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Biomedical subjects

T Crake

Publications and source records attributed to T Crake.

At least 55 records · Page 3Linked to original sources
PubMed1992

Response of the pulmonary circulation to acetylcholine, calcitonin gene-related peptide, substance P and oral nicardipine in patients with primary pulmonary hypertension.

Endothelium-dependent vasodilation of the pulmonary vascular bed was investigated in five patients with primary pulmonary hypertension. Three endothelium-dependent vasodilators (acetylcholine, calcitonin gene-related peptide and substance P [in two patients]) were infused sequentially into the right atrium, followed by nicardipine given orally during full hemodynamic monitoring. Acetylcholine, calcitonin gene-related peptide and substance P had no effect on pulmonary artery pressure, total pulmonary vascular resistance or cardiac output, although calcitonin gene-related peptide significantly decreased systemic arterial systolic pressure from 132 +/- 34 to 113 +/- 33 mm Hg. In contrast, oral nicardipine decreased total pulmonary vascular resistance from 23 +/- 12 to 13 +/- 8 U, with a concomitant increase in cardiac output from 3.1 +/- 1 to 4.7 +/- 2 liters.min-1 and decrease in systemic vascular resistance from 30 +/- 9 to 13 +/- 4 U. Thus, despite the presence of a reversible component in these five patients with primary pulmonary hypertension, pulmonary vascular resistance did not decrease in response to the infused endothelium-dependent vasodilator agents, indicating that endothelium-dependent vasodilation is impaired in these patients.

Acetylcholine↗
PubMed1991

Absence of myocardial dysfunction during stress in patients with syndrome X.

Stress two-dimensional echocardiographic studies were performed in 18 patients with angina, a positive exercise test and normal findings on coronary angiography (syndrome X). Rest and immediate posttreadmill exercise two-dimensional echocardiograms were performed with a digitized cine loop and side by side visual analysis in all patients. In 16 of these patients, right atrial pacing up to 160 beats/min was also performed and percent systolic wall thickening was calculated at five equally spaced segments around the left ventricle, each corresponding to an anterior, lateral and inferior wall and the posterior and the anterior ventricular septum. Measurements of percent systolic wall thickening were established in 10 age- and gender-matched normal persons for comparison. ST segment depression occurred in all patients during exercise and persisted for 42.1 s (range 18 to 75) into the recovery period. Immediate postexercise echocardiography was started within 20.1 +/- 5.4 s and completed in 54.1 +/- 11.3 s. No patient had regional wall motion abnormalities seen on two-dimensional imaging of any myocardial segment. Thirteen patients (72%) reported reproduction of their usual chest pain, which led to termination of the test. During rapid right atrial pacing, nine patients (56%) developed ST segment depression that was associated with angina in seven. In all 16 patients, percent systolic wall thickening increased over values at rest in each myocardial segment. Percent systolic wall thickening averaged 47.1 +/- 6.1% at rest and increased to 74 +/- 8% during right atrial pacing (p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Percutaneous catheter fragmentation and distal dispersion of proximal pulmonary embolus.

Rapid restoration of pulmonary blood flow is important in preventing death due to a massive pulmonary embolus. Devices developed specifically for percutaneous transvenous removal of pulmonary emboli are bulky and their insertion through a cut down or by the use of a large venous sheath can lead to bleeding at the entry site. In 3 patients with acute massive pulmonary embolism, conventional cardiac catheters were used to break up the embolus and disperse the fragments distally. Cardiac output was rapidly restored in all patients. There were no serious complications. This technique requires no more specialist equipment or skill than those needed for temporary cardiac pacing and could be important for the emergency management of patients with acute severe pulmonary embolism.

Acute Disease↗
PubMed1991

Inhibition by barium and glibenclamide of the net loss of 86Rb+ from rabbit myocardium during hypoxia.

STUDY OBJECTIVE: The aim was to determine the effects of barium ions and glibenclamide on the hypoxia induced K+ efflux from rabbit myocardium. DESIGN: Experiments were performed on the isolated interventricular septum of the rabbit perfused with a physiological solution through the septal artery. The stimulation rate was 90 beats.min-1 and the temperature 32 degrees C. The flux of 86Rb+ was used as a surrogate of K+ fluxes. EXPERIMENTAL MATERIAL: Septa were obtained from adult male New Zealand white rabbits. MEASUREMENTS AND MAIN RESULTS: The uptake of 86Rb+ by the septum could be fitted to a single exponential curve with a rate constant of 0.024(SEM 0.001) min-1 (n = 14). Washout experiments were performed in which septa were labelled with 86Rb+ and then perfused with unlabelled solution for 60 min. The rate constants for the efflux of 86Rb+ were similar and were 0.022(0.001) min-1 (n = 13) for radioactivity in the tissue and 0.029(0.001) min-1 (n = 13) for radioactivity in the effluent. These rate constants were similar to those reported previously for 42K+. Septa were labelled for 150 to 180 min with 86Rb+ and then perfused with a hypoxic substrate free solution for 15 min followed by reoxygenation. The net loss of 86Rb+ was calculated to be equivalent to 4.00(0.20) mmol.kg-1 wet tissue of K+ (n = 8) and in washout experiments (n = 6) this loss was shown to be due to increased efflux. Ba2+, 0.1 mM and 1.0 mM, added at the onset of hypoxia decreased net tissue loss of 86Rb+ by 64(6)% (n = 5) and 97(1)% (n = 6) respectively (both p less than 0.01). Glibenclamide (0.1 mM) decreased tissue net loss by 52(3)% (n = 6, p less than 0.01). CONCLUSIONS: Part of hypoxia induced net K+ loss in this preparation can be attributed to activation of ATP sensitive K+ channels but other mechanisms are also involved.

Animals↗
PubMed1991

Therapeutic implications of dynamic coronary stenosis in patients with single vessel coronary artery disease.

Ten patients with proven single-vessel coronary artery disease and a positive exercise test for ischaemia were investigated to establish the importance and therapeutic implications of dynamic coronary stenosis in such patients. All patients interrupted their anti-anginal therapy and under took serial exercise testing in an attempt to identify variability in the ischaemic threshold. Ergonovine testing was performed in nine patients and all underwent 48 h of ambulatory ST segment monitoring while treatment was discontinued. Patients then entered a randomized double-blind study of atenolol and nifedipine; treadmill exercise testing and 48 h of ambulatory ST segment monitoring were performed at the end of each treatment phase. Six (60%) patients showed evidence of variability in coronary vasomotor tone four of whom developed significant ST segment changes during administration of ergonovine; a further two had greater than 30% variability in time to onset of ischaemia during serial treadmill exercise testing. Atenolol significantly increased the time to ischaemia on exercise testing, both in the group as a whole and in the subgroup with evidence of altered vasomotor tone when compared with no therapy, and led to a non-significant reduction in the frequency and duration of ischaemia during the patients' daily lives. Nifedipine, conversely, did not significantly increase time to ischaemia on exercise testing or reduce the frequency or duration of ambulatory ischaemia in either the whole group or the subgroup. With evidence of altered vasomotor tone when compared to no therapy however it was beneficial in terms of reduction in chest pain and requirement for glyceryl trinitrate during daily life.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1990

Combining day patient treatment with family work in a child psychiatry clinic.

The 81 youngsters who began attending a day treatment programme within a 1-year period were assessed using an interval design. The children ranged in age from 18 months to 16 years and attended with similarly aged children for 1 day a week. The treatment programme combined family therapy with the day unit's milieu therapy and specific individual treatment programmes for the child. The results indicate that the combination of a 1 day a week attendance and family therapy had a significant clinical impact upon the problems. The pattern of improvement observed would suggest that the day-unit attendance made a unique contribution to the overall outcome.

Adolescent↗
PubMed1990

Calcium exchange in rabbit myocardium during and after hypoxia: role of sodium-calcium exchange.

Calcium uptake was measured using 47Ca2+ in the isolated and arterially perfused interventricular septum of the rabbit. Experiments were undertaken to determine whether calcium uptake on reoxygenation is linked to recovery of mechanical function and whether calcium uptake is through the sodium-calcium exchange mechanism. During substrate-free hypoxia for 45 min total tissue calcium remained unchanged but immediately upon reoxygenation there was a substantial net gain of calcium. Recovery of mechanical function upon reoxygenation was inversely related to the increase in tissue calcium. Activation of sodium-calcium exchange by perfusion with a low-sodium, zero-potassium, sucrose solution also increased tissue calcium and the relation to mechanical recovery was similar to that observed on reoxygenation. The sodium-calcium exchange mechanism was not affected by hypoxia and could be demonstrated during perfusion with a substrate-free hypoxic solution. Lithium (100 mM) substitution for sucrose prevented the calcium influx induced by a low-sodium and zero-potassium perfusate under normoxic conditions. Lithium substitution early during hypoxia or on reoxygenation did not affect the increase in myocardial calcium on reoxygenation. Amiloride (10(-4)M), presumed to inhibit sodium-hydrogen exchange during hypoxia, had no effect upon reoxygenation induced calcium uptake. It is concluded that the increase in calcium uptake that occurs on reoxygenation after a period of substrate-free hypoxia is related to mechanical recovery. Sodium-calcium exchange may contribute to calcium uptake on reoxygenation in this experimental model but is not the major mechanism.

Amiloride↗
PubMed1990

Potassium exchange in the human heart: effect of heart rate and myocardial ischemia.

The concentration of potassium ions, [K+], in the blood of the coronary sinus was recorded using catheter-tip potassium ion-selective electrodes during fixed rate atrial pacing for up to six minutes in five patients with normal hearts (control group) and in eight with coronary artery disease. Four patients with coronary artery disease developed pain in the chest and changes on the electrocardiogram during atrial pacing (ischemic group). In the control group, the coronary sinus [K+] began to rise after three seconds to a peak increase of 0.33 +/- 0.04 mmol.l-1 (p less than 0.001) and then returned to the resting value. On cessation of pacing, coronary sinus [K+] fell rapidly and transiently below the resting value. In the ischemic group, the coronary sinus [K+] began to rise after three seconds to a peak of 0.42 +/- 0.05 mmol.l-1 (p less than 0.01); it remained elevated throughout the period of atrial pacing (p less than 0.01) and fell rapidly and transiently below the resting value on cessation of pacing. Four patients with coronary artery disease did not develop ST segment depression during atrial pacing; in two the changes in coronary sinus [K+] were the same as those in the ischemic group, and in two they were similar to those in the control group. These data show that in man there is an immediate and transient loss of potassium from the myocardial cells when the heart rate is increased and that this loss is restored the heart rate returns to the resting rate. Myocardial ischemia causes a continuing efflux of potassium from myocardial cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiac Pacing, Artificial↗
PubMed1989

The enigma of syndrome X.

Syndrome X is characterised by chest pain suggestive of angina pectoris, normal epicardial coronary arteries on coronary angiography, and an exercise test with the characteristics (ST depression on the electrocardiogram) usually interpreted as myocardial ischaemia. The literature is confused because the last requirement, namely a positive exercise test, is not always present in groups of patients studied by a variety of techniques. The prognosis of patients with syndrome X is good. The cause is not known although many authors have argued that myocardial ischaemia due to small vessel disease is present. Coronary angiography cannot detect abnormalities of vessels less than 400 microns in diameter whilst electron-microscopy and light histology of biopsies visualise vessels less than 150 microns in diameter. Vessels of intermediate size could be abnormal and the abnormality be undetected. In many patients ischaemia cannot be the cause because the coronary sinus oxygen saturation is normal during an atrial pacing test when the patient complains of chest pain and changes are present on the surface electrocardiogram. Syndrome X describes an inhomogeneous group of patients with symptoms due to differing pathologies.

Angina Pectoris↗
PubMed1988

Effects of intracoronary isosorbide dinitrate during acute myocardial ischaemia: a study during angioplasty.

The effects of isosorbide dinitrate on acute myocardial ischaemia were studied in 19 patients during coronary angioplasty. The duration of balloon inflation to the onset of ST segment depression was increased by the administration of intracoronary isosorbide dinitrate from (mean +/- SEM) 13 +/- 2 to 20 +/- 2 s (48%) (P less than 0.01) and the duration to 1 mm ST segment depression increased form 23 +/- 2 to 29 +/- 3 s (28%) (P less than 0.01). Systolic blood pressure fell from 118 +/- 3 to 111 +/- 4 mmHg but there was no change in intracoronary distal occlusion pressure. Thus during coronary occlusion isosorbide dinitrate prolongs the time to the onset of myocardial ischaemia.

Acute Disease↗
PubMed1988

Labetalol in the treatment of stable exertional angina pectoris: a comparison with nifedipine.

Labetalol, a combined alpha- and beta-receptor antagonist, was compared with nifedipine in a placebo-controlled, randomized double-blind cross over study (four week treatment periods) of 11 normotensive patients with stable exertional angina pectoris. Standard recommended doses of both drugs (labetalol 200-400 mg twice daily, nifedipine 10-20 mg three times daily) were used. Angina frequency was similar during the placebo washout period and treatment with the two drugs. The duration of treadmill exercise to angina, ischaemia (greater than 1 mm ST segment depression), and end of exercise was increased by both labetalol and nifedipine when compared with placebo, but there was no difference between the two drugs. Ambulatory ST segment monitoring demonstrated that the frequency, duration and magnitude of ST segment depression, whether painful or silent, were unaffected by either drug. Labetalol is an effective agent in improving exercise tolerance in normotensive patients with stable exertional angina pectoris, with an efficacy similar to that of nifedipine.

Adult↗
PubMed1988

Continuous recording of coronary sinus oxygen saturation during atrial pacing in patients with coronary artery disease or with syndrome X.

Coronary sinus oxygen saturation was measured continuously during incremental atrial pacing in 34 patients undergoing cardiac catheterisation. In eleven patients with normal coronary arteriograms, negative exercise tests, and no ST segment depression on the electrocardiogram, an increase in the rate of atrial pacing transiently decreased coronary sinus oxygen saturation but within 20 s oxygen saturation returned to the control value. In six patients with coronary artery disease ST segment depression developed during atrial pacing. The coronary sinus oxygen saturation fell and remained reduced until pacing was discontinued. The size of the fall of coronary sinus oxygen saturation increased with increasing heart rate. In seven patients with coronary artery disease the ST segments were unaltered during atrial pacing and coronary sinus oxygen saturation did not fall. Ten patients with syndrome X were studied. In six ST segment depression developed on atrial pacing. In five, three of whom developed ST segment depression, the changes in coronary sinus oxygen saturation during atrial pacing were similar to those observed in patients without any evidence of coronary artery disease. In three, all of whom developed ST segment depression, coronary sinus oxygen saturation gradually increased throughout the period of atrial pacing. In two patients coronary sinus oxygen saturation fell in a manner similar to that observed in patients with obstructive coronary artery disease who developed ST segment depression on pacing. Thus regulation of coronary blood flow in normal persons in response to an increase of heart rate is rapid. Oxygen extraction across the coronary bed can increase by up to 30% and a persistent increase in oxygen extraction is an indicator of myocardial ischaemia. The term "syndrome X" does not describe a homogeneous group of patients but in the majority coronary sinus oxygen saturation does not fall despite symptoms and changes on the electrocardiogram, indicating that inadequate coronary blood flow is not the dominant mechanism.

Adult↗
PubMed1987

Potassium efflux from the myocardium during hypoxia: role of lactate ions.

To determine the role of lactate in the causation of potassium efflux during hypoxia, the effect of lactate ions on the uptake and efflux of 42potassium was studied in the isolated arterially perfused interventricular septum of the rabbit. Septa were equilibrated with lactate (50 mmol.litre-1) under isosmotic conditions before switching to a perfusate containing the inert and impermeant anion isethionate (50 mmol.litre-1). A reduction in tissue 42potassium content was detected, which could only partly be accounted for by increased efflux. During hypoxic substrate free perfusion potassium loss was due to an increased efflux with no evidence of altered influx. The extrusion of accumulating anions, such as lactate ions, from the myocardium is one mechanism for the early potassium loss during hypoxia.

Animals↗
PubMed1987

The role of ambulatory ST-segment monitoring in the diagnosis of coronary artery disease: comparison with exercise testing and thallium scintigraphy.

The value of ambulatory ST-segment monitoring in the detection of underlying coronary artery disease was investigated in one hundred consecutive patients who underwent exercise testing and coronary arteriography for chest pain. Forty-seven also had thallium-201 radioisotope imaging performed. Six of the 26 patients with normal coronary arteries and 52 of the 74 patients with significant coronary artery disease had ST-segment changes during 48 h of ambulatory monitoring (sensitivity 77%). In comparison, the sensitivity of conventional exercise testing was 73% and specificity was 81%. Previous myocardial infarction did not influence the results, but patients with poor left ventricular function more often had absence of ambulatory ST-segment changes. Three-vessel coronary artery disease was detected more efficiently (sensitivity 80%), compared with single vessel disease (sensitivity 50%). Thallium scintigraphy demonstrated defects of uptake in nine patients without ambulatory ST-segment changes (sensitivity 82%, specificity 71%). The majority of these patients had small inferior or posterior defects in thallium uptake. Only one patient with ambulatory ST-segment changes had normal coronary arteries and demonstrable spasm. Thus, ambulatory ST-segment monitoring is as valuable as stress testing in the detection of coronary artery disease and in addition helps detect patients with coronary spasm and normal coronary arteries.

Ambulatory Care↗