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Biomedical subjects

P Oldershaw

Publications and source records attributed to P Oldershaw.

At least 19 recordsLinked to original sources
PubMed2001

Sharing toxicological information on industrial chemicals.

A clear and comprehensive appreciation of the toxicological hazards of a substance is an essential prerequisite to establishing appropriate, balanced and effective risk management measures in the workplace. For many substances, there are currently numerous problems and issues surrounding: the adequacy of the toxicological information base; its interpretation; the transfer of key messages to, and their understanding by, those who need to take action; and the roles and practices of the various standard-setting bodies operating in this area and the interaction between them. This paper briefly touches on these issues, on a range of activities and initiatives directed at improving the current situation, and on the implications for all those involved, particularly the world occupational hygiene community.

Europe↗
PubMed1999

Acute right ventricular dilatation in response to ischemia significantly impairs left ventricular systolic performance.

BACKGROUND: Right ventricular (RV) dilatation that occurs as a consequence of RV infarction is thought to produce hemodynamic instability by reducing left ventricular (LV) preload and compliance. We hypothesized that these geometric changes may also adversely affect LV systolic performance. METHODS AND RESULTS: Twelve 40-kg pigs were studied. Integrated conductance catheters and micromanometers were placed in both the LV and RV to allow simultaneous recordings of pressure and volume and derivation of indices of contractile function. RV ischemia was induced by balloon occlusion of the proximal right coronary artery (RCA) under 3 conditions: 1) with the pericardium intact, 2) with the pericardium intact and inotropic support, and 3) with the pericardium wide open. With an intact pericardium, RCA occlusion produced a decrease in LV end-diastolic volume associated with a marked decline in the contractile function. With the pericardium open, the same ischemic insult resulted in both LV and RV dilatation, which produced a significantly smaller negative effect on cardiac output (P=0.03), LV systolic pressure (P=0.02), LV preload-recruitable stroke work (P<0. 01), and LV end-systolic pressure-volume relations (P<0.01). Similarly, administration of dobutamine during RCA occlusion decreased the ventricular volume changes and produced a relative improvement in LV contractile performance. CONCLUSIONS: The hemodynamic compromise seen in association with acute RV dilatation within an intact pericardium is partly attributable to impaired LV systolic performance and cannot be wholly ascribed to changes in LV preload or compliance.

Animals↗
PubMed1997

Resting right ventricular function in patients with coronary artery disease: pressure volume analysis using conductance catheters.

Right ventricular pressure volume cycles from patients with coronary artery disease were created in order to assess their characteristics and the effects of peak ventricular pressure and right and left artery coronary disease. Thirty-three patients undergoing diagnostic catheterisation for ischaemic heart disease underwent right ventricular catheterisation with a micromanometer and a conductance catheter. Simultaneous pressure and volume signals were recorded and analysed as functions of time, and of each other, forming pressure volume cycles. A total of 19/33 (58%) patients had an abnormal pressure volume loop with a clear end systolic shoulder, and an isovolumic relaxation phase. The mean peak ventricular pressure for all patients was raised (35.2 S.D. 11.8 mmHg), but there was no correlation between indices of shape and peak systolic pressure. Values of dP/dtmax were also raised, but there was no significant difference in this or any other index between patients with left or right coronary artery disease. Thus, in patients with coronary artery disease, the right ventricular pressure volume loop is frequently abnormal in a pattern that is recognised as a feature of an increased ventricular afterload.

Angina Pectoris↗
PubMed1997

Clinical application of the conductance catheter technique in the adult human right ventricle.

This study examines the use of conductance catheters to assess human right ventricular volume. Ten patients undergoing diagnostic cardiac catheterisation underwent right heart catheterisation with a conductance catheter and micromanometer, and a thermodilution catheter before and after fluid loading. Parallel wall conductance (Vc), and the multiplication factor relating conductance and thermodilution derived stroke volumes (å) were derived at each steady state. Pressure-volume cycles were analyzed at steady state and during fluid loading. Fluid loading resulted in a significant increase in cardiac output, and change in maximum and minimum cycle volume. There was no significant change in å (mean 0.40 S.D. 0.20) or Vc (mean 126.4 S.D. 59.6 ml) at higher cardiac outputs or ventricular volumes. Right ventricular pressure-volume cycles were formed demonstrating characteristic lack of clear isovolumic contraction and relaxation phases, and low cycle efficiencies (mean 0.62 S.D. 0.16). Serial cycles recorded during volume loading defined an end systolic pressure-volume relation more reliably than a stroke work end diastolic volume relation. Thus, a conductance derived volume signal can be obtained in the human right ventricle which can be interpreted as a continuous and instantaneous index of right ventricular volume, allowing the construction of real time pressure-volume cycles.

Adult↗
PubMed1997

Right ventricular dysfunction during coronary artery occlusion: pressure-volume analysis using conductance catheters during coronary angioplasty.

OBJECTIVE: To study the effects of coronary artery occlusion on the pressure-volume relations of the right ventricle. DESIGN: Right ventricular pressure-volume cycles were studied using conductance catheters and micromanometers in 19 subjects undergoing coronary angioplasty in a tertiary referral cardiac centre. RESULTS: Catheter occlusions of either the left anterior descending coronary artery or the right coronary artery were associated with a decline in stroke work (mean change (SD): left-13.3 (15.8)%, p = 0.008; right -13.5(16.5)%, p = 0.04). Two patterns of change were evident: an upward shift usually associated with occlusion in the left coronary artery, and a rightward shift in the right coronary artery. In the former there was an increase in maximum ventricular volume (mean change: 3.0(2.7)%, p = 0.004) and in minimum ventricular volume (mean change: 2.3(2.7)%, p = 0.01) and a fall in peak pressure (mean change: -4.8 (5.1)%, p = 0.04). In the latter there was an increase in peak pressure (mean change 9.9(16.3)%, p = 0.04) and an increase in minimum ventricular volume (mean change 3.7(5.0)%, p = 0.02) leading to a fall in stroke volume (mean change -13.3(15.8)%, p = 0.008). CONCLUSIONS: Occlusion of the left anterior descending coronary artery or the right coronary artery is associated with a decline in right ventricular work. However, different patterns of change in indices of preload and afterload lead to different effects on overall right ventricular pump function.

Angioplasty, Balloon, Coronary↗
PubMed1989

Right ventricular function 10 years after the Mustard operation for transposition of the great arteries: analysis of size, shape, and wall motion.

Biplane right ventriculograms were obtained in 18 symptom free patients 109 (26) months (mean (SD)) after Mustard repair of transposition of the great arteries. Ventricular size, shape, and wall motion were measured from the digitised angiograms and compared with previously published data on left ventricular function after anatomical correction of transposition of the great arteries, with right ventricular function in controls, and with patients before repair of tetralogy of Fallot. Global indices of ventricular function were depressed after Mustard repair and wall motion abnormalities were common. The presence of wall motion abnormalities in this group was associated with a reduction in ejection fraction and ventricular filling rates. In four of five patients in whom an appropriate preoperative angiogram was available a similar pattern of wall motion was seen before the Mustard operation, suggesting that preoperative events may be important in determining eventual outcome.

Child↗
PubMed1987

Relation of human cardiac action potential duration to the interval between beats: implications for the validity of rate corrected QT interval (QTc).

Fourteen patients undergoing routine cardiac catheterisation were paced at a steady frequency; after this test, stimuli were introduced with a variable preceding interval (test pulse interval). The QT interval of the electrocardiogram and the duration of the monophasic action potential of the right ventricle were measured. QT interval is a function of action potential duration; the two variables were very closely correlated in this study. Both these variables increased in duration with increasing test pulse interval. A biphasic response, as previously reported, was not seen. An increase in steady state pacing frequency caused QT interval and action potential duration to decrease for any given R-R interval. When frequency of stimulation was suddenly increased and then maintained, there was an immediate action potential shortening followed by a further more gradual shortening occurring over several minutes. These results imply that a simple correction of QT interval for heart rate (QTc) is inadequate. It is concluded that the relation between action potential duration (or QT interval) and heart rate depends on both the instantaneous interval between beats and the duration of the prevailing heart rate.

Action Potentials↗
PubMed1984

Cor triatriatum sinistrum. Diagnostic features on cross sectional echocardiography.

M mode and cross sectional echocardiography was carried out in three cases of cor triatriatum sinistrum (two infants and one adult). In two cases a peculiar double arch appearance, not previously reported, was found. All three cases were referred for surgery without cardiac catheterisation, and the diagnosis proved to be correct. The characteristic echocardiographic feature of cor triatriatum is an intra-atrial membrane detected in multiple planes of examination, curving anteroinferiorly and inserting some distance away from the mitral valve ring, proximal to the left atrial appendage. Superiorly the membrane runs parallel to, and a short distance behind, the aortic root creating a superior recess of the distal left atrial chamber. These features differentiate cor triatriatum from a supravalvar mitral ring. During diastole the membrane moves forward towards the mitral valve funnel. This, together with the arching appearance of the membrane on four chamber views and the more superior position of the membrane, makes it possible to distinguish cor triatriatum from total anomalous pulmonary venous drainage to the coronary sinus. From a review of past experience at the Brompton Hospital of the diagnostic accuracy of cardiac catheterisation in this condition, it is concluded that cross sectional echocardiography is superior to angiography as a technique for diagnosing cor triatriatum.

Adult↗
PubMed1982

Cardiac pacing in children.

Twenty patients aged between 12 months and 13 years underwent permanent pacemaker implantation. The main indication for pacing was post-surgical atrioventricular block. The complication rate was high and related mainly to infections and lead system problems. The use of small multiprogrammable pacemakers is expected to reduce the reoperation rate for system malfunction and elective replacement. Newer methods of electrode insertion and active fixation devices in smaller diameter leads make endocardial pacing a practical alternative to epicardial pacing in the larger child who did not require a pacing system at the time of surgery.

Adolescent↗
PubMed1981

Valve replacement without preoperative cardiac catheterization.

During the year 1978, the decision to perform cardiac catheterization in patients with valvular heart disease was delayed until clinical and noninvasive assessment have been completed. As a result, 184 patient underwent operation without invasive studies, and 59 had elective catheterization. Another 62 patients were referred during the same period for valve replacement after routine catheterization had been performed elsewhere. Age, sex distribution, symptoms, and cause of valve disease were similar in all three groups, although we managed emergencies and second operations more frequently without catheterization. In all patients, the preoperative diagnosis was confirmed, and no unexpected pathologic process was encountered. Operative mortality was the same in all three groups, and after two years of follow-up there was no difference in survival or symptoms. No uncorrected valve lesions became apparent in uncatheterized patients. We conclude that routine catheterization is unnecessary before valve replacement but can be reserved for specific indications in some patients.

Adolescent↗