A restrospective perspective.

Venous occlusion plethysmography is a simple but elegant technique that has contributed to almost every major area of vascular biology in humans. The general principles of plethysmography were appreciated by the late 1800s, and the application of these principles to measure limb blood flow occurred in the early 1900s. Plethysmography has been instrumental in studying the role of the autonomic nervous system in regulating limb blood flow in humans and important in studying the vasodilator responses to exercise, reactive hyperemia, body heating, and mental stress. It has also been the technique of choice to study how human blood vessels respond to a variety of exogenously administered vasodilators and vasoconstrictors, especially those that act on various autonomic and adrenergic receptors. In recent years, plethysmography has been exploited to study the role of the vascular endothelium in health and disease. Venous occlusion plethysmography is likely to continue to play an important role as investigators seek to understand the physiological significance of newly identified vasoactive factors and how genetic polymorphisms affect the cardiovascular system in humans.     

Venous cuff pressures from 30 mmHg to diastolic pressure are recommended to measure arterial inflow by plethysmography.

Venous occlusion strain gauge plethysmography (VOP) is based on the assumption that the veins are occluded and arterial inflow is undisturbed by the venous cuff pressure. Literature is not clear concerning the pressure that should be used. The purpose of this study was to determine the optimal venous occlusion pressure at which the highest arterial inflow is achieved in the forearm, calf, and leg by using VOP. We hypothesized that, for each limb segment, an optimal (range of) venous cuff pressure can be determined. Arterial inflow in each limb segment was measured in nine healthy individuals by VOP by using pressures ranging from 10 mmHg up to diastolic blood pressure. Arterial inflows were similar at cuff pressures between 30 and 60 mmHg for the forearm, leg, and calf. Arterial inflow in the forearm was significantly lower at 10 mmHg compared with the other cuff pressures. In addition, arterial inflows at 20 mmHg tended to be lower in each limb segment than flow at higher cuff pressures. In conclusion, no single optimum venous cuff pressure, at which a highest arterial inflow is achieved, exists, but rather a range of optimum cuff pressures leading to a similar arterial inflow. Venous cuff pressures ranging from 30 mmHg up to diastolic blood pressure are recommended to measure arterial inflow by VOP.     

Influence of tissue compressibility on calibration for strain-gauge plethysmography

Strain gauges employed in plethysmography for determination of limb blood flow tend to counter the expansion of the limb during venous occlusion. Traditionally a mechanical calibration is performed in situ to compensate for tissue compressibility. Greenfield, Whitney, and Mowbray stated that, otherwise, large errors would result (Br. Med. Bull. 19: 101-109, 1963). Nonetheless, not all of the recent reports on skin blood flow in humans have been based on a calibration procedure that corrects for tissue compressibility. To evaluate the significance of this problem, we developed a new strain-gauge holder that made possible frequent, reproducible, stretching of a single-strand Whitney gauge in situ. We compared the apparent sensitivity thus obtained to electrical or bench mechanical determinations. We independently determined tissue compressibility by recording limb circumference as tension in a circumferential tube was varied. Both techniques showed that tissue compressibility is a small source of error (5%) and that compressibility decreases during occlusion. Therefore the cumbersome holder and potential artifacts associated with the traditional technique need not be tolerated. We also investigated the consequences of nonuniform tension distribution and temperature changes; practical considerations for dealing with these are discussed.     

Alpha-adrenergic vascular responsiveness to sympathetic nerve activity is intact after head-down bed rest in humans

Space-flight and its ground-based simulation model, 6 degrees head-down bed rest (HDBR), cause cardiovascular deconditioning in humans. Because sympathetic vasoconstriction plays a very important role in circulation, we examined whether HDBR impairs alpha-adrenergic vascular responsiveness to sympathetic nerve activity. We subjected eight healthy volunteers to 14 days of HDBR and before and after HDBR measured calf muscle sympathetic nerve activity (MSNA; microneurography) and calf blood flow (venous occlusion plethysmography) during sympathoexcitatory stimulation (rhythmic handgrip exercise). HDBR did not change the increase in total MSNA (P = 0.97) or the decrease in calf vascular conductance (P = 0.32) during exercise, but it did augment the increase in calf vascular resistance (P = 0.0011). HDBR augmented the transduction gain from total MSNA into calf vascular resistance, assessed as the least squares linear regression slope of vascular resistance on total MSNA (0.05 +/- 0.02 before HDBR, 0.20 +/- 0.06 U.min-1.burst-1 after HDBR, P = 0.0075), but did not change the transduction gain into calf vascular conductance (P = 0.41). Our data indicate that alpha-adrenergic vascular responsiveness to sympathetic nerve activity is preserved in the supine position after HDBR in humans.     

Head-down bed rest alters sympathetic and cardiovascular responses to mental stress

Astronauts usually work under much mental stress. However, it is unclear how and whether or not an exposure to microgravity affects physiological response to mental stress in humans. To examine effects of microgravity on vasomotor sympathetic and peripheral vasodilator responses to mental stress, we performed 10 min of mental arithmetic (MA) before and after 14 days of 6 degrees head-down bed rest (HDBR), a ground-based simulation of spaceflight. Total muscle sympathetic nerve activity (MSNA, measured by microneurography) slightly increased during MA before HDBR, and this increase was augmented after HDBR. Calf blood flow (measured by venous occlusion plethysmography) increased and calf vascular resistance (calculated by dividing mean blood pressure by calf blood flow) decreased during MA before HDBR, but these responses were abolished after HDBR. Increases in heart rate and mean blood pressure during MA were not different between before and after HDBR. These findings suggest that HDBR augmented vasomotor sympathoexcitation but attenuated vasodilatation in the calf muscle in response to mental stress.     

MRI measures of perfusion-related changes in human skeletal muscle during progressive contractions.

Although skeletal muscle perfusion is fundamental to proper muscle function, in vivo measurements are typically limited to those of limb or arterial blood flow, rather than flow within the muscle bed itself. We present a noninvasive functional MRI (fMRI) technique for measuring perfusion-related signal intensity (SI) changes in human skeletal muscle during and after contractions and demonstrate its application to the question of occlusion during a range of contraction intensities. Eight healthy men (aged 20-31 yr) performed a series of isometric ankle dorsiflexor contractions from 10 to 100% maximal voluntary contraction. Axial gradient-echo echo-planar images (repetition time = 500 ms, echo time = 18.6 ms) were acquired continuously before, during, and following each 10-s contraction, with 4.5-min rest between contractions. Average SI in the dorsiflexor muscles was calculated for all 240 images in each contraction series. Postcontraction hyperemia for each force level was determined as peak change in SI after contraction, which was then scaled to that obtained following a 5-min cuff occlusion of the thigh (i.e., maximal hyperemia). A subset of subjects (n = 4) performed parallel studies using venous occlusion plethysmography to measure limb blood flow. Hyperemia measured by fMRI and plethysmography demonstrated good agreement. Postcontraction hyperemia measured by fMRI scaled with contraction intensity up to approximately 60% maximal voluntary contraction. fMRI provides a noninvasive means of quantifying perfusion-related changes during and following skeletal muscle contractions in humans. Temporal changes in perfusion can be observed, as can the heterogeneity of perfusion across the muscle bed.     

Melatonin differentially affects vascular blood flow in humans

Melatonin is synthesized and released into the circulation by the pineal gland in a circadian rhythm. Melatonin has been demonstrated to differentially alter blood flow to assorted vascular beds by the activation of different melatonin receptors in animal models. The purpose of the present study was to determine the effect of melatonin on blood flow to various vascular beds in humans. Renal (Doppler ultrasound), forearm (venous occlusion plethysmography), and cerebral blood flow (transcranial Doppler), arterial blood pressure, and heart rate were measured in 10 healthy subjects (29±1 yr; 5 men and 5 women) in the supine position for 3 min. The protocol began 45 min after the ingestion of either melatonin (3 mg) or placebo (sucrose). Subjects returned at least 2 days later at the same time of day to repeat the trial after ingesting the other substance. Melatonin did not alter heart rate and mean arterial pressure. Renal blood flow velocity (RBFV) and renal vascular conductance (RVC) were lower during the melatonin trial compared with placebo (RBFV, 40.5±2.9 vs. 45.4±1.5 cm/s; and RVC, 0.47±0.02 vs. 0.54±0.01 cm·s(-1)·mmHg(-1), respectively). In contrast, forearm blood flow (FBF) and forearm vascular conductance (FVC) were greater with melatonin compared with placebo (FBF, 2.4±0.2 vs. 1.9±0.1 ml·100 ml(-1)·min(-1); and FVC, 0.029±0.003 vs. 0.023±0.002 arbitrary units, respectively). Melatonin did not alter cerebral blood flow measurements compared with placebo. Additionally, phentolamine (5-mg bolus) after melatonin reversed the decrease in RVC, suggesting that melatonin increases sympathetic outflow to the kidney to mediate renal vasoconstriction. In summary, exogenous melatonin differentially alters vascular blood flow in humans. These data suggest the complex nature of melatonin on the vasculature in humans.     

Inhibition of vascular ATP-sensitive K+ channels does not affect reactive hyperemia in human forearm

The extent to which ATP-sensitive K(+) channels contribute to reactive hyperemia in humans is unresolved. We examined the role of ATP-sensitive K(+) channels in regulating reactive hyperemia induced by 5 min of forearm ischemia. Thirty-one healthy subjects had forearm blood flow measured with venous occlusion plethysmography. Reactive hyperemia could be reproducibly induced (n = 9). The contribution of vascular ATP-sensitive K(+) channels to reactive hyperemia was determined by measuring forearm blood flow before and during brachial artery infusion of glibenclamide, an ATP-sensitive K(+) channel inhibitor (n = 12). To document ATP-sensitive K(+) channel inhibition with glibenclamide, coinfusion with diazoxide, an ATP-sensitive K(+) channel opener, was undertaken (n = 10). Glibenclamide did not significantly alter resting forearm blood flow or the initial and sustained phases of reactive hyperemia. However, glibenclamide attenuated the hyperemic response induced by diazoxide. These data suggest that ATP-sensitive K(+) channels do not play an important role in controlling forearm reactive hyperemia and that other mechanisms are active in this adaptive response.     

Local vasoconstriction in spinal cord-injured and able-bodied individuals.

Local vasoconstriction plays an important role in maintaining blood pressure in spinal cord-injured individuals (SCI). We aimed to unravel the mechanisms of local vasoconstriction [venoarteriolar reflex (VAR) and myogenic response] using both limb dependency and cuff inflation in SCI and compare these with control subjects. Limb blood flow was measured in 11 male SCI (age: 24-55 yr old) and 9 male controls (age: 23-56 yr old) using venous occlusion plethysmography in forearm and calf during three levels of 1) limb dependency, and 2) cuff inflation. During limb dependency, vasoconstriction relies on both the VAR and the myogenic response. During cuff inflation, the decrease in blood flow is caused by the VAR and by a decrease in arteriovenous pressure difference, whereas the myogenic response does not play a role. At the highest level of leg dependency, the percent increase in calf vascular resistance (mean arterial pressure/calf blood flow) was more pronounced in SCI than in controls (SCI 186 +/- 53%; controls 51 +/- 17%; P = 0.032). In contrast, during cuff inflation, no differences were found between SCI and controls (SCI 17 +/- 17%; controls 14 +/- 10%). Percent changes in forearm vascular resistance in response to either forearm dependency or forearm cuff inflation were equal in both groups. Thus local vasoconstriction during dependency of the paralyzed leg in SCI is enhanced. The contribution of the VAR to local vasoconstriction does not differ between the groups, since no differences between groups existed for cuff inflation. Therefore, the augmented local vasoconstriction in SCI during leg dependency relies, most likely, on the myogenic response.     

Developing the methodology of examining the lower limb veins in cosmonauts for the space medicine practice

The article focuses on development of a methodology for evaluating the function of lower limb veins of cosmonauts in microgravity. The whys and wherefores of the choice of occlusive plethysmography equipment and procedure are explained. Much place is given to arguments for the body and limb positioning during venous plethysmography before and after space fight. To minimize the gravity effect on venous blood flow, the body should be in the level position, with the shin aligned with the hydrodynamically indifferent point. Determining the type of occlusion test, occlusion adjustments, venous parameters of interest, and data processing procedure constitute the methodology.     

Vascular adaptation to 4 wk of deconditioning by unilateral lower limb suspension

Physical inactivity or deconditioning is an independent risk factor for atherosclerosis and cardiovascular disease. In contrast to exercise, the vascular changes that occur as a result of deconditioning have not been characterized. We used 4 wk of unilateral lower limb suspension (ULLS) to study arterial and venous adaptations to deconditioning. In contrast to previous studies, this model is not confounded by denervation or microgravity. Seven healthy subjects participated in the study. Arterial and venous characteristics of the legs were assessed by echo Doppler ultrasound and venous occlusion plethysmography. The diameter of the common and superficial femoral artery decreased by 12% after 4 wk of ULLS. Baseline calf blood flow, as measured by plethysmography, decreased from 2.1 +/- 0.2 to 1.6 +/- 0.2 ml.min(-1).dl tissue(-1). Both arterial diameter and calf blood flow returned to baseline values after 4 wk of recovery. There was no indication of a decrease in flow-mediated dilation of the superficial femoral artery after ULLS deconditioning. This means that functional adaptations to inactivity are not simply the inverse of adaptations to exercise. The venous pressure-volume curve is shifted downward after ULLS, without any effect on compliance. In conclusion, deconditioning by 4 wk of ULLS causes significant changes in both the arterial and the venous system.     

The Effect of Lipemia on Peripheral Blood Flow

The effect of lipemia on peripheral blood flow was studied in patients with and without peripheral vascular disease. Blood flow was measured by venous occlusion plethysmography in the calf and/or finger four to six hours after a fatty meal and after intravenous heparin. The abolition of postprandial lipemia by heparin was determined by measuring the plasma lactescence.Heparin resulted in no change in finger flow of either group or in calf flow in the control group. In nine out of 10 patients with occlusive vascular disease of the legs, it resulted in a small but significant increase of calf blood flow. No such alteration was found when heparin was given following a non-fatty meal.In 12 patients with intermittent claudication the clearing of postprandial lipemia by heparin caused prolongation of claudication time, as measured by the appearance of pain on treadmill exercise.It is concluded that, in some cases, postprandial lipemia is associated with a decrease in blood flow in a limb which is already the site of occlusive vascular disease.     

Increased vascular resistance in paralyzed legs after spinal cord injury is reversible by training.

The purpose of the present study was to determine the effect of a spinal cord injury (SCI) on resting vascular resistance in paralyzed legs in humans. To accomplish this goal, we measured blood pressure and resting flow above and below the lesion (by using venous occlusion plethysmography) in 11 patients with SCI and in 10 healthy controls (C). Relative vascular resistance was calculated as mean arterial pressure in millimeters of mercury divided by the arterial blood flow in milliliters per minute per 100 milliliters of tissue. Arterial blood flow in the sympathetically deprived and paralyzed legs of SCI was significantly lower than leg blood flow in C. Because mean arterial pressure showed no differences between both groups, leg vascular resistance in SCI was significantly higher than in C. Within the SCI group, arterial blood flow was significantly higher and vascular resistance significantly lower in the arms than in the legs. To distinguish between the effect of loss of central neural control vs. deconditioning, a group of nine SCI patients was trained for 6 wk and showed a 30% increase in leg blood flow with unchanged blood pressure levels, indicating a marked reduction in vascular resistance. In conclusion, vascular resistance is increased in the paralyzed legs of individuals with SCI and is reversible by training.     

Sympathetic control of the forearm blood flow in man during brief isometric contractions

Experiments were performed to assess the possible neurally mediated constriction in active skeletal muscle during isometric hand-grip contractions. Forearm blood flow was measured by venous occlusion plethysmography on 5 volunteers who exerted a series of repeated contractions of 4 s duration every 12 s at 60% of their maximum strength of fatigue. The blood flows increased initially, but then remained constant at 20-24 ml X min(-1) X 100 ml(-1) throughout the exercise even though mean arterial blood pressure reached 21-23 kPa (160-170 mm Hg). When the same exercise was performed after arterial infusion of phentolamine, forearm blood flow increased steadily to near maximal levels of 38.7 +/- 1.4 ml X min(-1) X 100 ml(-1). Venous catecholamines, principally norepinephrine, increased throughout exercise, reaching peak values of 983 +/- 258 pg X ml(-1) at fatigue. Of the vasoactive substances measured, the concentration of K+ and osmolarity in venous plasma also increased initially and reached a steady-state during the exercise but ATP increased steadily throughout the exercise. These data indicate a continually increasing alpha-adrenergic constriction to the vascular beds in active muscles in the human forearm during isometric exercise, that is only partially counteracted by vasoactive metabolites.     

Strain-gauge plethysmography in the evaluation of the evolution of deep vein thrombosis of the legs

Previous research has shown that MVO (Maximum Venous Outflow), VR (Venous Reflux), VE (Venous Emptying) and the respiratory waves recording are useful in differentiating occlusion and recanalization in postphlebitic syndrome. In the present work strain-gauge plethysmography was employed to quantitate the venous function after deep venous thrombosis of the legs. The studies were performed in a vascular laboratory with controlled temperature (23 to 25 C); records were obtained by a plethysmograph Parks mod. 270 connected to a Hewlett-Packard multi-channel mod. 7700. 17 patients (12 males, 5 females), mean age 55 years (range 24-75) that presented femoropopliteal thrombophlebitis documented by phlebography at the admission to the hospital were examined. MVO with and without superficial veins occlusion was measured by a mercury in silastic strain-gauge placed circumferentially about the calf. A pneumatic cuff thigh was inflated to 60 mm Hg. VE was measured in patients lying in inclined bed with the lower extremities 100 cm below the heart level compressing the calf with a pneumatic cuff 10 times for 5 seconds; the strain-gauge was placed on the foot level. VR after Valsalva's maneuver and the respiratory waves were recorded by a strain-gauge positioned at the maximum girth about the calf in patients lying on inclinated bed with the lower extremities 50 cm below the heart level. The result are here indicated: (Table: see text) There was differences in the evolution of venous function after deep venous thrombosis of the legs for each patient. Strain-gauge plethysmography may become evaluable non invasive technique in the evaluation of deep venous thrombosis evolution in the legs. The therapeutic assessment of postphlebitic syndrome.     

Hypercapnia-induced cerebral and ocular vasodilation is not altered by glibenclamide in humans

Carbon dioxide is an important regulator of vascular tone. Glibenclamide, an inhibitor of ATP-sensitive potassium channel (K(ATP)) activation, significantly blunts vasodilation in response to hypercapnic acidosis in animals. We investigated whether glibenclamide also alters the cerebral and ocular vasodilator response to hypercapnia in humans. Ten healthy male subjects were studied in a controlled, randomized, double-blind two-way crossover study under normoxic and hypercapnic conditions. Glibenclamide (5 mg po) or insulin (0.3 mU. kg(-1). min(-1) iv) were administered with glucose to achieve comparable plasma insulin levels. In control experiments, five healthy volunteers received glibenclamide (5 mg) or nicorandil (40 mg) or glibenclamide and nicorandil in a randomized, three-way crossover study. Mean blood flow velocity and resistive index in the middle cerebral artery (MCA) and in the ophthalmic artery (OA) were measured with Doppler sonography. Pulsatile choroidal blood flow was assessed with laser interferometric measurement of fundus pulsation. Forearm blood flow was measured with venous occlusion plethysmography. Hypercapnia increased ocular fundus pulsation amplitude by +18.2-22.3% (P < 0. 001) and mean flow velocity in the MCA by +27.4-33.3% (P < 0.001), but not in the OA (2.1-6.5%, P = 0.2). Forearm blood flow increased by 78.2% vs. baseline (P = 0.041) after nicorandil administration. Glibenclamide did not alter hypercapnia-induced changes in cerebral or ocular hemodynamics and did not affect systemic hemodynamics or forearm blood flow but significantly increased glucose utilization and blunted the nicorandil-induced vasodilation in the forearm. This suggests that hypercapnia-induced changes in the vascular beds under study are not mediated by activation of K(ATP) channels in humans.     

Effects of aging and type 2 diabetes on resting and post occlusive hyperemia of the forearm; the impact of rosiglitazone

BACKGROUND: Both Diabetes and ageing are associated with reduced vascular endothelial function. The exact relationship between the 2 and any improvements from the insulin sensitizer rosiglitazone have not been explored. METHODS: Thirty controls and sixteen subjects with type 2 diabetes participated in a series of experiments to examine the interrelationships between age, diabetes and endothelial cell function. In subjects with diabetes, the insulin sensitizer rosiglitazone (RSG), a drug also known to improve vascular function, was administered for 3 months to see how it altered these relationships. Resting forearm flows (RF) and blood flows after 4 min of vascular occlusion (PF) were measured as an index of endothelial cell function. RESULTS: RF, measured by venous occlusion plethysmography, was negatively correlated to both age and diabetes. Administration of RSG for 3 months was associated with an increase in the blood flow response to venous occlusion so that it was not significantly different than that of age matched controls. Total PF in control subjects, compared to subjects with diabetes, averaged 56.58 +/- 12.57 and 13.6 +/- 8.01 cc/100 cc tissue per min respectively, and were significantly different (p < 0.01). After 3 months on RSG, differences between PF in the two groups were no longer evident. CONCLUSION: These studies suggest a different mechanism causing a reduction in vascular reactivity with aging and diabetes.     

Radionuclide plethysmography for noninvasive evaluation of peripheral arterial blood flow

We validated a noninvasive radionuclide plethysmography technique to evaluate peripheral arterial blood flow during reactive hyperemia. This method, based on the measurement of blood volume variations during repetitive venous occlusions, was compared with strain-gauge venous impedance plethysmography. The technique uses 99mTc-labeled autologous red blood cells scintigraphy to determine the rate of change of forearm scintigraphic counts during venous occlusion. Thirteen subjects were simultaneously evaluated with radionuclide and impedance plethysmography. Six baseline flow measurements were performed to evaluate the reproducibility of each method. Twenty-seven serial measurements were then made to evaluate flow variation during forearm reactive hyperemia. After 30 min of recovery, resting forearm blood flows were again evaluated. Impedance and radionuclide methods showed excellent reproducibility with intraclass correlation coefficients of 0.96 and 0.93, respectively. There was also good correlation of flows between both methods during reactive hyperemia (r = 0.87). Resting flows at 30 min after reactive hyperemia were slightly lower than at baseline with both methods. We conclude that radionuclide plethysmography could be used for the noninvasive evaluation of forearm blood flow and its dynamic variations during reactive hyperemia.     

Habituation of vasodilatation in the calf elicited by repeated sensory stimulation in man

In 28 subjects the cardiovascular response to repeated stimulation was monitored during six daily sessions. Calf blood flow was measured with mercury-in-silastic venous occlusion plethysmography, blood pressure with electronic sphygmomanometer. The stimuli used were: 1 kHz sound of 90 dB and 100 dB intensity and immersion of one foot for 60 s in water at 4 degrees C. Initially sounds induced large vasodilatation in the calf, immersion of one foot in the water induced in the contralateral calf vasodilatation in one group and vasoconstriction in another group of subjects. The blood pressure changes were less prominent and less consistent. After the first session of repeated stimulation the vascular response during the second session was significantly diminished. The reduction of the vasodilatation was the most rapid. During the remaining 5 days the responses were suppressed. It has been established that in the patients in the initial stage of hypertension the ability to habituate vascular response is impaired (Zbrozyna and Krebbel 1985). It is therefore suggested that the test of the ability for long-term vascular habituation could be used as a supplementary diagnostic test.     

膜片钳技术在动脉粥样硬化研究中的应用

膜片钳技术是一种先进的电生理技术,在生命科学研究中已得到了广泛的应用.最近几年已把它运用于研究动脉粥样硬化血管平滑肌细胞离子通道电生理特性的改变.研究发现血管平滑肌细胞的凋亡与K+通道活动增加有关,在动脉粥样硬化发生与发展过程中大电导型钙激活钾通道起着重要的功能作用.某些药物影响动脉粥样硬化血管平滑肌细胞离子通道而发挥作用.膜片钳技术给动脉粥样硬化发病机理研究带来了新的亮点.