sought to evaluate postural sway in control subjects with good and poor orthostatic tolerance (OT).

Background: Some asymptomatic volunteers, when subjected to a progressive orthostatic stress test, show early presyncope. We hypothesized that normal subjects with poor OT do not usually faint because they adopt a strategy of increased lower limb movement, which helps maintain venous return.

Prolonged latency in the baroreflex mediated vascular resistance response in subjects with postural related syncope.

In addition to the gain, the delay of the baroreflex response plays an important role in the maintenance of cardiovascular system stability. Additionally when postural changes induce sudden drops in blood pressure, a delayed response may fail to maintain sufficient cerebral perfusion pressure. We tested the hypothesis that the delay of the carotid baroreceptor reflex is impaired in subjects with poor orthostatic tolerance.

Effects of dietary salt loading on the responses of isolated rat mesenteric arteries to leptin.

Background: Leptin induces relaxation of vascular smooth muscle through an endothelium-dependent release of nitric oxide (EDNO) and administration of a high-salt diet reduces the relaxation of vessels to EDNO. We would, therefore, predict that salt loading would reduce the leptin-induced dilatation. However, in salt-loaded animals the relaxation to acetylcholine is maintained through an endothelial-dependent hypopolarizing factor instead of EDNO.

R-R interval-blood pressure interaction in subjects with different tolerances to orthostatic stress.

In addition to the gain, the time delay in the input-output response in a feedback system is crucial for the maintenance of its stability. Patients with posturally related (vasovagal) syncope have inadequate control of blood pressure and one possible explanation for this could be prolonged latency of the baroreflex. We studied 14 patients with histories of syncope and poor orthostatic tolerance (assessed by a progressive orthostatic stress test) and 16 healthy controls.

Pathophysiology of syncope.

Syncope or near-syncope is a not uncommon effect of gravitational or other stresses and it occurs when cerebral blood flow falls to below about half the normal value. It is not necessarily abnormal, and individuals who are usually asymptomatic show the same reaction if a stress is sufficiently great to result in hypotension. Blood pressure is regulated mainly by baroreceptor reflexes by their control of vascular resistance and heart rate.

Contrasting effects of carbohydrate and water on blood pressure responses to postural maneuvers in patients with posturally related (vasovagal) syncope.

Crouching then standing induces large changes in arterial blood pressure. Ingestion of carbohydrate and water are known to have contrasting effects on cardiovascular control in patients with various forms of autonomic dysfunction. We tested the hypothesis that, in patients with attacks of posturally related (neurogenic or vasovagal) syncope, postural maneuvers would cause greater changes in blood pressure than in normal controls and that they would be affected differently by carbohydrate and water.

Salt supplementation improves orthostatic cerebral and peripheral vascular control in patients with syncope.

Salt supplementation improves orthostatic tolerance in many patients with posturally related syncope (PRS). This study aimed to examine whether in those patients who responded to salt loading there was also evidence of improved cerebral autoregulation and more powerful peripheral vasoconstriction during orthostasis. Eleven PRS patients were studied before and after ingestion of 100 mmol/d slow sodium for 2 months.