Search PubMed⌕ Search

Biomedical subjects

D M Harris

Publications and source records attributed to D M Harris.

At least 73 records · Page 4Linked to original sources
PubMed1980

The role of extracellular products of Pseudomonas aeruginosa in the pathogenesis of infection; an experimental study employing intraperitoneal diffusion chambers.

Exotoxin A is currently thought to be the principal lethal factor in experimental Pseudomonas aeruginosa infection. This belief is founded on the demonstrable toxicity of purified preparations, and on detection of the toxin in the tissues of burned animals infected with Ps. aeruginosa. In the present study, strains of Ps. aeruginosa differing in their ability to produce exotoxin A and other virulence factors in vitro were enclosed within vinyl diffusion chambers and implanted i.p. into mice. Strains which produced much exotoxin A in vitro were not significantly more virulent when enclosed in chambers than strains which produced little exotoxin. In all cases, diffusion of exotoxin A produced within the chamber was impeded by dense adherence of the omentum. It is concluded that, although absorption of exotoxin A may be an important factor in causing death after infected burns, it is not necessarily equally significant in other types of infection.

Animals↗
PubMed1979

Action potential suppresion, tuning curves and thresholds: comparison with single fiber data.

The collection of compound action potential (AP) threshold curves and their use to define the sensitivity of individual animals are described. Forward masking AP tuning curves (APTC) have also been collected in the chinchilla. Characteristics of APTCs are compared with single fiber frequency-threshold curves (FTC) in the same group of animals. The two sets of data are quite similar when the probe frequency used to collect the APTC is equated with a fiber's characteristic frequency (CF). The major difference is that APTCs are usually broader than FTCs. A paradigm utilizing two maskers in a forward masking situation, developed to study psychophysical unmasking [19,37], has been modified for measuring AP suppression. AP suppression areas are described as similar to single fiber two-tone suppression areas when probe frequency and CF are above 3 kHz. Relationships among single fiber, AP and psychophysical thresholds, tuning curves and suppression areas are discussed.

Action Potentials↗
PubMed1979

Forward masking of auditory nerve fiber responses.

1. Responses of single fibers were obtained from the auditory nerve of chinchillas. Tone-burst stimuli consisted of a masking stimulus followed by a probe stimulus. Forward masking of a fiber's response is defined as a reduction in the magnitude of the probe-evoked response caused by the addition of the masking stimulus. 2. The recovery of probe response magnitude as a function of the time interval between masker offset and probe onset (delta T) follows an exponential time course. A relationship between the time course or magnitude of poststimulus recovery and the characteristic frequency (CF) of a fiber was not detected. 3. The iso-forward masking contour near the threshold of the masking effect across masker frequencies approximates a fiber's frequency threshold curve (FTC). In other words, forward masking tuning curves are essentially the same as frequency threshold curves. 4. The frequency dependence of forward masking is compared to that of two-tone suppression. Tonal stimuli outside the boundaries of a fiber's FTC that produce two-tone suppression are ineffective forward maskers. Certain frequency/intensity combinations within the FTC may produce both suppression and forward masking and tones within the remaining area of the FTC produce no suppression but are effective forward maskers. 5. Both the time course and the magnitude of the forward masking effect are dependent on the discharge rate evoked by the masker regardless of the masker's absolute level or spectral content. An increase in masker-evoked excitation causes an increase in time constant and a greater reduction in probe response magnitude, rd. The function relating rd to masker level parallels the firing rate/masker level function up to 40 dB above response threshold. 6. A decrease in masker duration from 100 ms leads to a decrease in both rd and the time constant of recovery. There is no significant difference between the 100 and 200 ms duration conditions. 7. Forward masking in single fibers is related to the period of poststimulus recovery of spontaneous activity, a component of a fiber's response pattern to the masker, and this component is tentatively identified as a period of recovery from short-term adaptation.

Adaptation, Physiological↗
PubMed1975

Pseudomonas aeruginosa infection in hospital: a comparison between 'infective' and 'environmental' strains.

One hundred and fifty-six infections or episodes of infection associated with Pseudomonas aeruginosa in six hospitals over 14 months were investigated. Pyocine typing and serotyping suggested that 145 distinct episodes had occurred, caused by 78 different strains. During this period 15 distinct strains were isolated from the environment at one of the hospitals; 12 of these were apparently unassociated with infection in the same ward during the period, and 4 were of types not encountered in infective processes at any hospital. There appeared to be a rather higher proportion of unclassifiable pyocine inhibition patterns among the environmental strains; in general these strains also produced smaller amounts of haemolysin. If failure to produce haemolysin in vitro is correlated with lack of virulence in vivo, this may partially explain the sporadic nature of hospital infection with Ps. aeruginosa, despite the prevalence of strains of this species in the environment.

Child↗
PubMed1975

The microbial flora of the vagina and its relationship to bacteriuria in diabetic and non-diabetic women.

The vaginal and urinary flora have been studied in 57 diabetic and 33 non-diabetic patients. In both populations, no correlation was found between urogenital symptoms and colonisation of the vagina. There was no greater prevalence of potentially pathogenic organisms in diabetic patients, even when control was poor. However, although not statistically significant, group B streptococci were isolated more frequently from poorly controlled diabetics. Bacteriuria was not significantly more common in diabetics. Gram-negative bacilli were found in the vagina significantly more often in bacteriuric patients; the prevalence of such organisms being four-fold greater after the menopause.

Adult↗
PubMed1975

Meningitis caused by Pseudomonas maltophilia.

A case of meningitis caused by Pseudomonas maltophilia is described, which was unusual in that it appeared to lack the predisposing factors commonly associated with this organism. Attention is drawn to the difficulties which may be encountered in the identification of Ps. maltophilia.

Aged↗
PubMed1975

Effect of population and health care environment on hospital utilization.

A path analytic test of a causal model linking a county population's demographic and socioeconomic characteristics, the way its hospital services are delivered, and the health care resources available to it with its rate of short-term general hospital utilization is performed using data from 56 New York State counties. The results generally support the model and point to the central importance of an area's hospital bed supply for an understanding of its hospitalization rates. The path analysis reveals the patterns of direct and indirect effects of population and health care environment variables on hospitalization rates and supports the contention that health care environment characteristics intervene between population and hospitalization. The practical implications of these results for those in the health care field are discussed.

Delivery of Health Care↗