Measurement station
With the help of Centre of Excellence funding from the Academy of Finland the SSSAG group was able to build two physiological signal measurement devices. By building the devices ourselves we were able to incorporate special amplifier to special sensors like the EMFi sensor which requires a charge amplifier and the measurement signals could be timed accurately. The signals from the amplifier are digitized with commercially available A/D cards to a laptop computer in raw ASCII or in the EDF format. The newer amplifier was inspected and accepted for hospital use enabling measurements with patients.

The driver's BCG measurement in a car with EMFi sensors.

Car BCG measurements
In our exploratory studies we applied the EMFi sensors to various places to see what is possible. In addition to building the measurement chair we tested the applicability of EMFi sensors in a car seat. Although we used a thick layer of foam plastic to damp the vibrations from the road to the sensor below the sitting driver, the vibrations during driving were of so high amplitude that the forces caused by the mechanical vibration of the human heart, the ballistocardiogram (BCG) were not detectable.

Baby monitoring
The study of a sleeping baby on the EMFi sensor was much more successful. We noticed that it was easy to detect the breathing and the heart originated activity of the baby from the recordings and these provided the information to calculate the breathing rate and pulse of the baby. This study has potential to provide help in preventing the sudden infant death syndrome (SIDS) as the cessation of breathing could be detected and the adults around could begin giving first aid.

EMFi sensors attached to the hand of the test subject.

Body sensing with EMFi
Attaching EMFi sensors on a human body and measuring the resulting signals reveals interesting things. One can follow how fast the blood pulse travels through the vain and see how the waveform alters on the way. We did not have the time to fully exploit these measurements yet, though.

Acceleration sensor measurements
We wanted to compare how acceleration sensors measure the mechanical movement of the heart with the EMFi sensors and set up a measurement for this. The applied ADXL 202 sensor has two outputs as it measures acceleration in two dimensions. Therefore the signals were not exactly similar as those obtained with a stripe of EMFi taped on top of the chest of the subject.

The Finnish sauna.

The effects of sauna on BCG
A small number of BCG measurements were performed to analyse the effect of sauna on the BCG signal. The test subject was measured before and after a 30 min sauna session. The result was that the so-called I-J amplitude of the BCG increased markedly and that the level of blood pressure decreased. The subjectively assessed relaxation was also one of the results of the sauna bath but that is a result which every Finn knows even without any scientific tests.

Some of these studies were conducted in co-operation with Tampere University Hospital.

Links
Emfit Ltd. EMFI sensors
ADXL 202 sensor
Cardiovascular System Dynamics Society

Designed by Alpo Värri 25.8.2008