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Pulse Oximetry

A revolutionary technology that allows blood oxygen saturation to be measured painlessly, continuously and in real time.

A technology that measures the oxygen in arterial blood (Arterial blood oxygen saturation: SpO_{2}) by a sensor attached the patient's finger or ear.
As a result of the COVID-19 pandemic, many people have become familiar with the term "Pulse Oximeter".

The principle of the pulse oximeter was discovered by the Nihon Kohden engineer Takuo Aoyagi in 1974.
Before that SpO_{2} measurement required sampling of arterial blood, which was painful for the patient and required time before the results were available. 
Thanks to the pulse oximeter, medical professionals have become able to measure this important parameter continuously, painlessly and in real time, with the result that surgery under general anesthetic has become dramatically safer.

This revolutionary measurement technology has become indispensible in clinical practice around the world for safety management and monitoring the patient condition.

CO_{2}sensor

To help medical professionals understand the patient condition even 1 second faster, we developed an extremely small sensor for measuring CO_{2} at the point of expiration.

CO_{2} sensors measure the partial pressure of carbon dioxide in exhaled air. End-tidal CO_{2} is an important index for deciding whether respiration, cirulation and metabolism are being conducted normally, and gathering this data as soon as possible leads to faster treatment.

There are two ways of measuring end tidal CO_{2},

• The mainstream method: A sensor is placed in front of the mouth and air passing through it is diectly measured.
• The sidestream method: Inspired air is sent to the device for measurement and measured by a sensor inside the measuring device. 

At Nihon Kohden, we have always used the mainstream method to measure CO_{2}.
The reason is that in general, the mainstream method has superior responsiveness and stability and can better respond to rapid and low-volume breathing. Because of the long-term stability of the measurements and the sensors' fast response time, mainstream CO_{2} sensors are widely used in both ICUs, where patients are connected to ventilators for long periods of time, and in emergency resuscitation, where speed is of the essence.

However, because large sensor components are directly attached to the mouth,  mainstream CO_{2} sensors could not be used for patients receiving supplementary oxygen through an oxygen mask, or for intubated* patients. Also,  because the tubes used for intubation of neonates are very thin, it was difficult to attach a sensor because it caused the tube to bend. Extracting blood and measuring the CO_{2} in the blood was possible but frequent extraction of blood is a large burden on a small body.

*Tracheal intubation: Insertion of a tube into the trachea through the mouth for mechanical ventilation during surgery under general anesthetic or in an ICU. 

To solve these kinds of problems, we started developing a small, lightweight sensor that could be used by both intubated and non-intubated patients, and even by neonates with thin breathing tubes. After trying many different shapes, we succeeded in creating a small, lightweight design that only weighed 4g. With this CO_{2} sensor, we were able to measure the end-tidal CO_{2} of a non-intubated neonate using the mainstream method while the neonate was receiving supplementary oxygen (such a through a mask).

Further, the small size and light weight of this sensor makes it possible to measure the CO_{2} of a patient wearing a mask. For that reason, we started work on developing a new type of oxygen mask and succeeded in creating a revolutionary new product, which is a mask that can measure CO_{2} at the same time as supplying oxygen.

This small CO_{2} sensor can be used to monitor the patient condition in a wide range of situations.

CO_{2} Sensor

Size, measurement method, and durability were all new challenges.

Developer: Masayuki Inoue

Challenges of conventional CO_{2} sensors

At Nihon Kohden, we have adopted the mainstream method*~{1}, which has excellent responsiveness and stability, as the measurement method for exhaled CO_{2} . However,  conventional mainstream CO_{2} sensors had the problem that they could only be used on patients with tracheal intubation*~{2} (intubated patients).

However, it has become increasingly important to measure exhaled CO_{2} to detect the presence or absence of breathing and respiratory depression*~{3} in patients who are not intubated (non-intubated patients), such as patients requiring sedation in the ICU (intensive care unit) or patients who have started spontaneous respiration *~{4} after surgery when anesthesia has worn off.

1 Mainstream method: A method in which a sensor is installed between the intubation tube and the breathing circuit.

2 Tracheal intubation: Insertion of a tube into the trachea to secure the airway for patients who require ventilator-assisted respiratory care.

3 Respiratory depression: A decrease in the frequency and depth of breathing (ventilation rate) below normal. When respiratory depression occurs, the lungs are unable to efficiently exchange oxygen and CO_{2} (gas exchange), and CO_{2} accumulates in the body, which is harmful for the patient. By measuring the CO_{2} in exhaled gas, it is possible to confirm whether gas exchange in the lungs is being performed normally or not.

4  Spontaneous respiration: Natural respiration that a person performs by himself/herself.

Development of a unique sensor unlike anything that had ever been seen before

Development of a ground breaking sensor that measures the respiration of non-intubated patients using the mainstream method began.

Creating the world's smallest CO_{2} sensor, developing a new measurement method that can measure both nasal and oral respiration, and achieving high durability... each of these goals was a new challenge. The key to success was assembling a team of highly sklled engineers from design, electrical engineering, mechanical design and manufacturing backgrounds.

For example, to increase the durability of the parts against impact, the design team repeatedly conducted drop tests and made improvements afterward. Also, embedding extremely small components such as printed circuits in the tiny sensor section required extremely advanced manufacturing technology. Therefore, the manufacturing team was involved in the development process from the design stage, working through a process of trial and error.

The development process involved numerous discussions with many doctors. It is difficult to obtain specific answers to the problems faced by medical professionals through direct interviews. Therefore, we observed the actions and treatments of medical professionals in clinical settings, extracted the key issues and put them into concrete terms to enhance our discussions.

Finally we succeeed in developing a revolutionary measurement method that placed the sensor between nose and mouth. In 2003 we launched the TG-920P CO_{2} sensor kit, which uses a new concept of measuring the respiration of non-intubated patients using the mainstream method, a concept which had not existed anywhere in the world until then*.

 * According to our own research

I believe that one of Nihon Kohden's great strengths is that we are able to overcome high barriers by integrating our capabilities from development to manufacturing into a single team.

Thoughts after commercialization

Now, we have made further improvements and the sensor can be used even during artificial respiration of newborns. In addition, we have developed an oxygen mask that can measure CO_{2} while administering oxygen, and an adapter that can be used during endoscopic examination/treatment, successfully expanding the possibilities of CO_{2} measurement.

Sensors are items that come into direct contact with human skin. When developing a sensor, I always try to imagine "what would happen if I put this sensor on a member of my family".  By thinking about the people close to me during the design process, before the product is used in a hospital, I can create products from the patient's point of view.

Non-invasive blood pressure

Measurement during inflation.
Nihon Kohden's unique new blood pressure measurement algorithm that reduces the burden on patients and responds to medical professionals' desire for faster results.

Measurement of blood pressure with a cuff wound around the arm is familiar from health checks and home use, but blood pressure measurement using the same principles in a clinical setting is an important parameter for understanding the patient condition.

In order to measure blood pressure continuously at regular intervals during procedures such as dyalisis or surgery, or in an intensive care unit, the cuff has to be strongly tightened several times and this is very painful for the patient. Sometimes tightening the cuff is even the cause of subcutaneous bleeding, which causes the skin to become red and swollen.

Nihon Kohden's engineers thought of ways to reduce the pain for these patients and worked hard to develop a new measurement format that improved the patient experience. After overcoming many obstacles and difficulties, the result was the new iNIBP blood pressure measurement algorithm.

iNIBP measures blood pressure using a "linear inflation method" which detects the pulse while inflating the cuff at slower rate than conventional measurement formats. In order to reduce the burden on the patient and respond to medical professionals' desire for faster results, we successfully developed a method of measuring blood pressure faster and with a lower inflation pressure compared to the conventional deflation method.  Use of the new iNIBP blood pressure measurement algorithm, which reduces the pain and discomfort for the patients and allows results to be obtained faster, has spread from Japanese clinical practice to medical practices around the world.

iNIBP

Aiming for a people-friendly blood pressure monitor

Developer: Takashi Usuda

Challenges of conventional blood pressure monitors

Conventional blood pressure monitors measure oscillations*~{1} by feeding air into a cuff wrapped around the upper arm, constricting it tightly once and then gradually releasing the air, and calculate the blood pressure value from the relationship between the size of the oscillations. This measurement method has disadvantages such as the cuff being too tight and painful, and the measurement time being long.

Furthermore, the pressure value was determined using an algorithm*~{2}, based on the most recent blood pressure value, so if the previous blood pressure value was high, the pressure would be increased to a higher level for the next measurement, and if the previous blood pressure value was low, the pressure for the next measurement would be low.

This had the disadvantage that when the blood pressure suddenly rose or fell, the medical personnel wanted to know the blood pressure quickly, but had to pressurize the cuff again (and repeat pressurization several times), which lengthened the measurement time.

1 Oscillation: waveform generated by arteries vibrating due to the beating of the heart.

2 Algorithm: a procedure or calculation method for solving a problem.

Features of iNIBP

iNIBP is a new measurement algorithm that solves these problems.

It applies the optimum pressure for the patient's "current" blood pressure value, resulting in less pain and faster measurement.

Furthermore, even if the blood pressure suddenly rises or falls, iNIBP applies the optimum pressure for the blood pressure value at that moment, making it a powerful tool in situations where healthcare professionals want to know results quickly.

Why we developed iNIBP

We asked ourselves, "What if we thought about a blood pressure monitor from the patient's point of view? Let's use 'measuring comfort' as a keyword!" This was the beginning of the development of iNIBP.

The first experiment we conducted was a comparison between our own and other companies' blood pressure monitors. The blood pressure monitors were hidden from the eyes of the test subjects and they were asked to choose the one that felt most comfortable to be measured with.

The result was that our product lost.

Afterwards, discussions with colleagues led to the idea of measuring while pressurizing the cuff.

Difficulties in development

Surprisingly, we were able to quickly create a prototype that only pressurised slowly. However, from this point on, we faced a series of difficulties.

First of all, there was the noise generated by the pump and cuff. The cuff also had to measure the same for all sizes, from small ones for infants to large ones for sumo wrestlers.

We also had to consider safety in the event of body movements or other large noises during pressurization, and the relationship between accuracy and measurement time.

Thoughts after commercialization

After all the hard work, the product was finally ready for market, and as a developer, I was thrilled to hear medical professionals say, "How much easier this will be for patients..." and patients say, "It feels like I'm not being measured".

It has been about 40 years since the oscillometric method, the measurement principle of non-invasive blood-pressure monitoring, first appeared.

Although the technology based on a well-established principle, a number of ideas were born from the simple change of mindset of 'measuring while pressurizing'. After overcoming one difficult hurdle after another, we were finally able to produce a technology that reduces the suffering of many patients and is also useful for healthcare professionals.

It's only blood pressure, but blood pressure is important.

Even with technology that we think is already available, in reality there are still patients who are in trouble.

We want to make the world a place where the sufferings of those patients can be eliminated one by one.

Nihon Kohden is home to many engineers and employees who share this vision. By harnessing the power of these employees we hope to continue to develop products that create a brighter future for patients.