Tech Spotlight: Pneumogram and Acid Reflux Study

Ellie is having her pneumogram and acid reflux study today which is enough to prompt a new tech spotlight. Okay, there's a lot of technology in this one so bear with me and I'll try to be as brief as my interest level allows me to be. During Ellie's pneumogram and acid reflux study they are measuring four things: 1) her heart rate 2) her blood oxygen levels 3) the pH in the lower part of her esophagus 4) her breathing. So she has a brand new set of sensors to take all that data: 1) A second set of EKG leads measure her heart rate and also obtains a calculated measurement of her breathing. 2) A second pulse oximeter to measure her blood oxygen levels. 3) A pH sensor inserted through her nose to the base of her esophagus. 4) A pair of thermistors, one placed under each nostril, measure her breathing pattern directly. All of this is in addition to the EKG leads, pulse oximeter and N. G. feeding tube that she always has. So there are two different systems measuring her heart rate and blood oxygen at the same time. (One for the NICU and one for the pneumogram.) And she has three different systems measuring her breathing. Since the thermistor directly measures her breathing it is considered a more reliable reading. (She's got a lot of wires coming from her.) A thermistor is a simple electronic device that changes resistance as the temperature changes. The temperature change is provided by Ellie's breathing. She breaths in cool air and breaths out warm air. Since the resistance of the thermistor is changing, the voltage across the thermistor changes as it's temperature changes. So the test equipment measures her breathing by measuring how much her breathing heats up the thermistor. Cool!

Tech Spotlight: Infant Hearing Test

If a Tree Falls in the Middle of a Forest ... As with any hearing test, the test equipment plays a sound for the subject to see if he/she will hear it. The central problem in testing the hearing of infants is determining whether or not they hear that particular sound. Of course it's easy with adults and school age children, you simply have them press a button every time they hear a sound. Ellie is not so cooperative. One way to detect whether or not she heard the sound is to play it so loud that she flinches. Aside from being very irritating for Ellie and her parents this wouldn't provide any information about how well she hears low volume sounds. What we need is a magical way of determining when she heard something. As usual when magic is required we turn to electronics. In this particular case we also need the help of some modern neurobiology. When a person hears something the ears send electrical impulses to the brain via the nervous system. As it turns out these impulses can be detected by sensors similar to the ones used for Ellie's EKG leads. As you can hopefully see in the picture the sensors are placed on Ellie's forhead (black), jaw (green) and at the base of her neck (white). (Click on the image to get a better view.) These sensors will detect the impulses in Ellie's brain stem. Then she is fitted with around-ear earphones. Finally the computer program plays a series of clicking noises. The clicking noises are all the same volume (35 dB) but in different patterns. The computer knows the pattern sounds that it has played and so it knows roughly what to expect from Ellie's brain stem. The software then "cross-correlates" what it expects with what it measures to determine whether or not Ellie heard the clicks. Now I know you're all thinking it, so I'll just say it: Technology is so cool!

Tech Spotlight: Isolette

Ellie's current bed is the isolette (commonly referred to as an incubator) pictured here. It monitors the temperature and humidity inside as well as Ellie's temperature. The humidity is set for a target value and keeps it there with the built-in humidifier. This is an example of an open-loop control system because there is no feedback loop. Meanwhile the temperature control system is a closed-loop control system. The nurse chooses the temp they want Ellie's body temp to be. So her body temp is the desired output of the system. But the temp probe on her tells the bed if she's too hot or too cold. This information is used as an input to decide whether to heat up the bed or keep it the same. Since the output is taken back and used as an input it's considered a closed loop system. When the nurse put clothes on Ellie she also changed this setup. She set the bed temperature at a certain value regardless of Ellie's body temp. Thus she converted it from a closed loop system to an open loop system. Nerds like me would say she "opened the loop." (Okay, now I'm off my control systems soap box for awhile.) Ellie's first isolette was the Omnibed, a scaled up model worth fifty large (that's $50k). The Omnibed, pictured here, includes a top that slides up quickly to allow easy access in urgent situations. (Notice the third pedal near the floor.) The only time this feature was needed for Ellie was shortly after her birth. This enabled a team of medical staff to easily access Ellie. Meanwhile the infrared heater in the hood kept Ellie warm even though she wasn't enclosed by radiating heat down upon her. (Basically a fancy heat lamp.) Oh by the way, these beds also raise up and down and can tilt Ellie's sleeping platform so she can be slightly upright for better digestion during feedings. There are portholes through which you can put your arms, or you can take down the entire side to remove Ellie. When you've got the bed open you can press a button to create an air curtain (like when you walk into Dillons) that keeps warm air in the bed separate from the colder room air. The bed also has a built in scale that the nurses use to weigh Ellie every evening. And currently I'm trying to program it to change Ellie's diaper. No luck yet, but if I succeed we might have to get one for home. I think I've left out a few features we don't know about, but this post is long enough anyway. These models both plug into the wall, so they are both different than the very first bed she used. We don't have any pictures of that bed, but it was the one that carried her from the OR where she was born down two floors to the NICU. So what does it all mean? Well for one thing it means that all of us are very blessed to have such technology available to take care of our little Ellie. We thank God daily for blessings like this. It also means that Ellie's first two weeks of life she slept in three beds whose combined value is greater than the house that Mandy and I don't even own yet. (Not that we're looking for a house ... I'm just saying.)

Tech Spotlight: Autosyringe

The aptly named Autosyringe slowly pushes a syringe in order to deliver a measured dose of medicine or nutrients at a steady rate. Ellie is currently using two autosyringes. One delivers her lipids and (as of 11:00 AM today) one delivers her 8 mL of mommy's milk every three hours. (A new syringe has to be loaded every three hours.) From an Electrical Engineering perspective the autosyringe is an interesting control system. A simple version of an autosyringe would make a great class project for some young, budding Electrical Engineering student. For those want to know, here is how the device most likely works. (Translation: this is how I would build one.) A microcontroller could be used to control a stepper motor. As stepper motor is just a type of motor that makes it easy to control the speed of rotation. The stepper motor would drive the arm that pushes in the syringe. For a user interface a keypad (or any collection of buttons) and an lcd display would form the user interface. The nurse would use these to input the amount of fluid in the syringe and the time period over which to deliver it. This information would be sent to the microcontroller which would then calculate the rate at which it would need to drive the stepper motor.