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Biomedical subjects

R R Taylor

Publications and source records attributed to R R Taylor.

At least 109 records · Page 6Linked to original sources
PubMed1985

Effect of beta-adrenergic blockade on the results of exercise testing related to the extent of coronary artery disease.

Maximal treadmill testing was carried out in 50 patients with angiographically documented coronary artery disease (CAD) in the presence and absence of beta-adrenoceptor blockade. The results were related to the extent of CAD and interpreted relative to the clinical value of exercise testing. Maximal heart rate and systolic blood pressure were significantly lower during treatment with beta-blocking drugs. The average exercise duration was 1.3 +/- 1.9 minutes greater (+/- standard deviation), regardless of coronary anatomy. Of the 20 subjects with 3-vessel or left main CAD (severe CAD), 8 patients completed 3 stages (9 minutes) of exercise during treatment; only 4 did so without treatment. Angina was significantly more often the limiting symptom with severe CAD, and this association was abolished by beta blockade; 1 of 20 with severe CAD completed 3 stages of exercise and was not limited by angina without beta-blocking treatment, whereas 7 had these features during beta-blockade therapy. Maximal ST-segment depression was not related to the extent of CAD with or without therapy. Beta blockade suppressed the occurrence of ST depression, or delayed its appearance by an average of 2.0 +/- 2.3 minutes and reduced its severity by 0.5 +/- 0.9 mm. All tests in which ST depression was completely suppressed were associated with inadequate heart rate response, regarded as diagnostically inconclusive rather than negative. However, during beta-blocking treatment, 14 tests (28%) were inconclusive, which, in routine practice, would have necessitated repeat testing.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic beta-Antagonists↗
PubMed1985

Hypoxemia after gastric bypass surgery for morbid obesity.

Fifty-six patients who underwent Roux-en-Y gastrojejunostomy for morbid obesity had arterial blood gas analysis before surgery and during the first five postoperative days. Preoperatively, seven subjects were hypoxemic and three were hypercapneic. Twenty-four hours after gastric bypass, 75% of the patients had an arterial oxygen pressure (Pao2) less than 60 mm Hg. Compared with preoperative measurements, blood gas values on the first postoperative day showed a 13.7-mm Hg decrease in the mean arterial Pao2 and a 5.0-mm Hg increase in the mean arterial carbon dioxide pressure. Arterial Pao2 determinations on the third, fourth, and fifth postoperative days returned toward, but remained significantly less than, paired values obtained before surgery. Patients with hypoxemia after gastrojejunostomy were significantly older and had significantly lower preoperative arterial Pao2 measurements than patients who were not hypoxemic after surgery. Weight, body mass index, and preoperative spirometric measurements did not distinguish between those patients who did and did not become hypoxemic postoperatively. We conclude that hypoxemia commonly follows gastric bypass for morbid obesity, and thus we recommend that all patients undergoing this procedure be treated with supplemental oxygen for at least the first three postoperative days.

Adolescent↗
PubMed1984

Cigarette smoking and ventricular arrhythmia in coronary heart disease.

With use of 24-hour ambulatory electrocardiographic monitoring, the effect of 1 hour of cigarette smoking on cardiac rhythm in 73 patients with coronary heart disease was studied. Fifteen subjects had no arrhythmia; 37 subjects had fewer than 2 atrial or ventricular premature complexes (APCs or VPCs)/hour, with APCs possibly related to smoking in 2 and VPCs related to smoking in 1. Nineteen subjects had more than 2 VPCs/hour (range 4 to 368) and had 16 +/- 29 VPCs/hour (+/- standard deviation) less during than before smoking (p less than 0.05), associated with an increase in heart rate of 4.6 +/- 6.8 beats/min (p less than 0.01). In none of the 9 subjects with unifocal VPCs did multiform beats develop during or after smoking, whereas 3 of 10 subjects with multiform VPCs had only unifocal beats during and immediately after smoking. In 1 of these 19 subjects, frequent APCs developed during smoking. One other subject had frequent APCs unaffected by smoking and another had sinoatrial block, which disappeared during smoking on 1 of 3 monitorings. In conclusion, no sustained or high-grade ventricular arrhythmia was provoked by smoking; although APCs may have been related to smoking in a few persons, the frequency and complexity of VPCs tended to be reduced in these subjects with coronary artery disease.

Arrhythmias, Cardiac↗
PubMed1984

A comparison of intravenous and intracoronary streptokinase in acute myocardial infarction.

A randomised study of intravenous and intracoronary streptokinase therapy was carried out in 20 subjects with acute myocardial infarction and angiographically confirmed complete obstruction of the associated coronary artery. Two dose levels of therapy were used. Although more recanalisations occurred with intracoronary than intravenous therapy at the low dose levels, overall there was not a significant difference between the two groups; one million IU intravenously over 20 minutes recanalised four of five arteries. While seven of nine recanalisations with intracoronary therapy occurred within an hour, only two of five with intravenous therapy did so. Hence prolonged angiographic observation is necessary to document recanalisation with intravenous therapy adequately. Nevertheless, the time disadvantage of large dose intravenous therapy is not great and it may yet prove as effective as, and more practical than, intracoronary therapy.

Female↗
PubMed1983

Increased protein synthesis and degradation in the dog heart during thyroxine administration.

Mongrel dogs were injected with 1-thyroxine (0.5 mg/kg body weight) for 7 or 14 days and fractional synthesis rates of total, sarcoplasmic and myofibrillar protein were measured in the left ventricle using continuous intravenous infusion of [14C]tyrosine. The synthesis rate of total protein was increased from 7.2% to 9.2% per day and 10.9% per day after 7 and 14 days respectively. The normally lower synthesis rate of myofibrillar protein was stimulated proportionately more than that of sarcoplasmic protein, increasing from 6.0% to 11.7% per day over 14 days, while that of sarcoplasmic protein increased from 10.3% to 13.1% per day. There was a significant increase in left ventricular RNA concentration and decrease in collagen, concentration. Left ventricular weight/body weight was 17% greater than normal after 7 days but the lack of further change in the second week suggests that, after the early development of hypertrophy, protein degradation was also increased, along with the markedly increased synthesis rate.

Animals↗
PubMed1981

Randomized controlled trial of vasodilator therapy after myocardial infarction.

Hemodynamic changes and mortality and morbidity were compared in a randomized controlled trial of sodium nitroprusside after acute myocardial infarction. Fifty patients with a mean pulmonary capillary wedge pressure of more than 20 mm Hg within 24 hours of acute infarction were randomly assigned to one of two groups: 25 patients treated with nitroprusside and 25 treated with furosemide. Nitroprusside rapidly produced a sustained decrease in systemic vascular resistance and increase in cardiac index (thermodilution). After 1 hour the cardiac index had increased 16 +/- 3 (mean +/- standard error of the mean) percent (p less than 0.001) compared with a decrease of 7 +/- 3 percent with administration of furosemide (p less than 0.01). Differences in systemic vascular resistance and cardiac index in the two groups persisted throughout the 48 hour treatment period (p less than 0.001). Pulmonary capillary wedge pressure decreased rapidly with nitroprusside and slowly with furosemide so that, although it was significantly lower in the former group overall (p less than 0.001), by 48 hours the values were not different. Although beneficial acute hemodynamic effects of nitroprusside were demonstrated, there was no difference in mortality or in morbidity assessed clinically, by chest X-ray film, echocardiogram or graded treadmill stress testing after 6 months or 1 year.

Acute Disease↗
PubMed1981

Collagen synthesis and content in right ventricular hypertrophy in the dog.

The fractional synthesis rate of collagen (the percent of total ventricular collagen synthesized in one day) was measured in the hearts of normal dogs and those with pulmonary artery stenosis using a continuous 6-h intravenous infusion of [14C]proline. The fractional synthesis rate in normal ventricles was slow, 0.56%/day, and it increased eightfold to 4.8%/day in the hypertrophying right ventricle after 5 days. After 12 and 28 days the synthesis rate was still significantly greater than in the control left ventricle, being 2.6 and 1.3%/day, respectively. However, the synthesis rate of noncollagen protein was significantly greater than normal at 5 days only. The collagen content (expressed as a mass fraction) of the right ventricle decreased over the first 12 days of hypertrophy but by 28 days was restored to the normal right ventricular value of 9.6 mg/g wet wt tissue. The total amount of collagen in the hypertrophied ventricle calculated from the synthesis rates was in accord with that measured chemically. In normal dogs the collage content of the right ventricle was greater than that of the left, and the epicardium contributed substantially to the total collagen in the ventricular walls.

Animals↗
PubMed1981

Age dependence of myocardial Na+-K+-ATPase activity and digitalis intoxication in the dog and guinea pig.

Infants and young animals tolerate higher doses of digitalis glycosides, relative to body weight, than adults. One possible explanation for this could be an age-dependent difference in the myocardial digitalis receptor, the Na+-K+-ATPase. Two functions of this enzyme were studied in adult, 1- and 6-week-old dogs and guinea pigs: in vitro myocardial uptake of rubidium (86Rb) and binding of ouabain. In guinea pigs, rubidium uptake (pmol Rb/mg LV per 15 min) was: 1 week old: 100.9 +/- 7.1 (mean +/- SE); 6 week: 79.8 +/- 6.7 adult: 55.2 +/- 7.9; (1 week: 6 week: P less than 0.025; 1 week: adult, P less than 0.001; 6 week: adult, P less than 0.025). Similarly in dogs, rubidium uptake was significantly greater at 1 week than at 6 weeks (208 +/- 13 vs. 144 +/- 9; P less than 0.001) and the latter greater than in adults (111 +/- 4) (P less than 0.005). Other groups of anesthetized adult and 6-week-old dogs were given digoxin, 0.3 mg/kg, iv. The young dogs took significantly longer to become cardiotoxic (17.3 +/- 3.4 min vs. 9.3 +/- 1.4 min; P less than 0.025), while their myocardial digoxin uptake was at least as great. Rubidium uptake showed an average decrease of 56% after digoxin but residual uptakes were not different in the two groups. Data for ouabain binding showed similar differences between the various groups of dogs studied. Increased myocardial Na+-K+-ATPase activity, reflected in greater active cation transport and specific enzyme binding, has been demonstrated in young animals and may be partly responsible for their greater tolerance to digitalis glycosides.

Age Factors↗
PubMed1980

Prazosin in the treatment of severe chronic congestive cardiac failure.

The acute haemodynamic effects of prazosin 5 mg were investigated in 11 patients with severe chronic congestive cardiac failure. Six patients had their antifailure therapy discontinued while five continued on their usual medication. Two patients were exercised before and after prozosin. Following the drug, pulmonary capilary wedge pressure diminished 7 +/- 2(SE) mmHg (P < 0.005) and cardiac index increased 17 +/- 6% (P < 0.02). Mean arterial pressure fell in all subjects (- 9 +/- 2 mmHg; P < 0.001) and systemic vascular resistance was reduced in all but one (- 19 +/- 5%; P < 0.005). There was no significant change in heart rate. Four of the five subjects whose regular medications were continued were evaluated by clinical examination, chest X-ray, echocardiogram and treadmill stress test, before and after four weeks of prazosin therapy, one subject having died in this time. Two improved, one deteriorated and one remained unchanged. Thus, chronic prazosin therapy benefited individual patients but did not consistently provide long term improvement.

Adult↗
PubMed1980

Exercise testing and thallium-201 myocardial imaging in relation to coronary artery disease in patients with severe aortic valve disease.

Thirty-three patients with aortic valve disease, fifteen with regurgitation, eleven with stenosis and seven with mixed disease, undergoing assessment for valve replacement which included adequate coronary angiography, were studied. A symptom limited graded treadmill exercise test was undertaken with administration of 40-70 MBq of 201Tl. Myocardial imaging was started within 15 minutes and repeated after four hours using a 37 PM tube Searle gamma camera. Myocardial images were read independently by three observed. Of the 33 sets of images, 21 were -ve, 5 +ve, 2 I (Indeterminate) and 5 D (Difference of opinion). Eight of the 33 patients had significant coronary artery disease (CAD) and of these three were scored +ve (all triple vessel). Two patients without CAD were scored +ve. Eight subjects developed angina during exercise testing, of whom four had CAD, and four with CAD did no develop angina. Historically, 13 of the 33 subjects had typical angina, six having CAD; an additional eight had other significant chest pain, two having CAD. In these subjects with severe aortic valve disease, exercise testing and myocardial imaging with 201 TI was of little value in detecting CAD. All patients with CAD gave a history of significant chest pain.

Adult↗
PubMed1980

Comparison of vasodilator drug prazosin with digoxin in aortic regurgitation.

Intravenous administration of the vasodilator sodium nitroprusside has beneficial haemodynamic effects in subjects with severe aortic regurgitation while acute digitalisation can produce unwanted effects associated with an increase in systemic vascular resistance. This study compares the haemodynamic effects of the vasodilator prazosin and digoxin in eight patients with isolated severe aortic regurgitation. Prazosin 5 mg orally resulted in a 12 +/- 3 (SE) per cent increase in cardiac index (thermodilution), maintained over four to six hours, while digoxin 0.75 mg intravenously did not change the cardiac index. Prazosin reduced mean arterial pressure by 9 +/- 3 mmHg and systemic vascular resistance by 18 +/- 4 per cent while digoxin resulted in a 6 +/- 2 per cent increase in the latter. Mean pulmonary capillary wedge pressure fell 3 mmHg with prazosin. In this group of patients with severe aortic regurgitation but without severe cardiac failure, the changes with either drug, studied in doses conventionally used, were small but those with prazosin were directionally more desirable than those resulting from digoxin.

Adult↗
PubMed1980

Collagen and muscle protein synthesis during cardiac hypertrophy in the dog.

The fractional synthesis rates of collagen and noncollagen protein in the right ventricle of the dog have been measured during hypertrophy after pulmonary artery stenosis. The synthesis rates of noncollagen protein were the same using a continuous infusion of either [14C]tyrosine or [14C]proline, and increased from 7.6% per day in the normal ventricle to 13.6% per day after 1 day of stenosis. This level was maintained at 5 days, but by 12 days stenosis had declined to near normal values. The increase in synthesis rate could almost entirely account for the increase in mass of the right ventricle (83%) that occurred after 24 days of hypertrophy. The synthesis rate of collagen in the normal myocardium was very slow, 0.64% per day, but after 5 days of hypertrophy increased sixfold to 4.0% per day, and was still elevated after 12 days of hypertrophy.

Animals↗
PubMed1977

Protein synthesis during right-ventricular hypertrophy after pulmonary-artery stenosis in the dog.

The rate of protein synthesis in the heart of normal dogs and those with pulmonary-artery stenosis was measured by a continuous intravenous infusion of [14C]tyrosine. The protein-synthesis rate of both ventricles was the same in normal dogs and averaged 7.5% per day. The right ventricle hypertrophied rapidly after the acute imposition of pulmonary-artery stenosis, the wet weight increasing by 84% after 24 days, with the rate of increase being most rapid over the first 5 days. The left ventricle remained largely unaffected and served as an internal control. During hypertrophy there was an increased incorporation of [14C]tyrosine into protein without a significant change in the specific radioactivity of free tyrosine in the ventricles. After 5 days of stenosis the synthesis rate of the total mixed proteins of the right ventricle had increased to 13.6% per day, compared with 6.2% in the control left ventricle. This increase in synthesis was reflected in both the myofibrillar and sarcoplasmic proteins. After 5 days the protein-synthesis rate decreased, but still remained significantly elevated above that in the control left ventricle by 24 days of stenosis.

Animals↗
PubMed1977

Myocardial ouabain content and susceptibility to ouabain cardiotoxicity associated with circulatory volume overload in the dog.

The influence of circulatory volume overload on the myocardial uptake of ouabain and on cardiotoxicity was studied in the unanaesthetised dog with aorto-caval fistula. One hour after tritiated ouabain (0-02 mg/kg IV) both ventricles and atria contained more ouabain than did those of normal dogs (left ventricle (LV), 166+/-23 (SD) ng/g vs. 97+/-19 ng/g, P less than 0-001) while concentrations in skeletal muscle, liver, kidney and plasma were not different in the two groups. In other experiments ouabain was infused to cardiotoxicity (7-5 microgram/kg followed by 3 microgram/kg/min). Cardiotoxicity occurred earlier in dogs with fistula than in normals (16-5+/-2-7 min vs. 24-1+/-2-4 min, P less than 0-001). Ouabain concentrations in myocardium were not different (LV, 434+/-58 ng/g, vs. 442+/-42 ng/g) while concentrations in liver and kidney were less in those with fistula (181+/-35 ng/g vs. 278+/-69 ng/g, P less than 0-001; 1422+/-189 ng/g vs. 2747+/-479 ng/g, P less than 0-001). Average content of skeletal muscle was also less, in proportion to administered dose. The increment in myicardial ouabain content associated with aorto-caval fistula appears to be physiologically active and hence is presumably specifically bound to the digitalis receptor. The observations in this model suggest the possibility of augmented cardiac glycoside uptake in some clinical cardiac diseases.

Animals↗