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NDT Advance Access originally published online on November 22, 2005
Nephrology Dialysis Transplantation 2006 21(3):736-742; doi:10.1093/ndt/gfi280
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© The Author [2005]. Published by Oxford University Press on behalf of ERA-EDTA. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org

Original Articles: Dialysis and Transplantation

Hypertension in dialysed children: the prevalence and therapeutic approach in Poland—a nationwide survey

Marcin Tkaczyk1, Michal Nowicki1, Irena Balasz-Chmielewska2, Hanna Boguszewska-Baczkowska3, Dorota Drozdz4, Barbara Kollataj5, Tomasz Jarmolinski6, Katarzyna Jobs3, Katarzyna Kilis-Pstrusinska7, Beata Leszczynska8, Irena Makulska7, Dariusz Runowski9, Roman Stankiewicz10, Maria Szczepanska11, Ryszard Wiercinski12, Ryszard Grenda3, Andrzej Kanik13, Jacek A. Pietrzyk4, Maria Roszkowska-Blaim8, Krystyna Szprynger11, Jacek Zachwieja9, Maria M. Zajaczkowska5, Walentyna Zoch-Zwierz12, Danuta Zwolinska7 and Aleksandra Zurowska2

1 Department of Nephrology and Dialysis, Polish Mother's Memorial Hospital Research Institute of Lódz and Pediatric Dialysis Centers in 2 Gdansk, 3 Warszawa (IP CZD), 4 Kraków, 5 Lublin, 6 Szczecin, 7 Wroclaw, 8 Warszawa (AM), 9 Poznan, 10 Torun, 11 Zabrze, 12 Bialystok and 13 Rzeszów, Poland

Correspondence and offprint requests to: Marcin Tkaczyk, MD, Department of Nephrology and Dialysis, Polish Mother's Memorial Hospital Research Institute, 281/289 Rzgowska St, 93-338 Lódz, Poland. Tel: ++48 42 2712001, Fax: ++48 42 2711381, Email: mtkaczyk{at}uni.lodz.pl



   Abstract
Top
 Abstract
Introduction
 Patients and methods
 Results
 Discussion
 References
 
Background. The aim of this nationwide analysis was to assess the incidence and current treatment profile of arterial hypertension in children undergoing chronic haemodialysis or peritoneal dialysis and attitudes of paediatric nephrologists towards the choice of antihypertensive drugs in their patients.

Methods. The study group consisted of 134 children (89 males, 45 females, mean age 10.7±5 years) from all 13 paediatric dialysis centres in Poland. The data were gathered through a questionnaire for each patient dialysed in November 2004.

Results. The overall incidence of hypertension in the study group was 55% (74 of 134 patients; 47 males, 27 females). The incidence rate was similar in boys and girls (53 vs 60%) and in those on haemodialysis and peritoneal dialysis (56 vs 54%). Chronic glomerulonephritis as an underlying renal disease was significantly more frequent in the hypertensive than in the normotensive subjects (37 vs 10%, P = 0.004). Residual urine output was higher in normotensives (41 vs 10 ml/kg body weight; P<0.001). Among those treated with antihypertensives: 32% were treated by monotherapy, 36% received two drugs, 22% received three drugs, while 7% received ≥4 drugs. The therapy was effective in only 57% of subjects. We observed no differences in biochemical and clinical parameters between those who responded to the therapy and those who failed to do so. Calcium channel blockers constituted the most frequently administered class of drugs [73% of children; in 43 out of 48 (90%) combined with other drugs, but in 11 out of 24 (46%) as a monotherapy]. In monotherapy, angiotensin-converting enzyme inhibitors and calcium channel blockers were administered most frequently.

Conclusion. We conclude that the incidence of hypertension in dialysis children in Poland is high (55%). The effectiveness of antihypertensive treatment is rather low (58%) and the choice of drugs is limited.

Keywords: antihypertensive therapy; arterial hypertension; children; dialysis



   Introduction
Top
 Abstract
 Introduction
Patients and methods
 Results
 Discussion
 References
 
Arterial hypertension occurs frequently in the clinical course of chronic kidney disease (CKD) and is one of the major cardiovascular risk factors in this population [1–5]. The cardiovascular mortality rate in dialysis patients is 20–30 times higher than in the healthy population [5–7] and >60% of dialysis patients die of cardiovascular causes [5,7]. In Poland, the annual mortality for adult dialysis patients is as high as 12.3%, but for children it is much lower at 3.3% [5]. The presence of hypertension increases the risk of cardiovascular or total mortality in dialysis patients [5,7]. Besides the classic risk factors for hypertension (race, weight, obesity, gender and salt intake), dialysis patients often develop overhydration, hyperlipidaemia, impaired calcium–phosphorus metabolism and autonomic dysfunction [4,8,9].

The studies on the adult dialysis population showed that the incidence of hypertension varies from 33 to 94% [1,5,9]. Surprisingly, despite a much lower incidence of hypertension in the general population (1–3 vs 20–30%), high blood pressure in children undergoing dialysis was detected as frequently as in adults [2,10,11].

Furthermore, arterial hypertension persists in most dialysis patients despite the nephrologists’ awareness of the problem [2,11,12]. It is in fact possible that a high percentage of dialysed patients with hypertension either are left untreated or are treated insufficiently [12]. Hypothetically, the other possible causes of persistent hypertension after the commencement of dialysis may include fluid overload, high dietary salt intake and patient incompliance.

A lack of data in this field in European countries prompted us to perform a nationwide multicentre survey in all paediatric dialysis units in Poland in order to assess the incidence of hypertension in children undergoing dialysis and the paediatric nephrologists’ therapeutic approach to antihypertensive therapy in this population which was expected to be very different from the management of hypertensive adults.



   Patients and methods
Top
 Abstract
 Introduction
 Patients and methods
Results
 Discussion
 References
 
We analysed data of 134 patients below 18 years of age who had been dialysed for at least 3 months in all 13 paediatric dialysis centres in Poland. As a cut-off date we chose November 30, 2004. The average age of the patients was 10.7±5 years, whereas the median duration of dialysis therapy was 19 months (range 3–111). Eighty-nine (66%) patients were on peritoneal dialysis (PD) whereas 45 (34%) were on chronic haemodialysis (HD). Among the PD patients, >95% were treated with automated PD.

The data were gathered through an individual questionnaire filled out by a treating physician for every patient qualified to participate in the study. We analysed past medical history concerning the details of primary kidney disease, renal failure, dialysis, hypertension and its treatment. Additionally, the family history was checked for the presence of hypertension.

The present status of the patients was assessed by basic anthropometrical measures [weight, height, body mass index (BMI)] and blood pressure (BP) measurement [systolic (SBP) and diastolic (DBP) with the classic Korotkoff or oscylometric method depending on the experience of the centre]. In the children on HD, BP was assessed as a mean value of at least three pre-dialysis measurements. In PD patients, we took the two values detected during the last scheduled control visit.

The SBP and DBP were indexed for age, gender and height according to the recently published reference values, which could be used for dialysis children [13].

For analysis, the children on dialysis were divided into a hypertensive group (n = 74, 47 males, 27 females) and a normotensive group (n = 60, 42 males, 18 females). The criteria for being included in the hypertensive group were checked by a treating physician and included BP values ≥95th percentile without medication or present antihypertentensive therapy. When blood pressure did not exceed the 95th percentile but target organ damage was detected, the child was also classified as hypertensive [13]. In the treated children, an inadequate BP control was defined as SBP and/or DBP ≥95th percentile during the therapy (based on pre-dialysis BP values in HD patients or control visit values in PD patients).

In hypertensives, physicians were asked to send additional information on previous and present medication (class and number of antihypertensive drugs, and their daily dose/kg) of body weight. In the case of inadequate blood pressure control, we tried to define the reason for the treatment failure, e.g. insufficient dose, non-compliance or fluid overload, by asking for the physician's opinion.

According to the response to the treatment (BP higher than or under the 95th percentile), we subdivided hypertensive patients into responders and non-responders in order to obtain more detailed information on possible reasons for treatment inefficacy.

As the basic biochemical parameters describing the adequacy of dialysis and clinical status, we chose haemoglobin concentration, total protein concentration and Kt/V calculated from serum and urine urea, and creatinine concentration. Residual urine output was assessed by 24 h collection (a day before a mid-week dialysis for HD patients and a day before a scheduled visit for ambulatory PD patients) and expressed per kg of body weight.

The study group was also divided for analysis of potential factors that might influence blood pressure into those treated with PD and HD. Eighty-nine patients (58 males, 30 females) were in the PD group and 45 in the HD group (31 males, 15 females).

In the second part of the survey, the treating physicians were asked to describe their preferences regarding the chronic antihypertensive therapy in children on dialysis. The questions included the preferences for using selected classes of antihypertensive drugs including calcium channel blockers (CCBs), angiotensin-converting enzyme inhibitors (ACEIs), angiotensin II receptor blockers (ARBs), ß-blockers (BBs) or others for chronic therapy. Furthermore, the physicians described the medication they preferred to use for hypertensive emergencies in their patients. At the end of the questionnaire, the physicians also gave their opinion on what classes of drugs are contraindicated in children undergoing dialysis.

After collecting all the questionnaires, the data analysis group (M.T. and M.N.) checked the accuracy of interpretation of BP values and performed an analysis of relationships between BP values (systolic or diastolic) with selected biochemical and clinical parameters.

Statistical analysis
Normality of the data was evaluated by the Kologomorow–Smirnov test with Lilliefor's correction. Results are expressed as median and 25th–75th interquartile range. Statistical comparisons between groups were made by two-sided unpaired t-test or Mann–Whitney test. {chi}2 and Fisher's exact test were applied to compare categorical variables. Linear correlation (Spearman correlation coefficient) analyses were used to assess relationships between different variables. Subsequently, the multivariate regression models were applied to reveal relationships between BP values and weight, height, BMI, Kt/V, haemoglobin concentration, total protein concentration, epoietin dose and residual urine output, i.e. variables that showed a significant linear correlation. A P-value of <0.05 was considered significant.



   Results
Top
 Abstract
 Introduction
 Patients and methods
 Results
Discussion
 References
 
Hypertension distribution
We found that amongst 134 children dialysed in Poland, 74 (55%) were hypertensive whereas 59 (45%) were normotensive. Isolated systolic hypertension was revealed in 12 cases, and diastolic-only hypertension in two children, whereas in the remaining children both BP values were higher than normal. Hypertensive and normotensive dialysis children did not differ with regard to gender distribution, age, weight, age at commencement of dialysis or duration of dialysis (Table 1). Hypertensives were taller than normotensives. The distribution of dialysis modalities (HD vs PD) was similar in both analysed groups. Hypertension was present in 56% of HD and 54% of PD patients. In the retrospective analysis, we found that in 65% of the hypertensives elevated BP had already been detected before the start of chronic dialysis.


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  		Table 1. Clinical characteristics of normotensive and hypertensive children on dialysis (median and 25th–75th interquartile range)

 
Since it was postulated that younger children are often at higher risk of hypertension, we also selected 27 children (25 PD and two HD) under 5 years of age [2,11]. In this group of children, the incidence of hypertension was not higher than in the older patients (44 vs 58%, P = 0.15).

Underlying kidney disease
The primary renal disease was known in 96% of children. The most frequent underlying kidney disease in the hypertensive group was chronic glomerulonephritis (37%), whereas in normotensives it was chronic interstitial nephritis with or without urinary tract obstruction (31%) (Figure 1a and b). The incidence of chronic glomerulonephritis (37 vs 10%, P = 0.032) was significantly higher, while that of renal hypoplasia or dysplasia was lower (5 vs 20%, P = 0.02) in hypertensives than in normotensives.


Figure 1
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  		Fig. 1. Primary causes of chronic kidney disease in dialysis children. (a) hypertensive patients; (b) normotensive patients.

 
Biochemical parameters
The biochemical characteristics of the studied population are presented in Table 2. The residual kidney function was better preserved in hypertensive than in normotensive children on dialysis (the residual urine output was assessed 41 vs 10 ml/kg body weight, respectively, P<0.001). It was also found that in normotensives, SBP and DBP correlated significantly with weight (r = 0.63 and r = 0.63, respectively, P<0.05), height (r = 0.52 and r = 0.51; P<0.05), residual urine output (r = –0.38 and r = –0.24; P<0.05) and the dose of epoietin (r = –0.31 and r = –0.46; P<0.05). Similar relationships were also found in the multiple regression analysis (for weight, ß = 0.56 for SBP, ß = 0.53 for DBP; for height, ß = 0.49 for SBP, ß = 0.48 for DBP; for residual urine output ß = –0.40 for SBP). In the hypertensives, only weight and height correlated with SBP (r = 0.38 and r = 0.47, respectively, P<0.05) and DBP (r = 0.32 and r = 0.23, respectively, P<0.05). In a multiple regression model, SBP was best explained by weight (ß = 0.32) and height (ß = 0.40), and DBP by weight (ß = 0.30). Total protein concentration correlated with SBP (r = –0.23, P<0.05, ß = –0.23) as well as haemoglobin concentration (r = –0.25, P<0.05) but the latter was not confirmed by the multiregression analysis.


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  		Table 2. Biochemical and clinical characteristics of hypertensive and normotensive dialysis patients (median value and 25th–75th interquartile range)

 
Table 3 shows the biochemical characteristics of the PD and HD patients. Children on HD were older, taller and heavier and were characterized by lower Kt/V values and higher epoietin weekly doses. In the PD group, height (r = 0.61, ß = 0.54, P<0.05), weight (r = 0.56, P<0.05), total protein concentration (r = –0.25, ß = –0.23, P<0.05), residual urine output (r = –0.31, ß = –0.29, P<0.05) and daily ultrafiltration (r = –0.46, ß = –0.45, P<0.05) were independent determinants for SBP, and height (r = 0.53, ß = 0.48, P<0.05), weight (r = 0.54, ß = 0.53, P<0.05), residual urine output (r = –0.24, ß = –0.23, P<0.05) and daily ultrafiltration (r = –0.46, ß = –0.42, P<0.05) for DBP. In children on HD, SBP correlated only with pre-dialysis body weight (r = 0.31, P = 0.033) but this relationship was not revealed in the multiregression model.


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  		Table 3. Biochemical and clinical characteristics of children treated with peritoneal dialysis and haemodialysis (median value and 25th–75th interquartile range)

 
Antihypertensive treatment
Amongst 74 hypertensive patients from the study, 97% were receiving antihypertensive medications. The generic names of all prescribed drugs are shown in Table 4. Monotherapy was implemented in 24 patients (32%) but 48 (66%) received two or more drugs.


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  		Table 4. The list of drugs most commonly administered to hypertensive children undergoing dialysis

 
ACEIs and CCBs were most commonly used as a monotherapy (in 50 and 46% of children, respectively). They also constituted an initial or preferred combination when the patients received more than one drug (Figure 2). Amlodipine was the most frequently prescribed CCB (51 patients) and its dose ranged from 0.08 to 0.5 mg/kg body weight/day (median 0.23 mg/kg/day). For enalapril, the dose ranged from 0.08 to 0.30 (median 0.16) mg/kg/day for monotherapy and it was significantly lower in combined therapy (0.08–0.51, median 0.27, P = 0.008).


Figure 2
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  		Fig. 2. Classes of drugs prescribed in the hypertensive patients. CCBs = calcium channel blockers; ACEIs = angiotensin-converting enzyme inhibitors; BBs = ß-blockers; ABs = {alpha}- and ß-blockers; ARBs = angiotensin II receptor blockers; others = mostly diuretics and peripheral vasodilatators.

 
Despite the fact that most patients received more than one drug, the treatment was not effective in 31 children (42% of patients, 46% on PD and 35% on HD, P = 0.24). Among all assessed parameters, the children who responded to the therapy differed from non-responders only with respect to the total protein serum concentration (61 vs 64 g/l, P = 0.04).

We also asked the treating physicians for an opinion regarding the most probable reasons for insufficient control of BP in their patients. Most responders indicated patient non-compliance (eight out of 31), fluid overload (eight out of 31) or inadequate daily dose of the drug (six out of 31).

In the last part of the questionnaire the responders described their preference for a therapy for acute BP increase in children. Most of them (98%) chose oral nifedipine and parenteral dihydralazine (2%) as a drug of the first choice. When they were ineffective, labetalol (intravenously) was the most frequently considered alternative therapeutic option (80%).



   Discussion
Top
 Abstract
 Introduction
 Patients and methods
 Results
 Discussion
References
 
To our knowledge, our analysis is one of the few comprehensive attempts to address the problem of arterial hypertension in children on chronic dialysis [7,14]. The importance of adequate control of hypertension in paediatric patients was confirmed by the study of Gruppen and colleagues where 187 patients (starting dialysis below the age of 14) showed hypertension in 54% at adulthood (29.2 years) [15]. Hypertension was described as an independent risk factor for cardiovascular disease, as were anaemia, hyperlipidaemia and left ventricular hypertrophy [4,16].

According to different sources, the incidence of hypertension in children on dialysis ranges from 33 to 86% [1,3,9,10,11,15]. This incidence has been confirmed by our study that showed the prevalence of hypertension of 55% in a whole group of children on dialysis in Poland. In a very recent study from North America, Mitsnefes et al. reported the incidence of 76.6% in a paediatric population but the racial distribution was different in their analysis since most of their patients were not Caucasians. In that study, data were also gathered for a longer period (1992–2004) [2]. In the other recent studies in paediatric populations, the prevalence of hypertension was similar to our results (Lerner et al., 53%; Holtta et al., 52%; Lingens et al., 47%) [3,10,11].

The differences in methods to measure BP between participating centres (Korotkoff vs oscylometric) may be regarded as a limitation of this study. It has been confirmed, however, that BP measured with the classic Korotkoff method can be used for both screening and routine monitoring in dialysis patients [12,18]. However, according to Sankaranarayanan et al., ambulatory BP measurement should be implemented to establish the diagnosis in a given patient with more certainty [18]. Some studies also used different methods of BP measurements, mainly ambulatory BP monitoring which may give different results due to a lack of ‘white coat’ effect. The ‘white coat’ effect cannot be avoided when BP is measured at the start of a HD session as was the case in our study. On the other hand, since BP is highly volume dependent in patients with end-stage renal disease (ESRD), the use of ambulatory BP monitoring to detect hypertension in dialysis patients might be disputable [10,11].

Our analysis also showed that isolated diastolic hypertension was detected incidentally in dialysis patients. Isolated systolic hypertension was diagnosed slightly more frequently, but most patients suffered from combined systolic and diastolic hypertension [12]. The low number of patients with isolated systolic hypertension in our population is probably due to the fact that this phenomenon is mainly linked to advanced atherosclerosis in large arteries which is unlikely to be found in children even with ESRD.

Most of the recently published studies have not resolved the longstanding dispute of whether the incidence of hypertension is lower in patients treated with PD or HD [3,4,10]. In our study population, the proportions of hypertensive and normotensive children dialysed with PD or HD were similar. This contrasts with the data published by Mitsnefes et al. [2] or Lerner et al. [3], where children treated with HD were more often hypertensive.

Both Holtta et al. [11] and Mitsnefes et al. [2] postulated that both younger and nephrectomized children were at higher risk of developing fluid imbalance and subsequent hypertension. Mitsnefes et al. also suggested that poorer control of hypertension might be the result of a smaller number of drugs given to younger patients due to various limitations. Our study did not support these observations because we did not detect any increase in hypertension incidence in younger children. The significant correlations detected in our study between residual urine output and SBP or DBP in normotensives may confirm that a fluid balance was relevant for BP control. Interestingly, these relationships remained weaker or disappeared in hypertensives, probably due to the influence of pharmacological treatment or other factors. The relationship of an adequate fluid management of BP became stronger in PD patients, in whom SBP and DBP positively correlated with residual urine output and daily ultrafiltration (P<0.05). We did not observe this phenomenon in HD subjects but the number of children treated with this method was lower. The role of overhydration in response to the antihypertensive treatment could be indirectly confirmed by lower total protein concentration in children who did not respond sufficiently to the treatment (61 vs 64 g/l, P = 0.04). Similar conclusions were derived from the study of Holtta et al. [11]. Our observations indicate the importance of sustaining residual urine output and careful fluid balance in the control of hypertensive dialysis patients. It could be achieved by administration of loop diuretics [4]. Paediatric nephrologists in Poland administered this class of drugs only as an additional therapy in cases where a combination of three or more drugs had already been ineffective (shown in Figure 2).

In general, antihypertensive therapy of hypertension in CKD children comprises similar classes of drugs as in the general hypertensive population [4,19]. Despite the fact that the choice of antihypertensive therapy is still widening, their use in the dialysis population and especially in children is limited due to a lack of uniformly accepted guidelines [19,20].

In our study, most of the hypertensive children on chronic dialysis were treated with two or more drugs. This observation is in contrast to studies of Griffith et al. [9] and Mitsnefes et al. [2] where monotherapy was preferred. In contrast, among adults on dialysis, multidrug regimens are more popular, most probably due to the longer duration of hypertension [19]. The mean number of drugs prescribed to our patients (2±1 per subject) was higher than in the study of Griffith et al. (1.66–1.76) or Mitsnefes et al. (1.8). It seems that in our country paediatric nephrologists tended to treat hypertension in their dialysis patients more aggressively and achieved better control of hypertension.

CCBs and ACEIs were chosen as drugs of first choice for chronic therapy in most Polish children on dialysis. Furthermore, these two drugs constituted the most popular combination in multidrug regimens. The drugs were generally prescribed in doses similar to those suggested by international guidelines [13]. This observation came from data derived from some studies where CCBs were most frequently chosen for therapy [1,9]. On the other hand, according to some analyses, BBs were more popular in adults on dialysis (68% of patients) [12]. Earlier studies in the general population showed that ACEIs, ARBs and BBs could lower all-cause mortality in hypertensive patients and CCBs could decrease the all-cause and cardiovascular mortality [4,19]. However, in the dialysis patients, no class of drugs gave a clear advantage in terms of cardiovascular mortality [2]. In our study, other classes of drugs (diuretics, peripheral vasodilators and centrally acting agents) were used less frequently and only in selected cases of resistant hypertension. Their role could be described as supportive. Interestingly, some nephrologists still used diuretics in patients receiving three or more drugs in order, in our opinion, to preserve residual diuresis.

In previous studies, it was clearly described that in patients treated with chronic dialysis antihypertensive therapy was very frequently ineffective (60–70%) [1,12,19]. Most authors suggested that in this population not only a choice of drugs is important but other non-pharmacological therapies such as salt-restricted diet and, most importantly, maintenance of fluid balance management are effective [1,2]. On the other hand, some authors postulated that insufficient BP control resulted mainly from underdiagnosed hypertension, inadequate dose or withholding the dose of a drug before a HD session [1,4,17]. Furthermore, it was clearly confirmed by Konings et al. that many patients treated with PD were overhydrated when compared with stable renal transplant patients [20]. In another study by Rahman et al., both left ventricular hypertrophy and the severity of hypertension correlated with interdialytic weight gain [8]. According to our analysis, in the opinion of Polish nephrologists who deal with dialysis, fluid imbalance constituted a major problem in adequate BP control (eight out of 31 responders). Apparently, however, some paediatric nephrologists refrain from applying strict fluid control and high ultrafiltration in order to preserve residual urine output or to avoid intradialytic hypotension.

Unfortunately, this study also demonstrated that patients’ incompliance should not be neglected as the key factor in BP control, as this was pointed out by doctors. In Poland, poor economic conditions and the lack of awareness concerning possible complications may cause patients to refrain from taking the drug regularly.

We also asked about the treatment preference in cases of acute BP rise. Our responders clearly indicated that they used nifedipine as a ‘drug of choice’ for hypertensive emergencies. The availability and simple dosing procedure (sublingual) was probably the main reason for the use of this short-acting CCB in cases of BP emergencies according to the questionnaires. Paediatricians preferred to use nifedipine instead of intravenous labetalol or dihydralazine despite the evidence of an increased risk of cardiovascular events in adults receiving short-acting CCBs [4,9]. According to the latest guidelines issued by the American Academy of Pediatrics, hypertension emergencies in children should be treated with esmolol, nicardipine or sodium nitroprusside instead of short-acting nifedipine [13]. However, most of these recently recommended drugs are not available in Poland.

In summary, our study revealed that although the prevalence of arterial hypertension in dialysis children in Poland was lower than in the USA, it was still high. Despite the combination therapy, the efforts to lower BP were unsuccessful in a significant proportion of the patients. Our results supported the crucial role of the preservation of residual urine output and adequate fluid balance in children on chronic dialysis. We postulate that further prospective studies in this population are necessary to improve the quality of antihypertensive treatment and widen the choice of antihypertensive therapies.



   Acknowledgments
 
The authors are grateful to Anna Jander for critical review of the study results and to Anna Kaminska for secretarial assistance.

Conflict of interest statement. None declared.



   References
Top
 Abstract
 Introduction
 Patients and methods
 Results
 Discussion
 References
 

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Received for publication: 25. 8.05
Accepted in revised form: 28.10.05


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