Study of blood flow in the anterior tibialis muscle by photoplethysmography during vibration applied to the foot

Swedish researchers from the Department of Orthopedics at Sahlgrenska University Hospital examined blood flow in the vessels of the tibialis anterior muscle when vibration is applied to the foot. They tested photoplethysmography (PPG), a method that has been used before (this is 2003) to study flows, but not in the context of vibration exposure, which can distort the reading signal. After the application of appropriate filters that cancel out the interference from vibration, the utility of PPG was demonstrated in the tested system. In addition, an increase in blood flow was observed under the influence of vibration therapy.

Since many blood flow testing methods are not inert to the human body, the researchers decided to see if a safe and non-invasive FPG could reliably test blood flow in tissue subjected to vibration.

• After using a properly designed filter, the FPG allowed them to obtain valid readings of blood flow in tissue subjected to vibration.
• Vibration increased blood flow in the tibialis anterior muscle by 20% compared to pre-vibration measurements.

Compiled from:

Blood flow in the tibialis anterior muscle by photoplethysmography during foot-transmitted vibration. Zhang Q, Ericson K, Styf J. Eur J Appl Physiol. 2003 Nov;90(5-6):464-9. doi: 10.1007/s00421-003-0904-5.

Study population

Six healthy people (3 men and 3 women; age: 19-42 years) participated in the study.

Study procedure

Blood flow through the tibialis anterior muscle of the left leg was measured using an FPG with a probe placed on the belly of the tibialis anterior muscle, in a semi-recumbent position, with the test leg raised to heart level. The left foot was placed in a properly fitted shoe located on the axis of the vibration generator. The FPG signal was filtered to exclude interference caused by the applied vibrations. Measurements were taken before, during and after the application of vibration.

Vibration therapy

Vibrations were generated by an electrodynamic vibrator. They were applied to the foot in a direction in line with the vibrator’s main axis. The vibrations were characterized by variable parameters of frequency (5-2000 Hz) and acceleration (16-46 ms2).

Results

The use of perturbation filtering of the signals read by the FPG probe allowed for correct readings of blood flow, regardless of the use or non-use of vibration.

When vibration was applied, blood flow through the tibialis anterior muscle increased by an average of 20% (p < 0.01) compared to before vibration administration.

Comment

The results indicated the usefulness of the FPG method in measuring blood flow in the tissue under study. This is important information because FPG is a harmless and non-invasive technique, so the study of blood flows in the human body subjected to vibration can be much easier than it has been so far (this is 2003). It was also shown that vibration applied to the foot increased blood flow in the tibialis anterior muscle belly compared to measurements made before vibration was applied.

The authors of the present publication cite examples of previous reports describing the effects of vibration on skeletal muscle tone. Vibration caused both contraction and relaxation of these muscles, depending on the parameters used and the site of vibration application. Reports examining the effects of vibration on the cardiovascular system were also pointed out. The effects of vibration on vasodilation in humans immediately after vibration was applied to the toe area, or an increase in blood flow through the gastrocnemius muscle of rabbits 1 – 2 s after the start of vibration application (22 – 62 Hz) were described. The increased blood flow persisted throughout the exposure. Thus, the mechanism of action of vibration was believed to be a direct effect on the state of the vascular musculature. Venous pressure increased, while effective blood flow pressure decreased, implying the dilation of resistance vessels (small, highly muscularized arterioles, crucial in maintaining adequate blood pressure). In the study presented here, blood flow through the tibialis anterior muscle increased with time of exposure to vibration and did not return to baseline immediately after the end of exposure.