Med Equipment & Diagnosis
Page 22
TMS
Pericarditis Cont.
the impact a slight deviation in an un-calibrated ECG device can cause to
a patient. Let’s look even further into the cell membrane to determine what
causes the resting cell membrane potential that the isoelectric point is referenced.
Bioelectricity: A potential exist due to differences in ion potentials
across a cell’s semi permeable membrane. Many ions exist inside and
outside the cell. However, certain ions exist in higher concentrations at
resting states; potassium, K+,exist inside the cell in higher concentrations
while, sodium, Na+,exist outside the cell in higher concentrations. (fig. 4)
The concentrations of these ions at resting state produce what’s called the
resting membrane potential. The ECG does not measure this resting
membrane potential rather measures the vector, amplitude and direction
of the signal as it changes. Looking at the diagram of the cell below, at
resting potential Na+ is found outside the cell and K+ is found inside the
cell. Voltage gated channels found within the cell membrane initiates an
influx of sodium into the cell, which is depolarization, while potassium exits. As the ions return back to normal, the cell is said to be repolarized.
This concentration in ions travels down the cell, so does the membrane
potential. This is how the membrane produces the resting potential and
how that potential travels down the cell.
There are many more biochemical reactions that occur, but for the
sake of this article, we will save that for another edition. These electrical
properties are what result in the isoelectric line in the ECG waveform. A
patient with a disease resulting in pericarditis, the inflammation in the pericardium will cause changes in these electrical properties. (fig. 5) A Biomed should not only know what they are doing but look into why they are
doing it. This is when you can become more effective to the healthcare
team. Knowing what happens from the physiology, the biophysics, to the
medical device, and how any pathology can change the normal physiology to include the biophysics, causes distinct changes of the indicators in
the device display. BMETs and Clinical Engineers often speak of becoming more involved in the clinical aspect of the job. While there are no clinical duties involved with learning about medical devices and medical diagnosis, as of yet, we should strive to explore new and old areas to ensure
we are providing everything we can.
…(Continued on next page)
Fig 4. Resting Potential heart
cell: Negative ions (K-) that
are INSIDE the cell. Positive
ions (Na ) are OUTSIDE the
cell. Photo by BMETWiki
University.
Fig 5. Movement of cells between depolarization and repolarization cycles.