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Biomedical subjects

P Dolan

Publications and source records attributed to P Dolan.

At least 91 records · Page 5Linked to original sources
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↗
PubMed1993

[Infusion of propofol or closed-circuit isoflurane. A study of cost].

The choice of an anaesthetic agent is influenced by its cost. The use of a circle absorber system decreases the cost of the maintenance of anaesthesia with halogenated agents. Fast recovery and low incidence of postoperative nausea and vomiting are the main advantages of propofol. The cost of propofol can limit its use for the maintenance of anaesthesia except for short procedures. This prospective study compared in 50 ASA 1 and 2 patients the cost of anaesthesia with either propofol (group P, n = 25) or the association thiopentone-isoflurane administered with a rebreathing circuit (group I, n = 25). Patients were premedicated the evening before surgery with 2.5 mg lorazepam. Anaesthesia was induced with either propofol (2-3 mg.kg-1) or thiopentone (4-6 mg.kg-1) and maintained with either propofol (6-10 mg.kg-1.h-1) in group P or isoflurane continuously injected as liquid in the expiratory limb of the circuit in group I. The side effects of anaesthesia and the delay of recovery and discharge from the recovery room were assessed. Peroperative cost of anaesthesia included nitrous oxide, isoflurane and i.v. agents, fluids volumes and disposable devices. The total cost of anaesthesia included also the recovery room stay. The mean duration of anaesthesia was not significantly different between the two groups (109.4 +/- 7.1 min vs 107.3 +/- 7.3 min group P vs group I). The delay lf recovery (eyes opening) was shorter in the propofol group (14.4 +/- 1.3 min vs 19.4 +/- 1.4 min) as well as the delay of discharge from the recovery room (70 +/- 4 min, vs 82.4 +/- 4.6 min).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

[Acute respiratory distress caused by a mediastinal pancreatic pseudocyst].

The pseudocyst of the pancreas is a frequent complication of acute pancreatitis. However to intrathoracic localization remains exceptional. A case of acute respiratory insufficiency in a 66-year-old man in whom artificial ventilation was required for such a complication is reported. This case stresses the difficulty often encountered for the differential diagnosis of these liquid tumors. The clinical signs are variable and non specific, especially in case of absence of any history of pancreatitis. The radiographic studies, in particular ultrasonography and CT-scanner defines its liquid nature and its connections. Endoscopy examination confirms its retro-oesophageal extension due to the migration through the oesophageal hiatus. Only the percutaneous needle aspiration of a collection or an associated pleural effusion confirms the diagnosis by the high content of amylases. The treatment of this type of localisation is surgical and essentially consists of an internal derivation.

Acute Disease↗
PubMed1993

The evaluation of the isolated perfused liver as a model for the assessment of liver preservation.

An ex vivo isolated perfused porcine liver model was tested to assess its suitability for rapid, reliable and relatively cheap testing of organ preservation solutions for liver transplantation. The model consists of a machine driven recirculating system incorporating an organ chamber, blood pump and membrane oxygenator. Autologous blood was used for perfusion for a period of 2 h at a temperature of 37 degrees C. The model was tested with five groups of livers which had sustained varying degrees of injury ranging from minimally damaged to those known to be incapable of sustaining life when used for liver transplantation. The groups of livers were: (i) controls; (ii) preserved in University of Wisconsin solution (UW) for 6 h; (iii) preserved in an albumin-based extracellular fluid (ALB) for 6 h; (iv) preserved in UW for 18 h; and (v) preserved in ALB for 18 h. Bile production was found to be a reliable parameter of preservation damage. Changes in perfusate levels of aspartate aminotransferase, potassium, glucose and calcium also occurred in relationship to preservation damage. In contrast, weight gain of the liver, sequestration of the white cells and platelets in the liver, urea production and oxygen consumption were unreliable predictors of liver damage. Histology of biopsy specimens revealed apparently well preserved livers in all cases after preservation but before perfusion, but serious abnormalities after perfusion in long preserved livers, with features in these suggestive of damage to the sinusoidal endothelium. We believe that the model is a worthwhile adjunct to research into liver preservation.

Adenosine↗
PubMed1992

Successful reversal of primary graft non-function in a liver transplant patient treated with prostaglandin E1.

A 63 year old woman with liver failure received a transplant from a 21 year old male diagnosed as brain dead following a motor accident. After the operation, bile production was virtually absent and aspartate transaminase (AST) values rose dramatically 40 h postoperatively. Primary non-function of the graft was diagnosed, and the patient put on an urgent list for retransplantation. At the same time a continuous intravenous infusion of PGE1 was administered. Aspartate transaminase levels decreased within 9 h and reached normal levels by the sixth postoperative day, when bile production began to increase. Liver function subsequently returned to normal.

Alprostadil↗
PubMed1991

A technique for quantifying the bending moment acting on the lumbar spine in vivo.

The bending properties of cadaveric lumbar spines were measured and used to convert in vivo measurements of lumbar flexion into bending moments ('stresses'). Forty-two lumbar motion segments were subjected to complex physiological loading and graphs were obtained of bending moment vs flexion angle. Variability was reduced by expressing both variables as a percentage of their values at the elastic limit. Data were averaged for each lumbar level, and a composite bending curve was compiled for the lumbar spine, L1-S1. A linear relationship was established between lumbar flexion measured in vitro and in vivo. This enabled values of 'per cent lumbar flexion' measured in vivo to be converted into 'per cent maximum bending moment' with a maximum likely error of about +/- 8%, which is equivalent to about +/- 5 Nm at L5-S1 for an average person. The technique was applied to 28 subjects, using dynamic measurements of lumbar flexion obtained with the '3-Space Isotrack' system. The bending moment at L5-S1 was 12 Nm on average when picking a pen up off the floor. Highly significant increases in bending moment were observed when heavier and bulkier objects were lifted.

Adult↗
PubMed1991

The in vivo and in vitro transmission ratio distortion of one complete and two partial t haplotypes in mice.

The effects of different types of insemination (normal and delayed matings and in vitro fertilization) on the transmission ratio distortion (TRD) of three t haplotypes were determined. The tw73 haplotype which contains all of the loci known to affect TRD is transmitted at equivalent frequencies in normal matings and in in vitro fertilizations (0.84 and 0.85, respectively) but at a significantly lower frequency (0.62) in delayed matings. The distal partial th18 haplotype is transmitted at equivalent frequencies in all types of insemination (0.66 to 0.70) while the proximal partial tw18 haplotype is transmitted in Mendelian frequencies in normal matings and in in vitro inseminations but at a significantly lower frequency in delayed matings. The results are discussed with reference to the current genetic model for transmission ratio distortion.

Animals↗
PubMed1990

Diurnal changes in spinal mechanics and their clinical significance.

Diurnal changes in the loads acting on the spine affect the water content and height of the intervertebral discs. We have reviewed the effects of these changes on spinal mechanics, and their possible clinical significance. Cadaveric lumbar spines subjected to periods of creep loading show a disc height change similar to the physiological change. As a result intervertebral discs bulge more, become stiffer in compression and more flexible in bending. Disc tissue becomes more elastic as its water content falls, and its affinity for water increases. Disc prolapse becomes more difficult. The neural arch and associated ligaments resist an increasing proportion of the compressive and bending stresses acting on the spine. Observations on living people show that these changes are not fully compensated for by modified muscle activity. We conclude that different spinal structures are more heavily loaded at different times of the day. Therefore, the time of onset of symptoms and signs, and any diurnal variation in their severity, may help us understand more about the pathophysiology of low back pain and sciatica.

Back Pain↗
PubMed1988

Commonly adopted postures and their effect on the lumbar spine.

The activity of the erector spinae muscles and the changes in lumbar curvature were measured in 11 subjects in a range of commonly adopted postures to see if there were any consistent trends. Surface electrodes were used to measure back muscle activity and lumbar curvature was measured using electronic inclinometers. The results showed that many commonly adopted postures reduced the lumbar lordosis when compared with erect standing or sitting, even at the expense of increasing the back muscle activity.

Adult↗
PubMed1988

The lumbar spine in backward bending.

Cadaveric lumbar motion segments were loaded to simulate backward bending (extension) movements of the lumbar spine. The motion segments' resistance was measured initially, and after the spinous processes and apophyseal joints had been cut through in turn. Compression tests were then performed on the discs while they were wedged in full extension. The results showed that extension is resisted mainly by the disc and spinous processes, and that, in hyperextension, damage usually occurs first in the spinous processes (or the soft tissue squashed between them). However, if the spinous processes are particularly widely spaced, then the apophyseal joints can become damaged first. The protection offered the disc by the neural arch is greater in young people, and after the disc height has been reduced by creep loading. The disc can be damaged in hyperextension if the spine is subjected to high compressive forces at the same time. A sudden application of compressive force can cause an anterior disc prolapse, while a cyclic (fatigue) compressive force can increase the posterior bulging of the lamellas in the posterior annulus.

Humans↗
PubMed1987

Human muscle function following prolonged eccentric exercise.

4 subjects performed repeated eccentric contractions with leg extensors during prolonged downhill walking (-25% gradient) at 6.44 km.h-1 until collapse due to muscle weakness (range of exercise duration 29 to 40 min). During the exercise oxygen uptake rose progressively from approximately 45% of the previously determined VO2max at 10 min to approximately 65% at the end of the exercise. Following the exercise there was an immediate, significant, and sustained reduction in maximal voluntary isometric contraction, and short term (anaerobic) power output measured concentrically on an isokinetic ergometer. These reductions in muscle function persisted for 96 hours post exercise, and were reflected by significant reductions in the tension generated at low frequency (20 Hz) relative to higher frequency (50 Hz) percutaneous stimulation of the quadriceps. All four subjects showed an increase in plasma levels of creatine kinase post eccentric exercise. Performing concentric contractions by walking uphill for one hour at a significantly greater metabolic cost failed to induce comparable reductions in muscle function. These results provide evidence for the consequences of prolonged eccentric work upon dynamic function which complements earlier reports of structural, enzymatic, and static function changes.

Adult↗
PubMed1987

Diurnal variations in the stresses on the lumbar spine.

Two complementary experiments were performed, the first on living people and the second on cadaveric spines. In the first experiment, electronic inclinometers were used to measure the range of lumbar flexion of 21 volunteers in the early morning and in the afternoon. The results showed that the range of movement increased by 5 degrees during the day. In the second experiment, cadaveric lumbar motion segments were creep loaded to simulate a day's activity and their bending properties were measured before and after creep. The results showed that creep loading reduces the spine's resistance to bending (the effect being particularly marked in the disc) and increases the range of lumbar flexion by 12.5 degrees. The results of the two experiments were combined to show that in life, forward bending movements subject the lumbar spine to higher bending stresses in the early morning compared with later in the day. The increase is about 300% for the discs and 80% for the ligaments of the neural arch. It is concluded that lumbar discs and ligaments are at greater risk of injury in the early morning.

Adolescent↗
PubMed1987

Effect of prior exercise on maximal short-term power output in humans.

The effect of prior exercise (PE) on subsequent maximal short-term power output (STPO) was examined during cycling exercise on an isokinetic ergometer. In the first series of experiments the duration of PE at a power output equivalent to 98% maximum O2 uptake (VO2max) was varied between 0.5 and 6 min before measurement of maximal STPO. As PE duration increased subsequent STPO fell to approximately 70% of control values after 3-6 min. In series ii the effect of varying the intensity of PE of fixed 6-min duration was studied in five subjects. After PE less than 60% VO2max there was an increase of 12% in STPO, but after greater than 60% VO2max there was a progressive fall in STPO as PE intensity increased, indicating a reduction of approximately 35% at 100% VO2max compared with control values. In series iii we examined the effect on STPO of allowing a recovery period after a fixed intensity (mean = 87% VO2max) of 6 min PE before measurement of STPO. This indicated a rapid recovery of dynamic function with a half time of approximately 32 s, which is similar to the kinetics of PC resynthesis and taken with the other findings suggests the dominant role that PC exerts on the STPO under these conditions.

Adult↗