Biomedical subjects

I Kingma

Publications and source records attributed to I Kingma.

At least 37 records · Page 2Linked to original sources

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↗

PubMed1999

Differential effects of endothelin-1 antagonists on erythropoietin-induced hypertension in renal failure.

Recently, it was reported that blood vessel immunoreactive endothelin-1 (irET-1) content is increased in hypertensive uremic rats treated with recombinant human erythropoietin (rhEPO). The present study was designed to evaluate whether ET-1 receptor blockade can prevent the progression of hypertension in renal failure rats receiving rhEPO and, if so, whether selective ET(A) and nonselective ET(A)/ET(B) receptor antagonists are equally effective. Renal failure was induced by a two-stage 5/6 nephrectomy; the animals developed uremia, anemia, and hypertension. After a 4-wk stabilization period, the animals received either rhEPO (100 U/kg, subcutaneously, three times per week) or the vehicle for 4 wk. In protocol A, half of the rats in each group were simultaneously treated with the ET(A)/ET(B) receptor antagonist bosentan (100 mg/kg per d). In protocol B, half of the rats in each group received the selective ET(A) receptor antagonist LU 135252 (50 mg/kg per d). Systolic BP was recorded before and at 2 and 4 wk after the onset of treatment. Serum creatinine levels and hematocrit were measured before treatment and at the end of the study. Creatinine clearance rates and plasma irET-1 concentrations were determined at the end of the study. rhEPO corrected the anemia, but aggravated the hypertension. There was a slight and similar increase in serum creatinine throughout the treatment period in all groups of rats. Both ET-1 receptor antagonists bosentan and LU135252 were effective in attenuating the progression of hypertension in uremic rats receiving the vehicle (P < 0.05). Treatment with LU135252 corrected the increase in BP in rhEPO-treated rats (160+/-7 mmHg versus 187+/-9 mmHg, P < 0.05). In contrast, bosentan did not attenuate the progression of hypertension in rhEPO-treated rats (172+/-10 mmHg versus 168+/-9 mmHg, NS). In summary, selective ET(A) but not ET(A)/ET(B) receptor blockade can prevent the aggravation of hypertension in renal failure rats treated with rhEPO. These results suggest that the endothelin system may be involved in the pathogenesis of rhEPO-induced hypertension in uremic rats with a differential role for ET(A) and ET(B) receptors.

Animals↗

PubMed1998

Monitoring of cytomegalovirus infections by the CD8+CD38+ T-cell subset in kidney transplant recipients.

BACKGROUND: The CD8+CD38+ T-cell subset can predict progression to acquired immune deficiency syndrome among human immunodeficiency virus-positive subjects. This T-cell subset usually increases during other active viral infections (cytomegalovirus [CMV], Epstein Barr virus). We report on its usefulness in the early detection of CMV infection in kidney transplant recipients. METHODS: Quantitation of CD8+CD38+ T cells was monitored by dual-color flow cytometry analysis on 77 patients during the posttransplantation period. Seventeen of the 52 patients at risk for CMV disease (33%) had primary infection or reactivation and three patients had herpes simplex virus infection only. RESULTS: In every patient with CMV disease, high values for the CD8+CD38+ subset were detected with a 90% positive predictive value for the primary infections. Elevated values were observed at the very first clinical signs of the viral disease or within the few preceeding days. Acute rejection episodes did not provoke false-positive results. CONCLUSION: This immunologic marker is sensitive and easily obtainable on a daily basis. It may help to direct therapy during rejection or serve as a tool for early detection of clinical viral diseases.

ADP-ribosyl Cyclase↗

PubMed1998

Accuracy of the sagittal vertical axis in a standing lateral radiograph as a measurement of balance in spinal deformities.

Sagittal balance of the spine is becoming an important issue in the assessment of the degree of spinal deformity. On a standing lateral full-length radiograph of the spine, the plumb line, or sagittal vertical axis (SVA), can be used to determine the spinal sagittal balance. In this procedure patients have to adopt a habitual standing position with the knees extended during radiographic examination, though it is not known whether small changes in the position of the lower extremities affects the location of the SVA. The purpose of the present study was to investigate the effect of postural change on shifts of the SVA, and to evaluate whether the SVA as measured on a standing full-length lateral radiograph can be used as an accurate measurement of spinal balance in clinical practice. Sagittal balance was analyzed using a patient with ankylosis of the entire spine due to ankylosing spondylitis, to eliminate segmental movement of the spine. A virtual SVA was constructed for seven different standing postures by cross-referring the coordinate systems from a standing full-length lateral radiograph of the spine with video analysis. The horizontal distance between the SVA and the anterior superior corner of the sacrum was measured for each posture. Small changes in the joint angles of the lower extremities affected the SVA significantly, and resulted in the horizontal distance between the SVA and the anterior superior corner of the sacrum varying from -4.5 to +14.9 cm. High correlations were found between this distance and the joint angle of the hip (r = -0.959), knee (r = -0.936), and ankle (r = 0.755) (P < 0.01). The results of the study showed that SVA translations during standing radiographic analysis in a patient with a fixed spine depend on small changes in the hip, knee, and ankle joints. Thus, sagittal spinal (im)balance in ankylosing spondylitis can not be measured from the SVA on a standing lateral full-length radiograph of the spine unless strict procedures are developed to control for the angle of the hip, knee, and ankle joints. The accuracy of the SVA as a measurement of sagittal spinal balance in other spinal deformities, with possible additional segmental movements, therefore remains questionable.

Adult↗

PubMed1998

Asymmetric low back loading in asymmetric lifting movements is not prevented by pelvic twist.

Asymmetric lifting is associated with an increased risk of low back disorders. Especially in lifting movements, characterized by a small amount of asymmetry, it is still the question if asymmetric lumbosacral torques occur, or if subjects try to avoid asymmetric back loading by twisting their pelvis with respect to the feet. An increase of the lifting speed or the box weight might amplify the lumbar torques but might also result in an attempt to limit further increase of asymmetric torques by increasing pelvic twist. In the current study, asymmetrical lifting movements were analyzed with the aid of a 3D linked segment model, using cuffs mounted to the body segments. Eight subjects performed lifting movements with five different asymmetry conditions, ranging from 0 to 90 degrees lifting asymmetry with respect to the sagittal plane, using two lifting speeds and two box weights. A significant increase in lateral flexing and twisting low back torque was found for each increase in asymmetry of the lifting movement. Pelvic twist accounted more or less constantly for about 25% of the lifting asymmetry and was hardly influenced by lifting speed or box weight. Even for 10 or 30 degrees of lifting asymmetry, subjects did not twist their pelvis far enough to avoid asymmetric loading of the low back. Assuming that asymmetric loading of the low back is more strenuous to the spine than symmetric loading, the current results indicate that even small deviations of a lifting movement from the sagittal plane can explain an increased risk of low back disorders.

Back↗

PubMed1998

Finite element aided tracking of signal intensity changes in deforming intervertebral disc tissue.

Tracking of signal intensity changes in soft tissue over time is often hampered by deformation of the tissue. In this study a method is described that uses finite element modeling to compensate for tissue deformation. The method is applied to the quantification of fluid redistribution in an intervertebral disc that deforms under mechanical load. The clinical importance of this application emerges from the increased susceptibility of the intervertebral disc to damage after a period of mechanical loading. The study shows that the use of the finite element aided approach results in a detailed map of tissue MRI signal changes, where the distorting effects of tissue deformation are eliminated.

Animals↗

PubMed1998

Effects of losartan and captopril on endothelin-1 production in blood vessels and glomeruli of rats with reduced renal mass.

Recently, we have reported that endothelin-1 (ET-1) production is increased in blood vessels and glomeruli of rats with chronic renal failure. This study was design to investigate the role of angiotensin II (Ang II) in endogenous ET-1 production in rats with reduced renal mass. One week after subtotal (5/6) nephrectomy, uremic rats were divided into three groups, and received either no treatment, the Ang II subtype 1 receptor (AT1) antagonist losartan (10 mg/kg/day), or the angiotensin-converting enzyme inhibitor (ACE-I) captopril (30 mg/kg/day) for 6 weeks. Sham-operated rats were used as controls and received no treatment. The levels of immunoreactive ET-1 (ir-ET-1) in plasma and urine, as well as in vascular and renal tissues, were determined by radioimmunoassay (RIA) after extraction. In uremic rats, losartan and captopril completely prevented the increase in systolic blood pressure. At week 6, plasma ir-ET-1 was similar in the different groups of uremic rats and in the controls. However, ir-ET-1 concentration in the mesenteric arterial bed, the thoracic aorta, preglomerular arteries, and glomeruli, as well as urinary ir-ET-1 excretion were significantly greater in uremic-untreated rats compared to controls (P < .01). Treatment of uremic rats with losartan or captopril reduced irET-1 concentration in the thoracic aorta and preglomerular arteries (P < .05), but ir-ET-1 concentration in the mesenteric arterial bed was unchanged. Although both drugs completely prevented the increase in proteinuria, losartan but not captopril significantly reduced ir-ET-1 concentration in glomeruli (P < .05) and normalized urinary ir-ET-1 excretion. This indicates that increased ET-1 production in blood vessels and glomeruli of uremic rats is modulated, at least in part, by Ang II through the AT1 receptor. The beneficial effects of the AT1 antagonist losartan could be attributable to the attenuation of Ang II-induced ET-1 production in this rat remnant kidney model of chronic renal failure, whereas those of the ACE-I captopril are not related to changes in ET-1 production in glomeruli.

Angiotensin II↗

PubMed1998

When is a lifting movement too asymmetric to identify low-back loading by 2-D analysis?

In ergonomics research, two-dimensional (2-D) biomechanical models are often used to study the mechanical loading of the low back in lifting movements. When lifting movements are asymmetric, errors of unknown size may be introduced in a 2-D analysis. In the current study, an estimation of these errors was made by comparing the outcome of a 2-D analysis to the results of a recently developed and validated 3-D model. Four subjects made two repetitions of five lifting movements, differing in the amount of asymmetry. The results showed a significant underestimation of the peak torque by 20, 36 and 61% when the initial position of a box was rotated 30, 60 and 90 degrees with respect to the sagittal plane of the subject. The main cause of this underestimation was a pelvic twist, resulting in an erroneous projection of a pelvic marker on to the sagittal plane due to pelvic twist. It is suggested that from 30 degrees box rotation a 2-D analysis may easily lead to wrong conclusions when it is used to study asymmetric lifting.

Adult↗

PubMed1998

Hemodynamic and hormonal changes during erythropoietin therapy in hemodialysis patients.

To better understand the mechanism of recombinant human erythropoietin (rhEPO)-induced increase in BP, hemodynamic parameters, body fluid volumes, and the hormones implicated in BP regulation were studied in 32 anemic hemodialysis patients before and after 3 to 4 mo of rhEPO therapy. Hemoglobin levels increased from 83 +/- 1.5 to 119 +/- 2.3 g/L (P < 0.01) after rhEPO therapy (25 to 43 U/kg) administered subcutaneously three times weekly. Mean 24-h systolic and diastolic ambulatory BP were significantly increased by 14 +/- 3 and 10 +/- 2 mmHg, respectively (P < 0.01 for both groups). Systemic vascular resistance consistently increased by 28 +/- 5% (P < 0.01), whereas cardiac output was decreased by 6 +/- 3% (P < 0.05). Red blood cell mass increased by 510 +/- 35 ml (P < 0.01), whereas plasma volume decreased by 420 +/- 66 ml (P < 0.01), which resulted in a nonsignificant increase in total blood volume. Extracellular fluid volume and exchangeable sodium were decreased by 873 +/- 255 ml (P < 0.01) and 125 mmol (P < 0.01), respectively. There was a positive correlation between the changes in exchangeable sodium and in systolic BP (r = 0.41, P < 0.05). Furthermore, a greater increase in 24-h systolic BP was observed in patients in whom exchangeable sodium increased or remained unchanged (n = 10) compared with patients (n = 22) with decreased exchangeable sodium (20 +/- 4 mmHg versus 8 +/- 2 mmHg, respectively, P < 0.01). Plasma catecholamines, plasma renin concentration, plasma atrial natriuretic peptide, and plasma endothelin-1 did not significantly change with rhEPO treatment, whereas plasma aldosterone increased significantly (P < 0.01). Although volume-independent mechanisms may contribute to rhEPO-induced BP increase, the results presented here suggest the importance of optimally reducing extracellular fluid volume to prevent, at least in part, the development of hypertension often observed with improved uremic anemia in these patients.

Adolescent↗

PubMed1998

Plasma and blood vessel endothelin-1 concentrations in hypertensive uremic rats treated with erythropoietin.

The present study was designed to evaluate whether changes in plasma and blood vessel endothelin-1 (ET-1) concentrations may play a role in the enhanced blood pressure response to recombinant human erythropoietin (r-HuEPO) replacement therapy in uremia. Renal failure was induced by 5/6 nephrectomy (Nx). Uremic rats received either r-HuEPO (100 u s.c. three times a week) or the vehicle for 5 weeks. They were compared to control rats receiving the vehicle. Systolic blood pressure (tail cuff method), hematocrit, serum creatinine, plasma and tissue ET-1 were measured at the end of the protocol. Immunoreactive ET-1 (ir-ET-1) was determined by radioimmunoassay of acid-extracts from the plasma, thoracic aorta and mesenteric arterial bed. Creatinine increased about three fold in Nx animals. Blood pressure in control rats was 120+/-3 mmHg compared to 161 +/-6 mmHg in the Nx + vehicle group (p <0.01) and 199+/-9 mmHg in the Nx + r-HuEPO group (p <0.01 vs Nx + vehicle). Hematocrit in control rats was 41.3+/-0.4% vs 32.6+/-1.8% in the Nx + vehicle group (p <0.01) and 47.6+/-1.5% in the Nx + r-HuEPO group (p <0.01). Plasma ir-ET-1 levels were similar in the Nx + vehicle and Nx + r-HuEPO groups (7.9+/-1.0 and 7.8+/-0.8 pg/ml). In contrast, thoracic aorta ir-ET-1 content was significantly higher in the Nx + r-HuEPO group than in the Nx + vehicle group (20.3+/-2.9 vs 13.4+/-1.9 pg, p <0.05). Similar results were obtained in the mesenteric arterial bed. There were significant correlations between blood pressure and ir-ET-1 content in the thoracic aorta (r= 0.45, p<0.05) and in the mesenteric arterial bed (r= 0.41, p<0.05). Vascular ET-1 content but not plasma levels are increased in uremic rats treated with r-HuEPO suggesting an increase in blood vessel ET-1 production which may play a role in the pathogenesis of r-HuEPO-induced hypertension.

Animals↗

PubMed1998

Plasma and peritoneal endothelin levels and blood pressure in CAPD patients with or without erythropoietin replacement therapy.

The aim of the study was to determine the ET-1 concentration in peritoneal dialysate fluid and to investigate the relationship between peritoneal and plasma ET-1 levels and blood pressure in stable continuous ambulatory peritoneal dialysis (CAPD) patients with and without human recombinant erythropoietin (r-HuEPO) replacement therapy. Twenty-seven stable CAPD patients were investigated. They completed their overnight exchange at the Dialysis Centre. Blood pressure was recorded and a blood sample was drawn. Biochemical parameters and ET-1 were measured in plasma and peritoneal dialysate fluid. Mean plasma ET-1 levels were increased by about four-fold in CAPD patients. ET-1 was detectable in peritoneal dialysate fluid and a significant correlation was observed between plasma and peritoneal ET-1 concentrations (r = 0.65, p < 0.01). The peritoneal clearance of ET-1 was lower than the creatinine clearance (1.69 +/- 0.08 ml/min vs. 3.96 +/- 0.15 ml/min, p < 0.01). There was also a significant correlation between the time (months) on dialysis and plasma (r = 0.68, p < 0.01) or peritoneal dialysate ET-1 levels (r = 0.46, p < 0.05). Mean blood pressure was higher in patients treated with r-HuEPO than in untreated patients (97 +/- 4 mmHg vs. 81 +/- 4 mmHg, p < 0.01). Plasma and peritoneal dialysate ET-1 concentrations were comparable in the two groups with or without r-HuEPO replacement therapy and plasma ET-1 values correlated significantly with mean blood pressure only in r-HuEPO-treated patients (r = 0.63, p < 0.05 vs. r = 0.10, N.S. in untreated patients). In conclusion, plasma ET-1 concentrations are elevated in CAPD patients and the levels appear to increase with time on dialysis. ET-1 is cleared by the peritoneal membrane but at a much lower rate than creatinine. Blood pressure is higher in CAPD patients or r-HuEPO replacement therapy and blood pressure correlates with plasma ET-1 levels in these patients.

Ascitic Fluid↗

PubMed1997

Increased immunoreactive endothelin-1 levels in blood vessels and glomeruli of rats with reduced renal mass.

Elevated plasma and urinary endothelin-1 (ET-1) levels have been reported in patients with renal failure as well as in remnant kidney models of chronic renal failure. We investigated whether these changes are related to increased ET-1 production in cardiovascular and renal tissues of rats with reduced renal mass. In uremic rats, systolic blood pressure rose in parallel with the progression of renal insufficiency. At week 6, changes in systolic blood pressure were positively correlated with serum creatinine levels (r = 0.728, p < 0.01). Plasma immunoreactive ET-1 (ir-ET-1) concentration was similar in uremic rats and sham-operated controls. In contrast, urinary ir-ET-1 excretion was significantly greater in uremic rats and was correlated with the elevation of serum creatinine and proteinuria (r = 0.795, and 0.922, p < 0.01, respectively). Compared to the controls, ir-ET-1 concentration in the thoracic aorta, preglomerular arteries and glomeruli were 1.4-, 3.5- and 6.7-fold higher, respectively, in uremic rats (p < 0.01) than in the controls. However, ir-ET-1 concentration in the mesenteric arterial bed and the left ventricle remained similar in the 2 groups, whereas it was significantly lower in the renal papilla of uremic rats (p < 0.01). Thus, ET-1 production is unchanged or slightly increased in extrarenal cardiovascular tissues of rats with reduced renal mass. In contrast, ET-1 production is significantly augmented in preglomerular arteries and glomeruli, but reduced in the papilla, suggesting that increased urinary ir-ET-1 excretion in uremic rats reflects ET-1 overproduction in the former renal tissues. Elevated ET-1 production in blood vessels and glomeruli may thus play a key role in the aggravation of hypertension and the progression of renal insufficiency in this rat remnant kidney model of chronic renal failure.

Animals↗

PubMed1997

Uremia enhances the blood pressure response to erythropoietin.

To investigate the role of uremia in the development of human recombinant erythropoietin (r-HuEPO)-induced hypertension, Wistar rats were divided into a uremic (subtotal nephrectomy) and a control group. After three weeks, both groups were again divided and each subgroup received either r-HuEPO (100 u/kg s.c., 3 times weekly) or the vehicle for a further 3 weeks. Hematocrit, blood pressure and blood chemistry were measured prior to surgery, before either vehicle or r-HuEPO treatment and before euthanasia. The uremic group developed anemia, hypertension and all the biochemical features observed in humans with end-stage renal disease. r-HuEPO therapy increased hematocrit from 29 +/- 2.5% to 46 +/- 2% (p < 0.01) in the uremic rats. The mean baseline blood pressure was 119 +/- 10 mmHg. At week 3, mean blood pressure was unchanged in control rats, but it was increased to 151 +/- 5 mmHg (p < 0.01) in the nephrectomized group. At week 6, mean blood pressure in the untreated uremic rats remained unchanged from week 3, but blood pressure in the uremic animals treated with r-HuEPO increased significantly to 187 +/- 8 mmHg (p < 0.01). There was no significant correlation between hematocrit and blood pressure in the r-HuEPO treated uremic group (r = 0.01, NS). r-HuEPO had no effect on blood pressure in control rats despite a significant increase in hematocrit. These results indicate that the blood pressure response to r-HuEPO is enhanced in rats with chronic renal failure.

Animals↗

PubMed1997

Economic analysis of Neoral in de novo renal transplant patients in Canada.

This pilot economic evaluation was performed as part of the Canadian arm of an international randomized, controlled, double-blind safety and tolerability trial (OLM-105/NOF-2). The clinical study compared the safety and tolerability of a new microemulsion oral formulation of cyclosporine A (Neoral) with the oral cyclosporine. A preparation currently in use (Sandimmune SGC)/(SGC). To assess the economic impact of Neoral in newly grafted renal transplant patients, primary cost data were collected at the five participating Canadian centers and evaluated from the Ministry of Health (MOH) and hospital perspectives. The results of this cost analysis are presented in this paper. Since the new formulation has shown more consistent absorption and a more predictable pharmacokinetic profile, medical resource utilization and, consequently, cost of treatment could be expected to be lower for those renal transplant recipients treated with Neoral than for those receiving standard SGC. The findings of this study support this hypothesis. Robustness of the conclusion was confirmed with sensitivity analyses. Reduced health care costs for patients treated with Neoral were primarily a result of fewer hospitalization days and lower physician costs for inpatient and outpatient procedures.

Administration, Oral↗

PubMed1996

Segment inertial parameter evaluation in two anthropometric models by application of a dynamic linked segment model.

The estimation of segment inertial parameters (SIPs) is an important source of error in inverse dynamic analysis. In most individual cases SIPs are derived from extrapolation of known SIPs of a certain population through regression equations (proportional models). Another well-known method is the use of mathematical approximation of the shape of human body segments combined with estimations of segment densities (geometric models). In the current study five males and five females performed four different lifting movements in the sagittal plane. A full body linked segment model was applied twice to the same data set, once using a proportional and once using a geometric anthropometric model. As a full body linked segment model is an overdetermined system of equations, four equations could be formed to test the summed effect of SIP errors on the inverse dynamic analysis. The overall performance in terms of coefficients of correlation was better for the geometric model as compared to the proportional model. When a back lifting movement was performed, the equations indicated systematic errors in the proportional model. However, when a leg lifting movement was performed, the equations indicated systematic errors in the geometric model. Therefore, analyzing only one kind of movement does not suffice to draw conclusions with respect to the reliability of an anthropometric model.

Adolescent↗

PubMed1995

Flexion relaxation during lifting: implications for torque production by muscle activity and tissue strain at the lumbo-sacral joint.

During the full flexion phase of the back lift movement the lumbar part of the erector spinae muscle exhibits a reduced activity level (flexion relaxation). This study addresses the question how the required extension torque in the lumbo-sacral joint (L5/S1 joint) is balanced during the period in which apparently the lumbar erector spinae ceases to take its share. Six subjects participated in the experiment in which they performed seven lifting tasks. The load, the range of movement, and the phase in which the load was handled (lifting or lowering) were varied. A dynamic linked segment model was applied to determine the momentary torques acting at the L5/S1 joint, while the EMGs of the lumbar and thoracic part of the erector spinae muscle were measured. Furthermore, the lengths between markers on the lumbar and thoracic part of the trunk were determined to reveal changes in length during the movement. The dynamic EMGs were normalized to trunk angle-dependent maximal levels. The L5/S1 joint torques were analysed and combined with the normalized EMG data and the kinematics of the trunk, which are assumed to indicate the elongation of passive tissues. Although in the normalization procedure the change of the length-force relationship of the erector spinae was taken into account, the dynamic lumbar EMG activity decreased to a low-activity level (the phenomenon of flexion relaxation). This coincided with a 25% increase in lumbar length suggesting that passive tissue strain provided part of the required extension torque. In the tasks where a barbell was handled a significant increase in EMG level of the thoracic part of the erector spinae occurred just before the flexion relaxation at the lumbar level. Apparently, the extensor function of the lumbar part is then taken over by the thoracic part of the erector spinae muscle. This suggests that an intricate coordinating mechanism is operative that apportions the load to be balanced over active--(lumbar and thoracic part of the erector spinae) and passive structures (post vertebral ligaments).

Adult↗

PubMed1995

Optimizing the determination of the body center of mass.

The position or trajectory of the body center of mass (COM) is often a parameter of interest when studying posture or movement. For instance, in balance control studies the body COM can be related to the ground reaction force or to the base of support. Since small displacements of the body COM are important in balance control studies, it is essential to obtain valid estimates of the body COM. The main source of error in the determination of the body COM is the estimation of the masses and centers of mass of the body segments. Especially the determination of the trunk COM is prone to error. In the current study five subjects maintained three postures, differing in trunk angle, during a few seconds. The relation between the center of pressure of the ground reaction force and the vertical projection of the body COM during the postures was used to optimize the trunk COM position. Additionally the subjects performed two lifting movements. The validity of the body COM trajectory estimation during the lifting movements, both with and without optimized trunk COM, was checked by relating the external moment of the ground reaction force with respect to the body COM to the rate of change of the angular momentum of the whole body. It was shown that the correspondence between the external moment and the rate of change of the angular momentum improved after optimization of the trunk COM. This suggests that the body COM trajectory estimation can be improved by the proposed optimization procedure.

Adult↗