Biomedical subjects

D Langton

Publications and source records attributed to D Langton.

6 recordsLinked to original sources

PubMed1991

Cardiovascular effects of volatile anesthesia in rabbits: influence of chronic heart failure and enalaprilat treatment.

Circulatory responses to isoflurane and halothane anesthesia were studied in eight rabbits with biventricular cardiomyopathy induced by doxorubicin (Adriamycin, 14 mg/kg IV over 7 wk) and in eight controls (saline injections). In preliminary operations pulsed-Doppler flow probes were placed on the ascending aorta, left renal artery, and lower abdominal aorta. Each group was studied after 4, 6, and 7 wk of treatment. The development of congestive heart failure (CHF) was associated with decreases in mean arterial pressure and cardiac output (CO) of 14% and 16%, respectively, (P less than 0.05) and an increase in heart rate. In controls, each anesthetic agent produced dose-related decreases in mean arterial pressure and increases in heart rate, but not significant changes in CO. Renal blood flow was reduced to a similar degree by 1.3 MAC halothane (24% decrease) and 1.3 MAC isoflurane (21% decrease); hindlimb blood flow was reduced only by halothane. As CHF developed there was an attenuation of the heart rate response to anesthesia. Halothane, but not isoflurane, significantly reduced CO in more advanced stages of CHF. The changes in renal blood flow and hindlimb blood flow with each anesthetic in the CHF group were similar to those observed in controls and did not vary with week of treatment. Administration of the angiotensin-converting enzyme inhibitor enalaprilat (0.2 mg/kg IV) reversed the CO and renal blood flow effects of halothane except after 7 wk of treatment in the CHF group, when the combination of halothane and enalaprilat resulted in severe circulatory depression.

Animals↗

PubMed1990

Cardiovascular responses to graded treadmill exercise during the development of doxorubicin induced heart failure in rabbits.

STUDY OBJECTIVE: The aim was to examine the haemodynamic and humoral responses to graded treadmill exercise, serially during the development of congestive heart failure. DESIGN: Doxorubicin (1 mg.kg-1) was given to rabbits twice weekly intravenously over 8 weeks to induce a low output congestive cardiomyopathy. Treadmill exercise at 8 and 16 m.min-1 was performed at weeks 0, 2, 4, 6, 7, and 8. During each exercise study, continuous recordings were made of cardiac output, mean arterial pressure, and heart rate, and central venous blood was sampled at rest and during the last 10 s of exercise for plasma noradrenaline and plasma renin activity. EXPERIMENTAL MATERIAL: Six cross-bred English rabbits, mean weight 2.6 kg, received doxorubicin treatment; three control rabbits received vehicle injection. MEASUREMENTS AND MAIN RESULTS: Over the first 2 weeks, resting haemodynamic variables and responses to exercise were normal in all rabbits. Thereafter, doxorubicin treated rabbits had progressive falls in resting cardiac index and mean arterial pressure, and rises in resting heart rate and systemic vascular resistance. The normal increases in cardiac index and mean arterial pressure with exercise were progressively attenuated, despite an increase in resting and exercising heart rate. The resting levels of plasma noradrenaline and plasma renin rose after the fourth week of doxorubicin treatment. Throughout the experiment, exercise consistently raised plasma noradrenaline and renin, but the exercising levels of both hormones increased as heart failure progressed. Four of the six doxorubicin treated rabbits became exhausted in the final run and there was an intense rise in systemic vascular resistance. CONCLUSIONS: In this rabbit model of chronic heart failure, sympathetic vasoconstrictor drive is greater than normal at rest, and is greatly exaggerated during exercise. It is suggested that this abnormal response to exercise results from a combination of failure of arterial pressure to reach the elevated set point of the arterial baroreflex, increased afferent input from exercising muscles due to their underperfusion, and increase in central command due to muscle fatigue.

Animals↗

PubMed1990

Vasoconstriction in the renal vascular bed during exercise: studies in control and heart failure rabbits.

1. The effects of graded treadmill exercise on renal blood flow (RBF) were examined in seven rabbits, in which congestive heart failure (CHF) was produced by the administration of doxorubicin, 1 mg/kg, twice weekly for 8 weeks, and in seven controls. A third group of five rabbits underwent doxorubicin treatment with the addition of surgical section of the left renal sympathetic nerve. 2. During submaximal exercise, there was a small reduction in RBF in controls, which was greatly exaggerated in CHF. 3. In both control and heart failure rabbits, there was a precipitous fall in RBF as exercise fatigue developed. 4. Renal sympathectomy ablated these changes in RBF during exercise. 5. It is concluded that in heart failure there is an exaggerated, sympathetically mediated, diversion of blood flow away from the kidney. The onset of exercise fatigue in both normal and heart failure rabbits is accompanied by a marked intensification of this process.

Animals↗

PubMed1989

Comparison of felodipine extended release and conventional tablets in essential hypertension using ambulatory blood pressure monitoring.

Two formulations of felodipine, conventional and extended release (ER) tablets, were compared in a double-blind, crossover study of patients whose blood pressure was not being controlled using metoprolol 100 mg once daily. Nineteen patients with a supine diastolic blood pressure greater than or equal to 95 mmHg after 4 weeks of taking metoprolol and placebo were randomly assigned to felodipine conventional (5 mg twice a day) or ER (10 mg once daily) for 4 weeks. A 2-week washout period was then followed by 4 weeks of treatment with the alternative formulation. Metoprolol once daily was taken concomitantly throughout the study. Clinic blood pressure was measured at 0 h (i.e. 12 h after the last dose of conventional, and 24 h after the last ER felodipine dose), and then 2 and 5 h after the following dose had been taken. Ambulatory blood pressure and the heart rate were monitored over 24 h using an Accutracker (Suntech Medical Instruments, Raleigh, North Carolina, USA). During the final treatment, both felodipine formulations caused similar substantial falls in supine blood pressure compared with pressures prior to randomized treatment. The falls in clinic blood pressures (systolic/diastolic) were similar with the conventional and ER formulations at all time points, i.e. 0 h (21/13; 19/11 mmHg), 2 h (39/18; 36/18 mmHg) and 5 h (30/12; 35/11 mmHg) after the morning dose was taken. Both formulations also produced similar falls in blood pressures over 24 h and during the daytime (21/12; 20/12 mmHg).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1989

Regional distribution of the cardiac output and renal responses to atrial natriuretic peptide infusion in rabbits with congestive heart failure.

1. A biventricular, low-output congestive cardiomyopathy was induced in 19 rabbits by administering adriamycin (16 mg/kg). The effects of alpha-rat atrial natriuretic peptide (ANP) infused at 0.1, 0.2 and 0.4 micrograms/kg per min, were then examined in terms of (i) central haemodynamics (ii) regional blood flow (iii) renal function and (iv) plasma norepinephrine and plasma renin. 2. In this dose range, ANP produced progressive and significant falls in stroke volume, cardiac output and mean arterial pressure, owing to a fall in venous return. The heart rate response to this was blunted. 3. Using radiolabelled microspheres, significant falls in the perfusion of cutaneous, gastrointestinal and musculoskeletal tissues were observed, due to reduced vascular conductances in these beds. These changes were accompanied by activation of the sympathetic nervous system as evidenced by a progressive rise in plasma norepinephrine. A significant increase in plasma renin was only observed with the highest infusion of ANP. 4. Renal blood flow was maintained in the face of a falling mean arterial pressure and cardiac output, but diuretic and natriuretic effects were absent. 5. It was concluded that the dominant influence of ANP infusion in this model of heart failure appeared to be a reduction in cardiac preload with detrimental overall haemodynamic consequences.

Animals↗

PubMedDate not supplied

Teaching the nursing process.

Gerard Carton, Dave Langton and David Robinson discuss a pilot study of an innovative approach to the design and implementation of a research-led, clinically-based and clinically-relevant teaching package for individualised care. The difficulties in transferring classroom-taught theory to psychiatric practice are considered. Nursing staff in the context of Rampton Hospital have, for example, experienced problems in applying the principles of the Open University OU P553 Course to the clinical setting.

Education, Nursing, Continuing↗