Application Areas of Intermittent Pneumatic Compression in the Prevention of Deep Vein Thrombosis During Dixon Surgery: A Randomized, Controlled Trial

PURPOSE

Deep vein thrombosis (DVT) is common in the lithotomy position after laparoscopic surgery. Intermittent pneumatic compression (IPC) plays an important role in DVT prevention. However, few studies have compared the different compression areas of IPC application. It was hypothesized that the location of the compression sleeves could have an impact on the effects of thromboprophylaxis.

METHODS

In this randomized, controlled trial performed from August 2020 to March 2021, 164 patients scheduled to undergo laparoscopic Dixon surgery were randomly assigned to one of four groups, based on the bilateral placement of compression sleeves during surgery: feet, calves, thighs, or control (no IPC). Both lower extremities were monitored for DVT on days 1 and 7 after surgery, using ultrasonographic assessment of mean blood velocity, blood flow volume, and diameter of the common femoral veins. Thrombosis-related hematologic analysis was performed.

FINDINGS

On day 1 after surgery, IPC of the feet or calves was associated with a reduced prevalence of DVT compared with controls (both: P = 0.024; OR = 0.09; 95% CI, 0.01-0.72), while IPC of the thighs had no significant benefit (P = 0.781; OR = 0.86; 95% CI, 0.29-2.55). The prevalence of DVT in the left extremity was lower with IPC of the feet and calves compared with controls (both, P = 0.048). The mean blood velocity in the common femoral vein was significantly increased after surgery with IPC of the left and right feet (P = 0.006 and 0.007, respectively) and calves (P = 0.011 and P = 0.026, respectively) compared with controls. Similarly, the volume of blood flow in the left common femoral vein was greater with IPC of the feet and calves (P = 0.03 and 0.027, respectively). However, on day 7 after surgery, the between-group differences in the prevalences of DVT and hematologic indicators of thrombosis were not significant.

IMPLICATIONS

On day 1 after surgery, IPC application at the feet or calves facilitated venous return and, hence, reduced the prevalence of DVT, especially in the left extremities. However, there were no significant differences in the prevalences of DVT or thrombosis-related hematologic indicators among the four groups on the day 7 after surgery. Chinese Clinical Trial Registration identifier: ChiCTR2000035325.

Factors related to the size of venous leg ulcers: A cross-sectional study

Venous leg ulcers (VLUs) are an important health problem, and the size of ulcers often affects patient care, healing time, and quality of life. However, the risk factors associated with ulcer size have been rarely reported. The aim of this study was to establish the risk factors for the size of venous ulceration by analyzing the patient demographics and the results of duplex ultrasonography.This study was an in-patient population-based cross-sectional study conducted at a single center during the period from 2013 to 2017. Men and women aged >18 years, who consecutively presented to our hospital with VLU, were included. According to the size of the ulcer, patients were divided into two groups, those with ulcers≤2 cm and those with ulcers >2 cm. Demographic, anthropometric, and clinical data were collected. For the analysis, univariate and multivariate logistic regressions were used.A total of 232 patients with VLUs were admitted to our hospital from 2013 to 2017, including 117 patients (50.4%) with ulcer diameters ≤2 cm and 115 patients (49.6%) with ulcer diameters >2 cm. According to the results of the multivariate analysis, the ulcer duration (P = .001), the diameter of perforating veins (PVs) around the ulcers (P = .025), the reflux time of common femoral veins (CFVs) (P = .013), the reflux time of great saphenous veins (GSVs) (P = .021), and the reflux time of PVs around the ulcers (P = .001) were independent risk factors for VLUs.These findings provide evidence that the size of VLU was significantly related to the ulcer duration, the diameter of PV around the ulcers, the CFV reflux time, the GSV reflux time, and the PV reflux time.

Cross-sectional areas of deep/core veins are smaller at lower core body temperatures

The cardiovascular system plays a crucial role in thermoregulation. Deep core veins, due to their large size and role in returning blood to the heart, are an important part of this system. The response of veins to increasing core temperature has not been adequately studied in vivo. Our objective was to noninvasively quantify in C57BL/6 mice the response of artery-vein pairs to increases in body temperature. Adult male mice were anesthetized and underwent magnetic resonance imaging. Data were acquired from three colocalized vessel pairs (the neck [carotid/jugular], torso [aorta/inferior vena cava (IVC)], periphery [femoral artery/vein]) at core temperatures of 35, 36, 37, and 38°C. Cross-sectional area increased with increasing temperature for all vessels, excluding the carotid. Average area of the jugular, aorta, femoral artery, and vein linearly increased with temperature (0.10, 0.017, 0.017, and 0.027 mm2 /°C, respectively; P < 0.05). On average, the IVC has the largest venous response for area (18.2%/°C, vs. jugular 9.0 and femoral 10.9%/°C). Increases in core temperature from 35 to 38 °C resulted in an increase in contact length between the aorta/IVC of 29.3% (P = 0.007) and between the femoral artery/vein of 28.0% (P = 0.03). Previously unidentified increases in the IVC area due to increasing core temperature are biologically important because they may affect conductive and convective heat transfer. Vascular response to temperature varied based on location and vessel type. Leveraging noninvasive methodology to quantify vascular responses to temperature could be combined with bioheat modeling to improve understanding of thermoregulation.

Vector and Doppler Ultrasound Velocities Evaluated in a Flow Phantom and the Femoropopliteal Vein

Ultrasound is used for evaluating the veins of the lower extremities. Operator and angle dependency limit spectral Doppler ultrasound (SDUS). The aim of the study was to compare peak velocity measurements in a flow phantom and the femoropopliteal vein of 20 volunteers with the angle-independent vector velocity technique vector flow imaging (VFI) and SDUS. In the flow phantom, VFI underestimated velocity (p = 0.01), with a lower accuracy of 5.5% (p = 0.01) and with no difference in precision, that is, error factor, compared with SDUS (VFI: 1.02 vs. SDUS: 1.02, p = 0.58). In vivo, VFI estimated lower velocities (femoral: p = 0.001; popliteal: p = 0.001) with no difference in precision compared with SDUS (femoral: VFI 1.09 vs. SDUS 1.14, p = 0.37; popliteal: VFI 1.13 vs. SDUS 1.06, p = 0.09). In conclusion, the precise VFI technique can be used to characterize venous hemodynamics of the lower extremities despite its underestimation of velocities.

The Venous Reflux

Venous reflux is the most common cause of venous hemodynamic disorders. In this paper 2 issues are discussed: how and where does reflux arise and what are the hemodynamic consequences of retrograde flow. Pressure gradient and incompetent vein connecting both poles of the gradient are the prerequisite for venous reflux to arise. Ambulatory pressure gradient occurs during the activity of the calf muscle venous pump between deep veins of the thigh and the lower leg. Thus the incompetent reflux-carrying vein must connect the popliteal, femoral, profunda femoris, or iliac vein with 1 of the deep veins of the lower leg. Reflux can be considered as shunting of blood from thigh veins into the lower leg veins. The most frequently found incompetent veins are the long and short saphenous veins and perforators communicating with deep veins of the thigh. On the other hand, calf perforators emptying into the deep veins of the lower leg, where the lower pole of the pressure gradient is located, cannot be the feeding source of reflux. A physiological bidirectional flow takes place in calf perforators connecting superficial and deep veins of the lower leg and making them conjoined vessels. Venous reflux produces ambulatory venous hypertension. The quantity of reflux volume and not the localization of retrograde flow in superficial or deep veins is the most important hemodynamic factor. Reflux in superficial veins, when large enough, can cause the most serious symptoms of chronic venous insufficiency including leg ulcers. Plethysmographic findings have shown that incompetence of the femoral and calf perforating veins is hemodynamically unimportant. Large incompetent calf perforators are not the cause of venous abnormality but are the consequence of saphenous retrograde flow.

Peripheral veins: influence of gender, body mass index, age and varicose veins on cross-sectional area

To investigate changes in the size of the deep and superficial venous systems associated with gender, age, body mass index and varicose veins, changes to the cross-sectional area of the femoral and the long saphenous veins were analysed in the Duesseldorf=Essen civil servant study population. Between December 1989 and July 1993 a total of 9935 employees were recruited; 9261 were then evaluated for this analysis. Diameters of the long saphenous and femoral veins were determined 2-3 cm distal to the confluence in lying (after 15 min rest) and standing (after 5 min) positions. Cross-sectional areas (CSA) were calculated. A total of 63% of all people were assigned to CEAP (clinical, etiological, anatomical pathophysiological) class 0, 27% to class 1, 8.5% to class 2, while 1.5% belonged to higher CEAP classes. In people without varicose veins (CEAP class 0) the CSA of the femoral and long saphenous veins were smaller in females than in males. In people with a normal body mass index (BMI) (20-25) the mean CSA of the femoral and long saphenous veins in a standing position was similar from the third up to the sixth decade of life. The volume increase due to a standing position expressed as the absolute increase in CSA of the femoral and long saphenous veins was not age-related, either. The relative volume increase expressed as a ratio remained unchanged with age. There was a strong relationship between the CSA of both veins and increasing BMI. In a lying position, the CSA of the femoral and long saphenous veins increased only slightly with increasing CEAP classes. In a standing position, the CSA of both veins increased even in CEAP class 1 (p < 0.001). In a stepwise multivariate regression analysis, the CSA of both veins in a standing position was not age-related but associated with BMI, CEAP classes and gender. The absolute increase in CSA was influenced by all four variables, but BMI and gender were most important. In Conclusion, this study shows that aging is not necessarily associated with an increase in venous CSA of the deep and superficial venous system. BMI is the most important determinant for an increase in CSA in standing position. Varicosity of the superficial venous system is always associated with similar changes in the deep venous system.

Novel method to assess arterial insufficiency in rodent hind limb

BACKGROUND

Lack of techniques to assess maximal blood flow capacity thwarts the use of rodent models of arterial insufficiency to evaluate therapies for intermittent claudication. We evaluated femoral vein outflow (VO) in combination with stimulated muscle contraction as a potential method to assess functional hind limb arterial reserve and therapeutic efficacy in a rodent model of subcritical limb ischemia.

MATERIALS AND METHODS

VO was measured with perivascular flow probes at rest and during stimulated calf muscle contraction in young, healthy rats (Wistar Kyoto, WKY; lean Zucker rats, LZR) and rats with cardiovascular risk factors (spontaneously hypertensive [SHR]; obese Zucker rats [OZR]) with acute and/or chronic femoral arterial occlusion. Therapeutic efficacy was assessed by administration of Ramipril or Losartan to SHR after femoral artery excision.

RESULTS

VO measurement in WKY demonstrated the utility of this method to assess hind limb perfusion at rest and during calf muscle contraction. Although application to diseased models (OZR and SHR) demonstrated normal resting perfusion compared with contralateral limbs, a significant reduction in reserve capacity was uncovered with muscle stimulation. Administration of Ramipril and Losartan demonstrated significant improvement in functional arterial reserve.

CONCLUSIONS

The results demonstrate that this novel method to assess distal limb perfusion in small rodents with subcritical limb ischemia is sufficient to unmask perfusion deficits not apparent at rest, detect impaired compensation in diseased animal models with risk factors, and assess therapeutic efficacy. The approach provides a significant advance in methods to investigate potential mechanisms and novel therapies for subcritical limb ischemia in preclinical rodent models.

Flow increase is decisive to initiate angiogenesis in veins exposed to altered hemodynamics

Exposing a vein to altered hemodynamics by creating an arteriovenous (AV) shunt evokes considerable vessel formation that may be of therapeutic potential. However, it is unclear whether the introduction of oscillatory flow and/or flow increase is decisive. To distinguish between these mechanical stimuli we grafted a femoral vein into the arterial flow pathway of the contralateral limb in rats creating an arterioarterial (AA) loop (n = 7). Alternatively, we connected the femoral artery and vein using the vein graft, whereby we created an AV-loop (n = 27). Vessel loops were embedded in a fibrin filled chamber and blood flow was measured by means of flow probes immediately after surgery (day 0) and 15 days after loop creation. On day 15, animals were sacrificed and angiogenesis was evaluated using μCT and histological analysis. Mean flow increased from 0.5 to 2.4 mL/min and was elevated throughout the cardiac cycle at day 0 in AV-loops whereas, as expected, it remained unchanged in AA-loops. Flow in AV-loops decreased with time, and was at day 15 not different from untreated femoral vessels or AA-loop grafts. Pulsatile flow oscillations were similar in AV-and AA-loops at day 0. The flow amplitude amounted to ~1.3 mL/min which was comparable to values in untreated arteries. Flow amplitude remained constant in AA-loops, whereas it decreased in AV-loops (day 15: 0.4 mL/min). A large number of newly formed vessels were present in AV-loops at day 15 arising from the grafted vein. In marked contrast, angiogenesis originating from the grafted vein was absent in AA-loops. We conclude that exposure to substantially increased flow is required to initiate angiogenesis in grafted veins, whereas selective enhancement of pulsatile flow is unable to do so. This suggests that indeed flow and most likely wall shear stress is decisive to initiate formation of vessels in this hemodynamically driven angiogenesis model.

High flow conditions increase connexin43 expression in a rat arteriovenous and angioinductive loop model

Gap junctions are involved in vascular growth and their expression pattern is modulated in response to hemodynamic conditions. They are clusters of intercellular channels formed by connexins (Cx) of which four subtypes are expressed in the cardiovascular system, namely Cx37, Cx40, Cx43 and Cx45. We hypothesize that high flow conditions affect vascular expression of Cx in vivo. To test this hypothesis, flow hemodynamics and subsequent changes in vascular expression of Cx were studied in an angioinductive rat arteriovenous (AV) loop model. Fifteen days after interposition of a femoral vein graft between femoral artery and vein encased in a fibrin-filled chamber strong neovascularization was evident that emerged predominantly from the graft. Blood flow through the grafted vessel was enhanced ∼4.5-fold accompanied by increased pulsatility exceeding arterial levels. Whereas Cx43 protein expression in the femoral vein is negligible at physiologic flow conditions as judged by immunostaining its expression was enhanced in the endothelium of the venous graft exposed to these hemodynamic changes for 5 days. This was most likely due to enhanced transcription since Cx43 mRNA increased likewise, whereas Cx37 mRNA expression remained unaffected and Cx40 mRNA was reduced. Although enhanced Cx43 expression in regions of high flow in vivo has already been demonstrated, the arteriovenous graft used in the present study provides a reliable model to verify an association between Cx43 expression and high flow conditions in vivo that was selective for this Cx. We conclude that enhancement of blood flow and its oscillation possibly associated with the transition from laminar to more turbulent flow induces Cx43 expression in a vein serving as an AV loop. It is tempting to speculate that this upregulation is involved in the vessel formation occuring in this model as Cx43 was suggested to be involved in angiogenesis.

[Effect of intermittent pneumatic compression on coagulation function and deep venous hemodynamics of lower limbs after rectal cancer resection]

OBJECTIVE

To investigate the effects of intermittent pneumatic compression (IPC) on coagulation function, deep venous hemodynamics and prevention of deep venous thrombosis (DVT) of lower limbs in patients after rectal cancer resection.

METHODS

A total of 120 patients undergoing rectal cancer resection were randomly divided into non-IPC group (control group, n=60) and IPC group (n=60). The control group received routine treatment after resection and the IPC group received IPC based on the routine treatments. Prothrombin time (PT), activated partial thromboplastin time (APTT), fibrinogen (FIB), international normalized ratio (INR) and volume of D-dimer (D-D) were detected before operation and 1-, 3-, 5- and 7-day after operation. Meanwhile, blood flow velocity and caliber of external iliac vein, femoral vein and popliteal vein were examined by color Doppler ultrasound, then the average blood flow velocity and blood flow volume were calculated.

RESULTS

Incidence of lower limb DVT was 13.3% (8/60) and 1.7% (1/60) in control group and IPC group respectively with significant difference (P<0.05). The differences in PT, APTT and INR were not significant (P>0.05) at 1-day after operation as compared to the preoperative level, while FIB and D-D both increased (P<0.05), all presented no significant difference among the two groups (P>0.05). PT shortened gradually (P<0.05), APTT and INR did not change significantly (P>0.05), FIB and D-D increased gradually (P<0.05), and no significant differences were found between the two groups at the same time point (all P>0.05). All the above parameters in the control group were significantly lower than those in IPC group (all P<0.05).

CONCLUSIONS

IPC can improve hemodynamics indexes of deep veins of lower limb in patients after rectal cancer operation, and prevent the lower limb DVT. IPC is a safe, simple and convenient physical therapy.

Intermittent pneumatic compression. A comparison of femoral vein velocity with five different devices

AIM

Different mechanical devices for thromboprophylaxis have different flow characteristics. A new device (Vadoplex) has been developed to provide a short impulse around the calf, a concept derived from the efficacy of foot impulse technology. New devices should be compared with existing devices to establish whether it has a comparable ability to augment venous velocity. Objectives of the study were to compare the venous velocity induced by the Vadoplex with established intermittent pneumatic calf and leg compressors (Covidien and Huntleigh).

METHODS

The venous velocity was established in ten healthy volunteers with standardised Duplex ultraonography of the common femoral vein. Measurements were taken at rest and on standing, with each device inactive and active.

RESULTS

The Vadoplex induced an increased femoral venous velocity at least as enhanced as established calf and full leg sleeves.

CONCLUSION

Calf impulse technology is an alternative to other systems in enhancing femoral vein blood flow, itself a surrogate for assumed thromboprophylactic effect.

Exercise reduces angiotensin II responses in rat femoral veins

The control of blood flow during exercise involves different mechanisms, one of which is the activation of the renin-angiotensin system, which contributes to exercise-induced blood flow redistribution. Moreover, although angiotensin II (Ang II) is considered a potent venoconstrictor agonist, little is known about its effects on the venous bed during exercise. Therefore, the present study aimed to assess the Ang II responses in the femoral vein taken from sedentary and trained rats at rest or subjected to a single bout of exercise immediately before organ bath experiments. Isolated preparations of femoral veins taken from resting-sedentary, exercised-sedentary, resting-trained and exercised-trained animals were studied in an organ bath. In parallel, the mRNA expression of prepro-endothelin-1 (ppET-1), as well as the ETA and ETB receptors, was quantified by real-time PCR in this tissue. The results show that, in the presence of L-NAME, Ang II responses in resting-sedentary animals were higher compared to the other groups. However, this difference disappeared after co-treatment with indomethacin, BQ-123 or BQ-788. Moreover, exercise reduced ppET-1 mRNA expression. These reductions in mRNA expression were more evident in resting-trained animals. In conclusion, either acute or repeated exercise adapts the rat femoral veins, thereby reducing the Ang II responses. This adaptation is masked by the action of locally produced nitric oxide and involves, at least partially, the ETB- mediated release of vasodilator prostanoids. Reductions in endothelin-1 production may also be involved in these exercise-induced modifications of Ang II responses in the femoral vein.

Dynamic ultrasound and treadling: novel approaches to assess and improve lower extremity circulation

The purpose of this study was to evaluate the safety and efficacy of a novel treatment of peripheral vascular disease through treadling and to report a dynamic vascular ultrasound technique. After informed consent, 17 volunteers were enrolled in the study. Ultrasound was used to measure venous and arterial waveforms at the superficial femoral artery and vein in the subject's right thigh during a 5-minute baseline evaluation (resting), a 10-minute treadling period, and a 5-minute cool down period. Comparisons between flow velocities were made during the three trial periods using a Repeated Measures Mixed Linear Model test with P < 0.05 considered significant. Twenty-six examinations were performed on subjects with an average age of 37 years (range, 25-75 years). Significant increases in maximum and minimum arterial and venous flow velocities during the treadling time compared with the resting and cool down period were observed (P < 0.0001) with no change in the subjects' vital signs. We found no significant difference in maximum and minimum arterial and venous flow velocities between the resting and cool down period (P > 0.05). There were no untoward side effects, and all subjects were able to complete the protocol. Low-resistance treadling is safe and improves venous and arterial flow. Dynamic peripheral ultrasonography is a viable technique to assess flow during treadling. Potential future implications of this study include the evaluation, treatment, and management of lower extremity vascular and chronic diseases and more sensitive peripheral vascular sonography through dynamic ultrasound.

[Ultrasonic study of deep-vein diameter and blood flow spectrum changes in full-term pregnant women]

OBJECTIVE

To explore the changes in lower limb deep vein diameters, blood flow velocity and blood biochemistry in full-term pregnant women for early diagnosis and treatment of prothrombotic state.

METHODS

One hundred and twenty-eight full-term pregnant women at high risk of thrombosis (Group A), 61 healthy full-term pregnant women (Group B), and 42 healthy non-pregnant women (Group C) underwent high-resolution color Doppler ultrasound (CDU) for examining the deep veins of the lower limbs. The hematological indexes such as D-D, PLT, HGB, HCT, TT, APTT, PT, and FbgC were also observed in these 3 groups.

RESULTS

Compared to Group B, the women in group A showed significantly increased diameters of the common femoral veins (CFV) and left superficial femoral vein (SFV), HCT and DD, but with significantly decreased peak blood flow in the bilateral popliteal veins (POPV) (P<0.01) and increased left POPV diameter (P=0.034). Compared to those in group C, the diameters of the bilateral CFVs, SFVs, POPV, and posterior tibial veins (PTVs) were significantly increased, but the peak blood flow in the bilateral CFVs and POPVs were significantly reduced in groups A and B; the PLT, HGB, HCT, DD, TT, APTT, PT, and FbgC also showed significant changes in groups A and B (P<0.01).

CONCLUSION

The full-term pregnant women are at higher risk of prothrombotic state than non-pregnant women, and the full-term pregnant women with the high risk factors for thrombosis are more likely to have prothrombotic state than healthy full-term pregnant women. CDU examination of the lower limb deep veins can be of value in the diagnosis of prothrombotic state.

Regional differences in veins wall viscosity, compliance, energetics and damping: analysis of the pressure-diameter relationship during cyclical overloads

BACKGROUND

The characterization of the dynamic process of veins walls is essential to understand venous functioning under normal and pathological conditions. However, little work has been done on dynamic venous properties.

AIM

To characterize vein compliance (C), viscosity (eta), peak-strain (W St) and dissipated (W(D)) energy, damping (zeta), and their regional differences in order to evaluate their role in venous functioning during volume-pressure overloads.

METHODS

In a mock circulation, pressure (P) and diameter (D) of different veins (anterior cava, jugular and femoral; from 7 sheep), were registered during cyclical volume-pressure pulses. From the P-D relationship, C, W(St) and zeta (at low and high P-D levels), eta and W(D) were calculated.

RESULTS

For each vein there were P-dependent differences in biomechanical, energetics, and damping capability. There were regional-differences in C, eta), W(St) and W(D) (p<0.05), but not in zeta.

CONCLUSION

The regional-dependent differences in dynamics and energetics, and regional-similitude in damping could be important to ensure venous functioning during acute overloads. The lower C and higher W(St) and W(D) found in back-limb veins (femoral), commonly submitted to high volume-pressure loads (i.e. during walking), could be considered relevant to ensure adequate venous system functionality and venous wall protection simultaneously.

[Baroreflexes originated in vertebral artery zones upon peripheral vein tonus, systemic arterial blood pressure, and external respiration]

The investigation was intended to study the role ofbaroreceptors ofhemodynamically isolated zone of vertebral arteries in regulation of peripheral veins tonus, arterial pressure and external respiration. Pressure decrease in this vascular reflexogenic zone led to reflex responses of increase in femoral vein tonus, elevation of blood pressure level and stimulation of external respiration. The opposite reflex responses of cardio-respiratory functional system to initial pressure activation of vertebral arteries baroreceptors are observed. Basing on generalization of our own findings and similar physiological and morphological researches of other authors, it is established that afferentation from the vertebral artery zone is a reflexogenic factor of somatic muscles' veins tonus regulation. These reflexes of capacity vessels tonic activity changes are part of cardio-respiratory responses of maintaining the tissue gaseous exchange.

Measurement of hemodynamic and anatomic parameters in a swine arteriovenous fistula model

PURPOSE

Although arteriovenous fistulae (AVFs) are currently the preferred mode of permanent hemodialysis access they do have significant problems due to initial non-maturation and a later venous stenosis. These problems appear to have been exacerbated following a push to increase AVF prevalence in the US. The reasons for both AVF non-maturation and the later venous stenoses are unclear but are thought to be related to abnormal hemodynamic wall shear stress (WSS) profiles. This technical note aims to describe the successful development of measurement techniques that can be used to establish a complete hemodynamic profile in a pig model with two different configurations of AVF.

METHODS AND RESULTS

The curved and straight AVF configurations were created in an in vivo pig model. Flow and pressure in the AVFs were measured using the perivascular flow probes and Doppler flow wires while the pressure was recorded using a pressure transducer. The anatomical configuration was obtained using two different approaches: a) combination of intravascular ultrasound (IVUS) and angiograms, (b) 64 slice CT angiography. 3D models were reconstructed using image processing and computer modeling techniques. Numerical calculations were then performed by applying the measured flow and pressure data into the configurations to obtain the hemodynamic WSS profiles.

CONCLUSION

The described methodologies will allow the calculation and optimization of WSS profiles in animal models. This information could then be translated to the clinical setting where it would have a positive impact on improving the early maturation rates of AVFs as well as reducing the late venous stenoses.

Immediate removal of femoral-sheath following protamine administration in patients undergoing intracoronary paclitaxel-eluting-stent implantation

BACKGROUND

Immediate sheath-removal using post-procedural reversal of heparin with protamine reduces groin complications, shortens bed rest and hospital stay after percutaneous coronary intervention (PCI) with bare-metal stents. No data are available with newer and possibly more thrombogenic paclitaxel-eluting stents (PES).

AIM

We assessed the safety and efficacy of post-procedural protamine administration after successful coronary PES implantation in elective PCI and in patients with acute coronary syndromes (ACS).

METHODS

A consecutive series of 291 patients received 0.5 mg of protamine per 100 units of heparin whenever the post-procedural ACT was > 180 seconds, followed by immediate removal of the sheath (protamine group). Outcomes were compared to a historic control group comprising 291 consecutive patients, who also underwent PCI with PES, but without reversal of anticoagulation by protamine (non protamine group). The incidence of post-procedural vascular complications and bleeding complications, as well as hospital stay, were compared; as were the incidence of major cardiac events at 24 h, 30 days and 6 months.

RESULTS

The post-procedural bleeding complications were significantly higher in the non-protamine group. Vascular complications were also more frequent in patients who were not treated with protamine. Hospitalisation length was significantly lower in the protamine group than in the non-protamine group (13.6 +/- 7 h versus 20.41 +/- 3.9 h; p < 0.001). The protamine-group patients also had a significantly reduced bed rest (10.3 h +/- 5.6 h versus 18 h +/- 3.5 h; p < 0.001). During hospitalisation, after PES implantation, no deaths or acute stent thrombosis were observed in either group. The overall incidence of thrombosis and major adverse cardiac events at follow-up were similar in the two groups.

CONCLUSIONS

Immediate heparin neutralisation by protamine after successful PES implantation appears to be safe and feasible, also in patients with ACS. Use of protamine and early sheath removal after PCI confers early deambulation and may significantly limit healthcare cost, reduce vascular complications, bedrest, delayed discharge and patient discomfort.

A randomized blinded comparison of two methods used for venous antistasis in tetraplegia

OBJECTIVE

The hemodynamic effects of slow sequential compression (SCD) were compared with rapid intermittent pulsatile compression (IPC) in subjects with complete tetraplegia.

METHODS

Twenty subjects underwent Doppler examination of the bilateral popliteal and femoral veins. Resting volume flow per minute (VFM), average venous velocity (AVV), and maximal venous velocity (MVV) were measured in both veins. SCD and IPC were then randomly applied to one limb each, followed by repeat Doppler measurements under compression conditions. Doppler spectral recordings were stored for future analysis, and then measured by an investigator blinded to testing conditions (rest versus compression) and device (SCD versus IPC).

RESULTS

Sequential compression and IPC compression both increased popliteal and femoral vein VFM, AVV, and MVV above resting levels (all p's < 0.001). In the femoral vein VFM (p < 0.05) and MVV (p < 0.05) were augmented during IPC compared to SCD compression.

CONCLUSION

As MVV best reflects performance effectiveness of compression devices, these data find IPC more effective than SCD for stimulating venous blood flow in subjects with tetraplegia.

Humming Is as Effective as Valsalva’s Maneuver and Trendelenburg’s Position for Ultrasonographic Visualization of the Jugular Venous System and Common Femoral Veins

STUDY OBJECTIVE

The purpose of this study is to compare ultrasonographic visualization of the jugular and common femoral veins by using a novel technique (humming) and 2 conventional techniques (Valsalva's maneuver and Trendelenburg's position). The Valsalva's maneuver and Trendelenburg's position are common methods for producing venous distention, aiding ultrasonographically guided identification and cannulation of the jugular and common femoral veins. We hypothesize that humming is as effective as either Valsalva's maneuver or Trendelenburg's position for distention and ultrasonographic visualization of these procedurally important blood vessels. Herein, we investigate a new method of venous distension that may aid in the placement of central venous catheters by ultrasonographic guidance.

METHODS

Healthy, normal volunteers aged 28 to 67 years were enrolled. Each subject's internal jugular, external jugular, and common femoral veins were measured in cross-section by ultrasonograph during rest (baseline), humming, Valsalva's maneuver, and Trendelenburg's position. Three measurements were recorded per observation in each position. Subjects were used as their own controls, and measurements were normalized to percentage increase in diameter during each maneuver or position for later comparison.

RESULTS

The study population consisted of 7 subjects, with a mean age of 47 years. Cross-sectional area was calculated for each vessel in 3 groups: baseline/control, Valsalva, Trendelenburg, and humming. The mean percentage change (+/-SD) relative to baseline cross-sectional area of the jugular vessels for each subject were external jugular vein: humming 134%+/-25% (95% confidence interval [CI] 124.9% to 146.9%), Valsalva 136%+/-23% (95% CI 121.3% to 147.5%), Trendelenburg 137%+/-32% (95% CI 120.7% to 156.9%); internal jugular vein: humming 137%+/-27% (95% CI 119.4% to 148.2%), Valsalva 139%+/-24% (95% CI 122.4% to 148.7%), Trendelenburg 141%+/-35% (95% CI 116.5% to 156.5%); common femoral vein: humming 131%+/-15% (95% CI 120.4% to 139.1%), Valsalva 139%+/-18% (95% CI 127.9% to 150.4%), Trendelenburg 132%+/-24% (95% CI 113.3% to 142.9%).

CONCLUSION

All 3 maneuvers distended the external jugular, internal jugular, and common femoral veins compared to baseline. There was no important difference in magnitude of cross-sectional area between any of the 3 maneuvers when compared with one another. Humming shares many physiologic similarities to Valsalva's maneuver and may be more familiar and easier to perform during procedures such as ultrasonographically guided central venous catheter placement and insertion of external jugular intravenous catheters.

Use of Stretch Expanded Polytetrafluoroethylene as a Microvascular Graft in a Low-pressure Situation

OBJECTIVE

Microvascular reconstruction is often limited by the availability and length of the pedicle. The harvesting of autologous vein grafts adds morbidity and may not provide a good match. Expanded polytetrafluoroethylene (ePTFE) grafts have been used routinely in macrovascular surgery. However, there are no conclusive data on the performance of small-diameter PTFE grafts for pedicle lengthening in free flaps in a low-pressure situation. In this study, we evaluated the efficacy of 3-mm diameter stretch ePTFE grafts to lengthen the venous pedicle of a free flap.

METHODS

Fifteen male New Zealand white rabbits were operated on under sterile conditions. Using an operating microscope, an epigastric flap was raised and the pedicle was exposed and dissected to its origin from the superficial femoral vessels. A segment of the vein of 1 cm to 3 cm was replaced with a stretch ePTFE graft. Microsurgical anastomoses were performed using 9-0 nylon sutures. Four weeks postoperatively, the flaps were raised again with the pedicles re-explored. The graft was then removed and examined histologically.

RESULTS

All the grafts demonstrated immediate patency. There were no cases of flap loss on the control side at 4 weeks postoperatively. When re-explored, the patent ePTFE grafts appeared to be covered by connective tissue. Light microscopy showed neoendothelialization with fibrovascular in growth.

CONCLUSION

From this study, we can conclude that 3-mm diameter stretch ePTFE grafts can be used successfully as an alternative to bridging autologous vein grafts in free-flap pedicles.

Fistula size and hemodynamics: an experimental model in canine femoral arteriovenous fistulas

PURPOSE

The objective was to evaluate the impact of anastomosis diameter on blood flow in an arteriovenous fistula (AVF), comparing two different anastomosis sizes with a modified side-to-side technique in canine femoral arteries.

METHODS

Ten mongrel dogs were subjected to two AVFs each, both using a modified side-to-side technique. On one side, the anastomosis diameter was 1.5 times the arterial diameter and on the other side 3.0 times the arterial diameter. Mean proximal and caudal blood flow and mean venous flow were measured using an electronic flowmeter 15, 20 and 25 min after surgery. The Mann-Whitney, Friedman and Wilcoxon non-parametric tests were used for data analysis (alpha < or = 0.05).

RESULTS

Femoral artery flow cranial to the fistula became 5.6 times greater in the 1.5 arterial diameter group, and 8.4 times greater in the 3.0 arterial diameter group, when compared to initial arterial flow. The mean flow in the cranial vein was greater in the 3.0 group (10.09 times greater vs. 6.46 times greater in the 1.5 group). Both in the proximal artery and in the vein there was a significantly greater flow in the group with the larger anastomosis diameter (Wilcoxon test). In the femoral artery caudal to the fistula, the flow in most of the animals was reversed: 3.5 times greater in the 1.5 group and 1.2 times greater in the 3.0 group, without statistical difference.

CONCLUSIONS

These results suggest that 3.0 times the arterial diameter for the AVF size in dogs leads to greater venous flow than with 1.5 times the arterial diameter, without increasing the reversed flow.

[Use of isolated epoprostenol or associated to heparin for the maintenance of the patency of the continuous renal replacement technical circuits]

OBJECTIVE

At present, there is no consensus on the best anticoagulant regimen for the maintenance of extrarenal clearance circuits (RRTC). We present our experience with the isolated use of epoprostenol in patients at risk of bleeding or associated to non-fractionated heparin (nFH) in patients with problems of early coagulation of the filters.

DESIGN

Prospective study of cohorts on all the RRTC filters used in our service since 1994.

SCOPE

Forty-two-bed polyvalent ICU in a tertiary hospital.

INTERVENTIONS

Anticoagulation was administered in prefilter perfusion, at doses of 5-7 U/kg/hour for nFH or 4-5 ng/kg/min for epoprostenol. The combined use was done with equal doses of epoprostenol and nFH at 2,5 U/kg/hour. VARIABLES OF MAIN INTEREST: We analyzed the duration of each filter, reason for removing the filter, existence of coagulopathy, platelet count, appearance of bleeding, anticoagulant used and dose.

RESULTS

We analyzed the use of 2,322 filters (66,957 hours) in 389 patients, 54% of whom had a clot. nFH was used in 74% of the filters for a median of 39 hours (interquartile range: 19-75), epoprostenol in 6% for 32 hours (interquartile range: 17-48) and combined therapy in 4% for 27 hours (interquartile range: 19-41). In the epoprostenol group, we detected a decrease in blood pressure in only two filters that became normal when the dose was decreased. The filters that were initially anticoagulated with nFH had a 14-hour survival as a median versus 27 hours in combined therapy (p < 0.001). In absence of coagulopathy or thrombopenia, we observed mild bleeding in 8%, moderate in 1% and serious in 1% in the 1,170 filters treated with nFH. We only observed mild bleeding in 3% in 66 filters with epoprostenol.

CONCLUSIONS

Isolated epoprostenol in patients at risk of bleeding provided a similar duration of the filters to nFH, decreasing the risk of bleeding. The use of epoprostenol plus low dose nFH significantly increases their duration in patients with early coagulation.

LOWER EXTREMITY VENOUS CHANGES IN PNEUMOPERITONEUM DURING LAPAROSCOPIC SURGERY

BACKGROUND

The effect of pneumoperitoneum on veins of the lower limbs related to the intra-abdominal working pressures during laparoscopic cholecystectomy has not been thoroughly investigated. We tested the hypothesis that working pressures do not affect the venous haemodynamics in the lower limbs.

METHODS

The cross-sectional area and peak flow rates of femoral and saphenous veins in the right groin were measured in 60 patients divided into two groups according to the intra-abdominal working pressures (11 vs 14 mmHg). All measurements were carried out preoperatively and at predetermined periods during and after laparoscopic cholecystectomy by colour Doppler ultrasonography. One-way anova and chi(2) test were used for the analysis of demographic data. For the repeated measures, anova and Student's t-test were used for statistical analysis. The probabilities less than 0.05 were accepted as statistically significant.

RESULTS

The cross-sectional area of the veins increased, whereas the peak flow rate in veins decreased during pneumoperitoneum. Comparing the peak flow rate in the saphenous vein at the third intraoperative measurement, there is statistically significant difference between the two groups (P < 0.05).

CONCLUSION

The degree of intra-abdominal pressure affects the haemodynamics of the peripheral veins. Pneumoperitoneum during laparoscopy causes stasis in the peripheral veins. It is reasonable to use routine prophylaxis for deep vein thrombosis, in the light of these findings.

Compliance changes in femoral veins of rabbits after 21 days of simulated weightlessness

Increased venous compliance in lower limbs may be contributed to postflight orthostatic intolerance; however, direct animal studies to address the changes of venous compliance to microgravity have been rare. The purpose of this study was to determine compliance changes in femoral veins of rabbits after 21 days of head-down rest. Head-down rest -20 dgrees rabbit model was used to simulate weightlessness. 24 healthy male New Zealand Rabbits were randomly divided into 21 days of head-down rest group (HDR), horizontal immobilization group (HIG) and Ctrl group (Ctrl), with 8 in each. We constructed pressure-volume relationships from femoral veins in vivo for all groups after simulation by changing the venous internal volume and measuring the corresponding pressure. Microstructure of femoral vein wall in 3 groups was observed. Compared among the groups, the corresponding intravenous pressure of Ctrl was the highest when intravenous volume was expanded and HDR was the lowest. The parameter 3 , and P 2 in quadratic equations of femoral venous P-V relationship of HDR group were significantly higher than these values of HIG group and Ctrl group. The structure of femoral vein wall of HDR rabbits changed significantly, outlines of some endothelium cells (EC) became short and columnar or cubic, some of EC fell off and smooth muscle layer became thinner. These results indicate that, the femoral venous compliance increased after weightlessness simulation. This may partially underlie the mechanism of orthostatic hypotension seen in astronauts during an orthostatic stress after exposure to microgravity.

Local changes in the insulin-like growth factor system in human skeletal muscle assessed by microdialysis and arterio-venous differences technique

IGF-I plays a direct role in whole body glucose homeostasis primarily by stimulating skeletal muscle glucose uptake. IGF-I is also involved in exercise induced muscle hypertrophy. Knowledge regarding local changes in muscle IGF-I bioavailability and its regulation by IGFBPs at rest and during exercise is limited. We have therefore explored changes in total IGF-I levels as well as circulating IGFBP levels and their post-translational modifications over an exercising leg. For the first time we have determined IGF-I levels in exercising skeletal muscle microdialysate in an attempt to assess local IGF-I bioavailability. Eighteen healthy young men performed one legged knee-extension exercise during 45min. Blood samples were taken from the femoral artery and vein of the exercising leg. No significant differences between arterial and venous concentrations of total IGF-I or IGFBP-1 were detected over the leg at any time. IGF-I concentrations increased significantly during exercise in the artery but not in the vein. Total IGFBP-1 increased after exercise in both artery and vein. The increase in non-plus less phosphorylated forms of IGFBP-1 was less pronounced and did not reach statistical significance. The proportion of fragmented IGFBP-3 (IGFBP-3 proteolysis) assessed by Western immunoblotting did not change significantly during or after exercise. Although optimization and validation of IGF-I determinations in muscle microdialysate (md) will be required, our first results using this technique demonstrate a significant 2-fold increase in mdIGF-I collected during and after exercise. We conclude that determination of A-V-differences appears to be of limited value in the assessments of local muscle change in the IGF-system. A substantial release of IGF-I during short time is required to detect significant change in the large circulating store of IGF-I. We suggest that an optimized and validated microdialysis technique for determination of local IGF-I may be advantageous in future studies.

Area-pressure relationship of lower limb main veins in man

Background: The mechanical properties of human veins remain incompletely known. However they play an important part in number of physiological and pathological situations, as hemodynamic adjustment to orthostasis, deep venous thrombosis (DVP) and chronic venous insufficiency (CVI). The aim of the study was to describe the pressure/volume (area) relationship of some important conduit veins of the human’s lower limb. Probands and methods: We investigated the area/pressure relationship of the femoral vein (FV) at mid thigh, the great saphenous vein (GSV) at lower third of the leg, and a deep leg vein (DLV), either the peroneal or posterior tibial vein, in fifteen healthy young men. The cross section areas were measured with B-mode ultrasound while various positive and negative venous pressures were generated by body’s tilting. Results: Over the range of pressures investigated, the area/pressure relationship was roughly linear, the classical sigmoid relation did not emerge from our data. The relative compliance of FV, GSV and DLV was 0.0312, 0.0118, and 0.0147 mmHg-1, respectively. Conclusions: The relative compliance of FV is more than two times higher than the relative compliance of both the DLV and the GSV.

Carbohydrate metabolism during prolonged exercise and recovery: interactions between pyruvate dehydrogenase, fatty acids, and amino acids

During prolonged exercise, carbohydrate oxidation may result from decreased pyruvate production and increased fatty acid supply and ultimately lead to reduced pyruvate dehydrogenase (PDH) activity. Pyruvate also interacts with the amino acids alanine, glutamine, and glutamate, whereby the decline in pyruvate production could affect tricarboxycylic acid cycle flux as well as gluconeogenesis. To enhance our understanding of these interactions, we studied the time course of changes in substrate utilization in six men who cycled at 44+/-1% peak oxygen consumption (mean+/-SE) until exhaustion (exhaustion at 3 h 23 min+/-11 min). Femoral arterial and venous blood, blood flow measurements, and muscle samples were obtained hourly during exercise and recovery (3 h). Carbohydrate oxidation peaked at 30 min of exercise and subsequently decreased for the remainder of the exercise bout (P<0.05). PDH activity peaked at 2 h of exercise, whereas pyruvate production peaked at 1 h of exercise and was reduced (approximately 30%) thereafter, suggesting that pyruvate availability primarily accounted for reduced carbohydrate oxidation. Increased free fatty acid uptake (P<0.05) was also associated with decreasing PDH activity (P<0.05) and increased PDH kinase 4 mRNA (P<0.05) during exercise and recovery. At 1 h of exercise, pyruvate production was greatest and was closely linked to glutamate, which was the predominant amino acid taken up during exercise and recovery. Alanine and glutamine were also associated with pyruvate metabolism, and they comprised approximately 68% of total amino-acid release during exercise and recovery. Thus reduced pyruvate production was primarily associated with reduced carbohydrate oxidation, whereas the greatest production of pyruvate was related to glutamate, glutamine, and alanine metabolism in early exercise.

Comparison of two intermittent pneumatic compression systems. A hemodynamic study

AIM

Sequential leg compression has been previously shown to be superior to uniform compression. The aim of our study was to compare the hemodynamic effectiveness of the portable sequential compression device (SCD Express Compression System, Tyco Healthcare Group LP, Mansfield, MA, USA) with a rapid inflation device (VenaFlow, Aircast, Inc, Summit, NJ, USA). The former, by sensing venous refill time, commences compression when the calf veins are refilled.

METHODS

The two devices were tested in 12 normal volunteers in the semirecumbent position using duplex ultrasound. Baseline and augmented flow velocity and volume flow were measured at the level of the common femoral vein, above the saphenofemoral junction. Refilling time was determined from velocity recordings of the common femoral vein. Total and peak volume of blood expelled per hour during compression were calculated using flow data and the individual cycling rate.

RESULTS

Both devices increased venous flow velocity, up to 3.8 times the baseline (all P<0.001). Refill time of the rapid inflation device was shorter in comparison with the sequential compression device (15+/-2.2 vs 25+/-4 s; P<0.001), suggesting incomplete vein evacuation. The sequential compression device, by augmenting flow throughout a significantly longer compression period per cycle (10.9 s vs 6.3 s), expelled significantly more venous blood (121+/-68 vs 81+/-63 mL; P<0.001). Similarly, the total volume of blood expelled per hour with the sequential compression device was 100% higher than the rapid inflation device (9685+/-5426 vs 4853+/-3658 mL; P<0.001). Although peak velocity enhancement was higher with the rapid inflation device, flow augmentation (a product of average blood flow velocity) was comparable (669+/-367 vs 771+/-574 cm/s; P=0.223) with the sequential compression device, mainly because the rapid inflation device failed to maintain flow enhancement beyond the initial flow surge.

CONCLUSIONS

Sequential compression showed hemodynamic superiority compared to a rapid inflation device. This was enhanced further by the sensing of refill time, which resulted in more compression cycles over time. The relative efficacy of the two devices in deep vein thrombosis prevention should be tested in future studies.

Non-invasive assessment of human large vein diameter, capacity, distensibility and ellipticity in situ: dependence on anatomical location, age, body position and pressure

The objective was to compare in-situ diameter, capacity and distensibility changes as well as ellipticity of large human veins of different locations, reveal alterations with age, body position and increased intraluminal pressure. Ultrasonographic assessment of mediolateral and anteroposterior diameters was performed of femoral, axillary and inner jugular veins, in erect and reclined positions as well as before and during controlled Valsalva test. Groups of young (24.0+/-0.4 years, n=11) and elderly (72.6+/-1.5 years, n=11) subjects were studied. Capacity of the femoral vein (reclined patients) gradually increased when a graded Valsalva test was applied. Its in situ distensibility was found to be 0.048+/-0.011 mm Hg(-1) between 0-15 mm Hg (1 mm Hg=0.133 kPa) pressure loads in reclined young subjects, which decreased to 0.009+/-0.005 mm Hg(-1) at 45-60 mm Hg. The femoral vein was considerably more rigid in the erect than in the reclined body position while an opposite correlation was found for the inner jugular vein. Axillary vein distensibility was very low and independent of body position. Ellipticity of femoral and axillary veins was minimal (the ratio of the two perpendicular diameters <1.25). Inner jugular veins were more elliptic in the erect position and without Valsalva (2.94+/-0.99 in young patients). Old femoral veins had higher capacity in the reclined position without Valsalva, while distensibility at low pressures was much more prominent in young vessels. The in situ femoral vein is more distensible in supine than in erect position, opposite to the inner jugular vein. The axillary vein is rather rigid in both positions. Only the inner jugular vein shows significant elipticity in situ. Aging decreases the distensibility of the femoral vein in reclined position.

Association between regional quadriceps oxygenation and blood oxygen saturation during normoxic one-legged dynamic knee extension

It is not clear whether muscle oxygenation (O(2-NIRS)) measured by near-infrared spectroscopy (NIRS) correlates with femoral venous SO2 (S(fv)o2) during normoxic exercise. Therefore, the purpose of this study was to compare physiologically calibrated O(2-NIRS) with S(fv)o2 in subjects performing one-legged dynamic knee extension exercise (1L-KEE). Five healthy male subjects (age 25+/-2 year, height 177.8+/-4.8 cm, body weight 67.1 +/- 5.0 kg; mean +/- SD) performed 1L-KEE at 20, 40, and 60% of peak work rate (WR-peak) each for 4 min. S(fv)o2 was measured at rest and during the 3rd minute of each work rate. O(2-NIRS) was continuously monitored in a proximal region of the vastus lateralis (VL-p), a distal region of VL (VL-d), and a proximal region of the rectus femoris (RF-p). S(fv)o2 was 56.0% at rest and decreased to 36.6 at 20% WR-peak, 35.8 at 40% WR-peak, and 31.1 at 60% WR-peak. There was a significant correlation between O(2-NIRS) and S(fv)o2(VL-p: r (2) = 0.62, VL-d: r2 = 0.35, RF-p: r2 = 0.62, with a moderate variation among individuals at each site; residual values = 4.83 - 11.75). These data indicate that NIRS measurement provides a reflection of S(fv)o2 during 20-60% WR-peak of normoxic 1L-KEE.

Countercurrent compartmental models describe hind limb skeletal muscle helium kinetics at resting and low blood flows in sheep

AIMS

This study evaluated the relative importance of perfusion and diffusion mechanisms in compartmental models of blood : tissue helium exchange in a predominantly skeletal muscle tissue bed in the sheep hind limb. Helium has different physiochemical properties from previously studied gases and is a common diluent gas in underwater diving where decompression schedules are based on theoretical models of inert gas kinetics.

METHODS

Helium kinetics across skeletal muscle were determined during and after 20 min of helium inhalation, at separate resting and low steady-states of femoral vein blood flow in six sheep under isoflurane anaesthesia. Helium concentrations in arterial and femoral vein blood were determined using gas chromatographic analysis and femoral vein blood flow was monitored continuously. Parameters and model selection criteria of various perfusion-limited or perfusion-diffusion compartmental models of skeletal muscle were estimated by simultaneous fitting of the models to the femoral vein helium concentrations for both blood flow states.

RESULTS

A model comprising two parallel perfusion-limited compartment models fitted the data well but required a 51-fold difference in relative compartment perfusion that did not seem physiologically plausible. Models that allowed a countercurrent diffusion exchange of helium between arterial and venous vessels outside of the tissue compartments provided better overall fit of the data and credible parameter estimates.

CONCLUSIONS

These results suggest a role of arterial-venous diffusion in blood : tissue helium equilibration in skeletal muscle.

[Shifts in human venous hemodynamics in long-term space flight]

Veins and venous hemodynamics before, during and after long-term space flights (SF) were evaluated with the ultrasonic (B-scan, Doppler) techniques and occlusion plethysmography. Fifteen cosmonauts were investigated in eight SFs of about 6 months in duration. In three SFs, 30 investigations of the main veins in different parts of the body were fulfilled with participation of 7 cosmonauts. In five SFs, 48 investigations of venous distensibility in legs were fulfilled with occlusion plethysmography with participation of 8 cosmonauts. Femoral veins tended to increase distension throughout SF. Exaggerated leg veins distensibility and compliance was persistently observed during application of occlusion from the early period of SF (wks 1-2) which, in our opinion, extenuates the reduction in LBNP tolerance and post-flight degradation of orthostatic stability. These shifts were growing markedly till months 2-3 of exposure to microgravity and tended to stabilize at the worst (as compared with prelaunch values) level at the end of six-month SFs.

Decreases in pulmonary artery oxygen saturation during total hip arthroplasty variations using 2 leg positioning techniques

When the femoral component is being inserted during total hip arthroplasty, venous obstruction occurs because of twisting and kinking of the femoral vein. Relocation of the hip joint is associated with an acute reduction in pulmonary artery oxygen saturation (s(v)O(2)). To determine whether changes in leg positioning could influence femoral venous occlusion, 19 patients undergoing 1-stage bilateral total hip arthroplasty were studied using a randomized crossover study design of 2 leg positioning maneuvers. Keeping the thigh flexed and internally rotated throughout implantation of the femoral component (technique 1) was compared to bringing the leg into extension while maintaining internal rotation (technique 2) after insertion of the femoral component. After relocation of the hip joint, the reduction in s(v)O(2) was significantly less with technique 2 than technique 1 (P < .0001).

Why do arms extract less oxygen than legs during exercise?

To determine whether conditions for O2 utilization and O2 off-loading from the hemoglobin are different in exercising arms and legs, six cross-country skiers participated in this study. Femoral and subclavian vein blood flow and gases were determined during skiing on a treadmill at approximately 76% maximal O2 uptake (V(O2)max) and at V(O2)max with different techniques: diagonal stride (combined arm and leg exercise), double poling (predominantly arm exercise), and leg skiing (predominantly leg exercise). The percentage of O2 extraction was always higher for the legs than for the arms. At maximal exercise (diagonal stride), the corresponding mean values were 93 and 85% (n = 3; P < 0.05). During exercise, mean arm O2 extraction correlated with the P(O2) value that causes hemoglobin to be 50% saturated (P50: r = 0.93, P < 0.05), but for a given value of P50, O2 extraction was always higher in the legs than in the arms. Mean capillary muscle O2 conductance of the arm during double poling was 14.5 (SD 2.6) ml.min(-1).mmHg(-1), and mean capillary P(O2) was 47.7 (SD 2.6) mmHg. Corresponding values for the legs during maximal exercise were 48.3 (SD 13.0) ml.min(-1).mmHg(-1) and 33.8 (SD 2.6) mmHg, respectively. Because conditions for O2 off-loading from the hemoglobin are similar in leg and arm muscles, the observed differences in maximal arm and leg O2 extraction should be attributed to other factors, such as a higher heterogeneity in blood flow distribution, shorter mean transit time, smaller diffusing area, and larger diffusing distance, in arms than in legs.

Blood flow velocity of the femoral vein with foot exercise compared to pneumatic foot compression

STUDY OBJECTIVE

To compare the effects of foot exercise with an intermittent pneumatic foot compression (IPC) device on blood flow velocity of the femoral veins.

DESIGN

Prospective, controlled study.

SETTING

General intensive care unit of a university hospital.

PATIENTS

20 patients on bed rest in the intensive care unit.

INTERVENTIONS

Patients were divided into 2 groups: group A, foot exercise (n = 10); and group B, IPC device (n = 10). The foot exercise was done once by a nurse for 5 minutes with the dorsiflexion of the ankle (15 times per minute) in group A patients. The IPC device (A-V Impulse System, compression setting: 130 mm Hg for 3 seconds followed by a resting period of 60 seconds) was used for 2 hours in group B.

MEASUREMENTS

Peak blood flow velocity of the femoral vein was measured using the ultrasound unit with a 7.5-MHz linear array probe (ALOKA SSD-5500) at 0, 5, 15, 30, 60, and 120 minutes.

MAIN RESULTS

Peak blood flow velocities in both groups increased significantly vs the control values during the study. At 5 minutes, group A showed a significant increase in the peak blood flow velocity compared with group B.

CONCLUSIONS

Foot exercise by a nurse for 5 minutes was equally or more effective compared with the IPC device in increasing peak blood flow velocity of the femoral vein. The effect of the 5-minute foot exercise lasted for 2 hours.

[Phlebohemodynamics in the femoral vein and postcava during a voluntary quick single contraction of shin muscles in supine and standing humans]

Effects of a voluntary single quick shin contraction on quantitative parameters of the venous outflow in the femoral vein and postcava were investigated in 65 normal males and females with the Doppler ultrasonic and duplex blood pool scanning techniques. Measured were linear spontaneous blood flow, mean linear and peak velocites of the transport of blood after the muscle contraction, baseline linear cross sections of the femoral vein and postcava cross section, and their extension in the course of mobilized blood evacuation. Based on these measurements calculated were weight power space velocities of the spontaneous blood flow and volumes of mobilized venous blood The investigations were made in supine and standing subjects. According to our data, hemodynamic productivity of the muscle contraction in vertical subjects was much higher than in horizontal with the peak and mean linear blood evacuation outrunning the mean spontaneous outflow from the femoral vein in 25.7 and 10.3 times, respectively. Besides, the weight power space velocity of the contraction-induced outflow exceeded that of the spontaneous blood flow 12.5 times. Simultaneous contraction of the muscles on both legs increased four times the weight power space velocity in the subdiaphragmatic part of the postcava.

Simple screening method for deep vein thrombosis by duplex ultrasonography using patients' active maximum ankle dorsiflexion

We hypothesized that venous obstruction by deep vein thrombosis (DVT) only slightly augments venous outflow from lower limbs by active ankle movements. If our hypothesis is true, we thought that we could develop a new screening method for DVT using duplex ultrasonography. Subjects were 22 lower limbs of 11 patients who gave informed consent for venography after total hip or knee arthroplasty. Around postoperative 19.0 days (range 15-32 days), we measured the ratios, called flow ratios, of the peak flow signal with active maximum ankle dorsiflexion and that at rest using duplex ultrasonography in the bilateral femoral veins. On the same day, we then performed bilateral venography. Thrombosis was detected in 5 of the 22 lower limbs. The mean flow ratios with and without DVT were 1.18 (range 1.0-1.3) and 3.31 (range 1.8-4.8), respectively. The flow ratios with DVT were significantly lower than those without DVT. Pain or difficulty performing active maximum ankle dorsiflexion was not observed in any of the operated or unoperated lower limbs during the ultrasound examination. In conclusion, ultrasonographic measurement of flow ratios may become a simple screening method for DVT in lower limbs without the pain or difficulty of performing active maximum ankle dorsiflexion.

Skeletal muscle pump versus respiratory muscle pump: modulation of venous return from the locomotor limb in humans

The vast majority of quantitative data examining the effects of breathing on venous return have been derived from anaesthetized or reduced animal preparations, making an extrapolation to an upright exercising human problematic due to the lack of a hydrostatic column and an absence of muscular contraction. Thus, this study is the first to quantitatively examine the effects of different breathing mechanics on venous return from the locomotor limbs both at rest and during calf contraction exercise in the semirecumbent human. When subjects inspired using predominantly their ribcage/accessory inspiratory muscles at rest (change in gastric pressure (DeltaP(GA)) = <2 cmH(2)O, change in oesophageal pressure (DeltaP(ES)) = approximately -6 cmH(2)O; inspiratory time/total breath time (T(I)/T(TOT)) = 0.5), a slight facilitation of femoral venous return was observed during inspiration (65% of all flow occurred during inspiration), with a slight reduction in femoral venous return during the ensuing expiratory phase of the breath. However, when subjects inspired using a predominantly diaphragmatic breath at rest (DeltaP(GA) = > 5 cmH(2)O, DeltaP(ES) = approximately -6 cmH(2)O; T(I)/T(TOT) = 0.5), femoral venous return was markedly impeded (net retrograde flow of 11%) and significantly lower than that observed during ribcage breathing conditions (P < 0.01). During the ensuing expiratory phase of a diaphragmatic breath, there was a large resurgence of femoral venous blood flow. The pattern of modulation during ribcage and diaphragmatic breathing persisted during both mild (peak calf force = 7 kg) and moderate (peak calf force = 11 kg) levels of calf contraction. Despite the significant within-breath modulation of femoral venous return by breathing, net blood flow in the steady state was not altered by the breathing pattern followed by the subjects. Though popliteal blood flow appeared to be modulated by respiration at rest, this pattern was absent during mild calf contraction where popliteal outflow was phasic with the concentric phase of calf contraction. We conclude that respiratory muscle pressure production is the predominant factor modulating venous return from the locomotor limb both at rest and during calf contraction even when the veins of the lower limb are distended due to the presence of a physiologic hydrostatic column.

Comparison of the effect of venovenous versus venoarterial extracorporeal membrane oxygenation on renal blood flow in newborn lambs

Venovenous extracorporeal membrane oxygenation (VV ECMO) using double lumen catheters is an alternative to venoarterial (VA) ECMO and allows for total blood flow using the patient's cardiac output in comparison to partial blood flow provided during VA ECMO.

OBJECTIVE

To compare the effects of VV versus VA ECMO on renal blood flow.

DESIGN

Prospective study.

SETTING

Research laboratory in a hospital.

SUBJECT

Newborn lambs 1-7 days of age (n = 15).

INTERVENTIONS

In anesthetized, ventilated lambs, femoral artery and vein were cannulated for monitoring and renal venous blood sampling. An ultrasonic flow probe was placed on the left renal artery for continuous renal blood flow measurements. Animals were randomly assigned to control (non-ECMO), VV ECMO and VA ECMO groups. After systemic heparinization, the animals were cannulated and studied at bypass flows of 120 mL/kg/min (partial bypass) for two hours in both ECMO groups and 200 mL/kg/min (full bypass) for an additional 30 min in the VA group. Changes in blood pressure and renal flow on ECMO and during ECMO bridge unclamping were recorded continuously. Plasma renin activity (PRA) levels were sequentially sampled.

RESULTS

Systemic blood pressure was not different in VV or VA ECMO at partial bypass flow. However, systemic blood pressure increased significantly at maximal bypass flow in the VA ECMO group. There was no change in renal flow in either VV or VA ECMO groups. PRA levels did not correlate with bypass flow change. During unclamping of the ECMO bridge, blood pressure and renal flow drop significantly in the VA group, but not in the VV group.

CONCLUSION

VV and VA ECMO at partial bypass flows had comparable effect on blood pressure, renal blood flow and PRA level in this short-term study. However, unclamping of the ECMO bridges did differentially affect blood pressure and renal blood flow between VV and VA groups. We speculate that this repeated acute change in long-run VA ECMO support may play a role in the persistent hypertension seen in some patients.

Effect of PPADS on P2X receptor-mediated responses of human blood vessels

In vitro experiments showed that pyridoxal-phosphate-6-azophenyl-2',4'-disulfonic acid almost completely suppressed contractile responses of the gallbladder artery to alpha,beta-methylene-ATP, while alpha,beta-methylene-ATP-induced contractions of the major subcutaneous vein of patients with varicose disease did not change under the effect of the antagonist. Pyridoxal-phosphate-6-azophenyl-2',4'-disulfonic acid significantly reduced contractions of the major subcutaneous veins induced by alpha,beta-methylene-ATP (in two highest concentrations) in patients without varicosity. These results indicate different sensitivity of human blood vessels to the studied P2 receptor agonist and antagonist.

Changes in femoral vein blood flow velocity by intermittent pneumatic compression: calf compression device versus plantar-calf sequential compression device

Intermittent pneumatic compression has become widely used to prevent deep venous thrombosis potentially causing fatal pulmonary embolism. Although uniform compression has been commonly applied, a new method of sequential compression from plantar to calf has recently been developed. In this report, changes in maximum blood flow velocity in the femoral vein were compared with compression of only the calf uniformly and compression from plantar to calf sequentially in 10 healthy adult volunteers. A compression pressure of 60 mm Hg was applied for 5 min, and the velocity was measured before and after this treatment by ultrasound echography. There was no statistically significant difference in the change in maximum velocity between calf compression and plantar-calf sequential compression. The maximum velocity increased significantly with both compressions. However, plantar-calf sequential compression tended to have a greater effect. Although the results did not demonstrate an advantage of plantar-calf sequential compression compared with calf compression only, if the former compression is applied for a long time, it may have a greater effect.

Changes in hemodynamic and post-flights orthostatic tolerance of cosmonauts under application of the preventive device--thigh cuffs bracelets in short-term flights

SPECIFIC AIMS

to evaluate the influence of the use thigh cuffs "Bracelet" on the hemodynamic adaptation to microgravity during short-term (up to a month) space flights, in-flight tolerance to LBNP-tests and post-flight orthostatic tolerance. 6 cosmonauts applied and 7 others did not apply the occlusive cuffs when on flight. The "Bracelet" device notably relieved the cosmonauts from the subjective discomfort following by the blood redistribution at initial period of exposure to microgravity. It was established that "Bracelet" lessened shifts in central and peripheral hemodynamics typical for exposure to microgravity, venous stasis in the cervical-cephalic region in particular. There were no differences between the hemodynamic reaction on LBNP-test in cosmonauts who applied and not applied "Bracelet" during short-term flights. The objective data are received, that the application of the device during short-term space flight does not make negative effects on post-flight orthostatic tolerance.

Counteracting effect of head-up tilt on increased femoral venous compliance after simulated weightlessness in rabbits

BACKGROUND

The increased femoral venous compliance is one of the factors of orthostatic intolerance after space flight. The purpose of this study was to observe the effect of daily head-up tilt (HUT) on stress-strain relationship of femoral vein during simulated weightlessness in rabbits.

METHODS

Head-down tilt (HDT) 20 degrees rabbit model was used to simulate weightlessness. Twenty-four healthy male New-Zealand rabbits were randomly divided into three groups: simultaneous control, 21 d HDT, and 21 d HDT plus daily 2 h HUT 45 degrees, with 8 in each. Twenty-one days later, stress-strain relationship of femoral vein was examined.

RESULTS

Under the same stress, the circumferential strain both in the 21 d HDT group and the 21 d HDT plus daily 2 h HUT group increased significantly than those in the control group. There were no significant differences between these two groups. There were no significant changes in the longitudinal strain among three groups under the same stress.

CONCLUSIONS

The femoral venous compliance of rabbits increase significantly after 21 days simulated weightlessness. Daily 2 h HUT 45 degrees could not prevent increase of femoral venous compliance in rabbits induced by 21 days simulated weightlessness.

Effects of ankle exercise combined with deep breathing on blood flow velocity in the femoral vein

Ankle exercises are commonly used to facilitate venous return in the lower extremity and to prevent deep vein thrombosis. Moreover, the respiratory cycle affects venous return. This study examined the effects of ankle exercise combined with deep breathing on the blood flow velocity in the femoral vein. Twenty healthy males (mean age 21.3 years), who had no medical history of lower extremity disease, were recruited for this study. The blood flow velocity in the femoral vein was measured while performing four exercise protocols: quiet breathing while resting (QR), deep breathing (DB), ankle exercise with quiet breathing (AQB), and ankle exercising combined with deep breathing (ADB). Using a Doppler ultrasound with an 8 MHz probe, peak blood flow velocities were collected for a 20 second period at the start of the inspiration phase in each protocol, three times. There were statistically significant differences in the peak blood flow velocity in the femoral vein with the four protocols (p lt 0.001). The mean (SD) peak blood flow velocity in the femoral vein was as follows: QR 10.1 (4.2) cm/sec, DB 15.5 (3.9) cm/sec, AQB 20.7 (6.6) cm/sec, and ADB 26.5 (9.4) cm/sec. Post hoc analyses revealed significant differences between each of the four protocols (p(adj) lt 0.01). The mean peak blood flow velocity in the femoral vein was greatest with the ADB protocol, which implies that the ADB protocol may be useful to prevent the blood stasis in patients at risk of deep vein thrombosis.

Increased spillover of norepinephrine to the portal vein during CO-pneumoperitoneum in pigs

BACKGROUND

Elevated intra abdominal pressure (IAP) during CO2-insufflation has been associated with increased catecholamine concentrations in plasma. We have previously indicated that this may be due to a regional increased spillover from the abdominal region. In this experimental study we investigated catecholamine spillover from the drainage area of the portal vein during CO2-pneumoperitoneum.

METHODS

Eight pigs under general anesthesia were investigated before and after CO2-pneumoperitoneum with an IAP of 15 mmHg. Regional spillover of catecholamines was determined by measuring plasma catecholamine concentrations and flow simultaneously. Plasma concentrations of catecholamines were measured from the portal and femoral veins, the pulmonary and carotid arteries. Flow data were collected with laser-Doppler transit time flow probes around the portal and femoral veins. Cardiac output was measured by the thermo-dilution technique. Estimated spillover was calculated by the veno-arterial difference multiplied by flow.

RESULTS

We found a significant increase in estimated spillover of norepinephrine from the drainage area of the portal vein from 10 (-1.2, 78) ng x min(-1) to 27 (1.8, 475) ng x min(-1)[median (range)] (P = 0.05), but no change in estimated spillover of norepinephrine from the drainage area of the femoral vein. Plasma concentrations of norepinephrine increased in central venous and arterial blood. There was no significant change in epinephrine concentrations in arterial blood.

CONCLUSION

Estimated norepinephrine spillover from the drainage area of the portal vein increased during CO2-pneumoperitoneum in pigs. This may indicate that the increased norepinephrine concentrations found in arterial plasma reflects a local activation of sympathetic nerves in the region of the portal drainage area.

Effects of monoamines formed in the cecum of horses on equine digital blood vessels and platelets

OBJECTIVE

To determine in vitro vasoactive potency of monoamines formed in the cecum and found in the systemic circulation of horses.

SAMPLE POPULATION

Segments of digital blood vessels obtained from 6 healthy mixed-breed horses and ponies euthanatized at an abattoir and platelets isolated from 4 healthy ponies.

PROCEDURE

Paired rings of digital artery and vein from the same horse were examined, and isometric tension was recorded. Concentration-response curves for tryptamine (TRP), tyramine (TYR), phenylethylamine (PEA), isoamylamine (IAA), and isobutylamine (IBA) were obtained. Vasoconstrictor mechanisms were investigated for TRP and TYR by the use of antagonists. Washed platelets loaded with [3H]-5-hydroxytryptamine (5-HT) were incubated with monoamines; the amount of radioactivity displaced after 30 minutes was estimated.

RESULTS

TRP, TYR, and PEA were potent constrictors of arteries and veins, with TRP and TYR being more potent in veins than arteries. Constrictions induced by TYR were inhibited by benextramine (alpha-antagonist) and nisoxetine (neuronal-uptake blocker), whereas TRP responses were inhibited by ketanserin (5-HT receptor antagonist). All 5 amines displaced 5-HT from platelets with the order of potency being TYR > TRP > PEA > IAA > IBA.

CONCLUSIONS AND CLINICAL RELEVANCE

Amines from the equine cecum cause digital vasoconstriction. The most potent (TRP and TYR) cause selective venoconstriction. Tyrosine activates predominantly alpha-adrenoceptors through the release of neuronal norepinephrine, whereas TRP activates 5-HT receptors. All amines tested released 5-HT from platelets. Amines formed in the cecum and released into the systemic circulation warrant additional investigation as trigger factors for digital ischemia and subsequent laminitis.

Improved venous return by elliptical, sequential and seamless air-cell compression

AIM

The risk of deep vein thrombosis (DVT) in the peri-operative period is significant, but can be reduced with the use of mechanical intermittent pneumatic compression (IPC). These devices have reached widespread use in hospitals and have been found to be effective prophylactic measures against DVT. This study evaluates the latest design features of one particular IPC device in comparison to current models.

METHODS

Duplex ultrasound scanning was performed on 40 lower extremities of 20 healthy volunteers before and during the application of the IPC device (VenaFlow System, Aircas, NJ, USA. Two hemodynamic parameters were measured, acceleration time from spontaneous baseline venous flow and peak vein velocity. All measurements were obtained by scanning proximal to the saphenofemoral junction in the common femoral vein in both extremities for each subject. Data were obtained from 3 compression cycles and averaged for each extremity. Results were compared with a recent prospective study form our center using a slow-filling and a rapid-filling sequential IPC devices.

RESULTS

The medians for spontaneous average peak velocities at rest of the right and left lower extremities were 26 cm/s and 24.1 cm/s. The median augmented peak velocities during the compression cycle of the device in the right and left side were 79.6 cm/s and 79.0 cm/s. This represented a 306.2% increase in average peak velocity on the right side and a 327.8% increase on the left side. The median acceleration time was 305 ms +/- 40 in the left and 310 ms +/- 50 in the right limb. There was no statistically significant difference in the spontaneous and augmented velocities between the right and left lower extremities in each subject. In comparison to existing slow- and rapid-filling IPC devices the VenaFlow System had superior peak velocities and shorter acceleration times.

CONCLUSION

The use of elliptical, sequential and rapid-filling compression of the leg with overlapping air-cells produces significant hemodynamic changes in the common femoral vein, which are superior to other sequential slow- or rapid-filling IPC devices. Randomized studies should be performed to determine the efficacy of this new device in DVT prevention.