Media
Enrico Agabiti RoseiDamiano RizzoniMaurizio CastellanoEnzo PorteriRoberto ZulliMaría Lorenza MuiesanGiorgio BettoniMassimo SalvettiPaolo MuiesanStefano Maria Giulini
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Background For the evaluation in humans of structural alterations in resistance arteries, most studies have used an indirect index, the measurement of minimal vascular resistance (mean blood pressure divided by maximal postischaemic blood flow) in suitable vascular beds. A sensitive and specific micromyographic technique was recently made available for the study of human small resistance arteries. Whether a correlation really exists between results obtained with the two techniques has not yet been investigated. Objective To evaluate both forearm minimal vascular resistance and media: lumen ratio of omental or subcutaneous small arteries in normotensive subjects and hypertensive patients. Design and methods Thirty-four individuals were included in the study (age range 35–74 years; 24 hypertensive, 10 normotensive). Twenty-five had elective abdominal surgery and nine hypertensive patients had a gluteal biopsy. Omental and subcutaneous small arteries were dissected and mounted on a wire micromyograph (Mulvany's technique), and media: lumen ratio and media thickness were measured. The dose-response curve to noradrenaline was constructed at cumulative concentrations from 3 ± 10–9 to 3 ± 10–5 mol/l. Venous occlusion plethysmography was used to measure blood flow in the forearm, and minimal vascular resistance was calculated from mean blood pressure and postischaemic maximal blood flow (13 min ischaemia plus exercise). Results A statistically significant correlation was found between media: lumen ratio and minimal vascular resistance (r = 0.74, P < 0.001) as well as between media: lumen ratio and systolic (r = 0.44, P < 0.01) and diastolic (r = 0.38, P < 0.05) blood pressures. Similar correlations were observed between media thickness and systolic and diastolic blood pressures. Small arteries from hypertensive patients had a significantly increased reactivity to noradrenaline (by analysis of variance) compared with those from normotensive subjects, in terms of wall tension but not of active media stress. Conclusions The present study demonstrated that the media: lumen ratio of small resistance vessels is significantly related to forearm minimal vascular resistance, suggesting that direct and indirect evaluations of vascular morphology will give similar results.Keywords:
Lumen (anatomy)
Plethysmograph
In the course of plethysmographic studies on the peripheral vascular responses of hypertensive patients, it was noted that in about 50% of the cases the resting blood flow in the forearm was much greater than that in subjects with normal blood pressure. Such findings differ from those presented previously by Prinzmetal and Wilson using a similar method, and from those obtained by Pickering, who utilized Stewart's calorimetric procedure. These investigators found that the average blood flow reading for the forearm in a series of hypertensive subjects was no greater than that in a normal group, and on the basis of these observations, together with some confirmatory studies, they concluded that the increased vascular resistance in hypertension is generalized throughout the systemic circulation rather than confined to the splanchnic area. Pickering subsequently pointed out, as did also Stead and Kunkel, that in the light of Grant and Pearson's work, the data included in the two investigations represented not only arterial inflow to the forearm, but also venous return from the hand. It is well known that blood flow through the hand can be affected by a variety of stimuli, and hence readings obtained under such conditions cannot be considered representative of peripheral blood flow generally. Further, as Prinzmetal and Wilson indicated, the opposite conclusion to the one presented by them, namely that the hypertonus is limited to the splanchnic region, could have been drawn if an increase in blood flow had been found in the forearm of hypertensive subjects of the magnitude of 1.5 times the normal figure, i.e., approximately 2.65 cc per min. per 100 cc of limb volume instead of 1.7 cc.
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Splanchnic Circulation
Essential hypertension
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Background and Purpose. The purpose of this study was to determine the effect of ultrasound on forearm, skin, and muscle blood flow. Subjects. Twenty volunteers without known vascular problems (10 male, 10 female) participated. Methods. All subjects received a treatment of continuous-wave ultrasound to the anterior forearm at a dosage of 1.5 W/cm2 for a duration of 5 minutes. The contralateral forearm served as the control and received identical treatment, except the ultrasound output remained at zero. Forearm blood flow was measured using venous occlusion plethysmography, and skin blood flow was measured using cutaneous laser-Doppler flowmetry before and after ultrasound administration, with the difference being muscle blood flow. Results. No differences between the control arm and the ultrasound-treated arm were found for muscle, skin, and forearm blood flow. Conclusion and Discussion. These results suggest that administration of continuous-wave ultrasound at the prescribed dosage had no effect on skeletal muscle blood flow for up to 30 minutes posttreatment. Thus, muscle hyperemia is probably not the primary mechanism responsible for the clinical benefits seen following the use of ultrasound as a therapeutic modality.
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Reactive hyperemia
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Forearm plethysmography affords a simple noninvasive method of studying dynamic changes in the microcirculation. This technic was used to study the peripheral circulation of normotensive nongravid women and normotensive and untreated hypertensive pregnant women during the third trimester. The variables of forearm blood flow, vascular resistance, venous capacitance, and capillary filtration coefficient were measured in the resting state and during and after exercise. The pregnant women demonstrated an increase in forearm blood flow over the nonpregnant women. As expected, vascular resistance was higher in the hypertensive pregnant patients than in normotensive pregnant women. The possible predictive value of these findings is discussed.
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Peripheral resistance
Photoplethysmogram
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Summary: Forearm or calf venous plethysmography has been used in pregnant women to examine the effects of pregnancy on the vascular system and more recently to measure blood flow changes in response to intra‐arterial infusion of vasoactive substances. To examine the assumption that venous capacitance and blood flow measurements are the same in the forearm and calf, venous plethysmography was conducted simultaneously on the forearm and calf in normal (NP) and hypertensive pregnant women (HTP) in their third trimester and in normal nonpregnant women (N). Ail studies were made on the right forearm and calf with subjects in the left lateral recumbent position. There was no significant difference between venous capacitance in the forearm (median: 124 times 10 3 rruV100mIVmrnHg for both NP and HTP) and leg (134 [NP] and 106 [HTP] x lO'mL/lOOmlVmmHg) for both pregnant groups but venous capacitance in the nonpregnant group was greater in the leg than arm (174 versus 112 x lO'mUlOOmL/mmHg, p <0.001). Blood flow was similar in the leg and forearm (median: 4.9 versus 3.9mL/100mL/min respectively) in nonpregnant women. Forearm blood flow was also similar to calf flow in NP women (6.2 versus 4.3mL/100mL/min respectively) but greater man calf blood flow in HTP (9.7 versus 5.3ml7100mL/min, p <0.01). Using left lateral recumbency, forearm and calf vein capacitances are similar in pregnant women, in contrast to nonpregnant women. Blood flow is higher in the forearm than the calf only in hypertensive pregnant women. These observations should be borne in mind when interpreting studies of regional blood flow in pregnancy.
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Venous blood
Superficial vein
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Abstract. The electrocapacitance plethysmograph was utilized to measure peripheral blood flow and venous distensibility in 17 newborn infants and 20 adults. Measurements were made in the upper and lower extremities in each subject under identical environmental conditions. Blood flow in the forearm and calf were found to be significantly higher in infants than adults. In infants there were no significant differences in the blood flow between the upper and lower extremities. In contrast, in the adults, the blood flow was significantly higher in the upper than in the lower extremities. Similarly, venous distensibility was observed to be higher in infants than in adults. While no significant differences were observed in the venous distensibility between the upper and lower extremities in infants, the venous distensibility was found to be higher in the forearm than in the leg in adults.
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Venous blood
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1. An investigation was carried out in five healthy lean adults to assess whether forearm and calf plethysmography largely reflect muscle blood flow as measured by 133Xe and whether there is substantial variability in the blood flow to muscles located at different sites in the body. 2. Blood flow to forearm and calf flexors and extensors, biceps, triceps and quadriceps was assessed using the 133Xe clearance technique. Blood flow to forearm skin and subcutaneous adipose tissue was also measured using the 133Xe clearance technique, whereas blood flow to the forearm and calf was measured using strain gauge plethysmography. 3. The mean blood flow to different muscles ranged from 1.4 ± 0.6 (gastrocnemius) to 1.8 ± 0.7 (forearm extensor) ml min−1 100 g−1 muscle (1.4 ± 0.6 and 1.9 ± 0.8 ml min−1 100 ml−1 muscle, respectively) but there were no significant differences between them. Forearm and calf blood flows (2.7 ± 0.3 and 3.0 ± 0.7 ml min−1 100 ml−1 limb tissue, respectively) were about 50% to more than 100% greater (P <0.025) than blood flow to the muscles within them (1.7 ± 0.5 and 1.4 ± 0.5ml min−1 100g−1 muscle, respectively, or 1.8 ± 0.6 and 1.5 ± 0.5 ml min−1 100 ml−1 muscle, respectively). In contrast, the blood flows to 100 g of forearm skin (9.1 ± 2.6 ml min−1 100 g−1) and adipose tissue (3.8 ± 1.1 ml min−1 100 g−1) were higher than the blood flow to 100 g of forearm (P <0.01 and not significant, respectively). 4. Although several possibilities can explain the discrepancy between muscle blood flow measured by 133Xe and blood flow to the distal limbs measured by plethysmography, the results suggest that non-muscular blood flow, especially that to skin, is substantially greater than muscular blood flow. Indeed, the overall blood flow to the forearm could be accounted for by summation of blood flows to individual constituent tissues, which were assumed to be present in proportions typical of lean subjects. The results have important implications in the use of arteriovenous catheterization studies for assessing flux of oxygen, carbon dioxide and metabolites across muscle.
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Calf muscle
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Twenty patient with severe atherosclerotic affection of the lower limbs, but without any symptoms of involvement of their upper extremities, and twenty healthy controls were examined. The investigation included measurement of arterial blood flow and resistance in the left forearm at rest and after a three-minute circulatory arrest, using a strain-gauge venous occlusion plethysmograph. Comparison of the results obtained in each group showed statistically significant differences in haemodynamic parameters such as maximal blood flow, resting resistance, and minimal resistance which suggested the presence of vascular changes also in the upper extremities. Arterial resistance proved to be a more sensitive indicator of circulatory disorder than blood flow.
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The human forearm is a well established model to study local vascular reactivity in humans in vivo, using strain-gauge venous occlusion plethysmography to measure blood flow and changes in blood flow in the forearm. To reduce the intra-individual variability of the forearm blood flow (FBF), it has been advocated that simultaneous measurements of contralateral forearm blood flow is obligatory. Therefore, the use of the calculated forearm ratio (FR) is recommended instead of using the actual FBF. In the present study we compared the intra-individual variability of forearm blood flow measurements and the forearm ratio, by using computerized R-wave triggered strain-gauge venous occlusion plethysmography, to test if bilateral expression of measurements is better than unilateral. Results were obtained in eight volunteers. Intra-arterial infused sodium nitroprusside induced a dose dependent increase in forearm blood flow and a dose dependent increase in the calculated forearm ratio. Intra-arterial infused norepinephrine induced a dose dependent decrease in forearm blood flow and a dose dependent decrease in the calculated forearm ratio. The differences between the variation coefficients of the forearm blood flow measurements and the calculated forearm ratio were different. These results support our hypothesis that by using a computerized, R-wave triggered system for unilateral forearm blood flow measurement is a more reliable outcome than the calculated forearm ratio derived from bilateral measurements.
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