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Biomedical subjects

R W Linden

Publications and source records attributed to R W Linden.

36 records · Page 2Linked to original sources
PubMed1990

Superior vena cava Doppler flow velocity patterns in pericardial disease.

Doppler superior vena cava (SVC) flow patterns were studied in 34 patients with pericardial disease and in 8 normal adults; the pulse transducer on the echocardiographic instrument was used for respiratory monitoring, rather than a separate nasal thermistor-based device. First expiratory SVC diastolic flow velocities (Dfe) did not differ in normal subjects and patients with hemodynamically insignificant pericardial effusions (23 +/- 3 cm/s and 29 +/- 13 cm/s, difference not significant). Dfe were less than 15 cm/s only in the 14 patients with cardiac tamponade (9 +/- 3 cm/s, p less than 0.01). A ratio of systolic to diastolic flow velocity less than or equal to 1.1 in the first expiratory beat distinguished constrictive pericarditis from all other groups (p less than 0.01), although not from restrictive cardiomyopathy. Expiratory ablation of diastolic SVC flow mimicking cardiac tamponade was not observed in constrictive pericarditis. Respiratory variation in SVC flow velocities was slight in normal subjects and patients with constrictive pericarditis, increased in patients with hemodynamically insignificant pericardial effusions (p less than 0.01) and greatest in patients with cardiac tamponade (p less than 0.01). Quantitative analysis of SVC flow velocity patterns is a useful addition to the echocardiographic evaluation of pericardial disease.

Adult↗
PubMed1989

The effect of tooth extraction on periodontal ligament mechanoreceptors represented in the mesencephalic nucleus of the cat.

When a force is applied to a tooth, mechanoreceptors in the periodontal ligament are stimulated. When teeth are extracted the remnants of the periodontal ligament break down and disappear, but it is not known what happens to the mechanoreceptor neurones that innervated it. The present study seeks to determine the effect of tooth extraction on the population of periodontal ligament mechanoreceptor neurones represented in the mesencephalic nucleus of the fifth cranial nerve. The incisor and canine teeth were extracted from adult cats; terminal experiments were performed between 7.5 months and 2 yr later. Recordings were made in the mesencephalic nucleus with microelectrodes, and neurones were identified in the inferior alveolar nerve that previously innervated the periodontal ligament of one of the extracted mandibular teeth. The majority of these neurones responded only to electrical stimuli applied to the edentulous ridge of the mandible in the area where the incisor or canine teeth had previously been. It was not possible to stimulate them mechanically, despite the use of large forces. A small number had reinnervated new soft-tissue sites. They could be mechanically stimulated and were found adjacent to the area in which the mandibular incisor and canine teeth had been. Thus the population of periodontal ligament mechanoreceptor neurones represented in the mesencephalic nucleus do not all degenerate after tooth extraction. As the majority of those still present do not appear to reinnervate new tissues in which they can be mechanically stimulated, it is unlikely that they have any functional role after tooth loss.

Animals↗
PubMed1989

The effect of vibration on the discharge of periodontal ligament mechanoreceptors to controlled loading of the cat canine tooth.

This study observes the maximum 1:1 following frequencies of these mechanoreceptors, as well as their response characteristics before and after vibratory stimuli. Mechanical stimuli were applied to the tip of the crown of the left mandibular canine tooth in cats anaesthetized with alpha-chloralose while recordings were made from functionally single fibres teased from the inferior alveolar nerve. Vibratory stimuli were applied at various frequencies and durations at twice the threshold to that stimulus. Controlled ramp-plateau forces were applied before and after the period of vibration. A temporary rise in the receptor discharge was recorded and the threshold to ramp-plateau stimuli fell to about one-third of its original value. The increased post-vibration response was dependent on the frequency and duration of the stimulus. It is suggested that vibration has some temporary effect on the receptor environment.

Action Potentials↗
PubMed1989

Distribution of mesencephalic nucleus and trigeminal ganglion mechanoreceptors in the periodontal ligament of the cat.

1. In anaesthetized cats recordings have been made in the mesencephalic nucleus of the fifth cranial nerve and the trigeminal ganglion from neurones that respond when forces are applied to the mandibular canine tooth. The site of the mechanoreceptors in the periodontal ligament and their distribution around the tooth root have been determined. 2. Receptors with their cell bodies in the mesencephalic nucleus were found to be situated in the periodontal ligament in a discrete area intermediate between the fulcrum and apex of the tooth, while those in the trigeminal ganglion were situated in the whole area of the periodontal ligament between the fulcrum and apex of the tooth. 3. All of the located mechanoreceptors responded maximally when that part of the ligament in which they lay was put under tension. 4. The directional sensitivities of the mechanoreceptors suggested that there was an uneven distribution around the tooth root of receptors with cell bodies in the mesencephalic nucleus. In contrast mechanoreceptors with cell bodies in the trigeminal ganglion were distributed more equally around the tooth root. The rationale for the differences requires further investigation.

Action Potentials↗
PubMed1989

The structure of physiologically located periodontal ligament mechanoreceptors of the cat canine tooth.

A correlative morphological study was carried out on physiologically located periodontal mechanoreceptors in anaesthetised cats. Three periodontal mechanoreceptors were electrophysiologically identified from functionally single fibres teased from the inferior alveolar nerve. One receptor was studied by recording in the mesencephalic nucleus. The four receptors were located by punctate stimuli in the labial aspect of the periodontal ligament of the left mandibular canine tooth in three cats. The receptors were within the intermediate to rapidly adapting part of the range of adaptation rates with conduction velocities of 39.6 ms-1 +/- 4.7 ms-1 and were typical of those recorded in previous studies. The receptor loci were marked and these regions were studied in silver-stained sections and ultrastructurally. Under each ink-marked region Ruffini terminals and smaller terminals resembling free nerve endings were observed. The Ruffini terminals were unencapsulated and the majority had diameters of 2-3 microns. The terminals were observed near the junction of the inner (cemental) and middle zones of the periodontal ligament with the axons running from the alveolar aspect. The results support the view that periodontal mechanoreceptors, even those with more rapidly adapting properties, are Ruffini terminals.

Action Potentials↗
PubMed1988

The effect of rate of force application on the threshold of periodontal ligament mechanoreceptors in the cat canine tooth.

Mechanical stimuli in the form of ramp-plateau forces were applied to the tip of the crown of the left mandibular canine tooth in cats anaesthetized with alpha-chloralose. Electrophysiological recordings were made from functionally single fibres teased from the inferior alveolar nerve. The force threshold was determined for 34 periodontal ligament mechanoreceptors at different controlled rates of force application. Force threshold was dependent on the rate of force application to the crown tip. Rate sensitivity was present for all receptors across the range from rapidly to slowly adapting; the degree of rate sensitivity was graded according to the adaptation rate of the receptor. The results suggest that the velocity of mechanical stimulus application to teeth needs to be considered in studies involving periodontal mechanoreceptor responses and their reflexes.

Animals↗
PubMed1988

The response characteristics of mechanoreceptors related to their position in the cat canine periodontal ligament.

The relation between threshold, adaptation properties and position of these receptors was studied in anaesthetized cats. Electrophysiological recordings were made from functionally single fibres teased from the inferior alveolar nerve as forces were applied to the tip of the left mandibular canine tooth. Receptors were located within the periodontal ligament by paring away the overlying bone. Threshold and adaptation properties were related to the receptor position relative to the fulcrum and apex of the tooth. These results support the hypothesis that there is only one type of periodontal-ligament mechanoreceptor, and that their response characteristics depend on position.

Adaptation, Physiological↗
PubMed1987

The possible role of periodontal mechanoreceptors in the control of parotid secretion in man.

In man, parotid flow has been recorded bilaterally using modified Lashley cups in response to mechanical stimulation of the teeth. The stimulus was defined and controlled by monitoring the rectified and integrated masseter electromyographic activity (e.m.g.) during repeated clenching on closely fitting bite-blocks placed between the molar teeth. Unilateral clenching on a bite-block resulted in a greater flow from the ipsilateral than the contralateral gland, and both exceeded the control values. There was also a positive correlation between the masseter e.m.g. activity and ipsilateral parotid flow. Parotid flow was also recorded before and during local anaesthesia of various intra-oral branches of the trigeminal nerve. Anaesthesia of two to three inputs always produced significant reductions in ipsilateral flow, but anaesthesia of a single input was not always effective. These results provide evidence in support of the hypothesis that intra-oral mechanoreceptors, particularly periodontal mechanoreceptors, are involved in the masticatory-salivary reflex.

Anesthesia, Dental↗
PubMed1985

The possible relation between mastication and parotid secretion in the rabbit.

Salivary flow has been recorded from conscious rabbits during 1 min periods whilst continuously chewing standard laboratory dry pellets or pieces of carrot and, in some animals, a mash of pellets with water. Flow was measured using contact drop recorders or a continuous flow recorder via Polythene tubes permanently inserted into one or both parotid ducts. Large variations in flow were obtained with unilateral recordings particularly during dry pellet chewing. Bilateral recordings showed that the flow was always greater on one side than on the other and that dominant secretion alternated from side to side in an apparently random manner. Rabbits chew unilaterally. Videotaped recordings of chewing movements showed that the greater secretion was always produced on the chewing side. To test the possibility that drying of the oral mucosa, or the prolonged hardness of the pellets may result in higher flow rates in animals with cannulated ducts than would normally be seen in intact animals, water was injected downstream into the mouth through a third cannula. This was inserted in an anterograde direction in the parotid duct on one side. Significant reductions in flow were recorded during dry pellet eating, but not during carrot eating. When animals were fed a soft pellet mash, salivary flow was significantly lower than with dry pellets. Recordings have been made from strain gauges attached to the ascending ramus of the mandible. Previous findings that dry pellets produce greater strain than carrots have been confirmed. It has also been shown that less strain is produced with soft pellet mash. The strain gauge data suggested that a relation exists between masticatory force and parotid salivary flow. The results are compatible with the hypothesis that intra-oral mechanoreceptors may be involved in a masticatory-salivary reflex.

Animals↗
PubMed1982

The effects of sympathetic trunk stimulation on the position and mobility of the canine tooth of the cat.

The effects of cervical sympathetic trunk stimulation on the position of the maxillary canine tooth and its movements in response to mechanical loading were studied using an ultrasonic transit time technique. Stimulation of the ipsilateral sympathetic trunk for 10-60s and frequencies between 1 and 20 Hz caused both longitudinal and transverse movements of the tooth. Bilateral carotid occlusion caused negligible movements in either direction. When a controlled force was applied in the palatal direction, sympathetic stimulation caused a labial shift of the tip of the tooth and usually an increase in the load-induced palatal displacement; i.e. the mobility of the tooth was increased and appeared to be dependent on the amount of labial shift of the tooth. It is concluded that interference with the vascular component has little, if any, direct effect on the tooth mobility.

Animals↗
PubMed1982

Effects of sympathetic nerve stimulation on intra-oral mechanoreceptor activity in the cat.

1. Micro-electrode recordings were made from intra-oral mechanoreceptor neurones in the trigeminal ganglion and mesencephalic nucleus of the fifth nerve in the cat.2. The effect of cervical sympathetic trunk stimulation on the discharge of the mechanoreceptors to a controlled force was observed.3. Almost half of the mechanoreceptor neurones studied were modulated by sympathetic stimulation. Sympathetic stimulation both decreased the impulse frequency to a controlled force application and raised the threshold in these receptors. The remainder were unaffected by sympathetic stimulation.4. In previous studies involving recordings from either the trigeminal ganglion or mesencephalic nucleus no spontaneously active slowly adapting intra-oral mechanoreceptors have been observed, yet in peripheral alveolar nerve studies many workers have reported spontaneously discharging neurones. In the present study spontaneous activity has been recorded from intra-oral mechanoreceptors both in the trigeminal ganglion and in the mesencephalic nucleus after cutting the cervical sympathetic trunk. The spontaneous activity could be abolished in all cases but one, by sympathetic stimulation. It is suggested that reported spontaneous activity from intra-oral mechanoreceptors could be due to cutting the peripheral nerve and therefore the sympathetic supply, thus removing an inhibitory influence from the sensory unit. The means by which the sympathetic supply inhibits the sensory unit has not been resolved.

Action Potentials↗
PubMed1982

The distribution of mechanoreceptors in the periodontal ligament of the mandibular canine tooth of the cat.

1. Periodontal mechanoreceptor activity has been recorded from fibres in the inferior alveolar nerve. 2. A method has been developed for punctate and electrical stimulation of the periodontal ligament mechanoreceptors through a thin layer of bone overlying the labial aspect of the left mandibular canine tooth root. 3. The distribution of periodontal mechanoreceptors in the labial aspect of the left mandibular canine tooth has been described. 4. All receptors located responded maximally when that part of the ligament in which they lay was in tension. 5. It is suggested that there may be only one type of mechanoreceptor and that the rate of adaptation is dependent on the location of the receptor within the periodontal tissues.

Animals↗
PubMed1978

Properties of intraoral mechanoreceptors represented in the mesencephalic nucleus of the fifth nerve in the cat.

1. The activity of neurones in the mesencephalic nucleus of the fifth nerve that respond to forces applied to the teeth were recorded using extracellular microelectrodes; the properties of these neurones have been studied. 2. Electrophysiological evidence consistent with the view that primary afferent intraoral mechanoreceptor fibres have their cell bodies in the trigeminal mesencephalic nucleus is presented. 3. Two groups of intraoral mechanoreceptor neurones were found. The first group, the periodontal mechanoreceptor neurones, which have been described by previous workers, responded to electrical stimulation of the ipsilateral superior or inferior dental nerves and to forces applied to single teeth in the ipsilateral maxilla or mandible respectively. The response characteristics of the mesencephalic periodontal mechanoreceptor neurones differed in two respects from those observed in peripheral nerve studies by previous workers: (a) there were no spontaneously active neurones, and (b) there were no neurones that responded for over 10 sec to a sustained application of a suprathreshold mechanical stimulus to the teeth. The second group, not described before, responded to electrical stimulation of the ipsilateral palatine nerve, and responded to forces applied to all the teeth in the maxillary arch, both contralateral and ipsilateral as well as to forces applied to the nose and hard palate. The site of these receptors is unknown. They have been termed 'Type P' intraoral mechanoreceptors. 4. The recording sites of both the periodontal and Type P mechanoreceptor neurones were all situated in the caudal part of the mesencephalic nucleus of the fifth nerve.

Action Potentials↗