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J Conway

Publications and source records attributed to J Conway.

At least 91 records · Page 5Linked to original sources
PubMed1993

Technical note: the development of quality assurance for Sheffield's radiotherapy treatment planning systems.

Quality assurance procedures have been defined and implemented for the treatment planning systems at Weston Park Hospital. The programme of tests and checks covers both hardware and software: hardware checks are concerned with the input and output performance of the system's peripheral devices; the software checks involve testing system data integrity, and testing the algorithms used for planning external photon and electron beams. Beam measurements from an ionization chamber scanned in water and air were compared with calculations from two independent treatment planning systems. Following the implementation of these quality assurance procedures, some improvements have been made to the system data used and changes have been introduced to planning practice.

Algorithms↗
PubMed1993

Effect of circadian variation in energy expenditure, within-subject variation and weight reduction on thermic effect of food.

Thermic effect of food (TEF) studies give conflicting answers to research questions and in many cases data from one laboratory to another is not comparable because of the utilization of different experimental methods. Likewise, how weight reduction affects measurement of TEF is controversial. Two studies were conducted on how TEF affects energy expenditure. The first study examined how resting energy expenditure (REE) measurements can affect TEF studies and how much within-subject variation is found in TEF studies. The TEF of a standard meal was measured in six subjects for 6.5 h on three different occasions by indirect calorimetry. REE was measured on each subject for 1 h before the meal was given on each measurement occasion. On a separate day, the energy expenditure was measured on each subject during the same time period as the TEF measurement, but without any food given to determine if a circadian increase in REE over the time period of the measurement was observed. We found no circadian increase in energy expenditure during the 6.5 h of the REE study. While the within-subject variation in REE (four measurements) had an average coefficient of variation of 5.2% (range 2.4-8.5%), the coefficient of variation of the TEF measured (three measurements) was 26.4% (range 13.6-50.9). In the second study, REF and the TEF were measured before and after weight reduction in moderately overweight adult women. Nine women weighing between 62.1 and 84.7 kg lost an average of 7.3 kg while on a reduced calorie, low fat diet for between 12 and 14 weeks. After weight reduction, the average REE of these subjects decreased by 8.8% or 515 kJ (123 kcal)/24 h. The TEF of these nine women was measured for 6.5 h before and after weight reduction using 16 oz of Sustacal, 2008 kJ (480 kcal). Before weight reduction the thermic effect of Sustacal was 264 kJ (63 kcal) or 13% of calories consumed, and after weight reduction it was 251 kJ (60 kcal) or 12.5% of calories consumed. We did not find the TEF to be lower than expected in these subjects before weight reduction, since TEF is often reported to be around 10% of energy consumed, and it was not changed after weight reduction.

Adult↗
PubMed1993

"Stiff red cell syndrome". A review of the treatment of sickle cell disease with pentoxifylline.

Pentoxifylline has been used extensively to improve microcirculation, particularly in peripheral vascular disease. Pentoxifylline appears to act by increasing red cell flexibility and inhibiting platelet aggregation and white cell adhesion. For that reason, experimental and clinical studies were initiated to explore its possible usefulness in the prevention of vaso-occlusive crises in sickle cell diseases. The current status of such studies is reviewed.

Animals↗
PubMed1992

Antihypertensive effect of carvedilol: a preliminary dose-response study.

The blood pressure (BP) lowering effect of low doses of antihypertensive agents is not usually explored because of the difficulty in detecting small changes in BP. Since ambulatory blood pressure monitoring in a cross-over trial design can reliably detect differences of 5 mmHg with less than 20 subjects, we have used this technique to assess the dose-response curve of a new beta-blocker, carvedilol. Twenty subjects were enrolled after diagnostic ambulatory BP monitoring had shown a day-time average diastolic BP of over 90 mmHg. Three doses of carvedilol (6.25, 12.5 and 25 mg daily) and placebo were then given double-blind in random order for periods of 4 weeks each. No period effects were detected. The antihypertensive effect was statistically significant at doses of 12.5 mg and 25 mg daily. There was, however, no evidence that 25 mg/day produced the peak effect. The lowest dose (6.25 mg/day) produced a small fall in both systolic and diastolic BP but neither of these were significant. We conclude that doses of 12.5 and 25 mg carvedilol once a day are adequate for the treatment of hypertension.

Adrenergic beta-Antagonists↗
PubMed1992

Severe paroxysmal hypertension induced by a subconscious Valsalva-like manoeuvres.

We describe the case history of a 32 year old male with severe paroxysmal hypertensive spikes when there was an increase in diastolic blood pressure to 150-200 mmHg. These spikes occurred during rest and especially during modest exercise. They were associated with headache and dyspnoea and were resistant to antihypertensive medication. After 5 years of observations and investigations he underwent further 24-h intra-arterial blood pressure monitoring and physiological testing. The 24-h blood pressure profile was near normal at rest. The observed hypertensive spikes seemed to be induced by involuntary Valsalva-like manoeuvres. This had not been detected previously by the investigators and the patient was unaware of inducing these manoeuvres.

Adult↗
PubMed1992

Experimental assessment of electrical impedance imaging for hyperthermia monitoring.

Two experimental studies are presented that attempt to assess the use of electrical impedance tomography (EIT) to map thermal changes deep in the body. The first was a joint study between our group in Sheffield and the Daniel den Hoed Cancer Center in Rotterdam, funded by the COMAC-BME Hyperthermia project. Phantom and in vivo experiments were conducted with a deep heating ring-capacitive hyperthermia device; the results highlighted some of the inherent problems (electromagnetic interference, nonuniform sensitivity) that remain to be solved for this application. The second experimental study involved heating the stomachs of volunteers by pumping known quantities of liquid (a salt/glucose solution, conductivity 5 mS) at controlled temperatures (25, 37 and 47 degrees C) in and out of the stomach via a nasogastric tube. Results indicated that the level of thermal change induced by these liquids could be reproducibly measured by impedance imaging. Both studies were a further step in assessing the capabilities of EIT for noninvasive monitoring of deep body hyperthermia. The results are encouraging and indicate the value of continued development of EIT for non-invasive thermometry.

Electric Conductivity↗
PubMed1992

Ascending aortic Doppler velocity and the prediction of exercise capacity in post-infarction left ventricular dysfunction.

A system to improve analysis of the aortic pulsed Doppler velocity signal has been developed and used to study cardiac performance during a 4 min, 25 W incremental stage supine bicycle exercise to exhaustion. Twenty-two male subjects with stable chronic ischaemic heart disease were studied (15 with NYHA class II/III heart failure, and seven age-matched class I subjects). None had evidence of reversible ischaemia. Peak velocity (PV) from the intensity weighted mean velocity profile, early acceleration (eA) and stroke distance (SD) were all significantly lower at rest in class II/III compared to class I. For the change from rest to 50 W, PV did not alter, eAC increased significantly (P less than 0.05) and to a similar extent in both groups (18.6% class II/III vs 16.4% class I) and SD was reduced from 7.8 to 5.9 in class II/III (P less than 0.01) but did not change in class I (12.4 vs 11.8, ns). There was also a greater increase in heart rate (HR) in class II/III subjects (P less than 0.05). The duration of exercise was correlated with resting PV (r = 0.48, P less than 0.025) but was correlated best with the change in blood momentum (PV x Stroke volume x HR) between rest and peak exercise (r = 0.80, P less than 0.001). Thus Doppler velocimetry can give quantitative information on the response to exercise which discriminates between grades of ventricular dysfunction and is predictive of exercise capacity.

Adult↗
PubMed1992

The influence of ambulatory blood pressure monitoring on the design and interpretation of trials in hypertension.

OBJECTIVE: To describe the reproducibility of diastolic blood pressure (DBP) measurement by clinic and ambulatory monitoring and to evaluate the effects of this reproducibility on the design and interpretation of clinical trials in hypertension research. DESIGN: Prospective single-blind study of repeat measurement reproducibility of blood pressure recording. SETTING: Tertiary referral hospital hypertension clinic. PATIENTS: One hundred untreated mild-to-moderate hypertensive subjects taking 1 month of single-blind placebo. MAIN OUTCOME MEASURES: A single clinic measurement of DBP was poorly reproducible and the results for single DBP estimates taken out of a daytime ambulatory recording were similar. Average ambulatory DBP was much more reproducible, although this improvement depended upon the averaging of many measurements taken throughout the day. CONCLUSIONS: Ambulatory monitoring would decrease antihypertensive trial size by a factor of four or halve the size of detectable DBP difference between treatments. The use of poorly reproducible DBP measurements such as single clinic readings may have led to an underestimation of the risks of minor degrees of blood pressure elevation because of a 'regression dilution' bias. For single clinic DBP readings, we calculate this underestimation to be as much as 69%, and for average ambulatory DBP approximately 20%.

Adult↗
PubMed1992

Baroreflex control of stroke volume in man: an effect mediated by the vagus.

1. Beat-by-beat changes in cardiac performance in response to arterial baroreceptor stimulation induced by phenylephrine were evaluated by pulsed-wave aortic Doppler ultrasound in eighteen subjects. Stroke distance was used as an index of stroke volume and minute distance as an index of cardiac output; peak velocity was also measured. 2. The sensitivity of the baroreceptor-cardiac reflex was assessed by calculating the slope of the regression lines relating the changes in heart period (R-R interval), peak velocity and stroke distance in response to the rise in systolic blood pressure (SBP) induced by phenylephrine. In ten subjects the experiment was repeated after vagal blockade by atropine. Since the tachycardia induced by vagal blockade could alter the sensitivity of the baroreflex, we compared the results obtained after atropine with those obtained during pacing at similar rates in six subjects with cardiac pacemakers. 3. As R-R interval lengthened in response to the rise in SBP, stroke distance and peak velocity fell sharply. The subjects with a highly sensitive baroreceptor-heart rate reflex showed the greatest fall in peak velocity and stroke distance. The slope of the relationship between R-R interval and SBP for each subject correlated closely with that of peak velocity/SBP (correlation coefficient, r = 0.88) and stroke distance/SBP (r = 0.93) relationships. 4. Atropine virtually abolished all the cardiac reflex changes, despite a considerable increase in SBP induced by phenylephrine. At comparable heart rates achieved by pacing the sensitivity of the baroreceptor-cardiac reflex (calculated from the slopes of the regression lines relating changes in stroke distance and in peak velocity to the rise in SBP) was maintained and was significantly greater when compared to that obtained after vagal blockade. 5. These results show that the stimulation of arterial baroreceptors is accompanied by a fall in the Doppler-derived indices of stroke volume and cardiac output. This response is neural and is abolished by atropine, which indicates that it is mediated through the efferent vagus.

Adult↗
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↗
PubMed1992

Validation of the beat to beat measurement of blood velocity in the human ascending aorta by a new high temporal resolution Doppler ultrasound spectral analyser.

OBJECTIVE: To develop and validate a high temporal resolution spectral analysis system for Doppler measurements of blood velocity in the ascending aorta. DESIGN: An observational laboratory and clinical study comparing Doppler velocity-based measurements with fluid collection, electromagnetic flow catheters and probes, and thermodilution. SETTING: Tertiary referral cardiology unit and cardiac catheter laboratory. PATIENTS: Patients undergoing routine cardiac catheterisation for ischaemic heart disease, cardiac failure, and primary pulmonary hypertension. RESULTS: There was good agreement between Doppler-derived and electromagnetic cuff or catheter measurements of velocity in an experimental flow rig (SD of differences 4.75% for velocity integral) and in the patients (SD of differences 4% for velocity integral). There was also reasonably good agreement between simultaneous Doppler-derived and thermodilution-estimated cardiac output measurements in patients undergoing cardiac catheterisation (SD of differences 12.6%). CONCLUSIONS: This new method of high temporal resolution spectral analysis improves the resolution of rapidly changing blood velocities and may improve the ability to describe blood velocity patterns in the ascending aorta.

Adolescent↗
PubMed1992

Treatment of obstructive sleep apnea with nasal continuous positive airway pressure. Patient compliance, perception of benefits, and side effects.

Obstructive sleep apnea is a chronic disease whose treatment may require long-term nightly use of relatively cumbersome and expensive breathing equipment that provides continuous positive airway pressure (CPAP) via nasal mask. Compliance with this treatment may be influenced not only by the objective improvement in sleep apnea but also by the patient's subjective perception of the benefit, bed mate or family support, side effects, and cost. The last factor may not be important in Ontario, where 75% of the cost is paid by the Ministry of Health. The goal of this study was to analyze the factors that may influence patient acceptance of nasal CPAP. This was done by tabulating the responses to a detailed questionnaire mailed to 148 patients with obstructive sleep apnea (OSA). There were 96 replies. We were able to contact by telephone an additional 42 patients. The results showed that 105 patients continued to use CPAP at a mean follow-up time of 17 +/- 11 months, some for as long as 6 yr. The majority of patients (81%) perceived CPAP as an effective treatment of the disorder, 5% were unsure, and 14% believed that CPAP was ineffective, despite the resolution of sleep apnea on polysomnography. Subjective improvement reported by the patients was also observed by the family members in 83% of the patients. The most common complaint, voiced by 46% of the patients, was nocturnal awakenings. Nasal problems, such as dryness, congestion, and sneezing, were the second most frequent complaint present in 44% of the responders.(ABSTRACT TRUNCATED AT 250 WORDS)

Costs and Cost Analysis↗
PubMed1992

Electrical impedance tomography: prospects for non-invasive control of deep hyperthermia treatments.

Electrical Impedance Tomography (EIT) is assessed as a means of monitoring deep hyperthermia treatments in both phantom and in vivo studies. EIT measurements during heating of an inhomogeneous leg phantom show good correlation with internal temperatures measured with invasive probes. Measurements whilst altering the temperature of the stomach contents in volunteers demonstrate the capability of EIT for imaging temperature change at depth in the torso. Significant problems remain to be overcome before EIT can be used in the clinic; however, the technique may be an important additional control factor as a complement to invasive monitoring.

Body Temperature↗
PubMed1991

Effects of endurance training on baroreflex sensitivity and blood pressure in borderline hypertension.

Physical training offers a potential nonpharmacological strategy for control of mild and borderline hypertension, but its effect on blood pressure is controversial. We investigated the effects of endurance training on waking and sleeping blood pressure and on baroreflex sensitivity in 16 borderline hypertensive patients. First, 8 patients were assessed before and after a 6-month endurance training programme. Then, when it was clear that blood pressures were lower after training, a further 8 patients were studied not only at the end of the training programme but also after 4 months' abstention from exercise (detraining). Measurements were taken of baroreflex sensitivity (response to iv phenylephrine), blood pressure, R-R interval, and blood pressure and R-R variability. Ambulatory blood pressures were measured in 13 patients (7 trained, 6 detrained) and sleep blood pressures in 6 patients (3 trained, 3 detrained). Increased fitness was associated with a decline in resting arterial blood pressure of 9.7 (SE 2.0) mm Hg systolic and 6.8 (1.2) mm Hg diastolic, and with a decline in ambulatory blood pressure of 4.8 (1.4) mm Hg and 7.5 (2.1) mm Hg, respectively; both p less than 0.05. Baroreflex sensitivity was 14.0 (1.8) ms/mm Hg in the unfit and 17.5 (2.0) ms/mm Hg in the fit; p less than 0.05. Sleep blood pressures were not lower in the fit despite longer sleep R-R intervals. These findings indicate that, in some subjects with borderline or mild hypertension, a physical training programme is sufficient to bring the blood pressure within normal limits.

Adult↗
PubMed1991

Energy requirements of a postobese man reporting a low energy intake at weight maintenance.

Three experiments were performed to test the validity of the low reported energy intake of weight maintenance in a postobese man. In the first experiment the subject reported a mean energy intake of 8008 kJ/d during 16 d and he maintained a stable body weight. This finding was not reproduced in the second experiment, which consisted of a 6-d inpatient study during which the subject was confined to a whole-body calorimeter for 5 d. Indeed, he lost weight when fed a controlled energy intake of 7950 kJ/d. Moreover, this experiment showed that direct and indirect calorimetry provided comparable energy-expenditure measurements during this period. Finally, when the subject was refed a controlled energy intake of 7950 kJ/d for 21 d, body weight and fat losses were observed. Therefore, these observations do not support the validity of the low energy intake that may be reported by people predisposed to obesity.

Body Weight↗
PubMed1991

Interdependence of blood pressure and heart period regulation in mild hypertension.

Blood pressure and heart period variability have been measured directly in 142 subjects with mild hypertension over 24 h. The variabilities have been expressed as the standard deviation of 2 min averages of all beats over 24 h. Baroreflex sensitivity was assessed in 102 subjects by the phenylephrine method. Blood pressure varies over a range of approximately 40% around the mean by day and by approximately 20% at night. The variability of blood pressure by day was inversely proportional to the sensitivity of the baroreflex (r = -0.33, P less than .001), while the variability of heart period was directly related to the sensitivity of the reflex (r = 0.27, P less than .01). Neither of these relationships was significant at night. An inverse relationship between heart period and blood pressure was shown by regression analysis of blood pressure and heart period averages over 24 h. The steepness of the slope of the heart period-systolic blood pressure relationship was strongly correlated with the baroreflex sensitivity (r = -0.55, P less than .001), suggesting that blood pressure variations are substantially buffered by changes in heart frequency. Thus, a more stable heart rate that results from an ineffective baroreflex is associated with a more variable systolic blood pressure.

Adolescent↗