Hemodynamic effects of habituation to a week-long program of neuromuscular electrical stimulation.

OBJECTIVES: Neuromuscular electrical stimulation (NMES) of the calf muscles has been shown to cause instantaneous increases in venous outflow from the lower leg and could be used as an adjunct to current gold-standard compression therapies for the prevention of venous stasis and its related pathologies. However, little is known about the effects of NMES in combination with compression therapies on subject comfort, compliance and popliteal venous blood flow over the course of a week-long NMES protocol. This study aimed to assess the effects of a NMES and compression protocol for the prevention of venous stasis on the compliance, comfort and venous blood flow of healthy volunteers over the course of seven days. DESIGN: Twenty-four healthy subjects were assigned to either a stimulation or control group. The stimulation group received 1.5 h of NMES daily while the control group received none. Daily measures of popliteal venous blood flow, subject compliance and comfort were recorded over 7 days. RESULTS: Ejected blood flow volumes and peak velocities in the popliteal vein during NMES were sustained over a 30-min stimulation session and increased by approximately 100% over the course of seven days. Mean stimulation intensities increased progressively throughout the week, while perceived pain during NMES decreased significantly. Mean compliance to the 7-day protocol was 100%. CONCLUSION: User habituation to a combined NMES and compression protocol resulted in significant increases in ejected venous volume and peak velocity over the course of 7 days. This resulted in the highest ejected venous volume reported from a single NMES induced contraction of the calf muscles to date which was twice the magnitude of values previously reported in the literature. These findings suggest that NMES based protocols applied over an extended period of days, weeks or months may provide greater hemodynamic effect for the prevention of venous stasis than previously observed during NMES sessions lasting less than a few hours.

Venous emptying from the foot: influences of weight bearing, toe curls, electrical stimulation, passive compression, and posture.

This study investigated the hemodynamic properties of the plantar venous plexus (PVP), a peripheral venous pump in the human foot, with Doppler ultrasound. We investigated how different ways of introducing mechanical changes vary in effectiveness of displacing blood volume from the PVP. The contribution of the PVP was analyzed during both natural and device-elicited compressions. Natural compressions consisted of weight bearing on the foot and toe curl exercises. Device-elicited compressions consisted of intermittent pneumatic compression (IPC) of the foot and electrically elicited foot muscle contractions. Ten healthy participants had their posterior tibial, peroneal, anterior tibial, and popliteal vein blood flow monitored while performing these natural and device-elicited compressions of the PVP supine and in an upright position. Results indicated that 1) natural compression of the PVP, weight bearing and toe curls, expelled a significantly larger volume of blood than device-elicited PVP compression, IPC and electrical stimulation; 2) there was no difference between the venous volume elicited by weight bearing and by toe curls; 3) expelled venous volume recorded at the popliteal vein under all test conditions was significantly greater than that recorded from the posterior tibial and peroneal veins; 4) there was no significant difference between the volume in the posterior tibial and peroneal veins; 5) ejected venous volume recorded in the upright position was significantly higher than that recorded in the supine position. Our study shows that weight bearing and toe curls make similar contributions to venous emptying of the foot.

The anatomy and physiology of the venous foot pump.

The presence of a venous pumping mechanism in the foot may be significant for venous return in the lower extremities. However, there has been a lack of conclusive research in the area to date and controversy still exists over the detailed anatomy and physiologic mechanism of the venous foot pump. A full understanding of the anatomy and physiology of the venous foot pump is essential for designing effective interventions for the prevention, treatment, and management of venous disease in the lower limbs. This article highlights and discusses the relevant literature relating to the anatomy and physiology of the venous foot pump. In addition, the plantar aspects of 10 cadaveric feet were dissected. These dissections revealed the presence of a previously unreported secondary deep plantar arch and/or deep system of venous connections in the foot and facilitated a more detailed description of the patterns of doubling and branching of the primary veins of the foot. The results of these dissections are discussed within the context of previous work in the field with the aid of detailed diagrams of the dissected feet and may provide a backdrop for the physiology of the venous foot pump and its potential role in lower limb circulation. This is discussed in the last section of the article, which also highlights existing controversy regarding the role of weight bearing and muscular contraction as the dominant mechanisms for venous pumping in the foot.

Popliteal blood flow and plantar flexion force due to neuromuscular electrical stimulation (NMES) of the calf muscle pump are strongly associated with NMES intensity.

In spite of significant gains in venous flow using Neuromuscular Electrical Stimulation (NMES) of the calf muscles, little is known about the relationship between the applied electrical stimulus and the resulting venous blood flow in the deep veins of the leg. This retrospective study of repeated measures of blood flow, muscle force and NMES signals of 14 healthy subjects undergoing a week long NMES protocol aimed to determine the relationship between the applied NMES signals and the resulting muscle force and blood flow measures. Statistical analyses revealed strong correlations between NMES blood flow, NMES plantar flexion force and the applied NMES intensity.

Detecting electroporation by assessing the time constants in the exponential response of human skin to voltage controlled impulse electrical stimulation.

We propose a new method for extracting the electrical properties of human skin based on the time constant analysis of its exponential response to impulse stimulation. As a result of this analysis an adjacent finding has arisen. We have found that stratum corneum electroporation can be detected using this analysis method. We have observed that a one time-constant model is appropriate for describing the electrical properties of human skin at low amplitude applied voltages (<30V), and a two time-constant model best describes skin electrical properties at higher amplitude applied voltages (>30V). Higher voltage amplitudes (>30V) have been proven to create pores in the skin's stratum corneum which offer a new, lower resistance, pathway for the passage of current through the skin. Our data shows that when pores are formed in the stratum corneum they can be detected, in-vivo, due to the fact that a second time constant describes current flow through them.

A programmable and portable NMES device for drop foot correction and blood flow assist applications.

The Duo-STIM, a new, programmable and portable neuromuscular stimulation system for drop foot correction and blood flow assist applications is presented. The system consists of a programmer unit and a portable, programmable stimulator unit. The portable stimulator features fully programmable, sensor-controlled, constant-voltage, dual-channel stimulation and accommodates a range of customized stimulation profiles. Trapezoidal and free-form adaptive stimulation intensity envelope algorithms are provided for drop foot correction applications, while time dependent and activity dependent algorithms are provided for blood flow assist applications. A variety of sensor types can be used with the portable unit, including force sensitive resistor-based foot switches and MEMS-based accelerometer and gyroscope devices. The paper provides a detailed description of the hardware and block-level system design for both units. The programming and operating procedures for the system are also presented. Finally, functional bench test results for the system are presented.

The effect of surface neuromuscular electrical stimulation and compression hosiery applied to the lower limb, on the comfort and blood flow of healthy subjects.

Chronic venous insufficiency (CVI) is a severe disease affecting the venous system of the lower limbs. Compression therapy aims to counteract the venous hypertension caused by CVI. However, in spite of significant advances in compression treatments in recent years, CVI and its associated diseases are frequently characterized by slow healing rates and a need for more aggressive therapies such as surgery. Surface neuromuscular electrical stimulation (SNMES) offers potential benefits when used in conjunction with compression therapy by increasing venous return through muscular compression of the calf muscles. In order to assess the long term feasibility of SNMES with compression hosiery as a treatment modality for CVI, it is necessary to evaluate the effects of such a treatment on subject blood flow and comfort levels. This paper presents the results of a study investigating the effects of long term SNMES and compression hosiery applied to the lower limb, in the comfort and blood flow of healthy subjects.

A haemodynamic study of the physiological mechanisms of the venous pump in the healthy human foot.

Presented is a physiological study of the plantar venous plexus in the context of venous return. It is accepted that the plantar venous plexus acts as a peripheral venous pump, capable of emptying blood from the foot into the posterior tibial veins. Controversy still exists, however, over the precise physiological mechanism which is responsible for completely emptying the deep plantar veins of the foot. This study was designed to investigate whether weight bearing or muscular contraction was the dominant mechanism involved. This was achieved by comparing blood flow measurements taken from the posterior tibial and popliteal veins while performing specific foot exercises. Measurements were taken using Doppler ultrasound. Neuromuscular electrical stimulation was also used to study the blood flow obtained by artificially inducing contraction of the plantar venous plexus.

A programmable and portable NMES device for drop foot correction and blood flow assist applications.

The Duo-STIM, a new, programmable and portable neuromuscular stimulation system for drop foot correction and blood flow assist applications is presented. The system consists of a programmer unit and a portable, programmable stimulator unit. The portable stimulator features fully programmable, sensor-controlled, constant-voltage, dual-channel stimulation and accommodates a range of customized stimulation profiles. Trapezoidal and free-form adaptive stimulation intensity envelope algorithms are provided for drop foot correction applications, while time dependent and activity dependent algorithms are provided for blood flow assist applications. A variety of sensor types can be used with the portable unit, including force sensitive resistor based foot switches and NMES based accelerometer and gyroscope devices. The paper provides a detailed description of the hardware and block-level system design for both units. The programming and operating procedures for the system are also presented. Finally, functional bench test results for the system are presented.