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Biomedical subjects

R Shannon

Publications and source records attributed to R Shannon.

At least 55 records · Page 3Linked to original sources

Heparin lock intravenous line. Use in newborn infants. A controlled trial.

The heparin lock technique has been available for parenteral access in older children and adults but has not yet been described for use in newborns. We randomized 39 newborns who needed parenteral medication in the intermediate care nursery to receive a heparin lock catheter (17) or an intravenous line kept patent by continuous low infusion rate (22). There were no differences between study groups with regard to birthweight, gestational age, or distribution of diagnoses. Infants in the heparin lock group were enrolled in the study on average 1 day longer than the continuous intravenous group (p less than 0.05). Subcutaneous infiltration occurred twice as frequently with the continuous intravenous line (p = 0.0015), and the life span was significantly less than heparin lock (1.0 +/- 0.5 days versus 2.1 +/- 1.0 days, p = 0.0003). Infants with continuous intravenous lines received approximately 20 ml/kg/day greater quantity of fluid (p less than 0.0001). There was no difference between groups with regard to mean heparin activity level. None of the infants developed hemorrhagic complications, thrombophlebitis, or documented nosocomial infection. Nurses significantly favored heparin locks over continuous intravenous lines for ease of use. The heparin lock technique is a safe and reasonable alternative to a continuous low infusion intravenous line for administering parenteral medications to intermediate care newborns.

Catheters, Indwelling↗

Prevalence, intensity and ocular manifestations of Onchocerca volvulus infection in Dimbelenge, Zaire.

In the zone of Dimbelenge (West Kasai region), Zaire we studied the prevalence, intensity and ocular manifestations of Onchocerca volvulus infection. We used the cluster sampling method to draw a sample of 327 people from a total population of 17,870. The prevalence of microfilaria in skin snips was 82.1% in people 20 years of age and older. The Community Microfilarial Load was 3.5. Blindness in 12 of 13 adults (92.3%) was caused by onchocerciasis. The rate of onchocercal blindness in the adult population was 5.1%. Twenty-four percent of adults had retinal changes as a result of onchocercal infection.

Adolescent↗

Respiratory pattern changes produced by intercostal muscle/rib vibration.

Large-amplitude vibration of the intercostal muscles/ribs has an inhibitory effect on inspiratory motor output. This effect has been attributed, in part, to the stimulation of intercostal muscle tendon organs. Intercostal muscle/rib vibration can also produce a decrease or increase in respiratory frequency. Studies were conducted 1) to determine whether, in addition to intercostal tendon organs, costovertebral joint mechanoreceptors (CVJR's) contribute to the inspiratory inhibitory effect of intercostal muscle/rib vibration (IMV) and 2) to explain the different respiratory frequency responses to IMV previously reported. Phrenic (C5) activity was monitored in paralyzed thoracotomized, artificially ventilated cats. Vibration (125 Hz) at amplitudes greater than 1,200 micron of one T6 intercostal space in decerebrated vagotomized rats reduced phrenic activity. This response was still present but weaker in some animals after denervation of the T6 intercostal muscles. Subsequent denervation of the T6 CVJR's by dorsal root sections eliminated this effect. Respiratory frequency decreased during simultaneous vibration (greater than 1,200 micron) of the T5 and T7 intercostal spaces in vagotomized cats. Respiratory frequency increased during IMV of two intercostal spaces (greater than 1,300 micron) in vagal intact cats. The use of different anesthetics (pentobarbital, allobarbital) did not alter these results. We conclude that CVJR's may contribute to the inhibitory effect of IMV on medullary inspiratory activity. The presence or absence of pulmonary vagal afferents can account for the different respiratory frequency responses to IMV, and different anesthetics did not influence these results.

Animals↗

Medullary neurons mediating the inhibition of inspiration by intercostal muscle tendon organs?

Studies were conducted to test the hypothesis that nonrespiratory-modulated units are last-order interneurons mediating the effects of intercostal muscle tendon organs on medullary inspiratory neuron activity. Vagotomized, anesthetized, or decerebrate cats were used. Results show the following. 1) Afferents from different receptor types (i.e., intercostal tendon organs and chest wall cutaneous receptors) that inhibit medullary inspiratory neuron activities evoke the same units. 2) Gastrocnemius muscle group I afferent fibers evoke some of the same units as intercostal afferents but do not alter respiratory activity. 3) The "pneumotaxic center" and laryngeal nerve afferents, which inhibit medullary inspiratory activity, evoke different medullary units than intercostal afferents. 4) Evoked units are not active in spontaneously breathing cats. Additional results suggest that a few respiratory neurons near the retrofacial nucleus may be involved in the mediation of the inspiratory inhibitory effects of intercostal tendon organs. These results do not establish the mechanism by which intercostal muscle tendon organs reduces medullary inspiratory activity.

Afferent Pathways↗

Expiratory neurons in the region of the retrofacial nucleus: inhibitory effects of intercostal tendon organs.

Intercostal muscle tendon organs have an inhibitory effect on the medullary neurons driving all inspiratory muscles, and on a subpopulation of medullary bulbospinal expiratory neurons. Results from this study showed that the activity of expiratory related neurons in the region of the retrofacial nucleus (Botzinger complex) decreases during tendon organ afferent stimulation; the response is similar to that of caudal bulbospinal expiratory neurons. We conclude that these expiratory neurons do not mediate the tendon organ inhibition of medullary inspiratory neuronal activity.

Action Potentials↗

Medullary inspiratory activity: influence of intercostal tendon organs and muscle spindle endings.

Studies were conducted to determine the effects of intercostal muscle spindle endings (MSEs) and tendon organs (TOs) on medullary inspiratory activity in decerebrate and allobarbital-anesthetized cats. Impeded muscle contractions, elicited by electrical stimulation of the peripheral cut end of the T6 ventral root, were used to stimulate external and internal intercostal TOs without MSEs. Impeded contractions of either the external or internal intercostal muscles reduced phrenic and medullary inspiratory neuronal activities. Vibration was used to selectively stimulate external or internal intercostal MSEs (90 and 40 micron amplitude, respectively). Selective stimulation of either external or internal intercostal MSEs did not change phrenic or medullary inspiratory neuronal activities. It is concluded that both external and internal intercostal TOs have a generalized inhibitory effect on medullary inspiratory activity and intercostal MSEs have no effect on medullary inspiratory activity.

Animals↗

Medullary expiratory activity: influence of intercostal tendon organs and muscle spindle endings.

Studies were conducted to determine the effects of intercostal muscle spindle endings (MSEs) and tendon organs (TOs) on medullary expiratory activity in decerebrate cats. Impeded intercostal muscle contractions, elicited by electrical stimulation of the peripheral cut end of the T6 ventral root, were used to stimulate intercostal TOs without MSEs. Impeded contractions of the intercostal muscles augmented expiratory laryngeal motoneuron activity, and either had no effect on or reduced the activity of bulbospinal expiratory neurons. Vibration was used to stimulate intercostal MSEs. Intercostal MSEs had no effect on medullary expiratory neuron activity. It is concluded that both external and internal intercostal TOs have an excitatory effect on expiratory laryngeal motoneuron activity and an inhibitory effect on a subpopulation of expiratory neurons driving intercostal and/or abdominal muscles, and intercostal MSEs have no direct influence on medullary expiratory activity.

Animals↗

Functional associations among simultaneously monitored lateral medullary respiratory neurons in the cat. I. Evidence for excitatory and inhibitory actions of inspiratory neurons.

Data were obtained from 45 anesthetized (Dial), paralyzed, artificially ventilated, bilaterally vagotomized cats. Arrays of extracellular electrodes were used to monitor simultaneously the activities of lateral medullary respiratory neurons located in the rostral and caudal regions of the ventral respiratory group. The average discharge rate as a function of time in the respiratory cycle was determined for each neuron and concurrent phrenic nerve activity. Most cells were tested for axonal projections to the spinal cord or the ipsilateral vagus nerve using antidromic stimulation techniques. Seven hundred and sixty-one pairs of ipsilateral respiratory neurons that contained at least one neuron whose maximum discharge rate occurred during the inspiratory phase were analyzed by cross-correlation of the simultaneously recorded spike trains. Twenty-three percent of the 410 pairs of inspiratory (I) neurons showed short time scale correlations indicative of functional association due to paucisynaptic connections or shared inputs. Eight per cent of the 351 pairs composed of an I cell and and expiratory (E) neuron were correlated. We found evidence for excitation of both bulbospinal I neurons and I cells that were not antidromically activated by stimulation of the spinal cord and vagus nerve (NAA neurons) by NAA I cells. We also obtained data suggesting inhibitory actions of cells whose maximum discharge rate occurred in the first half of the I phase (I-DEC neurons). These actions included inhibition of other I-DEC neurons, inhibition of cells whose greatest firing rate occurred in the last half of the I phase (I-AUG neurons), inhibition of E-DEC neurons, and inhibition of E-AUG cells. Sixty-two percent (31/50) of the correlations that could be interpreted as evidence for an excitatory or inhibitory paucisynaptic connection were detected in pairs composed of a caudal and a rostral ventral respiratory group neuron. Eighty-eight percent (14/16) of proposed intergroup excitatory connections involved a projection from the rostral neuron of the pair to the caudal cell, whereas 73% (11/15) of proposed inhibitory connections involved a caudal-to-rostral projection. These results support and suggest several hypotheses for mechanisms that may help to control the development of augmenting activity in and the timing of each phase of the respiratory cycle.

Animals↗

Functional associations among simultaneously monitored lateral medullary respiratory neurons in the cat. II. Evidence for inhibitory actions of expiratory neurons.

Arrays of extracellular electrodes were used to monitor simultaneously several (2-8) respiratory neurons in the lateral medulla of anesthetized, paralyzed, bilaterally vagotomized, artificially ventilated cats. Efferent phrenic nerve activity was also recorded. The average discharge rate as a function of time in the respiratory cycle was determined for each neuron. Most cells were tested for spinal or vagal axonal projections using antidromic stimulation methods. Cross-correlational methods were used to analyze spike trains of 480 cell pairs. Each pair included at least one neuron most active during the expiratory phase. All simultaneously recorded neurons were located in the same side of the brain stem. Twenty-six percent (33/129) of the expiratory (E) neuron pairs exhibited short time scale correlations indicative of paucisynaptic interactions or shared inputs, whereas 8% (27/351) of the pairs consisting of an E neuron and an inspiratory (I) cell were similarly correlated. Evidence for several inhibitory actions of E neurons was found: 1) inhibition of I neurons by E neurons with both decrementing (DEC) and augmenting (AUG) firing patterns; 2) inhibition of E-DEC and E-AUG neurons by E-DEC cells; 3) inhibition of E-DEC and E-AUG neurons by E-AUG neurons; and 4) inhibition of E-DEC neurons by tonic I-E phase-spanning cells. Because several cells were recorded simultaneously, direct evidence for concurrent parallel and serial inhibitory processes was also obtained. The results suggest and support several hypotheses for mechanisms that may help to generate and control the pattern and coordination of respiratory motoneuron activities.

Animals↗

Foramen magnum stenosis in homozygous achondroplasia.

A 4-month-old female with homozygous achondroplasia and daytime apnea was found to have a small foramen magnum by computerized tomography. Following suboccipital craniectomy and C1-C2 laminectomy respiratory problems did not recur during a 7 month post-operative period. We suggest that the respiratory problems in homozygous achondroplasia may be due to brainstem compression from an abnormally small foramen magnum.

Achondroplasia↗

Non-vagal reflex effects on medullary inspiratory neurons during inspiratory loading.

Studies were conducted to compare the first-breath responses of medullary Dorsal and Ventral Respiratory Group inspiratory (I) neurons to the mechanical loading (tracheal occlusion, TO) of inspiration in unanesthetized (decerebrate) and anesthetized (Dial) vagotomized cats, and to determine the sources of the sensory activity causing the changes in I-neuron activity. In decerebrate cats, TO resulted in a prolongation of the firing duration in 49% of the I-neurons. There was a delayed onset of firing in 7% of the I-neurons. The responses of I-neurons to TO in anesthetized cats were similar to the responses in decerebrate cats. Changes in I-neuron activity with TO were still present in cats with their cervical (C3-7) or thoracic (T1-9) dorsal roots cut, and absent when both cervical and thoracic dorsal roots were cut. The most probable sources of the cervical and thoracic afferent information altering medullary I-neuron activity during loading are the diaphragm and inspiratory intercostal muscles.

Anesthesia↗

Interactions between rostral pontine and ventral medullary respiratory neurons.

Lesioning studies have demonstrated that the respiratory rhythm is generated within the brain stem and that connections between the pons and the medulla must be intact for the generation of eupneic breathing in the decerebrate or anesthetized vagotomized cat. However, the nature of proposed functional connections between pontine and medullary respiratory neurons is not well understood. The possibility of interactions between respiratory neurons of the rostral pons (n. parabrachialis medialis, Kölliker-Fuse nucleus) and the ipsilateral ventral respiratory group (VRG; n. retroambigualis, n. ambiguus, retrofacial nucleus) was investigated because of neuroanatomical and electrophysiological evidence for such connections. Phrenic nerve activity and pontine and medullary single-unit respiratory related activities were recorded extracellularly in 44 decerebrate, vagotomized, paralyzed, and artificially ventilated cats. Cross-correlation analysis was employed to detect and evaluate functional associations of pairs of cells. Eighteen (7%) of the 255 pairs of respiratory neurons analyzed showed evidence of short time scale correlations indicative of a functional interaction. The interpretations of the detected correlations suggest that some cell pairs were correlated due to mono- or paucisynaptic connections, while others were correlated due to the influence of an unobserved shared input. The interpretations for 11 of the 15 cell pairs for which a monosynaptic connection may be postulated involve a projection from a tonically active respiratory neuron. Twelve of the 18 positive correlations involved neurons whose maximum rates of discharge occurred during different parts of the respiratory cycle. The results of this study provide the first evidence of functional connections among pontine and medullary respiratory neurons based on the evaluation of simultaneously recorded spike trains and suggest that the role of the rostral pontine respiratory neurons in the control of the respiratory rhythm may be mediated by various types of interactions. When considered with the results of other studies, our data suggest that monosynaptic interactions between VRG and rostral pontine respiratory neurons play a limited role in the control of the respiratory cycle in the decerebrate vagotomized cat. It is likely that the influence of the pons on ventral medullary neurons (and vice-versa) is also exerted via polysynaptic pathways and/or via brain stem neurons not sampled in this study.

Animals↗

Cryptosporidiosis in an urban community.

Over three months Cryptosporidium oocysts were identified in faecal samples from 43 (5%) of 867 patients presenting to their general practitioners with gastrointestinal symptoms. Cryptosporidium was the second most common enteric pathogen identified. Of the 867 patients, 329 were children aged under 5, of whom 24 (7%) excreted Cryptosporidium. A characteristic clinical presentation of infection with Cryptosporidium was recognised--namely, mild gastroenteritis with four to six watery, mucoid, and offensive motions a day, which lasted for one to two weeks. The source of infection was not identified, but direct contact with farm animals was not a feature and no association with a common water supply could be established.

Adolescent↗

A national task analysis of infection control practitioners, 1982. Part One: methodology and demography.

A task analysis survey was conducted in 1982 by the Certification Board of Infection Control ( CBIC ) to determine the tasks performed by ICPs and the knowledge and abilities needed to perform these tasks. Data were obtained from 473 (78.8%) respondents to a nationwide mail survey of 600 ICPs . The respondents represent a randomized, stratified sample of ICPs in various types of U.S. acute care hospitals ranging in size from fewer than 50 beds to more than 500 beds. The results of the survey were used, in part, to develop the Infection Control Certification Examination, offered for the first time on November 19, 1983. According to the survey results, the modal or typical ICP is a white woman between the ages of 31 and 50 years using the title of infection control nurse. She has been employed full time for 2 to 10 years in infection control practice in a Joint Commission on Accreditation of Hospitals (JCAH)--accredited community acute care hospital having 301 to 500 beds. She is working at the supervisory level, is on the nursing department payroll, votes as a member of the hospital's infection control committee, and received her last degree or diploma more than 15 years ago.

Adult↗

A national task analysis of infection control practitioners, 1982. Part Two: Tasks, knowledge, and abilities for practice.

Respondents (N = 473) from a randomized stratified sample (N = 600) of U.S. hospital ICPs in a national survey sponsored by the Certification Board of Infection Control were asked to rate specific task, knowledge, and ability statements related to infection control for frequency and importance. The questions included 175 items, of which 99 were for specific tasks and 76 were for knowledge and abilities for practice. Areas covered included patient care practices, infectious diseases, epidemiology and statistics, microbiologic practices, sterilization and disinfection, education, employee health services, and management and communications. A "profile respondent" group (N = 317) was defined as persons most likely to be practicing the full scope of infection control practice and was used to identify key tasks, knowledge, and abilities for practice. Results showed that patient care practices (i.e., suctioning, dressing changes, and catheterization) were rarely performed. The development of infection control policies and procedures were key tasks. Knowledge of microbiology and infectious diseases in order to interpret laboratory reports and other patient data was rated as essential; however, few respondents actually performed laboratory procedures. Epidemiologic principles were frequently used for surveillance and problem investigation. Although presentation of epidemiologic data was rated as important, analytic statistics were rarely used. Assessment of educational needs and teaching were large components of ICPs' activities.

Certification↗

A national task analysis of infection control practitioners, 1982. Part Three: The relationship between hospital size and tasks performed.

One aspect of the Certification Board of Infection Control's (CBIC) task analysis survey was to determine those tasks done most frequently and considered most important by ICPs. A randomized stratified sample of ICPs was taken from U.S. hospitals of various bed-size categories. There were 473 responses (78.8%) from a targeted sample of 600 ICPs. Statistical analyses were done to find if a relationship existed between hospital size and the tasks performed. The frequency of performance and importance of the majority of infection control tasks studied were found to vary in relation to hospital size. Some tasks were found to be both important and frequently performed by the majority of ICPs in all hospital bed-size categories. These included performing and reporting epidemiologic surveillance, educating personnel, developing infection control policies and procedures, and consulting with hospital personnel. Other tasks were found to be relatively less important and infrequently performed by the majority of ICPs in all hospital bed-size categories. These included performing bedside patient care procedures, recommending specific antimicrobial therapy, and using statistical methods. The greatest differences in the performance of tasks were found in the subsample of the ICPs from hospitals with less than or equal to 100 beds.

Communicable Disease Control↗

Intercostal and abdominal muscle afferent influence on pneumotaxic center respiratory neurons.

The experiments were performed on mid-collicular decerebrated, vagotomized, paralyzed, artificially ventilated cats. Phrenic (PA) and pneumotaxic center (PC) respiratory neuron (extracellular) activities were recorded during electrical stimulation of intercostal nerve proprioceptor afferents (external, internal or lateral intercostal nerves). Intercostal nerve stimulation (INS) of sufficient intensity to reduce PA also reduced the activity of phasic PC I-neurons and the I-modulated portion of tonic firing I-neurons. The stimulus-response latency for the reduction in PA was always shorter than the latency for the reduction in I-neuron activity. Baseline tonic activity (during E-phase) was unaffected by INS in most tonic I-neurons. The predominant response of PC IE- and E-neurons to INS was augmentation of their activity. Stimulus-response latency studies showed that the increase in IE- and E-neuron activity occurred after the decrease in PA. It is concluded that: (1) the reduced PC I-neuron activity following INS is due primarily to disfacilitation resulting probably from decreased activity in medullary I-neurons that drive the PC I-neurons, (2) PC IE- and E-neurons are not the primary neurons mediating the inspiratory inhibitory effects of intercostal and abdominal muscle proprioceptors on medullary I drive, (3) the changes in PC IE- and E-neuron activity is not due secondarily to changes in DRG and VRG IE- or E-neuron activities, and (4) the reflex effects are due to stimulation of low threshold Group I afferent fibers.

Abdomen↗