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Biomedical subjects

J Conway

Publications and source records attributed to J Conway.

At least 73 records · Page 4Linked to original sources
PubMed1998

Leg blood flow and increased potassium release during exercise in chronic heart failure: effect of physical training.

BACKGROUND: Exercise-induced hyperkalemia, which may contribute to exercise hyperpnea and exertional fatigue, is increased in patients with chronic heart failure (CHF). This study examined whether differences in leg blood flow during exercise could be responsible for alterations in the level of hyperkalaemia, as well as the effect of physical training. METHODS AND RESULTS: We studied 10 subjects with CHF (ejection fraction 23 +/- 3.9%; mean +/- SD) and 10 subjects with normal left ventricular function (NLVF) who had undergone previous coronary bypass graft surgery (ejection fraction 64 +/- 8.0%; mean +/- SD). Subjects performed incremental cycle exercise to exhaustion before and after physical training. The rises in femoral venous potassium concentration ([K+]), heart rate, lactate, and ventilation (VI) with exercise were all greater in the subjects with CHF than in those with NLVF (P < .05). There was no difference between the groups in leg blood flow during submaximal exercise but peak leg flow was greater in the group with NLVF (P < .01). Physical training was well tolerated and both groups increased their peak VO2 (8 +/- 3.2% CHF (P < .05); 11 +/- 2.7% NLVF (P < .01); mean +/- SE). Training resulted in a reduced rise in femoral venous [K+] and VI (P < .05), but did not affect leg blood flow during submaximal exercise in either group. CONCLUSIONS: The rise in the femoral venous [K+] with exercise is increased in patients with CHF and can be reduced by physical training. These changes are not a consequence of different leg blood flows, either between groups or with training. The study also suggests that femoral venous [K+] is not a powerful regulator of leg blood flow during exercise.

Aged↗
PubMed1998

Audit of ambulatory blood pressure monitoring in the diagnosis and management of hypertension in practice.

This study was carried out to ascertain the value of ambulatory blood pressure monitoring (ABPM) in the diagnosis and treatment of hypertension in routine clinical practice. ABPM was performed during the daytime hours in 410 patients believed to be hypertensive after at least three measurements by their physician and one measurement by a nurse in a hypertension clinic. The diagnosis was confirmed in 70% of patients when 90 mm Hg diastolic blood pressure (BP) was used as the upper limit of normal, and 86.3% when 85 mm Hg was used. In 204 patients who were reviewed 5 years later there were 108 on medical treatment. This reduced diastolic pressure from a mean of 100.6 +/- 8.8 to 85.7 +/- 8.8 mm Hg. However, in 30% of patients the diastolic pressure was still above 90 mm Hg. In the 49 patients with isolated clinic hypertension (ICH), who had remained untreated, diastolic pressure increased from 84.0 +/- 4.8 to 88.1 +/- 8.4 mm Hg over the 5 years. In 19 of these the level exceeded 90 mm Hg. ABPM therefore improves diagnostic accuracy and prevents treatment of patients with ICH. This condition, however, requires follow-up since BP tends to rise with time in some patients. The audit also identified patients who had had a suboptimal response to medical treatment.

Antihypertensive Agents↗
PubMed1997

CT virtual simulation.

Advances in computer technology and software design have enabled the concept of virtual simulation, first suggested by George Sherouse, to be realized. This article reviews the hardware and software requirements that provide a system that feels like a simulator and can facilitate the 3D planning process. Fast digital reconstruction of a radiograph from a CT data set provides true verification of treatment field design within the constraints of the virtual method. The clinical application of this technique is discussed in detail in relation to particular treatment sites.

Breast Neoplasms↗
PubMed1997

Clarity of purpose and administrative accountability: an empirical study in long-term residential care.

Experienced social workers in an Australian residential aged care facility mounted a practice research project over three years. Aims included meeting agency accountability requirements and illustrating social work roles. In consultation with a university school of social work lecturer, the staff members devised a tool to document their practice on a per case basis across the care continuum as well as non case-related work associated with resident needs and agency purpose. A three-month pilot indicated that casework comprised 70% of work time, the 405 cases incorporating higher than expected time on preadmission, gatekeeping and admission tasks. Analyses of the most time-consuming cases revealed complex interacting factors inadequately captured by available and physically-driven case classification and costing tools.

Aged↗
PubMed1996

Prediction of patient responses to antihypertensive drugs using genetic polymorphisms: investigation of renin-angiotensin system genes.

OBJECTIVE: To investigate whether the M235T polymorphism of the angiotensinogen (AGT) gene and the insertion/deletion (I/D) polymorphism of the angiotensin-1 converting enzyme (ACE) gene predict blood pressure response to different antihypertensive agents. DESIGN: Sixty-three patients with untreated essential hypertension were randomly assigned in a placebo-controlled crossover comparison to atenolol 50 mg once daily, lisinopril 10 mg once daily and nifedipine SR 20 mg twice daily, and the effect on blood pressure was assessed by ambulatory blood pressure monitoring (ABPM). In a further 44 patients, placebo-controlled ABPM data were available after treatment with a single agent (atenolol 50 mg once daily in 16 cases and lisinopril 10mg once daily in 28 cases). The change in systolic and diastolic blood pressure achieved by each agent was analysed for association with genotypes at the AGT and ACE gene loci. METHODS: Polymerase chain reaction (PCR) amplification of genomic DNA from each individual was used to identify the I/D polymorphism of the ACE gene. The M235T polymorphism of the AGT gene was detected by Tth111I digestion of PCR product. RESULTS: There was no significant association between response to any drug and either the AGT M235T or ACE I/D polymorphisms. CONCLUSIONS: The large variability between individuals in the observed blood pressure response to these agents cannot be attributed to the polymorphisms analysed at the ACE and AGT loci.

Alleles↗
PubMed1996

Handling harassment.

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Adaptation, Psychological↗
PubMed1996

Effect of low doses of scopolamine on RR interval variability, baroreflex sensitivity, and exercise performance in patients with chronic heart failure.

OBJECTIVE: To study the effect of transdermal scopolamine on heart rate variability, baroreflex sensitivity, and exercise performance in patients with heart failure and age matched healthy volunteers. DESIGN: Double blind, randomised, placebo controlled, crossover study. PATIENTS: 16 patients with chronic, stable heart failure due to ischaemic cardiomyopathy (mean (SEM) age 58 (2) years; mean (SEM) radionuclide left ventricular ejection fraction 28 (2)%; New York Heart Association class II-III) and eight age matched healthy controls. INTERVENTION: Transdermal scopolamine (500 micrograms delivered over 72 h) or a placebo patch was administered for 48 h. MAIN OUTCOME MEASURES: Indices of tonic and reflex cardiac vagal activity and exercise performance. RESULTS: In both groups scopolamine produced a reduction in the 24 h average heart rate and an increase in the time domain measures of heart rate variability. Both the incidence and severity of ventricular arrhythmias remained unchanged. Baroreflex sensitivity, evaluated by the phenylephrine technique, increased significantly (P < 0.001) with scopolamine in patients with heart failure (6.22 (2.81) ms/mm Hg) and in healthy volunteers (5.97 (2.20) ms/mm Hg) as did the amplitude of respiratory sinus arrhythmia, computed by autoregressive spectral analysis of 10 min electrocardiographic recordings (319.9 (123.5) and 657.3 (126.6) ms2 respectively, P < 0.001). While exercise performance did not change, heart rate at submaximal exercise was significantly reduced by scopolamine in each group. CONCLUSIONS: In patients with mild to moderate heart failure low doses of scopolamine increased tonic and reflex cardiac vagal activity. This was achieved without affecting exercise tolerance or the incidence and severity of ventricular arrhythmias.

Baroreflex↗
PubMed1996

Three-dimensional description of pulmonary deposition of inhaled aerosol using data from multimodality imaging.

UNLABELLED: Three-dimensional assessment of pulmonary deposition of inhaled aerosol may be performed using SPECT. The use of aligned anatomical images enables improved accuracy of quantification and anatomical localization of deposition. METHODS: Techniques of analyzing these data and their application to deposition studies of two nebulizer-generated aerosols (mass median diameter 1.5 and 6.5 microM respectively) in 12 normal subjects are described. The deposition data were transformed to a standard hemispherical shape and the mean distribution pattern for each aerosol evaluated. Deposition by airway generation was then calculated using a spatial model of airway morphology. The results were compared to those from planar image analysis. RESULTS: The hemispherical transform yielded considerably more qualitative information on deposition pattern. The central-to-peripheral concentration ratio between conducting and alveolated airways was 5.27 for the coarser aerosol and 2.43 for the fine. The two-dimensional spatial estimates of the ratio were 2.61 and 2.03 respectively. CONCLUSION: Analysis of multimodality imaging data considerably enhanced information on deposition compared to planar imaging. It provides new data on aerosol deposition which will be of value to physicians involved in drug inhalation therapy.

Aerosols↗
PubMed1995

Pitfalls in the interpretation of spectral analysis of the heart rate variability during exercise in humans.

The recent use of spectral analysis of the R-R interval variability to assess the autonomic drive during exercise has produced inconsistent results. The purpose of this study was to assess whether the spectral components of the R-R interval variability reflect different mechanisms at rest and during exercise. Autoregressive spectral analysis of the electrocardiographic and breathing signals was performed in 11 healthy young men at rest and during incremental cycle ergometry. The amplitude of respiratory sinus arrhythmia, i.e. the absolute power of the high frequency spectral component, fell at the onset of exercise, consistent with a reduction in cardiac vagal activity. Conversely, the normalized power of the high frequency component, (i.e. the percentage of R-R interval variance due to the respiratory sinus arrhythmia) increased with increasing work rates. The low frequency spectral component of the R-R interval variability, which when expressed in normalized units is believed to reflect cardiac sympathetic activity, was no longer detectable in severe exercise when the adrenergic drive is known to be elevated. In conclusion, autoregressive spectral analysis of the R-R interval variability does not adequately reflect the autonomic changes that occur during incremental exercise. In particular, the evidence indicates that as the cardiac vagal tone falls with increasing levels of exercise, a greater percentage of the residual power of the high frequency component may be due to non-neural mechanisms.

Adult↗
PubMed1994

Effect of physical training on exercise-induced hyperkalemia in chronic heart failure. Relation with ventilation and catecholamines.

BACKGROUND: The exercise-induced rise in arterial potassium concentration ([K+]a) may contribute to exercise hyperpnea and could play a role in exertional fatigue. This study was designed to determine whether the exercise-induced rise in [K+]a is altered in patients with chronic heart failure (CHF) and whether physical training affects K+ homeostasis. METHODS AND RESULTS: We evaluated 10 subjects with CHF (ejection fraction, 23 +/- 3.9%) and 10 subjects with normal left ventricular function (NLVF) who had undergone previous coronary artery graft surgery (ejection fraction, 63 +/- 8.6%). Subjects performed an incremental cycle ergometer exercise test before and after a physical training or detraining program. Changes in [K+]a and ventilation (VE) during exercise were closely related in both groups. Subjects with CHF did less absolute work and had reduced maximal oxygen consumption (VO2max) compared with subjects with NLVF (P < .01). Exercise-induced rises in [K+]a, VE, norepinephrine, lactate, and heart rate were greater at matched absolute work rates in subjects with CHF than in subjects with NLVF (P < .01). However, when the rise in [K+]a was plotted against percentage of VO2max to match for relative submaximal effort, there were no differences between the two groups. Physical training resulted in reduced exercise-induced hyperkalemia at matched submaximal work rates in both groups (P < .01) despite no associated change in the concentration of arterial catecholamines. At maximal exercise when trained, peak increases in [K+]a were unaltered, but peak concentrations of catecholamines were raised (P < .05). The decrease in VE at submaximal work rates after training was not significant with this incremental exercise protocol, but both groups had an increased peak VE when trained (P < .01). CONCLUSIONS: Exercise-induced rises in [K+]a, catecholamines, and VE are greater at submaximal work rates in subjects with CHF than in subjects with NLVF. Physical training reduces the exercise-induced rise in [K+]a but does not significantly decrease VE during submaximal exercise with this incremental cycle ergometry protocol. The reduction in exercise-induced hyperkalemia after training is not the result of altered concentrations of arterial catecholamines. The pathophysiological significance of the increased exercise-induced hyperkalemia in CHF and the mechanisms of improved K+ homeostasis with training have yet to be established.

Epinephrine↗
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

Inherited abnormalities in platelet organelles and platelet formation and associated altered expression of low molecular weight guanosine triphosphate-binding proteins in the mouse pigment mutant gunmetal.

Gunmetal (gm/gm) is a recessively inherited mouse pigment dilution mutant that has high mortality and poor reproductive rates. In these studies, several hematologic defects were found associated with the mutation, including prolonged bleeding times, together with thrombocytopenia and increased platelet size. A unique feature is the presence of simultaneous abnormalities in two platelet organelles, dense granules and alpha-granules. The dense granule component serotonin is present at about half the normal concentration, as are visible dense granules. Three alpha-granule components (fibrinogen, platelet factor 4, and von Willebrand factor) are also significantly reduced. Thus, in several respects the gunmetal mutant resembles the human gray platelet syndrome. A novel abnormality in expression of low molecular weight guanosine triphosphate (GTP)-binding proteins occurs in platelets of gunmetal. In Western blot assays, two additional GTP-binding proteins of 28.5 and 25 Kd were detected. The abnormal expression of GTP-binding proteins is, like the hematologic defects, genetically recessive and is tissue specific. Liver, kidney, brain, spleen, macrophages, and neutrophils have normal GTP-binding protein expression. The additional GTP-binding proteins are soluble. The data indicate that platelet formation and platelet organelle biogenesis are under common genetic control and that abnormal regulation of GTP-binding proteins may affect one or both processes.

Animals↗
PubMed1993

Pre-admission clinic.

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Anesthesia Department, Hospital↗
PubMed1993

Persistent peripheral vasodilation and sympathetic activity in hypotension after maximal exercise.

Hemodynamics (by aortic Doppler), autonomic factors (power spectrum analysis of heart rate and blood pressure variabilities and baroreceptor sensitivity), and plasma renin activity during the hypotension after maximal exercise were studied in 10 normal subjects on two separate days: a nonexercise (control) day (30 min of upright rest followed by 60 min of supine rest) and an exercise day (maximal upright bicycle exercise followed by 60 min supine) in random order. After exercise, diastolic pressure was reduced for the entire hour, cardiac output increased (+33.8%, P < 0.05), stroke volume was unchanged, and systemic vascular resistance fell (-28.6%, P < 0.01). Indexes of vagal activity were reduced for 60 min, whereas the sympathetic indexes were elevated. Baroreflex sensitivity was also reduced for the first 10 min after exercise. Renin activity increased threefold after exercise. The postexercise hypotension results from a persisting peripheral vasodilation despite an increase in renin activity: the persistent sympathetic activity and reduced vagal tone are probably reflex responses to this vasodilatation.

Adult↗
PubMed1993

Low doses of scopolamine increase cardiac vagal tone in the acute phase of myocardial infarction.

BACKGROUND: Reduced cardiac vagal tone in patients with myocardial infarction (MI) is associated with a high risk of sudden death. Muscarinic blocking agents in small doses induce a paradoxical increase in cardiac vagal activity in normal subjects. We tested whether low doses of scopolamine delivered transdermally enhance tonic and reflex cardiac vagal activity in patients in the acute phase of MI. METHODS AND RESULTS: Patients were randomized to a scopolamine (n = 17) or a placebo patch (n = 19) in a double-blind fashion 4.20 +/- 0.18 days after acute MI. Cardiac vagal activity was assessed by testing the arterial baroreflex sensitivity (BRS) using the phenylephrine method and by power spectral analysis of the RR interval variability. Twenty-four hours after scopolamine, we found a significant increase in BRS (from 7.05 +/- 1.21 to 13.99 +/- 2.33 ms/mm Hg, P < .05) and in RR variability, expressed as the mean standard deviation of 512 normal consecutive RR intervals (from 18.09 +/- 2.64 to 31.16 +/- 4.16 milliseconds, P < .05). The amplitude of respiratory sinus arrhythmia, measured by the absolute power of the high-frequency spectral component, was also enhanced (from 62.55 +/- 21.49 to 305.33 +/- 95.68 milliseconds squared, P < .05), whereas the power in the low-frequency spectral component of the RR variability, which results from the interaction between cardiac sympathetic and vagal activity, did not change significantly (from 73.12 +/- 24.44 to 126.46 +/- 44.29 milliseconds squared, P = .93). CONCLUSIONS: In patients in the acute phase of MI, low doses of scopolamine cause a sustained increase in cardiac vagal tone and improve the autonomic indices associated with mortality.

Arteries↗