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Biomedical subjects

A Coats

Publications and source records attributed to A Coats.

At least 37 records · Page 2Linked to original sources
PubMed1994

Mechanisms of exercise intolerance in cardiac failure: abnormalities of skeletal muscle and pulmonary function.

The syndrome of chronic heart failure is characterized by exercise intolerance. Exercise is limited by shortness of breath and fatigue, and either symptom occurs in the same patient depending on the type of exercise performed. Exercise capacity correlates poorly with indices of central hemodynamic function, but the increased ventilatory response in chronic heart failure correlates well with exercise capacity. Possible pulmonary causes have been explored, including increased dead space ventilation, abnormal airway function, and abnormal diffusion capacity. However, the finding of hypocapnia and hyperoxemia in arterial blood during exercise in patients with heart failure suggests that blood gas values reflect hyperventilation, and that any abnormality of pulmonary function is secondary to changes elsewhere. Skeletal muscle is abnormal in chronic heart failure, and shows changes in structure, bulk, exercise capacity, blood flow, and intrinsic metabolic activity. The relative importance of these abnormalities is not clearly determined, but the possible presence of an ergo- or metaboloreceptor connection between abnormal exercising muscle and the ventilatory response to exercise suggest a mechanism linking the two cardinal symptoms of chronic heart failure.

Airway Resistance↗
PubMed1994

Within-patient correlation between the antihypertensive effects of atenolol, lisinopril and nifedipine.

OBJECTIVE: To investigate whether there are definable subgroups of patients with essential hypertension who respond specifically to particular antihypertensive drugs. DESIGN: Randomized cross-over comparison of the antihypertensive effect of 50 mg atenolol per day, 10 mg lisinopril per day and 20 mg nifedipine retard twice a day. Ambulatory blood pressure monitoring was used to assess the blood pressure level both for recruitment and at the end of each treatment period. The treatment periods lasted 4 weeks and were preceded by 4 weeks of placebo. PATIENTS: Seventy-two untreated hypertensive patients with a mean age of 52 (SD 8.4) years were recruited from six general practices and from the hospital outpatient clinic. Sixty-eight patients completed the trial. MAIN OUTCOME MEASURES: To assess the within-patient correlations among the blood pressure responses to each drug and explore the possible role of simple characteristics, such as the initial blood pressure, plasma renin concentration and age, in identifying the responders to a particular drug. RESULTS: Systolic/diastolic blood pressure fell significantly with each agent (P < 0.001): atenolol reduced it by 16.3 +/- 13.3/9.9 +/- 8.8, lisinopril by 14.8 +/- 15.0/9.4 +/- 9.1 and nifedipine by 11.6 +/- 12.3/6.7 +/- 8.3 mmHg. There was a low degree of correlation between the changes in blood pressure with the three drugs in individual patients. With each drug there was a small percentage (8.9-14.7%) of non-responders. The initial level of systolic blood pressure was weakly correlated with the antihypertensive effect of nifedipine (r = 0.47, P < 0.001) and plasma renin concentration was related to the effect of atenolol (r = 0.32, P < 0.01). Age did not predict the blood pressure response to any agent. CONCLUSIONS: The low level of the correlation between the blood pressure changes with the three drugs suggests that different mechanisms may be involved in the aetiology of essential hypertension. Plasma renin concentration and the initial level of systolic blood pressure contribute only weakly to the identification of responders to the three drugs.

Adolescent↗
PubMed1993

Hemodynamic effects of captopril and isosorbide mononitrate started early in acute myocardial infarction: a randomized placebo-controlled study.

OBJECTIVES: The aim of this study was to study the hemodynamic effects of orally administered captopril and isosorbide mononitrate in suspected acute myocardial infarction. BACKGROUND: Early treatment with converting enzyme inhibitors and nitrates in acute myocardial infarction may limit infarct expansion and prevent left ventricular dilation. METHODS: In a double-blind study, 81 patients were randomized within 36 h of the onset of symptoms of suspected acute myocardial infarction to 1 month of oral captopril (6.25 mg initial dose, followed 2 h later by 12.5 mg and continuing with 12.5 mg three times daily), isosorbide mononitrate (initial dose 20 mg followed by 20 mg three times daily) or matching placebo. The effects of treatment on changes from baseline in mean arterial blood pressure, heart rate, stroke volume, cardiac output and systemic vascular resistance were assessed noninvasively using Doppler echocardiography 1 h after the first dose, 1 week after infarction and at 6 weeks (that is, 2 weeks after the scheduled end of trial treatment). RESULTS: One hour after the start of treatment, blood pressure was reduced by approximately 10% with both captopril and isosorbide mononitrate, but this difference did not persist at 1 week. Captopril was associated with a significant increase in cardiac output compared with placebo of 13 +/- 3% at 1 h (p < 0.01), 23 +/- 5% at 1 week (p < 0.001) and 22 +/- 6% (p < 0.05) at 6 weeks (2 weeks after the end of trial treatment). This increase in cardiac output with captopril was mainly due to a substantial and sustained increase in stroke volume, although there was also a small increase in heart rate at 1 week. Both captopril and isosorbide mononitrate reduced systemic vascular resistance within 1 h of the start of treatment, but only the effect of captopril was sustained (perhaps because the three-times daily nitrate regimen induced tolerance). Study treatment was well tolerated, and the incidence of withdrawal of study treatment for hypotension was not significantly different from that with placebo. CONCLUSIONS: This study indicates that the hemodynamic effects of both captopril and isosorbide mononitrate are well tolerated in the acute phase of myocardial infarction and that captopril favorably influences cardiac function.

Aged↗
PubMed1992

Age and blood pressure measurement: experience with the TM2420 ambulatory blood pressure monitor and elderly people.

The accuracy of the TM-2420 ambulatory blood pressure monitor was assessed in elderly people. Ninety-four subjects (44 men and 50 women), aged 60-94 with systolic blood pressure (SBP) of 97-208 mmHg and diastolic blood pressure (DBP) of 45-109 mmHg, including 23 with isolated systolic hypertension, were studied in three centres. The monitor was compared simultaneously with pairs of observers using the Hawksley random zero sphygmomanometer. The standard deviation of the difference (SDD) between observers was 4.2 mmHg (SBP), 2.9 mmHg (DBP). The mean difference was 0.49 mmHg (SBP) and 0.27 mmHg (DBP). The SDD between the monitor and the average of the observers' readings was 6.7 mmHg (SBP), 5.5 mmHg (DBP); the mean differences were 4.4 mmHg (SBP) and 4.8 mmHg (DBP). There were no significant differences between the two versions of the monitor used (5 and 7) or between the three pairs of observers. The monitor was equally accurate in isolated systolic hypertension (SDD observers and monitor 6.2 mmHg for SBP, 3.9 mmHg for DBP, mean differences 4.3 mmHg for SBP, 4.5 mmHg for DBP). Twenty-four-hour ambulatory blood pressure monitoring was carried out in 129 subjects aged 60-79; 89% of the monitoring attempted were successful with error rates of < 10%. The mean error rate was 3.8%. The device was well tolerated with only 4.7% of the subjects not completing a monitoring.

Aged↗
PubMed1992

Ventilation in chronic heart failure: effects of physical training.

OBJECTIVE: To assess the effects of exercise training on ventilatory function in chronic heart failure. DESIGN: Observer blinded random allocation crossover training and detraining trial. SETTING: Assessment in hospital based clinical laboratory; training home based. PATIENTS: 22 patients with chronic heart failure (New York Heart Association (NYHA) class II or III) recruited from a tertiary referral centre. All finished the study. INTERVENTION: Bicycle ergometer exercise for 20 minutes a day, five days a week for eight weeks at 70%-80% of maximum heart rate. MAIN OUTCOME MEASURES: Exercise capacity on graded incremental exercise test, minute ventilation, oxygen consumption and carbon dioxide output. RESULTS: Peak work load increased from 96 W to 112 W and peak oxygen consumption from 14.1 ml/kg/min to 15.4 ml/kg/min (p < 0.01). At submaximal workloads carbon dioxide excretion (VCO2) and minute ventilation (Vi) decreased significantly (p < 0.05) though oxygen consumption was unchanged. The relation between Vi and carbon dioxide excretion changed: the slope of the Vi to VCO2 plot decreased from 38.6 to 35.3, indicating an improvement in overall ventilary efficiency. The instantaneous carbon dioxide ventilatory equivalent (Vi/VCO2) decreased at submaximal workloads, and reached a lower minimum value after training, indicating that optimum ventilatory performance improved. The exercise capacity of patients was related to the optimum ventilatory performance. It is suggested that this may in part be mediated through changes in skeletal muscles. CONCLUSION: Exercise training reduces the ventilatory abnormalities in chronic heart failure; thus some of these changes may be due to physical deconditioning.

Aged↗
PubMed1991

Postexercise hypotension is not sustained in normal and hypertensive humans.

Blood pressure falls after a single session of exercise. The duration for which this fall in blood pressure persists is not known. Sustained hypotension after a single session of exercise may have important implications in the treatment of patients with mild hypertension. We studied 24 subjects (12 normotensive subjects and 12 patients with mild or borderline hypertension). Blood pressure was measured in the laboratory for 30 minutes before and for an hour after graded bicycle exercise to maximal voluntary capacity. Subjects then left the hospital and measured their blood pressures at home (three measurements every 2 hours) following a strict measurement protocol for the rest of the day (usually between 8 and 12 hours). These home blood pressure measurements were compared with home blood pressure measurements recorded at the same times on a nonexercise control day. At 30 minutes after the graded maximal exercise test, the hypertensive patients experienced a fall in blood pressure from 142 +/- 3.5/93 +/- 6.5 mm Hg (mean +/- SEM) to 124 +/- 4.5/79 +/- 2.8 mm Hg (p less than 0.01). For the normotensive subjects, blood pressure after exercise fell from 117 +/- 3.1/70 +/- 2.1 mm Hg to 109 +/- 3.1/62 +/- 2.8 mm Hg (p less than 0.01). Despite these striking blood pressure reductions for the second half hour after exercise, blood pressure measurements recorded at home were not significantly different on the exercise and control days in either group. We conclude that although a single bout of exercise lowers blood pressure for a short (1-hour) period, this hypotension is not sustained.

Blood Pressure↗
PubMed1991

Ambulatory blood pressure monitoring: validation of the accuracy and reliability of the TM-2420 according to the AAMI recommendations.

The accuracy of the TM-2420 ambulatory blood pressure monitor (A&D Co, Japan) has been assessed by the indirect method according to the recommendations of the Association for the Advancement of Medical Instrumentation (AAMI). Ninety subjects (43 men and 47 women), aged 19-89 with a range of systolic blood pressures (SBP) of 81-211 mmHg and diastolic blood pressures (DBP) of 32-113 mmHg were studied. The monitor was compared with two observers using the Hawksley random zero sphygomomanometer. The standard deviation of the difference (SDD) between the observers was 3.0 mmHg for SBP and 2.3 mmHg for DBP. The mean differences between observers were -0.31 mmHg for SBP and 0.32 mmHg for DBP (both NS). The average of three readings for each subject recorded by the monitor was compared with the average of the simultaneous readings by the observers. The SDD was 7.2 mmHg for SBP and 5.5 mmHg for DBP (within the recommendations for accuracy). The differences between methods were -0.98 mmHg for SBP and 0.18 mmHg for DBP; these differences were not significant (NS). The monitor was also assessed against direct intra-brachial artery pressure in 12 subjects (36 readings). The mean difference between the monitor and simultaneous individual intra-arterial reading was -9.5 mmHg for SBP (P less than 0.001) and 3.7 mmHg for DBP (P less than 0.001). The SDD's between methods were 12 mmHg for SBP and 5.0 mmHg for DBP. Use of the monitor in general clinical practice in 100 patients was also assessed. The rate of errors was low (6.8%), and the device found to be acceptable.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1990

Ambulatory blood pressure in relation to drug treatment and clinical trials.

Spontaneous differences in blood pressure from one clinic visit to another inevitably lead to the use of unnecessarily high doses of drugs in the treatment of hypertension and to unnecessarily high recommended doses of new antihypertensive drugs. This can be avoided by the use of ambulatory blood pressure monitoring. The improved reproducibility achieved by ambulatory monitoring substantially reduces the number of subjects required to detect small differences in pressure between one treatment and another. Furthermore, 24-h monitoring eliminates time-related fluctuations and makes it possible to use crossover trials to compare the antihypertensive effects of different drugs. Differences of 5 mmHg in diastolic pressure between two treatments can thus be detected in a trial on less than 20 subjects.

Antihypertensive Agents↗
PubMed1989

Value of ambulatory blood pressure monitoring in clinical pharmacology.

Ambulatory monitoring of blood pressure can improve clinical trials in two ways, first, by the identification and exclusion of those patients in whom the blood pressure is raised only in the clinic environment and second, by improving the repeatability of blood pressure estimations. In 75 subjects the standard deviation of the difference in diastolic pressure between two clinic readings taken a month apart was 12.3 mmHg. On ambulatory monitoring this fell to 6.3 mmHg. Since the number of subjects needed in a trial is related to the square of the standard deviation of the difference, the improved repeatability leads to a substantial reduction in the number of subjects needed. However, to achieve an adequate repeatability, at least 20 blood pressure readings are required per day.

Antihypertensive Agents↗
PubMed1988

Doppler ultrasound signal analysis based on the TMS320 signal processor.

Doppler ultrasound is an established method for the study of haemodynamics. Considerable improvement in accuracy and resolution can be achieved by utilizing advanced data processing techniques. Such a system has been developed and used to assess the cardiac component of the Baroreceptor Reflex in adults and to examine cerebral blood flow in neonates.

Blood Flow Velocity↗
PubMed1988

The use of ambulatory blood pressure monitoring to improve the accuracy and reduce the numbers of subjects in clinical trials of antihypertensive agents.

A low-cost ambulatory blood pressure measuring device has been developed from a commercially available stationary apparatus. The device, which has been compared for accuracy with a mercury manometer, has functioned satisfactorily as an ambulatory monitor for 4 years. To minimize errors, blood pressure readings were made in the sitting position at half-hourly intervals over the waking day. The utility of the device in clinical trials has been investigated. On repeated readings no placebo effect on blood pressure was detectable and the mean difference between two readings in 42 subjects was 1.9/-0.33 mmHg. The standard deviation of the difference were 8.1/5.6 mmHg. This should make it possible to detect differences of 8/5 mmHg between two treatments in about 16 subjects. There was no detectable tendency for blood pressure to change during the day but the variability between readings was substantially increased if the observation periods were reduced to 4 h.

Adult↗