Intermittent pneumatic compression: Physiologic and clinical basis to improve management of venous leg ulcers

Venous leg ulcers (VLUs) are a significant health problem that afflicts 1% of the population at some point during their lifetime. Intermittent pneumatic compression (IPC) is widely used to prevent deep venous thrombosis. However, IPC seems to have application to a broader base of circulatory diseases. The intermittent nature of pulsatile external compression produces beneficial physiologic changes, which include hematologic, hemodynamic, and endothelial effects, which should promote healing of VLUs. Clinical studies of the management of VLUs show that IPC increases overall healing and accelerates the rate of healing, leading to current guideline recommendations for care of patients with VLUs. Proper prescription of IPC to improve the management of patients with VLUs requires further definition. It seems that application of IPC in combination with sustained graduated compression improves outcome in patients with the most advanced venous disease

Physiological responses to prolonged bed rest in humans: A compendium of research, 1981-1988

Clinical observations and results form more basic studies that help to elucidate the physiological mechanisms of the adaptation of humans to prolonged bed rest. If the authors' abstract or summary was appropriate, it was included. In some cases a more detailed synopsis was provided under the subheadings of purpose, methods, results, and conclusions

Impact of posture and gravity on the cardiovascular system: a validated multiscale modeling approach for ground-based and spaceflight applications

L'abstract è presente nell'allegato / the abstract is in the attachmen

Analysis of Venous Blood Flow and Deformation in the Calf under External Compression

Deep vein thrombosis (DVT) is a common post-operative complication, and a serious threat to the patient’s general recovery. In recent years, there has been increasing awareness of the risk of DVT in healthy individuals after prolonged immobility, such as people taking long-period flights or sitting at a computer. Mechanical methods of DVT prophylaxis, such as compression stockings, have gained widespread acceptance, but the haemodynamic mechanism of their action is still not well understood. In this study, computational modelling approaches based on magnetic resonance (MR) images are used to (i) predict the deformation of calf and deep veins under external compression, (ii) determine blood flow and wall shear stress in the deep veins of the calf, and (iii) quantify the effect of external compression on flow and wall shear stress in the deep veins. As a first step, MR images of the calf obtained with and without external compression were analysed, which indicated different levels of compressibility for different calf muscle compartments. A 2D finite element model (FEM) with specifically tailored boundary conditions for different muscle components was developed to simulate the deformation of the calf under compression. The calf tissues were described by a linear elastic model. The simulation results showed a good qualitative agreement with the measurements in terms of deep vein deformation, but the area reduction predicted by the FEM was much larger than that obtained from the MR images. In an attempt to improve the 2D FEM, a hyperelastic material model was employed and a finite element based non-rigid registration algorithm was developed to calculate the bulk modulus of the calf tissues. Using subject-specific bulk modulus derived with this method together with a hyperelastic material model, the numerical results showed better quantitative agreement with MR measured deformations of deep veins and calf tissues. In order to understand the effect of external compression on flow in the deep veins, MR imaging and real-time flow mapping were performed on 10 healthy volunteers before and after compression. Computational fluid dynamics was then employed to calculate the haemodynamic wall shear stress (WSS), based on the measured changes in vessel geometry and flow waveforms. The overall results indicated that application of the compression stocking led to a reduction in both blood flow rate and cross sectional area of the peroneal veins in the calf, which resulted in an increase in WSS, but the individual effects were highly variable. Finally, a 3D fluid-structure interactions (FSI) model was developed for a segment of the calf with realistic geometry for the calf muscle and bones but idealised geometry for the deep vein. The hyperelastic material properties evaluated previously were employed to describe the solid behaviours. Some predictive ability of the FSI model was demonstrated, but further improvement and validation are still needed

Venous Pulse Wave Velocity variation in response to a simulated fluid challenge in healthy subjects

Purpose: The evaluation of a mini or simulated fluid challenge is still a complex and open issue in the clinical setting and it is of paramount significance for the fluid therapy optimization. We here investigated the capacity of a new hemodynamic parameter, the venous Pulse Wave Velocity (vPWV), to detect the effect of passive leg raising (PLR). Materials and methods: In 15 healthy volunteers (7 M, 8 F, age 26 ± 3) venous pressure pulses were elicited by pneumatic compressions of the left hand and proximally detected by ultrasound for calculation of the vPWV. We also non-invasively measured the basilic vein (BV) cross-sectional perimeter, and peripheral venous pressure (PVP). The PLR manoeuvre was performed twice to evaluate reliability of the assessment. Results: The PLR had an overall statistically significant effect on the entire set of variables (MANOVA, p < 0.05): vPWV increased from 2.11 ± 0.46 to 2.30 ± 0.47 m/s (p = 0.01; average increase: 10%). This effect was transient and dropped below 5% after about 3 min. A significant increase was also exhibited by BV size and PVP. In consecutive measurements vPWV showed little intra-subject variability (CoV = 8%) and good reliability (ICC = 0.87). Finally, the vPWV responses to the two PLRs exhibited good agreement (paired T-test: p = 0.96), and moderate reliability (ICC = 0.57). Conclusion: These results demonstrated that vPWV can be non-invasively, objectively and reliably measured in healthy subjects and that it is adequate to detect small pressure/volume variations, as induced by PLR-from-supine. These characteristics make it suitable for clinical applications

Risk of Orthostatic Intolerance During Re-Exposure to Gravity

Post-spaceflight orthostatic intolerance remains a significant concern to NASA. In Space Shuttle missions, astronauts wore anti-gravity suits and liquid cooling garments to protect against orthostatic intolerance during re-entry and landing, but in-flight exercise and the end-of-mission fluid loading failed to protect approximately 30% of Shuttle astronauts when these garments were not worn. The severity of the problem appears to be increased after long-duration space flight. Five of six US astronauts could not complete a 10-minutes upright-posture tilt testing on landing day following 4-5 month stays aboard the Mir space station. The majority of these astronauts had experienced no problems of orthostatic intolerance following their shorter Shuttle flights. More recently, four of six US astronauts could not complete a tilt test on landing day following approximately 6 month stays on the International Space Station. Similar observations were made in the Soviet and Russian space programs, such that some cosmonauts wear the Russian compression garments (Kentavr) up to 4 days after landing. Future exploration missions, such as those to Mars or Near Earth Objects, will be long duration, and astronauts will be landing on planetary bodies with no ground-support teams. The occurrence of severe orthostatic hypotension could threaten the astronauts' health and safety and success of the mission

The Haemodynamic effect of the Geko TM Device

Intermittent electrical stimulation of the common peroneal nerve by the Geko device TM has an effect on haemodynamics. The Geko TM is a device, which prevents the formation of venous thromboembolism (VTE). The Geko TM works to stimulate the foot and calf muscle pumps in the leg to increase venous return. VTE carries a significant morbidity and mortality for patients, and so it is a valid scientific question to ascertain whether the Geko TM can also have a beneficial secondary effect, on the haemodynamics, which could be used clinically, to improve patient outcomes. Increasing the venous return to the heart should theoretically increase cardiac output and possibly arterial blood pressure. Firstly, we examined whether there could be any arterial blood pressure increases caused by the Geko TM, which could then be used to stabilize the blood pressure changes that occur after an anaesthetic induction. We did not find any significant change in blood pressure in 13 patients using a cross-over design pilot study. Secondly, we examined the haemodynamic changes produced by the Geko TM in healthy volunteers (n=21) using non-invasive cardiac output monitoring. We found that the cardiac output increased by 12% at the ten-minute stimulation period (p= 0.02), this effect ceased after the Geko TM was switched off for ten minutes. We also found that this effect of increased cardiac output by the Geko TM was not sustained if the device was left on for longer periods of up to 45 minutes, n=10. Thirdly we sought to examine this finding of increased cardiac output using invasive cardiac monitoring. Although we did find a slight increase in cardiac output, when using the Geko for a tenminute stimulation, (2.5%), p= 0.17, N-=5, the finding is not statistically significant. In conclusion, this thesis points to some mild central haemodynamic changes from the Geko TM device that needs more investigation. The haemodynamic changes are small and unlikely to be beneficial clinically. This thesis also highlights the lack of knowledge, research and measuring equipment for the venous circulatory syste