Chapter 2
PPG Extraction and Heart Rate Calculation
The block diagram of Camera-based PPG briefs the set-up of the system.
Hardware used
Camera:
Camera is the main focus of the project. AVT Stingray F-046B cameras are used with different filters. AVT Stingray F-046B is a progressive scan CCD, monochrome camera. It is an IEEE 1394b standard camera with 780x580 resolutions. The frame rate is up to 61 fps.
Optical monochrome filters:
Optical monochrome filters are used to filter out all the wavelengths except desired one. Since we are interested in Green, Red and Near Infrared wavelengths the following filters are used.
• Green (559 nm)
• Red (675 nm)
• Near Infrared (842nm)
NI DAQ:
National Instrumentation Data Acquisition system is used to drive Cameras. NI DAQ controls cameras via fire wire. And it mediates between the Software used in the computer to process the video and extract PPG and calculate heart rate.
Philips pulse oximetry
Philips pulse oximetry probe and device is used for a reference heart rate.
Software used
National Instruments LabVIEW is used for the purpose. LabVIEW stands for Laboratory Virtual Instrument Engineering Workbench. LabVIEW supports Data Acquisition, Instrument control, Signal processing etc. LabVIEW files are saved in .vi extension where vi stands for virtual instrument.
The Algorithm
For the moment, the PPG extraction and heart rate calculation is done using the pre-recorded videos. That is offline processing.
The pre-recorded video of the subject (measurement data) is saved NI - TDMS file format. TDMS - Technical Data Management Streaming is a file format from National Instruments to save well- documented measurement data. Data from TDMS are read frame by frame in Read Frame VI. The TDM...
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...ves error Median.vi
Input Output
X (array of data) Median error Step vii: calculate average AC value
Average AC value is calculated just by adding the median values of peak and valley median amplitudes.
Step viii: Calculate heart rate
Heart rate, the main focus of the work:
The time taken by the total number of PPG cycles (frequency) multiplied by 60;
The number of cycles = no. of peaks – 1;
Time = (location of last peak – location of the first peak) / frame rate;
So HR = total number of cycles / time * 60;
Step ix: Calculate mNP mNP = AC / DC *1000;
Step x: Display PPG, Heart rate and mNP
The process block or the Filter.vi outputs PPG signal, HR and mNP
Filter SubVI.vi
Input Output
Array in(signal)
Filter type
Sampling rate
High cut off frequency
Low cut off frequency
Order
Truncation length
Window size
Heart rate
Ac value
DC value mNP PPG
There are several different heart problems that show up as an abnormal EKG reading. For example, a heart block can occur when there is a delay in the signals coming from the SA node, AV node, or the Purkinje fibers. However, clinically the term heart block is used to refer to an AV block. This delays or completely stops communication between the atria and the ventricles. AV block is shown on the EKG as a delayed or prolonged PR interval. The P wave represents the activity in the atria, and the QRS complex represents ventricular activity. This is why the PR interval shows the signal delay from the AV node. There are three degrees of severity, and if the delay is greater than .2 seconds it is classified as first degree. Second degree is classified by several regularly spaced P waves before each QRS complex. Third degree can be shown by P waves that have no spacing relationship to the QRS complex. Another type of blockage is bundle branch block. This is caused by a blockage in the bundle of His, creating a delay in the electrical signals traveling down the bundle branches to reach the ventricles. This results in a slowed heart beat, or brachycardia. On an EKG reading this is shown as a prolonged QRS complex. A normal QRS is about .8-.12 seconds, and anything longer is considered bundle branch block. Another type of abnormal EKG reading is atrial fibrillation, when the atria contracts very quickly. On the EKG this is shown by no clear P waves, only many small fibrillating waves, and no PR interval to measure. This results in a rapid and irregular heartbeat. On the other hand, ventricular fibrillation is much more serious and can cause sudden death if not treated by electrical defibrillation.
Results: The experiments required the starting, ending, and total times of each run number. To keep the units for time similar, seconds were used. An example of how to convert minutes to seconds is: 2 "minutes" x "60 seconds" /"1 minute" ="120" "seconds" (+ number of seconds past the minute mark)
In this lab, I took two recordings of my heart using an electrocardiogram. An electrocardiogram, EKG pg. 628 Y and pg. 688 D, is a recording of the heart's electrical impulses, action potentials, going through the heart. The different phases of the EKG are referred to as waves; the P wave, QRS Complex, and the T wave. These waves each signify the different things that are occurring in the heart. For example, the P wave occurs when the sinoatrial (SA) node, aka the pacemaker, fires an action potential. This causes the atria, which is currently full of blood, to depolarize and to contract, aka atrial systole. The signal travels from the SA node to the atrioventricular (AV) node during the P-Q segment of the EKG. The AV node purposefully delays
The first participant measured her pulse rate for 30 seconds before starting the exercise. Her pulse rate was calculated to determine the number of beats per minute. She then stepped on the platform (up and down) and continued at a slow pace for 3 minutes. After three minutes of the exercise, she measured her pulse rate every minute to determine her recovery time. This process was repeated until her pulse rate returned to normal.
Currently, it is not possible to prescribe isometric exercise at an intensity that corresponds to given heart rates or systolic blood pressures1. This might be useful in optimizing the effects of isometric exercise training1. According to further study on this topic, linear relationships that have been discovered could be used to identify isometric exercise training intensities that correspond to precise heart rates or systolic blood pressures. Training performed in this way might provide greater insight into the underlying mechanisms for the cardiovascular adaptations that are known to occur as a result2. Studies have also shown a direct, strong, independent and continuous relation between blood pressure and cardiovascular mortality without any evidence of a threshold down to at least 115/75 mm Hg3. Further, it has been demonstrated that, as compared with optimal BP, normal and high-normal BP are associated with a higher incidence of CV disease3.
bpm as opposed to 247 bpm in water. After fifteen minutes, the AHR was 297
Jones, W. P., Loe, S. A., Krach, S. K., Rager, R. Y., & Jones, H. M. (2008). Automated Neu
by the internal computers of the instrument, to create an image of internal body tissues. These images were then displayed on the screen for the user,
body has to work harder I think that the heart will then increase at a
= The results that I have gathered from my experiment I have put into graph form. From my results I have found out that the more I exercise the longer I exercise the longer it takes for my pulse to return to normal, I think that I did not reach my potential maximum heart rate because the exercised was not strenuous enough for my body. I also discovered that when taking my pulse it takes a few seconds for the strong pulse to get back to the surface.
As humans we need the heart to pump blood all around the body in order
The two major things that will help an athlete while measuring the cardiovascular drift are progression and hydration levels. The heart rate of an athlete working hard during a workout should be no more than their maximum heart rate which is found by, if you’re a female take 226-age, if you’re a male take 220-age. If while doing a workout the maximum heart rate is exceeded by too much it may be necessary to take a break or slow down greatly. This may also help with traking the hydration of an athlete. If an athlete stays hydrated their core temperature will stay regulated which means they won’t sweat as much, which also means the heart won’t be under as much stress while transporting the oxygenated blood throughout the body to the
Gaussian filter is exclusively used for this purpose as the mask is simple. The standard convolution method is performed once the mask is calculated. Since the convolution mask is usually much smaller than the actual image, the mask slides over the image , manipulating the pixels in the image. The large width Gaussian masks are not preferred as detector's sensitivity to noise is low and moreover, the localization error in the detected edges also increases with increase in Gaussian mask width.
This new technology helps the commanding officers know what is going on by that they can be back at there command base and watch raids unfold on large screens and watch real time footage. This allows them to know what exactly what is taking place.
Many soft wares and tools were developed to help in storing, retrieving and processing the data, some examples of these tools