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Biomedical subjects

P A Lynn

Publications and source records attributed to P A Lynn.

At least 19 recordsLinked to original sources
PubMed2001

Vagal and spinal mechanosensors in the rat stomach and colon have multiple receptive fields.

Mechano- and chemosensitive extrinsic primary afferents innervating the gastrointestinal tract convey important information regarding the state of ingested nutrients and specific motor patterns to the central nervous system via splanchnic and vagal nerves. Little is known about the organization of peripheral receptive sites of afferents and their correspondence to morphologically identified terminal structures. Mechano- and chemosensory characteristics and receptive fields of single vagal fibers innervating the stomach as well as lumbar splanchnic nerves innervating the distal colon were identified using an in vitro perifusion system. Twenty-three (17%) of one-hundred thirty-six vagal units identified were found to have multiple, punctate receptive fields, up to 35 mm apart, and were distributed throughout the stomach. Evidence was based on similarity of generated spike forms, occlusion, and latency determinations. Most responded with brief bursts of activity to mucosal stroking with von Frey hairs (10-200 mg) but not to stretch, and 32% responded to capsaicin (10(-5) M). They were classified as rapidly adapting mucosal receptors. Four (8%) of fifty-three single units recorded from the lumbar splanchnic nerve had more than one, punctate receptive field in the distal colon, up to 40 mm apart. They responded to blunt probing, particularly from the serosal side, and variously to chemical stimulation with 5-hydroxytryptamine and capsaicin. We conclude that a proportion of gastrointestinal mechanosensors has multiple receptive fields and suggest that they integrate mechanical and chemical information from an entire organ, constituting the generalists in visceral sensation.

Afferent Pathways↗
PubMed1999

In vitro recordings of afferent fibres with receptive fields in the serosa, muscle and mucosa of rat colon.

1. Colonic afferent fibres were recorded using a novel in vitro preparation. Fibres with endings in the colonic mucosa are described, along with those in muscle and serosa, and their responses to a range of mechanical and chemical luminal stimuli. 2. Mechanical stimuli were applied to the tissue, which included stretch, blunt probing of the mucosa and stroking of the mucosa with von Frey hairs (10-1000 mg). Chemical stimuli were applied into a ring that was placed over the mechanoreceptive field of the fibre; these were distilled water, 154 and 308 mM NaCl, 100 microM capsaicin, 50 mM HCl, and undiluted and 50% ferret bile. 3. Recordings were made from 52 fibres, 12 of which showed characteristics of having endings in the mucosa. Mucosal afferents were sensitive to a 10 mg von Frey hair and were generally chemosensitive to >= 1 chemical stimulus. 4. Ten fibres showed characteristics of having receptive fields in the muscular layer. These fibres responded readily to circumferential stretch, as well as to blunt probing. 5. Twenty-seven fibres showed characteristics of having endings in the serosal layer. They adapted rapidly to circumferential stretch and responded to blunt probing of the serosa. Fifteen of 19 serosal fibres tested also responded to luminal chemicals. 6. Three fibres were unresponsive to all mechanical stimuli but were recruited by chemical stimuli. 7. This is the first characterization of colonic afferent fibres using an in vitro method and the first documentation of afferent fibres with their endings in the mucosa of the colon. These fibres are likely to be important in aspects of colonic sensation and reflex control.

Animals↗
PubMed1998

Activation of non-adrenergic non-cholinergic inhibitory pathways by endogenous and exogenous tachykinins in the ferret lower oesophageal sphincter.

Repeated oesophageal acidification causes lower oesophageal sphincter (LOS) relaxation in the anaesthetized ferret which is mediated by a peripheral neurokinin (NK-1) receptor mechanism. Our aim in this study was to characterize neural pathways in the LOS activated by capsaicin and tachykinin receptor agonists in vitro. Circular muscle strips of LOS (two per animal) from a total of 24 ferrets were maintained in organ baths. Electrical field stimulation (EFS, 50 V, 5-50 Hz) caused frequency-dependent LOS relaxation which was abolished by tetrodotoxin (TTX; 10(-6) M: P < 0.001) and reduced by N(G)-nitro-L-arginine (L-NNA; 10(-4) M: P < 0.01). Substance P and [Sar9, Met (O2)11]-substance P (selective NK-1 agonist) caused dose-dependent relaxation, while the NK-2 receptor agonist [beta-Ala8]-NKA 4-10 evoked excitation. Capsaicin (10(-6) M) caused relaxation and desensitization that was overcome by long recovery periods and substance P dosing (10(-8) M). After pretreatment with the NK-1 receptor antagonist CP 99994 (10(-7) M), substance P (10(-8) M; P < 0.001) and capsaicin (10(-6) M: P < 0.01)-induced relaxations were reduced. In the presence of TTX (10(-6) M), excitation resulted in response to substance P (10(-8) M; P < 0.05) and [Sar9, Met (O2)11]-substance P (10(-8) M; P < 0.001), while the response to [beta-Ala8]-NKA 4-10 (10(-7) M) was unaffected. In the presence of L-NNA (10(-4) M), substance P and [Sar9, Met (O2)11]-substance P-induced relaxations were reduced (10(-8) M; P < 0.01), while the response to [beta-Ala8]-NKA 4-10 (10(-7) M) was unaffected. These results show that functional coupling between capsaicin-sensitive sensory neurones and NANC inhibitory neural pathways occurs via NK-1 receptors in the ferret LOS. NK-2 (and some NK-1) receptors activate non-neural excitatory mechanisms. Substance P and NK-1 receptors coupling sensory and NANC inhibitory neurones may be important in the reflex control of LOS motility.

Animals↗
PubMed1996

Relationship between total quality management, critical paths, and outcomes management.

Total quality management (TQM), clinical paths, and outcomes management are high-profile strategies in today's health care environment. Each strategy is distinct, yet there are interrelationships among them. TQM supports a customer-focused organizational culture, providing tools and techniques to identify and solve problems. Clinical paths are tools for enhancing patient care coordination and for identifying system-wide and patient population specific issues. Outcomes management is an integrated system for measuring the results in patient populations over time. There is a recent shift in outcomes measurement towards expanding both the nature of the outcomes examined and the timeframes in which they are studied.

Continuity of Patient Care↗
PubMed1984

A computerized neuromuscular blockade monitor with visual-display unit: a preliminary report.

A programmable microprocessor has been developed to control a nerve stimulator, to accept electromyographic potentials and to process them to produce derivatives related to neuromuscular function which can then be stored and displayed. Examples are given of its use to assess the physiological state of the neuromuscular junction and to quantify the degree of blockade in clinical situations.

Action Potentials↗
PubMed1981

Optimizing the acquisition and processing of surface electromyographic signals.

Electromyographic (EMG) signals, detected on the skin surface over active muscles, are being used increasingly for the control of prostheses and for investigating and retraining human movement. However, the statistical characteristics of the signal make it difficult toi achieve a processing delay of less than about 100 ms, which is marginal in some applications. Two techniques for reducing this delay are described: (i) signal pre-whitening, based upon digital autoregressive modelling or analogue filtering; an (ii) the use of a multiple electrode array. Successful discrimination between several states in a single muscle is possible in about 50 ms.

Action Potentials↗
PubMed1980

Assessment of recovery of arm control in hemiplegic stroke patients. 2. Comparison of arm function tests and pursuit tracking in relation to clinical recovery.

In a preliminary study, return of arm function in hemiplegic patients has been assessed for periods up to 64 weeks after stroke using two methods of testing. The first method concerns the performance of simple motor tasks involving the arm and hand. The second method is a pursuit tracking task using elbow movements. Patients were divided into two groups depending on whether they scored above 80% (Group I) or below 80% (Group II) on the first method at 16 weeks after stroke. When the two arm assessment methods were compared with clinical assessments for all the patients, general agreement was shown. Among Group I patients there was also significant agreement between the assessments; among Group II patients the agreement was poor. The two arm assessment methods, however, showed mutual agreement. In conclusion, both arm assessments provide a general prediction of the recovery of movement control of patients following stroke.

Aged↗