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PubMed1990

Habitation and recovery of vascular responses in calf and forearm and of the level of pain sensation during the cold pressor test in man.

Forearm and calf blood flow were measured using a mercury-in-silastic gauge during immersion of one foot in water at 4 degrees C. The subjects were asked to assess the level of pain on a scale 0-10. The effects of one session of repeated immersions on the vascular response in the calf, forearm and on subjective pain sensation were studied. In 6 of the 14 subjects vasodilatation was elicited in both forearm and calf during the first immersion. During the first session the vasodilation diminished, while subjective pain sensation remained at the level of 7 on the scale. In 4 subjects vasoconstriction in both calf and forearm occurred during the first immersion. During repeated immersions forearm vasoconstriction subsided, while in the calf it remained at the same level. The level of the subjective pain sensation diminished from 7.5 to 5 in 1 subject. Repeated immersions in six to ten daily sessions led to reduction of vasodilatation in calf and forearm while there was a small change in the pain sensation, i.e. reduction from the level of 6.9 to 5.7 (P less than 0.01). In subjects in whom vasoconstriction in forearm and calf was observed no clear trend in vascular responses was observed during the repeated daily sessions while the pain sensation in 1 subject was reduced from 6 to 4.8. In 3 subjects the change of vascular responses was different in the forearm and calf.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1994

The effects of 7-hour local hyperglycaemia on forearm macro and microcirculatory blood flow and vascular reactivity in healthy man.

Animal studies suggest that hyperglycaemia directly affects local blood flow and vascular reactivity. We studied the effects of 7 h of local forearm hyperglycaemia, on forearm (muscle) and skin microcirculatory blood flow in 12 healthy men. Furthermore, the effects of this local hyperglycaemia on forearm vasoreactivity to noradrenaline were studied. Using the perfused forearm technique, a local hyperglycaemia of approximately 16 mmol/l was induced by continuous intraarterial infusion of 5% glucose. All subjects received both glucose and placebo (0.9% NaCl) infusions on two different occasions, in random order and blinded for the subjects. Forearm (muscle) blood flow and vascular reactivity to noradrenaline were measured using venous occlusion plethysmography. Skin microcirculatory blood flow was evaluated using intravital capillary microscopy (nutritive blood flow) and laser-Doppler fluxmetry (thermoregulatory blood flow). Measurements were performed at baseline, after 4 h, and after 7 h of intraarterial glucose or placebo infusion. During local glucose infusion there was a slight increase in the levels of insulin, C-peptide, systemic glucose, and blood pressure, compared to the placebo experiments. No differences were observed in forearm blood flow and laser-Doppler flux ratio (infused: contralateral arm), as well as in capillary blood cell velocity between glucose and placebo experiments. Noradrenaline produced similar reductions in forearm blood flow ratio during glucose and placebo experiments. We conclude that in contrast to animal studies, local hyperglycaemia (approximately 16 mmol/l) for 7 h does not affect forearm macro and microcirculatory blood flow or vascular reactivity to noradrenaline in man.

Adult↗

PubMed1992

Forearm temperature profile during the transient phase of thermal stress.

The transient temperature response of the resting human forearm immersed in water at temperatures (Tw) ranging from 15 to 36 degrees C was investigated. Tissue temperature (Tt) was continuously monitored by a calibrated multicouple probe during the 3-h immersions. Tt was measured every 5 mm, from the longitudinal axis of the forearm to the skin surface. Skin temperature, rectal temperature, and blood flow (Q) were also measured during the immersions. The maximum rate of change of the forearm mean tissue temperature (Tt, max) occurred during the first 5 min of the immersion. Tt, max was linearly dependent on Tw (P less than 0.001), with mean values (SEM) ranging from -0.8 (0.1) degrees C.min-1 at 15 degrees C to 0.2 (0.1) degrees C.min-1 at 36 degrees C. The maximum rate of change of compartment mean temperature was dependent (P less than 0.001) on the radial distance from the longitudinal axis of the forearm. The half-time for thermal steady state of the forearm mean tissue temperature was linearly dependent on Tw between 30 and 36 degrees C (P less than 0.01), with mean values (SEM) ranging from 15.6 (0.6) min at 30 degrees C to 9.7 (1.2) min at 36 degrees C and not different between 15 and 30 degrees C, averaging 16.2 (0.6) min. There was a significant linear relationship between the half-time for thermal steady-state of the compartment mean temperature and the radial distance from the longitudinal axis of the forearm for each value of Tw tested (P less than 0.001). The data of the present study suggest that the forearm Q is an important determinant of the transient thermal response of the forearm tissue during thermal stress.

Adult↗

PubMed1991

Impaired forearm vasodilatation by acetylcholine in patients with hypertension.

The aim of this study was to examine if vasodilatory responses to acetylcholine or sodium nitroprusside are altered in subjects with essential hypertension. In patients with essential hypertension (mean BP; 121 +/- 4 mmHg, n = 14) and age-matched control subjects (mean BP; 88 +/- 3 mmHg, n = 10), the forearm vasodilatory responses to acetylcholine and sodium nitroprusside were examined. The brachial artery was cannulated with a cannula through which drugs were locally infused. During the drug infusions, forearm blood flow was continuously measured using plethysmography. Basal forearm vascular resistance was higher in patients with essential hypertension than in control subjects (27.5 +/- 3.8 vs 13.8 +/- 1.7 units, P less than 0.01). The increases in forearm blood flow or decreases in forearm vascular resistance in response to the infusions of acetylcholine were smaller in patients with essential hypertension than in control subjects (P less than 0.01). However, the increases in forearm blood flow or decreases in forearm vascular resistance in response to the infusions of sodium nitroprusside were similar for the 2 groups. These results may suggest that the endothelium-dependent vasodilatory response to acetylcholine in the forearm resistance arteries is impaired in patients with essential hypertension.

Acetylcholine↗

PubMed1992

Impaired forearm vasodilation to hyperosmolal stimuli in patients with congestive heart failure secondary to idiopathic dilated cardiomyopathy or to ischemic cardiomyopathy.

Patients with congestive heart failure (CHF) have impaired peripheral vasodilation during exercise. Hyperosmolality is one local stimulus that produces vasodilation during exercise in normal subjects. This study addressed the hypothesis that vasodilation to hyperosmolal stimuli is impaired in patients with CHF. Forearm blood flow responses to intrabrachial artery infusions of isoosmolar (280 mosm/kg) and hyperosmolal (480 and 660 mosm/kg) solutions of saline and glucose were compared in 9 patients with CHF and 13 normal subjects. Forearm blood flow was measured by strain gauge plethysmography. In the normal subjects, hyperosmolal infusions of 480 and 660 mosm/kg increased forearm blood flow by 3.12 +/- 0.40 and 6.80 +/- 0.67 ml/min/100 ml forearm volume, respectively (both p < 0.001 compared with isoosmolal infusions). In contrast, in the patients with CHF, these infusions increased forearm blood flow by 2.19 +/- 0.44 and 4.06 +/- 0.92 ml/min/100 ml forearm volume (p < 0.05 normal vs CHF). The impaired forearm blood flow responses in heart failure occurred despite significantly greater (p < 0.05, normal vs CHF) increases in venous osmolality (17.3 +/- 6.5 vs 9.6 +/- 1.3 mosm/kg for the 660 mosm/kg infusion). There were no differences between groups in forearm venous hematocrit, calcium, and sodium or potassium changes during hyperosmolal infusions. It is concluded that peripheral vasodilation to hyperosmolal stimuli is impaired in patients with CHF.

Adult↗

PubMed1990

Unresponsiveness of forearm hemodynamics to omega-3 polyunsaturated fatty acids and aspirin.

Prostaglandin synthesis has been reported to change with aspirin ingestion via cyclooxygenase enzyme inhibition and with marine oil supplementation via an increase in the metabolism of 3-series eicosanoids. This study investigated the effects of pharmacological manipulations of prostaglandin metabolism on forearm hemodynamics and blood pressure. The agents studied were omega-3 fatty acids and aspirin. In the omega-3 fatty acid study, two groups of normal volunteers (N = 10/group) supplemented their diets with either marine oil capsules or placebo. Hemodynamic variables (Mercury-in-Silastic forearm plethysmography) were measured initially and weekly for 4 weeks. There were no significant differences between the two groups in blood pressure, forearm blood flow, venous capacitance, or forearm vascular resistance. Parallel changes occurred for forearm blood flow and venous capacitance. Six normal volunteers took daily dosages of aspirin, increasing from 162 to 2600 mg. Hemodynamic measurements, ADP-induced platelet aggregation, and serum salicylate levels were obtained daily. Maximum inhibition of platelet aggregation occurred after 162 mg. (serum salicylate = 17.7 +/- 6.4 mg/l). Though serum salicylate levels rose to 165.0 +/- 20.0 mg/l, no significant changes occurred in blood pressure or forearm blood flow. Even at aspirin levels 16-fold greater than those required to impair platelet aggregation, the changes in forearm vascular resistance were not found to be significant. These results suggest that under resting conditions in normotensive males, neither pharmacological inhibition nor stimulation of vascular prostaglandin metabolism alters forearm vascular resistance or arterial blood pressure.

Adult↗

PubMed2004

The effect of forearm support on musculoskeletal discomfort during call centre work.

Using a computer keyboard with the forearms unsupported has been proposed as a causal factor for neck/shoulder and arm/hand diagnoses. Recent laboratory and field studies have demonstrated that forearm support might be preferable to working in the traditional "floating" posture. The aim of this study was to determine whether providing forearm support when using a normal computer workstation would decrease musculoskeletal discomfort in intensive computer users in a call centre. A randomised controlled study (n = 59), of 6 weeks duration was conducted. Thirty participants (Group 1) were allocated to forearm support using the desk surface with the remainder (Group 2) acting as a control group. At 6 weeks, the control group was also set up with forearm support. Both groups were then monitored for another 6 weeks. Questionnaires were used at 1, 6 and 12 weeks to obtain information about discomfort, workstation setup, working posture and comfort. Nine participants (Group 1 n = 6, Group 2 n = 3) withdrew within a week of commencing forearm support either due to discomfort or difficulty in maintaining the posture. At 6 weeks, the group using forearm support generated significantly fewer reports of discomfort in the neck and back, although the difference between the groups was not statistically significant. At 12 weeks, there were fewer reports of neck, back and wrist discomfort when preintervention discomfort was compared with post intervention discomfort. These findings indicate that for the majority of users, forearm support may be preferable to the "floating" posture implicit in current guidelines for computer workstation setup.

Adult↗

PubMed2000

A new kinematic model of pro- and supination of the human forearm.

We introduce a new kinematic model describing the motion of the human forearm bones, ulna and radius, during forearm rotation. During this motion between the two forearm extrem-positions, referred to as supination (palm up) and pronation (palm down), effects occur, that cannot be explained by the the established kinematic model of R. Fick from 1904. Especially, the motion of the ulna is not properly reproduced by Fick's model. During forearm rotation an evasive motion of the ulna is observed by various authors, using magnetic resonance imaging MRI) technology. Our new kinematic model also simulates this evasive motion. Furthermore, the model is enlarged to include angulations of the forearm bones. Using these results the influence of forearm fractures on the range of forearm motion can be predicted. This knowledge can be used by surgeons to choose the optimal therapy in re-establishing free forearm mobility.

Biomechanical Phenomena↗

PubMed2001

The effect of forearm rotation on laxity and stability of the elbow.

OBJECTIVE: The purpose of this study was to quantify the relationship between forearm rotation and valgus/varus laxity of the elbow joint over the range of elbow flexion. BACKGROUND: There is little known about the influence of forearm rotation on the laxity and stability of the elbow joint. The general opinion exists that forearm rotation does not significantly influence the laxity and stability of the elbow joint. METHODS: Nine fresh-frozen cadaver elbows were used. Passive elbow flexion with the forearm in neutral rotation and in 40 degrees and 80 degrees of pronation and supination was performed under valgus/varus loads: (1) in intact elbows; (2) after a lateral surgical approach (lateral epicondylar osteotomy of the distal humerus); (3) after release of the anterior bundle of the medial collateral ligament; and (4) after release of the anterior bundle of the medial collateral ligament plus radial head resection. Valgus/varus elbow laxity was quantified using an electromagnetic tracking device. RESULTS: There was a statistically significant effect (P < 0.05) of forearm rotation on valgus/varus laxity throughout the range of flexion. The laxity was always greater in pronation than in supination, regardless of the surgical approach or the integrity of the anterior bundle of the medial collateral ligament or radial head. CONCLUSIONS: Valgus/varus laxity of the elbow is forearm rotation-dependent. The potential role of this effect should be considered and controlled for in the design of studies examining laxity and stability of the elbow joint. RELEVANCE: The observation that forearm pronation increases valgus/varus laxity, particularly in medial collateral ligament deficient elbows, implies a possible additional factor in throwing kinematics that might put professional baseball pitchers at risk of medial collateral ligament injury due to chronic valgus overload. Our data indicate that forearm rotation should be considered during the clinical examination of elbow instability.

Aged↗

PubMed1999

Effects of dobutamine on ischemic vasodilation of the forearm in patients with severe congestive heart failure.

BACKGROUND: The significant changes that occur in the peripheral circulatory system in heart failure are well known. Although the central hemodynamic effects of dobutamine have been well described, data on its effect on peripheral vascular function in patients with severe left ventricular dysfunction are limited. METHODS AND RESULTS: Resting and hyperemic forearm blood flow and resistance were measured using forearm venous occlusion plethysmography in patients with advanced congestive heart failure (CHF) before and during the infusion of increasing doses of dobutamine. Total hyperemia was also calculated. We studied eight patients with New York Heart Association classes III to IV CHF who had a mean age of 62 +/- 5 years and a mean ejection fraction of 17.4% +/- 2.9%. Resting forearm blood flow increased from 2.3 +/- 0.2 to 3.4 +/- 0.4 mL/min/100 mL during peak dobutamine infusion (P < .05). Resting forearm vascular resistance decreased from 39 +/- 3 to 29 +/- 4 units (P < .02). Peak hyperemic forearm blood flow increased from 25 +/- 3 to 34 +/- 6 mL/min/100 mL of tissue (P < .02) and peak hyperemic vascular resistance decreased from 3.7 +/- 0.4 to 2.9 +/- 0.3 units (P < .01). Total hyperemia increased from 14.3 +/- 1.9 to 19.4 +/- 2.4 mL/100 mL (P < .01). CONCLUSIONS: The data show that in patients with advanced CHF, intravenous dobutamine not only increases resting forearm blood flow and decreases resting forearm vascular resistance, but augments the reactive hyperemic flow and improves the vasodilatory response of the forearm vessels to transient ischemic occlusion. The underlying mechanism for this response and its clinical significance remain to be identified.

Adrenergic beta-Agonists↗

PubMed1996

Smooth muscle-derived nitric oxide is elevated in isolated forearm veins in human alcoholic cirrhosis.

1. Cirrhosis is often complicated by disturbances in the systemic circulation. We have previously demonstrated decreased vascular responses to vasoconstrictors in forearm resistance arteries in subjects with alcoholic cirrhosis. In the current study we investigate the role of the potent endogenous vasodilator nitric oxide in the peripheral circulation of these patients. 2. Ten patients with alcoholic cirrhosis (Pugh grade A) and 10 age-matched control subjects were studied. The effect of blockade of nitric oxide synthesis was studied both in vivo in forearm resistance arteries using forearm venous occlusion plethysmography and in vitro in veins isolated from the forearm. The role of endothelium-derived nitric oxide was studied in vivo using the endothelium-dependent vasodilator acetylcholine. 3. Mean arterial pressure and forearm basal flow in vivo were similar in the two groups. The constrictor response (percentage decrease in forearm blood flow) to noradrenaline (100 ng/min) was 26% smaller in patients with cirrhosis (31.65 +/- 2.64%) than in control subjects (42.75 +/- 3.87%, P = 0.037). Constrictor responses to the nitric oxide synthase inhibitor NG-monomethyl-L-arginine were not different in the two groups. Dilator responses to acetylcholine were significantly attenuated in cirrhotic patients compared with control subjects. 4. To investigate the role of smooth muscle-derived nitric oxide in vitro, all veins were stripped of their endothelium. Responses to noradrenaline were significantly diminished in veins isolated from patients with cirrhosis compared with control subjects. Incubation with the nitric oxide synthase inhibitor N omega-nitro-L-arginine had no effect on responses to noradrenaline in veins from control subjects but significantly enhanced the maximal response to noradrenaline by 23.95% (range 3.77-100%, P = 0.043) in veins from patients with cirrhosis. 5. Responses to noradrenaline were attenuated in vivo in forearm resistance arteries in patients with alcoholic cirrhosis. This impairment was also apparent in forearm isolated veins, stripped of the endothelium. Our data exclude a major role for endothelium-derived nitric oxide but highlight a possible role for smooth muscle-derived nitric oxide.

Acetylcholine↗

PubMed2000

Forearm metabolism during infusion of adrenaline: comparison of the dominant and non-dominant arm.

Human skeletal muscle metabolism is often investigated by measurements of substrate fluxes across the forearm. To evaluate whether the two forearms give the same metabolic information, nine healthy subjects were studied in the fasted state and during infusion of adrenaline. Both arms were catheterized in a cubital vein in the retrograde direction. A femoral artery was catheterized for blood sampling, and a femoral vein for infusion of adrenaline. Forearm blood flow was measured by venous occlusion strain-gauge plethysmography. Forearm subcutaneous adipose tissue blood flow was measured by the local 133Xe washout method. Metabolic fluxes were calculated as the product of forearm blood flow and a-v differences of metabolite concentrations. After baseline measurements, adrenaline was infused at a rate of 0.3 nmol kg-1 min-1. No difference in the metabolic information obtained in the fasting state could be demonstrated. During infusion of adrenaline, blood flow and lactate output increased significantly more in the non-dominant arm (8.12 +/- 1.24 versus 6.45 +/- 1.19 ml 100 g-1 min-1) and (2.99 +/- 0.60 versus 1.83 +/- 0.43 micromol 100 g-1 min-1). Adrenaline induced a significant increase in oxygen uptake in the non-dominant forearm (baseline period: 4.98 +/- 0.72 micromol 100 g-1 min-1; adrenaline period: 6.63 +/- 0.62 micromol 100 g-1 min-1) while there was no increase in the dominant forearm (baseline period: 5.69 +/- 1.03 micromol 100 g-1 min-1; adrenaline period: 4. 94 +/- 0.84 micromol 100 g-1 min-1). It is concluded that the two forearms do not respond equally to adrenaline stimulation. Thus, when comparing results from different studies, it is necessary to know which arm was examined.

Adipose Tissue↗

PubMed2002

Odds ratios for hip- and lower forearm fracture using peripheral bone densitometry; a case-control study of postmenopausal women.

BACKGROUND: Dual-energy X-ray absorptiometry (DXA) measured at the lumbar spine and particularly at the hip remain the gold-standard for diagnosing osteoporosis. However, devices for assessing the peripheral skeleton present several advantages in terms of lower price and portability. A major concern when using peripheral densitometry is the poor correlation with the central measurements. The main aim of this study is, therefore, to assess the possibility of expressing ultrasound measurements at the heel and bone mineral density (BMD) measured at the distal forearm as fracture odds ratios rather than an absolute measure of bone mass. METHODS: A total of 76 women with lower forearm fracture, 47 women with hip fracture and 231 age-matched women (controls) were included. All had broadband ultrasound attenuation (BUA) and speed of sound (SOS) measured at the heel using the DTU-one ultrasound scanner as well as BMD measured by dual X-ray absorptiometry on the DTX-200 at the distal forearm. RESULTS: BUA, SOS and BMD at the distal forearm were all significantly lower in fracture patients compared with their respective control groups. The odds ratio for lower forearm fracture was 3.1 (95% CI: 1.8; 5.2) for heel-BUA (T-score cutoff: -2.3), 4.1 (2.3; 7.4) for heel-SOS (-2.1) and 2.2 (1.3; 3.7) for lower forearm BMD (-2.7). The odds ratio for hip fracture was 3.4 (1.5-7.7) for heel-BUA (-2.7), 3.6 (1.6; 8.1) for heel-SOS (-2.6) and 3.2 (1.4; 7.4) for lower forearm BMD (-2.9). CONCLUSION: Peripheral densitometry can discriminate between hip- and lower forearm fracture patients and age-matched controls. Significantly elevated odds ratios for incurring these fractures can be calculated using device- and site specific t-score cutoff values. The results from this case-control study need to be confirmed by prospective cohort studies.

Absorptiometry, Photon↗

PubMed1994

The effect of arterialization of blood by hand warming on the interpretation of forearm metabolic studies.

Although sampling of arterialized blood is widely used as an alternative to arterial sampling in metabolic studies, the arterialization procedures have been criticized because they may produce metabolic and haemodynamic effects that confound interpretation of results, especially in studies involving arteriovenous exchange of metabolites across the contralateral forearm. This study aimed to assess the effect of warming the hand for 10 or 20 min (a procedure which may be used to arterialize superficial venous blood) on the blood flow to the skin and muscle of the whole of the contralateral forearm. Hand warming, produced by placing the hand in a box kept at 67 +/- 3 degrees C for 10 min (standard errors of mean, SEM), produced no significant change in the blood flow of the whole forearm (4.14 +/- 0.28 versus 4.34 +/- 0.26 ml per 100 ml forearm min-1, measured with the hand circulation occluded), muscle (1.9 +/- 0.12 versus 1.82 +/- 0.15 ml per 100 ml forearm min-1, measured by 133Xe) or skin (5.2 +/- 4.0 versus 4.6 +/- 2.9 arbitrary units, measured by photoplethysmography). After 20 min of hand warming, there was no significant change in the concentration of a variety of metabolites in the deep venous blood draining the contralateral forearm. It is concluded that, unlike other 'arterialization' procedures, that used in this study had no important effect on the blood flow to the contralateral forearm or its distribution between muscular and non-muscular tissues. Therefore, this procedure of arterialization can be employed in arteriovenous studies that aim to assess the exchange of metabolites between blood and forearm tissues.

Adult↗

PubMed2006

Criteria for conduction block based on computer simulation studies of nerve conduction with human data obtained in the forearm segment of the median nerve.

The finding of conduction block (CB) on nerve conduction studies supports the diagnosis of potentially treatable immune-mediated neuropathies. CB in a number of axons may result in reduction of the compound muscle action potential (CMAP) on proximal versus distal stimulation (decrement). Decrement may also result from increased temporal dispersion (TD) as this leads to desynchronization and phase cancellation of the motor unit action potentials (MUAPs) out of which the CMAP is built up; polyphasia of MUAPs possibly yields additional decrement. To prove the occurrence of CB, decrement has to be larger than can be explained by increased TD or increased phase cancellation. This was established previously by simulations using MUAPs recorded in rats assuming maximal TD. Unfortunately, criteria based on human data and criteria for nerves with limited TD are not available. In the present study, criteria for CB were derived using simulations with thenar surface recorded MUAPs affected by collateral reinnervation that were obtained in patients with lower motor neurone disease (LMND). The effect of TD on decrement was determined for a wide range of TDs in the forearm segment of the median nerve and the segment distal to this. Our criteria for CB were based on area decrement because this was less influenced by TD and more by CB than amplitude decrement. The maximal area decrement in the forearm segment increased as TD in the forearm segment increased but decreased as TD in the distal segment increased. This suggests that, when desynchronization and phase cancellation occur in the distal segment due to TD, less phase cancellation and, therefore, less decrement can occur due to TD in the forearm. The finding that duration prolongation on proximal versus distal stimulation reflected TD within the forearm segment and that distal duration reflected TD in the distal segment allowed proposal of a more flexible set of criteria for forearm segments when TD in the forearm segment is limited or TD in the distal segment is pronounced. A separate investigation showed that the maximal TD in chronic inflammatory demyelinating polyneuropathy was within the range of our simulations, indicating that these were realistic. Our criteria were validated retrospectively in patients with multifocal motor neuropathy and patients with LMND. In the forearm segment of the median nerve, our criteria were more sensitive and equally specific for CB as compared with criteria for CB based on the study using rats. Our criteria have to be evaluated prospectively.

Action Potentials↗

PubMed1993

Digitalis restores the forearm sympathetic response to cardiopulmonary receptor unloading in hypertensive patients with left ventricular hypertrophy.

OBJECTIVE: To investigate whether the impaired reflex response to cardiopulmonary baroreceptor unloading in hypertensive patients with left ventricular hypertrophy can be promptly improved by a pharmacological challenge. For this purpose we studied the effects of acute digitalis administration on cardiopulmonary baroreflex, evaluated by forearm noradrenaline spillover. METHODS: Eleven hypertensives with left ventricular hypertrophy and 10 age- and sex-matched normotensives underwent the application of -5 and -10 mmHg lower-body negative pressure (LBNP) before and after the administration of digitalis. Forearm noradrenaline spillover, measured using a tracer technique, was used to estimate the reflex sympathetic response. RESULTS: Under control conditions LBNP evoked a similar fall in right atrial pressure in the two study groups. In the normotensives there was a significant increase in forearm noradrenaline spillover. In the hypertensives no significant changes in forearm noradrenaline spillover were found. Intravenous administration of 0.02 mg/kg lanatoside C was associated with an increase in systolic blood pressure and a reduction in forearm noradrenaline spillover in both groups. In the normotensives the percentage change in forearm noradrenaline spillover induced by LBNP increased significantly in response to digitalis administration. However, digitalis restored the response of forearm noradrenaline spillover to LBNP in the hypertensives, so that no significant difference in this response was detected between the two study groups. Digitalis did not modify the effects of LBNP on cardiac pressures in either group. CONCLUSIONS: The present results demonstrate that administration of lanatoside C restores the response of forearm noradrenaline spillover to cardiopulmonary baroreceptor unloading in hypertensive patients with left ventricular hypertrophy. This indicates that the impairment of cardiopulmonary baroreflexes in these patients can be reversed by acute pharmacological treatment. Therefore, impairment of this reflex response seems to be related to functional rather than to structural abnormalities of the hypertrophied ventricle.

Digitalis Glycosides↗

PubMed1998

Forearm vasorelaxation in hypertensive renal transplant patients: the impact of withdrawal of cyclosporine.

OBJECTIVE: To determine whether cyclosporine A-induced hypertension in renal transplant recipients is accompanied by impairment of endothelium-dependent vasodilatation, which has been suggested by in-vitro and in-vivo animal experiments. DESIGN AND METHODS: In-vivo endothelium-dependent and endothelium-independent vasodilatation, and plasma concentrations of vasoactive hormones in 16 renal transplant patients were determined while they were being treated with cyclosporine A, and 16 weeks later, after their treatment had been changed to azathioprine therapy. The vasodilator response of the forearm vascular bed was measured by strain gauge venous occlusion plethysmography during intra-arterial infusion of acetylcholine (endothelium-dependent vasodilatation) and nitroprusside (endothelium-independent vasodilatation). Postischemic reactive flow was measured after 10 min of arterial occlusion. In addition, plasma concentrations of norepinephrine, and the prostanoids prostaglandin E2 and thromboxane B2, and also concentration of cyclosporine A in blood, were measured. Glomerular filtration rate and renal blood flow were estimated 1 day before the plethysmography study during each treatment period. RESULTS: Upon changing from cyclosporine A to azathioprine treatment, mean arterial pressure fell significantly by 12+/-3% (P< 0.05). Glomerular filtration rate and renal blood flow increased by 13+/-5 and 19+/-8%, respectively (both P< 0.05), while renal vascular resistance fell by 48+/-11% (P< 0.01). Both baseline forearm blood flow and baseline forearm resistance did not change after conversion (5.7+/-0.7 versus 4.9+/-0.6 ml/100 ml/min, and 27.3+/-4.2 versus 26.2+/-3.2 arbitrary units). The absolute and relative forearm blood flow responses, and forearm vascular resistance responses to infusions of acetylcholine and nitroprusside were similar during treatments with cyclosporine A and azathioprine. Peak postischaemic forearm blood flow was 42+/-12% higher during cyclosporine A treatment than it was during azathioprine treatment (P< 0.05), but the minimal postischaemic forearm vascular resistance did not differ for these treatments. Plasma prostaglandin E2 and thromboxane B2 levels decreased by 34+/-7 and 45+/-8%, respectively, after changing treatment, but norepinephrine levels did not change. CONCLUSIONS: Our data indicate that cyclosporine A-induced hypertension in renal transplant recipients is not accompanied by an increase in forearm vascular resistance. In addition, changing from cyclosporine A to azathioprine treatment did not cause changes in endothelial vasodilator functioning, although mean arterial pressure decreased significantly. Our results do not support the hypothesis that attenuation of endothelial vasodilator functioning contributes to the development of cyclosporine A-induced hypertension.

Adult↗

PubMed1992

Endothelium-dependent forearm vasodilation is reduced in normotensive subjects with familial history of hypertension.

Endothelium-dependent vasodilation is reduced in essential hypertensive subjects. To evaluate whether this abnormality is a primary defect or is a consequence of blood pressure increment, in offspring of essential hypertensive and normotensive subjects (n = 13 subjects for each group) matched for age, sex, body weight, and blood pressure, we studied the response of forearm vasculature to acetylcholine (ACh) (an endothelium-dependent vasodilator), sodium nitroprusside (a direct vasodilator of vascular smooth muscle), and forearm ischemia (13 min plus 1 min of exercise) to induce maximal vasodilation. Drugs were infused into the brachial artery at cumulative doses (ACh: 0.15, 0.45, 1.5, 4.5, and 15 micrograms/100 ml of forearm tissue/min; sodium nitroprusside: 1, 3, and 10 micrograms/100 ml of forearm tissue/min) while forearm blood flow was measured by strain-gauge venous plethysmography. The intra-arterial blood pressure and heart rate were continuously monitored. Despite a comparable forearm vascular response to sodium nitroprusside and to forearm ischemia, the effect of ACh was significantly (p < 0.001) reduced in offspring of hypertensive subjects compared to the offspring of normotensive subjects. These data indicate that ACh-mediated forearm vasodilation is reduced in normotensive subjects with a familial history of essential hypertension, a finding that suggests that endothelium dysfunction can precede the appearance of hypertension and that this abnormality might play a role in the pathogenesis of essential hypertension.

Acetylcholine↗