Biomedical subjects

M A Adams

Publications and source records attributed to M A Adams.

At least 91 records · Page 5Linked to original sources

PubMed1995

Fatigue of the erector spinae muscles. A quantitative assessment using "frequency banding" of the surface electromyography signal.

STUDY DESIGN: The authors investigated fatigue-induced changes in the frequency content of the surface electromyographic (EMG) signal from the erector spinae muscles. OBJECTIVES: The objective of the study was to understand the EMG changes in fatiguing muscle and to obtain a reliable index of fatigue. SUMMARY OF BACKGROUND DATA: Power spectral analysis has been used increasingly in recent years to monitor muscle fatigue, but parameters other than the mean or median frequency have received little attention. METHODS: Thirty-five healthy volunteers participated. They pulled upward with constant force on a handlebar attached to a floor-mounted load cell while the EMG signal from the erector spinae was recorded at the levels of T10 and L3 at 1024 Hz; 1.0-sec "windows" of the signal were analyzed using fast Fourier transforms, and the resulting power spectra were divided into 10 frequency bands between 5 Hz and 300 Hz. The median frequency, total power, and peak amplitude of the spectra were also calculated. Changes in the frequency content of the EMG signal were examined during submaximal contractions of different intensity and duration. RESULTS: Median frequency decreased steadily during the contractions, whereas total power and peak amplitude increased. The most repeatable and linear index of change was the increase in the EMG signal in the 5-30 Hz frequency band. The middle-to-high frequency component of the EMG signal increased during the early stages of the contractions, but decreased as the endurance limit was approached. CONCLUSIONS: Changes in the 5-30 Hz band of the EMG power spectrum provide a more reliable and linear index of fatigue in the erector spinae muscles than do changes in median frequency. In the erector spinae, the early effects of fatigue appear to be delayed by the recruitment of additional motor units.

Adult↗

PubMed1995

Recovery of erectile function by the oral administration of apomorphine.

OBJECTIVES: Apomorphine has been reported to be effective in causing erections in animals and man when administered parenterally. The side effects, notably nausea, have seriously limited its clinical usefulness. We formulated apomorphine for controlled sublingual absorption and herein report on four preliminary studies evaluating efficacy and side effects in men with no documentable organic cause of erectile dysfunction. METHODS: Patients complaining of erectile dysfunction underwent a careful evaluation. Those with measurable organic dysfunction or known organic factors were excluded. Men with primarily psychogenic impotence were tested with one of four protocols of an apomorphine preparation (preliminary sublingual liquid, preliminary 5 mg tablet, aqueous nasal spray, and new 3 and 4 mg controlled absorption tablets). The erectile response of these men to the drug with visual erotic or sexually neutral stimulation was studied with the Rigiscan. RESULTS: Seven of 10 evaluable patients responded to the sublingual liquid preparation but the majority experienced significant nausea. The preliminary 5 mg tablet and aqueous forms did not produce useful responses free of side effects. The newly formulated controlled absorption 3 and 4 mg tablets were tested in 12 men. Eight of 12 (67%) developed erections in response to apomorphine. Erectile activity was seen during sexually neutral visual stimulation to a significantly greater extent than with placebo. Home trial use was found to be successful and sustained by 7 of 11 (64%) patients. CONCLUSIONS: We have shown that apomorphine will act as an erectogenic agent when absorbed through the oral mucosa. In a carefully selected group of impotent patients with no documentable organic causes of erectile dysfunction, but with proven erectile potential, 67% will experience significantly durable erections with a dose of 3 or 4 mg of apomorphine when formulated for controlled absorption. The results in these small groups appear to justify larger clinical studies of this proprietary formulation.

Administration, Sublingual↗

PubMed1995

Recent advances in lumbar spinal mechanics and their clinical significance.

Of the many problems associated with low back pain, those which are most amenable to biomechanical investigation are identified. Recent advances in lumbar spinal mechanics are then reviewed in five sections dealing with mechanical function, mechanisms of failure, movements in vivo, loading in vivo, and the biological consequences of mechanical loading. The discussion suggests that mechanical fatigue damage may frequently be the underlying cause of low back pain, even when degenerative changes are evident in the tissues, and the review ends by suggesting some priority areas for future research.

Journal Article↗

PubMed1995

Isolation and perfusion of the pudendal vasculature in male rats.

PURPOSE: The present study outlines a novel in situ technique to assess the regulation of vascular resistance in the penile vascular bed of the Wistar rat. MATERIALS AND METHODS: The isolation and perfusion of the pudendal artery were achieved by ligating all branches of the external iliac artery not directly connected to the internal pudendal artery. RESULTS: A linear flow-perfusion pressure curve was generated to ensure a viable preparation. A cumulative concentration-vascular response curve to the alpha 1-adrenoceptor agonist methoxamine (0.5-64 micrograms./ml.) was obtained. CONCLUSIONS: This novel methodology will allow reproducible and consistent quantitative assessments of the numerous factors (both neural and hormonal) that are proposed to govern the flow of blood in the penile vascular bed.

Animals↗

PubMed1995

Regional myosin heavy chain expression in volume and pressure overload induced cardiac hypertrophy.

Although the overall shift towards the V3 myosin heavy chain (MHC) has been shown to be associated with cardiac hypertrophy, quantitative evidence describing regional expression is sparse. The aim of this study was to compare and contrast the regional ventricular myosin isoform expression in two distinct haemodynamic states: pressure and volume overload. Volume overload was achieved using an aortocaval fistula (ACF) model and pressure overload by two-kidney-one-clip (2K1C) hypertension. A separate group (UC-2K1C) had the clip removed 1 week prior to investigation. Sham operated rats (SHAM) served as controls. All groups were studied 4 weeks after surgery. Ventricular tissue samples (approximately 50 mg) were taken from the walls of the right ventricle (RV), septum and left ventricular (LV) free wall. Tissue samples (excluding RV) were divided into endocardium and epicardium, and myosin expression was determined using polyacrylamide gel electrophoresis. Cardiac hypertrophy was substantial in both LV (1.7-fold) and RV (1.9-fold) in ACF rats. The 2K1C rats had similar LV enlargement (1.6-fold) whereas RV hypertrophy was not as great (1.2-fold). Blood pressure (BP) was increased 65% in 2K1C rats, whereas there was no change in ACF rats with respect to SHAM animals. After unclipping (UC-2K1C), LV hypertrophy and BP had returned towards control levels. In general, V3 MHC expression was associated with increasing LV hypertrophy in both 2K1C and ACF models. However, there was a marked endo-epi differential (1.5:1) in the LV free wall and septum of 2K1C rats. In contrast, in ACF rats there was no differential V3 MHC expression in the LV or septal tissue, i.e. expression was similar in both endo- and epi-samples. Elevated expression of V3 MHC persisted despite normotension and regression of cardiac hypertrophy in UC-2K1C rats. Taken together with published results demonstrating that relative transmural myocyte hypertrophy in ACF rats (endo > epi) is in contrast to that seen in 2K1C rats (epi > endo), the present findings reveal that regional V3 myosin expression represents a distinct adaptational component of the overall cardiac hypertrophic response in both volume and pressure overload.

Animals↗

PubMed1995

Cardiac hypertrophy and related growth processes: the role of insulin-like growth factor-I.

For the heart and resistance vessels in general, increases in pressure load represent a major local stimulus for structural adaptation by elevating the wall tension against which cardiac and vascular smooth muscle contract. Under such conditions the wall thickness of the left ventricle and of the resistance vessels will increase, keeping wall tension per unit muscle layer (wall stress) normal. Alternatively, chronic volume overload and enhanced cardiac filling will induce a structurally based widening of the ventricular lumen. This pattern is associated with a corresponding increase in myocardial mass, so that the wall thickness to internal radius ratio remains more or less constant. A number of extrinsic influences such as the sympathetic nervous system, hormonal factors and growth factors, may superimpose their effects to modulate the final "trophic influence" on the cardiovascular system. Hyperactivity of the renin-angiotensin system, the sympathetic nervous system and various growth factors, have all been suggested to initiate cardiovascular growth in a way that is load-independent. The mechanisms involved in the conversion of a mechanical hypertrophic stimulus into an actual increase in tissue mass are likely to involve many substances and enzyme systems, including transcription factors, enzymes such as ornithine decarboxylase and various growth factors. The presence of the insulin-like growth factor-I (IGF-I) in the heart and vessels suggests a paracrine/autocrine role for this potent growth factor in the regulation of cardiovascular growth. The relationships between ornithine decarboxylase, cardiovascular hypertrophy and IGF-I gene expression are also reviewed.

Adaptation, Physiological↗

PubMed1995

Evidence in vivo for induction of cardiovascular growth processes by vasoconstrictor systems.

Greater smooth muscle growth is an important feature of the changes in blood vessel morphology in hypertension. The increase in vessel wall thickness: lumen ratio resulting from vascular hypertrophy impacts directly on total peripheral vascular resistance thereby influencing the severity of hypertension. The roles played by mechanical forces, vasoactive substances, growth factors and endocrine hormones in mediating hypertrophic vascular growth responses in vivo are currently under investigation. Here we review our current research aimed at: (a) defining the roles in vivo, of the renin-angiotensin system (RAS) and sympathetic nervous system (SNS), in the development of cardiovascular hypertrophy; (b) defining the importance of endogenous vasodilator systems, in particular, the ability of nitric oxide to inhibit trophic responses induced by the RAS and SNS and (c) examining whether trophic stimulation via the two neurohumoral systems as well as the antitrophic activity of the vasodilator systems is in part dependent on changes in blood pressure. In these studies the obligatory enzyme ornithine decarboxylase has proved to be a useful marker of ongoing hypertrophic cardiovascular growth.

Animals↗

PubMed1994

Spondylolysis. Bending of the inferior articular processes of lumbar vertebrae during simulated spinal movements.

STUDY DESIGN: This was a cadaveric lumbar motion segment experiment. OBJECTIVES: To measure bending about the pars interarticularis during simulated flexion and extension movements, with and without high compressive forces. This was designed to indicate which activities are most likely to cause spondylolysis. SUMMARY OF BACKGROUND DATA: The mechanical etiology of spondylolysis is controversial. METHODS: Motion segments were loaded to simulate: A, full flexion; B, full extension; C, high compression in flexed posture, and D, high compression in lordotic posture. Bending of the inferior articular processes about the pars was measured in the sagittal plane, using a two-dimensional "MacReflex" infrared motion analysis system. RESULTS: In full flexion, tension in the intervertebral ligaments bent the processes forward and down (by 3.25 degrees +/- 3.07 degrees), whereas in the loading conditions B, C, and D, inter-facet compressive forces caused the processes to bend backward and upward, by 2.24 +/- 2.48 degrees, 0.40 +/- 0.23 degrees, and 0.74 +/- 0.56 degrees respectively. CONCLUSIONS: Activities that involve alternating flexion and extension movements cause large stress reversals in the pars and pose the greatest threat of spondylolysis. Compressive loading has little effect.

Adolescent↗

PubMed1994

The strength in anterior bending of lumbar intervertebral discs.

STUDY DESIGN: This was a motion segment experiment. OBJECTIVES: To determine the strength in bending of lumbar intervertebral discs. METHODS: Eighteen "motion segments" consisting of two vertebrae and the intervening disc and ligaments were loaded to simulate forward bending movements in life. The range of flexion and the resistance to bending of each specimen was compared before and after removal of the posterior elements. Nine of the discs were tested after the intradiscal pressure had been reduced by damaging the vertebral end plate in compression. RESULTS: The posterior elements restricted the disc to 80% of its full range of flexion. The strength in anterior bending of isolated discs decreased with age and was 33 Nm on average. Reducing intradiscal pressure did not affect the discs' strength in bending. CONCLUSIONS: Disc failure in bending occurs through overstretching of the outer anulus in the vertical direction. In life, the posterior elements may not adequately protect the posterior anulus from fatigue damage.

Adolescent↗

PubMed1994

Passive tissues help the back muscles to generate extensor moments during lifting.

We examined the possibility that passive tissues can help the erector spinae to generate large extensor moments during lifting. One hundred and forty-nine healthy men and women participated in the study. Subjects pulled upwards with steadily increasing force on a floor-mounted load cell, while EMG activity was recorded from electrodes overlying the erector spinae at L3 and T10. Extensor moment was calculated from the load cell data, and was plotted against the full-wave rectified and averaged EMG signal. The relationship was linear with an intercept on the extensor moment axis (I) which indicated the flexion moment resisted by 'passive' (electrically silent) tissues. The dependence of I on lumbar flexion angle was studied by repeating the isometric pulls between 6 and 12 times, with the subject positioned in varying amounts of flexion, as measured by the '3-Space Isotrak'. Subjects then lifted weights of up to 20 kg from the floor, using 'stoop', 'squat' and 'freestyle' techniques, while lumbar flexion and EMG activity were recorded at 28 Hz. The isometric pulls showed that, on average, I increased from 25 Nm in lordotic postures to 120 Nm (for men) and 77 Nm (for women), in full flexion. During the lifts, peak extensor moment was generated with the lumbar spine flexed by 78-97% of the range between erect standing and full flexion.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗

PubMed1994

Bending and compressive stresses acting on the lumbar spine during lifting activities.

Cadaveric studies have shown that intervertebral discs and ligaments are most vulnerable to injury when loaded simultaneously in bending and compression. The purpose of the present experiment was to measure bending and compressive stresses acting on the lumbar spine during forward bending and lifting activities, and to identify those aspects of lifting which increase the risk of injury. Twenty-one men and eighteen women lifted objects from the ground while the following parameters were varied: the angle of the knees ('squat' lift or 'stoop' lift), the mass of the object, its bulk, its distance in front of the feet, its distance away from the sagittal plane, and the speed of movement. Spinal compression was assessed by measuring the peak extensor moment generated by the back muscles and fascia during the lift. Extensor moment was calculated from the EMG activity of the erector spinae muscles, using corrections for muscle length, contraction velocity and electro-mechanical delay. The bending moment ('bending torque') acting on the intervertebral discs and ligaments was quantified by comparing dynamic measurements of lumbar flexion, obtained with the '3-Space Isotrak', with the normalised bending properties of cadaveric lumbar spines. Results showed that stoop lifting reduced the peak extensor moment by about 10% compared to squat lifting, but increased the bending torque by about 75%. Extensor moment and bending torque both increased substantially with increasing mass, bulk and distance from the feet. Non-sagittal plane lifts increased the bending torque by about 30%. The fastest lifts increased peak extensor moment by 60% but did not increase bending torque. We conclude that complex spinal loading during lifting tasks depends as much on the speed of movement, and the size and position of the object lifted, as on its mass. Analyses of spinal loading which consider only compressive forces do not give a full indication of the risk of injury to the intervertebral discs and ligaments.

Adult↗

PubMed1994

Renin-angiotensin system in neonatal rats: induction of a renal abnormality in response to ACE inhibition or angiotensin II antagonism.

In experiments designed to analyze cardiovascular structure in response to antihypertensive therapy with an ACE inhibitor, we decided to start very early in life with the aim to prevent blood pressure increases and the development of vascular structural changes. In these treated groups of rats we unexpectedly observed that after they were weaned, their water consumption and urine volume, respectively, increased substantially. The present study was designed to determine if inhibition of the renin-angiotensin system produced similar effects in different strains of rats, and focused on characterizing the abnormal fluid balance occurring as a consequence to neonatal treatment with ACE inhibitors or angiotensin II blockers. Three-day-old Wistar Kyoto (WKY), Wistar (WR) and spontaneously hypertensive rats (SHR) were given either saline, enalapril, captopril, losartan and the AT2 blocker, PD123319, in the same amount of volume for 20 days. Treatment was stopped and rats were examined with regard to renal morphology at 4, 14 and 30 weeks of age. In addition, water consumption, urine volume, urine electrolytes and osmolality were analyzed at 14 weeks of age, that is, 10 weeks off treatment. Early treatment with the ACE inhibitors, enalapril and captopril, and the AT1 blocker, losartan, but not the AT2 blocker, PD 123319, in the SHR and in the normotensive strains WKY and WR produced persistent, irreversible histopathological renal abnormalities in adult life, long after the rats had been taken off treatment. These abnormalities consisted of mainly cortical tubulointerstitial inflammation, various degrees of papillary atrophy and pelvic dilation.(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensin I↗

PubMed1994

Increased expression of growth hormone receptor mRNA and insulin-like growth factor-I mRNA in volume-overloaded hearts.

Recent results suggest that insulin-like growth factor-I (IGF-I) may be involved in the transition of a hemodynamic load into cardiac hypertrophy and that the expression of IGF-I seems to be coupled to increased wall stress. The present study investigated the role of growth hormone (GH) and IGF-I in myocardial hypertrophy induced by volume overload. An aortocaval fistula (ACF) was created in male Wistar rats, and experiments were performed 2, 4, and 7 days after the onset of volume overload. Right and left ventricular (RV and LV, respectively) myocardial expression of GH receptor mRNA and IGF-I mRNA were quantitated by a solution hybridization RNase protection assay. RV GH receptor mRNA content was elevated on the fourth and seventh days after the induction of the shunt, with peak levels (0.63 +/- 0.16 versus 0.14 +/- 0.03 amol/microgram DNA for the sham-operated animals; P < .01) after 4 days. Similarly, IGF-I mRNA was significantly increased in the RV of shunted animals (1.26 +/- 0.13 versus 0.56 +/- 0.05 amol/micrograms DNA; P < .01) 7 days after surgery. In the left ventricle, where systolic pressure was reduced in ACF rats, no differences could be detected in GH receptor and IGF-I mRNA content between ACF and sham-operated rats on any of the experimental days. There was no difference in the ratio of RV to LV weight during the experimental period. We have shown that the thin-walled right ventricle responds to volume overload with an increase of GH receptor mRNA content followed by elevated expression of IGF-I mRNA.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1994

Differential effect of short-term ethanol on cardiac and vascular growth responses.

OBJECTIVE: To determine in rats the acute effect of ethanol on the activity of a marker of cardiac and vascular growth processes (ornithine decarboxylase) and on alpha 1-adrenergic-induced vascular trophic responses, and whether ethanol-induced sympathoadrenal hyperactivity stimulated vascular structural changes after a more prolonged treatment. METHODS: Acute treatment was as follows: ethanol (5 g/kg, intubation), alpha 1-adrenergic agonist (10 mg/kg methoxamine subcutaneously), methoxamine plus ethanol, or control. Left ventricular, aortic and mesenteric vascular ornithine decarboxylase activity was determined 4 h later by measuring 14CO2 evolved from [14C]-ornithine. Three-day treatment was as follows: ethanol (every 8 h, intubation, 5 g/kg initial dose, subsequent doses based on intoxication level) or isocaloric quantities of maltose dextrin. The left ventricular: body weight ratio, hindlimb vascular resistance properties and indices of cardiac and vascular hypertrophy were determined. RESULTS: In the acute treatment methoxamine-induced pressor responses and the activation of vascular ornithine decarboxylase were both inhibited by ethanol treatment. Ethanol alone elevated the heart rate and decreased mean arterial pressure while stimulating left ventricular but not vascular ornithine decarboxylase activity. Methoxamine did not alter left ventricular ornithine decarboxylase activity. Three-day ethanol treatment induced cardiac hypertrophy but had no effect on the hindlimb vascular resistance properties measured at maximum dilation and maximum constriction. CONCLUSIONS: Acute and short-term ethanol exposure induces cardiac growth processes. Ethanol prevents alpha 1-adrenergic activated vascular growth response by a mechanism that may be similar to the attenuation of alpha 1-adrenergic-induced elevation of arterial pressure.

Animals↗

PubMed1994

Mechanical properties of articular cartilage in knees with unicompartmental osteoarthritis.

We studied the mechanical properties of cartilage from the apparently unaffected compartment of knees with unicompartmental osteoarthritis (OA). Plugs of cartilage and subchondral bone, 8 mm in diameter, were obtained from the tibial plateau of seven patients treated by total knee replacement. Control specimens were obtained from eight cadaver knees of similar age. Specimens were loaded by a plane-ended indentor in a hydraulic materials testing machine; we measured thickness, 'softness', rate of creep, and compressive strength of the articular cartilage. We found that the 'unaffected' cartilage from OA knees was significantly thinner and softer than control cartilage, and it was slightly, although not significantly, weaker. We conclude that the apparently unaffected cartilage in knees with unicompartmental OA is mechanically inferior to normal cartilage, even although clinically, radiologically and morphologically it appears to be sound.

Adult↗

PubMed1993

Can intervertebral disc prolapse be predicted by disc mechanics?

The hypothesis was tested that stress concentrations in the posterior anulus of an intervertebral disc predispose it to prolapse under high compressive loads and anterolateral bending. The distribution of compressive stress inside the intervertebral discs of 22 cadaveric lumbar motion segments was measured with the specimens loaded in pure compression and in compression combined with anterolateral bending. Each motion segment was then loaded to failure in combined compression and anterolateral bending. Failure occurred in the vertebral body (n = 12) or posterolateral anulus (n = 10); the latter group showed a significantly greater incidence of stress concentrations (P < 0.001) in the posterior anulus, when loaded in compression and bending. It was concluded that some discs are predisposed to prolapse because of damaging, localized concentrations of stress in the posterior anulus in combined anterolateral bending and compression.

Cadaver↗

PubMed1992

Development and validation of a new transducer for intradiscal pressure measurement.

Potentially damaging tensile stresses in the annulus fibrosus are directly related to the hydrostatic pressure in the centre of an intervertebral disc: the design and development of a miniature strain gauge pressure transducer is described for measuring such pressures. Static calibration tests in bulk liquid demonstrated that measurements made with the transducer were of sufficient accuracy and stability for in vitro and in vivo investigations of spinal mechanics, and a study of the dynamic behaviour of the transducer demonstrated that it had a frequency response suitable for in vitro and in vivo investigations. Tests within loaded cadaveric discs showed that the transducer could be used to make repeatable measurements which were free from significant artefacts, when the disc was subjected to forces of up to 4000 N and when deformed in full flexion/extension.

Adult↗

PubMed1992

Internal intervertebral disc mechanics as revealed by stress profilometry.

A technique was developed for measuring the distribution of stress within loaded cadaveric intervertebral discs. A strain-gauged membrane mounted on the side of a 1.3-mm diameter needle was pulled through the disc at constant speed. The orientation of the membrane was changed by rotating the needle, so that profiles of vertical and horizontal components of compressive stress could be obtained. The measurements were reproducible and did not perturb the tissue to any significant extent. Stress profiles varied considerably between discs and were highly dependent on the severity of degenerative changes. They also showed that the mechanical behavior of individual disc tissues was dependent not only on their location, but also on the loading and loading history of the disc. The new insight into internal disc mechanics revealed by stress profilometry may lead to a greater understanding of the mechanisms of disc function and failure.

Aging↗