Another promising application for capacitive tactile sensors is arterial line placement, a common, but difficult, procedure performed in a clinical setting. An arterial line is a thin catheter inserted into an artery. It is most commonly used in intensive care medicine and anesthesia to monitor blood pressure continuously and to obtain samples for blood gas analysis. This type of intra-arterial measurement is much more accurate than noninvasive alternatives.

Arterial lines are typically inserted by respiratory therapists, and sometimes by physicians, phlebotomists, anesthesiologist assistants, and nurse anesthetists. The catheter is usually inserted into the radial artery in the wrist, but can also be inserted in other arteries in the body.

Overall, arterial line insertion is considered safe, with a rate of major complications below 1 percent. However, insertion of an arterial catheter is an invasive procedure and complications can occur. Locating the artery can prove difficult, even for trained clinicians. The mean diameter of the radial artery is only about 2.3 mm in adults. A weak pulse can make it even more difficult. To insert the arterial line, the clinician typically uses the left hand to detect and feel for the pulsating artery, then inserts the needle and extracts a blood sample using the right hand.

To hit the artery, the clinician may need to insert the needle multiple times, which can be painful and uncomfortable to the patient. Because the artery is innervated, the patient sometimes jumps or twitches when the needle is inserted leading to clinicians’ needle-stick injuries. This is, unfortunately, relatively common and can be a transmission path for blood-borne infections such as Hepatitis and HIV.

In fact, an accidental needle-stick of a physician in the United Kingdom ultimately became the stimulus for a grant from the Scottish government to seek a safer, more reliable method of inserting arterial catheters. Through a partnership with the University of Strathclyde in Glasgow, Scotland, the company set out to develop a device to simplify arterial localization and make it safer.

For this particular project, the goal was to design a low-cost, portable sensing system capable of locating an artery accurately to within 0.5 mm. The device needed to enable a one-shot procedure by relatively untrained staff that was significantly safer than existing methods.

The device uses tactile sensor arrays in a conformable material that is worn over the clinician's index and middle fingers. The tactile sensor identifies the location of the pulse and indicates the location using LEDs and a needle guide to facilitate needle insertion. The device also protects the clinician's fingers against needle-stick injuries.

OSHA regulations require all compliance officers in hospitals to perform annual assessment of new personal protective equipment. Not only does this device provide a more effective means to perform artery punctures, the newly developed device offers an ideal solution for eliminating needle-stick injuries.

BLOOD PRESSURE AND CONSUMABLE WEARABLES: SMART WATCHES AND FITNESS BANDS

Today, the holy grail of blood pressure monitoring is to be integrated into consumer wearables such as smart watches and fitness bands. Currently, most are limited to measuring heart rate, but many are already developing next-generation devices with wristbands capable of taking blood pressure, pulse, and other key arterial measurements.

Seoul, Korea-based Kairos Watches, for example, has developed several products designed to deliver high-tech elements such as text messages, push alerts, and apps to those that otherwise still want to own and wear a traditional high-end Swiss analog watch. The options include a transparent display that fits over the lens of an analog watch, as well as a Bluetooth-enabled wristband with integrated display and touch sensors, called the T-Band.

More advanced models of the T-band include a nine-axis gyroscope, accelerometer, compass, optical sensors, and a galvanic skin sensor that detects skin temperature and sweat. The company is currently working to integrate capacitive tactile pressure sensors into the slim form factor of the T-band for daily monitoring of pulse and blood pressure.

CHINESE PULSE MEDICINE

In addition to being embedded in watch-like monitoring devices, tactile pressure sensors for pulse pressure measurement also lend themselves to technologically enhancing traditional Chinese medicine.

Chinese pulse diagnosis has been used for thousands of years as one of the primary diagnostic tools in Chinese medicine. Even with the advent of x-rays and ultrasounds, the practice continues to be paramount in the recognition of disease patterns for treatment with Chinese medicine.

Pulse diagnosis is used to isolate the malfunctioning organ or system that is causing the symptoms to identify the cause. This is observed in the pulse, because as the function of the organ changes, it will also produce changes in the artery due to causes such as inflammation, volume of blood, or quality of blood.

Traditionally, Chinese practitioners use three fingers to take a person's pulse, and factors such as pulse velocity and width are considered. Reliable diagnosis requires an experienced practitioner to differentiate the nuances of pressure. This is a particularly challenging and often subjective procedure that can lead to misdiagnosis by less-experienced physicians. PPS is currently working with medical device manufacturers to develop clinical systems that would help make Chinese pulse medicine more quantitative. Many Chinese companies are also using sensors to develop applications specifically for Chinese pulse wave analysis — not only to assess health, but also to monitor the effects of herbal treatments.

SUMMARY

Capacitive tactile pressure sensing technology is enabling a new wave of healthcare products based on noninvasive arterial pressure measurement. This new technology can measure pressure in a way that is different from traditional methods. It will revolutionize how easily people can take blood pressure.

This article was written by Jae S. Son, PhD, founder and CEO of Pressure Profile Systems, Los Angeles, CA. For more information, Click Here. A video demonstrating capacitive sensing for single point and distributed areas is available here.