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Biomedical subjects

K Johnston

Publications and source records attributed to K Johnston.

At least 109 records · Page 6Linked to original sources
PubMed1977

Cross-sectional echocardiographic examination of the interatrial septum.

The interatrial septum has not been readily appreciated by M-mode echocardiography. Cross-sectional echocardiography has the capability of recording the shape and location of the interatrial septum. Real-time cross-sectional echograms using a mechanically oscillating transducer were obtained on 100 consecutive patients. Echocardiographic examination of the left atrium and aorta was obtained in a plane perpendicular to the long axis of the atria. In 15 normal patients and 17 patients with atrial septal defects (ASD) and 51 patients with other forms of heart disease, the interatrial septum was recorded as a linear echo from the aorta to the posterior wall of the left atrium. In six patients who had ostium primum ASDs, the echoes from the interatrial septum disappeared near its expected junction with the interventricular septum. Drop out of echoes in the mid portion of the septum was noted in those patients who had ostium secundum atrial septal defects but this could not be differentiated from normal. These preliminary data indicate that examination of the interatrial septum is feasible and may be specific in those few patients examined so far with ostium primum atrial septal defect. The ability to locate and record the shape of the interatrial septum could have many investigate and clinical uses.

Adolescent↗
PubMed1976

Analog computer assisted beat-by-beat measurement of stroke volume and related variables in man.

A technique for the beat-by-beat measurement of stroke volume is described. Aortic blood velocity signals are obtained from a catheter-mounted electromagnetic velocity transducer and analysed by a purpose-built analog computer. The stroke volume is computed by integration of each period of systolic forward flow using the velocity signal as its sole input. Automatic compensation of flowmeter drift is incorporated and inappropriate triggering of integration by diastolic artefact is prevented by applying both amplitude and duration criteria for the recognition of systolic forward flow. Early diastolic reverse flow is excluded from integration. The cardiac output, mean aortic flow per beat, and interbeat interval are also computed from the velocity signal. With aortic pressure as an additional input signal the mean arterial pressure per beat and systemic vascular resistance can be computed. The computer outputs are calibrated by a manual method. Preliminary studies comparing values for the cardiac output measured by this system and the direct Fick technique have indicated an excellent correlation between the two methods.

Aorta↗
PubMedDate not supplied

A new focus of onchocerciasis in Mwanza District, Malawi.

Anecdotal information suggested that a new focus of onchocerciasis had recently developed in Mwanza in Malawi, a district not contiguous with Thyolo, the only district in Malawi with recognized autochthonous transmission. We carried out a survey of the northern half of Mwanza district, randomly selecting 62 villages for assessment. Two iliac crest skin snips were taken from 2215 residents over the age of 15 years; one-quarter had Onchocerca volvulus microfilariae. Prevalence increased with age and was higher overall among men than women. The age-adjusted prevalence among migrants from Thyolo was 31%. Among residents who had never been outside Mwanza, the gender-specific prevalences and microfilarial loads were similar. The intensity of infection was low. Autochthonous transmission of O. volvulus has thus been demonstrated in Mwanza and illustrates the possibility of the spread of the disease to new foci in Malawi and the surrounding countries, due to significant population shifts.

Adolescent↗
PubMedDate not supplied

WHO derides vaccine scare.

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Acquired Immunodeficiency Syndrome↗
PubMedDate not supplied

New AIDS drug.

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Acquired Immunodeficiency Syndrome↗