Tuesday, 27 March 2012

So How Do We Apply NMES?


As mentioned before, we intend to discuss some of the important clinical parameters in the use of NMES for kids with CP. Another important component of applying NMES is how to get children to tolerate it. The current literature describes multiple parameters for the application of NMES we will discuss their approaches to introducing and applying NMES to children with CP as there are no current recommended guidelines.

Familiarizing children with the application of NMES is important for compliance and the addition of educating the parents can be equally as important. Initially Carmick [1] introduced NMES to children by demonstrations first on the therapists arm and then on the parent’s arm. The children who hadn’t experienced EMG before were introduced to a hand-held vibrator. They were then informed that they would feel a tapping sensation similar to the vibrator. After the skin was prepared, the electrode was placed on the limb and the amplitude was slowly increased to a threshold that could either be seen as a trace contraction or was felt by the child.

The dose/effect relationship of NMES has not been explored to any great extent and so there is no way of confidently prescribing a ‘safe’ range or set of parameters when applying NMES. The common protocol is to begin with minimal parameters i.e. intensity, frequency and pulse duration, and then slowly increase these parameters until the desired result is reached in each individual. This has to be repeated on every application as patient tolerance will vary and so will equipment performance and environmental variables can alter the overall treatment effect.

Ozer, Chesher [2] used a constant current output that ranged from 0 to 100mA and used a stimulus waveform that consisted of biphasic symmetric rectangular pulses 200ms in duration. They had a pulse rate which ranged between 40 and 60 pulses/second and had an adjustable stimulus amplitude (30-40mA) which was used to produce tolerable muscle contractions. After going through the process of demonstrating the NMES on the physicians then parents arms, a 5sec on ramp, 2sec off ramp, 10sec on duty, and 7sec off duty cycle was selected to produce rhythmical muscle contraction. Ozer, Chesher [2] did not justify these parameters but mentioned that the that “the stimulus amplitude threshold was determined by increasing the stimulus until the muscle started to contract, then gradually reduced it until no contractions were apparent. This amplitude was then doubled and used routinely.” The amplitude was only altered after that to make contractions tolerable.

Cauraugh [3] conducted a meta-analysis on gait and electrical stimulation in children with cerebral palsy. Of the 40 cerebral palsy and electrical stimulation studies, the studies using NMES as their treatment protocol have been listed in Table II to provide a comparison of the parameters, duration, frequency and intensity used.

Study
E-Stim Parameters
Tx Sessions
Duration (total min)
Comeaux et.al 1997
32Hz stimulation ,0.5 onset amplitude turned up slowly until visible contraction observed, in comfort range for 15min.
Daily for 4 weeks.
840
Kerr et.al 2006
35Hz stimulation, pulse duration 300ms, on:off time 7:12s, ramp up 2s ramp down 1s, 60min at highest intensity tolerated.
5 days/week for 16 weeks.
4800
Maenpaa et.al 2006
10-20 Hz stimulation at sensory threshold, pulse duration 300ms, intensity ranged 4-20mA, on:off time 1:1s
8 times
256
Nunes et.al
50Hz stimulation, pulse width 250us, current intensity 28-44mA, on:off time 5:10s
Group 1: 14 sessions
Group 2: 7 sessions
420
210
Stackhouse et.al 2007
(percutaneous NMES)
50Hz stimulation, pulse duration 5-200us, intensity 20mA, 3s ramp up time, on:off time 15:45s
3 days/week for 8 weeks.
1080
Table II; customized from Cauraugh, Naik [3].

Considerations that need to be taken into account when determining neuromuscular electrical stimulation effects on children with cerebral palsy include; age, location on body for stimulation, stimulus parameters (intensity, duration, frequency and number ofsessions) and physiological responses. A better understanding of these effects will allow for more controlled studies as well as help clinicians make decisions about parameter values for individual children [3]. The parameters and dose ranges required for a safe application of NMES must be individualised to the child.

By Ailsa Walker



References:


Wednesday, 14 March 2012

An Introduction: What is NMES?


Welcome to NMES for CP.com! The aim of this blog is to provide physiotherapists and students an overview of the use of NMES in children with cerebral palsy. Over the next few weeks, we will be posting information regarding clinically important treatment parameters, precautions and contraindications, as well as research and support for it’s use. But to start off with, here’s some information about what NMES is, what it’s used for and how to differentiate it from other electrical stimulation modalities.

Figure 1. Photograph taken the first time NMES was used 
on the forearm of a child for wrist extension and finger
flexion, 21 months of age [3].
Neuromuscular Electrical Stimulation (NMES) describes the application of electrical stimulation to weakened, but otherwise normally innervated muscles. Treatments are performed transcutaneously, using surface electrodes over motor points within a target muscle/group of muscles. Percutaneous electrodes are available but are generally reserved for experimental conditions. Most researchers use biphasic rectangular pulses that are symmetrical to avoid accumulation of charge within the tissue, thereby decreasing risk of injury to the patient [1].

Stimulation can be applied while performing functional tasks (for example walking or reaching), and this is termed Functional Electrical Stimulation (FES) [1].

The two main types of electrical stimulation used in children with cerebral palsy (CP) are:

1) Neuromuscular electrical stimulation (NMES) – this is a high intensity, short duration stimulation which elicits a muscle contraction. NMES is predominantly based on the principle of overload, as well as its’ selective recruitment of Type II muscle fibres.

2) Threshold electrical stimulation (TES) – a low level sub-contraction stimulation generally applied during sleep. TES is thought to increase blood flow to the target musculature causing heightened trophic hormone secretion, thereby increasing the bulk of the muscle [2].

Kerr, McDowell [2] compared the effects of NMES and TES in children with CP. The following parameters were used:
Table 1 - Stimulation Parameters [2]

NMES
TES
Intensity (mA)
Max tolerated with muscle
Sensory Threshold
contraction elicited
<10mA
Freqency (Hz)
35
35
Pulse Duration (µs)
300
300
On:Off (s)
7:12
7:12
Ramp Up (s)
2
2
Ramp Down (s)
1
1
Daily Session Time (Hr)
1
8
Treatments Per Week (Days)
5
5
Total Duration Of Treatment (Wks)
16
16

As seen in the table above, the only difference between NMES and TES is the intensity and daily session time. There is a much lower intensity required for TES as there is no muscle contraction elicited, but rather a sensory stimulation, where as NMES requires a larger amplitude to achieve a muscle contraction. Due to the lower intensity of TES, it requires a longer application time, hence the TES is applied overnight for 8 hours, five nights per week.

Note that in contrast to microcurrent modalities, NMES has an amplitude measured in milliamps (mA), and low frequency values are used in comparison to modalities used for treatment of pain (such as traditional transcutaneous electrical nerve stimulation).


References: