Energy transfer is the single most important factor for the difference in vascular response between isolated ultrafiltration and hemodialysis

Differences in vascular reactivity between isolated ultrafiltration (i-UF) and hemodialysis (UF + HD) have been attributed to various factors, including differences in core temperature (CT) and energy transfer (ET). However, the relative importance of these thermal factors is not known. The aim of this study was to elucidate to what extent differences in ET are responsible for the divergent vascular response between i-UF and UF + HD. During four different dialysis treatments in 15 patients, four measurements were performed that consisted of 1 h of i-UF, UF + HD at a dialysate temperature (T(d)) of 37.5 degrees C (UF + HD(37.5)), UF + HD at T(d) 35.5 degrees C (UF + HD(35.5)), and UF + HD with a similar ET as during i-UF(UF + HD(ET-set)). The UF rate in all sessions was 1 L/h. CT ( degrees C) decreased significantly during i-UF and UF + HD(ET-set) (P < 0.05), increased significantly during UF + HD(37.5) (P < 0.05), and remained unchanged during UF + HD(35. 5) (NS). Forearm vascular reactivity increased significantly during i-UF, UF + HD(ET-set), and UF + HD(35.5) (P < 0.05), but not during UF + HD(37.5) (NS). Venous tone increased significantly during i-UF, UF + HD(35.5), and UF + HD(ET-set) (P < 0.05), and decreased significantly during UF + HD(37.5) (P < 0.05). When i-UF and UF + HD are matched for ET, all differences in vascular response disappear, showing that differences in ET are the single most important factor for the observed difference in vascular response between i-UF and UF + HD. In contrast to UF + HD(37.5), vascular reactivity was improved when the increase in CT was prevented during UF + HD(35.5) and appeared to increase more when CT was lowered. Preventing the increase in CT during UF + HD appears to be mandatory for optimization of hemodynamic stability during dialysis.     

Thermal effects and blood pressure response during postdilution hemodiafiltration and hemodialysis: the effect of amount of replacement fluid and dialysate temperature

It has been suggested that the incidence of hypotensive episodes is less with hemodiafiltration (HDF) than with hemodialysis (HD). The aim of the present study was to assess the BP response during HD and postdilution HDF in relation to the thermal effects of these different treatment modalities by manipulating the dialysate temperature (Td) during HD and the amount of replacement fluid during HDF. In 12 patients, energy transfer rate (in watts) and maximal decline in mean arterial pressure during HD at Td 37.5 degrees C, HD at Td 35.5 degrees C, and postdilution HDF with amounts of replacement fluids infused at room temperature of 1 L/h and 2.5 L/h, respectively, were assessed. All measurements were done twice in each patient. Energy transfer rate was comparable between HD 35.5 degrees C (-26.61 +/- 5.33) and HDF 2.5 L/h (-25.25 +/- 7.91) and was significantly more negative compared with HD 37.5 degrees C (-3.53 +/- 6.44) and HDF 1 L/h (-15.88 +/- 6.94). The maximum decline in mean arterial pressure was significantly higher during HD 37.5 degrees C (-25.6 +/- 13.5) than during HD 35.5 degrees C (-15.1 +/- 13.8) and HDF 2.5 L/h (-19.2 +/- 17.7), whereas there was no significant difference with HDF 1 L/h (-23.0 +/- 14.0). In conclusion, thermal effects during postdilution HDF are dependent on the amount of replacement fluid. Also during HDF, the BP response is strongly related to thermal effects. The use of postdilution HDF with low or intermediate amounts of replacement fluids infused at room temperature seems to have no advantage in preventing hemodynamic instability, compared with HD 35.5 degrees C.     

Thermal effects of different dialysis techniques and blood pump speeds: an in vitro study

Thermal effects have a pivotal impact on hemodynamic stability during dialysis procedures. In contrast to conventional dialysis techniques, there are no data in the literature regarding the thermal energy balance during on-line techniques. Secondly, little data exist on the effect of extracorporeal blood pump speed (EBPS) on thermal energy balance. In this study we assessed, first, relative differences in energy transfer rate (ETR) over the extracorporeal circuit during on-line hemo(dia)filtration (H(D)F) procedures and hemodialysis (HD) at different dialysate temperatures during an in vitro procedure using a blood temperature monitor (BTM). Secondly, we assessed the thermal effects of different blood pump speed (BPS) rates during the various treatment modalities. ETR was different among all treatment modalities (p < 0.05) studied, except for HD at 36.5 degrees C vs. pre-dilution hemofiltration (HF) and post-dilution HDF vs. HD at 37.5 degrees C. ETR had the most negative result, indicating the largest energy loss, during HD at 35.5 degrees C (-58.5.2 +/- 2.6 W), whereas it was almost comparable between pre-dilution HF (-30.7 +/- 4.1 W) and HD at 36.5 degrees C (-35.1.2 +/- 2.4 W). Post-dilution HDF (-17.7 +/- 1.2 W) resulted in an ETR comparable to that of HD at 37.5 degrees C (-15.0 +/- 3.9 W). ETR during post-dilution HF was -43.8 +/- 1.3 W. The thermal effect of the BPS was more pronounced during the procedures with the more negative ETR. In conclusion, on-line techniques and BPS have widely varying effects on ETR during dialysis, which should be considered when the hemodynamic effects among different treatment modalities are compared.     

Haemodynamics and electrolyte balance: a comparison between on-line pre-dilution haemofiltration and haemodialysis.

BACKGROUND: An important advantage of convective therapies is improved vascular reactivity. However, it is not well known whether the vascular response during convective therapies remains superior when compared to haemodialysis (HD) with an adjusted temperature of the dialysate. It has also been suggested that convective therapies may impair small electrolyte removal through an effect on the Donnan equilibrium. In the present study, we compared the haemodynamic response and small electrolyte removal between pre-dilution on-line haemofiltration (HF) and HD procedures. METHODS: Cardiac output (CO), central blood volume (CBV) and peripheral vascular resistance (PVR) were assessed, using the saline dilution technique, in 12 stable patients during HF and HD with two different temperatures of the dialysate [36.5 and 35.5 degrees C (HD(36.5) and HD(35.5))]. Balances for sodium, potassium, calcium and conductivity were assessed using total dialysate/filtrate collections. Target filtration volume for HF was 1.2 times body weight. The temperature of the infusate was 36.5 degrees C. RESULTS: The change (Delta) in CBV was less during HD with a dialysate temperature of 35.5 degrees C (-0.03+/-0.14 l; P<0.05) compared to HF (-0.16+/-0.05 l) and HD(36.5) (-0.11+/-0.14 l), but the other haemodynamic parameters did not differ between the studied techniques. DeltaPVR was significantly related to DeltaCBV (r = -0.46; P<0.01), whereas DeltaCBV was related to ultrafiltration rate (r = -0.34; P = 0.05). DeltaCO was related to DeltaCBV (r = 0.62; P<0.001). Solute balances did not differ between HF and HD. CONCLUSION: Using the saline dilution method, no difference in the change in CO and PVR was observed between on-line HF vs HD(36.5) and HD(35.5). Only CBV declined to a significantly lesser degree during HD(35.5), although absolute differences were small. Changes in the other haemodynamic variables appeared more dependent upon the degree and rapidity of fluid removal than upon the treatment modality. No difference in small electrolyte balance was observed between HF and HD, suggesting that ionic removal is not impaired during on-line HF.     

Effect of ultrafiltration on thermal variables, skin temperature, skin blood flow, and energy expenditure during ultrapure hemodialysis

The cause of the increase in core temperature (CT) during hemodialysis (HD) is still under debate. It has been suggested that peripheral vasoconstriction as a result of hypovolemia, leading to a reduced dissipation of heat from the skin, is the main cause of this increase in CT. If so, then it would be expected that extracorporeal heat flow (Jex) needed to maintain a stable CT (isothermic; T-control = 0, no change in CT) is largely different between body temperature control HD combined with ultrafiltration (UF) and body temperature control HD without UF (isovolemic). Consequently, significant differences in DeltaCT would be expected between isovolemic HD and HD combined with UF at zero Jex (thermoneutral; E-control = 0, no supply or removal of thermal energy to and from the extracorporeal circulation). During the latter treatment, the CT is expected to increase. In this study, changes in thermal variables (CT and Jex), skin blood flow, energy expenditure, and cytokines (TNF-alpha, IL-1 receptor antagonist, and IL-6) were compared in 13 patients, each undergoing body temperature control (T-control = 0) HD without and with UF and energy-neutral (E-control = 0) HD without and with UF. CT increased equally during energy-neutral treatments, with (0.32 +/- 0.16 degrees C; P = 0.000) and without (0.27 +/- 0.29 degrees C; P = 0.006) UF. In body temperature control treatments, the relationship between Jex and UF tended to be significant (r = -0.51; P = 0.07); however, there was no significant difference in cooling requirements regardless of whether treatments were done without (-17.9 +/- 9.3W) or with UF (-17.8 +/- 13.27W). Changes in energy expenditure did not differ among the four treatment modes. There were no significant differences in pre- and postdialysis levels of cytokines within or between treatments. Although fluid removal has an effect on thermal variables, no single mechanism seems to be responsible for the increased heat accumulation during HD.     

Effect of sodium balance and the combination of ultrafiltration profile during sodium profiling hemodialysis on the maintenance of the quality of dialysis and sodium and fluid balances

Excessive sodium gain is a major hindrance of sodium profiling hemodialysis (HD) that offsets the benefit in reducing intradialytic hypotension-related discomforts (IHD). Patients who showed frequent IHD (>30% of the sessions; n = 11) were enrolled in a prospective study that consisted of two phases. In the phase 1 study, eight treatment modalities were evaluated: Conventional HD (control), sodium balance-positive step-down sodium profiling HD (PS), sodium balance-neutral step-down sodium profiling HD (NS), sodium balance-neutral alternating sodium profiling HD (NA) without ultrafiltration (UF) profile, and all those with UF profile (UF only, PS+U, NS+U, and NA+U). The incidences of "dialysis failure," defined as the occurrence of one or more of (1) session failure (discontinuation of session <75% of planned time), (2) UF failure (%UF achieved <70%), and (3) delivery failure (Kt/V <1.1), were 48.5, 21.2, 42.4, 39.4, 45.5, 18.2, 21.2, and 18.2% in control, PS, NS, NA, UF only, PS+U, NS+U, and NA+U, respectively. Four treatments, PS, PS+U, NS+U, and NA+U, reduced the incidence of dialysis failure significantly as compared with control (P < 0.05) and were evaluated in the phase 2 study, a randomized controlled 6-wk crossover study. Parameters were measured in the steady state after a 6-wk maintenance of each treatment. Diffusive sodium gain (DeltaNa) was significantly increased with sodium balance-positive profiles with or without UF profile, PS and PS+U (PS 1.9 +/- 1.1, PS+U 1.7 +/- 1.0 mEq/L; both P < 0.05 to control -0.1 +/- 0.2, NS+U 0.5 +/- 0.4, NA+U 0.4 +/- 0.2 mEq/L). They also increased the interdialytic weight gain (PS 3.8 +/- 0.6, PS+U 4.0 +/- 0.6 kg; both P < 0.05 to control 2.7 +/- 0.6, NS+U 3.3 +/- 0.6 kg; both P = NS to NA+U 3.5 +/- 0.6 kg). Predialysis weight and the required amount of UF also increased significantly with these sodium balance-positive profiles. Although the absolute amount of UF was larger with PS and PS+U, %UF achieved targeting dry weight was higher with sodium balance-neutral profiles with UF profiles, NS+U and NA+U (NS+U 92.7 +/- 3.8, NA+U 93.7 +/- 6.8%; both P < 0.05 to control 72.6 +/- 14.0, PS 88.3 +/- 6.6, PS+U 88.2 +/- 8.2%). Postdialysis weight was closest to dry weight with these treatments showing Delta (postdialysis weight - dry weight) of 0.3 +/- 0.1 and 0.3 +/- 0.2 kg in NS+U and NA+U (both P < 0.05 to control 1.0 +/- 0.6 kg; both P = NS to PS 0.5 +/- 0.3, PS+U 0.5 +/- 0.4 kg). Incidence of excessive weight gain and subjective discomforts during the interdialytic period increased significantly with PS. In conclusion, continuous use of sodium balance-positive sodium profiles resulted in an undesirable steady state with sodium and fluid expansion offsetting their hemodynamic benefit. Sodium balance-neutral sodium profiles in combination with UF profile were associated with less sodium and weight gains, better UF performance with postdialysis weight closest to dry weight, and fewer interdialytic problems with the equivalent hemodynamic benefit. Therefore, it is proposed that sodium balance-neutral sodium profiling HD with UF profile is a better choice, ensuring the dialysis of quality without sodium gain-related complications.     

Reduction of hypotensive side effects during online-haemodiafiltration and low temperature haemodialysis.

BACKGROUND: This study compares the effect of online-haemodiafiltration (o-HDF, post-dilution mode) with conventional haemodialysis (HD) and 'temperature-controlled' HD (Temp-HD) on the haemodynamic stability of hypotension-prone patients. METHODS: Seventeen patients with a history of frequent hypotensive episodes during dialysis sessions were studied, each patient serving as his or her own control. The first 25 HD treatments in comparison with 25 o-HDF sessions were evaluated using identical dialysate temperature. In the second part of the study, o-HDF (n = 25) was compared with Temp-HD (n = 25). In the latter method, the temperature of the dialysate was adjusted to result in identical energy transfer rates to those in the corresponding o-HDF. The number of hypotensive episodes, blood temperature and blood volume regulation were assessed. RESULTS: Symptomatic hypotension was much more frequent during HD (40%) than during o-HDF (4%) (P < 0.001). During o-HDF, an enhanced energy loss within the extracorporeal system occurred (o-HDF, 16.6 +/- 4.0 W; HD, 5.4 +/- 5.1 W; P < 0.0001), despite identical temperature settings for dialysate and substitution fluid. As a result, the blood returning to the patient was cooler during o-HDF than during HD (o-HDF 35 +/- 0.2 degrees C vs HD 36.5 +/- 0.3 degrees C; P < 0.0001). In o-HDF, even in the patients' circulation, the mean blood temperature was lower (o-HDF 36.7 +/- 0.2 degrees C vs HD 36.9 +/- 0.3 degrees C; P < 0.0001) and blood volume was significantly more reduced (o-HDF, 91.8 +/- 3.1%; HD, 94.0 +/- 3.2%; P < 0.05). Energy transfer rates and blood temperature did not differ significantly between o-HDF and Temp-HD. The rate of hypotensive episodes was low and not different between o-HDF (4%) and Temp-HD (4%). Neither was there any significant difference in blood volume reduction. CONCLUSIONS: O-HDF showed a significant reduction of hypotensive episodes compared with HD. Surprisingly, o-HDF resulted in cooling of the blood via enhanced thermal energy losses within the extracorporeal system, despite use of replacement fluid prepared from pre-warmed dialysate. The incidence of symptomatic hypotension was reduced to that of o-HDF by using cooler Temp-HD. Thus, unexpected blood cooling appears to be the main blood pressure-stabilizing factor in o-HDF.     

Effect of ultrafiltration on peripheral urea sequestration in haemodialysis patients.

BACKGROUND: Ultrafiltration (UF) is assumed to enhance urea removal during haemodialysis (HD) because of convective transport and because of contraction of urea distribution volume. However, UF-induced blood volume reduction has been hypothesized to enhance peripheral urea sequestration and post-dialysis urea rebound (PDUR), possibly reducing HD effectiveness. The effect of UF on PDUR was investigated in this study. METHODS: Nine HD patients were studied on two subsequent treatment days. The first HD was performed with UF (UF-rate=0.78+/-0.27 l/h), and the second treatment without UF. Serial measurements of serum water urea nitrogen concentration, arterial blood pressures (BP), and relative blood volume changes (BV%) were obtained over the duration of HD. RESULTS: BP and BV% decreased with UF (BP(sys)= -9%, BP(dia)=-8%, BP(mean)=-9%, BV%=-15%) but increased or remained unchanged without UF (BP(sys)= 9%, BP(dia)=12%, BP(mean)=11%, BV%=1%). PDUR was 28.6+/-9.6% without UF, and increased in every single patient with UF (40.7+/-13.2%, P<0.01). Modelled perfusion of the peripheral low-flow compartment decreased from 1.45+/-0.54 l/min without UF to 0.91+/-42 l/min with UF (P<0.05), thereby explaining an enhanced two-compartment effect and increasing PDUR. CONCLUSION: The significant increase in the two-compartment effect of urea kinetics observed in current HD accompanied by UF can be explained by compensatory, intradialytic blood flow redistribution induced by blood volume reduction. Because of the link between UF and blood flow, limited solute clearance treatment modes that optimize fluid removal such as variable UF will also have favourable effects on delivered dose of dialysis.     

Mathematical modeling of thermal and circulatory effects during hemodialysis

Intradialytic hypotension (IDH) is one of the most common complications of hemodialysis (HD) treatment. The initiating factor of IDH is a decrease in blood volume, which is related to an imbalance between ultrafiltration (UF) and refilling rate. Impaired reactivity of resistance and capacitance vessels in reaction to hypovolemia plays possibly a major role in the occurrence of IDH. These vessels also fulfill an important function in body temperature regulation. UF‐induced cutaneous vasoconstriction would result in a reduced surface heat loss and an increase in core temperature. To release body heat, skin blood flow is increased at a later stage of the HD treatment, whereby possibly IDH can occur. The aim of the study is to develop a mathematical model that can provide insight into the impact of thermoregulatory processes on the cardiovascular (CV) system during HD treatment. The mathematical procedure has been created by coupling a thermo‐physiological model with a CV model to study regulation mechanisms in the human body during HD + UF. Model simulations for isothermal versus thermoneutral HD + UF were compared with measurement data of patients on chronic intermittent HD (n = 13). Core temperature during simulated HD + UF sessions increased within the range of measurement data (0.23°C vs. 0.32 ± 0.41°C). The model showed a decline in mean arterial pressure of ?7% for thermoneutral HD + UF versus ?4% for isothermal HD + UF after 200 min during which relative blood volume changed by ?13%. In conclusion, simulation results of the combined model show possibilities for predicting circulatory and thermal responses during HD + UF.     

氯诺昔康与吗啡术后镇痛对胃肠肿瘤手术患者代谢调理的比较

目的比较联合应用吗啡和氯诺昔康与单纯应用吗啡进行术后镇痛对胃肠手术患者蛋白质代谢的调理作用。方法选择胃肠道肿瘤根治术患者100例，随机分为2组。每组50例：A组为氯诺昔康联合吗啡镇痛组；B组为吗啡镇痛组。两组患者均在术后3d内禁食并自外周静脉给予营养支持。测定并比较两组患者术后3d的视觉模拟评分（VAS）、体温和氮平衡，以及两组患者术前、术后第1天、第3天的白介素．6（IL-6）、肿瘤坏死因子α（TNF-α）、皮质醇（Cor）和肾上腺素（E）水平。结果两组术后24、48和72h静止与活动时的VAS分值差异无统计学意义（P〉0．05）。术后3d两组患者的体温均较术前的增高（P〈0．05），B组术后第1、3天的体温明显高于A组（P〈0．05）。术后3d两组患者均出现负氮平衡，第1天的负值最高，与第3天比较差异有统计学意义（P〈0．05）；B组术后3d的负氮平衡值均明显高于A组（P〈0．05）。两组患者术后第1、3天的血浆Cor和E水平均较术前明显增高（P〈0．05），术后第3天则较术后第1天显著降低（P〈0．05）；两组间差异无统计学意义（P〉0．05）。B组患者术后第1、3天的TNF-α及IL-6值明显高于A组（P〈0．05），且较术前显著增高（P〈0．05）。结论术后联合应用吗啡与氯诺昔康镇痛与单纯应用吗啡比较，镇痛作用相近，但前者能产生更好的代谢调理作用。     

Rapid body cooling by cold fluid infusion prolongs survival time during uncontrolled hemorrhagic shock in pigs

OBJECTIVE: The purpose of this study was to examine whether cold fluid infusion could rapidly decrease the core temperature and prolong survival during uncontrolled hemorrhagic shock in pigs. METHODS: Fourteen pigs under light halothane anesthesia and spontaneous breathing underwent initial blood withdrawal of 25 mL/kg over 15 minutes, followed by uncontrolled hemorrhage (5-mm aortotomy). Immediately after the aortotomy, the pigs were randomized to receive 500 mL lactated Ringer's solution at either 4 degrees C (group 1, n = 7) or 37 degrees C (group 2, n = 7) over 20 minutes through the internal jugular vein and observed until their death or for a maximum of 240 minutes. RESULTS: The pulmonary artery temperature of group 1 decreased to 35.5 degrees +/- 0.3 degrees C after the infusion, then remained at 35.5 degrees C during the observation period. Pulmonary artery temperature values of group 2 remained at around 37.5 degrees C throughout the experiment. The mean survival time was 220 +/- 45 minutes in group 1 versus 136 +/- 64 minutes in group 2 (p < 0.05, life table analysis). The additional intraperitoneal blood loss of group 1 was similar to that of group 2 (9 +/- 4 g/kg vs. 10 +/- 5 g/kg). CONCLUSION: In lightly anesthetized pigs during uncontrolled hemorrhagic shock, infusion with 4 degrees C lactated Ringer's solution (which seems to be feasible in the clinical setting) decreases the core temperature rapidly and prolongs survival.     

Hemodialysis hypoxemia: evaluation of mechanisms utilizing sequential ultrafiltration-dialysis

We studied the role of blood-dialyzer-membrane interactions in hemodialysis-induced hypoxemia by measuring PaO2 and white blood cell counts during isolated ultrafiltration (UF). These values were compared to those obtained from the same patients during subsequent hemodialysis (HD; utilizing the same dialyzer and membrane). Patients in the UF period displayed no hypoxemia, rather a slight increase in PaO2 (from 82.5 +/- 3.0 to 88.5 +/- 2.0 mm Hg, mean +/- SE, p greater than 0.05). In contrast, these patients displayed significant hypoxemia when HD was imposed (88.5 +/- 2.0-78.0 +/- 1.5 mm Hg, mean +/- SE, p less than 0.02). We suggest that the hypoxemia characteristic of HD initiation is not solely dependent on blood-dialyzer-membrane interactions, but also requires blood-dialysate interactions.     

Differential scanning calorimetry of the thermal denaturation of human serotransferrin.

The thermal denaturation of iron-free and iron human serotransferrin has been studied by differential scanning calorimetry. At pH 7.9 in 0.05M Tris, 0.1M NaHCO3 buffer, two transitions (Td = 60.1 degrees, 70.7 degrees C), at a 5 degrees C/min heating rate, were observed for iron-free serotransferrin. The respective enthalpies of denaturation were found to be 143 and 229 kcal/mol. Iron serotransferrin exhibits a single thermogram peak with Td = 83.4 degrees C and delta H = 616 +/- 15 kcal/mol (linearly extrapolated to 0 degrees C/min heating rate), at pH 7.8. An activation energy of 104 kcal/mol was computed by the procedure of Beech. A value of 112 kcal/mol was calculated from a first-order kinetics Arrhenius plot. Rate constants were determined at several temperatures from the onset temperature to Td. Denaturation temperatures and enthalpies were linearly dependent on heating rates. The thermal denaturations of iron-free and iron serotransferrins are irreversible, under the experimental conditions used. In contrast to conalbumin, thermograms of serotransferrin solutions partially saturated with ferric ions exhibit only the peaks corresponding to those obtained on separate DSC scans of iron-free and iron serotransferrin, respectively.     

Thermoregulatory responses of spinal cord injured and able-bodied athletes to prolonged upper body exercise and recovery

STUDY DESIGN: Single trial, two factor repeated measures design. SETTING: England, Cheshire. OBJECTIVES: To examine the thermoregulatory responses of able-bodied (AB) athletes, paraplegic (PA) athletes and a tetraplegic (TP) athlete at rest, during prolonged upper body exercise and recovery. METHODS: Exercise was performed on a Monark cycle ergometer (Ergomedic 814E) adapted for arm exercise at 60% VO2 peak for 60 min in cool conditions ('normal' laboratory temperature; 21.5+/-1.7 degrees C and 47+/-7.8% relative humidity). Aural and skin temperatures were continually monitored. RESULTS: Mean (+/-S.D.) peak oxygen uptake values were greater (P<0. 05) for the AB when compared to the PA (3.45+/-0.45 l min-1 and 2. 00+/-0.46 l min-1, respectively). Peak oxygen uptake for the TP was 0.91 l min-1. At rest, aural temperature was similar between groups (36.2+/-0.3 degrees C, 36.3+/-0.3 degrees C and 36.3 degrees C for AB, PA and TP athletes, respectively). During exercise, aural temperature demonstrated relatively steady state values increasing by 0.6+/-0.4 degrees C and 0.6+/-0.3 degrees C for the AB and PA athletes, respectively. The TP athlete demonstrated a gradual rise in aural temperature throughout the exercise period of 0.9 degrees C. Thigh skin temperature increased by 1.3+/-2.5 degrees C for the AB athletes (P<0.05) whereas the PA athletes demonstrated little change in temperature (0.1+/-3.4 degrees C and -0.7 degrees C respectively). Calf temperature increased for the PA athletes by 1.0+/-3.6 degrees C (P<0.05), whereas a decrease was observed for the AB athletes of -1.0+/-2.0 degrees C (P<0.05) during the exercise period. During 30 min of passive recovery, the AB athletes demonstrated greater decreases in aural temperatures than those for the PA athletes (P<0. 05). Aural temperature for the TP increased peaking at 5 min of recovery remaining elevated until the end of the recovery period. Fluid consumption and weight losses were similar for the AB and PA athletes (598+/-433 ml and 403+/-368 ml; 0.38+/-0.39 kg and 0.38+/-0. 31 kg, respectively), whereas changes in plasma volume were greater for the AB athletes (-9.8+/-5.8% and 4.36+/-4.9%, respectively; P<0. 05). CONCLUSION: The results of this study suggest that under the experimental conditions PA athletes are at no greater thermal risk than AB athletes. A relationship between the available muscle mass for heat production and sweating capacity appears evident for the maintenance of thermal balance. During recovery from exercise, decreases in aural temperature, skin temperature and heat storage were greatest for the AB athletes with the greatest capacity for heat loss and lowest for the TP athlete with the smallest capacity for heat loss. Initial observations on one TP athlete suggest substantial thermoregulatory differences when compared to AB and PA athletes.     

Convective and diffusive losses of vitamin C during haemodiafiltration session: a contributive factor to oxidative stress in haemodialysis patients.

BACKGROUND: Enhanced oxidative stress in haemodialysis (HD) patients may be considered as a risk factor for accelerated atherosclerosis. Reduced antioxidant defences include impairment in enzyme activities and decreased plasma levels of hydrophilic vitamin C (vit C), and cellular levels of lipophilic vitamin E (vit E). METHODS: We investigated plasma levels of vit C in 19 patients undergoing regular haemodiafiltration (HDF) (mean age 62+/-7 years) and in 1846 healthy elderly subjects (HS) (mean age 69+/-5 years). The contribution of convection and diffusion was determined using paired filtration dialysis (PFD), a modified HDF technique which physically separates convective from diffusive fluxes. Blood samples were collected before and after the HDF session; in addition at 60 min of HDF, samples were drawn from arterial lines (AL) and venous lines (VL), dialysate (D) and ultrafiltrate (UF). Blood levels of total vit C were determined using an HPLC fluorescence method. Markers of oxidative stress were also assessed in both populations as follows: levels of malondialdehyde (MDA) were determined by fluorometric assay, measurements of advanced oxidation protein products (AOPP) and glutathione peroxidase (GSH-Px) activity were performed by spectrophotometric assay, and plasma vit E content was obtained by an HPLC procedure. RESULTS: A significant reduction in plasma vit C level was observed in HDF patients when compared with HS (1.6+/-1.4 microg/ml in HDF vs 6.6+/-3.7 microg/ml in HS; P<0.01). The HDF session was associated with a dramatic reduction in vit C levels (1.87+/-1.57 microg/ml before HDF and 0.98+/-0.68 microg/ml after HDF); at 60 min of HDF, concentrations were as follows: AL=1.35+/-1.27 microg/ml; VL=0.37+/-0.31 microg/ml, D=0.40+/-0.34 microg/ml, UF=1.24+/-1.18 microg/ml; corresponding to a diffusive flux of 271 microg/min and a convective flux of 126 microg/min. Total loss of vit C could be assessed at 66 mg/session (8--230 mg/session). According to this loss of vit C, presence of an oxidative stress was demonstrated in HD population as shown by a significant increase in MDA (1.66+/-0.27 microM in HD vs 0.89+/-0.25 microM in HS; P<0.01) and AOPP (77.5+/-29.3 microM in HD vs 23.5+/-13.2 microM in HS; P<0.01) levels, and a decrease in GSH-Px activity (259.2+/-106.3 U/l in HD vs 661.2+/-92.2 U/l in HS; P<0.01). No change in plasma vit E between both populations (30.7+/-9.1 microM in HD vs 35.3+/-7.34 microM in HS) was observed. CONCLUSIONS: These results suggest that HDF with highly permeable membranes is associated with a significant loss of vit C. Diffusive transport is responsible for two-thirds whereas convective phenomenon accounts for only one-third of this loss.     

Ultrafiltration method for measuring vascular access flow rates during hemodialysis.

BACKGROUND: The vascular access blood flow rate (QA) has been shown to be an important predictor of vascular access failure; therefore, the routine measurement of QA may prove to be a useful clinical method of vascular access assessment. METHODS: We have developed a new ultrafiltration (UF) method for determining QA during HD from changes in arterial hematocrit (H) after abrupt changes in the UF rate with the dialysis blood lines in the normal (DeltaHn) and reverse (DeltaHr) configurations. This method accounts for cardiopulmonary recirculation and requires neither intravenous saline injections nor accurate knowledge of the dialyzer blood flow rate. Clinical studies were conducted in 65 chronic HD patients from three different dialysis programs to compare QA determined by the UF method with that determined by saline dilution using an ultrasound flow sensor. RESULTS: Arterial H increased (P<0.0001) after abrupt increases in the UF rate when the lines were in the normal and reverse configurations. An increase in the UF rate from the minimum setting to 1.8 liter/hr resulted in a DeltaHn of 0.3+/-0.2 (mean +/- SD) H units and a DeltaHr of 1.6+/-1.0 H units. Q(A) values determined by the UF method (1050+/-460 ml/min) were 16+/-25% higher (P<0.001) than those determined by saline dilution (950+/-440 ml/min); the calculated QA values by the UF and saline dilution methods correlated highly with each other (R = 0.92, P<0.0001). The average coefficient of variation for duplicate measurements of QA determined by the UF method in a subset of these patients (N = 21) was approximately 10% when assessed in either the same dialysis session or consecutive sessions. CONCLUSIONS: The results from this study show that changes in arterial H after abrupt changes in the UF rate can be used to assess Q(A).     

The vascular endothelin system is not overactive in normotensive hemodialysis patients

BACKGROUND: The hemodynamic significance of elevated endothelin-1 (ET) plasma levels in hemodialysis (HD) patients is unknown. Therefore, we studied the role of ET in the regulation of vascular tone in normotensive HD patients and matched healthy controls (C). METHODS: The forearm blood flow (FBF) responses to adenosine, norepinephrine, the ET-A receptor antagonist BQ-123 (40 nmol/min), the ET-B receptor antagonist BQ-788 (1 and 50 nmol/min), and ET (5 pmol/min) were measured. Results are percent of baseline change +/- SEM (baseline = 100%). RESULTS: Responses to adenosine and norepinephrine were both unchanged in HD. In HD, BQ-123 increased FBF less than in C (133 +/- 9 vs. 178 +/- 27%; P = 0.02). BQ-788 failed to change FBF in C but decreased FBF to 83 +/- 4% in HD. Compared to BQ-123 alone, BQ-123 plus BQ-788 (50 nmol/min) caused an additional increase of FBF (234 +/- 32%, P < 0.001) in C, but not in HD (139 +/- 14%). This additional increase was absent when BQ-788 was co-infused at 1 nmol/min. ET reduced FBF comparably in both groups. CONCLUSIONS: Resistance vessels of HD patients have unremarkable contractile properties, as shown by responses to adenosine and norepinephrine. In HD, the basal vascular ET-mediated tone is reduced. The main action of the ET-B receptor in C is vasoconstrictive, which also is blunted in HD. The intact response to exogenous ET indicates the normal function of ET receptors in HD. Our results could be explained by a reduced generation or reduced metabolic clearance rate of ET in normotensive HD patients. Controversy remains concerning the role of the ET-B receptor when comparing the present data with previously published literature.     

Role of the venous system in hemodynamics during ultrafiltration and bicarbonate dialysis.

A reduced venous compliance (VC) and inadequate venoconstriction may impair hemodynamics during hemodialysis, the first by impairing plasma volume preservation and by inducing a steep fall in central venous pressure (CVP) during minor plasma volume loss, the second by inadequate mobilization of hemodynamically inactive blood volume. For the protocol A, the relation between VC, the fall in plasma volume and the decline in central venous pressure (CVP) was assessed in 12 hemodialysis (HD) patients, aged 40 to 74 years, during isolated ultrafiltration (UF). The patients were ultrafiltrated for one hour at an UF rate of 1 to 1.5 liter/hr. VC was measured by strain gauge plethysmography with direct i.v. pressure measurements. CVP was assessed directly via a subclavian catheter. PVP was measured using the serial hematocrit method. VC correlated inversely with the fall in plasma volume (r = -0.66; P less than 0.025) and with the fall in CVP (corrected for UF volume) (r = -0.62; P less than 0.025). In the protocol B, the constriction of veins and resistance vessels was assessed sequentially during isolated UF and during UF combined with bicarbonate HD (UF + HD) by measuring the change in venous tone (VT) and vascular resistance (FVR) of the forearm. Twelve HD patients were studied (age 30 to 64 years). VT and FVR were measured using strain gauge plethysmography. The UF rate was equal during isolated UF and UF + HD (1 liter/hr). In six patients, the measurements were started with isolated UF and in six patients with UF + HD.(ABSTRACT TRUNCATED AT 250 WORDS)     

Impact of sodium and ultrafiltration profiling on haemodialysis-related hypotension.

BACKGROUND: Symptomatic hypotension is the most frequent complication in patients receiving haemodialysis (HD). Previous studies have reported that the use of modulating dialysate sodium concentration or ultrafiltration (UF) rates, or the combination use of sodium profile and UF profile may better preserve blood volume and reduce the incidence of hypotensive episodes. The aim of this study was to evaluate the effects of sodium balance-neutral sodium profile and UF profile and their combination on preservation of blood volume, cardiac function and occurrence of hypotensive episodes. METHODS: Using Fresenius MC 4008S, eight stable HD patients underwent four treatments: (1) control, constant dialysate sodium concentration of 138 mmol/l with constant UF; (2) sodium profile, a linearly decreasing dialysate sodium concentration (148-131 mmol/l) with constant UF; (3) UF profile, a linearly decreasing UF rate with dialysate sodium concentration of 138 mmol/l; (4) sodium+UF profile, combination of sodium and UF profile. Each treatment was applied in 10 dialysis sessions. Relative blood volume (RBV), mean blood pressure (MBP), heart rate (HR), interior vena cava diameter (IVCD), stroke volume (SV), cardiac output (CO), plasma sodium concentration and the frequency of symptomatic hypotension were monitored. RESULTS: There were no significant differences in the IVCD, MBP, SV, CO and body weight before dialysis between the three profiles and the control. The total plasma protein, haemoglobin, and intradialytic sodium mass removal showed similar results. Compared with the control, better preservation of RBV and MBP at 4 and 5 h and a higher stability in SV variation, but larger UF volume were achieved during sodium+UF profile (P<0.05, respectively), the incidence of intradialytic hypotension was significantly reduced (P<0.05). CONCLUSIONS: With the similar intradialytic sodium removal, during sodium balance-neutral linearly decreasing sodium profile combined with linearly decreasing UF profile, greater intradialytic stability of the blood volume, blood pressure and cardiac function could be obtained, and hypotensive episodes were significantly reduced.