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Biomedical subjects

A Mäkelä

Publications and source records attributed to A Mäkelä.

At least 19 recordsLinked to original sources
PubMed2001

The fixation properties of carbon fiber-reinforced liquid crystalline polymer implant in bone: an experimental study in rabbits.

A novel composite material with ultra-high strength and a low elastic modulus called carbon fiber-reinforced liquid crystalline polymer (LCP/CF) has been developed. We studied the fixation properties of an intramedullary LCP/CF rod in rabbit bone. The medullary canals of both femora were reamed with a drill 3.2 mm in diameter starting from the trochanteric fossa in eleven New Zealand White rabbits weighing on average 4.8 kg. A smooth LCP/CF rod 3.2 mm in diameter and 50 mm in length was introduced into the medullary canal of both femora. The follow-up intervals were 0, 6, 12, and 52 weeks. The upper part of the harvested femora was cut into two pieces, each 25 mm in length. A mechanical push-out test was performed within 48 h to determine bone-implant interface attachment strength in the proximal (cancellous) and distal (cortical) locations. The mean push-out strength values at 0, 6, 12, and 52 weeks were 61, 250, 382, and 612 KPa in the cancellous location and 0, 32, 41, and 68 KPa in the cortical location, respectively. The strength of the bone/implant interface appeared to be quite low, similar to other uncoated or nonporous implants, but it was found to increase with time.

Animals↗
PubMed2001

The ratio of NPP to GPP: evidence of change over the course of stand development.

Using Scots pine (Pinus sylvestris L.) in Fenno-Scandia as a case study, we investigate whether net primary production (NPP) and maintenance respiration are constant fractions of gross primary production (GPP) as even-aged mono-specific stands progress from initiation to old age. A model of the ratio of NPP to GPP is developed based on (1) the classical model of respiration, which divides total respiration into construction and maintenance components, and (2) a process-based model, which derives respiration from processes including construction, nitrate uptake and reduction, ion uptake, phloem loading and maintenance. Published estimates of specific respiration and production rates, and some recent measurements of components of dry matter in stands of different ages, are used to quantify the two approaches over the course of stand development in an average environment. Both approaches give similar results, showing a decrease in the NPP/GPP ratio with increasing tree height. In addition, we show that stand-growth models fitted under three different sets of assumptions-(i) annual specific rates of maintenance respiration of sapwood (mW) and photosynthesis (sC) are constant; (ii) m(W) is constant, but sC decreases with increasing tree height; and (iii) total maintenance respiration is a constant fraction of GPP and s(C) decreases with increasing tree height-can lead to nearly identical model projections that agree with empirical observations of NPP and stand-growth variables. Remeasurements of GPP and respiration over time in chronosequences of stands may be needed to discern which set of assumptions is correct. Total (construction + maintenance) sapwood respiration per unit mass of sapwood (kg C (kg C year)-1) decreased with increasing stand age, sapwood stock, and average tree height under all three assumptions. However, total sapwood respiration (kg C (ha year)-1) increased over the course of stand development under (i) and (ii), contributing to a downward trend in the time course of the NPP/GPP ratio after closure. A moderate decrease in mW with increasing tree height or sapwood cross-sectional area had little effect on the downward trend. On the basis of this evidence, we argue that a significant decline in the NPP/GPP ratio with tree size or age seems highly probable, although the decline may appear insignificant over some segments of stand development. We also argue that, because stand-growth models can give correct answers for the wrong reasons, statistical calibration of such models should be avoided whenever possible; instead, values of physiological parameters should come from measurements of the physiological processes themselves.

Mathematics↗
PubMed1999

Fine root biomass of Scots pine stands differing in age and soil fertility in southern Finland.

The biomass of small and large fine roots (</= 2 mm and 2-5 mm in diameter, respectively) in mineral soils of southern Finland was compared with estimated foliage biomass in the same stands. Study material was collected from stands differing in site fertility and age. The humus layer was deeper at the more fertile sites than at the less fertile sites. Fine root density was greater in humus than in mineral soil, and the fine root density in mineral and humus layers was greater at the less fertile sites than at the more fertile sites. Although the amount of fine root biomass was not correlated with any commonly recorded stand characteristic, small fine root biomass was proportional to foliage biomass for both site types. The coefficient of proportionality was larger for the less fertile sites than for the more fertile sites, supporting the theory of functional balance. A similar relationship could not be established for the large fine roots. A trend of increasing fine root:needle mass ratio with stand age was observed for stands on the less fertile sites.

Journal Article↗
PubMed1999

Phospholipase A2 activity in body fluids and pancreatic tissue in patients with acute necrotising pancreatitis.

OBJECTIVE: To measure pancreatic and non-pancreatic phospholipase A2 activity in human acute necrotising pancreatitis. DESIGN: Prospective study. SETTING: University hospital, Finland. SUBJECTS: 20 patients with acute necrotising pancreatitis. INTERVENTIONS: Serum and urine samples were taken daily for a week and fluid from peritoneal lavage for six days after admission. Samples from the pleural cavity were taken from patients in whom pleural drainage was considered necessary. Pancreatic tissue was recovered from the patients who were operated on for acute pancreatitis or for pancreatic tumour. MAIN OUTCOME MEASURES: Serum phospholipase A2, amylase, and lipase activities. RESULTS: Serum phospholipase A2 activity increased up to eightfold, 25.0 (5.4) IU/L (n = 20, range 9.0-77 IU/L) (reference value <3 IU/L) and remained high during the first week, whereas serum amylase and lipase returned to the reference range during the first four days. The maximal phospholipase A2 activity in urine was 4.5 IU/L, in the fluid from peritoneal lavage 16.9 IU/L, and in the fluid from the pleural cavity 37.0 IU/L. Phospholipase A2 activity in necrotic pancreatic tissue ranged from 0.25 to 5.70 IU/g and in normal pancreatic tissue from 9.85 to 15.0 IU/g. Preincubation at 60 degrees C showed non-pancreatic phospholipase A2 activity predominated in serum, whereas part of the enzyme activity in the fluids from pleural cavity and peritoneal lavage proved to be of pancreatic derivation. CONCLUSIONS: The results suggest a role for both pancreatic and non-pancreatic phospholipase A2 in acute pancreatitis. Preincubation at 60 degrees C proved useful in the differentiation between pancreatic and non-pancreatic phospholipase A2 activity.

Adult↗
PubMed1999

Fixation of femoral shaft osteotomy with an intramedullary composite rod: an experimental study on dogs with a two-year follow-up.

A novel composite material with an ultra-high strength and a low elastic modulus called carbon fibre-reinforced liquid crystalline polymer (LCP/CF) has been developed. An experimental diaphyseal osteotomy of the proximal femur in fourteen Beagle dogs was fixed with an intramedullary LCP/CF rod of 4.5 mm in diameter and 80 mm in length. The radiological follow-up intervals were 1, 3, 6, 12, 24, 52, and 104 weeks. Five dogs were killed at 1 year and three dogs at 2 years for histological studies; six dogs were retained for longer follow-up. Radiographs showed an uncomplicated healing of the diaphyseal osteotomy with an external callus formation in all dogs in 12 weeks. Histological analysis revealed a benign host tissue response with few inflammatory cells. Both bone and fibrous tissue were seen at the LCP/CF-host tissue interface. The cross-sectional cortical area of the operated femur was slightly greater than that of the control femur in the 2-year follow-up. LCP/CF showed promising properties for high-load applications.

Animals↗
PubMed1999

Fixation of distal femoral osteotomy with an intramedullary rod: early failure of carbon fibre composite implant in rabbits.

A novel composite material with an ultra-high strength and a low elastic modulus, comprising a carbon fibre reinforced liquid crystalline polymer (LCP/CF) has been developed. An experimental osteotomy of the distal femur in nineteen rabbits weighing on average 4.8 (3.7-6.3) kg was fixed with an intramedullary LCP/CF rod of 3.2 mm in diameter and 50 mm in length. The initial mechanical properties of the rods had a mean shear strength of 180 MPa, a flexural strength of 450 MPa, and a flexural modulus of 40 GPa. The rods were implanted for periods of 3, 6, 12, 24, and 52 weeks. The healing of the osteotomy was analyzed by radiographic, histological, microradiographic, and oxytetracycline fluorescence studies. The strength retention of the LCP/CF rods was measured by mechanical testing. Solid union of the osteotomy was seen within 6 weeks. The implants retained their original strength properties up to 52 weeks. In three rabbits, a non-union with granulation tissue and carbon fibre particles was noticed at the osteotomy site, where disruption of the implant surface was seen at the level of the osteotomy. Further studies with a special interest in the fabrication process of the LCP/CF-implants are needed.

Animals↗
PubMed1998

The effect of an intramedullary carbon-fiber-reinforced liquid crystalline polymer implant on bone: an experimental study on rabbits.

A novel composite material with an ultra-high strength and a low elastic modulus called carbon-fiber-reinforced liquid crystalline polymer (LCP/CF) has been developed. We studied the effects of an intramedullary LCP/CF rod on bone in rabbits. A LCP/CF rod of 3.2 mm in diameter and 50 mm in length was introduced into the intramedullary canal of the right femur in ten rabbits weighing an average of 3.6 (3.1-4.2) kg. The follow-up intervals were 3 and 52 weeks. No signs of deformity or osteopenia were seen in the operated femurs in the radiographic, histological, and histomorphometric studies. Histologically, the implant was enclosed by cancellous bone in the metaphyseal area and by a thin cancellous bone cuff in medullary cavity. Bone was able to grow in direct contact with the LCP/CF rod. No signs of degradation of the implants or of adverse tissue reaction were seen. The intramedullary LCP/CF rod had no harmful effects on bone in rabbits. The biocompatibility of the LCP/CF appeared to be good. This novel composite material demonstrates properties that may be useful in orthopedic applications.

Animals↗
PubMed1998

Duodenal secretion of phospholipase A2, amylase, and bicarbonate in chronic pancreatitis.

Phospholipase A2 has been suggested to be involved in the pathogenesis and pathophysiology of acute pancreatitis. We determined phospholipase A2 and amylase activities in duodenal juice collected during a secretin test from 30 consecutive patients who were suspected to have chronic pancreatitis or biliary disease. The patients underwent endoscopic retrograde cholangiopancreatography (ERCP) the following day. In the 8 patients with ERCP findings of advanced chronic pancreatitis, the mean outputs of phospholipase A2, amylase, and bicarbonate were reduced by 74%, 72%, and 60% compared to the respective values in the 13 (control) patients without a diagnosis of any pancreatic disorder or jaundice. In the 3 patients with recurrent pancreatitis but normal ERCP findings and in the 6 patients with jaundice the output values were not significantly reduced compared to those in the patients without any pancreatic disorder or jaundice. The outputs of amylase and phospholipase A2 were not significantly interrelated, whereas the outputs of phospholipase A2 and bicarbonate correlated well. Receiver characteristic (ROC) curves confirmed the high specificity and sensitivity of phospholipase A2 or bicarbonate output in patients with ERCP findings of advanced chronic pancreatitis compared to those with no changes in pancreatic ducts, with similar probability values of 0.880 +/- 0.111 (SEM), compared to the respective lower value of amylase, 0.676 +/- 0.118. Phospholipase A2 and bicarbonate output proved of equal value as markers of chronic pancreatitis and were superior to amylase output in the secretin test.

Acute Disease↗
PubMed1997

Inhibition of serum phospholipase-A2 in acute pancreatitis by pharmacological agents in vitro.

Phospholipase-A2 has been suggested as having a role in the pathophysiology of acute pancreatitis. The inhibition of phospholipase-A2 was studied in vitro using 17 pharmacological agents in the search for a specific therapy for acute pancreatitis. The inhibitory effect was tested using an isotopic assay system with 2-palmitoyl-(1-14C)-labelled dipalmitoyl phosphatidylcholine as a substrate and 10 microliters of serum from patients with acute necrotizing pancreatitis as an enzyme source. Among all agents tested, anti-inflammatory drugs inhibited enzyme activity most significantly: indomethacin (9.0 x 10(-3) mol l-1) decreased the phospholipase-A2 activity to one- tenth. The weak inhibitory effect could also be demonstrated using a lower concentration of 2 x 10(-5) mol l-1, which can be achieved after intravenous administration of 50 mg of this drug. The other drugs inhibited the enzyme activity at concentrations higher than those achieved after intravenous injections in clinical use. Diclofenac (3.1 x 10(-2) mol l-1) reduced the phospholipase-A2 activity by 93%, ketoprofen (2.0 x 10(-2) mol l-1) or chlorpromazine (1.4 x 10(-2) mol l-1) by 90%, tobramycin (1.7 x 10(-2) mol l-1) by 84%, doxycycline (9.0 x 10(-3) mol l-1) by 61%, dexamethasone (1.7 x 10(-3) mol l-1) by 62%, methylprednisolone (3.8 x 10(-2) mol l-1) by 50%, and pindolol (1.0 x 10(-4) mol l-1) by 59%. A weak inhibition of phospholipase-A2 activity was demonstrated by betamethasone, bupivacaine, digoxin, hydrocortisone, lidocaine, metoprolol, propranolol, and vancomycin. Indomethacin proved the most potent of the tested agents in inhibiting phospholipase-A2 activity in serum from patients with acute pancreatitis and should be further studied in vivo.

Acute Disease↗
PubMed1997

Serum phospholipase A2, amylase, lipase, and urinary amylase activities in relation to the severity of acute pancreatitis.

OBJECTIVE: To compare serum phospholipase A2 activity with measurements of conventional enzymes as an indicator of the severity of acute pancreatitis. DESIGN: Prospective study. SETTING: University hospital, Finland. SUBJECTS: 80 Consecutive patients with acute pancreatitis. INTERVENTIONS: Serum and urine samples were taken daily for a week after admission. MAIN OUTCOME MEASURES: Serum phospholipase A2, amylase, lipase, and urinary amylase activities. RESULTS: On admission, the serum amylase and lipase activities increased in parallel in all patients. However, the mean serum phospholipase A2 activity was three times higher in the patients with acute fulminant pancreatitis than in those with milder disease. The phospholipase A2 activity remained high during the course of the severe disease, whereas the other enzyme activities decreased appreciably during the first week. In contrast to the other enzyme activities that of serum phospholipase A2 correlated well with the severity of the acute pancreatitis. Heating at 60 degrees C for 45 minutes to inactivate the non-pancreatic thermolabile phospholipase A2 reduced the total serum phospholipase A2 activity more than the enzyme activity in the homogenates of pancreatic tissue, which suggests that extrapancreatic phospholipase A2 is present in serum. The receiver operating characteristic (ROC) curves confirmed the high sensitivity and specificity of serum phospholipase A2 activity with a mean (SEM) area under the curve up to 0.870 (0.062) compared with the other enzyme activities of which the highest area under the curve was 0.52 (0.089). CONCLUSIONS: In contrast to amylase and lipase activities, measurement of serum phospholipase A2 activity is important in the assessment of the severity of acute pancreatitis so that optimal treatment may be given.

Acute Disease↗
PubMed1996

Quality of life in early adolescence: a sixteen-dimensional health-related measure (16D).

While data on the health-related quality of life (HRQOL) of adults are accumulating, very little is known about the HRQOL--and especially the perceived HRQOL--of children. In our study we introduced a 16-dimensional, generic self-assessment measure of HRQOL (16D) for early adolescents, and demonstrated its use with four populations of children aged 12-15: (1) 239 normal schoolchildren, (2) patients waiting for organ transplantation (n = 5), (3) patients with genetic skeletal dysplasias (n = 19), and (4) patients with epilepsy (n = 32). The HRQOL profiles of the patients differed significantly according to the diagnosis, giving support to its construct validity. The reliability of the measure was high: its repeatability coefficient was 91%. The quality of life ratings of the healthy boys and their parents differed on the dimensions of distress, vitality, speech, mental function, and discomfort and symptoms (p < 0.05). In addition, there were significant differences in the health-related valuations between the girls, boys and their parents. We conclude that the assessment of quality of life of adolescents should be based on data collected from the adolescents themselves. Further, the 16D is so far the only generic HRQOL measure designed specifically for this purpose. It is capable of differentiating the HRQOL of healthy adolescents as well as patients with various diagnoses. Our experience also indicates that it is easy to use, yet it seems comprehensive, reliable, and valid.

Adolescent↗
PubMed1996

Quality of life in pre-adolescence: a 17-dimensional health-related measure (17D).

Although interest in the health-related quality of life (HRQOL) of children has increased in the last years, validated methods for assessing the HRQOL- and especially the perceived HRQOL-of children have been missing. We introduced a 17-dimensional, illustrated, generic measure of perceived HRQOL (17D) for pre-adolescents, and demonstrated its application to three populations of children aged 8-11 years: (1) 244 normal schoolchildren; (2) 22 patients surviving organ transplantation and (3) 10 patients with genetic skeletal dysplasias. The HRQOL scores and profiles of the patients differed significantly according to the diagnosis, giving support to its construct validity. The reliability of the measure was high: its repeatability coefficient was 95%. As a structured interview of 20-30 minutes, the measurement burden is reasonable. We conclude that the assessment of quality of life of pre-adolescents can and should be based on data collected from the children themselves. Our initial experience indicates that 17D is comprehensive, reliable, and valid.

Bone Diseases, Developmental↗
PubMed1996

Health-related quality of life of adults surviving malignancies in childhood.

While sophisticated data on specific problems are available, very little is known about the overall quality of life of long-term survivors of malignancies in childhood. We used a previously validated 15-dimensional questionnaire to examine the perceived health-related quality of life of 168 survivors, currently aged 16-35 years, who had been treated for a malignancy at a single institution between 1961 and 1993. All had been off therapy for at least 1 year (median, 12 years). In statistical terms, the quality of life score of the survivors was significantly better than that of 129 normal controls [0.966 versus 0.941 (theoretical maximum 1), respectively; P < 0.001]; however, a difference of this magnitude is most likely not clinically significant. There were no associations between original diagnosis and present quality of life, but the numbers in each diagnostic group were small. The survivors reported significantly better levels of vitality, distress, depression, discomfort, elimination and sleeping dimensions than the controls. Although we are presently not able to identify all the contributing factors, we speculate that the high perceived quality of life of long-term survivors of childhood malignancies is at least in part a consequence of denial mechanisms which compensate or even overcompensate the objectively measurable late effects of childhood cancer.

Adolescent↗
PubMed1994

CRIB and SNAP: assessing the risk of death for preterm neonates.

The performance of three scoring systems for assessing mortality risk for neonates--clinical risk index for babies (CRIB), score for neonatal acute physiology (SNAP), and SNAP's perinatal extension (SNAP-PE)--were tested in the same set of patients. In 222 neonates weighing less than 1500 g at birth, CRIB scores were significantly better for assessing mortality risk than SNAP (p = 0.017) or SNAP-PE (p < 0.001), areas under receiver operating characteristic curves being 0.89 (SE 0.02), 0.82 (0.03), and 0.79 (0.03), respectively. Male sex was independently associated with poor prognosis after taking the CRIB score into account with a risk ratio of 2.75. We conclude that CRIB is the most useful score for comparing the performance of neonatal intensive-care units. New treatment methods, however, may require modifications to the system.

Female↗
PubMed1994

Facilitation of experimental allergic encephalomyelitis by irradiation and virus infection: role of inflammatory cells.

Infection with an avirulent strain of Semliki Forest virus (SFV-A7) facilitates the development of experimental allergic encephalomyelitis (EAE) in a genetically resistant BALB/c mouse strain. Irradiation which is necessary for EAE induction caused a decrease in the total number of lymphocytes and an increase in CD4+/CD8+ T cell ratio in the spleen of BALB/c mice. EAE induction increased the ratio further until clinical and histological signs of EAE appeared. Entry of perivascular CD4+ and CD8+ cells preceded the onset of clinical signs and the appearance of MAC-1+ cells in the central nervous system (CNS). In the acute phase of EAE, cellular infiltrates, which were sparse, consisted mainly of MAC-1+ cells and a few CD4+ and CD8+ cells. Inflammatory cells gradually disappeared during the recovery phase. SFV-A7 infection after irradiation and EAE induction did not significantly change the CD4+/CD8+ ratio in the spleen or in the CNS infiltrates but enhanced the entry of inflammatory cell into the CNS. Similar perivascular cell influx was also seen in untreated mice infected with SFV-A7. We conclude that observed rapid reduction of splenic mononuclear cells and increase of the CD4+/CD8+ T cell ratio caused by irradiation prior EAE induction are early crucial events in disease induction in this resistant strain of mice. SFV-A7 infection, which further facilitates the development of EAE, does not induce immunoregulatory changes but provides its effect by enhancing the entry of inflammatory cells into the CNS. The combination of these two mechanisms thus effectively breaks the natural resistance against EAE in this genetically resistant mouse strain.

Animals↗
PubMed1994

Early effects of the self-reinforced PGA implant on a growing bone: an experimental study on growing rats.

The purpose of the study was to investigate the immediate/early effects of a bioabsorbable implant on a growing bone and monitor the strength retention. Fifty-eight rats were used as experimental animals. In 29 animals a 1.1 mm self-reinforced (SR-PGA) polyglycolic acid implant was placed through a transphyseal drill channel up to the diaphysis of the femur. In another 29 rats similar implants were placed in both femora and in the dorsal subcutis. After a follow-up time of 1-28 days a histologic and a roentgenographic analysis of the femora was undertaken and the shear and bending strengths of the removed implants in the other group were measured. The implant was broken at the plane of the growth plate by 21 days. No permanent growth disturbance occurred in the operated femora compared to the control side. The SR-PGA implants lost a substantial part of their mechanical strength in 2 weeks.

Animals↗
PubMed1994

Absorbable membranes for bone repair: an experimental study on rabbits.

To study the use of absorbable self-reinforced polyglycolide (SR-PGA) membranes for bone repair, distal femoral metaphyseal osteotomies were created in 10 rabbits and diaphyseal osteotomies in five. Osteotomies were fixed with intramedullary PLLA rods and PGA membranes were applied over the osteotomy. They were followed up for 6, 12 and 24 weeks. Radiography, histology, microradiography and oxytetracycline fluorescence labelling studies were used to evaluate the outcome. Healing occurred without complications in the metaphyseal series while failure was recorded in the diaphyseal series. In metaphyseal osteotomies, new bone formation was seen medially (on the side of PGA membrane), more proximal and medial to the membrane than at the inlet of osteotomy.

Animals↗