Biomedical subjects
M McGregor
Publications and source records attributed to M McGregor.
The Hmax/Mmax ratio as an outcome measure for acute low back pain.
OBJECTIVE: To evaluate the use of the Hmax/Mmax (H/M) ratio as an outcome measure for acute low back pain and to determine the change of this ratio in acute low back pain patients treated with spinal manipulation. DESIGN: Randomized clinical trial. SETTING: Chiropractic college teaching clinic. PATIENTS: Thirty-six patients with acute low back pain (pain of less than 2 wk duration) were referred by clinicians of the teaching clinic. Eligibility criteria for inclusion into the study consisted of the following: a score of eight or more on the Oswestry questionnaire, 33 mm or greater on a 100-mm visual analog scale, no involvement in litigation related to the low back pain complaint, patient not pregnant and no physical or electrodiagnostic signs of nerve root entrapment. INTERVENTIONS: The patients were randomly assigned to either a treatment or control group. The treatment group (n = 17) received treatment deemed appropriate by the clinician as long as it included a side-lying manipulation to the appropriate level. The control group (n = 19) received detuned ultrasound, application of a cold pack and 15-30 sec of very gentle soft tissue massage. Patients were treated three to five times over a period of 10 days and were subsequently reevaluated. MEASUREMENTS: The Hmax/Mmax ratio was calculated from the results of electrodiagnostic testing of the posterior tibial nerve. Extension/flexion ratio of the trunk musculature, Oswestry score and Visual Analog Scale score were also measured. MAIN RESULTS: The mean difference between H/M ratios pre- and postintervention for the group treated by chiropractic methods was -0.101 on the left and -0.117 on the right. The mean difference for the control group was 0.038 on the left and 0.036 on the right. Although not statistically significant, trends suggest that at the time of final assessment, the group receiving chiropractic care had improved more than the control group. CONCLUSIONS: The H/M ratio was found to be within normal limits in subjects with acute low back pain. The H/M ratio showed greater change in the group which received spinal manipulation, but the change was subtle. The results indicate that the H/M ratio may be of limited value in clinical practice.
A comparison of outcome measures for use with back pain patients: results of a feasibility study.
OBJECTIVE: To compare the reliability, validity and change in patient clinical status over time with treatment for six potential outcome questionnaires in a defined population of patients. SETTING: Physician based, multidoctor teaching practice. PATIENTS: Three hundred thirty-five consecutive patients presenting with new complaints were solicited. One hundred eighty-six agreed to participate. INTERVENTIONS: The six questionnaires being studied were administered to each of the participants on three separate occasions. They were: a) prior to clinical evaluation for their chief complaint, b) immediately after clinical evaluation and before treatment and c) 6 wk later. MEASUREMENTS: Each instrument was scored following the prescribed methods of interpretation from the original literature describing it. Results were submitted for analysis by Pearson correlation and two-way analysis of variance as appropriate. MAIN RESULTS: Differences were found in the mean value of the modified Zung with respect to both gender and time. An unexpected drop in patients' somatic perceptions in association with the process of clinical evaluation was found for the Modified Somatic Pain Questionnaire. Overall, the Oswestry and Visual Analogue Pain Scale were the most reliable and responsive to clinical change for musculoskeletal disorders. CONCLUSIONS: This investigation demonstrated substantial differences in the validity and reliability of commonly referenced self-administered instruments for quantifying patient perceptions of pain and disability. The Oswestry and Visual Analogue Pain Scale were both more reliable and valid than other instruments.
The effect of auxiliary conditions on intestinal unstirred layer diffusion modelled by numerical simulation.
Estimation of intestinal unstirred layer thickness usually involves inducing transmural potential difference changes by altering the content of the solution used to perfuse the small intestine. Osmotically active solutes, such as mannitol, when added to the luminal solution diffuse across the unstirred water layer (UWL) and induce osmotically dependent changes in potential difference. As an alternative procedure, the sodium ion in the luminal fluid can be replaced by another ion. As the sodium ion diffuses out of the UWL, the change in concentration next to the intestinal membrane alters the transmural potential difference. In both cases, UWL thickness is calculated from the time course of the potential difference changes, using a solution to the diffusion equation. The diffusion equation solution which allows the calculation of intestinal unstirred layer thickness was examined by simulation, using the method of numerical solutions. This process readily allows examination of the time course of diffusion under various imposed circumstances. The existing model for diffusion across the unstirred layer is based on auxiliary conditions which are unlikely to be fulfilled in the same intestine. The present simulation additionally incorporated the effects of membrane permeability, fluid absorption and less than instantaneous bulk phase concentration change. Simulation indicated that changes within the physiologically relevant range in the chosen auxiliary conditions (with the real unstirred layer length kept constant) can alter estimates of the apparent half-time. Consequently, changes in parameters unassociated with the unstirred layer would be misconstrued as alterations in unstirred layer thickness.
The choice of contrast media: medical, ethical and legal considerations.
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Processing of the herpes simplex virus assembly protein ICP35 near its carboxy terminal end requires the product of the whole of the UL26 reading frame.
The herpes simplex virus (HSV) type 1 assembly protein ICP35 consists of a family of polypeptides, ranging in molecular weight from about 45,000-39,000. The lower molecular weight forms of ICP35 are derived from the higher molecular weight species by slow post-translational modification. The reading frame of gene UL26 and the region within this gene which exhibited homology to the cytomegalovirus assembly protein, the analogous protein to ICP35, were expressed separately under immediate-early (IE) gene regulation in a HSV vector containing a temperature-sensitive mutation in the major transcriptional regulator Vmw175. Monoclonal antibody specific for ICP35 immunoprecipitated several polypeptides with molecular weights around 75,000 from extracts of cells infected with a recombinant expressing the IE gene UL26 at the nonpermissive temperature (NPT). These results suggested that the UL26 gene specified a protein distinct from ICP35 but which had some antigenic sites in common with ICP35. In extracts of cells infected at the NPT with a recombinant expressing only the carboxy terminal half of UL26 coding sequences, the monoclonal antibody immunoprecipitated large amounts of the high molecular weight forms of ICP35. The lower molecular weight processed forms of ICP35, however, were not detectable. When cells were coinfected with both recombinants ICP35 was processed to its lower molecular weight forms. This processing step, which occurred near the carboxy terminus of ICP35, was not dependent on capsid formation. The work, together with previous information on the processing of the CMV assembly protein, suggests that UL26 product may be a protease.
The cost-effectiveness of replacing high-osmolality with low-osmolality contrast media.
OBJECTIVE: Our purpose was to assess the cost-effectiveness of substituting low-osmolality contrast media for high-osmolality media in noncardiac parenteral use in radiology. MATERIALS AND METHODS: Estimates of effectiveness, taken as the reduction in risks of reactions affecting safety and comfort, were based on a recent meta-analysis of data published since 1980. Costs were those of the contrast medium and of treating reactions. RESULTS: One hundred thousand uses of low-osmolality media instead of high-osmolality media would cost an additional $7.7 million. No deaths would be prevented, but there would be 80% fewer life-threatening events and 75% fewer minor reactions. Considering only life-threatening events, complete conversion to low-osmolality media costs $62,000 per event prevented. If only minor reactions are considered, this figure is $800 per event prevented. The cost-effectiveness of partial substitution of low-osmolality media in "high-risk" patients only cannot be estimated with confidence. With one set of assumptions, a 33% reduction in life-threatening reactions at a cost of $22,000 per event prevented is estimated. These estimates are insensitive to all inputs except the cost differential between high- and low-osmolality media: for every dollar decrease in cost differential per use, the cost per life-threatening event prevented drops by $790. CONCLUSION: The allocation of limited resources requires the best available information on the relevant costs and benefits. A policy of substitution of low- for high-osmolality media will not influence mortality and will bring fairly small benefits at a considerable cost.
Enhanced neutrophil respiratory burst as a biological marker for manipulation forces: duration of the effect and association with substance P and tumor necrosis factor.
A critical need in assessing the clinical utility of manipulative therapy for back pain is the identification of biological changes associated with the forces applied by spinal manipulation. Such changes could then serve as markers for both sham treatment and manipulation. We determined the priming of polymorphonuclear neutrophils for an enhanced respiratory burst and its duration, the priming of mononuclear cells for enhanced endotoxin-stimulated tumor necrosis factor production and plasma levels of substance P following a single thoracic spine manipulation. There was a significant difference in the respiratory burst of polymorphonuclear neutrophils in response to a particulate challenge, depending on the time of blood sample collection. The response of polymorphonuclear neutrophils isolated from blood collected 15 min after manipulation was significantly higher than the response of cells isolated from blood collected 15 min before and 30 and 45 min after manipulation. Mononuclear cells were also primed for enhanced endotoxin-stimulated tumor necrosis factor production by spinal manipulation. Both of these priming effects were accompanied by a slight, but significant elevation in plasma substance P. The mean manipulation force associated with these biological effects was 878 +/- 99 N. These biological effects may provide a means of monitoring the delivery of both sham and manipulative treatment and, therefore, provide a crucial tool for understanding the efficacy of manipulative therapy.
The reuse of cardiac pacemakers.
OBJECTIVE: To provide decision makers with a synthesis of the relevant information concerning the safety of pacemaker reuse, the ethical and legal issues which it raises and the extent of financial savings which may result. DATA SOURCES: Medline data bank and the bibliographies of review articles in English concerning refurbishment and reuse of cardiac pacemakers published up to June 1991. DATA SYNTHESIS: Since 1978, reports of safe reuse of pacemakers have appeared in 11 countries. By 1984, review of nearly 2000 installations had produced no evidence of increased mortality or morbidity. The norms which must be respected to ensure safety are now well-known. The savings that might result from reuse can only be approximated. In Canada in 1989, 8684 pacemakers were installed. Assuming that 20% might be available for reuse, this practice might save approximately $4,000,000 per year to the Canadian health care system. CONCLUSIONS: Properly carried out, pacemakers can be reused at an acceptably low risk. Any institution contemplating pacemaker reuse should define and approve appropriate guidelines and protocols governing the process. A registry to document the reuse of pacemakers for the next few years is desirable.
Differences in treatment history with manipulation for acute, subacute, chronic and recurrent spine pain.
Preference for treatment protocols used in the care of spine disorders are based more upon clinical impressions than upon systematic study of the pathology or treatment efficacy. As social emphasis moves to cost containment strategies, quantitative data is necessary to give guidance for rational policy decisions. This study sets a description of the clinical experience obtained in a group practice, teaching clinic engaged in management of spine disorders. The same subjects were separately reported as being broadly representative of those seen in private using a cash payment policy. Clinical characteristics were quantified on 241 patients. A total of 149 volunteered to complete follow up evaluations. The total number of treatment sessions were tallied to case resolution on all 241 patients and were evaluated by stratifying them according to chronicity of the chief complaint. The range of treatment for all cases was 1-22. Chronic complaints required the most care, with a mean of 8.2 sessions (F = 2.833, p = .014). Thoracic disorders required approximately half the care as lordotic spine regions (F = 2.372, p = .04). No differences were observed based upon descriptive classifications of entrapment, mechanical or muscular pain. All but 25 cases reached resolution well within 6 wk, requiring a mean of 3.8 (range 1-11) additional treatment sessions.
Clinical features and treatment of obstructive sleep apnea.
OBJECTIVE: To review the clinical features and treatment of obstructive sleep apnea (OSA). DATA SOURCE AND SELECTION: All articles on OSA published in French and English between 1970 and 1990 and indexed in Index Medicus were reviewed. Studies addressing the epidemiologic features and clinical aspects of OSA were selected, and special emphasis was given to articles reporting the effects of treatment on morbidity and mortality rates. MAIN RESULTS: OSA is characterized by episodes of upper airway obstruction during sleep that result in repetitive hypoxemia and sleep disruption. OSA leads to various neuropsychologic and cardiovascular complications, including daytime hypersomnolence, cognitive impairment, systemic and pulmonary hypertension and cardiac arrhythmias. There is suggestive evidence that the death rate among affected people is increased. The true incidence of OSA is unknown, but estimates have varied from 1% upwards among men. The current treatment with the greatest overall effectiveness and acceptability is nasal continuous positive airway pressure. CONCLUSION: This common, readily treatable disorder is associated with serious complications and therefore must be widely recognized by health professionals.
The risks of death and of severe nonfatal reactions with high- vs low-osmolality contrast media: a meta-analysis.
Estimates of the risks associated with the use of radiologic contrast agents frequently are based on a subjective review of some of the numerous articles that have been published on the subject. We have chosen instead to synthesize the existing evidence in an objective, quantitative way by statistically combining the data from individual studies through meta-analysis. Although meta-analysis is subject to whatever biases may exist in the underlying data, and may inappropriately pool data from studies with significant differences, the estimates draw proportionately from each original study and, in addition, gain considerable precision owing to the increased amounts of data considered. Using this technique, we analyzed the data from all available original reports appearing since 1980. Crude rates derived from all reports were used to estimate risks with high-osmolality media. Weighted rate differences based on comparative studies only were used in the estimation of the reductions in risk obtainable with low-osmolality media. The risk of death with high-osmolality media was 0.9 per 100,000 uses (95% confidence interval, 0.3-2.6 per 100,000). The difference in risk produced by using low-osmolality media was 0 (95% confidence interval, -1.1 to 1.1 per 100,000). The risk of severe reactions associated with high-osmolality media was 157 per 100,000 uses (95% confidence interval, 144-172 per 100,000). The reduction in risk that can be obtained by the use of low-osmolality media was estimated to be 126 per 100,000 (95% confidence interval, 110-142 per 100,000). This meta-analysis shows that the risk of death is very low with either type of contrast material and that there is no difference between them. Severe nonfatal reactions with high-osmolality media, although more frequent, are still rare; approximately 80% of them can be prevented by using low-osmolality media.
Enhanced phagocytic cell respiratory burst induced by spinal manipulation: potential role of substance P.
The effect of spinal manipulation on the respiratory burst of polymorphonuclear neutrophils (PMN) and monocytes from treated adults was measured by zymosan-stimulated chemiluminescence (CL). Peripheral blood was collected 15 min before and 15 min after treatment (sham manipulation, thoracic spine manipulation, or soft tissue manipulation), the cells were isolated, challenged with a standardized, opsonized luminol-containing suspension of zymosan, and monitored for CL. Plasma from two subsets of subjects was radioimmunoassayed for Substance P (SP). PMN were also preincubated with SP in vitro over the dose range 5 x 10(-12) M to 5 x 10(-8) M and the CL response monitored. The CL responses of both PMN and monocytes from subjects who received spinal manipulation were significantly higher after than before treatment, and significantly higher than the response in sham or soft-tissue treated subjects. Measurement of the force applied by sham and spinal manipulation suggested a force threshold for the enhancement of the CL response. Plasma levels of SP before and after treatment in sham treated subjects did not differ significantly; however, elevated plasma SP was observed in subjects after spinal manipulation. Preincubation of PMN with 1 x 10(-11) M, 5 x 10(-11) M or 1 x 10(-10) M SP in vitro primed PMN for an enhanced respiratory burst when the cells were subsequently challenged.
Effects of dosing intervals on the development of tolerance to high dose transdermal nitroglycerin.
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The tuberculosis epidemic--correction of misconceptions posited as scientific fact.
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The role of experience in clinical accuracy.
A randomized controlled trial was performed to study the effect of various teaching techniques on students performing sacroiliac motion palpation tests. This trial assessed the interexaminer reliability of interns in their final year at a chiropractic college, and compared their results prior to and following 1 year of clinical experience. The study also compared the intra- and interexaminer reliability of experienced clinicians. The results were analyzed via the Kappa coefficient. Kappa values for interns ranged from 0.00 to 0.30, with no significant differences noted at the end of 1 year of clinical experience. The interexaminer reliability of experienced clinicians was 0.00 to 0.167, whereas their intraexaminer reliability ranged from 0.15 to 1.00. These results question the role of experience in improving clinical accuracy between examiners performing sacroiliac motion palpation. Results analyzed for intraexaminer agreement were moderate to almost perfect. We conclude that experience does not play a significant role in the diagnostic test analyzed, but rather that clinicians may establish their own criteria by which to determine the standards of a given test.
Mechanism underlying Kussmaul's sign in chronic constrictive pericarditis.
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