Deep Forearm Vein Research Articles

Homocysteine exchange across skeletal muscle in patients with chronic kidney disease.

Sites and mechanisms regulating the supply of homocysteine (Hcy) to the circulation are unexplored in humans. We studied the exchange of Hcy across the forearm in CKD patients (n=17, eGFR 20 ± 2ml/min), in hemodialysis (HD)-treated patients (n=14) and controls (n=9). Arterial Hcy was ~ 2.5 folds increased in CKD and HD patients (p < 0.05-0.03 vs. controls). Both in controls and in patients Hcy levels in the deep forearm vein were consistently greater (+~7%, p < 0.05-0.01) than the corresponding arterial levels, indicating the occurrence of Hcy release from muscle. The release of Hcy from the forearm was similar among groups. In all groups arterial Hcy varied with its release from muscle (p < 0.03-0.02), suggesting that muscle plays an important role on plasma Hcy levels. Forearm Hcy release was inversely related to folate plasma level in all study groups but neither to vitamin B12 and IL-6 levels nor to muscle protein net balance. These data indicate that the release of Hcy from peripheral tissue metabolism plays a major role in influencing its Hcy plasma levels in humans and patients with CKD, and that folate is a major determinant of Hcy release.

Reliability of forearm oxygen uptake during handgrip exercise: assessment by ultrasonography and venous blood gas.

Assessment of forearm oxygen uptake (V˙O2) during handgrip exercise is a keenly investigated concept for observing small muscle mass metabolism. Although a combination of Doppler ultrasound measurements of brachial artery blood flow (Q˙) and blood gas drawn from a deep forearm vein has been utilized to calculate forearm V˙O2 for more than two decades, the applicability of this experimental design may benefit from a thorough evaluation of its reliability during graded exercise. Therefore, we evaluated the reliability of this technique during incremental handgrip exercise in ten healthy young (24 ± 3(SD) years.) males. V˙O2 and work rate (WR) exhibited a linear relationship (1.0 W: 43.8 ± 10.1 mL·min−1; 1.5 W: 53.8 ± 14.1 mL·min−1; 2.0 W: 63.4 ± 16.3 mL·min−1; 2.5 W: 72.2 ± 17.6 mL·min−1; 3.0 W: 79.2 ± 18.6 mL·min−1; r = 0.65, P < 0.01). In turn, V˙O2 was strongly associated with Q˙ (1.0 W: 359 ± 86 mL·min−1; 1.5 W: 431 ± 112 mL·min−1; 2.0 W: 490 ± 123 mL·min−1; 2.5 W: 556 ± 112 mL·min−1; 3.0 W: 622 ± 131 mL·min−1; r = 0.96; P < 0.01), whereas arteriovenous oxygen difference (a‐vO2diff) remained constant following all WRs (123 ± 11–130 ± 10 mL·L−1). Average V˙O2 test–retest difference was −0.4 mL·min−1 with ±2SD limits of agreement (LOA) of 8.4 and −9.2 mL·min−1, respectively, whereas coefficients of variation (CVs) ranged from 4–7%. Accordingly, test–retest Q˙ difference was 11.9 mL·min−1 (LOA: 84.1 mL·min−1; −60.4 mL·min−1) with CVs between 4 and 7%. Test–retest difference for a‐vO 2diff was −0.28 mL·dL−1 (LOA: 1.26mL·dL −1; −1.82 mL·dL−1) with 3–5% CVs. In conclusion, our results revealed that forearm V˙O2 determination by Doppler ultrasound and direct venous sampling is linearly related to WR, and a reliable experimental design across a range of exercise intensities.

Validity Of Forearm Oxygen Uptake During Handgrip Exercise

: Assessment of forearm oxygen uptake (V[Combining Dot Above]O2) during handgrip exercise is a keenly investigated concept for observing small muscle mass metabolism. Although a combination of Doppler-ultrasound measurements of brachial artery blood flow and blood gas drawn from a deep forearm vein has been utilized to calculate forearm V[Combining Dot Above]O2 for more than two decades, this experimental design has, somewhat surprisingly, not been validated. PURPOSE: To evaluate the reliability and accuracy of this technique following handgrip exercise. METHODS: Test-retest measurements were performed with ~0.25 watt (W) steady state increments in ten healthy young (24±3(SD) yrs.) males during handgrip exercise. RESULTS: V[Combining Dot Above]O2and workload exhibited a linear relationship(p<0.01)following all submaximal workloads (0.50W:43.8±10.1mL·min-1; 0.75W:53.8±14.1mL·min-1;1.00W:63.4±16.3mL·min-1;1.25W:72.2±17.6mL·min-1), while the final increment before exhaustionwas non-significant, marking a V[Combining Dot Above]O2-plateau (1.5W:79.2±18.6mL·min-1). In turn, blood flow exhibited a concomitant relationship (p<0.01) with V[Combining Dot Above]O2(0.50W:359±86mL·min-1; 0.75W:431±112mL·min-1; 1.00W:490±123mL·min-1; 1.25W:556±112mL·min-1; 1.50W:622±131mL·min-1) while arteriovenous oxygen difference (a-vO2diff) remained constant following all workloads (123±11-130±10mL·L-1).The average V[Combining Dot Above]O2test-retest difference was -0.4mL·min-1 with ±2SD limits of agreement (LOA) of 8.4 and -9.2mL·min-1, respectively, while coefficients of variation (CV) ranged from 4-7%. Accordingly, test-retest blood flow difference was 11.9mL·min-1(LOA:84.1mL·min-1; -60.4mL·min-1) andagain CV ranged between 4-7%. Test-retest difference for a-vO2diff was -0.28mL·dL-1(LOA: 1.26mL·dL-1; -1.82mL·dL-1) with CV ranging from 3-5%. CONCLUSION: Our results reveal that forearm V[Combining Dot Above]O2-assessment by Doppler-ultrasound and direct venous sampling is a valid experimental design across a range of exercise intensities, and suggest that this method can be applied for assessment of small muscle mass metabolism in occupationally relevant forearm musculature.

Blood Flow Regulation and Oxygen Uptake during High Intensity Forearm Exercise

The vascular strain is very high during heavy handgrip exercise, but the intensity and kinetics to reach peak blood flow, and peak oxygen uptake, are uncertain. PURPOSE: We included 9 young (25±2yr) healthy males to evaluate blood flow and oxygen uptake responses during continuous dynamic handgrip exercise with increasing intensity. METHODS: Blood flow was measured using Doppler-ultrasound and venous blood was drawn from a deep forearm vein to determine arteriovenous oxygen difference (a-vO2diff) during 6-minutes bouts of 60, 80 and 100% of maximal work rate (WRmax), respectively. RESULTS: Blood flow and oxygen uptake increased (p<0.05) from 60%WRmax (557±177(SD) mL[BULLET OPERATOR]min-1; 56.0±21.6 mL[BULLET OPERATOR]min-1) to 80%WRmax (679±190 mL[BULLET OPERATOR]min-1; 70.6±24.8 mL[BULLET OPERATOR]min-1), but no change was seen from 80%WRmax to 100%WRmax. Blood velocity (49.5±11.5 cm[BULLET OPERATOR]sec-1 to 58.1±11.6 cm[BULLET OPERATOR]sec-1) and brachial diameter (0.49±0.05cm to 0.50±0.06 cm) showed concomitant increases (p<0.05) with blood flow from 60% to 80%WRmax, while no differences were observed in a-vO2diff. Shear rate also increased (p<0.05) from 60% (822±196 s-1) to 80% (951±234 s-1) of WRmax. The mean response time (MRT) was slower (p<0.05) for blood flow (60%WRmax:50±22s; 80%WRmax:51±20s; 100%WRmax:51±23s) than a-vO2diff (60%WRmax:29±9s; 80%WRmax:28±5s; 100%WRmax:20±5s), but not different from oxygen uptake (60%WRmax:44±25s; 80%WRmax:43±14s; 100%WRmax:41±32s). No differences were observed in MRT for blood flow or oxygen uptake with increased exercise intensity. CONCLUSION: When approaching maximal intensity, oxygen uptake appeared to reach a critical level at ~80% of WRmax and be regulated by blood flow. This implies that high, but not maximal, exercise intensity may be an optimal stimulus for shear stress-induced small muscle mass training adaptations.

Blood flow regulation and oxygen uptake during high-intensity forearm exercise.

The vascular strain is very high during heavy handgrip exercise, but the intensity and kinetics to reach peak blood flow, and peak oxygen uptake, are uncertain. We included 9 young (25 ± 2 yr) healthy males to evaluate blood flow and oxygen uptake responses during continuous dynamic handgrip exercise with increasing intensity. Blood flow was measured using Doppler-ultrasound, and venous blood was drawn from a deep forearm vein to determine arteriovenous oxygen difference (a-vO2diff) during 6-min bouts of 60, 80, and 100% of maximal work rate (WRmax), respectively. Blood flow and oxygen uptake increased (P < 0.05) from 60%WRmax [557 ± 177(SD) ml/min; 56.0 ± 21.6 ml/min] to 80%WRmax (679 ± 190 ml/min; 70.6 ± 24.8 ml/min), but no change was seen from 80%WRmax to 100%WRmax Blood velocity (49.5 ± 11.5 to 58.1 ± 11.6 cm/s) and brachial diameter (0.49 ± 0.05 to 0.50 ± 0.06 cm) showed concomitant increases (P < 0.05) with blood flow from 60% to 80%WRmax, whereas no differences were observed in a-vO2diff Shear rate also increased (P < 0.05) from 60% (822 ± 196 s-1) to 80% (951 ± 234 s-1) of WRmax The mean response time (MRT) was slower (P < 0.05) for blood flow (60%WRmax 50 ± 22 s; 80%WRmax 51 ± 20 s; 100%WRmax 51 ± 23 s) than a-vO2diff (60%WRmax 29 ± 9 s; 80%WRmax 29 ± 5 s; 100%WRmax 20 ± 5 s), but not different from oxygen uptake (60%WRmax 44 ± 25 s; 80%WRmax 43 ± 14 s; 100%WRmax 41 ± 32 s). No differences were observed in MRT for blood flow or oxygen uptake with increased exercise intensity. In conclusion, when approaching maximal intensity, oxygen uptake appeared to reach a critical level at ~80% of WRmax and be regulated by blood flow. This implies that high, but not maximal, exercise intensity may be an optimal stimulus for shear stress-induced small muscle mass training adaptations.NEW & NOTEWORTHY This study evaluated blood flow regulation and oxygen uptake during small muscle mass forearm exercise with high to maximal intensity. Despite utilizing only a fraction of cardiac output, blood flow reached a plateau at 80% of maximal work rate and regulated peak oxygen uptake. Furthermore, the results revealed that muscle contractions dictated bulk oxygen delivery and yielded three times higher peak blood flow in the relaxation phase compared with mean values.

Prior Exercise And Ischemia Affect Blood Flow And Oxygen Uptake During Subsequent Heavy Forearm Exercise

Enhanced blood flow (BF) by prior exercise is associated with acceleration of muscle oxygen uptake (VO2musc) kinetics during subsequent heavy exercise. PURPOSE: We tested the influence of enhanced forearm BF by exercise and circulatory occlusion on VO2musc onset kinetics. METHODS: Seven varsity ice hockey players completed three heavy forearm exercise bouts (5-min at 30 % MVC 14.1 ± 1.2 kg) in two different sessions: [1] control, heavy exercise followed immediately by 2 minutes of circulatory occlusion; [2] heavy bout 8-min after control; [3] heavy bout 3-min after release of 5-min forearm occlusion that included 1-min moderate hand-grip exercise. BF was measured continuously using Doppler ultrasound and venous blood was sampled every 15 seconds from a deep forearm vein to determine O2 extraction. RESULTS: BF was elevated prior to bout [2] and [3] compared to the control at baseline ([2], 318.2 ± 51.7; [3], 282.1 ± 30.9 vs. control, 69.0 ± 13.4 mL/min, P< 0.01), however baseline VO2musc was significantly higher only prior to bout [2] (10.1 ± 2.6 vs. 4.0 ± 1.0 mLO2/min, P< 0.01). Neither BF nor VO2musc were different at end exercise among the three heavy bouts. BF and VO2musc were significantly higher during the first 2-min of bout [2] compared to both bout [3] and control. Prior occlusion slightly enhanced the onset BF and VO2musc kinetics during bout [3] with a significant increase at 45 sec compared to control (BF: 375.8 ± 75.4 vs. 312.9 ± 79.9 mL/min; VO2mus: 51.2 ± 15.9 vs. 41.9 ± 16.1 mLO2/min, P< 0.05). The calculated VO2mus area during the first two minutes of exercise was significantly greater in bout [2] than the areas of both bout [3] and control ([2], 113.9 ± 39.1 vs. [3], 93.7 ± 28.7; control, 84.3 ± 30.2 mLO2, P< 0.01). These results indicate a greater contribution from oxidative phosphorylation at the onset of a heavy bout that followed heavy exercise and occlusion compared to that which followed occlusion with moderate exercise. CONCLUSION: We employed two protocols which enhanced BF prior to a subsequent heavy exercise bout (heavy exercise followed by occlusion and moderate exercise during occlusion); however the major impact on oxidative metabolism was seen only following heavy exercise. Supported by Egyptian Culture and Educational Bureau in Canada and NSERC

Use of Deep Forearm Veins as an Outflow for Arteriovenous Graft Access

An adequate strategy for selecting venous outflow for repeated vascular access plays a major role in determining the long term survival of patients in a haemodialysis programme. Since the first description of the method for creating an arteriovenous (AV) fistula by Brescia et al., numerous techniques and materials have been tried in order to achieve better patency rates. However, failure of vascular access continues to be the main cause of hospital admission in haemodialysis patients. Although surgery for vascular access is commonly performed by most vascular surgeons, the search for a suitable venous outflow is often hampered by the progressive exhausting of superficial veins, due to repeated punctures or failure of previously fashioned access conduits. An AV graft constructed in a loop fashion, between the brachial artery and the superficial forearm veins, is the usual technique in most centres. However, the use of deep forearm veins as an outflow for an AV, and their role as an alternative choice after a previously failed fistula, has scarcely been analysed. In this short report, a description of the procedure and preliminary results are discussed.

Post-absorptive and insulin-mediated muscle protein metabolism in liver-transplanted patients.

Cirrhotic patients after liver transplantation show a near-normal glucose homeostasis when in stable condition. In contrast, the basal and insulin-mediated whole-body protein metabolism remain altered several years after the graft. To examine whether the persisting defect of protein metabolism was due to the muscle, 7 non-diabetic liver-transplanted patients in stable condition were studied by means of the catheterization of the brachial artery and the deep forearm vein (to measure the balance across the forearm) and the infusion of labelled leucine and phenylalanine associated with indirect calorimetry. Whole-body proteolysis (as determined by endogenous leucine flux, ELF), protein synthesis (from non-oxidative leucine disposal, NOLD) and leucine oxidation (LO) were reduced in comparison to previously obtained values in a normal population. Insulin infusion (while maintaining euglycemia) induced a not significant variation of forearm phenylalanine Ra (24.4-->16.5 micromol/100 ml forearm min(-1); proteolysis) and Rd (18.5-->19.7; protein synthesis). In contrast, the whole-body insulin-dependent inhibitions of ELF (31.5-->21.8 micromol/m(2) min) and NOLD (27.3-->18.4) were impaired with respect to a normal population. On the basis of the present results, we conclude that skeletal muscle is not responsible for the alterations of leucine metabolism persisting after liver transplantation. By exclusion, this points to the liver as the major determinant of the leucine metabolism defect.

Early Result of Arteriovenous Graft with Deep Forearm Veins as an Outflow in Hemodialysis Patients

The purpose of this study was to evaluate the result of arteriovenous (A-V) grafting with the deep forearm veins as an outflow system in hemodialysis patients. Between June 1999 and July 2001, 27 A-V grafts consisting of ePTFE and deep forearm veins were constructed in 26 patients. All patients followed up for assessment of all relevant values, and the median follow-up period was 17.3 months. Seven grafts (26%) failed during the follow-up. The patency rates were 93% and 80% at 3 months and 12 months, respectively. No difference in patency rate was found between males and females, or between diabetics and nondiabetics. Graft-related complications, excluding graft thrombosis, occurred in five patients. These included operative wound dehiscence in two cases, a graft infection, a seroma, and a mild hypoperfusion in the hand. We conclude that the early patency rate of A-V graft using the forearm deep veins as an outflow system is very good and that this technique may be a recommended surgical modality for vascular access in patients with exhausted superficial veins.

Prosthetic Graft Placement Using the Deep Forearm Veins in Hemodialysis Patients: A Preliminary Report

When the superficial arm veins are not suitable for the creation of a conventional endogenous arteriovenous (A-V) fistula or the placement of a prosthetic graft in the forearm, the use of the deep forearm veins as an outflow system to construct an A-V graft access seems to be a reasonable alternative. Using this approach, we placed 6 prosthetic grafts in 6 hemodialysis patients in whom conventional methods had failed. Adequate functioning of this ‘deep vein’-type vascular access in these 6 patients has been maintained for 3, 6, 11, 15, 19 and 24 months, respectively, without complications or any need for further interventions. Only one graft failed after 6 months. Our preliminary results indicate that this technique can be used successfully when the superficial forearm veins have been exhausted, thus avoiding the use of upper-arm or axillary veins.

Direct measurement of the lumped constant for 2-deoxy-[1-14C]glucose in vivo in human skeletal muscle

The lumped constant (LC) is used to convert the clearance rate of 2-deoxy-D-glucose (2-DG(CR)) to that of glucose (Glc(CR)). There are currently no data to validate the widely used assumption of an LC of 1.0 for human skeletal muscle. We determined the LC for 2-deoxy-[1-(14)C]glucose (2-DG) in 18 normal male subjects (age, 29+/- 2 yr; body mass index, 24.8+/-0.8 kg/m(2)) after an overnight fast and during physiological (1 mU x kg(-1) x min(-1) insulin infusion for 180 min) and supraphysiological (5 mU x kg(-1) x min(-1) insulin infusion for 180 min) hyperinsulinemic conditions. Normoglycemia was maintained with the euglycemic clamp technique. The LC was measured directly with the use of a novel triple tracer-based method. [3-(3)H]glucose, 2-[1-(14)C]DG, and [(12)C]mannitol (Man) were injected as a bolus into the brachial artery. The concentrations of [3-(3)H]glucose and 2-[1-(14)C]DG (dpm/ml plasma) and of Man (micromol/l) were determined in 50 blood samples withdrawn from the ipsilateral deep forearm vein over 15 min after the bolus injection. The LC was calculated by a formula involving blood flow calculated from Man and the Glc(CR) and 2-DG(CR). The LC averaged 1.26+/-0.08 (range 1.06-1.43), 1.15+/-0.05 (0.99-1.39), and 1.18+/-0.05 (0.97-1.37) under fasting conditions and during the 1 and 5 mU x kg(-1). min(-1) insulin infusions (not significant between the different insulin concentrations, mean LC = 1.2, P<0.01 vs. 1.0). We conclude that, in normal subjects, the LC for 2-DG in human skeletal muscle is constant over a wide range of insulin concentrations and averages 1. 2.

Antecubital Jump Revisions for Salvaging Hemodialysis Grafts

When expanded polytetrafluoroethylene (PTFE) is used for hemodialysis access, the authors' initial preference is a forearm loop arteriovenous (AV) graft below the antecubital fossa. However, AV graft thrombosis remains a significant problem caused mainly by venous outflow hyperplasia and managed often by either surgical or radiologic thrombectomy and angioplasty. At the time of surgical revision, the lack of an adequate superficial or deep forearm outflow vein below the elbow would require an antecubital (across the elbow) jump bypass revision to a more proximal upper arm vein to salvage the original forearm AV graft. With an increasing interest in monitoring the specific outcomes of the different surgical interventions used to salvage thrombosed hemoaccess, the authors reviewed their most recent 24--month experience of 32 antecubital jump revisions using ring reinforced PTFE. The mean primary patency of these antecubital jump revisions was 8.2 months with 18 presently patent. AV grafts revisions using antecubital jump grafts confer additional patency; they are another important method for salvaging thrombosed AV hemodialysis grafts.

Glycerol and nonesterified fatty acid metabolism in human muscle and adipose tissue in vivo.

To determine the relationship between glycerol and nonesterified fatty acid (NEFA) release from adipose tissue, and to test whether forearm muscle and abdominal adipose tissue are capable of extracting these two lipolytic products from the circulation, 13 male subjects were studied after an overnight fast during combined infusion of radiolabeled palmitate and glycerol. Blood samples were taken from a radial artery, a deep forearm vein, and a superficial abdominal vein before and during a 2-h infusion of glucose at approximately 7 mg. kg-1. min-1. The ratio of the appearance rates of total NEFA to glycerol was approximately 3/1 during the baseline period but decreased to 1.3/1 during glucose infusion. There was significant extraction of both glycerol and NEFA by forearm muscle. In contrast, there was no apparent uptake of glycerol by adipose tissue. Adipose tissue NEFA uptake was undetectable during the baseline period but became significant during glucose infusion. These data indicate that there is very little to no in situ reesterification of NEFA in adipose tissue after an overnight fast. During glucose infusion, there was apparently a relative increase in the fraction of glycerol derived from the action of lipoprotein lipase and an increase in reesterification in situ.

An in vivo study of the cortisol-cortisone shuttle in subcutaneous abdominal adipose tissue.

Previous in vitro studies have demonstrated significant 11-beta hydroxysteroid dehydrogenase (11 beta-HSD) oxo-reductase activity in visceral, but not subcutaneous adipose stromal cells. We have conducted an in vivo study of the cortisol-cortisone shuttle in subcutaneous abdominal adipose tissue. We measured arteriovenous (A-V) differences in serum cortisol and cortisone across subcutaneous abdominal adipose tissue and forearm muscle in a heterogeneous group of subjects. We studied 34 subjects (male:female = 12:22), age median (interquartile range) 45 (19-65) years, body mass index 32.7 (20.4-77.1) kg m-2, total body fat 34.4 (5.6-119.1) kg. Serum cortisol and cortisone were measured in serum samples from a radial artery, superficial epigastric vein and deep forearm vein. Abdominal adipose and forearm blood flow rates were measured by 133Xenon washout and plethysmography, respectively. For cortisone, there was significant (P < 0.001) clearance by adipose tissue, with an A-V difference of 4 (1-7) nmol/l. For cortisol there was a trend for arterial concentrations (203 (142-292) nmol/l) to be lower than venous (225 (152-263) nmol/l), but this was not significant. The adipose tissue cortisone clearance rate correlated with total body fat (r = 0.35, P = 0.05). We have demonstrated 11 beta-HSD oxo-reductase activity in subcutaneous abdominal adipose tissue, which may be increased in obesity.

Whole body, adipose tissue, and forearm norepinephrine kinetics in lean and obese women

We evaluated whole body and regional (subcutaneous abdominal adipose tissue and forearm) norepinephrine (NE) kinetics in seven lean (body mass index 21.3 +/- 0.5 kg/m2) and six upper body obese (body mass index 36.4 +/- 0.4 kg/m2) women who were matched on fat-free mass. NE kinetics were determined by infusing [3H]NE and obtaining blood samples from a radial artery, a deep forearm vein draining mostly skeletal muscle, and an abdominal vein draining subcutaneous abdominal fat. Mean systemic NE spillover tended to be higher in obese (2.82 +/- 0.49 nmol/min) than in lean (2.53 +/- 0.40 nmol/min) subjects, but the differences were not statistically significant. Adipose tissue and forearm NE spillover rates into plasma were greater in lean (0.91 +/- 0.08 pmol. 100 g tissue-1. min-1 and 1.01 +/- 0.09 pmol. 100 ml tissue-1. min-1, respectively) than in obese (0.26 +/- 0.05 pmol. 100 g tissue-1. min-1 and 0.58 +/- 0.11 pmol. 100 ml tissue-1. min-1, respectively) subjects (P < 0.01). These results demonstrate that adipose tissue is an active site for NE metabolism in humans. Adipose tissue NE spillover is considerably lower in obese than in lean women, which may contribute to the lower rate of lipolysis per kilogram of fat mass observed in obesity.

Role of tissue-specific blood flow and tissue recruitment in insulin-mediated glucose uptake of human skeletal muscle.

Conflicting evidence exists concerning whether insulin-induced vasodilation plays a mechanistic role in the regulation of limb glucose uptake. It can be predicted that if insulin augments blood flow by causing tissue recruitment, this mechanism would enhance limb glucose uptake. Twenty healthy subjects were studied with the forearm perfusion technique in combination with the euglycemic insulin clamp technique. Ten subjects were studied at physiological insulin concentrations (approximately 400 pmol/L) and the other 10 at supraphysiological insulin concentrations (approximately 5600 pmol/L). Four additional subjects underwent a saline control study. Pulse injections of a nonmetabolizable extracellular marker (1-[3H]-L-glucose) were administered into the brachial artery, and its washout curves were measured in one ipsilateral deep forearm vein and used to estimate the extracellular volume of distribution and hence the amount of muscle tissue drained by the deep forearm vein. Both during saline infusion and at physiological levels of hyperinsulinemia we observed no changes in blood flow and/or muscle tissue drained by the deep forearm vein. However, supraphysiological hyperinsulinemia accelerated total forearm blood flow (45.0+/-1.8 versus 36.5+/-1.3 mL x min(-1) x kg(-1), P<0.01) and increased the amount of muscle tissue drained by the deep forearm vein (305+/-46 versus 229+/-32 g, P<0.05). The amount of tissue newly recruited by insulin was strongly correlated to the concomitant increase in tissue glucose uptake (r=0.789, P<0.01). Acceleration of forearm blood flow mediated by supraphysiological hyperinsulinemia is accompanied by tissue recruitment, which may be a relevant determinant of forearm (muscle) glucose uptake.

Primary antecubital jump bypass grafts for hemoaccess

The endogeneous Brescia-Cimino arteriovenous (AV) fistula remains the gold standard for longterm hemoaccess in patients on chronic hemodialysis, but can only be constructed in a minority of patients. AV bridge grafts, usually of expanded polytetrafluoroethylene (PTFE), have been a reasonable alternative for most of the remaining hemodialysis patients, however. Our initial preference when PTFE is required for hemoaccess is to construct an AV graft configured as a forearm loop anastomosed to vessels located totally below the antecubital fossa. When both the superficial and deep forearm outflow veins are considered inadequate, a primary antecubital jump bypass (PAJB) across the elbow to a more proximal upper arm vein salvages use of that forearm hemoaccess site (Fig. 1). With no identified series to reference for concerns of longterm patency after crossing the antecubital fossa we decided to review both our specific surgical technique and our most recent patient experience.

Glycerol production and utilization in humans: sites and quantitation

Liver is assumed to be the major site of glycerol uptake and fatty acid reesterification. [U-13C]glycerol was infused into ten 60 h-fasted healthy subjects. Measured were 1) blood glycerol concentrations and 13C enrichments in brachial and pulmonary arteries and in hepatic, renal, superficial, and deep forearm veins; 2) glycerol appearance rates in systemic circulation; and 3) splanchnic bed and kidney glycerol uptakes with use of balance and tracer methodology. Glycerol concentrations were one-fifth in hepatic, one-half in renal, 40% more in superficial, and the same in deep vein and pulmonary artery as in brachial artery blood. Glycerol enrichments were one-fifth in hepatic, two-thirds to three-quarters in renal and superficial veins, and the same in pulmonary as in brachial artery blood. Splanchnic glycerol uptake was 29% and kidney glycerol uptake was 17% of glycerol's rate of appearance, 5.11 mumol.min-1.kg-1. Splanchnic fatty acid uptake was 25% of calculated fatty acid release. Glycerol contributed 15% to glucose production. Most of the [13C]glycerol uptake by splanchnic bed and kidneys was incorporated into glucose. Thus, in 60 h-fasted individuals, most glycerol uptake does not occur in liver, and the extent of fatty acid reesterification in liver is in doubt.

Phenylalanine kinetics in human adipose tissue.

Very little is known about the regulation of protein metabolism in adipose tissue. In this study systemic, adipose tissue, and forearm phenylalanine kinetics were determined in healthy postabsorptive volunteers before and during a 2-h glucose infusion (7 mg.kg-1.min-1). [3H]Phenylalanine was infused and blood was sampled from a radial artery, a subcutaneous abdominal vein, and a deep forearm vein. Adipose tissue and forearm blood flow were measured with 133Xe and plethysmography, respectively, and body fat mass was determined by dual energy x-ray absorptiometry. During glucose infusion, glucose concentration increased from 86 +/- 2 to 228 +/- 13 mg/dl and insulin concentration increased from 6.6 +/- 0.6 to 35.0 +/- 3.9 mU/liter, both P < 0.001. Systemic phenylalanine appearance decreased from 40.3 +/- 1.9 to 37.0 +/- 1.6 mumol/min during glucose infusion (P < 0.05). Baseline whole body adipose tissue phenylalanine release (5.2 +/- 1.4 mumol/min) was approximately 12% of systemic phenylalanine appearance and decreased (P < 0.05) to 2.3 +/- 0.9 mumol/min during glucose infusion. In contrast, phenylalanine release from the forearm did not change during glucose infusion. These results indicate that adipose tissue is a small but significant contributor to systemic phenylalanine appearance. Phenylalanine release from adipose tissue like lipolysis, is relatively sensitive to hyperinsulinemia.

Roles of Glucose Transport and Glucose Phosphorylation in Muscle Insulin Resistance of NIDDM

Insulin resistance for glucose metabolism in skeletal muscle is a key feature in NIDDM. The quantitative role of the cellular effectors of glucose metabolism in determining this insulin resistance is still imperfectly known. We assessed transmembrane glucose transport and intracellular glucose phosphorylation in vivo in skeletal muscle in nonobese NIDDM patients. We performed euglycemic insulin clamp studies in combination with the forearm balance technique (brachial artery and deep forearm vein catheterization) in five nonobese NIDDM patients and seven age- and weight-matched control subjects (study 1). D-Mannitol (a nontransportable molecule), 3-O-[14C]methyl-D-glucose (transportable, but not metabolizable) and D[3-3H]glucose (transportable and metabolizable) were simultaneously injected into the brachial artery, and the washout curves were measured in the deep venous effluent blood. In vivo rates of transmembrane transport and intracellular phosphorylation of D-glucose in forearm muscle were determined by analyzing the washout curves with the aid of a multicompartmental model of glucose kinetics in forearm tissues. At similar steady-state concentrations of plasma insulin (approximately 500 pmol/l) and glucose (approximately 5.0 mmol/l), the rates of transmembrane influx (34.3 +/- 9.1 vs. 58.5 +/- 6.5 micromol x min(-1) x kg(-1), P < 0.05) and intracellular phosphorylation (5.4 +/- 1.6 vs. 38.8 +/- 5.1 micromol x min(-1) x kg(-1), P < 0.01) in skeletal muscle were markedly lower in the NIDDM patients than in the control subjects. In the NIDDM patients (study 2), the insulin clamp was repeated at hyperglycemia, (approximately 13 mmol/l) trying to match the rates of transmembrane glucose influx measured during the clamp in the controls. The rate of transmembrane glucose influx (62 +/- 15 micromol x min(-1) x kg(-1)) in the NIDDM patients was similar to the control subjects, but the rate of intracellular glucose phosphorylation (16.6 +/- 7.5 micromol x min(-1) x kg(-1)), although threefold higher than in the patients during study 1 (P < 0.05), was still approximately 60% lower than in the control subjects (P < 0.05). These data suggest that when assessed in vivo, both transmembrane transport and intracellular phosphorylation of glucose are refractory to insulin action and add to each other in determining insulin resistance in skeletal muscle of NIDDM patients. It will be of interest to compare the present results with the in vivo quantitation of the initial rate of muscle glucose transport when methodology to perform this measurement becomes available.