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At least 91 records · Page 5Linked to original sources
PubMed1984

[The effect of thoracic pressoreceptors on heart rate in man].

Sinus arrhythmia (SA) is a physiological event related to the respiratory activity. The aim of this study was to find a relation between SA and different deep breathings. A transductor monitored the chest respiratory movements and a cardiotachometer calculated and plotted the instantaneous heart rate, synchronously during different breathing efforts. In 10 normal subjects a good linear correlation was found between the breathing depth and SA quantifying the relation between the chest receptor activity and SA also with limited chest expansion.

Adult↗
PubMed1968

Pharmacology of pH effects on carotid body chemoreceptors in vitro.

1. The carotid body and the carotid nerve were removed from anaesthetized cats and placed in a small Perspex channel through which Locke solution (at various pH values and usually equilibrated with 50% O(2) in N(2)) was allowed to flow. The glomus was immersed in the flowing solution while the nerve was lifted into oil covering the saline. Sensory discharges were recorded from the nerve and their frequency was used as an index of receptor activity. At times, a small segment of carotid artery, containing pressoreceptor endings, was removed together with the glomus. In this case, pressoreceptor discharges were recorded from the nerve.2. The amplitude of either chemo- or pressoreceptor discharges was not changed by strong acid solutions. Acid decreased the frequency of the baroreceptor discharges only when pH fell to less than 4.0. Solutions at low pH increased the chemosensory discharge, but acid depressed the increased chemoreceptor discharge elicited by KCl. These experiments indicated that H(+) ions probably acted as membrane ;stabilizers' without depolarizing either the nerve fibres or endings.3. Acid solutions increased the action of acetylcholine chloride (AChCl) (100-200 mug) on chemoreceptors. This effect probably was due either to inactivation of tissue cholinesterase or to enhanced sensitivity of the sensory endings to ACh.4. Choline chloride (10(-3)M), which favours ACh synthesis, protected the preparation against decay during prolonged experimentation. Hemicholinium-3 (HC-3), which blocks ACh synthesis in low concentrations (10(-5)M), depressed the chemosensory response to acid and to hypoxia when such stimuli were applied repeatedly. This concentration of HC-3 did not change effects of applied ACh.5. Substances which affect ACh release markedly changed the chemoreceptor discharge increase induced by acidity and other forms of stimulation. In the absence of Ca(2+), acid, anoxia, and interruption of flow provoked receptor depression while receptor excitation induced by ACh and KCl persisted. All stimuli excited and showed increased effectiveness as the Ca(2+) concentration was raised, but their effects declined as Ca(2+) was increased above normal values. Mg(2+) ions depressed the chemoreceptor effects induced by all these stimuli. The action of Mg(2+) was not due entirely to nerve ending block. Morphine sulphate (which decreases ACh release in other structures) also depressed the receptor response to acid and flow interruption.6. Cholinergic blocking agents such as mecamylamine, hexamethonium, atropine, dihydro-beta-erithroidine (DHE), HC-3 (10(-4)M), choline and acetylcholine (in combination with choline) depressed the effects of acid and ACh on the chemoreceptors. The effect induced by interruption of flow was depressed only by mecamylamine and DHE.7. Agents which affect the fate of released ACh, such as acetylcholinesterase and eserine salicylate, did not affect clearly the response of chemoreceptors to acid.8. The results suggest that acid stimulates chemoreceptor fibres through an indirect mechanism, viz. through increased release and/or decreased destruction of a presynaptic transmitter from the glomus cell. This transmitter is probably ACh (see following paper, Eyzaguirre & Zapata, 1968).

Acetylcholine↗
PubMed1988

Multi- and single-fibre mesenteric and renal sympathetic responses to chemical stimulation of intestinal receptors in cats.

1. In cats anaesthetized with alpha-chloralose and artificially respired, stimulation of intestinal receptors with bradykinin caused greater reflex excitation of mesenteric than of renal efferent multifibre nerve activity and significant pressor responses. 2. Activity of all nerve bundles used in this study was inhibited by stimulation of pressoreceptors. Increases in systemic arterial pressure caused inhibition of activity of renal nerves which was significantly greater than that of mesenteric nerves. 3. Spinal transection caused significant decreases in tonic renal nerve activity without altering the ongoing discharge rate of mesenteric nerves. Stimulation of intestinal receptors in spinal cats still caused significant increases is discharge of mesenteric and renal nerves, indicating that this reflex contains a spinal component. 4. Recordings of activity of individual fibres within mesenteric (21) and renal (23) nerves provided information regarding the basis for the multifibre responses to stimulation of intestinal receptors. The same proportion of fibres from both nerves was excited, but the increase in activity of mesenteric fibres was significantly greater than that of renal fibres. 5. Mesenteric fibres could be classified into two groups, based on their sensitivity to pressoreceptor influences. Fibres that exhibited pressoreceptor-independent discharge had the greatest responses to stimulation of intestinal receptors. 6. Following spinal transection the majority of mesenteric fibres continued to fire, whereas most renal fibres became quiescent. 7. The non-uniform pattern of neuronal excitation to chemical stimulation of intestinal receptors was manifest after spinal transection, demonstrating that exclusively spinal pathways can mediate this differential response pattern. 8. These results support the hypothesis that viscero-sympathetic reflexes may be organized to cause preferential excitation of neural activity directed to the organ from which the reflex originates.

Action Potentials↗
PubMed1993

Postural control and age.

We quantified the effect of vision, pressoreceptor function and proprioception on the postural stability at different ages. Altogether 212 healthy volunteers (ages from 6 to 90 years) were examined by using a computerised force platform. The sway velocity (SV) was measured with eyes open and eyes closed during quiet stance on a bare platform and a foam plastic covered surface. In addition, to study the proprioceptive system, pseudorandom vibration perturbation was applied on the calf muscles. The SV showed a U-shaped curve: the children and the oldest swayed most. Equilibrium was most stable around 50 years. The visual system was of most importance for balance control in the old. The children were sensitive of pressoreceptor and proprioceptive perturbation, indicating the importance of these systems for their postural control.

Adult↗
PubMed1990

Postural control in elderly subjects.

The postural stability of 23 subjects aged 85 years or over was studied with a force platform. The sensory function of the lower limbs was disturbed with small vibrators placed on both calf muscles and/or by placing the subjects on a platform covered with foam plastic. When compared with a group (n = 100) of 50-60-year-old subjects, the elderly subjects had significantly higher sway velocities even during nonperturbed conditions. The perturbation of muscle spindles with vibration and/or pressoreceptor function with foam plastic did not increase the postural instability of the elderly subjects. Visual deprivation had a significant effect on postural stability, and the visual influx contributed about 50% of the postural stability. Postural control is reduced as a result of loss of sensory cues of pressoreceptors and also deterioration in function of stretch reflexes initiated from muscle spindles. The very elderly seem to rely on visual control of posture; this is slow, which can be one reason for susceptibility to falls.

Age Factors↗
PubMed1988

Characteristics of ongoing and reflex discharge of single splenic and renal sympathetic postganglionic fibres in cats.

1. Electrical discharge of thirty-nine single splenic and renal postganglionic nerve fibres was recorded in artificially respired, chloralose-anaesthetized cats. 2. Ongoing discharge rates, averaged over 10 s periods, did not differ between renal and splenic fibres. All neurones of both groups had irregular discharge frequencies. 3. Half of the splenic population and all renal fibres had cardiac-related discharge patterns. Of those tested for respiratory-related firing, 30% of the splenic fibres and 69% of the renal fibres exhibited this pattern. 4. Firing of splenic fibres was less inhibited than that of renal fibres by stimulation of pressoreceptors with phenylephrine-induced increases in blood pressure. Firing of splenic fibres also was less excited than that of renal fibres by unloading pressoreceptors with depressor doses of sodium nitroprusside. 5. Chemical stimulation of splenic afferent nerves with bradykinin consistently elicited greater increases in splenic than renal nerve discharge by causing large increases in firing of all splenic fibres and smaller excitatory responses in 75% of the renal fibres. 6. Application of bradykinin to the intestinal serosa produced greater increases in renal than splenic nerve discharge by consistently causing increased firing of renal fibres and by causing excitation, inhibition, or no change in splenic fibre discharge. 7. Responses of splenic and renal fibres to stimulation of splenic and intestinal afferent nerves after spinal cord transection were similar to those responses elicited when the neuraxis was intact. 8. In conclusion, the differential reflex responses of splenic and renal neuronal populations can be due to the heterogeneity or to the intensity of responses within a neuronal population.

Action Potentials↗
PubMedDate not supplied

Respiratory responses following lifting the legs in normal man.

This study reinvestigates the problems of ventilatory drive linked to the rate of CO2 flow to the pulmonary circulation, and the respiratory response to the changes in cardiac output, which are both known to be capable of matching ventilation to perfusion so that the arterial blood remains isocapnic. Taking advantage of the known influence of posture on venous return, 21 healthy humans were subjected to the experimental maneuver which consisted of lifting the legs from the lower to uppermost position. This maneuver increased venous return to the right heart by bringing stagnant blood from the legs carrying more CO2. In all, 34 tests were performed. The results showed a rapid increase in minute ventilation of 12.3 percent. There were also increases in end-tidal CO2, CO2 production and cardiac output. All of the changes were fully reversible and reproducible. The results support the concept that a higher gain CO2 receptor system is operating during increased CO2 delivery to the lungs via the circulation. The possibility of reflex hyperpnea elicited from pressoreceptors localized in pulmonary circulation is also considered.

Adult↗
PubMed1997

Modeling arterial hypotension during hemodialysis.

A mathematical model of the hemodynamic response to hemodialysis is presented. This model includes the dynamics of sodium, urea, and potassium in the intracellular and extracellular pools; fluid balance equations for the intracellular, interstitial, and plasma volumes; systemic and pulmonary hemodynamics; and the action of several short-term arterial pressure control mechanisms. The control mechanisms are triggered by information coming from both arterial and cardiopulmonary pressoreceptors, and they work on systemic arterial resistance, heart rate, and systemic venous unstressed volume. Moreover, the model hypothesizes that decreasing left atrial pressure below a given threshold causes a paradoxical withdrawal of the sympathetic drive and a consequent vasodepressor syncope. The model is used to simulate the pattern of the main hemodynamic quantities (systemic arterial pressure, heart rate, total systemic resistance, and cardiac output) during hemodialysis in several groups of patients (both hypotension resistant and hypotension prone) whose data were drawn from the clinical literature. The simulation results point out that the model is able to reproduce a variety of different conditions, including no hypotension, moderate hypotension, and severe hypotension with ultimate vasodepressor syncope, by adjusting a few parameters with clear physiological meanings. Hypotension is principally imputed to a loss of the sympathetic mechanisms working on systemic resistance and to an impairment of vascular refilling at the capillary wall. The results suggest that hypotension during hemodialysis is a complex phenomenon that depends on the superimposition of several concomitant factors working together that can lead to a variety of distinct individual patterns.

Baroreflex↗
PubMed1980

A fixed charge system as a formal model for the behaviour of smooth muscles and the heart.

An extension of the theory of the "fixed charge" controlled "membrane oscillator" is used for simulation of a variety of excitability phenomena in nerves, presso-receptors, smooth muscle and the heart. A central issue is the prediction of water movements across the cell membrane resulting in "swelling" and "shrinkage". The presented "electrohydraulic excitability analog" (EHEA) deals particularly with the generation of action potentials, volume-pressure changes and contractility in response to externally applied mechanical stimuli, i.e. the EHEA is applied as a pressoreceptor analog. The agreement between the theoretical model results and some experimental physiological observations cited from the literature is quite satisfactory.

Animals↗
PubMed1980

Distortion of maximal elevator activity by unilateral premature tooth contact.

In four subjects the electrical activity in the anterior and posterior temporal and masseter muscles during maximal bite was recorded bilaterally with and without premature unilateral contact. Muscle activity was measured as the average level and the peak of the mean voltage with layers of strips of 0.05, 0.10, 0.15 and 2.0 mm, placed between first molars either on the left or the right side, and compared with the level of activity with undistrubed occlusion. Unilateral premature contact caused a significant asymmetry of action in all muscles under study with stronger activity ipsilaterally. With increasing thickness of the overlay the mean voltage decreased in parallel on both sides. We suggest that the asymmetry was caused by larger spindle afferent activity on the ipsilateral as compared to the contralateral side, and that the all-over decrease of muscle activity was due to a gradual reduction of activity from periodontal pressoreceptors.

Adult↗
PubMed1992

Occlusal control of mandibular elevator muscles.

Occlusal stability and mandibular elevator muscle function was studied in 25 women (20-30 yr of age). They had 27-32 fully erupted teeth with few treated occlusal surfaces, and craniomandibular function including mandibular mobility was normal. The aim was to analyze the influence of natural patterns of occlusal contact on electromyographic activity, unaffected by pain and functional disorders. Occlusal stability was assessed in the intercuspal and in lateral contact positions as the number of teeth with physical contact and the number of opposing pairs of teeth in contact. Electromyographic activity was recorded by surface electrodes over anterior and posterior temporalis and masseter muscles. In general, positive correlations were found between occlusal stability in intercuspal position and moderate to strong static and dynamic contractions, most significant in masseter muscles, indicating that forceful contraction of these muscles implies stable occlusion. Systematically, the duration of activity during chewing was negatively correlated with occlusal stability in the intercuspal position, most pronounced in working-side muscles. This pointed to shorter contractions with stable occlusion and is interpreted as the result of less need for stabilizing activity. It is concluded, that the correlations between occlusal stability and elevator muscle function are probably based on feedback mechanisms from periodontal pressoreceptors.

Adult↗
PubMed1993

Mandibular elevator muscles: physiology, action, and effect of dental occlusion.

In spite of differences in embryologic origin, central nervous organization, and muscle fiber distribution, the physiology and action of mandibular elevator muscles are comparable to those of skeletal muscles of the limbs, back, and shoulder. They also share the same age-, sex-, and activity-related variations of muscular strength. With respect to pathogenesis, the type of muscular performance associated with the development of fatigue, discomfort, and pain in mandibular elevators seems to be influenced by the dental occlusion. Clinical research comparing the extent of occlusal contact in patients and controls as well as epidemiologic studies have shown reduced occlusal support to be a risk factor in the development of craniomandibular disorders. In healthy subjects with full natural dentition, occlusal support in the intercuspal position generally amounts to 12-14 pairs of contacting teeth, with predominance of contact on first and second molars. The extent of occlusal contact clearly affects electric muscle activity, bite force, jaw movements, and masticatory efficiency. Neurophysiologic evidence of receptor activity and reflex interaction with the basic motor programs of craniomandibular muscles tends to indicate that the peripheral occlusal control of the elevator muscles is provided by feedback from periodontal pressoreceptors. With stable intercuspal support, especially from posterior teeth, elevator muscles are activated strongly during biting and chewing with a high degree of force and masticatory efficiency, and with relatively short contractions, allowing for pauses. These variables of muscle contraction seem, in general, to strengthen the muscles and prevent discomfort. Therefore, occlusal stability keeps the muscles fit, and enables the masticatory system to meet its functional demands.

Dental Occlusion↗
PubMed1962

Distribution of nerve endings in the pulmonary artery of the cat.

The density distribution of nerve endings in the wall of the extrapulmonary portion of the cat's pulmonary artery was studied in serial sections after staining by a supravital methylene blue procedure. The greatest concentration of endings occurred at the bifurcation, in the adjacent parts of the pulmonary artery, and in its right and left main branches. The morphology and distribution of these endings is consistent with a pressoreceptor function.

Animals↗