The main task of the tonometer is to measure blood pressure as accurately as possible.
In addition, it is useful in evaluating the functioning of the distal renal arteries which are the big vessels supplying blood to the kidneys.
While the apical or distal electrode is attached to the finger, the central electrode, on the index finger, is connected to the button, which can be opened or closed to provide pressure.
Also, a pair of sensors can be attached to the finger, which can be used to estimate blood pressure in a second position.
The instruments can also measure blood volume, pulse, and respiration.
Each instrument works with one tonometer.
In particular, they all work in the same way.
The upper electrode (the reference electrode) is attached to the index finger, and the lower electrode (the electrode for monitoring the function of the distal renal arteries) is attached to the thumb of the same finger.
The upper electrode is placed so that it receives the blood flow coming from the distal renal arteries.
The central electrode is then pressed to open the button, so that it is usually pressed into the middle of the index finger (apical) of the opposite hand, by the thumb.
In this position, the blood flow in the distal renal arteries becomes detectable.
To activate the monitoring function, the button is released from the finger.
The central electrode is now read as blood pressure, which is sent via the cable to the computer for measurement.
If a visual analogue scale is used to measure blood pressure, then the index finger is pulled to near/below the center of the patient’s body so that the red blood cells on the index finger, sitting in the capillaries, are at the top of the scale, then the blood pressure is recorded on the scale.
The index finger is then closed back in to the palm so that the capillaries become visible on the tip.
This form of measurement is commonly used by first responders in cases where blood pressure readings were collected at the scene.
An important function of the tonometer is that it measures both intra-articular pressure and distal renal arterial pressure simultaneously.
Although a different nerve is stimulated in each leg, it is the distal renal arteries that provide most of the pressure.