Blood flow changes in RSI subjects:

an introduction of a pen with biofeedback

Marijke C. Dekker Rob L. Krullaards

Delft University of Technology Erasmus MC, University Medical Center Rotterdam

Faculty of Industrial Design Engineering Department of Biomedical Physics and Technology

Landbergstraat 15, 2628 CE Delft, NL Dr. Molewaterplein 50, 3015 GE Rotterdam, NL

Gert-Jan Kleinrensink

Erasmus MC, University Medical Center Rotterdam

Department of Neuroscience

Dr. Molewaterplein 50, 3015 GE Rotterdam, NL

Chris J. Snijders

Erasmus MC, University Medical Center Rotterdam

Department of Biomedical Physics and Technology

Dr. Molewaterplein 50, 3015 GE Rotterdam, NL


Impaired blood flow is seen as one of the main causes of Repetitive Strain Injuries (RSI) in the upper limbs. Several physiological mechanisms were proposed in literature as an explanation for the impeded circulation. This paper describes an alternative mechanism responsible for the reduced blood flow in the whole arm, originating at the costoclavicular gate, where the subclavian artery and vein leave the thorax and enter the upper limb. In the long run this may cause a cascade of effects resulting in pain and dysfunction in the more distal parts of the arm.

Furthermore, a sensor pen is developed based on this explanation. It is hypothesised that the use of the pen relaxes the relevant muscles to increase the blood flow. In this way, the sensor pen may function as an over all tension feedback device for the user. The presented explanation and functioning of the pen will be investigated in futurestudies.

1 Introduction

Various underlying mechanisms were suggested in literature to explain the cause of Repetitive Strain Injuries (RSI)-a medical syndrome affecting the neck, upper back, shoulders, arm or hand, or a combination of these areas. They relate to abnormalities affecting the muscles, nerves and tendons, or even the central nervous system, separately or in combination. There are multiple possible mechanisms that do not form a complete explanation and that are not sufficiently supported by empirical data (Visser, 2004). Still, more scientific research into the pathophysiology of RSI is needed to formulate effective preventive policies. Moreover this will enable industry to design effective RSI preventive products or systems. From a medical or a human perspective it would be very helpful to find a phy siological predictor of RSI.

There is mutual consensus concerning the risk factors of heterogeneous RSI complaints such as stiffness, paresthesia, numbness, loss of power, ischaemia and pain. These are preceded by activities that involve repeated movements, excessive use of force, awkward positions and static strain - keeping one or more body parts for longer time in a static position ("Health Council of the Netherlands: RSI", 2000). In addition, long hours of repetitive movements (Blatter et al., 2004) and precision demands of the task (Visser, 2004) are also indicated. Psychosocial factors such as pressure of work, high levels of stress, high working tempo, mentally demanding work and inadequate social support do not themselves lead to RSI problems, but contribute to an improved risk on RSI. On the other hand almost nothing is known about the extent to which personal factors (such as physical build and ability to handle stress) help to determine an individual’s chance to develop RSI ("Health Council of the Netherlands: RSI", 2000).

1.1 Blood flow

Reduced blood supply in the upper extremities is one of the main causes of RSI (e.g, Larson, 2003). Several physiological mechanisms were proposed as an explanation for the impaired blood flow. It is usually ascribed to static contractions of the muscles in neck and shoulders (e.g, Järvholm et al.,1991). The assumption is that the mechanical pressure in the muscles reduces the diameter of the blood vessels. Consequently, the blood flow through the whole arm will be affected. In other studies the focus is on the muscle motor units of distal areas of the arm (Søgaard, Sjøgaard, Finsen, Olsen & Christensen, 2001). These small parts of the arm muscles are almost constantly in use. Therefore the complaints may also result from lower force exertions (e.g., common in computer work).

Overloaded muscles can still occur in these circumstances, because the subject is not aware of any over all feeling of muscle fatigue. In the aforementioned muscle related perspectives, the assumption is that inefficient blood flow to and in the muscles will lead to anaerobe metabolism. Consequently, a deficit in substrates (including oxygen) and an accumulation of metabolites (mainly lactic acids) will result. In prolonged contractions these acids cause discomfort and finally pain. These complaints can be intensified because a decrease in muscular microcirculation might lead to the sensitisation of pain receptors (nociceptors) in the muscle, meaning that low threshold stimuli can activate the pain system (Johansson, 1991). Armstrong et al. (1993) found that reduction in muscle blood flow will lead to a cascade of responses in other body tissues (e.g., degeneration of the tendons and impaired circulation in the nerves), resulting in a range of complaints characteristic for RSI.

1.1.1 Alternative explanation for blood flow reduction

An alternative explanation

1 for blood flow reduction in people with RSI will be presented here. Starting point is that the flow impairment is not caused by mechanisms in the proximal or distal muscles, but at the costoclavicular gate where the artery and vein enter the upper limb (Figures 1 and 2).

Figure 1: The arterial system in relation to the costoclavicular gate (restricted by the subclavia and the first rib)

1 The second author of this article developed this explanation. He has his own physiotherapist consultancy. Furthermore he is researcher at Erasmus MC since 2004.

Figure 2: The venous system in relation to the costoclavicular gate

Prolonged posture and stress result in sustained static contractions. These contractions might create high tension in the deep neck muscles (mm. scaleni), which are attached to the first rib. Increased tension in the deep neck muscles results in lifting the first rib, causing a hypothetical decrease in the costoclavicular space between the first rib and the clavicle. Consequently, a constriction of the subclavian vein and artery may occur. Therefore, a decreased blood flow to the upper limb will result. In the long run this may cause a cascade of effects in the more distal parts of the arm.

1.1.2 The sensor pen

A new device based on this explanation is the so-called sensor pen, developed by the second author. The sensor pen (Figure 3) is a classical writing pen equipped with biofeedback.

Figure 3: The sensor pen

The shaft of the pen contains a sensor, registering the force and pressure in the hand while writing. When the user applies too much pinch force on the shaft, a red light in the top of the pen will warn the writer. By reducing the pinch force the light will switch off. The user is asked to write with the pen and to attempt to keep the light off.When the pen is used properly, the method of writing is altered in such a way that less muscular grip force is applied. In this manner, it is hypothesised that the use of the pen relaxes not only the hand muscles but may also affect all muscles of arm and neck. By relaxing the deep neck muscles, the space between the clavicle and the first rib might increase and the blood flow in the subclavian vein and artery might recover. In this way, the sensor pen may function as an over all tension feedback device for the user.

1.2 Future study

The presented explanation is plausible and the functioning of the pen renders promising results. However, further research is needed. There are several aspects to be investigated. The blood flow in the subclavian artery in a group of subjects with RSI when compared to a group of healthy controls will be tested. In addition the immediate and long-term effect in blood flow after writing with the sensor pen will be part of a future study.


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