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Biomedical subjects

W Johnson

Publications and source records attributed to W Johnson.

At least 145 records · Page 8Linked to original sources
PubMed1989

Perinatal transmission of the human immunodeficiency virus.

Vertical transmission of human immunodeficiency virus (HIV) from an infected mother to her fetus or infant can occur in utero and probably during labor and delivery. Transmission via breast milk has also been documented. Because of limitations of conventional HIV testing in infants, it is difficult to determine the rate of transmission from an infected mother to her fetus or infant, but it is probably between 20% and 60%, depending on the mother's health status. Perinatal HIV infection is a significant problem particularly in "Pattern II" countries, where HIV is spread primarily by heterosexual contact. In "Pattern I" countries, where HIV predominantly affects homosexual and bisexual men, children are infected by mothers who acquired the infection through I.V. drug abuse or sexual contact with an infected partner.

Acquired Immunodeficiency Syndrome↗
PubMed1989

Unilateral external fixation. Methods to increase and reduce frame stiffness.

Unilateral configurations with stiffness characteristics similar to those of the most rigid one- and two-plane bilateral constructs are easily built. Mechanically, most effective were two-plane unilateral frames with a short bone-rod distance. But single- and double-bar anterior unilateral frames had the best combination of clinical and mechanical features. To put gradual frame builddown on a rational basis, a sequence of stepwise frame reduction was developed. This sequence leads from the most rigid unilateral constructs to frames that allow almost complete force transmission across the fracture site while still providing adequate protection against the prevailing sagittal bending moments.

Elasticity↗
PubMed1988

The effect of variation of residual ridge angle on partial denture abutment tooth movement.

Using a laboratory model simulating a free-end saddle partial denture situation, the effect of variation of the angulation of the crest of the residual alveolar ridge to the horizontal on movement of the abutment tooth and saddle was observed. It was found that the inclination of the residual ridge affected the direction and magnitude of abutment tooth movement. The direction of abutment tooth movement was not related to the position of the occlusal rest. However, the magnitude of saddle and abutment tooth movement is affected by the design of the clasp used.

Alveolar Process↗
PubMed1988

Eighteen months' experience with a manual polybrene crossmatch in a large hospital transfusion laboratory.

For 18 months in this laboratory the manual polybrene technique (MP) has been used as the only crossmatching procedure preceded or accompanied by an antibody screen comprising two-stage papain and LISS antiglobulin techniques. There were 17,161 requests representing 43,006 blood units crossmatched and 20,841 units transfused. Non-specific reactivity with the MP required use of an antiglobulin crossmatch in approximately 0.2% of patient samples. Heparin in excess of 20 IU/ml reduced polybrene aggregation of red cells necessitating an antiglobulin crossmatch for 2 patients. Of 288 antibodies detected 20 reacted exclusively by MP compared with 18 by the papain procedure. The data supported the use of MP as an alternative to enzymes in antibody screening protocols. The polybrene technique was found to be a superior abbreviated crossmatch compared with the immediate spin technique and was applicable to all patients including those with known antibodies.

Blood Grouping and Crossmatching↗
PubMed1988

Virulence conversion of Legionella pneumophila: a one-way phenomenon.

Previous investigations have shown that Legionella pneumophila converts from virulence to avirulence after passage on supplemented Mueller-Hinton (SMH) agar and may convert back to virulence after passage in guinea pigs. However, there is no additional information concerning the apparent interconversion of virulent and avirulent derivatives of L. pneumophila cultures. We investigated the stability of a parental virulent culture and its avirulent derivatives and the growth and viability of these cultures on charcoal-yeast extract (CYE) and SMH agars. Avirulent derivatives of a highly virulent L. pneumophila culture were obtained by passage of the virulent parent culture on SMH agar. The only time a virulent L. pneumophila culture was recoverable from an avirulent culture was when the avirulent culture was derived from a saline suspension of a virulent culture which had been passaged only five times on SMH agar. When an avirulent culture was derived from a virulent culture passaged 25 times on SMH agar or from an isolated colony which grew on a SMH agar plate, we were unable to recover a virulent culture after successive passage through guinea pigs. These results suggest that the conversion process which occurs between virulent and avirulent forms of L. pneumophila is a one-way phenomenon from virulence to avirulence and that stable avirulent derivatives can be isolated. Furthermore, our findings suggest that SMH agar acts as a selective medium for the growth of avirulent L. pneumophila, and growth on SMH agar may be a phenotypic marker for avirulence. Virulent cells, although unable to grow on SMH agar, may remain viable for several passages on SMH agar and propagate when inoculated into guinea pigs.

Animals↗
PubMed1988

Immunologic diversity among serogroup 1 Legionella pneumophila urinary antigens demonstrated by monoclonal antibody enzyme-linked immunosorbent assays.

We tested urine specimens from 222 patients with serogroup 1 Legionella pneumophila pneumonia in two enzyme-linked immunosorbent assays (ELISAs) which used different monoclonal antibodies (A and B) as detector antibodies. Of 171 specimens which contained enough antigen to be detected in the ELISAs, 169 reacted in only one of the two assays. A total of 25 patients whose infections were acquired in any of three Indianapolis hospitals excreted antigen reactive with monoclonal antibody B, but 18 patients who were treated for infections acquired elsewhere reacted with monoclonal antibody A. The urinary antigen ELISA reactivity patterns correlated with the reactivity patterns of L. pneumophila isolates when a separate panel of seven monoclonal antibodies was used. The isolate patterns, in turn, correlated well with environmental isolate patterns from two of the hospitals with nosocomial cases. We conclude that at least two different epitopes exist on the antigen molecules in urine from patients with serogroup 1 L. pneumophila pneumonia and that the subtyping of urinary antigens can be useful epidemiologically.

Animals↗
PubMed1987

Automated computation of relative flow resistance using a pulsed Doppler flowmeter.

Use of a pulsed Doppler flowmeter to assess changes in blood flow resistance often requires a laborious series of calculations, and full characterization of resistance changes frequently necessitates replotting of calculated data. To facilitate the interpretation of pulsed Doppler flowmetry data, a simple, inexpensive device was constructed that computes the signal ratio of mean arterial pressure (MAP) to directional pulsed Doppler outputs. With this device, relative flow resistance can be recorded and quantitatively assessed at a glance in three vascular beds in real time. This computer-like device was designed around the Burr-Brown DIV100HP integrated circuit. C741G OpAmps provide input buffering, zeroing, and ranging adjustments enabling the user to accurately follow resistance over a very broad range of changes without exceeding the device's operating limits. A LM339 quad comparator monitors the input of each DIV100 and indicates when operating limits are exceeded via a channel-specific LED indicator and an audible alarm. No significant attenuation of the input signals occurs over the range of direct current to 50 kHz, and the output is without significant phase shift. Comparisons with calculated changes in resistance derived from the MAP and pulsed Doppler flowmetry in unanesthetized, unrestrained rats confirmed that resistance changes can be measured with precision and accuracy.

Animals↗
PubMed1987

Coital behaviors, attitudes, and knowledge of students who experience early coitus.

The purpose of this study was to investigate coital behavior, contraceptive practices, and attitudinal and knowledge differences between "early coital initiators" (subjects having initial coitus at 16 years or younger) and "late coital initiators" (subjects having initial coitus from 17 to 20 years of age). Data were compiled from the results of a questionnaire administered to 929 students enrolled in personal health courses at 14 colleges and universities. The sample used for analysis included only the never-married coitally experienced males and females aged 20 and older (N = 396). The results suggested that late coital initiators: were more effective contraceptors during initial coitus; had more committed relationships with their initial sex partners; engaged in more discussion about and planning for contraceptive use; and used more authoritative and reliable sources for contraceptive information than their younger counterparts. Both groups scored very low on basic knowledge questions concerning fertility, contraception, and sexually transmitted diseases. These results mandate greater public concern and involvement to delay early coital experiences and prevent unprotected sexual intercourse.

Adolescent↗
PubMed1986

The instantaneous centre of rotation of a fixed unilateral distal extension partial denture.

A photographic technique was used to determine the instantaneous centre of rotation of a fixed unilateral distal extension partial denture and the teeth to which it was attached. The teeth involved were the lower canine and first premolar. When the two crowns were splinted together to provide support, both vertical and lateral saddle movement was reduced. Saddle support using only the first premolar produced a centre of rotation in the sagittal plane below the canine crown--which became located anterior to the canine when the two supporting teeth were splinted together. In the coronal plane, canine support produced an axis of rotation buccal to, and outside the confines of, the model; splinting of the canine and first premolar caused the centre of rotation in this plane to be located buccally and superior to the abutment tooth roots. The more posteriorly the saddle was loaded, the greater was the magnitude of the resultant movement.

Biomechanical Phenomena↗
PubMed1986

The effect of partial denture design on abutment tooth and saddle movement.

A laboratory investigation designed to simulate the effect of loads applied to a free-end saddle partial denture was carried out. Abutment tooth and also saddle movement were monitored using a photogrammetric method. Loads applied to the denture saddle were transmitted through the occlusal rest and also the clasp components causing movement of both denture saddle and the abutment tooth. The direction of abutment tooth movement was towards the mesial, whether the occlusal rest was situated on the mesial or distal aspect of the tooth crown. It was also evident that the design of the clasp unit used affects the magnitude and direction of abutment tooth movement.

Dental Abutments↗