Biomedical subjects

G P Lawrence

Publications and source records attributed to G P Lawrence.

5 recordsLinked to original sources

PubMed1992

Autonomic function testing in diabetic subjects using sequential measurements.

The repeatability of commonly used electrocardiographic (ECG) related autonomic function tests was investigated in 25 diabetic subjects, mean age 44 (range 18-67) years and mean duration of diabetes 10 (< 1-35) years. Tests were based on deep breathing, the Valsalva manoeuvre, relaxed normal breathing, and standing up from a lying position. All tests were repeated twice at each session, with two sessions separated by a mean of 5 (range 3-8) months. ECG and respiratory data were recorded for subsequent analysis. Maximum (max) and minimum (min) RR intervals and instantaneous heart rate (HR) were determined. The mean and repeatability data (within-subject standard deviation) for 21 different test results were calculated, and included deep breathing sitting (max-min)RR 226 +/- 39 ms and (max-min)HR 19.3 +/- 3.2 beats min-1, Valsalva manoeuvre 1.74 +/- 0.18, and lying-to-standing RR ratio 1.19 +/- 0.07. The within-subject repeatability to between-subject variability ratios consistently demonstrated that it is better to perform the deep breathing test sitting (with the smaller mean ratio of 0.37) rather than supine (0.46), with the use of three respiratory cycles rather than a single cycle (0.33 compared with 0.50 for (max-min)RR). A significant (p = 0.037) relationship was found between variability in heart rate changes and variability in air volume breathed during the deep breathing test.

Adolescent↗

PubMed1992

Repeatability of measurements and sources of variability in tests of cardiovascular autonomic function.

OBJECTIVE: To determine the repeatability and sources of variability of clinical tests of cardiovascular autonomic function. DESIGN: The commonly used electrocardiographic related tests of autonomic function were studied. Two repeat measurements of all tests were made on all subjects on four separate days over a four week period. SUBJECTS: Ten normal subjects with no known autonomic dysfunction were investigated. MAIN OUTCOME MEASURES: These were deep breathing (subject seated and supine), Valsalva manoeuvre, standing up from lying position, and normal relaxed breathing (subject supine). During the tests the electrocardiogram and respiratory pattern were recorded by computer. Beat to beat RR intervals were measured automatically from the electrocardiogram, and from these the results of the tests were calculated. RESULTS: Variance analysis showed significant between subject variability for all tests (p < 0.005), but some tests showed a much smaller relative within subject variability than others. Average repeatability data (within subject SD) for each test were calculated, and included deep breathing sitting (max-min) RR (46 ms), Valsalva ratio (0.17), and lying to standing RR ratio (0.11). These compare with between subject SDs of 65 ms, 0.38, and 0.13 respectively, at mean values of 305 ms, 1.92, and 1.15 respectively. The data highlighted one subject with the poorest repeatability, whose electrocardiogram turned out on closer inspection to be under atrial rather than sinus control at times. Poor repeatability in the other subjects was related to variability in the respiratory pattern, and in the deep breathing test, repeat variability was significantly correlated (r = 0.79) with variability in the respiratory amplitude (p < 0.05). CONCLUSIONS: Repeatability data should be available to each laboratory carrying out autonomic function tests. The data provided in this study could be used as a baseline. Poor repeatability highlights the need to re-examine the test procedures, or the test data from specific subjects. Variability of respiratory pattern is associated with poor repeatability, and so careful instructions on respiration should be given to each subject before the tests.

Adult↗

PubMed1991

Which vasodilator drug in patients with chronic heart failure? A randomised comparison of captopril and hydralazine.

1. Fifty patients with symptoms due to chronic heart failure despite diuretic therapy were randomised to receive additional treatment with either hydralazine or captopril. The dose was titrated; 24 received hydralazine and 26 captopril up to a maximum daily dosage of 225 mg and 75 mg respectively. Forty-three patients had coronary heart disease and seven dilated cardiomyopathy. 2. Dyspnoea and tiredness were assessed using a visual analogue scale (0-100) before and during 12 weeks' treatment. Captopril produced a significantly greater reduction in breathlessness (F = 31.6, P less than 0.001) and tiredness (F = 65.8, P less than 0.001) compared with hydralazine. 3. There was an increase in treadmill exercise time during treatment with both hydralazine (from 5.5 (3.47-7.53) min to 6.9 (4.87-8.93) min), and captopril (from 5.0 (3.05-6.95) min to 7.8 (5.85-9.75) min), but the degree of improvement was significantly greater in the patients treated with captopril (F = 7.4, P less than 0.001). 4. There was no significant change in right ventricular ejection fraction (from 27.9 (19.3-36.5)% to 28.7 (20.1-37.3)%) or left ventricular ejection fraction (from 22.2 (14.2-30.2)% to 23.9 (15.9-31.9)%) during treatment with hydralazine. However, both right and left ventricular ejection fraction increased significantly during treatment with captopril (from 27.1 (18.9-35.3)% to 32.0 (23.8-40.2)%, P less than 0.05; and from 25.0 (17.2-32.8)% to 29.6 (21.8-37.4)%, P less than 0.05 respectively). 5. These results suggest that in patients with symptoms due to chronic heart failure despite diuretic therapy, treatment with captopril produces a greater symptomatic and haemodynamic improvement than treatment with hydralazine.

Adult↗

PubMed1991

Repeatability of dynamic eye pupil response measurement using the Pupilscan instrument.

The repeatability of pupil response measurements made with the Pupilscan instrument has been assessed. Two operators made 32 repeat recordings of the pupil response in each eye of eight normal subjects over four days. A total of 512 recordings were made and the results analysed by variance analysis. Room light levels were carefully controlled. The instrument measured initial pupil diameter, and after a 0.2 s light stimulus measured minimum and final diameters, maximum diameter change, constriction velocity and time to minimum diameter. For all measurements except time to minimum, there were significant differences (P less than 0.001) between the normal subjects. Day-to-day variation was also significant (P less than 0.005), but did not mask the differences between subjects. It is concluded that the average of at least four repeat measurements are made, giving error ranges similar to those observed from day-to-day changes.

Adult↗

PubMed1989

Evaluation of myocardial thallium tomography in patients with chest pain.

Thirty-seven patients with chest pain have been studied by exercise thallium tomography and coronary arteriography to assess the accuracy of thallium tomography in the identification of patients with coronary artery disease and to evaluate whether knowledge of clinical data improves this accuracy. Thallium tomography was also used to identify which coronary arteries were stenosed. Thallium tomography when compared with coronary arteriography has a sensitivity of 97%, a specificity of 75%, and an overall accuracy of 92% for the detection of coronary artery disease. When clinical information was made available, these results improved to a sensitivity of 100%, a specificity of 75%, and an overall accuracy of 95%. In the identification of which coronary arteries were stenosed, thallium tomography had a sensitivity of 85%, a specificity of 89%, and an overall accuracy of 86%. These results show that exercise thallium tomography can be an accurate non-invasive screening test in patients with chest pain thought to be angina.

Angina Pectoris↗