Biomedical subjects

M A Adams

Publications and source records attributed to M A Adams.

At least 37 records · Page 2Linked to original sources

PubMed2001

Telemetric blood pressure monitoring in conscious rats before and after compression injury of spinal cord.

Abnormal cardiovascular control after spinal cord injury (SCI) results in hypotension soon after injury. Later, paroxysmal hypertension and bradycardia in response to sensory stimulation below the level of injury develop in most people with SCI. In this study, we used a radiotelemetry system, in rats (n = 7), to investigate the effect of a clinically relevant compression model of SCI at T5 spinal segment on mean arterial pressure (MAP) and heart rate (HR) at rest and in response to colorectal distension. The transducers were implanted 1 month before clip compression (50-g) injury and continuous recording of MAP and HR was established for a period of 2.5 months. SCI was associated with hypotension (86+/-3 mm Hg) at 1 day after injury. In the following 2 days, MAP gradually returned to preinjury levels. By contrast, HR increased at 1 day after SCI and remained unchanged thereafter. Three days after SCI, colorectal distension caused an increase in MAP of 8+/-2 mm Hg accompanied by bradycardia (-18 bpm). One week after SCI, colorectal distension induced an increase in MAP of 9+/-2 mm Hg and bradycardia (-41 bpm). In the following days, the magnitude of reflex hypertension gradually increased, reaching 21+/-4 mm Hg at 1.5 months after SCI. In summary, our data show that resting MAP rapidly returns to control values after SCI. Episodic hypertension associated with autonomic dysreflexia can develop in rats within 1 month after incomplete SCI.

Analysis of Variance↗

PubMed2001

An improved heat pulse method to measure low and reverse rates of sap flow in woody plants.

The compensation heat pulse method (CHPM) is of limited value for measuring low rates of sap flow in woody plants. Recent application of the CHPM to woody roots has further illustrated some of the constraints of this technique. Here we present an improved heat pulse method, termed the heat ratio method (HRM), to measure low and reverse rates of sap flow in woody plants. The HRM has several important advantages over the CHPM, including improved measurement range and resolution, protocols to correct for physical and thermal errors in sensor deployment, and a simple linear function to describe wound effects. We describe the theory and methodological protocols of the HRM, provide wound correction coefficients, and validate the reliability and accuracy of the technique against gravimetric measurements of transpiration.

Eucalyptus↗

PubMed2001

The feasibility and efficacy of tobacco use prevention in orthodontics.

SMILES PLUS was the first study to extend the clinician-delivered logic model to prevention of tobacco use among adolescents. This multi-site trial with 154 participating offices, based on social learning theory and a behavioral ecological model, was designed to test whether orthodontists can prevent preteens from initiating smoking. The study found that orthodontists do not automatically adhere to anti-tobacco prevention services. Social learning variables can enhance both adherence to counseling guidelines and content of counseling to increase prevention effects. Providing financial incentives, tracking prescriptions, prompting positive feedback from patients, and adopting anti-tobacco counseling models in the office are likely to enhance anti-tobacco preventive services. Training orthodontists to be comfortable when advising nonsmoking youth not to start and to use social consequences to justify youth avoidance of tobacco might increase adherence to protocols and make their counseling more powerful. Adolescent smokers prior to intervention were more likely to start other risky behaviors later. Preventing tobacco use may halt additional risk behaviors and thereby reduce morbidity/mortality even more than expected from tobacco control alone. New and refined clinical trials should be conducted to determine the most effective interventions for adolescent tobacco control by clinicians.

Adolescent↗

PubMed2001

Antihypertensive drugs induce structural remodeling of the penile vasculature.

PURPOSE: There is a strong association between hypertension and erectile dysfunction. Studies of the treatment of hypertension have shown that some pharmacological agents are capable of inducing regression of the vascular structure during treatment. We determined whether penile vascular structure is as susceptible as other vascular beds to regression during antihypertensive drug treatment. MATERIALS AND METHODS: Adult spontaneously hypertensive rats were treated for 1 or 2 weeks with 30 mg./kg. enalapril daily, or for 2 weeks with 45 mg./kg. hydralazine daily. Structurally based vascular resistance was determined in isolated penile and skeletal muscle vascular beds perfused with Tyrode-dextran. A cumulative alpha1-adrenoceptor concentration constrictor response curve to 1 to 100 microg./ml. methoxamine was constructed and the maximum constrictor response (vasopressin, methoxamine and angiotensin II) indicating the tissue yield point (that is the average medial bulk of vascular smooth muscle) was determined. The hearts were excised and the ventricles were separated and weighed. RESULTS: Enalapril treatment progressively regressed cardiac and vascular structure during the 1 and 2-week treatment periods with a mean tissue yield point plus or minus standard deviation of -5.91% +/- 5.1% (p <0.05) and -12.1% +/- 6.0% (p <0.05), and a mean left ventricle mass of -11.8% +/- 2.2% (p <0.05) and -13.6% +/- 3.2% (p <0.05), respectively. Hydralazine treatment for 2 weeks was less effective on vascular regression with a mean yield of -7.3% +/- 2.9% (p <0.05) and it did not alter left ventricle hypertrophy compared with controls (3.7% +/- 5.0%). CONCLUSIONS: The data suggest that renin-angiotensin system inhibition may at least partially normalize penile vascular structure. The impact of these changes on erectile function must be determined.

Angiotensin II↗

PubMed2000

Hypoxia induces the expression of a 43-kDa protein (PROXY-1) in normal and malignant cells.

This study was designed to determine the expression of cellular factors that may participate in phenotypic changes that occur under conditions of hypoxia. Using the RT-PCR differential display method, we isolated a cDNA fragment corresponding to a gene whose expression was induced in trophoblast and breast carcinoma cells cultured under 1 or 2% oxygen vs 4% oxygen or higher. This gene encodes a 43-kDa protein initially identified in homocysteine-treated endothelial cells and later shown to be upregulated in various human and mouse cell types (termed RTP, Drg1, Cap43, rit42, Ndr1). Herein we refer to this gene product as PROXY-1, for Protein Regulated by OXYgen-1. Elevated mRNA and protein levels were first observed in cells cultured in 1% oxygen for 8 h. Although PROXY-1 mRNA levels returned to near-control values within 2 h of reexposure to 20% oxygen, protein levels remained high 72 h after reexposure to 20% oxygen. Treatment of cells with hypoxia mimics such as cobalt or iron chelators also increased PROXY-1 expression. Moreover, presence of 30% carbon monoxide in the hypoxic atmosphere abrogated the upregulation of PROXY-1 expression. These findings suggest that hypoxia upregulates PROXY-1 levels through a heme protein-dependent pathway and that assessment of PROXY-1 expression may be of potential use in evaluating tissue hypoxia.

Animals↗

PubMed2000

Mechanical initiation of intervertebral disc degeneration.

STUDY DESIGN: Mechanical testing of cadaveric lumbar motion segments. OBJECTIVES: To test the hypothesis that minor damage to a vertebral body can lead to progressive disruption of the adjacent intervertebral disc. SUMMARY OF BACKGROUND DATA: Disc degeneration involves gross structural disruption as well as cell-mediated changes in matrix composition, but there is little evidence concerning which comes first. Comparatively minor damage to a vertebral body is known to decompress the adjacent discs, and this may adversely affect both structure and cell function in the disc. METHODS: In this study, 38 cadaveric lumbar motion segments (mean age, 51 years) were subjected to complex mechanical loading to simulate typical activities in vivo while the distribution of compressive stress in the disc matrix was measured using a pressure transducer mounted in a needle 1.3 mm in diameter. "Stress profiles" were repeated after a controlled compressive overload injury had reduced motion segment height by approximately 1%. Moderate repetitive loading, appropriate for the simulation of light manual labor, then was applied to the damaged specimens for approximately 4 hours, and stress profilometry was repeated a third time. Discs then were sectioned and photographed. RESULTS: Endplate damage reduced pressure in the adjacent nucleus pulposus by 25% +/- 27% and generated peaks of compressive stress in the anulus, usually posteriorly to the nucleus. Discs 50 to 70 years of age were affected the most. Repetitive loading further decompressed the nucleus and intensified stress concentrations in the anulus, especially in simulated lordotic postures. Sagittal plane sections of 15 of the discs showed an inwardly collapsing anulus in 9 discs, extreme outward bulging of the anulus in 11 discs, and complete radial fissures in 2 discs, 1 of which allowed posterior migration of nucleus pulposus. Comparisons with the results from tissue culture experiments indicated that the observed changes in matrix compressive stress would inhibit disc cell metabolism throughout the disc, and could lead to progressive deterioration of the matrix. CONCLUSIONS: Minor damage to a vertebral body endplate leads to progressive structural changes in the adjacent intervertebral discs.

Adult↗

PubMed2000

Sudden and unexpected loading generates high forces on the lumbar spine.

STUDY DESIGN: A cross-sectional study of spinal loading in healthy volunteers. OBJECTIVES: To measure the bending and compressive forces acting on the lumbar spine, in a range of postures, when unknown loads are delivered unexpectedly to the hands. SUMMARY OF BACKGROUND DATA: Epidemiologic studies suggest that sudden and unexpected loading events often lead to back injuries. Such incidents have been shown to increase back muscle activity, but their effects on the compressive force and bending moment acting on the spine have not been fully quantified. Furthermore, previous investigations have focused on the upright posture only. METHODS: In this study, 12 volunteers each stood on a force plate while weights of 0, 2, 4, and 6 kg (for men, 40% less for women) were delivered into their hands in one of three ways: 1) by the volunteer holding an empty box with handles, into which an unknown weight was dropped; 2) by the same way as in 1, but with volunteer wearing a blindfold and earphones to eliminate sensory cues; or 3) by the volunteer sliding a box of unknown weight off a smooth table. Experiments were carried out with participants standing in upright, partially flexed, and moderately flexed postures. Spinal compression resulting from muscular activity was quantified using electromyographic signals recorded from the back and abdominal muscles. The axial inertial force acting up the long axis of the spine was calculated from the vertical ground reaction force. The bending moment acting on the osteoligamentous spine was quantified by comparing measurements of lumbar curvature with the bending stiffness properties of cadaveric lumbar spines. RESULTS: The contribution from abdominal muscle contraction to overall spinal compression was small (average, 8%), as was the axial inertial force (average, 2.5%), and both were highest in the upright posture. Peak bending moments were higher in flexed postures, but did not increase much at the moment of load delivery in any posture. Peak spinal compressive forces were increased by 30% to 70% when loads were suddenly and unexpectedly dropped into the box, and by 20% to 30% when they were slid off the table, as compared with loads simply held statically in the same posture (P < 0.001). The removal of audiovisual cues had little effect. CONCLUSIONS: Sudden and alarming events associated with manual handling cause a reflex overreaction of the back muscles, which substantially increases spine compressive loading. Manual handling regulations should aim to prevent such events and limit the weight of objects to be lifted.

Abdominal Muscles↗

PubMed2000

Effects of backward bending on lumbar intervertebral discs. Relevance to physical therapy treatments for low back pain.

STUDY DESIGN: Mechanical testing of cadaveric motion segments. OBJECTIVES: To test the hypothesis that backward bending of the lumbar spine can reduce compressive stresses within lumbar intervertebral discs. SUMMARY OF BACKGROUND DATA: Lumbar extension affects the distribution of compressive stress inside normal cadaveric discs, but little is known about its effect on mechanically disrupted and degenerated discs. METHODS: Nineteen lumbar motion segments (mean donor age, 48 years) were subjected to complex mechanical loading to simulate the following postures: moderate lumbar flexion, 2 degrees of extension, 4 degrees of extension, and the neutral position (no bending). The distribution of compressive stress within the disc matrix was measured in each posture by pulling a miniature pressure transducer along the midsagittal diameter of the disc. Stress profiles were repeated after a mechanical treatment that was intended to simulate severe disc degeneration in vivo. RESULTS: The "degeneration" treatment reduced pressure in the nucleus pulposus and generated stress concentrations within the anulus, in a manner similar to that found in severely degenerated discs in vivo. When all discs were considered together, 2 degrees of extension increased the maximum compressive stress within the posterior anulus by an average of 16%, compared with the neutral posture. The size of localized stress peaks within the posterior anulus was increased by 43% (P = 0.02). In 4 degrees of extension, changes observed between 0 degree and 2 degrees were usually exaggerated. In contrast, moderate flexion tended to equalize the distribution of compressive stress. In 7 of the 19 discs, 2 degrees of lumbar extension decreased maximum compressive stress in the posterior anulus relative to the neutral posture by up to 40%. Linear regression showed that lumbar extension tended to reduce stresses in the posterior anulus in those discs that exhibited the lowest compressive stresses in the neutral posture (P = 0.003; R2 = 41%). CONCLUSIONS: The posterior anulus can be stress shielded by the neural arch in extended postures, but the effect is variable. This may explain why extension exercises can relieve low back pain in some patients.

Adult↗

PubMed2000

Autonomic circulatory and cerebrocortical responses during increasing depth of propofol sedation/hypnosis in humans.

PURPOSE: To describe the relative effects of graded central nervous system (CNS) depression, using increasing propofol infusion rates, on neurovegetative brainstem-mediated circulatory control mechanisms and higher cortical activity in healthy humans. METHODS: Propofol was administered using an infusion scheme designed to achieve three target blood concentrations in ten healthy volunteers. Blood propofol concentrations and sedation scores were determined at baseline, during the three propofol infusion levels, and 30 min into the recovery period. Electroencephalographic (EEG) power was measured in three frequency bands to quantify cortical activity, and autonomic heart rate control was quantified using spontaneous baroreflex assessment and power spectral analysis of pulse interval. RESULTS: Sedation scores closely paralleled propofol blood concentrations (0, 0.53 +/- 0.34, 1.24 +/- 0.21, 3.11 +/- 0.80, and 0.96 +/- 0.42 microg x mL(-1) at baseline, three infusion levels and recovery respectively), and all subjects were unconscious at the deepest level. Indices of autonomic heart rate control were decreased only at the deepest levels of CNS depression, while EEG effects were apparent at all propofol infusion rates. These EEG effects were frequency specific, with power in the beta band being affected at light levels of sedation, and alpha and delta power altered at deeper levels. CONCLUSIONS: The results of this study support a relative preservation of neurovegetative circulatory control mechanisms during the early stages of CNS depression using gradually increasing rates of infusion of propofol. Indices of circulatory control did not reliably reflect depth of sedation.

Adult↗

PubMed2000

The conditioned response erection (CRE)--a new approach to modelling erectile responses in the rat.

Several animal models are currently used in erectile (dys)function research; these models fail to account for the conditions involving the more spontaneous erections in humans. Recently, we observed an increase in the number of 'spontaneously' occurring erections in rats with previous exposure to apomorphine (APO), a centrally acting drug that initiates penile erections and yawns. Based on this observation, we designed a series of experiments to characterize the development of enhanced, non-apomorphine-induced erections or 'spontaneous' erectile responses to vehicle administration in rats with previous exposure to APO. We further examined the effects of castration on these conditioned erections. Naive (ie never received APO) rats were administered vehicle (1 ml/kg saline) to determine the frequency of baseline erections and yawns. An alternating series of APO (80 microg/kg s.c.) and vehicle administrations were performed over several days and subsequent erectile and yawning responses were recorded. Following 3 sets of 3 APO administrations (with vehicle administered between sets), and the 3rd vehicle administration, these rats were then surgically castrated and allowed 30 days to recover. Following this, APO was administered 3 times to determine erectile and yawning responses post-castration, followed by vehicle administration to determine the effects of castration on conditioned APO responses. The major findings were: (1) that although naive rats had a basal spontaneous erectile response (0.75 +/- 0.88; 4 of 8 rats with at least one erection), repetitive administration (up to 22 treatments) of the central initiator apomorphine significantly increased the number of erections (1.8 +/- 0.7; 7 of 8 rats with at least one erection) and yawning (2.5 +/- 2.47) responses to vehicle administration; and (2) both spontaneous yawning and erectile responses were found to be androgen dependent since castration dramatically lowered the number of erections (0.13 +/- 0.35; 1 of 8 rats with at least one erection) and yawns (0). Therefore, this method of producing erections without a pharmacological manipulation provides an additional animal model which can be used in conjunction with the APO-induced erections in characterizing the physiology and pathophysiology of erectile function in conscious rats.

Androgens↗

PubMed2000

Pre-penile arteries are dominant in the regulation of penile vascular resistance in the rat.

The amount of blood flow into the penis that will produce an erection is dependent on the sum of inflow resistance from the feeder arteries, arterioles and the intra-penile vasculature. In the present study, our objective was to determine quantitatively the contribution to inflow resistance of these different components of the rat penile vasculature. Using methods developed previously, we determined the resistance properties of the isolated perfused whole penis in situ, both in an intact system and after serial transactions of the vessels. These cuts eliminated progressively larger distal segments of the vascular bed. Perfusion pressures were recorded at different flow rates (0.5-3 ml/min/kg body weight) under conditions of maximal dilatation and maximal vasoconstriction induced by methoxamine (MXA, 40 microg/ml). Regardless of the level of vascular tone, the pudendal artery contributes approximately 70% of the total resistance of the penile vasculature. In contrast, the vasculature within the penis (tip, shaft, crus) contributes only about one quarter of the resistance. Penile arterial inflow resistance properties both at maximal vasodilation and maximal alpha1-adrenergic constriction are dominated by the extra-penile vasculature in the rat. The implications of these findings are that alterations in the pudendal-artery (eg vasodilation, vasoconstriction, stenosis) would have primary control of arterial inflow and suggest an important role for pharmacological agents which can promote a more generalized vasodilation (eg phosphodiesterase inhibitors) in contrast to selective corpus cavernosal agents.

Adrenergic alpha-Agonists↗

PubMed2000

Capillary electrophoresis for the determination of major amino acids and sugars in foliage: application to the nitrogen nutrition of Sclerophyllous species.

Amino acids and sugars are probably the most commonly measured solutes in plant fluids and tissue extracts. Chromatographic techniques used for the measurement of such solutes require complex derivatization procedures, analysis times are long and separate analyses are required for sugars and amino acids. Two methods were developed for the analysis of underivatized sugars and amino acids by capillary electrophoresis (CE). Separation of a range of sugars and amino acids was achieved in under 30 min, with good reproducibility and linearity. In general, there was close agreement between amino acid analyses by CE and HPLC with post-column derivatization. An alternative, more rapid method was optimized for the common neutral sugars. Separation of a mixture of fructose, glucose, sucrose, and fucose (internal standard) was achieved in less than 5 min. How the source of N applied (nitrate or ammonium) and its concentration (8.0 or 0.5 mM) affects the amino acid and sugar composition of leaves from Banksia grandis Willd. and Hakea prostrata R. Br. was investigated. The amino acid pool of Banksia and Hakea were dominated by seven amino acids (aspartic acid, glutamic acid, asparagine, glutamine, serine, proline, and arginine). Of these, asparagaine and glutamine dominated at low N-supply, whereas at high N-supply the concentration of arginine increased and dominated amino-N. Plants grown with nitrate had a greater concentration of proline relative to plants with ammonium. In Banksia the concentration of amides was greatest and arginine least with a nitrate N-source, whereas in Hakea amides were least and arginine greatest with nitrate N-source. The concentration of sugars was greater in Banksia than Hakea and in both species at greater N-supply.

Amino Acids↗

PubMed2000

Measurement of sap flow in roots of woody plants: a commentary.

Measurements of sap flow in roots have recently been used to study patterns of resource acquisition by woody plants; however, the various thermometric methods employed have yielded disparate findings. These findings may be harmonized by accounting for the phenomenon of reverse sap flow in roots. We suggest that only methods capable of measuring slow and reverse rates of flow and that do not require assumptions of zero flow during the night are applicable to studies with roots. The heat ratio method and the constant power heat balance method fit these criteria, whereas the constant temperature heat balance, compensation heat pulse and thermal dissipation methods do not.

Plant Roots↗

PubMed2000

Effects of an environmental anti-androgen on erectile function in an animal penile erection model.

PURPOSE: Erectile function is testosterone dependent. For example, interference with either the levels or receptor binding of this steroid hormone may induce erectile dysfunction. Several environmental contaminants can interfere with the actions of endogenous hormones and have been termed 'endocrine disrupters.' p,p-DDE, a prominent and persistent metabolite of the insecticide DDT, has been shown to be an androgen receptor antagonist. The objective was to determine whether endocrine disrupters, as exemplified by p,p-DDE, are factors in the etiology of erectile dysfunction. MATERIALS AND METHODS: Using the established rat model of apomorphine-induced (80 microg./kg, s.c.) erections we assessed the dose-response effects of p,p-DDE in comparison to the known androgen receptor antagonist flutamide in acute (0.5 to 12 hours) and short-term (up to 8 weeks) experiments in both intact (Study 1) and castrated (Study 2) rats. As a follow up (Study 3), castrated rats treated with p,p-DDE were given increasing doses of testosterone (0.48 to 2.4 mg./kg., i.p.), eight weeks after p,p-DDE administration, to assess reversibility of p,p-DDE effect. RESULTS: A single dose of flutamide (50 mg./kg., i.p.) was found to significantly decrease apomorphine-induced erections to less than 50% over 12 hours following flutamide administration with recovery of erectile response within 48 hours. In comparison, a single dose of p,p-DDE (500 mg./kg., i.p.) decreased apomorphine-induced erections for at least two weeks (1.15+/-0.3 versus 2.5+/-1.1). Castration significantly decreased apomorphine-induced erections to approximately 0.5 erections/30 minutes. Flutamide (50 mg./kg.; i.p.) or p,p-DDE (50 mg./kg.; i.p.) did not further suppress the apomorphine erections in castrated rats. Testosterone supplementation (480 microg./kg; s.c.) in vehicle treated castrated rats recovered erectile response to pre-castrated levels, whereas p,p-DDE treated castrated rats required 4 times the dose of testosterone (2 mg./kg.; s.c.) given to vehicle treated rats to recover erections. CONCLUSIONS: The endocrine disrupter p,p-DDE can markedly interfere with erectile function and demonstrates persistence after a single dose. This supports our novel concept that environmental hormones may cause erectile dysfunction.

Androgen Antagonists↗

PubMed2000

Irbesartan: review of pharmacology and comparative properties.

The recently developed and marketed angiotensin II type 1 (AT1) receptor blockers (ARBs) have demonstrated efficacy equivalent to that of other leading classes of antihypertensive agents, with superior tolerability profiles. The specific targeting of the AT1 receptor afforded by these agents has demonstrated more complete blockade of the renin-angiotensin system than that offered by angiotensin-converting enzyme inhibitors. These data notwithstanding, differentiation within the class of ARBs has been limited. With the accumulation of additional data with ARBs, it has recently become possible to make within-class distinctions, based in large part on the individual pharmacological profiles of the ARBs. To this end, absorption, distribution, half-life, dose response and level of angiotensin II antagonism are of special note. When these properties are viewed as a group, the ARB irbesartan appears to offer advantages beyond those attained with other ARBs. Irbesartan is well absorbed, does not require biotransformation to an active metabolite to exert its antihypertensive activity, offers a large volume of distribution, has a half-life that is sufficient to allow once-daily dosing, is associated with a strong and consistent dose-response and has been demonstrated to provide a level of angiotensin II antagonism that is statistically superior to that offered by some other ARBs. These pharmacological differences may explain the clinical superiority of irbesartan compared with losartan, the first member of the ARB class. As even more data on the ARBs become available, the ability to determine the advantages of specific members of this class will be enhanced, distinctions that already have begun to come to light.

Angiotensin Receptor Antagonists↗

PubMed2000

Endothelin receptor antagonism does not prevent the development of in vivo glyceryl trinitrate tolerance in the rat.

There is evidence that increased endothelial production of endothelin-1 (ET-1) may contribute to glyceryl trinitrate (GTN) tolerance. We used the competitive ET(A) receptor antagonist ZD2574 to determine whether chronic ET(A) receptor blockade affected the biochemical and functional responses to GTN during the development of GTN tolerance in vivo. Tolerance induced using transdermal GTN patches resulted in a 5.3 +/- 1.2-fold increase in the EC(50) value for GTN relaxation in isolated aorta from GTN-tolerant rats. Coadministration of ZD2574 (100 mg kg(-1) t.i.d. for 3 days) during tolerance induction had no effect on GTN-induced relaxation. This dose of ZD2574 markedly blunted the pressor response to ET-1, indicating effective blockade of ET(A) receptors, and also abolished the initial transient depressor response to ET-1, indicating that blockade of endothelial ET(B) receptors also occurred using this dosage regimen for ZD2574. Consistent with the relaxation data, coadministration of ZD2574 had no effect on the decrease in GTN-induced cGMP accumulation or on the decrease in GTN biotransformation that occurred in aortae from GTN-tolerant animals. Radioimmunoassay data indicated that the GTN tolerance induction protocol caused a 2.3 +/- 0.4-fold and a 2.2 +/- 0.5-fold increase in total tissue ET-1 levels in tolerant aorta and vena cava, respectively. These data suggest that chronic inhibition of ET receptors by ZD2574 was not sufficient to prevent or diminish the tolerance-inducing effects of GTN, and that the increase in ET-1 levels observed in tolerant tissues may occur as a consequence of the vascular changes that occur during chronic GTN exposure.

Animals↗

PubMed1999

Personal risk factors for first-time low back pain.

STUDY DESIGN: A prospective study of personal risk factors for first-time low back pain. OBJECTIVES: To construct and validate a multivariate model to predict low back pain. SUMMARY OF BACKGROUND DATA: Various physical and psychological factors have been reported to increase the risk of low back pain, but conflicting results may be attributable to inaccurate "clinical" measures and to poorly validated statistical models. METHODS: A total of 403 health care workers aged 18-40 years volunteered for the study. None had any history of "serious" back pain requiring medical attention or time off work. The volunteers completed the following questionnaires: the modified somatic perception questionnaire, the Zung depression scale, and the Health Locus of Control. Anthropometric factors were quantified using standard techniques. The 3Space Isotrak device (Polhemus, VT) was used to measure lumbar curvature and hip and lumbar spine mobility. Leg and back strength and back muscle fatiguability were measured in functional postures. Postal follow-up questionnaires, sent after 6, 12, 18, 24, 30, and 36 months, inquired about back pain, and multivariate logistic regression was used to identify risk factors at each follow-up. RESULTS: The response rate fell from 99% at 12 months to 90% at 36 months, at which time 90 volunteers reported "serious" back pain and 266 reported "any" back pain. The following were consistent predictors of serious back pain: reduced range of lumbar lateral bending, a long back, reduced lumbar lordosis, increased psychological distress, and previous nonserious low back pain. Only the latter three were consistent predictors of "any" back pain. Physical factors had the most influence in a sub-population of volunteers who were new to the job. CONCLUSIONS: Personal risk factors explained up to 12% of first-time low back pain.

Adolescent↗

PubMed1999

Dynamic forces acting on the lumbar spine during manual handling. Can they be estimated using electromyographic techniques alone?

STUDY DESIGN: Compressive loading of the lumbar spine was analyzed using electromyographic, movement analysis, and force-plate techniques. OBJECTIVES: To evaluate the inertial forces that cannot be detected by electromyographic techniques alone. SUMMARY OF BACKGROUND DATA: Links between back pain and manual labor have stimulated attempts to measure spine compressive loading. However, direct measurements of intradiscal pressure are too invasive, and force plates too cumbersome for use in the workplace. Electromyographic techniques are noninvasive and portable, but ignore certain inertial forces. METHODS: Eight men lifted boxes weighing 6.7 and 15.7 kg from the ground, while joint moments acting about L5-S1 were quantified 1) by using a linked-segment model to analyze data from Kistler force plates and a Vicon movement-analysis system, and 2) by measuring the electromyographic activity of the erector spinae muscles, correcting it for contraction speed and comparing it to moment generation during static contractions. The linked-segment model was used to calculate the "axial thrust," defined as the component of the L5-S1 reaction force that acts along the axis of the spine and that is unrelated to trunk muscle activity or static body weight. RESULTS: Peak extensor moments predicted by the two techniques were similar and equivalent to spinal compressive forces of 2.9-4.8 kN. The axial thrust "hidden" from the electromyographic technique was negligible during slow lifts, and remained below 4% of peak spinal compression even during fast heavy lifts. Peak axial thrust was proportional to the peak vertical ground reaction (R2 = 0.74). CONCLUSIONS: Electromyographic techniques can measure dynamic spinal loading, but additional force-plate data would improve accuracy slightly during lifts requiring a vigorous upward thrust from the legs.

Adult↗