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Biomedical subjects

I Kingma

Publications and source records attributed to I Kingma.

At least 19 recordsLinked to original sources
PubMed2001

In vitro torsion-induced stress distribution changes in porcine intervertebral discs.

STUDY DESIGN: A cadaveric porcine spine motion segment experiment was conducted. OBJECTIVE: To test the hypothesis that small vertebral rotations cause increased stress in the anulus while decreasing stress in the nucleus through stiffening of the anulus. SUMMARY OF BACKGROUND DATA: Stress profiles of the intervertebral disc reportedly depend on degeneration grade and external loading. Increased stress in the anulus was found during asymmetric loading. In addition, depressurization of the nucleus combined with an instantaneous disc height increase was found when small (<2 degrees ) axial vertebral rotations were applied. METHODS: Seven lumbar porcine cadaveric motion segments consisting of two vertebrae and the intervening disc with ligaments were loaded in the neutral position with 340 N of compression. Stress profiles were obtained in the neutral position, then after 0.5 degrees and 1 degrees axial rotation of the bottom vertebral body. The distribution of compressive stress in the disc matrix was measured by pulling a miniature pressure transducer through the disc along a straight path in the midfrontal plane. Stress profiles were measured in vertical (0 degrees ) and horizontal (90 degrees ) orientation. RESULTS: Deformation of the anulus by small axial rotations of the lower vertebra instantaneously decreased the horizontally and vertically measured stress in the nucleus while increasing stress in the anulus. A 1-hour period of creep loading decreased the stresses in the nucleus and the anulus 20% to 30%, depending on the orientation, but the effect of an increasing stress in the anular region after axial rotation persisted. CONCLUSIONS: The compressive Young's modulus of the composite anulus tissue increases instantaneously when small axial rotations are applied to porcine spine motion segments. This is accompanied by decreased stress in the nucleus pulposus, increased stress in the anulus fibrosus, changes in the stress profile superimposed on and independent of prolonged viscoelastic creep and dehydration, and changes in stress distribution independent of horizontal and vertical orientation.

Animals↗
PubMed2001

The effect of passive vertebral rotation on pressure in the nucleus pulposus.

To study the immediate effects of axial rotation on the intervertebral disc, six pig cadaver lumbar functional spinal units were exposed to rotations of up to 2 degrees, while disc height and intradiscal pressure were measured. The results showed that rotary movements are capable of causing an immediate increase in disc height and drop in nucleus pressure. However, the long-term effects were opposite in direction.

Analysis of Variance↗
PubMed2001

An EMG technique for measuring spinal loading during asymmetric lifting.

OBJECTIVES: To compare two methods of calibrating the erector spinae electromyographic signal against moment generation in order to predict extensor moments during asymmetric lifting tasks, and to compare the predicted moments with those obtained using a linked-segment model. METHODS: Eight men lifted loads of 6.7 and 15.7 kg at two speeds, in varying amounts of trunk rotation. For each lift, the following were recorded at 60 Hz; the rectified and averaged surface electromyographic signal, bilaterally at T10 and L3, lumbar curvature using the 3-Space Isotrak, movement of body segments using a 4-camera Vicon system, and ground reaction forces using a Kistler force-plate. Electromyographic (EMG) and Isotrak data were used to calculate lumbosacral extensor moments using the electromyographic model, whereas movement analysis data and ground reaction forces were used to estimate net moments using the linked-segment model. For the electromyographic technique, predictions of extensor moment were based on two different sets of EMG-extensor moment calibrations: one performed in pure sagittal flexion and the other in flexion combined with 45 degrees of trunk rotation. RESULTS: Extensor moments predicted by the electromyographic technique increased significantly with load and speed of lifting but were not influenced by the method of calibration. These moments were 7-40%greater than the net moments obtained with the linked-segment model, the difference increasing with load and speed. CONCLUSIONS: The calibration method does not influence extensor moments predicted by the electromyographic technique in asymmetric lifting, suggesting that simple, sagittal-plane calibrations are adequate for this purpose. Differences in predicted moments between the electromyographic technique and linked-segment model may be partly due to different anthropometric assumptions and different amounts of smoothing and filtering in the two models, and partly due to antagonistic muscle forces, the effects of which cannot be measured by linked-segment models. RelevanceAsymmetric lifting is a significant risk factor for occupationally-related low back pain. Improved techniques for measuring spinal loading during such complex lifting tasks may help to identify work practices which place the spine at risk of injury.

Adult↗
PubMed2001

Stress distribution changes in bovine vertebrae just below the endplate after sustained loading.

OBJECTIVE: To describe the pattern of stress distribution in the vertebral body just behind the endplate, and to document its changes due to sustained loading. METHODS: Twelve fresh bovine coccygeal motion segments were dissected and tested. Each specimen was axially loaded with a sustained compressive force of 50% of its estimated compressive strength. Before loading, after 1.5 h and after 3 h of loading, the distribution of the axial pressure under the bottom vertebra (i.e., just below its top endplate) was recorded at three force levels (25%, 37.5% and 50% of the estimated compressive strength), using pressure-sensitive film. RESULTS: Stress distribution over the endplate was found to be fairly uniform. At low compression forces, the stress was the highest centrally. With increased compression and after sustained compression the uniformity improved through a significant redistribution of stress to the periphery. No stress peaks were found to occur after sustained loading. CONCLUSION: Stress peaks after sustained loading cannot explain the occurrence of endplate fractures in sustained cyclic compression in non-degenerated discs. Competing explanations, such as creep, and fatigue failure, would appear more likely candidates. RELEVANCE: It has been hypothesised that compression induced fractures of the lumbar vertebral endplate constitute an important etiological factor for low back pain. Competing theories exist on the fracture mechanism in sustained loading and these would have different implications with respect to prevention. The present study evaluated one of these theories.

Analysis of Variance↗
PubMed2001

Lumbar loading during lifting: a comparative study of three measurement techniques.

Low back loading during occupational lifting is thought to be an important causative factor in the development of low back pain. In order to regulate spinal loading in the workplace, it is necessary to measure it accurately. Various methods have been developed to do this, but each has its own limitations, and none can be considered a "gold standard". The purpose of the current study was to compare the results of three contrasting techniques in order to gain insight into possible sources of error to which each is susceptible. The three techniques were a linked segment model (LSM), an electromyographic (EMG)-based model, and a neural network (NN) that used both EMG and inertial sensing techniques. All three techniques were applied simultaneously to calculate spinal loading when eight volunteers performed a total of eight lifts in a laboratory setting. Averaged results showed that, in comparison with the LSM, the EMG technique calculated a 25.5+/-33.4% higher peak torque and the NN technique a 17.3+/-10.5% lower peak torque. Differences between the techniques varied with lifting speed and method of lifting, and could be attributed to differences in anthropometric assumptions, antagonistic muscle activity, damping of transient force peaks by body tissues, and, specific to the NN, underestimation of trunk flexion. The results of the current study urge to reconsider the validity of other models by independent comparisons.

Adult↗
PubMed2000

Monitoring water content in deforming intervertebral disc tissue by finite element analysis of MRI data.

Mechanical loading, occurring during normal daily life, causes fluid to be expelled from intervertebral discs. Excessive fluid loss during heavy loading might make the disc more vulnerable to damage. In this study, fluid loss was investigated in vitro through monitoring the loss of MRI signal intensity in four bovine coccygeal intervertebral discs, compressed at 2000 N during 1.5 hr. The MRI signals were analyzed with the aid of finite element models to account for the deformation of the tissue. A gradual signal loss over time was found during loading, the most pronounced loss occurring in the central disc region. Initial patterns of signal distribution were quite variable between specimens but repeatable within specimens.

Animals↗
PubMed2000

Effects of positive intrathoracic pressure on pulmonary and systemic hemodynamics.

The Frank-Starling Law accounts for many changes in cardiac performance previously attributed to changes in contractility in that changes in contractility might have been incorrectly inferred from changing ventricular function curves (i.e. systolic performance plotted against filling pressure) if diastolic compliance also changed. To apply the Frank-Starling Law in the presence of changing diastolic compliance, it is necessary to measure end-diastolic volume directly or to calculate end-diastolic transmural pressure, which requires that pericardial pressure be known. Under most normal circumstances, increased intrathoracic pressure (and other interventions, such as vasodilators or lower-body negative pressure, that decrease central blood volume) decreases the transmural end-diastolic pressures of both ventricles, their end-diastolic volumes and stroke work. However, when ventricular interaction is significant, the effects of these interventions might be quite different; this may be important in patients with heart-failure. Although these interventions decrease RV transmural pressure, they may increase LV transmural pressure, end-diastolic volume, and thus stroke work by the Frank-Starling mechanism.

Animals↗
PubMed2000

Effect of hemoglobin levels in hemodialysis patients with asymptomatic cardiomyopathy.

BACKGROUND: Hemoglobin levels below 10 g/dL lead to left ventricular (LV) hypertrophy, LV dilation, a lower quality of life, higher cardiac morbidity, and a higher mortality rate in end-stage renal disease. The benefits and risks of normalizing hemoglobin levels in hemodialysis patients without symptomatic cardiac disease are unknown. METHODS: One hundred forty-six hemodialysis patients with either concentric LV hypertrophy or LV dilation were randomly assigned to receive doses of epoetin alpha designed to achieve hemoglobin levels of 10 or 13.5 g/dL. The study duration was 48 weeks. The primary outcomes were the change in LV mass index in those with concentric LV hypertrophy and the change in cavity volume index in those with LV dilation. RESULTS: In patients with concentric LV hypertrophy, the changes in LV mass index were similar in the normal and low target hemoglobin groups. The changes in cavity volume index were similar in both targets in the LV dilation group. Treatment-received analysis of the concentric LV hypertrophy group showed no correlation between the change in mass index and a correlation between the change in LV volume index and mean hemoglobin level achieved (8 mL/m2 per 1 g/dL hemoglobin decrement, P = 0.009). Mean hemoglobin levels and the changes in LV mass and cavity volume index were not correlated in patients with LV dilation. Normalization of hemoglobin led to improvements in fatigue (P = 0.009), depression (P = 0.02), and relationships (P = 0.004). CONCLUSIONS: Normalization of hemoglobin does not lead to regression of established concentric LV hypertrophy or LV dilation. It may, however, prevent the development of LV dilation, and it leads to improved quality of life.

Adult↗
PubMed2000

Trunk muscle activation and low back loading in lifting in the absence of load knowledge.

People who know the actual mass of an object to be lifted normally prepare themselves before attempting a lift to control the movement and to minimize low back loading. In this study, the trunk muscular reactions and low back torque were investigated in the situation in which the individual did not know the actual mass but only had some idea of the range within which the mass lay. Nine males lifted boxes weighing 6.5 or 16.5 kg under the condition in which they knew the actual mass before attempting a lift (the 'known' condition) and the condition in which they only had the information that the mass would be within the range of 6.5-16.5 kg (the 'unknown' condition). The ground reaction forces and body movements were measured in the trials and, from these, the L5/S1 torques were calculated. The activation of back and abdominal muscles was also measured. For the 6.5 kg weight, a higher (16%) back muscle activation in grasping the box and a higher (10%) peak L5/S1 torque in actual lifting were observed in the 'unknown' compared with the 'known' weight condition. For the 16.5 kg weight, the back muscle activation was lower (10%) during grasping, and higher (10%) during lifting in the 'unknown' compared with the 'known' weight condition. Knowledge of the load had no effect on the activation of the abdominal muscles. It was concluded that in the so-called 'unknown' conditions, the risks of low back injury were increased in comparison with the conditions where the actual weight was known in advance.

Abdominal Muscles↗
PubMed2000

Force direction and physical load in dynamic pushing and pulling.

In pushing and pulling wheeled carts, the direction of force exertion may, beside the force magnitude, considerably affect musculoskeletal loading. This paper describes how force direction changes as handle height and force level change, and the effects this has on the loads on the shoulder and low back. Eight subjects pushed against or pulled on a stationary bar or movable cart at various handle heights and horizontal force levels while walking on a treadmill. The forces at the hands in the vertical and horizontal direction were measured by a force-transducer. The forces, body movements and anthropometric data were used to calculate the net joint torques in the sagittal plane in the shoulder and the lumbosacral joint. The magnitudes and directions of forces did not differ between the cart and the bar pushing and pulling. Force direction was affected by the horizontal force level and handle height. As handle height and horizontal force level increased, the pushing force direction changed from 45 degrees (SD 3.3 degrees) downward to near horizontal, while the pulling force direction changed from pulling upward by 14 degrees (SD 15.3 degrees) to near horizontal. As a result, it was found that across conditions the changes in force exertion were frequently reflected in changes in shoulder torque and low back torque although of a much smaller magnitude. Therefore, an accurate evaluation of musculoskeletal loads in pushing and pulling requires, besides a knowledge of the force magnitude, knowledge of the direction of force exertion with respect to the body.

Adult↗
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↗
PubMed1999

Object size effects on initial lifting forces under microgravity conditions.

Individuals usually report for two objects of equal mass but different volume that the larger object feels lighter. This so-called size-weight illusion has been investigated for more than a century. The illusion is accompanied by increased forces, used to lift the larger object, resulting in a higher initial lifting speed and acceleration. The illusion holds when subjects know that the mass of the two objects is equal and it is likely that this also counts for the enlarged initial effort in lifting a larger box. Why should this happen? Under microgravity, subjects might be able to eliminate largely the weight-related component of the lifting force. Then, if persistent upward scaling of the weight-related force component had been the main cause of the elevated initial lifting force under normal gravity, this elevated force might disappear under microgravity. On the other hand, the elevated initial lifting effort in the large box would be preserved if it had been caused mainly by a persistent upward scaling of the force component, necessary to accelerate the object. To test whether the elevated initial lifting effort either persists or disappears under microgravity, a lifting experiment was carried out during brief periods of microgravity in parabolic flights. Subjects performed whole-body lifting movements with their feet strapped to the floor of the aircraft, using two 8-kg boxes of different volume. The subjects were aware of the equality of the box masses. The peak lifting forces declined almost instantaneously with approx. a factor 9 in the first lifting movements under microgravity compared with normal gravity, suggesting a rapid adaptation to the loss of weight. Though the overall speed of the lifting movement decreased under microgravity, the mean initial acceleration of the box over the first 200 ms of the lifting movement remained higher (P=0.030) in the large box (1.87+/-0.127 m/s2) compared with the small box (1.47+/-0.122 m/s2). Under normal gravity these accelerations were 3.30+/-0.159 m/s2 and 2.67+/-0.159 m/s2, respectively (P=0.008). A comparable trend was found in the initial lifting forces, being significant in the pooled gravity conditions (P=0.036) but not in separate tests on the normal gravity (P=0.109) and microgravity (P=0.169) condition. It is concluded that the elevated initial lifting effort with larger objects holds during short-term exposure to microgravity. This suggests that upward scaling of the force component, required to accelerate the larger box, is an important factor in the elevated initial lifting effort (and the associated size-weight illusion) under normal gravity.

Adult↗
PubMed1999

Adaptation of center of mass control under microgravity in a whole-body lifting task.

Human balance in stance is usually defined as the preservation of the vertical projection of the center of mass (COM) on the support area formed by the feet. Under microgravity conditions, the control of equilibrium seems to be no longer required. However, several reports indicate preservation of COM control in tasks such as arm or leg raising, tiptoe standing, or trunk bending. It is still unclear whether COM control is also maintained in complex multijoint movements during short term exposure to microgravity. In the current study, the dynamics of equilibrium control were studied in four subjects performing two series of seven whole-body lifting movements under microgravity during parabolic flights. The aims of the study were to examine whether the trajectory of horizontal COM motion during lifting movements changes in short-term exposure to microgravity and whether there is any sign of recovery after several lifting movements. It was found that, compared with control movements under normal gravity, the horizontal position of the COM was shifted backward during the entire lifting movement in all subjects. In the second series of lifting movements under microgravity, a partial recovery of the COM trajectory toward the normal gravity situation was found. Under microgravity, angles of the ankle, knee, hip, and lumbar joints differed significantly from the angles found under normal gravity. Recovery of joint angular trajectories in the second series of lifting movements mainly occurred for those angles that could contribute to a reduction of the backward COM shift. It is to be pointed out that COM control under microgravity is not redundant but functional. Persisting COM control under microgravity may be required for pure mechanical reasons, since rotational movements of the body are dependent on adequate control of the COM position with respect to external forces. It is shown that, from a mechanical perspective, subjects can benefit from a backward displacement of the COM in the downward as well as the upward phase of the lifting movement under microgravity.

Adaptation, Physiological↗
PubMed1999

Total trunk muscle force and spinal compression are lower in asymmetric moments as compared to pure extension moments.

The aim of the present study was to test the assumption that asymmetric trunk loading requires a higher total muscle force and consequently entails a higher compression forces on the spine as compared to symmetric loading. When the trunk musculature is modelled in sufficient detail, optimisation shows that there is no mechanical necessity for an increase in total muscle force (or compression force) with task asymmetry. A physiologically based optimisation does also not predict an increase in total muscle force or spinal loading with asymmetry. EMG data on 14 trunk muscles collected in eight subjects showed antagonistic coactivity to be present in both conditions. However, estimates of total muscle force based on the EMG were lower when producing an asymmetric moment. In conclusion, producing an asymmetric moment appears to cause slightly lower forces on the lumbosacral joint as compared to a symmetric moment. Only lateral shear forces increase with asymmetry but these remain well below failure levels.

Abdominal Muscles↗
PubMed1999

Abdominal muscles contribute in a minor way to peak spinal compression in lifting.

In lifting, the abdominal muscles are thought to be activated to stabilize the spine. As a detrimental effect, they contribute to spinal compression. The existing literature is not conclusive about the biological relevance of this effect. From biological, mechanical and anatomical considerations it was hypothesised that the relative abdominal contribution to compression would be minor in the beginning of the lift, that the relative and absolute abdominal contribution to compression would rise throughout the lift, and that the obliques would contribute to a larger extent than the rectus abdominis. To investigate these hypotheses, 10 subjects lifted 0.5, 10.5 and 22.5 kg. EMG levels obtained from the rectus abdominis and the obliques were converted into force using normalized EMG, muscle potential and area values, and modulating factors for muscle length and contraction velocity. An anatomical model was applied to compute the abdominal effects on spinal compression in three consecutive phases within a lift. If expressed relative to the total spinal compression, the abdominal contribution for the three weight conditions was 7.1% (SD, 1.7), 10.4% (4.7) and 12.5% (4.4) in the begin and 21.0% (5.8), 19.0% (5.3) and 22.2% (6.6) in the end phase. Thus, the relative abdominal contribution to compression was minor in the beginning and increased towards the end. The absolute abdominal contribution was constant throughout the lift. The contributions could be retraced to the obliques rather than the rectus, while during the lift a shift in activation from the obliquus externus to internus was observed.

Abdominal Muscles↗
PubMed1999

Endothelin ET(A) receptor blockade prevents the progression of renal failure and hypertension in uraemic rats.

BACKGROUND: Elevated plasma and urine endothelin-1 (ET-1) levels have been reported in renal failure and may be involved in renal disease progression. We investigated whether these changes are related to increased vascular and renal ET-1 production in the pole resection remnant kidney model of chronic renal failure in the rat. METHODS: Uraemic Wistar rats were prepared by surgical renal mass 5/6 ablation and compared with sham-operated controls (protocol 1). Immunoreactive-ET-1 (ir-ET-1) concentration was measured by radioimmunoassay after sample extraction and purification. To investigate the functional role of ET-1 during the progression of chronic renal failure, uraemic rats (protocol 2) were treated with either the vehicle or the ET-1 type A (ET(A)) receptor antagonist LU135252 (LU). RESULTS: Systolic blood pressure and serum creatinine, as well as urinary volume and proteinuria, were significantly higher, whereas creatinine clearance was reduced in uraemic rats compared with sham-operated controls. As expected, plasma and urine ir-ET-1 concentrations were increased in uraemic rats (P<0.01) and were related to the increased ir-ET-1 levels in blood vessels and glomeruli (P<0.001). Positive correlation was found between plasma, thoracic aorta and mesenteric arterial bed ir-ET-1 levels and systolic blood pressure, as well as blood vessel hypertrophy. In addition, increased urinary ir-ET-1 excretion correlated with the rise in serum creatinine and proteinuria. In protocol 2, a 3-week treatment period with LU was initiated once uraemia and hypertension were established. In untreated uraemic rats, systolic blood pressure increased further (P<0.05), but this was not the case in LU-treated uraemic rats. At the end of treatment, serum creatinine and proteinuria were significantly lower (P<0.05) and creatinine clearance was higher (P<0.01) in LU-treated rats compared with uraemic-untreated animals. While plasma ir-ET-1 concentration was similar in the two groups, ir-ET-1 concentration in thoracic aorta, mesenteric arterial bed, renal cortex and urine was significantly lower in LU-treated animals (P<0.01). In addition, heart, thoracic aorta and mesenteric arterial wet weight to body weight ratios were also significantly reduced in LU-treated uraemic rats (P<0.05). CONCLUSIONS: Elevated plasma ET-1 concentration and urinary ET-1 excretion in rats with renal mass ablation are related to enhanced ET-1 production in vascular and renal tissues, thus suggesting an important role for ET-1 in the aggravation of hypertension and vascular hypertrophy as well as in the progression of renal insufficiency. These pathophysiological effects are prevented by treatment with selective ET(A) receptor blockade.

Animals↗
PubMed1999

Biomechanical analysis of posture in patients with spinal kyphosis due to ankylosing spondylitis: a pilot study.

OBJECTIVES: Patients with ankylosing spondylitis may experience a progressive spinal kyphosis, which induces a forward and downward displacement of the centre of mass (COM) of the trunk. In this pilot study, the possible mechanisms used to compensate for the displacement of the trunk COM were analysed. METHODS: Joint angles of hip, knee and ankle were determined in four patients with ankylosing spondylitis and compared to data of 18 healthy subjects. Each patient stood on a force platform and had to adopt several predefined postures, which were recorded by a video camera. RESULTS: In three patients, the hips were flexed when standing relaxed, and in all patients hip extension was limited. The knee angles of three patients were smaller and in two patients the angle of the ankles was larger compared to healthy subjects. CONCLUSIONS: The results suggest that the hip joints are at least no longer involved in balance control. This may imply that conservative therapy should focus on the prevention of restriction of the hip joints.

Adult↗