Friday, December 23, 2011

Heart Rate Data Logging

Universal Wireless Heart Rate Data Logger with PC Download by Oregon Scientific

The device works reliably after replacement of battery although the instructions are easy to ignore. They didn't survive translation for me. It will log up to 30 hours with a variable interval for data collection making even longer tracking possible. Others have noted that the data can be exported to a CVS file for other uses. Kubios accepts such files but whether the data granularity would be acceptable is the issue.

Fine display of the printable data:


The 150 BPM is my exercise period followed by a cool down and three separate trips up and down 10 flights of stairs to deal with keys and locking myself out.of my apartment.

Wednesday, November 16, 2011

Piezo Film Pulse Sensor and Non-Invasive BP

Phoenix Ambulatory Blood Pressure Monitor Project
Sub-project: Piezo Film Pulse Sensor

By Wade D. Peterson, David A. Skramsted and Daniel E. Glumac

Project Description

The purpose of the piezo film pulse sensor project is to identify and build a reliable, low power, low cost blood flow sensor. The sensor is intended for two proposed designs for the ambulatory blood pressure monitor (ABPM). They are: (a) an oscillometric cuff design (as a Korotkoff sound sensor) and (b) the blood flow velocity design. The project includes the following deliverables:
  • Selection of the piezo film sensing element(s).
  • Design of a sensing circuit, including filtering and amplification stages.
  • Layout and fabrication of a small, low noise circuit board.
  • Bill of material
  • Evaluation of the completed sensor system.
  • Public invention disclosure and release.
  • A written report.

Piezo Film Sensor Element

The piezo film sensor element selected for this test was the SDT1-028K made by Measurement Specialties, Inc. It was selected because (a) it is very sensitive to low level mechanical movements, (b) it has an electrostatic shield located on both sides of the element (to minimize 50/60 Hz AC line interference), (c) it is responsive to low frequency movements in the 0.7 - 12 Hz range of interest, (d) the foil size was about right (1 inch / 2.54 cm long) and (e) it has an integral connector and cable for simple connections. The sensor is shown in Figure 1. An RG-174 BNC connector was attached to the opposite end of the cable (not shown).
Figure 1. The SDT1-028K piezo film sensor.

Filter/Amplifier Circuit

The filter/amplifier circuit shown in Figure 2 was created for the piezo film sensor. It was specifically designed for battery powered operation from three AA or AAA cells (3.6 - 4.5 VDC), and consumes just 100 uA of current. The BNC connector located on the left side of the board connects to the piezo film sensor. The output is monitored with oscilloscope probe(s) via test points located on the board. The board dimensions are 2.5 inch (6.4 cm) x 3.8 inch (9.7 cm).
Figure 2. Filter/amplifier circuit.
The circuit has a three-pole low pass filter with a lower (-3 dB) cutoff frequency at about 12-13 Hz. The main purpose of the low-pass filter is to prevent unwanted 50/60 Hz AC line interference from entering the sensor. However, the piezo film element has a wide band frequency response so the filter also attenuates any extraneous sound waves or vibrations that get into the piezo element. The DC gain is about +30 dB. Click here to see the Bode plot of the circuit (i.e. the frequency response).
The circuit has a very high input impedance. Applications notes from Measurement Specialties, Inc. report that the low-end frequency response of the piezo film can be lowered from 5-6 Hz to 0.7 Hz by using a 10 Megohm or higher input impedance. The front end of the filter/amplifier circuit uses an op-amp follower in parallel with a 10 Megohm parallel resistor.
Complete documentation for the circuit is given here, including a schematic diagram, bill of material (BOM) and PCB artwork. All parts (except for the PCB artwork) can be ordered on-line from Digi-key Corporation at www.digi-key.com. The PCB artwork can be modified and ordered on-line from ExpressPCB at www.expresspcb.com. Just download their free CAD software and the board artwork file named PiezoAmp.pcb. The board conforms to the specifications for their low cost 'miniboard' service. The board assembly uses surface mounted components and can be hand assembled with the aide of a small soldering iron and a microscope.

Wrist Pulse Response

The piezo film was attached to the wrist with cloth athletic tape. The sensor was placed over the pulse point as shown in Figure 3. The adhesive on this tape is designed to be attached to the skin, and is breathable. It's a fairly weak adhesive which also allows the tape to be removed without damage to the piezo element.
Figure 3. Piezo film attached to the wrist with athletic tape.
Figures 4 and 5 signal response from the filter/amplifier circuit when the sensor is placed over the wrist. Figure 4 is a single sweep waveform as obtained from an HP 54615B storage oscilloscope. Figure 5 uses the same configuration, except that the output signal is averaged over 64 waveform samples. The vertical and horizontal scales for the two waveforms are identical, with a horizontal sweep of 200 mS/div, and a voltage gain of 100 mV/div. All measurements were obtain at test point TP3 shown on the PCB schematic diagram.

Figure 4. Wrist pulse single sweep waveform.

Figure 5. The wrist pulse waveform averaged over 64 samples.
Waveform averaging is a well known noise reduction technique. It reinforces the waveform of interest by minimizing the effect of any random noise. These pulses were obtained when the arm was motionless. If the arm was moved while capturing the data the waveform did not look nearly as clean. That's because motion of the arm causes the sonic vibrations to enter the piezo film through the arm or by way of the cable.

Mid-arm Response

The piezo sensor was moved from the wrist to the mid forearm area. The response there was less dramatic as shown in Figure 6. In this case the piezo film is probably picking up the acoustic sound wave rather than any physical motion of the skin surface. This is an area that needs improvement because the acoustic sound waves are probably more valuable in the measurement system, because they permit simplified attachment to the skin.
Figure 6. Mid forearm Response.

Blood Velocity Response Between Elbow and Wrist

Two identical piezo film sensors and filter/amplifier circuits were configured as a non-invasive velocity type blood pressure monitor. The first sensor was located on the inner left elbow at the same location where Korotkoff sounds are monitored during traditional blood pressure measurements with a spygmometer. The second sensor was located on the left wrist as described above (about 12 inch / 30cm from each other). Figure 7 shows the results.

Figure 7. Blood velocity response.

Correlation Between Pulse Delay & Blood Pressure

The correlation between pulse delay and blood pressure is well known in the art of non-invasive blood pressure monitors. Some of the best descriptions of this phenominon can be found in several US Patents, including those listed in the Phoenix patent references under the heading of Non-invasive Blood Pressure Monitors Using Pulse Velocity Methods. These can be found via the hotlinks located at the top of the same page. Several techniques are described in those patents including relative pulse delay, EKG to pressure pulse delay and pulse width.
One of the best patent references is Chen et. al, US Patent No. 6,599,251. Besides being an excellent summary of prior art in the field of non-invasive blood pressure measurement, Chen descripbes how blood pressure measurements are obtained using the pulse delay technique, as well as his data correlating pulse delay and pressure. However, Chen uses optoelectric sensors rather than the piezo film elements that are shown in this page. It is believed by the author that good, non-invasive blood pressure sensors using the techniques described on this page can be designed around Chen's claims.

Conclusions

The data show that piezo film can simultaneously monitor two pulse signals located at a fixed distance from each other. This forms a two-point blood velocity monitor that can be adapted for the measurement of blood pressure. The data show that a 12 inch (30 cm) span results in a time lag of about 32 milliseconds.
The technique worked quite well, but does need improvement. Additional experimentation is needed. The following ideas have been generated by the Phoenix group:
  • Use a smaller piezo element for improved signal-to-noise ratio.
  • Use a piezo cable. It is hoped that this will improve the sonic sensitivity (over the current sensitivity to mechanical movement).
  • Attenuate extraneous acoustic vibrations that are transmitted up the cable. Layers of 'Silly-putty', 'fun-tak' and Sorbathane(tm) are good candidates for sonic absorbing materials that could be attached to the cable.
  • Use an acoustic coupling compound (such as K-Y jelly) between the skin and the piezo film element.

Addendum

  • A commercial varient of this product has been found at Tensys Medical (SanDiego, CA). Also see US Patents 6,514,211; 6,228,034; 6,176,831.

About This Page

This page is maintained by David A. Skramsted. It was last updated on 19 September 2005.

The author(s) provide this information as a public service, and agree to place any novel and useful inventions disclosed herein into the public domain. They are not aware that this material infringes on the patent, copyright, trademark or trade secret rights of others. However, there is a possibility that such infringement may exist without their knowledge. The user assumes all responsibility for determining if this information infringes on the intellectual property rights of others before applying it to products or services.

(C) 2004-2005 Wade D. Peterson, David A. Skramsted and Daniel E. Glumac. Copying and distribution of this page is permitted in any medium, provided this notice is preserved.

Tuesday, October 4, 2011

Body, Mind, Spirit Together with Tensegrity

Buckminster Fuller mentioned anywhere draws my attention. Tension joined to "living in" a better body helps my mapping.

 Near the conclusion of the review, just before the worthwhile comment section, comes this pointer:

[For those interested, here is a link to a 20-page read-only PDF that provides an overview of much of what is included in the book.--OH]

From that PDF overview:

Larger Considerations

One of the sequelae from the recent industrial and electronic revolutions is a society increasingly alienated from its body. While a few hone their kinesthetic skills through sport and dance (while others hone their reflexes with sophisticated computer games), many more are losing muscle mass, losing an accurate body image, and generally losing ‘touch’.

Physical education and manual therapy, in both their traditional and holistic forms, seek to restore balance, awareness, proper functioning, and a healthy relationship with the physical self. New models, such as the concepts outlined above and other systems-oriented views, open new avenues for a populace weakened by constant sitting, fixed focal lengths, improper footwear treading relentlessly flat surfaces, cheapened sexuality, reduced contact with the natural world, lack of activity, and poor education concerning their physical selves from infancy on up. One major challenge for the 21st century is to adapt body systems forged in a Neolithic world to the socially crowded and almost entirely man-made environment we are rapidly constructing worldwide.

We are accustomed to the idea of IQ – measuring the intelligence of the brain. We are becoming more accustomed to EQ – the idea of emotional intelligence. What is needed is a map to the territory of KQ – kinesthetic intelligence, the intelligence of the body in motion. From the skill and awareness that makes an awkward body graceful to the inherent sense that warns us of impending danger; from the precise coordination required in a basketball lay-up to the body memory involved in plucking just the right strings on a harp; from the wisdom of rest and activity cycles to the cellular letting go required to forgive – there is great intelligence in the body that is not yet well understood. Therefore it is not being taught, and therefore it is being progressively lost, except for small pockets within Eastern and Western medicine where what the great physiologist Walter Cannon called the 'wisdom of the body' is being honored and developed. The most reasonable part in us is the part that does not reason.

These various lines of inquiry into KQ could be gathered under the banner of ‘Spatial Medicine’ (as opposed to the medicine of Matter [allopathic or nutritional], or the medicine of Time [psychotherapy or shamanism]). What can we learn from how humans are arranged in space, and how they perceive and work with their spatial arrangement? Osteopathy, chiropractic, orthopedics and physiotherapy would qualify as Spatial Medicine. So do the entire alphabet of new (and old) therapies from Alexander, Bioenergetics and Continuum, through Feldenkrais and Gyrotonics, to Rolfing, Somatics, and Tai Chi, all the way to Yoga and Zero Balancing. All these (and the many more not named) are inquiries into our spatial relationships and their meaning, and all seem to contribute to the whole picture. Shifting the positions of bones, altering the length of fascial and myofascial tissues, and training the neuro-muscular system all aim for the same goal – easy, generous, poised movement, structural stability, and the extension of healthy movement into later life.

In short, a systems view (as opposed to the symptoms view) of our structural and movement selves is required to counter the destructive effects of the world we have created for ourselves. The anatomical details so vividly and economically set forth in this book can help with the task of finding, restoring, appreciating, and properly using our amazing locomotor system. So can new overall organizing schemes like the Anatomy Trains – the ever-smaller can be put into service of the ever-larger, and vice versa. True human intelligence – what Norbert Weiner called ‘the human use of human beings’ – will be attained not by transcending the physical self, but only through our full participation with our marvelous physicality.

Sunday, September 18, 2011

Listen to Your Heart - Go with It

Sometimes you hear your heartbeat. you can almost always take a pulse reading and the chest strap with wrist display wireless fitness equipment does an excellent job of collecting data and displaying an array of information. For about $20 in parts this receiver (exploded view) allows headphone, earbud, or other audio connection monitoring of each heartbeat.


This is the most powerful feedback tool I have experienced. It is a surprizing advance in a pursuit. The following text was posted earlier at QuantifiedSelf:

RE: suggestions for simple data vizualization tools?

Keep it simple and real time, except for long term trends on more complex questions or issues. Sonification of HRV is my target. Got interested before cardiac ablation resolved atrial fibrillation and continue exploring with a simple Polar monitor and attachments based upon the Polar Heart Rate Module - RMCM01.

SuperCollider programming is still developing, but my real-time heart beat in my ears turned out to be a terrific feedback instrument. Never much for exercise groups or formal equipment, going with the flow of the tick of my heartbeat lets me explore movement in new ways. Walking down the street now has dance elements woven into the internal visualization of body and mind state. Bliss is remarkably easy to recognize and propagate - shifts in attention are markers for a drifting state that is absorbing on many levels. Having this tool allows for lots of tiny experiments with interesing results.

This is a much smaller second version. The first had two AAA batteries. With 6 hours on the battery I'm considering slimming down the other unit. The other end of the plastic plumbing fitting can take a larger battery.

Update 9/20/11
Wore a Polar Chest Transmitter and display watch to a dental appointment. Encouraged by a NuCalm System experience, noise isolating earbuds were used with the audio pulse unit. No science here, but I've had pain, panic, and problematic dentistry and relaxing was never this easy. I neared sleep twice. There was a mouth block disabling jaw movement witb a dam and local numbing for a root canal. Not bliss, but focused calm with a reminder pace.

Monday, July 4, 2011

Mindfulness Rules

With mindfulness there is greater awareness. With practice, the need for gear to monitor being or doing becomes superficial. You have the best possible sensors, processing power, and limitless memory capacity for storage and reflection. Why bother with biofeedback?

OK, you need a few hints. Download the free .pdf, study the text and prosper.

http://www.springerlink.com/content/w931n733l4575424/

So is guidance inb the exploration of the benefits of of mindfulness available for curious individuals? Yes.

www.urbandharma.org/pdf/mindfulness_in_plain_english.pdf

But wait, there's more, a whole page of links to ebooks such as:
 

Anapanasati - Mindfulness of Breathing

Loving-kindness Meditation

Meditation on a Coke Can

Long-Term Meditators Self-Induce high-Amplitude Gamma Synchrony


http://www.urbandharma.org/udharma5/ebooks.html