Biomedical subjects

J W Williamson

Publications and source records attributed to J W Williamson.

At least 19 recordsLinked to original sources

PubMed1995

Instantaneous heart rate increase with dynamic exercise: central command and muscle-heart reflex contributions.

R-R interval (RRI) changes were recorded from 15 healthy volunteers in response to volitional unloaded cycling and passively induced cycling (PC). PC was also combined with electrical stimulation (n = 5) to increase muscle mechanoreceptor activation. The electrocardiogram and leg electromyographic activity were continuously sampled by computer at 1,000 Hz, and an electronic trigger was used to designate the instant of pedal movement within an RRI. Changes in RRI were expressed as the difference of the interval in which the trigger was activated (onset RRI) and the average of resting intervals (4-8 intervals). Volitional unloaded cycling produced the greatest decrease in the onset RRI [907 +/- 11 (SE) to 855 +/- 10 ms; -5.4 +/- 0.4%; P < 0.01] when movement was initiated within the first one-third of the interval. A shortening of the onset RRI was also detected when trigger activation occurred in the last one-third of the interval (906 +/- 12 to 875 +/- 11 ms; -3.1 +/- 0.4%; P < 0.01). There were no significant effects of PC alone on the onset RRI. However, PC+electrical stimulation shortened the onset RRI (906 +/- 12 to 883 +/- 11 ms; -2.5 +/- 0.2%; P < 0.05) but only when the movement was initiated within the first one-third of the interval.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1994

Reflex increase in blood pressure induced by leg compression in man.

1. We tested the hypotheses that the increase in mean arterial pressure with the application of external leg compression in man is (i) blocked with epidural anaesthesia, and (ii) dependent upon the level of external pressure applied, the quantity of leg muscle mass compressed and the vascular volume of the leg. Fourteen healthy subjects were fitted with an anti-shock trouser garment to provide three levels (30, 60 and 90 mmHg) of leg compression, while cephalad translocation of fluid was prevented by upper-thigh cuffs inflated to a supra-systolic pressure. Cardiovascular responses were recorded during leg compression before and after the administration of epidural anaesthesia in eight subjects, while blood pressure responses from six subjects were compared with their single leg pressor response. 2. Both mean arterial and diastolic pressures were elevated with increasing leg compression, with no changes in heart rate, cardiac output, thoracic impedance, and central venous pressure. The leg compression-induced blood pressure increases were abolished by epidural anaesthesia. Furthermore, when only one leg was compressed at 90 mmHg, the pressor response was less than that elicited from compression of both legs at the same external pressure. Changes in vascular volume of the leg did not influence the pressor response to leg compression. 3. The results indicate that the mean arterial pressure increases in response to external compression of the legs and that a reflex mechanism, mediated by muscle afferent nerves, is involved. The response is dependent upon both the changes in intramuscular pressure and the quantity of muscle mass compressed.

Adult↗

PubMed1994

Heart rate and blood pressure responses at the onset of dynamic exercise: effect of Valsalva manoeuvre.

The influence of respiration on the mean blood pressure (Pa) and R-R interval responses at the onset of dynamic exercise was studied in 15 healthy subjects who performed 4 s of unloaded cycling at 1.5-2.0 Hz, 4 s of Valsalva manoeuvre at 5.3 kPa, and a combination of both, each during a 12-s long apnoea at total lung capacity. The R-R intervals were obtained from the electrocardiogram, Pa was measured continuously by finger plethysmography, and intra-oral pressure was used to estimate the changes in intrapleural pressure. There was an immediate and significant shortening of the R-R intervals during exercise [mean (SE): 790 (20) to 642 (20) ms] that was not modified when Valsalva manoeuvre was added [783 (28) to 654 (21) ms]. Although 4 s of exercise alone did not alter Pa [13.8 (0.5) to 13.7 (0.7) kPa], this may indicate a pressor response, since Pa decreased during apnoea alone. When exercise was performed simultaneously with Valsalva manoeuvre, Pa increased significantly [13.6 (0.4) to 15.8 (0.5) kPa] and of similar magnitude during Valsalva alone [13.2 (0.4) to 15.3 (0.7) kPa]. In conclusion, 4 s of unloaded cycling elicited a fast R-R shortening with no change in Pa from rest. A concomitant Valsalva manoeuvre had no effect on the R-R interval response but caused a marked increase in Pa. From these findings, it is suggested that respiratory influences should be controlled in studies concerned with the cardiovascular responses at the onset of dynamic exercise.

Adult↗

PubMed1994

Issues and challenges in quality assurance of health care.

In this paper I review the health care crisis in the United States and conclude that fundamental changes must be made. I then present: (1) an organizational approach that might be encompassed in President Clinton's program for health care reform; (2) my "dream" of a national quality improvement system for reform, based on The Netherlands Model; and (3) a suggestion that strengthening primary care will be the key to the success of this reform in the coming years.

Health Care Reform↗

PubMed1994

Blood pressure responses to dynamic exercise with lower-body positive pressure.

Cardiovascular responses were obtained during cycling with graded levels of lower-body positive pressure (LBPP) applied to the exercising limbs. Seven men performed four incremental work rate (25 W.min-1) exercise (IWREx) tests to their limit of tolerance while exposed to 0, 15, 30, or 45 Torr LBPP. They also performed four, 6-min constant work rate exercise (CWREx) bouts at two work rates with LBPP's of 0 and 45 Torr. Cardiovascular data were obtained at rest and at 40%, 55%, 75%, and 90% of VO2peak, as well as at minute 5 of CWREx. LBPP did not alter VO2, HR, SV, or cardiac output (Qc) responses at rest or during exercise. However, both 30 and 45 Torr LBPP produced increases in MAP at rest and during exercise (P < 0.05). During CWREx, elevations in blood pressure were mediated via increases in TPR (P < 0.05). Only 45 Torr LBPP elicited a significantly greater blood pressure increase during exercise than rest, suggesting muscle blood flow restriction at this level of LBPP was sufficient to activate a muscle metabo-reflex. These findings suggest that the muscle metabo-reflex is not tonically active during dynamic exercise under normal conditions, but may instead require a critical reduction in muscle blood flow before it is activated.

Adult↗

PubMed1994

Cardiovascular responses to active and passive cycling movements.

Ten healthy subjects were evaluated at rest and at 5 min of unloaded active (AC) and passive (PC) cycling. Passive limb movements were accomplished using a tandem bicycle with a second rider performing the movements. We measured heart rate (HR), mean arterial pressure (MAP), cardiac output (CO), oxygen uptake (VO2), rating of perceived exertion (RPE), and electrical activity (EMG) of lower limbs muscles. Values for stroke volume (SV) and peripheral vascular resistance (PVR) were calculated. EMG, RPE, and VO2 were higher during AC than during PC (P < 0.001). CO increased during both modes of cycling, but during AC it resulted from a HR acceleration (73 +/- 2 at rest to 82 +/- 2 beats.min-1 at 60 rpm; P < 0.001) with no change in SV whereas during PC, SV increased from rest (65 +/- 4 at rest to 71 +/- 3 ml at 60 rpm; P = 0.003) along with no change in HR. PVR remained constant during PC, but decreased by 13% during AC (P < 0.001) and MAP increased only during PC (93 +/- 2 at rest to 107 +/- 2 mm Hg at 60 rpm). These results supports the concept that central command determines the HR response to dynamic exercise. The increase in SV and consequently in MAP during PC was probably due to increased venous return and/or to muscle mechanoreceptor-evoked increased myocardial contractility.

Adult↗

PubMed1994

Development and implementation of a computer-generated reminder system for diabetes preventive care.

Diabetes mellitus is a chronic condition with several late complications that can be delayed or avoided through proper preventive health care. Although practice guidelines have been established to improve the preventive care in diabetics, dissemination of these guidelines among physicians and educational programs have been only moderately successful in changing physicians' practice patterns. Previous efforts, however, did not utilize computer-generated reminders. We developed a system of computer-generated reminders for diabetic preventive care. We completed an implementation of the system in the outpatient clinics of internal medicine residents at our institution. This paper describes the development and implementation of this system. Our results showed that the system flagged an average of 13 items that deviated from diabetes guideline compliance, out of a possible 21 items per patient. The residents completed encounter forms used by the system for 37% of patients seen during a six month period. Physician users exhibited positive attitudes toward the use of guidelines which they judged improved quality at no additional cost of care. However, the complexity and length of the guideline encounter forms and the additional time demands proved to be significant obstacles to current routine use. Our experience will help to improve the system so that it is more usable and acceptable to physicians, especially in the future as health care increasingly makes use of electronic medical record systems.

Attitude to Computers↗

PubMed1992

The effects of ocean sounds on sleep after coronary artery bypass graft surgery.

OBJECTIVE: To investigate the influence of ocean sounds (white noise) on the night sleep pattern of postoperative coronary artery bypass graft (CABG) patients after transfer from an intensive care unit. DESIGN: A before and after trial with an experimental and a control group was used in this intervention study. SETTING: A large public hospital with primary, secondary, and tertiary care facilities. PATIENTS: A consecutive sample of 60 first-time CABG patients was systematically assigned to the experimental or the control group. INTERVENTION: For the experimental group, the sounds were played on the Marsona Sound Conditioner (Marpac Corporation, Wilmington, NC) for three consecutive nights posttransfer from the ICU. No control of environment, except for the elimination of white noise, was done for the control group. MAIN OUTCOME MEASURES: The Richards-Campbell Sleep Questionnaire, a visual analog scale, provided self-reported sleep scores on six variables. Analysis of covariance was used to test the difference between the posttest scores of the groups, with the pretest used as the covariate. RESULTS: There were significant differences in sleep depth, awakening, return to sleep, quality of sleep, and total sleep scores; the group receiving ocean sounds reported higher scores, indicating better sleep. There was no difference in the falling asleep scores. CONCLUSION: The use of ocean sounds is a viable intervention to foster optimal sleep patterns in postoperative CABG patients after transfer from the ICU.

Adult↗

PubMed1992

Aerobic fitness: I. Response of volume regulating hormones to head-down tilt.

We investigated the relationship of aerobic fitness to the response of volume-regulating hormones to acute simulated microgravity. Six untrained (UT) and six endurance-trained (ET) healthy young males were studied in the head-down tilt (HDT) position of -6 degrees for 4 h. Peak oxygen uptake (VO2peak) and plasma volume (PV) were significantly greater in the ET (VO2peak = 61.7 +/- 1.6 ml.min-1.kg-1 and PV = 53.1 +/- 2.8 ml.kg-1) than in the UT (VO2peak = 38.4 +/- 1.7 ml.min-1.kg-1 and PV = 38.8 +/- 1.0 ml.kg-1). Plasma concentrations of atrial natriuretic peptide (ANP), arginine vasopressin (AVP), norepinephrine (NE), renin activity (PRA), and aldosterone (PA) were measured prior to HDT and at minutes 2, 5, 15, 30, 60, 120, 180, and 240 during HDT. PRA and PA significantly decreased during the time of HDT in both groups. The changes in ANP and NE concentrations were not significantly different between the groups nor across time. However, in the ET subjects, the changes in PRA and NE were significantly correlated with the changes in ANP (r = 0.49, P less than 0.01; and r = 0.86, P less than 0.001, respectively); in the UT subjects, the changes in AVP, PRA, and PA were significantly associated with changes in NE (r = 0.34, P less than 0.03; and r = 0.59; and r = 0.53, P less than 0.01, respectively). PV significantly decreased during HDT, and was primarily related to the decrease in PA in both groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1992

Aerobic fitness: II. Orthostasis and VO2peak following head-down tilt.

To determine whether endurance exercise trained (ET) subjects would experience greater reductions in peak oxygen delivery and orthostatic tolerance (OT) than untrained (UT) subjects, both peak oxygen uptake (VO2peak) during upright bicycle ergometry and tolerance time during 70 degrees head-up tilt (HUT) were compared within and between groups before and after 4 h of -6 degrees head-down tilt (HDT). Eight ET subjects with a mean VO2peak of 61.7 +/- 1.6 ml.kg-1.min-1 were matched for age, height, and weight with eight UT subjects (VO2peak = 38.4 +/- 1.7 ml.kg-1.min-1). Following HDT, decreases in plasma volume (PV) were larger for ET subjects (-3.7 +/- 0.5 ml.kg-1) than for UT subjects (-2.3 +/- 0.3 ml.kg-1), P less than 0.03. Reductions in VO2peak for ET subjects (-5.4 +/- 1.1 ml.kg-1.min-1) were also greater than for UT subjects (-2.4 +/- 0.8 ml.kg-1.min-1), P less than 0.05. The ET (N = 6) subjects also had a significant decrease in OT time (-13.0 +/- 4.2 min) during post-HDT HUT, which was not observed for the UT group (N = 6). A significant inverse correlation was found pre-HDT VO2peak and the change in OT time, r = -0.74, P less than 0.01. The decrease in OT was also significantly correlated to the PV decrease, r = 0.59, P less than 0.04. The UT subjects had significantly augmented pressor responses to HUT manifested by the increases in both HR and MAP following HDT.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1992

Iliad's role in the generalization of learning across a medical domain.

Medical informatics could facilitate more effective analysis and use of clinical knowledge by means of expert systems. To be most effective, such systems should be constructed in a manner which is consistent with physicians' cognitive processes. Our past five years' work with a system called Iliad indicates that it provides effective medical training and education. The current research extends our previous work by using a wider array of training and test cases. We also evaluated whether training on specific cases could generalize to improved testing performance on related cases, which featured similar complaints and pathophysiologic mechanisms, but different final diagnoses. In their junior internal medicine clerkship, students (n = 100) completed 1300 Iliad training cases covering 48 diagnoses. The findings indicated improved problem solving on the specifically trained cases as well as the generalization cases. We discuss a possible training model for expert systems such as Iliad.

Computer-Assisted Instruction↗

PubMed1991

Iliad training enhances medical students' diagnostic skills.

Iliad is a computerized, expert system for internal medical diagnosis. The system is designed to teach diagnostic skills by means of simulated patient case presentations. We report the results of a controlled trial in which junior students were randomly assigned to received Iliad training on one of two different simulated case mixes. Each group was subsequently tested in both their "trained" and "untrained" case domain. The testing consisted of computerized, simulated patient cases for which no training feedback was provided. Outcome variables were designed to measure the students' performance on these test cases. The results indicate that students made fewer diagnostic errors and more conclusively confirmed their diagnostic hypotheses when they were tested in their trained domain. We conclude that expert systems such as Iliad can effectively teach diagnostic skills by supplementing trainees' actual case experience with computerized simulations.

Clinical Clerkship↗

PubMed1991

Assessing quality of ambulatory care. A comparative analysis in rural versus tertiary general medical clinics.

The purpose of this study is to report the results and feasibility of a "multi-methods" assessment of ambulatory health care in both rural and tertiary care settings. Our method used an expert panel's assessment of patient health and satisfaction outcomes (measured by follow-up telephone interviews) and care processes (measured by chart review) for assessing complete episodes of care. Subjects consisted of a matched cohort of ambulatory adult patients from the above two settings. We identified and analyzed specific clinical errors to confirm the expert panel's judgment of inadequacy. Results indicate that in both settings unacceptable health outcomes were found, at least partially explained by serious care deficiencies for 1 out of 2 to 3 patients seen. The problems, which involved mostly laboratory and pharmaceutic management, are probably preventable using newer education and computer technologies. Our method, though dependent on adequate medical records, proved feasible in both the rural and tertiary ambulatory care settings studied.

Ambulatory Care↗

PubMed1991

Health science information management. An approach to improving QA and clinical practice.

To help quality assurance (QA) professionals and clinical practitioners keep up with advances in health care knowledge and technology, we describe a prototype Health Science Information Management (HSIM) publication. We conceptualize HSIM to include: (a) identification of unique science information needs; (b) rapid retrieval of valid needed information; and (c) use the information to improve health care benefits. To more adequately accomplish these functions, we suggest that five specific categories of information will be essential: (1) reports of recent advances in Science Information Management methods; (2) original reports of Science Information Syntheses (SISs) providing information immediately applicable for QA; (3) previously published reports of "classic" SISs relevant to QA; (4) reviews of new technologies and products immediately applicable to quality management; (5) cumulative indexing of the above methods and products. Making the above information available to QA professionals might substantially improve the impact of quality management.

Abstracting and Indexing↗

PubMed1991

Iliad training effects: a cognitive model and empirical findings.

Iliad is a diagnostic expert system consisting of an "inference engine" (collection of rules and procedures for making decisions) and a "knowledge base" (collection of medical facts). Iliad's internal medicine knowledge base recognizes 5000 medical findings and covers 1150 diagnostic conditions in 10 subspecialty fields. We used Iliad's simulator mode to train diagnostic skills in junior-year medical students. The results corroborate previous findings documenting Iliad's teaching efficacy. Recent developments in cognitive psychology provide a framework for explaining Iliad's training effects.

Clinical Clerkship↗

PubMed1990

Changing patient management: what influences the practicing pediatrician?

To explore some determinants of physicians' decisions to change practice habits, we posed three questions: To what extent are some particular innovations diffused among office-based primary care physicians? What characterizes the physicians who have adopted these innovations? And, what caused them to change their behavior and adopt the innovations? Three "markers," recent innovation in medical practice, were chosen using an expert consensus technique. A telephone survey of 200 office-based pediatricians was conducted, and the physicians were asked whether or not they used the following three innovations in medical practice: continuous rather than intermittent phenobarbital for the prevention of febrile seizures, glycosylated hemoglobin measurement in the management of diabetes, and slow release theophylline in the management of asthma. The questionnaire was completed by 156 pediatricians. Of the 110 pediatricians who cared for diabetics, 73% used glycosylated hemoglobin measurement; of the 145 who saw patients with febrile seizures, 77% prescribed the continuous use of phenobarbital (if they used it at all); and, of the 152 pediatricians who cared for asthmatics, 86% reported using slow-release theophylline. The characteristics significantly associated with using the innovations were board certification, group rather than solo practice, teaching, medically related publications, academic appointment, younger age, and caring for a greater number of patients per week. For two of the innovations, discussion with a colleague was the most important source of information leading to a change of practice. The subjects cited local specialists as the colleagues who most often sparked the adoption of an innovation.

Biomarkers↗

PubMed1990

Splenic artery aneurysm. A rare cause of upper gastrointestinal bleeding.

Most splenic artery aneurysms (SAAs) are asymptomatic at the time of discovery, being found incidentally during laparotomy or angiography. SAAs are most likely to be found in multiparous women. Complications of SAAs include free intraperitoneal rupture and erosion into abdominal viscera or vessels, with resultant high mortality. Surgery is indicated for symptomatic, enlarging, or large (greater than or equal to 2.5 cm) SAAs as well as any SAA found in women of childbearing age. Treatment of such aneurysms depends on the location and includes excision, ligation, and splenectomy. The present report presents the first known case, to our knowledge, of SAA presenting with massive upper gastrointestinal bleeding from erosion into the stomach in a nulliparous woman. Prompt surgical intervention resulted in correct diagnosis and patient survival.

Aged↗

PubMed1989

Health science information management and continuing education of physicians. A survey of U.S. primary care practitioners and their opinion leaders.

PURPOSE: To identify self-perceived problems in managing science information needs of U.S. primary practitioners and their opinion leaders. SAMPLE: A two-stage random sample of the American Medical Association's "Masterlist of Physicians" to identify 625 office-based physicians, including general practice, family practice, internal medicine, obstetrics and gynecology, and pediatrics, and 100 physician opinion leaders. DATA COLLECTION: A formal telephone survey was completed for 79% of practitioners and 90% of opinion leaders sampled, using a pretested instrument applied by trained telephone surveyors. RESULTS OF DATA ANALYSIS: Both practitioners and opinion leaders claimed that published reviews were the most useful means of identifying their information needs. When asked about use of six recent clinical advances, that is, "markers," for example, hemoglobin-A1C for diabetic control, as many as one fifth to one half were not using or were not aware of such an advance. Less than 1 in 3 practitioners personally searched the literature when information was needed; 2 in 3 claimed literature volume was unmanageable; 9 of 10 practitioners and opinion leaders assessed the scientific value of literature obtained, primarily from their own experience, with less than 1 in 10 contacting research methods specialists. Respondents suggested various innovations to better manage their science information needs in the future. CONCLUSIONS: Primary practitioners require substantial help in meeting current science information needs. Increase in such resources as "validated reviews" or "expert networks" might help meet these needs.

Education, Medical, Continuing↗