The increase of leg fibrinolytic potential after reduction of hydrostatic stimulus.

Eleven patients were studied sequentially from the beginning of recumbency due to trauma up to the complete mobilization. The first blood sampling was performed 12 hr to 4 days after injury, the second after 12 to 33 days of recumbency and the third after one or more months of mobilization. The blood was drawn each time before and after venous occlusion of the arm and the leg for 20 min. Fibrinolytic potential was calculated as the difference between post- and preocclusion values of plasminogen activator activity, measured with the euglobulin clot lysis time (ECLT) and on fibrin plates. The results showed that fibrinolytic potential of legs after the period of recumbency was approaching that of the arms, being ten times higher as measured with ECLT and five times higher as measured on fibrin plates in comparison with the period after mobilization. It was concluded that hydrostatic pressure was the main, if not the only factor responsible for the difference in the content of plasminogen activator in veins of arms and legs and their fibrinolytic potential.

Increase of tissue plasminogen activator in limbs during venous occlusion: a simple haemodynamic model.

Venous occlusion of a limb is an established procedure for increasing the venous plasma concentration of tissue plasminogen activator (t-PA). In this paper a simple haemodynamic model was developed to describe the venous plasma t-PA concentration as a function of haemodynamic parameters and the local release rate of t-PA during venous occlusion of the limb. The venous plasma pool of a limb was regarded as a single well-mixed compartment with a constant input rate of t-PA. The intravascular volume, blood flow and total limb volume of the upper extremity were also measured in three healthy subjects in order to characterise the haemodynamics during venous occlusion. Venous occlusion was shown to cause such an intense decrease of blood flow through the limb that the postocclusion increase in concentration of t-PA need not be explained by an increased release rate of t-PA but could be attributed merely to the diminished dilution of the venous compartment by inflowing arterial plasma. According to our model and haemodynamic measurements, the significant differences in the postocclusion concentration of t-PA between the arm and leg can be explained by different local release rates of t-PA.

Different tissue plasminogen activator release in the arm and leg during venous occlusion is equalized after DDAVP infusion.

The mechanism of tissue plasminogen activator (t-PA) release during arm and leg venous occlusions and DDAVP (1-desamino-8-D-arginine vasopressin) infusion was studied in 10 healthy males. The following determinations were carried out on venous blood: t-PA antigen (ELISA), t-PA activity, and t-PA inhibitor (PAI) activity (amidolytic assays). Before DDAVP, there was a 270% t-PA antigen increase in the arm at the end of occlusion as opposed to only a 40% increase in the leg. After DDAVP, t-PA antigen at the end of arm and leg occlusion reached an equal level which was significantly higher than in the arm before DDAVP. The study produced no evidence of PAI release during venous occlusion of a limb. It is concluded that DDAVP is able to elicit t-PA release from arm as well as from leg vessels. The poor fibrinolytic response of leg vessels to venous occlusion is not due to a high PAI release or t-PA stores depletion in leg vessels, but rather to low basal t-PA release in leg vessels.

Tissue plasminogen activator release in chronic venous hypertension due to heart failure.

In order to study the effects of chronic venous hypertension due to heart failure on blood fibrinolytic activity, tissue plasminogen activator (t-PA) antigen, plasminogen activator inhibitor 1 (PAI-1) antigen, t-PA activity and PAI activity were measured before and after venous occlusion of the arm for 20 min in 15 patients with right-sided heart failure, 15 patients with left-sided heart failure, and 30 control healthy subjects. Central venous pressure, measured by observing the jugular veins, was above 15 cm of the blood column in all patients with right-sided heart failure, and normal (below 8 cm) in all patients with left-sided heart failure and control subjects. There was no difference in the basal concentrations of t-PA (11.0, 10.2 and 10.8 ng/ml; all values medians) and PAI-1 antigens and their activities between right and left-sided heart failure and the control subjects. After the occlusion, t-PA antigen increased significantly less in right-sided heart failure (28.6 ng/ml) than in left-sided heart failure and the control subjects (54.5 and 45.9 ng/ml, respectively). It was concluded that the poor increase in fibrinolytic activity that had already been reported in patients with heart failure, was due to low t-PA release during occlusion and not to a high basal PAI level. It was limited to the patients with right-sided heart failure and was probably the consequence of chronic systemic venous hypertension.

Influence of moderate and strenuous daily physical activity on fibrinolytic activity of blood: possibility of plasminogen activator stores depletion.

Fibrinolysis was studied in 10 alpinists during regular physical activity of different intensity. Blood was sampled at rest and after exposure to submaximal workload on the treadmill on three occasions: before and after 6 months physical conditioning (moderate physical activity), and after 6 weeks of an alpinistic expedition (strenuous physical activity). Measurements included submaximal working capacity, fibrinogen, euglobulin clot lysis time (ELT), whole plasma clot lysis time, and estimations derived from ELT--percent increase in fibrinolytic activity after exercise (RFS), and absolute increase in fibrinolytic activity after exercise (PAR). Regular moderate activity increased the resting level of ELT, but strenuous activity decreased is. After each treadmill testing, a marked increase in fibrinolytic activity was observed. RFS was unaltered at all three testings. PAR increased after moderate activity, but decreased after strenuous activity. The results indicate that regular physical activity can lead from enhanced to decreased resting activity of plasminogen activator in blood. It is presumed that increased release of activator during prolonged stress causes partial depletion of endothelial stores with the consequence of decreased activator activity in the blood.

Effect of retraction on the lysis of human clots with fibrin specific and non-fibrin specific plasminogen activators.

The effect of the serum content of human clots on their sensitivity to lysis with plasminogen activators was studied in a system composed of 125I-fibrin labeled clots immersed in buffer or in citrated plasma. The effect was studied with plasma clots before or after mechanical compression and with whole blood clots before or after retraction, using either the fibrin specific plasminogen activators recombinant tissue-type plasminogen activator (rt-PA) or recombinant single chain urokinase-type plasminogen activator (rscu-PA), and the non-fibrin specific activators recombinant two chain urokinase-type plasminogen activator (rtcu-PA), or streptokinase (SK). In a buffer milieu, all plasminogen activators had a similar fibrinolytic potency towards serum-rich clots (non-compressed plasma clots or non-retracted blood clots): 50% clot lysis in 4 h required 50 to 85 ng plasminogen activator per ml. Serum-poor clots (compressed plasma clots or retracted blood clots) were resistant to lysis in a buffer milieu but became sensitive to lysis following preincubation in plasma for 48 h. These findings indicate that plasma proteins entrapped in clots contribute significantly to their sensitivity to lysis and suggest that the amount of bound or entrapped plasminogen may be a limiting factor. In a plasma milieu, all plasminogen activators lysed serum-rich plasma or blood clots, albeit at higher concentrations (3 to 40 times higher than in the buffer milieu) and with different efficiencies: 50% clot lysis in 4 h required approximately 600 ng/ml of rtcu-PA but 1,500 to 2,000 ng/ml of rscu-PA.(ABSTRACT TRUNCATED AT 250 WORDS)

Correlation between progressive adsorption of plasminogen to blood clots and their sensitivity to lysis.

The binding of plasminogen to preformed human plasma clots immersed in citrated human plasma was measured and correlated with the sensitivity of these clots to lysis with recombinant tissue-type plasminogen activator (rt-PA), recombinant single-chain urokinase-type plasminogen activator (rscu-PA) or two chain urokinase-type plasminogen activator (tcu-PA, urokinase). When 0.15 ml plasma clots were compressed mechanically to about 1% of their original weight, and immersed in 0.15 ml plasma, 131I-labeled native plasminogen (Glu-plasminogen) adsorbed progressively from the plasma milieu onto the clot; binding was 3 +/- 1% (n = 10) after 1 h, 7 +/- 1% after 12 h and 12 +/- 1% after 48 h. This was associated with an increased sensitivity of the clot to lysis; 50% clot lysis in 4 h was obtained with 65 +/- 5 ng/ml (n = 3) rt-PA before and 30 +/- 5 ng/ml (n = 3) after 48 h preincubation in plasma (p less than 0.01), with corresponding values of 660 +/- 55 ng/ml (n = 3) and 280 +/- 25 ng/ml (n = 3) for rscu-PA, (p less than 0.01), and 800 +/- 85 ng/ml (n = 3) and 270 +/- 35 ng/ml (n = 3) for urokinase (p less than 0.01). Additional binding of plasminogen and increased sensitivity to lysis were reduced or abolished when the clot was preincubated in plasminogen-depleted or in t-PA-depleted plasma, or when 20 mM 6-aminohexanoic acid or 2,000 KIU/ml aprotinin were added.(ABSTRACT TRUNCATED AT 250 WORDS)

Dependence of blood clot lysis on the mode of transport of urokinase into the clot--a magnetic resonance imaging study in vitro.

Magnetic resonance imaging was employed to study the dependence of clot lysing patterns on two different modes of transport of urokinase into whole blood clots. In one group of clots (nonperfused clots, n1 = 10), access of urokinase to the fibrin network was possible by diffusion only, whereas in the other group (perfused clots, n2 = 10) bulk flow of plasma containing urokinase was instituted through occlusive clots by a pressure difference of 3.7 kPa (37 cm H2O) across 3 cm long clots with a diameter of 4 mm. It was determined separately that this pressure difference resulted in a volume flow rate of 5.05 +/- 2.4 x 10(-2) ml/min through occlusive clots. Perfused clots diminished in size significantly in comparison to nonperfused ones already after 20 min (p less than 0.005). Linear regression analysis of two-dimensional clot sizes measured by MRI showed that the rate of lysis was more than 50-times faster in the perfused group in comparison to the nonperfused group. It was concluded that penetration of the thrombolytic agent into clots by perfusion is much more effective than by diffusion. Our results might have some implications for understanding the differences in lysis of arterial and venous thrombi.

Lysing patterns of retracted blood clots with diffusion or bulk flow transport of plasma with urokinase into clots--a magnetic resonance imaging study in vitro.

Fresh retracted clots are known to be poorly lysable by fibrinolytic agents. We have studied whether lysis of retracted clots could be enhanced by bulk transport in comparison to pure diffusion of plasma containing urokinase (400 IU/ml) into the clots. Cylindrical retracted blood clots were occlusively glued by a polyester into plastic tubes and put in contact with plasma through the clot bases. One group of clots (perfused clots, n = 10) was placed under a pressure difference of 6 kPa (60 cm H2O) which resulted in an average plasma flow of 0.97 +/- 0.34 microliters/min through the clot during the first hour. Another group of clots (non-perfused clots, n = 10) was incubated in the lytic plasma without a pressure difference. Clot sizes were measured during lysis by magnetic resonance imaging (MRI). Channels representing lysed areas penetrated into perfused clots with a velocity of 5.4 +/- 1.6 mm/h (n = 10), whereas the boundaries of non-perfused clots subsided with a velocity of less than 0.1 mm/h. Eight of the 10 perfused clots were recanalized after 8 h and the sizes of the perfused group were reduced to 64.0 +/- 10.7% of the initial values. The relative sizes of non-perfused clots after 8 h remained significantly higher: 95.0 +/- 1.3%, p < 0.005. In a separate experiment good agreement was obtained between the measured clot sizes by MRI and the residual radioactivity of 125I-fibrin in the clot.(ABSTRACT TRUNCATED AT 250 WORDS)

Carotid intima-media thickness in young patients with familial hypercholesterolaemia.

OBJECTIVE: To assess the extent of early atherosclerotic changes of the carotid arteries in young patients with familial hypercholesterolaemia (FH) detected as increased intima-media thickness (IMT), and to determine the relations between IMT and some clinical and blood variables such as lipid and lipoprotein(a) (Lp(a)) concentration and haemostatic factors. DESIGN: The IMT of the carotid bifurcation, the proximal 1 cm of the internal carotid artery, and the distal 1 cm of the common carotid artery was determined in all subjects using B mode ultrasonography. Blood lipids, fasting glucose, and several haemostatic variables were also analysed. SUBJECTS: 28 patients with FH (12 males and 16 females aged 11 to 27 years, one homozygote, 27 heterozygotes) and 28 sex and age matched normolipidaemic healthy subjects. RESULTS: The mean carotid IMT (the average of six measurements of the maximum far wall IMT in the three carotid segments on each side) was significantly greater in patients with FH than in controls (mean (SD) 0.71 (0.15) v 0.49 (0.08) mm, P < 0.001). In all subjects, the mean IMT was significantly correlated with total cholesterol (r = 0.59), low density lipoprotein (LDL) cholesterol (r = 0.60), triglycerides (r = 0.27), and systolic blood pressure (r = 0.47). No correlation was found between the mean IMT and Lp(a), fibrinogen, tissue plasminogen activator, and plasminogen activator inhibitor 1. CONCLUSIONS: The majority of young patients with FH have a greater intima-media thickness of the carotid arteries than healthy subjects. Since the individual susceptibility of patients with FH to increased LDL cholesterol is different, B mode ultrasonography could provide a useful tool to identify those who are more likely to develop premature atherosclerotic disease.

Exhaustion of arm fibrinolytic potential after repeated venous occlusions and local exercise.

The effect of repeated venous occlusions of the arm combined with local exercise was assessed in 10 healthy volunteers. The blood was drawn before and after three venous occlusions of 20 minutes. Between occlusions I - II, and II - III, twelve occlusions of 10 minutes were performed on the same arm while a small rubber ball was compressed 30 times per minute. Plasminogen activator (PA) activity was measured on plasminogen rich fibrin plates and by the euglobulin clot lysis time. A high increase in PA activity after venous occlusion (fibrinolytic potential) was present in all three occlusions on the first day, but fell to a very low level on the fourth day. The restitution of potential followed, but was not complete even on fifteenth day. These results indicate that PA continues to be released even after the termination of stimulation and can be temporarily depleted some days afterwards. An increase of fibrin(ogen) degradation products together with a slight decrease of alpha-2-antiplasmin in postocclusion samples, but no change in fibrinogen concentration speak in favour of a small fibrin(ogen)olysis during venous occlusion.

Aspirin decreases fibrinolytic potential during venous occlusion, but not during acute physical activity.

It has previously been observed that aspirin diminishes the increase in blood fibrinolytic activity during arm venous occlusion. We studied the duration of this inhibitory effect on fibrinolytic response during 20 minutes arm venous occlusion and its effect on fibrinolytic response during acute physical activity (standardized stress testing on treadmill) in 10 healthy male volunteers. Fibrinolytic activity was measured with euglobulin clot lysis time and fibrin plates before and after both stimuli, and t-PA release estimated as the difference between post- and prestimulation values (fibrinolytic potential: FP). Venous occlusions were performed before aspirin ingestion and then on the first, second, third, and fourth to eighth day after aspirin. Stress testing was carried out on two successive days before and after aspirin ingestion. Aspirin did not affect basal fibrinolytic activity, but significantly decreased FP during occlusion. This effect was sustained for the whole period of observation. To the contrary, aspirin did not influence FP during acute physical activity. The different effect of aspirin on fibrinolytic response during venous occlusion and physical activity suggested that different mechanisms were involved in t-PA release during both stimuli.

Poor fibrinolytic response to venous occlusion by different criteria in patients with deep vein thrombosis.

Five criteria for poor response to a 20 min venous occlusion test were applied to 58 patients 3 months or more after acute deep vein thrombosis (DVT). The criteria were arbitrarily defined as the last 5 percentiles of response distributions in an age- and sex-matched healthy control group of 51 subjects. The criteria were: 1. euglobulin clot lysis time after venous occlusion greater than or equal to 140 min; 2. t-PA activity after venous occlusion less than or equal to 0.04 IU/ml; 3. increase in t-PA antigen above resting value less than or equal to 2-fold; 4. ratio between t-PA antigen increase and resting PAI activity less than or equal to 0.5 ng/IU; 5. PAI activity after venous occlusion greater than or equal to 6 IU/ml. The last criterion of poor response was the only one that was significantly more frequently reached by patients than by controls: 28% (p less than 0.005) of all DVT patients and 35% (p less than 0.005) of the subgroup with idiopathic DVT (N = 34) were found to be poor responders. The percentage of poor responders according to the other four criteria was 7-11% in all patients and 9-15% in the subgroup with idiopathic DVT and thus was not significantly higher than in controls (5% by definition). It was concluded that residual PAI activity after venous occlusion might be a useful criterion for prospective studies on recurrence of DVT.

Carotid arteries in central retinal vessel occlusion as assessed by Doppler ultrasound.

Doppler ultrasound was used to detect possible flow changes in the carotid arteries of patients with central retinal artery and vein occlusion. Twenty-three patients with central retinal artery occlusion (mean age 56, SD 11, years) were examined 4 to 48 months after the development of the occlusion and compared with age and sex matched control subjects with no history of any disease known to be associated with pathological changes in carotid vessels. Significant stenosis or occlusion of one or more carotid arteries was discovered in eight patients with retinal artery occlusion, while the ultrasonic findings were normal in all the controls (p less than 0.005). Blood flow was evaluated by the same method in 16 patients with central retinal vein occlusion (mean age 57, SD 9, years) six to 48 months after the event. A control group was chosen according to the same criteria as in previous comparison. Pathological ultrasonic findings were observed neither in the patients with retinal vein occlusion nor in the control group. The results suggested a possible aetiological relation between pathological changes in the carotid arteries and occlusion of the central retinal artery, but not occlusion of the central retinal vein.

Carotid intima-media thickness of young coronary patients.

BACKGROUND: Although a greater than normal intima-media thickness (IMT) has been found in older coronary patients, the data for younger patients are lacking. OBJECTIVE: To determine the carotid IMT in patients with premature myocardial infarction. METHODS: We measured IMT (common and internal carotid, carotid bifurcation) in 30 coronary patients, aged 30-50 years (mean 46 years), who had survived myocardial infarctions 1-9 years (mean 6 years) earlier, and in 30 age-matched men without clinically evident coronary heart disease (controls) by B-mode ultrasonography. Blood levels of lipoproteins, glucose, iron and transferrin, fibrinogen, tissue plasminogen activator (t-PA) antigen level and activity and plasminogen activator inhibitor (PAI-1) antigen level and activity were also determined. RESULTS: IMT in all segments of carotid arteries in the patients was significantly greater than that in the controls (P < 0.0001). The presence of atherosclerotic plaques was correlated to greater than normal carotid IMT. Other risk factors displaying statistically significant correlations to mean carotid IMT were t-PA antigen level and activity, PAI-1 antigen level and level of high-density lipoprotein cholesterol. CONCLUSIONS: The significant association between carotid IMT and coronary heart disease suggests that carotid and coronary atherosclerosis evolve simultaneously. Hence carotid IMT can be used as a predictor of coronary atherosclerosis.

Urokinase-type plasminogen activator system predicts risk of cardiovascular events in patients with angina pectoris: results of the ECAPTURE study. European Concerted Action on Prevention from Thrombosis by URokinase Enhancement.

In most Westernized societies cardiovascular diseases are the leading cause of death over the age of 45 years and one-quarter of these deaths occur in men below the age of 65 years. The haemostasis system has been identified as an important system in cardiovascular disease (CVD). The European Concerted Action on Prevention from Thrombosis by URokinase Enhancement (ECAPTURE) has focused on the contribution of the urokinase system to CVD. In 2298 patients with angina pectoris the relationship between plasma levels of single-chain urokinase (scu-PA), urokinase antigen (u-PA) and u-PA-inhibitor complex and the risk of cardiovascular events (n = 84) during a 2 year follow-up period was studied. Plasma levels of total u-PA and u-PA-inhibitor complex predicted the risk of cardiovascular events, the adjusted relative risks of the highest quintile versus the lowest were 2.71 [95% confidence interval (CI), 1.34-5.48] and 2.34 (95% CI, 1.08-5.11), respectively. These results suggest that the urokinase system plays a role in cardiovascular disease.

Late results of local thrombolytic treatment of peripheral arterial occlusions.

One hundred thirty-four patients, in whom acute and subacute arterial occlusions of lower limbs were treated with low dose intraarterial streptokinase, were observed for periods of up to five years. Primary recanalization of occluded vessels was achieved in 66 patients, but in the remaining 68 patients recanalization was not observed. In 45% of the patients with successful thrombolytic treatment, percutaneous dilatation (PTA) of remnant stenosis was performed. In patients with successful recanalization the reocclusion rate was greatest in the first year (17.4%); the first two weeks after therapy were most critical in this respect. The reocclusion rate during the succeeding years ranged from 4% to 9% per year. The cumulative patency rate after five years was 63.4%. Late results were better in patients in whom more proximal vascular segments were affected. The preservation of vessel patency was highly dependent on the severity and extent of the previous atherosclerotic process and especially on the state of peripheral (runoff) arteries. Presence of diabetes mellitus increased the reocclusion rate of recanalized vessels. Of the patients with unsuccessful recanalization, only 5 reported some symptomatic improvement during the observation period, 39 (57%) needed immediate amputation, and an additional 8 (4.7%) were amputated later on. Considering the fact that all patients were previously refused for bypass surgery owing to unsuitable runoff vessels or bad general condition, the long-term results were surprisingly good, suggesting that thrombolytic treatment, combined in remnant stenosis with PTA, was an efficient method in patients with acute or subacute arterial occlusions.

Increased plasminogen activator inhibitor activity in survivors of myocardial infarction is associated with metabolic risk factors of atherosclerosis.

To assess the relationship between the fibrinolytic system and coronary risk factors, several fibrinolytic parameters were measured in 72 male survivors of myocardial infarction and in 53 age-matched healthy controls. The coronary patients had significantly higher plasminogen activator inhibitor (PAI) activity than the control subjects, while t-PA antigen did not differ between the groups. After stratifying the coronary patients in 14 diabetic and 58 nondiabetic patients, the elevated PAI activity remained limited to the diabetic group. PAI activity correlated significantly with systolic blood pressure, blood glucose, body mass index and LDL cholesterol. In multivariate regression analysis, significant associations persisted between PAI and diabetes, body mass index and LDL cholesterol. Coronary disease had no impact on the regression model. Our results suggest that the increased PAI-1 in selected groups of coronary patients is not a consequence of coronary disease itself, but is rather related to the metabolic risk factors of atherosclerosis, especially diabetes.