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Biomedical subjects

D J Parker

Publications and source records attributed to D J Parker.

At least 19 recordsLinked to original sources
PubMed1992

Geometrically accurate transaortic mapping of left ventricular endocardial activation during surgery.

A device was developed for mapping left ventricular endocardial activation through the aortic valve during surgery. It uses an exploring electrode at the tip of a hand-held probe that is mounted on a mechanical arm with six joints whose movements are digitized by a computer while the position of the probe tip is calculated continuously. The probe is inserted by the surgeon into the left ventricle retrogradely through the aortic valve after the patient is on total cardiopulmonary bypass, the aorta has been opened and the coronary arteries cannulated. The electrode position relative to the aortic valve and left ventricular apex is displayed continuously on a computer screen. When electrograms are recorded from the probe, their positions are displayed on the screen relative to a stylized grid of the left ventricular endocardial surface and are color-coded to indicate the activation sequence. In a patient with nonischemic ventricular tachycardia, the arrhythmia was successfully mapped and cryoablated with use of the device. The device will be developed so that a cryoprobe can be substituted for the exploring electrode and positioned at the source of activation determined by the map.

Adult↗
PubMed1992

The period evoked potential: a rapid technique for acquisition of phase-locked responses to continuous pure-tone stimulation.

In view of the current audiological need to obtain rapidly recorded and objective threshold information, particularly for frequencies below 1 kHz, we have developed an evoked potential technique based on the frequency following response. The technique involves the acquisition of a single captured epoch of EEG containing phase-locked responses to 1000 cycles of a continuous pure-tone stimulus. The captured epoch is partitioned into segments representing the responses to single cycles of the stimulus. The segments are then averaged to produce the period evoked potential. The process takes less than five seconds.

Acoustic Stimulation↗
PubMed1992

Acoustic evaluation of earmoulds in situ: a comparison of impression and earmould materials.

Laboratory research has been carried out on the accuracy of both ear impression and earmould materials. The present work was undertaken to assess such materials in vivo. An objective clinical method of earmould evaluation was developed, based on estimation of the attenuation in the acoustic feedback path. The method was used to assess the acoustic performance of earmoulds made from three earmould materials of different texture, when prepared from two different impression materials. It was shown that the choice of impression material made a significant difference to earmould performance. For greatest accuracy, addition cured silicone impression materials are recommended.

Adolescent↗
PubMed1991

Pericardial haemorrhage causing right atrial compression after cardiac surgery: role of transoesophageal echocardiography.

After cardiac surgery transoesophageal echocardiography showed a large thrombus compressing the right atrium in three hypotensive patients. No satisfactory images were obtained by transthoracic imaging, which is often difficult in ventilated patients after cardiac surgery. Transoesophageal echocardiography, however, provided rapid diagnostic information and permitted prompt surgical intervention.

Aged↗
PubMed1990

Myocardial protective effects of lidoflazine during ischemia and reperfusion.

The myocardial protective effect of intravenous (i.v.) lidoflazine with potassium cardioplegia and hypothermia (28 degrees C) was investigated in 21 greyhounds. Animals were injected a single dose of cardioplegia (30 ml/kg body weight) and subjected to 120 minutes of ischaemia and 60 minutes of reperfusion. Ten dogs served as controls (Group C) and 11 dogs received i.v. lidoflazine (1.25 mg/kg b.w.) (Group L). Myocardial drill biopsies for the adenosine triphosphate (ATP) and the creatine phosphate (CP) levels were obtained. Hemodynamic measurements were made at intervals. In Group C, no dog could be weaned from bypass, whereas all 11 dogs in Group L came off bypass and maintained their circulation for 15 minutes. After a 120 minute ischemic period, the ATP and CP contents diminished significantly in both groups. Following reperfusion, the ATP level was 28% of the control level in Group C (p less than 0.005) and 38% in Group L (p less than 0.01). The CP levels showed an overshoot in both groups. There was no significant difference between the groups. In Group L animals, cardiac output (CO) and mean aortic pressure (MAP) were significantly reduced after bypass; from 5 +/- 1/min to 3.2 +/- 1, from 156 +/- 26 mmHg to 82 +/- 11 mmHg respectively (p less than 0.005). Left ventricular minute work (LVMW) also deteriorated markedly from 9.7 +/- 2 kg-m to 3.2 +/- 1 (p less than 0.005). The use of lidoflazine achieved considerable protection in terms of survival, but did not prevent the severe loss of high-energy phosphates in this experimental model.

Adenosine Triphosphate↗
PubMed1990

Major complications of coronary arteriography: the place of cardiac surgery.

The records of the catheter laboratory at St George's Hospital between 1983-1988 were reviewed to determine how often emergency coronary bypass surgery was performed because of a complication arising during elective coronary arteriography. A total of 11,216 cardiac procedures were performed; 5781 were confined to left ventricular angiography and coronary arteriography in patients with suspected coronary artery disease. Fourteen patients, whose investigation had been considered routine, suffered profound circulatory collapse during the procedure. Emergency cardiac surgery was undertaken in 13, with long term survival in 10. This experience suggests that, even in patients considered to be at low risk, there were major complications requiring emergency coronary surgery in at least 2.4 per 1000 coronary arteriograms performed. Survival after emergency cardiac surgery in these patients was 77%. These findings and the access to cardiac surgery should be considered when the development of facilities for cardiac catheterisation is planned.

Adult↗
PubMed1990

Immunosuppression by pulmonary surfactant: mechanisms of action.

Pulmonary surfactant has been shown by this group to suppress peripheral blood lymphocyte responses to mitogens and alloantigens in a dose dependent manner, though the mechanism of action of the suppressive effect is not clearly understood. To try to clarify this, attempts were made to reverse the effects of preincubation with surfactant, obtained by bronchoalveolar lavage from pigs, on lymphocytes and accessory monocytes obtained from the blood of normal volunteers, by washing and incubating the cells in medium alone for various periods up to 24 hours. Immunosuppression, measured as the reduction in thymidine incorporation in response to the mitogen phytohaemagglutinin, could not be reversed by these methods. The addition of indomethacin (up to 100 micrograms/ml for 72 hours) also had no effect, indicating that the immunosuppression was not related to synthesis of prostaglandins. Incubation with surfactant for as little as two hours before addition of mitogen suppressed in vitro lymphoproliferative responses by half, but surfactant added two hours after mitogen had no observed effect. Preincubation of purified lymphocytes in surfactant, before they were cultured with accessory monocytes and mitogen, caused significant suppression of response, but preincubation of purified monocytes had no suppressive effect. There was no change in the intensity of HLA-DR expression on monocytes. These results support the hypothesis that surfactant exerts its effects on the resting uncommitted lymphocyte rather than on antigen presenting monocytes.

Animals↗
PubMed1990

Increases in HLA-DQ, DP, DR, and transferrin receptors on alveolar macrophages in sarcoidosis and allergic alveolitis compared with fibrosing alveolitis.

We have used flow cytometric methods to detect and quantify HLA-DR, DQ, and DP antigens and transferrin receptors on alveolar macrophages in lavage samples from 36 patients with granulomatous lung diseases (extrinsic allergic alveolitis [EAA], n = 13; sarcoidosis, n = 23), and 12 patients having fibrosing alveolitis (FA) (cryptogenic fibrosing alveolitis, n = 3; FA and scleroderma, n = 8; FA and primary biliary cirrhosis, n = 1). HLA-DR, DQ, and DP antigens were expressed on the majority of alveolar macrophages in all the patients, and the percentages of positive cells were similar to those in control subjects without lung disease. However, the amounts expressed were higher in those with EAA and sarcoidosis than in the FA group or control subjects, the most significant differences being in HLA-DQ and HLA-DP expression. Transferrin receptor expression was also higher in the granulomatous lung diseases. In sarcoidosis, higher levels of HLA-DQ correlated with lower lung function measurements (Dco p less than 0.025, FVC p less than 0.025, FEV1 p less than 0.005), suggesting this may be a marker of disease activity. HLA-DP levels also showed a trend (p less than 0.1) of inverse correlation with lung function. Levels of HLA-DQ (p less than 0.005) and HLA-DP (p less than 0.001) correlated more closely than HLA-DR with numbers of lymphocytes in the lavage fluids, and HLA-DQ levels correlated with increasing proportions of lymphocytes in proliferation (p less than 0.05). We suggest that high levels of HLA-DQ and DP on alveolar macrophages may be more relevant than HLA-DR to the enhanced antigen-presenting function of these cells in sarcoidosis, and possibly also in EAA.

Adult↗
PubMed1989

Efficacy of flecainide acetate for atrial arrhythmias following coronary artery bypass grafting.

The antiarrhythmic efficacy of intravenous flecainide and intravenous digoxin was assessed in 29 patients (26 men), aged 43 to 73 (63 +/- 7) years who developed atrial arrhythmias in the first 96 hours after coronary artery bypass grafting. Twenty-seven had atrial fibrillation and 2 had atrial flutter. Patients were entered into the study if the arrhythmia persisted for at least 15 minutes with a ventricular rate greater than 120 beats/min. Fifteen patients were randomized to flecainide (group 1) and 14 to digoxin (group 2). Flecainide was given as a bolus of 1 mg/kg over 10 minutes followed by an infusion of 1.5 mg/kg/hr for 1 hour and then 0.25 mg/kg/hr for the rest of the study period (24 hours). Digoxin was given as 3 bolus doses (0.5 mg followed after 6 and 12 hours by 0.25 mg). In both groups, 10 mg of verapamil was given intravenously after 45 minutes if the arrhythmia persisted with a mean ventricular rate greater than 100 beats/min. The antiarrhythmic efficacy was assessed by 24-hour Holter monitoring and frequent 15-second rhythm strips. Within 45 minutes control of arrhythmia, which was maintained for the rest of the study period, was achieved in 10 of 15 patients in group 1 and 2 of 14 in group 2 (p less than 0.01). Nine of 15 reverted to sinus rhythm in group 1 compared to 0 of 14 in group 2 and 1 of 15 remained in arrhythmia with a controlled ventricular rate in group 1 compared to 2 of 14 in group 2.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1988

A new method to improve the discrimination between lymphocytes and contaminating erythrocytes in flow cytometric analytical techniques.

A method is described for the removal of contaminating erythrocytes from immunofluorescence labelled lymphocyte preparations and allowing accurate gating on the lymphocyte population during flow cytometric analysis. The technique involves an improved erythrolytic fixative combined with the DNA stain propidium iodide permitting non-nucleated cells (i.e., red blood cells) to be gated out during analysis. The erythrolytic fixative was shown not to be detrimental to the major T cell markers detected using indirect immunofluorescence. This method will improve the analysis of blood lymphocytes and their subsets in mononuclear cell preparations and more particularly in samples of body fluids and tissue washings or extracts which may contain variable and often large numbers of erythrocytes.

Ammonium Chloride↗
PubMed1986

Oral beta-blockade with hypothermic potassium cardioplegia in cardiac surgery: is there an additive protective effect?

The possible myocardial protective effect of oral propranolol in combination with potassium cardioplegia and hypothermia was investigated in 30 greyhounds, divided into 2 sub-groups, by determining the changes in myocardial ATP and CP levels, ultrastructural changes and the changes in hemodynamics after a 2-hour period of myocardial ischemia. In group 1, in animals with multiple doses of cardioplegia during the 2-hour ischemic period, preoperative treatment with propranolol did not have a significant myocardial protective effect. In group 2, in animals with a single dose of cardioplegia, during the 2-hour ischemic period, propranolol resulted in a trend of improved survival, although the myocardial ATP and CP levels were the same in both sub-groups. In addition, the multiple doses of cardioplegia in group 1 caused increased subcellular edema in the myocardium. This study suggests that oral propranolol treatment may provide additional myocardial protection during ischemic periods when used with potassium cardioplegia and hypothermia. The mechanism of this effect is not established, but could relate to reduced transmembrane calcium influx.

Adenosine Triphosphate↗
PubMed1979

An experimental assessment of macroscopic enzyme techniques for the autopsy demonstration of myocardial infarction.

Experimental cardiac infarction produced in dogs by coronary artery ligation has been used to investigate the value of macroscopic histochemical enzyme loss in the diagnosis of myocardial infarction at post-mortem. Creative phosphokinase and non-specific dehydrogenase methods gave the best results but became positive only 5-6 hr after infarction. It is concluded that the method is of limited value in autopsy practice.

Animals↗