The musculovenous pumps of the human lower limb

Usefulness of Elastic Bandage Compression Compared to Calf Massage to Prevent Venous Thromboembolism-A Retrospective Evaluation

Background: Manual calf massage and passive ankle motion (CaM) can reduce the incidence of venous thromboembolism (VTE) after total hip arthroplasty (THA). However, these methods cannot be used in all patients; thus, elastic bandage (EB) compression is an alternative method. The efficacy of EB compression in preventing VTE has not yet been investigated; thus, this study aimed to compare the effects of EB compression and manual calf massage. Methods: Of the 363 patients who underwent unilateral primary THA at our hospital between 1 August 2018 and 31 October 2023, CaM without anticoagulation therapy was administered to 206 patients (CaM group) and 157 patients underwent EB without anticoagulation therapy (EB group). Duplex ultrasonography was performed 7 days postoperatively to check for deep vein thrombosis (DVT) in both legs. Results: The surgical time (122.2 min vs. 155.5 min), the incidence of DVT (4.5% vs. 4.8%) and pulmonary thromboembolism (PTE) (0% vs. 0.7%), intraoperative bleeding (305.4 mL vs. 301 mL), and estimated actual blood loss (846.6 mL vs. 811.6 mL) were not significantly different between the CaM and EB group. However, there was one case of symptomatic PTE in the EB group. Conclusions: The incidences of DVT, PTE, and intraoperative bleeding were not significantly different between the groups. Moreover, EB can be administered to patients with DVT and is considered to be a DVT prophylaxis method that can be used in a larger number of patients. Therefore, we recommend that EB be performed in all the patients undergoing THA.

The impact of ankle movements on venous return flow: A comparative study

OBJECTIVE

To compare the haemodynamic effects of different ankle movements combined ankle and toe movements on the femoral vein of the lower extremity.

METHODS

28 healthy volunteers participated in the study. Doppler ultrasound was used to measure peak systolic velocity and time-averaged mean velocity of the common femoral vein during ankle dorsiflexion, ankle dorsiflexion with simultaneous toe extension, ankle plantarflexion, and ankle plantarflexion with simultaneous toe flexion.

RESULTS

In comparison to the resting state, both ankle alone or ankle combined with toe movement showed statistically significant differences (p < .01). However, there were no significant difference in the velocity of the common femoral vein between ankle alone and ankle combined with toe movement (p > .05). It is noteworthy that dorsiflexion of the ankle resulted in the highest peak velocity of blood flow.

CONCLUSION

The impact of ankle movement, with or without toe movement, the velocity of the common femoral vein is not significantly correlated.

Vicious Circle With Venous Hypertension, Irregular Flow, Pathological Venous Wall Remodeling, and Valve Destruction in Chronic Venous Disease: A Review

Substantial advances occurred in phlebological practice in the last two decades. With the use of modern diagnostic equipment, the patients' venous hemodynamics can be examined in detail in everyday practice. Application of venous segments for arterial bypasses motivated studies on the effect of hemodynamic load on the venous wall. New animal models have been developed to study hemodynamic effects on the venous system. In vivo and in vitro studies revealed cellular phase transitions of venous endothelial, smooth muscle, and fibroblastic cells and changes in connective tissue composition, under hemodynamic load and at different locations of the chronically diseased venous system. This review is an attempt to integrate our knowledge from epidemiology, paleoanthropology and anthropology, clinical and experimental hemodynamic studies, histology, cell physiology, cell pathology, and molecular biology on the complex pathomechanism of this frequent disease. Our conclusion is that the disease is initiated by limited genetic adaptation of mankind not to bipedalism but to bipedalism in the unmoving standing or sitting position. In the course of the disease several pathologic vicious circles emerge, sustained venous hypertension inducing cellular phase transitions, chronic wall inflammation, apoptosis of cells, pathologic dilation, and valvular damage which, in turn, further aggravate the venous hypertension.

The effect of lower limb strengthening exercise on orthostatic blood pressure and the skeletal muscle pump in older people with orthostatic hypotension

INTRODUCTION

Activation of muscles during standing is recommended to activate the skeletal muscle pump, increasing venous return and increasing blood pressure (BP) in people with orthostatic hypotension (OH).

AIM

The aim of this study is to determine if increasing the strength of the lower limb muscles can improve the effectiveness of the venous pump and postural BP in older people with OH.

METHODS

Ten older people with OH underwent an 8-week lower limb strengthening intervention. Repeated measurements of orthostatic BP, calf venous ejection fraction (EF) and muscle strength took place before, during and after intervention.

RESULTS

The intervention increased calf muscle strength by 21% (interquartile range: 18-28), p = 0.018, from a median baseline of 38 (34-45) kg. Participants had normal levels of venous EF 64% (51-75) at baseline, with little to no venous reflux. The median ejection volume at baseline was 44 (36-58) mL per calf. Despite increasing muscle strength, venous EF did not increase (percentage change -10% (-16 to 24), p = 0.8) and systolic BP drop did not improve (percentage change 0% (-17 to 16), p = 1.0). Similarly, visual analysis of individual case-series trends revealed increasing muscle strength with no clinically meaningful change in EF or orthostatic BP.

CONCLUSIONS

Muscle strengthening exercise does not increase the effectiveness of the skeletal muscle pump and is not an efficacious intervention for OH. As there is little to no venous pooling in the calf during standing in older people with OH, below knee compression is unlikely to be clinically effective.

Calf muscle pump pressure-flow cycle during ambulation

OBJECTIVE

Calf muscle pump (CMP) failure contributes to the severity and progression of chronic venous disease. Attempts to improve CMP function through resistance exercise have failed to improve chronic venous disease severity or quality of life, partially because the selection of the type of exercise was based on the assumption that the CMP ejects blood from the intramuscular venous sinuses (VSs), which has never been tested in humans. In the present study, we investigated the real-time changes in the pressure and size of the VS during the entire gait cycle of ambulation.

METHODS

We studied 12 lower extremities of nine healthy volunteers at rest and while walking on a treadmill at three different speeds (60, 90, and 120 steps/min). The changes in the VS cross-sectional area (CSA) and pressure were measured. Myography of the gastrocnemius muscle (GCM) and anterior tibial muscle (ATM) was used to register muscle activity. The relationship between the phases of the gait cycle and the measured parameters was analyzed using video records of all experiments.

RESULTS

The observed timing of events was consistent among all limbs studied. At rest, with the participants standing still, the VS pressure and CSA was 70.3 ± 4.2 mm Hg and 23.3 ± 14.6 mm2, respectively. During ambulation, at the first half of the stance, the GCM and ATM eccentrically contract, and the pressure is low (17 ± 8 mm Hg, 20 ± 12 mm Hg, and 29 ± 13 mm Hg at 1, 1.5, and 2 Hz, respectively), and the VS is collapsed. When the heel starts rising (the second half of the stance), the GCM concentrically contracts, the pressure increases, reaching its maximum value (143 ± 37, 134 ± 46, and 128 ± 41 mm Hg), and the VS opens, reaching its maximal size (1.8 ± 1.4 and 2.3 ± 2.2 mm2 at 1 and 1.5 Hz, respectively), followed by collapse of the VS. During the swing phase, the GCM relaxes, and the ATM concentrically contracts, resulting in a rapid decrease in pressure (2.6 ± 4.7, 1.1 ± 6.2, and -4.7 ± 3.2 mm Hg). The VS CSA remained negligible.

CONCLUSIONS

The GCM concentric contraction was associated with a simultaneous increase in VS pressure and CSA. GCM relaxation with ATM concentric contraction coincided with a decrease in VS pressure to negative values. The VSs do not fill but remain empty during the swing phase of ambulation, acting, not as a reservoir, but as a conduit, transferring blood from the network of intramuscular veins to the axial deep veins.

Chronic Venous Disease of the Lower Extremities: A State-of-the Art Review

Chronic venous disease is a common disease, the prevalence of which increases with age, and can cause debilitating symptoms that adversely affect the quality of life. The risk factors include family history, female sex, obesity, pregnancy, parity, and history of deep vein thrombosis. Moreover, it is associated with venous obstruction, reflux, or both, which, in turn, leads to ambulatory venous hypertension. Chronic venous disease is the leading cause of leg ulcers, which place a significant cost burden on the health care system. Compression therapy remains the cornerstone of treatment, particularly for more advanced disease. Superficial saphenous vein reflux can be associated with significant symptoms. Catheter techniques, both thermal and nonthermal, have demonstrated efficacy and safety in successful closure and symptom improvement. Deep vein obstruction can be broadly divided into thrombotic and nonthrombotic and can lead to symptomatic chronic venous disease. Recanalization using balloons and stents has been increasingly used and studied in such patients. It is critical to develop training opportunities and guidelines to improve evidence-based and appropriate care for cardiologists treating chronic venous disease.

Venous reflux in the great saphenous vein is driven by a suction force provided by the calf muscle pump in the compression-decompression maneuver

OBJECTIVE

The gravitational pressure gradient is considered the driving force of venous reflux. The results from our previous study demonstrated that gravitational force is not a necessary condition for the occurrence of venous reflux. We hypothesized that a force exists in addition to gravity that drives venous reflux. The present study was designed to test this hypothesis by measuring the acceleration of blood flow during venous reflux in a clinical study and by simulating reflux ex vivo in physical models.

METHODS

A total of 80 lower extremities of 80 patients with primary incompetence of the great saphenous vein were included in the present study. The cross-sectional area of the great saphenous vein, peak velocity of venous reflux (PV), and time required to achieve the PV (_Δt, seconds) were measured on duplex ultrasound scans taken with the patient in the standing rest position. Noncycling operator-dependent distal cuff inflation-deflation was used as the reflux provoking maneuver. The acceleration of venous reflux (a_reflux) was calculated as a_reflux = PV/_Δt in m/s². Physical models were used to demonstrate the difference in acceleration between the free-fall stream and the flow forced by suction.

RESULTS

The magnitude of a_reflux was greater than gravity in 24 of 80 extremities (30%), with a range of 9.83 to 24.13 m/s². The maximum observed value of a_reflux was approximately 2.5g (24.13 m/s²). The a_reflux weakly, but statistically significant inversely, correlated with the subject height (r = -0.26; P = .001). The difference in water flow acceleration was 2.5 times between the free-fall model and suction model (9.07 ± 0.2 m/s² vs 23.32 ± 2.6 m/s², respectively).

CONCLUSIONS

The acceleration of blood flow during reflux exceeded the value of gravitational acceleration, suggesting the action of an additional nongravitational force. The calf muscle pump might create such force by negative pressure during muscle diastole.

Attenuated spontaneous postural sway enhances diastolic blood pressure during quiet standing

PURPOSE

Spontaneous postural sway during quiet standing has been considered a simple output error of postural control. However, as postural sway and inherent body orientation evoke compensatory activity of the plantar flexors, they might contribute to blood circulation under gravitational stress via the muscle pump. Hence, the present study employed an external support device to attenuate the plantar flexor activity in supported standing (SS), to experimentally identify its physiological impact on blood circulation.

METHODS

Eight healthy young subjects performed two 5-min quiet standing trials (i.e., normal standing (NS) and SS), and the beat-to-beat interval (RRI) and blood pressure (BP) were compared between trials. We confirmed that postural sway and corresponding plantar flexor activity, quantified by the anteroposterior displacement of the foot center of pressure and lower back position with respect to the wall, and by the amplitude of electromyography and mechanomyography, respectively, were attenuated in SS, while mean body orientation angle and relative position of the BP sensor were comparable to NS.

RESULTS

The 5-min averages of diastolic BP and mean arterial pressure during SS were significantly higher than during NS, while RRI and systolic BP did not change. These could be interpreted as an increase in peripheral vascular resistance; meanwhile, in NS, this effect was replaced by the muscle pump of the plantar flexors.

CONCLUSION

The muscle contractions related to spontaneous postural sway and body orientation produce substantial physiological impact on blood circulation during quiet standing.

Simulated trawling: Exhaustive swimming followed by extreme crowding as contributing reasons to variable fillet quality in trawl-caught Atlantic cod (Gadus morhua)

Trawl-caught Atlantic cod (Gadus morhua) often yield highly variable fillet quality that may be related to capture stress. To investigate mechanisms involved in causing variable quality, commercial-sized (3.5±0.9 kg) Atlantic cod were swum to exhaustion in a large swim tunnel and subsequently exposed to extreme crowding (736±50 kg m^-3) for 0, 1 or 3 hours in an experimental cod-end. The fish were then recuperated for 0, 3 or 6 hours in a net pen prior to slaughter to assess the possibility to reverse the reduced fillet quality. We found that exhaustive swimming and crowding were associated with increased metabolic stress, as indicated by increased plasma cortisol, blood lactate and blood haematocrit levels, accompanied by reduced quality of the fillets due to increased visual redness and lower initial muscle pH. The observed negative effects of exhaustive swimming and crowding were only to a small degree reversed within 6 hours of recuperation. The results from this study suggest that exhaustive swimming followed by extreme crowding can reduce fillet quality, as measured by fillet redness and muscle pH, and contribute to the variable fillet quality seen in trawl-caught Atlantic cod. Recuperation for more than six hours may be required to reverse these effects.

Effects of ankle pump exercise frequency on venous hemodynamics of the lower limb

PURPOSE

The purpose of this study was (1) to compare the effects of ankle pump exercise(APE) frequency on hemodynamics of the common femoral vein(CFV) and (2) to analyse the relationship between APE duration and lower limb fatigue.

METHODS

Twenty-seven males and thirty-three females performed APE. Among them, there were thirty participants with non-lower limb fracture (N-LLF) and thirty participants with lower limb fracture (LLF).The colour doppler ultrasound was used to record the time-averaged mean velocity (TAMV) of common femoral venous flow when the participants at rest and move at different frequencies of 6 times/min, 10 times/min, 30 times/min, 60 times/min. The ratings of perceived exertion (RPE) was used to assess the lower limb fatigue of the participants when performing APE at the frequency of 60 times/min after 1 min, 2 mins, 3 mins, 4 mins and 5 mins.

RESULTS

With the increase of frequency, TAMV increased significantly in both the participants with N-LLF and LLF (p < 0.01). The TAMV were 19.82±3.86, 33.78±8.76, 37.06±8.67, 43.82±10.40, 52.18±10.53, respectively in the participants with N-LLF and 16.98±3.01, 22.20±4.96, 24.01±5.78, 29.20±7.05, 35.75±9.28, respectively in the injured limb of patients with LLF when at rest and moving at the frequency of 6 times/min, 10 times/min, 30 times/min, 60 times/min. There was a positive correlation (p < 0.01) between lower limb fatigue and exercise duration.When the RPE was 16 points (the corresponding fatigue degree is "tired"), the exercise duration of the participants with N-LLF was 3 mins and that of the injured limb of patients with LLF was 2 mins.

CONCLUSIONS

Both fast and slow-frequency APE can promote venous blood return in the lower limb. Despite of the equivalent APE duration, fast-frequency APE can promote venous blood return more effectively. When the frequency of APE was 60 times/min, participants with N-LLF can exercise for 3 mins, and the injured limb of patients with LLF can exercise for 2 mins.

Evolution and Functional Differentiation of the Diaphragm Muscle of Mammals

Symmorphosis is a concept of economy of biological design, whereby structural properties are matched to functional demands. According to symmorphosis, biological structures are never over designed to exceed functional demands. Based on this concept, the evolution of the diaphragm muscle (DIAm) in mammals is a tale of two structures, a membrane that separates and partitions the primitive coelomic cavity into separate abdominal and thoracic cavities and a muscle that serves as a pump to generate intra-abdominal (Pab ) and intrathoracic (Pth ) pressures. The DIAm partition evolved in reptiles from folds of the pleural and peritoneal membranes that was driven by the biological advantage of separating organs in the larger coelomic cavity into separate thoracic and abdominal cavities, especially with the evolution of aspiration breathing. The DIAm pump evolved from the advantage afforded by more effective generation of both a negative Pth for ventilation of the lungs and a positive Pab for venous return of blood to the heart and expulsive behaviors such as airway clearance, defecation, micturition, and child birth. © 2019 American Physiological Society. Compr Physiol 9:715-766, 2019.

Latest Innovations in the Treatment of Venous Disease

Venous disease is more common than peripheral arterial disease. Pathophysiologically, venous disease can be associated with obstruction, reflux, or both. A common feature in chronic venous disease is ambulatory venous hypertension. Inflammatory and pro-thrombotic mechanisms can be activated. The current therapies, including compression, ablation, and recanalization are discussed.

Rehabilitation of patients with venous diseases of the lower limbs: State of the art

BACKGROUND

To date, no document comprehensively focused on the complex issue of the rehabilitation of chronic venous diseases of the lower limbs.

METHOD

This article overviews and summarizes current strategies concerning venous rehabilitation of lower limbs.

RESULTS

Venous rehabilitation is based on four main strategies: (1) lifestyle adaptations and occupational therapies; (2) physical therapies; (3) adapted physical activities; (4) psychological and social support. Rehabilitative protocols must be tailored to the specific needs of each patient, depending on the severity of chronic venous disease and on the location and pattern of venous lesion(s), but also on age, motor deficits, co-morbidities and psychosocial conditions.

CONCLUSIONS

Venous rehabilitation consists of non-pharmacologic and non-surgical interventions aiming at prevention of venous disease progression and complications, reduction of symptoms and improvement of quality of life. Well-designed clinical trials are required to evaluate the efficacy of the described rehabilitative protocols in influencing the evolution of venous disorders.

MRI analysis and clinical significance of lower extremity muscle cross-sectional area after spinal cord injury

Shortly after spinal cord injury (SCI), the musculoskeletal system undergoes detrimental changes in size and composition, predominantly below the level of injury. The loss of muscle size and strength, along with increased immobility, predisposes persons with SCI to rapid and severe loss in bone mineral density and other health related consequences. Previous studies have highlighted the significance of measuring thigh muscle cross-sectional area, however, measuring the size and composition of muscles of the lower leg may provide insights on how to decrease the risk of various comorbidities. The purpose of the current review was to summarize the methodological approach to manually trace and measure the muscles of the lower leg in individuals with SCI, using magnetic resonance imaging. We also intend to highlight the significance of analyzing lower leg muscle cross-sectional area and its relationship to musculoskeletal and vascular systems in persons with SCI.

Ankle Motility is a Risk Factor for Healing of Chronic Venous Leg Ulcers

Objective:

To investigate the effect of ankle motility on chronic venous leg ulcer healing, and to relate this to calf pump function and muscle bulk.

Methods:

This was a prospective cohort study undertaken in a leg ulcer clinic. Ankle motility, calf-ankle circumference ratio and calf pump power (derived from digital photoplethysmography) were assessed as to their effect on ulcer healing rate. Thirty consecutive patients undergoing multi-layer compression bandaging for open chronic venous ulcers were included.

Results:

Ankle motility was an independent risk factor for ulcer healing ( p = 0.001, hazard ratio 1.08, 95% CI 1.03–1.13). Ankle motility correlated with calf-ankle circumference ratio ( r = 0.48, p<0.01). No relationship was found between photoplethysmography-derived calf pump power, ankle motility or ulcer healing rate.

Conclusions

Ulcers in legs with poor ankle motility are slower to heal and this may be related to reduced calf muscle bulk. Ankle exercises or physiotherapy could be considered in such patients.

A Study of Venous Return from the Leg during Exercise

Bi-directional ultrasound velocity detector tracings were made of venous blood flow through the popliteal vein in the following situations: (1) walking normally; (2) walking in place; (3) sitting, foot on floor, with rhythmic plantar and dorsi-flexion; (4) sitting, foot on a treadle device requiring 20 degrees of plantar-flexion and 20 degrees of dorsi-flexion to complete a cycle; (5) using the treadle device while in recumbent position, and (6) pushing the foot in plantar flexion against a pedal equipped with a spring resistance.

These studies show that active walking, which consists of both plantar flexion and dorsi-flexion, produces cephalad return of venous blood from the foot and leg. When the walking cycle is accompanied by weight bearing, plantar flexion produces a greater blood velocity. However, when there is no weight bearing, dorsi-flexion produces a greater blood velocity than plantar flexion.

Therefore, when not bearing weight on the foot, a full range of dorsi-flexion as well as a full range of plantar flexion is essential to utilizing maximum efficiency of the lower extremity muscle pump.

Anatomy and physiology of the lower-extremity deep and superficial veins

A thorough understanding of venous anatomy and physiology is foundational to the diagnosis and management of venous disease. Compared with the arterial system, there is significantly greater developmental variation in the venous system. The veins of the lower extremity include the superficial and deep veins, which are defined by their respective relationships to the muscular fascia. Perforating veins traverse the muscular fascia to connect superficial and deep veins. Communicating veins connect veins within the same venous compartment, either deep to deep or superficial to superficial. The deep veins of the lower extremities primarily drain muscles and are encompassed by muscular fascia. The veins located between the skin and the muscular fascia are considered superficial veins. Superficial veins drain the cutaneous microcirculation. The pelvic venous system is a complex transitional outflow pathway between the lower extremities, the pelvic structures, and the inferior vena cava. The terminology used to describe lower-extremity, pelvic, and abdominal vasculature conforms to published international standards.

Combined hypertension and orthostatic hypotension in older patients: a treatment dilemma for clinicians

The combination of hypertension and orthostatic hypotension in older individuals is becoming increasingly recognized. Managing this combination of disorders presents a treatment dilemma -- how to lower blood pressure to provide cardiovascular risk protection without predisposing to syncope. At present, there is no specific evidence base available with regard to managing such patients. Some antihypertensive drug classes (e.g., alpha-blockers) appear more problematic in this regard than others. In the absence of controlled-trial evidence, use of antihypertensives with a more gradual onset of effect commenced at lower doses and use of lower-limb compression hosiery appears to be a reasonable approach. Abdominal compression devices and elevating the head of the bed may also help to combat orthostatic hypotenstion in older patients with hypertension and warrant future research.

Influence of wearing an unstable shoe on thigh and leg muscle activity and venous response in upright standing

PURPOSE

To quantify the effect of unstable shoe wearing on muscle activity and haemodynamic response during standing.

METHODS

Thirty volunteers were divided into 2 groups: the experimental group wore an unstable shoe for 8 weeks, while the control group used a conventional shoe for the same period. Muscle activity of the medial gastrocnemius, tibialis anterior, rectus femoris and biceps femoris and venous circulation were assessed in quiet standing with the unstable shoe and barefoot.

RESULTS

In the first measurement there was an increase in medial gastrocnemius activity in all volunteers while wearing the unstable shoe. On the other hand, after wearing the unstable shoe for eight weeks these differences were not verified. Venous return increased in subjects wearing the unstable shoe before and after training.

CONCLUSIONS

The unstable shoe produced changes in electromyographic characteristics which were advantageous for venous circulation even after training accommodation by the neuromuscular system.

Anatomy of the foot venous pump: physiology and influence on chronic venous disease

The aim of this paper is to demonstrate the location of the venous foot pump using an anatomical study. Four hundred cadaveric feet were injected with green neoprene latex followed by a dissection. A coloured segmentation of the venous system was achieved. The Lejars’ concept of the venous sole of the foot is incorrect: the true blood venous reservoir of the foot is located deeply in the plantar veins, between the plantar muscles. The medial and mostly lateral plantar veins converge into the plexus shaped calcaneal crossroad, where the blood is ejected upwards into the two posterior tibial veins. In addition, the several medial perforators of the foot directly connect the deep system (medial plantar veins) to the superficial venous system (medial marginal vein). This forms a true ‘medial functional unit’ which is unique in the limb given its directional flow is from deep to superficial. In conclusion, the plantar veins play an important role in the physiology of the venous return since a venous reservoir of 25 mL of blood is mobilized upwards with each step during walking. Therefore, the impairment of the foot pump by a static foot disorder should be considered as an important risk factor for chronic venous disease, and should be evaluated and corrected in any patient with venous insufficiency.

Histamine and H1 -histamine receptors faster venous circulation

The study has analysed the action of histamine in the rabbit venous system and evaluated its potential role in contraction during increased venous pressure. We have found that a great variety exists in histamine sensitivity and H(1) -histamine receptor expression in various types of rabbit veins. Veins of the extremities (saphenous vein, femoral vein, axillary vein) and abdomen (common iliac vein, inferior vena cava) responded to histamine by a prominent, concentration-dependent force generation, whereas great thoracic veins (subclavian vein, superior vena cavas, intrathoracic part of inferior vena cava) and a pelvic vein (external iliac vein) exhibited slight sensitivity to exogenous histamine. The lack of reactivity to histamine was not due to increased activity of nitric oxide synthase (NOS) or heme oxygenase-1. H(1) -histamine receptor expression of veins correlated well with the histamine-induced contractions. Voltage-dependent calcium channels mediated mainly the histamine-induced force generation of saphenous vein, whereas it did not act in the inferior vena cava. In contrast, the receptor-operated channels were not involved in this response in either vein. Tyrosine phosphorylation occurred markedly in response to histamine in the saphenous vein, but not in the inferior vena cava. Histamine induced a prominent ρ kinase activation in both vessels. Protein kinase C and mitogen-activated protein kinase (MAPK) were not implicated in the histamine-induced intracellular calcium sensitization. Importantly, transient clamping of the femoral vein in animals caused a short-term constriction, which was inhibited by H(1) -histamine receptor antagonist in vivo. Furthermore, a significantly greater histamine immunopositivity was detected in veins after stretching compared to the resting state. We conclude that histamine receptor density adapts to the actual requirements of the circulation, and histamine liberated by the venous wall during increased venous pressure contributes to the contraction of vessels, providing a force for the venous return.

G tolerance vis-à-vis pressure-distension and pressure-flow relationships of leg arteries

During increased gravitoinertial (G) load in the head-to-foot direction, pressures in dependent vascular beds are commonly raised to levels capable of distending precapillary vessels, which, in turn, may reduce arterial pressure, and hence compromise the capacity to withstand G load (G tolerance). We hypothesized that distensibility in precapillary leg vessels would be lower in a group of subjects possessing high G tolerance (H; n = 7; relaxed G tolerance = 6.6 ± 0.8 G) than in a group with low G tolerance (L; n = 8; G tolerance = 3.9 ± 0.3 G). The groups were matched with regard to gender, age, weight, height, and resting arterial pressure. Arterial pressure-distension and pressure-flow experiments were performed with the subject supine in a pressure chamber with a lower leg protruding to the outside. Increased intravascular pressure in the blood vessels of the outside leg was accomplished by stepwise increasing chamber pressure to 240 mmHg. Diameter and flow in the posterior tibial artery were measured by ultrasonographic/Doppler techniques. Pressure-induced increments in arterial diameter and flow were more pronounced (p < 0.03) in the L (14.1 ± 4.2% and 32 ± 21 ml/min respectively) than in the H (1.7 ± 5.0% and 1.6 ± 25 ml/min) group, and the pressure thresholds at which these increments commenced were lower (by 52 and 48 mmHg, respectively) in the L than in the H group (p < 0.04). Negative correlations were observed between G tolerance and the increments in diameter and flow (p < 0.02). Thus, the wall stiffness of precapillary leg vessels is greater in individuals with high relaxed G tolerance; whether a causal relationship exists remains to be established.

Lower extremity venous anatomy

The lower extremity venous system includes the superficial, deep, and perforating veins. The antegrade flow of blood within these veins is ensured by a system of muscular venous pumps and bicuspid valves. Dysfunction of the system may result from degeneration of the vein wall, post-thrombotic valvular damage, chronic venous obstruction, or dysfunction of the muscular pumps. Although chronic venous disease often receives less attention than arterial disease, it includes an array of manifestations resulting from a complex interaction of anatomy and hemodynamic failure. A thorough understanding of the highly variable venous anatomy is essential to understanding the underlying pathophysiology as well as in directing treatment.

Effects of lower-leg rhythmic cuff inflation on cardiovascular autonomic responses during quiet standing in healthy subjects

To determine the effects of muscle pump function on cardiac autonomic activity in response to quiet standing, we simulated the muscle pump effect by rhythmic lower-leg cuff inflation (RCI) with four cuff pressures of 0 (sham), 40, 80, and 120 mmHg at 5 cycles/min. The R-R interval (RRI) and beat-to-beat blood pressure (BP) were acquired in healthy subjects (6 males and 5 females, aged 21-24 yr). From the continuous BP measurement, stroke volume (SV) was calculated by a pulse-contour method. Using spectral and cross-spectral analysis, RRI and systolic BP variability as well as the gain of spontaneous cardiac baroreflex sensitivity (sBRS) were estimated for the low- and high-frequency (HF) bands. Compared with the sham condition, RCI with cuff pressures of 80 and 120 mmHg led to increases in the mean RRI (P < 0.01) and HF power of RRI fluctuation (P < 0.05 for 80 mmHg and P < 0.01 for 120 mmHg) during quiet standing. Reduction in SV during standing was suppressed, and the sBRS of the HF band for standing were increased by RCI for either cuff pressure (P < 0.05 for 80 mmHg and P < 0.01 for 120 mmHg). However, at 40 mmHg RCI, these remained unchanged. These results suggest that, during standing, RCI of the lower leg increases cardiac vagal outflow when the cuff pressure is raised enough to oppose the hydrostatic-induced venous pressure in the calf.

[New results in the research of the biomechanics of the venous system]

The upright posture of man had been a major evolutional challenge. The mechanisms responsible for orthostatic tolerance mostly affect the venous system. In this paper, we discuss new results regarding the biomechanics of the venous system highlighting a rather neglected field, the biomechanical properties of the vein wall. These properties change according to localization of veins, age, gender and body mass. The anti-gravitational adaptation of veins is a complex process involving all three layers of the venous wall. Local myogenic and humoral mechanisms as well as systemic hormonal and nervous influences control the adaptive processes in the veins. Long term adaptation involves structural and functional remodeling of the venous wall. Disorders of the veins mostly cause pathological remodeling. Hemodynamic factors (pressure and flow) together with inflammatory processes may lead to pathological alterations, changing the biomechanical properties of the vein wall, which further contribute to the reservation and progression of venous dysfunction. Appropriate testing of venous function can reveal biomechanical disorders even in clinically asymptomatic patients. Thus, biomechanical investigation of veins not only helps to understand the underlying pathomechanism but it also can contribute to early diagnosis and follow-up of venous disorders. When recognized in time, pathological remodeling can be prevented or treated. In this way, the incidence of venous disorder could be cut back reducing both human suffering and material loss.

Percutaneous management of chronic deep venous reflux: review of experimental work and early clinical experience with bioprosthetic valve

Lower extremity chronic deep venous insufficiency (CDVI) is common and remains a major health problem worldwide. Selected patients benefited from direct deep vein valve surgical repair or valve transplantation. A major limitation of this approach is that most of the patients are not candidates for these procedures due to obstructions or residual thrombus throughout the vein. The past 15 years have witnessed experimental efforts at catheter-based management of CDVI. This review describes the initial designs and experimental evolution of a mechanical and bioprosthetic venous valve that can be implanted by using a transcatheter technique. These valves consisted of single, double, or triple cusp leaflets made of synthetic or biological materials attached to a carrier or frame. All described devices for percutaneous transcatheter valve placement rely on some form of a vascular stent for valve attachment.

Assessment of orthostatic fluid shifts with strain gauge plethysmography

In the present study we evaluated the use of SGP (strain gauge plethysmography) for the assessment of orthostatic fluid shifts during HUT (head-up tilting). Subjects wore a parachute harness fixed to the tilt table to avoid muscle tension in the lower limbs during HUT. Twenty-two healthy subjects (nine women) were tilted for 5 min. Changes in calf volume, as measured by SGP, surface EMG (electromyography), heart rate and blood pressure were measured continuously. Ten subjects underwent a second tilt test during which circulation in one leg was occluded with a pressure cuff at 250 mmHg. During HUT with occlusion, calf volume in the non-occluded leg increased by 1.9±0.3% (mean±S.E.M.) and 0.2±0.2% in the occluded leg (P<0.001). During HUT without occlusion a significant correlation (r=0.9) was found between measurements in the left and right leg with a mean difference of 0.03±0.1%. HUT did not cause significant changes in surface EMG measurements. An unexpected gender effect was observed: calf volume increased significantly more in men than in women. Men were significantly taller, but the haemodynamic response to HUT did not differ between both genders. The gender effect on orthostatic increases in calf volume remained significant after adjustment for heart-to-calf distance. SGP during HUT with a parachute harness is a new promising method to assess orthostatic fluid shifts. The gender differences in orthostatic pooling in the calf may be explained by a higher calf compliance in men together with a greater hydrostatic pressure due to a greater height in men.

Pathophysiological basis of orthostatic hypotension in autonomic failure

In patients with autonomic failure orthostatic hypotension results from an impaired capacity to increase vascular resistance during standing. This fundamental defect leads to increased downward pooling of venous blood and a consequent reduction in stroke volume and cardiac output that exaggerates the orthostatic fall in blood pressure. The location of excessive venous blood pooling has not been established so far, but present data suggest that the abdominal compartment and perhaps leg skin vasculature are the most likely candidates. To improve the orthostatic tolerance in patients with autonomic failure, protective measures that reduce excessive orthostatic blood pooling have been developed and evaluated. These measures include physical counter-manoeuvres and abdominal compression.

Venous outflow of the leg: anatomy and physiologic mechanism of the plantar venous plexus

PURPOSE

Mechanisms of venous outflow from the leg and foot have not been clearly defined. The purpose of this study was to evaluate the anatomy and physiologic mechanism of the plantar venous plexus and its impact on venous drainage from the tibial veins.

METHODS

Fifty phlebograms that contained complete foot and calf films were reviewed. On lateral films, the number of veins in the plantar venous plexus and its tibial outflow tract were counted. The length and diameter of the longest vein in the plantar venous system and the length of the foot arch were measured. The ratio of the length of the plantar venous plexus to the arch length was calculated. The presence or absence of valves within the plexus was recorded. Plantar venous plexus outflow was evaluated by an duplex ultrasonographic scan of the posterior tibial, anterior tibial, and peroneal veins during intermittent external pneumatic compression of the plantar surface of the foot.

RESULTS

The plantar venous plexus was composed of one to four large veins (mean, 2.7 veins) within the plantar aspect of the foot. The diameter of these veins was 4.0 +/- 1.2 mm. The veins coursed diagonally from a lateral position in the forefoot to a medial position at the level of the ankle, spanning 75% of the foot arch. Prominent valves were recognized within the plantar veins in 22 of 50 patients. The plexus coalesced into an outflow tract of one to four veins (mean, 2.5 veins) that flowed exclusively into the posterior tibial venous system. Small accessory veins that drained the plantar surface of the forefoot flowed into either the posterior tibial or peroneal veins. This pattern of selective drainage of the plantar venous plexus was confirmed by duplex imaging. Mechanical compression of the plantar venous plexus produced a mean peak velocity in the posterior tibial veins of 123 +/- 71 cm/sec, in the anterior tibial veins of 24 +/- 14 cm/sec, and in the peroneal veins of 29 +/- 26 cm/sec.

CONCLUSIONS

The plantar venous plexus is composed of multiple large-diameter veins that span the arch of the foot. Compression of the plantar venous plexus, such as that which occurs during ambulation, is capable of significantly increasing flow through the posterior tibial venous system into the popliteal vein. Its function may be integral to venous outflow from the calf and priming of the more proximal calf muscle pump.

Diagnosis and treatment of varicose veins: a review

Varicose veins are superficial vessels that are abnormally twisted, lengthened, or dilated and are usually caused by inefficient or defective valves within the vein. They represent a medical condition accompanied by symptoms deserving treatment. Varicose veins are a manifestation of venous disease that may precede later severe complications. Varicosities cause cutaneous disease in addition to complications specific to the venous system. This article reviews the epidemiology, adverse sequelae, anatomy, pathophysiology, evaluation, and treatment of varicose veins.

Posture and the circulation: the age effect

The primary instigator of circulatory response to the upright posture is the rapid displacement of about 10% of blood volume from the thorax to the lower body. The resultant hemodynamic deficit induces postural intolerance, especially orthostatic hypotension, in elderly over 70 years of age and in some young subjects after exposure to weightlessness. In this review, our objectives have been: 1) to describe in the normal subject the hemodynamic consequences of the headup posture, as well as lower body negative pressure, the compensatory responses intended to cope with these stresses, and their mechanisms; 2) to outline the effect of age on the circulatory responses to these stresses; and (3) to analyze and compare the tests currently used to assess circulatory tolerance. Our ability to design effective countermeasures to orthostatic circulatory intolerance is severely handicapped by our inadequate knowledge of the basic hemodynamic events incident to normal and abnormal orthostatic tolerance. We believe that better understanding and standardization of the postural tests, better experimental design to include greater emphasis on inter and intra-individual variability, and wider application of currently available noninvasive circulatory techniques would greatly improve the prospects for success in this research area.

On the edema-preventing effect of the calf muscle pump

During motionless standing an increased hydrostatic pressure leads to increased transcapillary fluid filtration into the interstitial space of the tissues of the lower extremities. The resulting changes in calf volume were measured using a mercury-in-silastic strain gauge. Following a change in body posture from lying to standing or sitting a two-stage change in calf volume was observed. A fast initial filling of the capacitance vessels was followed by a slow but continuous increase in calf volume during motionless standing and sitting with the legs dependent passively. The mean rates of this slow increase were about 0.17%.min-1 during standing and 0.12%.min-1 during sitting, respectively. During cycle ergometer exercise the plethysmographic recordings were highly influenced by movement artifacts. These artifacts, however, were removed from the recordings by low-pass filtering. As a result the slow volume changes, i.e. changes of the extravascular fluid were selected from the recorded signal. Contrary to the increases during standing and sitting the calf volumes of all 30 subjects decreased during cycle ergometer exercise. The mean decrease during 18 min of cycling (2-20 min) was -1.6% at 50 W work load and -1.9% at 100 W, respectively. This difference was statistically significant (p less than or equal to 0.01). The factors which may counteract the development of an interstitial edema, even during quiet standing and sitting, are discussed in detail. During cycling, however, three factors are most likely to contribute to the observed reduction in calf volume: (1) The decrease in venous pressure, which in turn reduces the effective filtration pressure.(ABSTRACT TRUNCATED AT 250 WORDS)

Responses of spinal cord neurons following stimulation of A beta femoral-saphenous venous afferent fibers

A population of large (A beta) afferents is known to have endings in the wall of the femoral-saphenous vein. These afferents project to the lower lumbar spinal cord. The purpose of the present study was to identify, localize, and characterize spinal neurons that receive inputs from such afferents. Responses of 50 neurons in the L6 spinal cord segment of decerebrate-spinal cats or intact cats anesthetized using alpha-chloralose were recorded following electrical stimulation of these afferents. Observations were also made on the convergence of muscle and cutaneous afferent inputs onto neurons driven by stimulation of afferents terminating in the femoral-saphenous vein. All recording sites were marked either by intracellularly staining the element characterized with HRP or by extracellularly iontophoresing a small quantity of this tracer. The cells were driven for long durations (mean of 51.5 ms, S.E.M. of 10.0) by single-shock stimulation of femoral-saphenous venous afferents. The recording sites were located in Rexed's laminae IV-VIII and X. Eight of the 50 neurons were activated by venous afferent stimulation at latencies equal to or shorter than that of the first negative wave of the cord dorsum potential; these units were driven at a mean latency of 1.4 ms (S.E.M. of 0.25) following the arrival of the afferent volley at the cord and were assumed to receive monosynaptic, or at least relatively direct, inputs from the primary afferents. Most of these cells (6 of 8) were located in lamina V. The majority of the neurons studied (37 of 50) were activated at latencies longer than 3 ms following the arrival of the afferent volley at the cord; about half (19 of 37) of those activated at longer latencies were located in lamina VII, and the rest were scattered among the other laminae. Twenty-eight of 40 venous afferent-driven cells tested could also be activated by electrical stimulation of either the posterior tibial or sural nerve. In general, the stimulation intensities necessary to activate the neurons were only sufficient to excite large (A alpha or A beta) muscle and cutaneous afferents. Neurons receiving the shortest latency inputs from the femoral-saphenous vein were less likely to receive convergent inputs from muscle or skin than were neurons activated by venous afferents at longer latency.