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Biomedical subjects

J Conway

Publications and source records attributed to J Conway.

At least 109 records · Page 6Linked to original sources
PubMed1991

Angiotensin-converting enzyme inhibition and physical training in heart failure.

A total of 12 patients (mean age +/- SEM 63 +/- 2.6 years) with moderate to severe heart failure (ejection fraction = 23 +/- 3.2%) were included in a placebo-controlled crossover trial. Patients were randomly allocated to 4 periods of 6 weeks each: placebo, placebo and physical training, lisinopril 10 mg daily, and lisinopril and physical training. The exercise time increased from 13.6 +/- 0.9 min with placebo to 15 +/- 1 min with training alone, and to 16.1 +/- 0.7 min with lisinopril and training. With lisinopril alone there was a non-significant increase in exercise time, to 14.5 +/- 0.6 min. Improvements in exercise time were accompanied by a similar increase in peak oxygen consumption. Overall, the most significant improvements in symptoms and indices of cardiorespiratory fitness were achieved with a combination of lisinopril and training. Thus physical training is not only a useful adjunct to the existing medical therapy for heart failure, but it may also provide symptomatic benefits in its own right.

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

Cardiac and blood pressure responses to mental stress in reactive hypertensives.

To study the haemodynamic response to a standardized mental stress, we measured ascending aorta velocity using Doppler ultrasonography in 20 reactive ("white-coat") hypertensives and 20 age and sex matched normal controls (NC) familiar with the hospital setting. Reactive hypertensives (RH) had 3 office diastolic BP recordings between 90-110 mmHg and ambulatory BP less than 140/90 mmHg. The cardiac response to mental arithmetic was greater in RH than NC (minute distance, RH: +36.7 +/- 40.2% vs NC: +10.3 +/- 19%, p less than 0.05; peak velocity, RH: +8.4 +/- 16.5% vs NC: -1.4 +/- 11.9%, p less than 0.05), and there was a different peripheral resistance response (RH: -12.2 +/- 24.2% vs NC: +6.5 +/- 22%, p less than 0.05). We suggest that subjects with reactive hypertension have a strong cardiac response to mental stress and this could be a characteristic of this condition.

Adult↗
PubMed1991

Analysis of ambulatory blood pressure data.

Many statistical techniques can be used to describe different aspects of ambulatory records, but it is highly unlikely that any single parameter will suffice. A more realistic aim is for a combination of measures that combine statistical validity with physiological meaning and clinical usefulness. This will require compromises between conflicting demands, and only experience and research will ultimately determine the best summary statistics. Some of the available techniques are described here in terms of their value to research and to clinical practice, and an approach is proposed based on considerations of the physiology of blood pressure in free-living man.

Activities of Daily Living↗
PubMed1991

Ambulatory blood pressure monitoring in the design of antihypertensive drug trials.

The reproducibility of blood pressure estimates is considerably improved by ambulatory blood pressure monitoring compared to clinic or office readings. This reduces the number of patients required for clinical trials or improves the statistical power of the trials. Non-uniformity in the response to antihypertensive drugs makes it preferable to use crossover trials with ambulatory monitoring when comparing different antihypertensive agents. However, inherent variability of blood pressure limits the potential of these trials to determine the time-course of the action of drugs.

Antihypertensive Agents↗
PubMed1991

Ambulatory blood pressure and clinical trials.

Ambulatory blood pressure monitoring essentially estimates the average value of systolic and diastolic pressure from readings that fluctuate with mental and physical activity throughout the day. The improved reproducibility of blood pressure measurement achieved in this way increases the precision of clinical trials and/or reduces the number of subjects needed in a trial. Thus it is possible to detect a 5 mmHg diastolic difference between two treatments (with a statistical power of 0.9) using less than 20 subjects in a crossover trial. Ambulatory monitoring has its limitations. Since it is an averaging process, the ability to follow the effect of drugs over short periods of time is strictly limited. To overcome this handicap it is necessary to reduce the spontaneous variability of blood pressure, which can be done by limiting mental and physical activity while the drug action is being monitored. This can be achieved in the laboratory but not in freely moving subjects.

Antihypertensive Agents↗
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

Effects of physical training in chronic heart failure.

Eleven patients with chronic heart failure secondary to ischaemic heart disease (mean [SEM] age 63.0 [2.3] years; left ventricular ejection fraction 19 [8]% undertook 8 weeks of home-based bicycle exercise training and 8 weeks of activity restriction (rest) in a physician-blind, random-order, crossover trial. Training increased exercise duration from 14.2 (1.1) min to 16.8 (1.3) min and peak oxygen consumption from 14.3 (1.1) ml.min-1.kg-1 to 16.7 (1.3) ml.min-1.kg-1. Heart rates at submaximum workloads and rate-pressure products were significantly reduced by training, and there was also a significant improvement in patient-rated symptom scores. No adverse events occurred during the training phase. Thus home-based physical training programmes are feasible even in severe chronic heart failure and have a beneficial effect on exercise tolerance, peak oxygen consumption, and symptoms. The commonly held belief that rest is the mainstay of treatment of chronic heart failure should no longer be accepted.

Aged↗
PubMed1990

Clinical assessment of cardiac output.

Cardiac output estimation is an important and much needed measurement for assessing patients in heart failure. In hypertension, it is vital for understanding the haemodynamic basis of the disease and the mode of action of drugs. Measurements of blood pressure and cardiac output provide the only means of estimating peripheral resistance. Of the available methods to determine cardiac output, thermodilution is the most practical, although it has its difficulties and care has to be exercised in its use. When intra-arterial blood pressure measurements are needed, the dye-dilution method is equally valid, and if respiratory techniques are available the Fick principle may also be used. Of the non-invasive methods, none is yet developed to a stage suitable for general clinical use. Doppler velocimetry is the most promising technique, but it requires complex computer analysis and, as yet, can reliably be used only to measure changes in cardiac output in an individual. The technique has been assessed against the electromagnetic flowmeter in man and gives reasonable accuracy and repeatability. Echocardiography and impedance cardiography are not yet satisfactory for clinical use; neither are the radionuclide methods, apart from the 'first pass' method, but this also needs further verification.

Cardiac Output↗
PubMed1990

Thermodilution method for measuring cardiac output.

The thermodilution technique has been shown to measure cardiac output accurately. The technique violates ideal conditions for indicator dilution methods and is liable to gross errors unless certain requirements are strictly adhered to. The quantity of injectate must be accurately measured and injected rapidly. The dilution curve must be available for inspection and show a smooth rapid ascent and monoexponential decline.

Blood Flow Velocity↗
PubMed1990

Mortality associated with captopril and enalapril: a report from the DHSS Hypertension Care Computing Project.

In 1986, the Committee on Safety of Medicines published a report suggesting that enalapril may have an adverse effect on renal function. The prescription event monitoring scheme subsequently published figures on adverse drug reactions and mortality for patients treated with enalapril. They concluded that enalapril did not have an adverse effect on renal function and survival. Similar data were not available for captopril, as the drug was marketed before prescription event monitoring had been developed. In the Department of Health and Social Security (DHSS) Hypertension Care Computing Project (DHCCP), 368 hypertensive patients treated with captopril and 371 treated with enalapril were followed for an average of 3.1 and 1.6 years, respectively. Thirty-two patients died; none had renal failure as an underlying cause of death. The death rate was similar in both drug groups, at 17.5 (enalapril) and 24.0 (captopril) per 1000 patient-years. The present report shows that, for patients treated for high blood pressure, the relative risk of mortality with captopril compared with enalapril was 1.37, an insignificant difference (95% confidence interval 0.63, 2.98).

Acute Kidney Injury↗
PubMed1990

A comparison of indirect methods for continuous estimation of arterial PCO2 in men.

Four different measures (PETCO2, PACO2, PADCO2, and PJCO2) for indirectly estimating arterial PCO2 (PaCO2) from respired gas at the mouth have been investigated. PETCO2 was the end-tidal PCO2. PACO2 was calculated using a reconstruction of the alveolar oscillation of PCO2 obtained from the end-tidal "plateau" in PCO2. PADCO2 was calculated as for PACO2 except that the effects of dead space were incorporated. PJCO2 was calculated from an empirical relationship involving PETCO2 and tidal volume. Six subjects were studied at rest and during cycle ergometry at 50 and 100 W while breathing a variety of gas mixtures. Arterial samples were drawn for determination of true PaCO2. The differences for each method between estimated and true PaCO2 at rest and at 50 and 100 W were as follows: PETCO2, -1.35 +/- 2.64, 1.67 +/- 2.31, and 2.67 +/- 2.02 (SD) Torr; PaCO2, -2.15 +/- 2.73, -0.80 +/- 2.18, and -0.35 +/- 2.31 (SD) Torr; PADCO2, -1.55 +/- 2.54, 0.25 +/- 2.16, and 0.63 +/- 2.26 (SD) Torr; and PJCO2, -1.41 +/- 2.30, 0.12 +/- 1.79, and 0.08 +/- 1.96 (SD) Torr. It is concluded that, at rest, all methods significantly underestimate true PaCO2 and during exercise PETCO2 significantly overestimates PaCO2, but no bias was detected for any of the other methods.

Adolescent↗
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↗
PubMed1990

Lisinopril and enalapril in hypertension: a comparative study using ambulatory monitoring.

Detecting differences in the effect of two antihypertensive agents is bedevilled by the inherent variability of blood pressure itself. Using an ambulatory blood pressure monitoring technique, we compared, in a cross-over design study, the effects of four weeks' treatment with enalapril, 10 mg once daily, to lisinopril, 10 mg once daily, on the blood pressure of 19 patients with mild to moderate hypertension. A significant reduction in blood pressure was shown by both drugs. However, lisinopril produced a greater fall in mean 24 hour systolic pressure than did enalapril (difference; 5.94 (C.I. -0.77 to -11.1) mmHg, P = 0.027). The difference of 3.3 mmHg (C.I. +0.54 to -7.10) in diastolic pressure between the two agents, though in the same direction, was not significant. Plasma renin activity did not predict the responses to either agent. Studying the prevailing information for these two drugs one might expect there to be little difference between them when administered once daily in terms of antihypertensive effect. The explanation for the superiority of lisinopril may lie in the slightly longer pharmacokinetic half-life and possibly in differences in tissue distribution or persistence. The side effects of both drugs were mild and of similar frequency to those recorded during placebo treatment, illustrating the generally well tolerated nature of this class of antihypertensive therapy. The use of ambulatory blood pressure monitoring provides a method that can detect small, but possibly important differences between drugs. In the clinical setting it allows a more thorough assessment of a particular patient's response to therapy.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗