This the first part in a four part series about how to analyse a continuous heart rate signal, extract those measures often used in scientific publications, and filter the signal and detect error.
Important: The code in this tutorial is licensed under the GNU 3.0 open source license and you are free to modify and redistribute the code, given that you give others you share the code with the same right, and cite my name (use citation format below). You are not free to redistribute or modify the tutorial itself in any way. By reading on you agree to these terms. If you disagree, please navigate away from this page.
Citation format
van Gent, P. (2016). Analyzing a Discrete Heart Rate Signal Using Python. A tech blog about fun things with Python and embedded electronics. Retrieved from: http://www.paulvangent.com/2016/03/15/analyzing-a-discrete-heart-rate-signal-using-python-part-1/
Github rep: Github repository located here
- Part 1: Opening the data, detecting the first peaks and calculating the BPM;
- Part 2: Extracting complex measures from the heart rate signal;
- Part 3: Automatic error detection, outlier rejection and signal filtering;
- Part 4: Detecting and rejecting noisy signal parts.
The following tutorial assumes intermediate knowledge of the Python programming language, FIR-filters and fast fourier transform methods. The tutorial should be suitable for those with intermediate levels of Python skill. It is divided into separate parts so that you can easily skip over those parts you understand. The data was collected with a simple data logger based on an ATTiny45, as described in another post.
Some theory and background
The heart rate contains a lot of information about you. Apart from the obvious number of beats per minute there is information about your health, physical fitness and even mental activity in there. If you got yourself a heart rate sensor and some data, you could of course buy an analysis package or try some of the open source things available, but not all of them might do the things you want or need. This was the case for me as well. So, why not try to make one yourself? If you’re reading this, chances are you want to try this. This tutorial series is for those interested in learning more about heart rate analysis and how to write a simple but effective analysis algorithm in Python using a few basic modules.
For the first part of this series there isn’t a lot of relevant theory. Just know that when talking about the shape of the heart rate signal, each beat is characterized by a QRS-complex as shown below in a.), I-III (Q-R-S). There is also a P-wave (IV), and a T-wave (V). The R component is the large peak (II). This is the one of interest to us:
In photoplethysmogram signals (PPG) the signal is slightly different. The PPG signal is shown in b.) of the image. Components here are the Diastolic peak (I), which is the point of highest blood pressure, and the Diastolic peak (III). The two waves are separated by what is called the Dicrotic Notch (II). In this case the Systolic Peak (I) is used for heart rate extraction.
For the development of a peak-detection algorithm this is a nice coincidence: for both signals we need to label the highest peak in each complex.
First things first
First let’s download the dataset and plot the signal, just to get a feel for the data and start finding ways of meaningfully analysing it. I use pandas for most of my data tasks, and matplotlib for most plotting needs.
import pandas as pd
import matplotlib.pyplot as plt
dataset = pd.read_csv("data.csv") #Read data from CSV datafile
plt.title("Heart Rate Signal") #The title of our plot
plt.plot(dataset.hart) #Draw the plot object
plt.show() #Display the plot
The signal looks nice and clean. Keep in mind that this will not always be the case, even with good sensors and especially not when measuring outside the lab! More on dealing with noise and automatically determining signal quality in part 3.
Detecting the first peaks
The first step is to find the position of all the R-peaks. To do this we need to determine Regions of Interest (ROI’s), namely for each R-peak in the signal. After we have these, we need to determine their maxima. There are a few ways to go about doing this:
- Fit a curve on the ROI datapoints, solve for the x-position of the maximum;
- Determine the slope between each set of points in ROI, find the set where the slope reverses;
- Mark datapoints within ROI, find the position of the highest point.
The first provides an exact mathematical solution (more accurately: as exact as you want), but is also the most expensive computationally. With our example dataset the difference does not matter, but at the time I was developing this algorithm I had to go through almost half a billion datapoints quickly, and future datasets seemed only to get larger. Most of this code will also be re-written to C for use on an embedded ARM chip, so we need to keep it simple and efficient.
The latter two methods are computationally much less expensive, but also less precise. High precision with these methods relies much more strongly on a high sampling rate than it does with the curve fitting method. After all, the actual maximum of the curve will probably lie somewhere between two data points rather than on an actual data point, with a higher sampling rate this error margin will decrease. In Part 4 (currently in writing) we will also work with the curve fitting method for a more accurate approximation of the R-peaks, for now we’ll use the position of the highest point in the ROI as the position of the beat.
Now to work: first separate the different peaks from one another. For this we draw a moving average, mark ROI’s where the heart rate signal lies above the moving average, and finally find the highest point in each ROI as such:
import pandas as pd
import matplotlib.pyplot as plt
import numpy as np
import math
dataset = pd.read_csv("data.csv")
#Calculate moving average with 0.75s in both directions, then append do dataset
hrw = 0.75 #One-sided window size, as proportion of the sampling frequency
fs = 100 #The example dataset was recorded at 100Hz
mov_avg = dataset['hart'].rolling(int(hrw*fs)).mean() #Calculate moving average
#Impute where moving average function returns NaN, which is the beginning of the signal where x hrw
avg_hr = (np.mean(dataset.hart))
mov_avg = [avg_hr if math.isnan(x) else x for x in mov_avg]
mov_avg = [x*1.2 for x in mov_avg] #For now we raise the average by 20% to prevent the secondary heart contraction from interfering, in part 2 we will do this dynamically
dataset['hart_rollingmean'] = mov_avg #Append the moving average to the dataframe
#Mark regions of interest
window = []
peaklist = []
listpos = 0 #We use a counter to move over the different data columns
for datapoint in dataset.hart:
rollingmean = dataset.hart_rollingmean[listpos] #Get local mean
if (datapoint < rollingmean) and (len(window) < 1): #If no detectable R-complex activity -> do nothing
listpos += 1
elif (datapoint > rollingmean): #If signal comes above local mean, mark ROI
window.append(datapoint)
listpos += 1
else: #If signal drops below local mean -> determine highest point
maximum = max(window)
beatposition = listpos - len(window) + (window.index(max(window))) #Notate the position of the point on the X-axis
peaklist.append(beatposition) #Add detected peak to list
window = [] #Clear marked ROI
listpos += 1
ybeat = [dataset.hart[x] for x in peaklist] #Get the y-value of all peaks for plotting purposes
plt.title("Detected peaks in signal")
plt.xlim(0,2500)
plt.plot(dataset.hart, alpha=0.5, color='blue') #Plot semi-transparent HR
plt.plot(mov_avg, color ='green') #Plot moving average
plt.scatter(peaklist, ybeat, color='red') #Plot detected peaks
plt.show()
We have marked the highest point in each R-complex in our signal, not bad! However, this is an idealized signal. In part 3 of this series we will see how to deal with noise, measurement error, detection error and prevent our module from throwing errors at poor quality signal sections.
Some may ask: why the moving average, why not just use a horizontal line at around 700 as a threshold? This is a valid question and would work fine with this signal. Why we use a moving average has to do with less idealized signals. The amplitude of the R-peaks can change over time, especially when the sensor moves a bit. The amplitude of the smaller secondary peak can also change independently of the amplitude of the R-peak, sometimes having almost the same amplitude. One approach to reducing incorrectly detected peaks discussed in part 3 is by fitting the moving average at different heights and determining which fit seems best. More on this later.
Calculating heart rate
We know the position of each peak in time, so calculating the average ‘beats per minute’ (BPM) measure over this signal is straightforward. Just calculate the distance between the peaks, take the average and convert to a per minute value, like so:
RR_list = []
cnt = 0
while (cnt < (len(peaklist)-1)):
RR_interval = (peaklist[cnt+1] - peaklist[cnt]) #Calculate distance between beats in # of samples
ms_dist = ((RR_interval / fs) * 1000.0) #Convert sample distances to ms distances
RR_list.append(ms_dist) #Append to list
cnt += 1
bpm = 60000 / np.mean(RR_list) #60000 ms (1 minute) / average R-R interval of signal
print "Average Heart Beat is: %.01f" %bpm #Round off to 1 decimal and printAlso update the plot method to show the BPM in the legend:
plt.title("Detected peaks in signal")
plt.xlim(0,2500)
plt.plot(dataset.hart, alpha=0.5, color='blue', label="raw signal") #Plot semi-transparent HR
plt.plot(mov_avg, color ='green', label="moving average") #Plot moving average
plt.scatter(peaklist, ybeat, color='red', label="average: %.1f BPM" %bpm) #Plot detected peaks
plt.legend(loc=4, framealpha=0.6)
plt.show()
Pretty cool! You have taken the first step in analyzing the heart rate signal. The number of beats per minute is a useful measure that is very often used in scientific studies and has many non-scientific uses as well, but the signal contains much, much more information. Part 2 of this series will deal with extracting more complex information from the heart rate signal.
Rounding up
Finally let’s tidy up our code and put it in callable functions. This will make our life much easier in the next part, and our code much more organized and re-usable. Note that probably the tidy thing to do is to make the functions part of a Class, but to keep the tutorial accessible also to those less experienced in Python (and perhaps not familiar or confident with classes), I’ve chosen to omit this from all code in this tutorial series.
Let’s put the BPM value and the lists we calculate in a dictionary that we can call, and can append with the measures we will calculate in part 2. Also let’s write a wrapper function process() so that we can call our analysis with as little code as possible:
import pandas as pd
import matplotlib.pyplot as plt
import numpy as np
import math
measures = {}
def get_data(filename):
dataset = pd.read_csv(filename)
return dataset
def rolmean(dataset, hrw, fs):
mov_avg = dataset['hart'].rolling(int(hrw*fs)).mean()
avg_hr = (np.mean(dataset.hart))
mov_avg = [avg_hr if math.isnan(x) else x for x in mov_avg]
mov_avg = [x*1.2 for x in mov_avg]
dataset['hart_rollingmean'] = mov_avg
def detect_peaks(dataset):
window = []
peaklist = []
listpos = 0
for datapoint in dataset.hart:
rollingmean = dataset.hart_rollingmean[listpos]
if (datapoint < rollingmean) and (len(window) < 1):
listpos += 1
elif (datapoint > rollingmean):
window.append(datapoint)
listpos += 1
else:
maximum = max(window)
beatposition = listpos - len(window) + (window.index(max(window)))
peaklist.append(beatposition)
window = []
listpos += 1
measures['peaklist'] = peaklist
measures['ybeat'] = [dataset.hart[x] for x in peaklist]
def calc_RR(dataset, fs):
RR_list = []
peaklist = measures['peaklist']
cnt = 0
while (cnt < (len(peaklist)-1)):
RR_interval = (peaklist[cnt+1] - peaklist[cnt])
ms_dist = ((RR_interval / fs) * 1000.0)
RR_list.append(ms_dist)
cnt += 1
measures['RR_list'] = RR_list
def calc_bpm():
RR_list = measures['RR_list']
measures['bpm'] = 60000 / np.mean(RR_list)
def plotter(dataset, title):
peaklist = measures['peaklist']
ybeat = measures['ybeat']
plt.title(title)
plt.plot(dataset.hart, alpha=0.5, color='blue', label="raw signal")
plt.plot(dataset.hart_rollingmean, color ='green', label="moving average")
plt.scatter(peaklist, ybeat, color='red', label="average: %.1f BPM" %measures['bpm'])
plt.legend(loc=4, framealpha=0.6)
plt.show()
def process(dataset, hrw, fs): #Remember; hrw was the one-sided window size (we used 0.75) and fs was the sample rate (file is recorded at 100Hz)
rolmean(dataset, hrw, fs)
detect_peaks(dataset)
calc_RR(dataset, fs)
calc_bpm()
plotter(dataset, "My Heartbeat Plot")
Call it like this:
import heartbeat as hb #Assuming we named the file 'heartbeat.py'
dataset = hb.get_data("data.csv")
hb.process(dataset, 0.75, 100)
#We have imported our Python module as an object called 'hb'
#This object contains the dictionary 'measures' with all values in it
#Now we can also retrieve the BPM value (and later other values) like this:
bpm = hb.measures['bpm']
#To view all objects in the dictionary, use "keys()" like so:
print hb.measures.keys()Note that we have kept the get_data() function separate from our wrapper. This way our module can also accept dataframe objects already stored in memory, useful for example when these are generated by another program. This keeps our module flexible.
Tu
January 17, 2017Is the data.csv file have inter beat interval values in millisecond ?
Paul van Gent
January 17, 2017No, it is the raw heart rate signal.
Tu
January 17, 2017You mean the heart beats ? can you please tell the unit?
Paul van Gent
January 17, 2017What you see is the change in sensor conductance in response to the discoloration of the skin as the heart beats. There is an arbitrary time scale, but that is not relevant to the tutorial. Follow the series and it should become clear!
Manujaya
April 21, 2017sir when i compile this code there is an error given
”
raise ValueError(“window must be an integer”)
ValueError: window must be an integer”
can you please help me to solve this problem. This is really need for my project
thank you
Paul van Gent
April 21, 2017Hi Manujaya. The error should tell you all you need to fix it. I suggest you start with a few more basic Python tutorials. This one assumes at least an intermediate familiarity.
edge-python
April 2, 2018use in Calculate moving average: window=int(hrw*fs)
Pingback: Start coding for Bobbi – the open source ECG monitor! | Pavlov | A dash of code, a pinch of science
Kamil
May 25, 2017Could you tell me how to process the ECG signal, which I have stored as a ndarray? It’s a standard numpy ndarray with one row (but there isn’t any key like ‘hart’). I wanted to pass it to the processing functions.
Paul van Gent
May 26, 2017Hi Kamil. This is part of the 4th part in this series, which I’m still writing. You can see the code on my GitHub, it’s nearing V1.0, when I’ll be making it installable through pip: https://github.com/paulvangentcom/heartrate_analysis_python
Eina
June 14, 2017Hai Mr. van Gent,
I’m doing this project for my thesis. I have some question that I want to ask.
1. Is the data in csv raw (not in Hz)? If yes, why it’s so high? is it like the frequency of the pulse or the pulse it self? Because I’m trying to implement your code in my data that I get.
2. If you get the raw pulse and you change it to frequency (in Hz), how did you change it? Because I haven’t found it yet.
Thanks
Paul van Gent
June 14, 2017Hi Eina.
1. Yes it’s raw sensordata. I’m not sure what you mean here by ‘why is it so high’. I would suggest you follow the tutorial and plot the data, then you see why it’s sensordata. What sensor are you using and what data comes out of it?
2. What do you mean with ‘raw pulse’? If you mean the raw signal, that’s what the tutorial series is about. If you mean you already have BPM but want Hz, well, BPM=beats per minute, think of Hz as beats-per-second.
Let me know.
-Paul
Marcus Holzberger
July 7, 2017Very nice . Thank you
Santosh
July 8, 2017Hai Mr. van Gent,
i am research student i am working on real time heart rate monitoring and analysis signal and calculate RR interval ,can i do real time data analysis code using in python
for access real time data using pulse sensor please help me how can access? .
Paul van Gent
July 8, 2017Santosh, I’m not sure what you mean exactly. Do you want to read the sensor? Do you want help with the algorithm? Let me know
-Paul
Santosh
November 17, 2017Hai Mr. van Gent
i am working disease prediction using HRV , so my question is how to predict diseases using real time HRv and which algorithm is best for prediction
Wadaane
July 21, 2017Hello,
Me too, I also wanted to do real time analyse and graph, but matplotlib animations are too slow.
I gave up the idea to draw all datapoint, I think to reduce the number of samples to draw.
You get me ?
Like 10 beats take almost 4000 samples at 500Hz, I’ll use the 4000 samples for analysing, but only draw half, or quarter, like draw every fourth datapoint.
I didn’t try it yet, but I think that’ll speed things up.
Paul van Gent
July 21, 2017That probably won’t work, the library isn’t fast enough for anything real-time. You could look at some c or c++ libs. An alternative is to buffer 5 sec, analyse&plot, and repeat
Anam
July 8, 2017Hello Paul, could you explain why you took 0.75s as your window size? What proportion are you talking about?
Paul van Gent
July 8, 2017Hi Anam. I see I’ve made a mistake in the code. It’s not 0.75s (unless your sampling rate is 60Hz), but rather 0.75*sampling rate in both directions. The reason for this is that the larger this threshold, the less like the HR signal the rolling average will be, the smaller, the more similar. I would recommend you plot the signal + rolling average with different window sizes. See what happens, and why in this case 0.75 (or similar sizes) work.
-Paul
Anam
July 8, 2017Yep my signal is actually quite noisy and with 0.75, it actually considered the T-peaks to be R as well! I experimented with the value a little and 0.45-0.5 helped. Another problem I’m having is that my ECG sensor gives me the signal shape in a negative range of voltages sometimes (I think I need to read up on lead configurations a little) so I actually have to multiply the moving average by a value lesser than 1 instead of 1.2 or 1.1 like you’ve used. So I guess I’m just stuck with good ol’ trial and error!
Paul van Gent
July 8, 2017Before tweaking I recommend you pass through part 2 and part 3 as well. There are some bits about signal filtering there, which is (always) a good idea, especially if you are having troubles with noise.
Alternatively, if you don’t care about how it works, look at my repo: https://github.com/paulvangentcom/heartrate_analysis_python
Paul van Gent
July 8, 2017Regarding the negative range: you can consider shifting it all up by some amount so it’s all positive, or cut off the negative ranges (if these don’t contain peak data, which I suspect based on your explanation).
Becky
August 31, 2017Hi,
I tried the final version on github for my data-set but was receiving an error and just decided to walk through the tutorial and make sure I was following. I know there is more to come but wanted to point out a couple of adjustments I had to make at this point for things to work:
1. In the peak detection loop, I had to add in a check for ‘nan’. I also added in the option to start the peak detection at a later sample because a had a lot of nan values at the start that were throwing things off.
if ((datapoint < rollingmean) and (len(window) < 1)) or (math.isnan(datapoint)) or (listpos<3000):
2. Negative values seemed to be an issue so I subtracted off the min if it was negative:
ECGmin=np.nanmin(dataset.ECG)
if ECGmin<1: dataset.ECG=dataset.ECG-ECGmin
I'm just curious if there was something I missed in adding these work arounds or thought I would share if they are helpful to others.
This library is great, thanks for sharing!
Paul van Gent
August 31, 2017Hi Becky. Thanks for your suggestions!
1. That is correct, NaN’s are not handled. I Recommend interpolating your signal to fill in the NaN values, rather than handling them separately in the detection. I’ll put an interpolation preprocessing handler on the to-do list for github
2. Correct, I recently ran into this when using a different ECG device as well, as well as a device where the signal needed to be flipped in its entirety. The fixes are there but not merged to github yet, on the to-do list.
Meera
September 6, 2017Hi,
Your project is amazing. Thank you. Is it also possible to apply the moving average filter in real-time? As in when I’m acquiring the signal at 20 Hz i would like to see my raw data, filtered data and beats per minute.
Paul van Gent
September 11, 2017Hi Meera. 20Hz is much too low to get any meaningful results, I would look at 100Hz minimum. Python is not fast enough for this kind of real-time thing. You could, however, generate one plot each second..
Amelia
September 15, 2017Hello Paul, your work is superb… I came across it while I was working on a project of wireless ecg transmission, and thought of using the same to verify whether the ecg has been received at the receiver side correctly- using the total number of beats and bpm…..Unfortunately I had some trouble with the python language and sorry to ask this but the .hart parameter – what exactly is that – when I run the code I often get errors saying the hart parameter is not available for the dataset etc.
<the portions I am refering to are:
…
plt.plot(dataset.hart)
…
….
mov_avg = pd.rolling_mean(dataset.hart, window=(hrw*fs))
….
etc…. Is it something that is available only to .csv files with both time and hr columns?
(Sorry if the question is inapproprriate w.r.t to the topic…but it would be really helpful if you could answer this)
Paul van Gent
September 19, 2017Hi Amelia. Thanks for the kind words!
the .hart parameter refers to a specific column in the dataframe, so if you name your dataframe “df”, then you can access the column “hart” by calling df.hart. Does that make sense?
As a reference, take a look at the github version, this drops the Pandas dependency and adds some optimizations. You might find using this one + documentation easier than following the tutorial if you’re not that familiar with Python.
Amelia
September 15, 2017(also my sampling frequency is 244 Hz….will that sampling frequency have any negative effects on the calculation?
-also how large the sample dataset can be (i.e. the minimum maximum allowed dataset size) for the code to work well..?
Paul van Gent
September 19, 2017That should be fine. Generally a higher sampling rate is better as the signal will contain more data (resulting in more precision) to base measures on.
amulya
October 11, 2017hi
at step 2 plotting peaks….yea……im getting an error like
validate
raise ValueError(“window must be an integer”)
ValueError: window must be an integer
what do i do
Paul van Gent
October 12, 2017What’s happening is that the Pandas function ‘rolling_mean’ expects the window size to be an integer. You can ensure an integer either by setting the window size parameters appropriately (lines 9,10), or force it like so:
mov_avg = pd.rolling_mean(dataset.hart, int(window=(hrw*fs)))
-Paul
emily
October 24, 2017i seem to have a issue : window in an undefined function.
Paul van Gent
October 25, 2017Emily, please share the details. With this I have no idea what’s happening. You can either post it here or mail me your code and a screenshot of the full error message to info@paulvangent.com
-Paul
M. Chowdhury
October 30, 2017mov_avg = pd.rolling_mean(dataset.hart, window=int(hrw*fs))
worked for me, even though I got some warning. You can try and update us.
amulya
October 24, 2017ohhh okay thats a lot of help thank you so much and for this blog.
General
November 1, 2017Amazing tutorial THANK YOU SO MUCH!
meredith
November 3, 2017the code
***
dataset = pd.read_csv(“data.csv”)
#Calculate moving average with 0.75s in both directions, then append do dataset
hrw = 0.75 #One-sided window size, as proportion of the sampling frequency
fs = 100 #The example dataset was recorded at 100Hz
mov_avg = pd.rolling_mean(dataset.hart, int(window=(hrw*fs)))
#Impute where moving average function returns NaN, which is the beginning of the signal where x hrw
avg_hr = (np.mean(dataset.hart))
mov_avg = [avg_hr if math.isnan(x) else x for x in mov_avg]
mov_avg = [x*1.2 for x in mov_avg] #For now we raise the average by 20% to prevent the secondary heart contraction from interfering, in part 2 we will do this dynamically
dataset[‘hart_rollingmean’] = mov_avg #Append the moving average to the dataframe
#Mark regions of interest
window = []
peaklist = []
listpos = 0 #We use a counter to move over the different data columns
for datapoint in dataset.hart:
rollingmean = dataset.hart_rollingmean[listpos] #Get local mean
if (datapoint < rollingmean) and (len(window) do nothing
listpos += 1
elif (datapoint > rollingmean): #If signal comes above local mean, mark ROI
window.append(datapoint)
listpos += 1
else: #If signal drops below local mean -> determine highest point
maximum = max(window)
beatposition = listpos – len(window) + (window.index(max(window))) #Notate the position of the point on the X-axis
peaklist.append(beatposition) #Add detected peak to list
window = [] #Clear marked ROI
listpos += 1
ybeat = [dataset.hart[x] for x in peaklist] #Get the y-value of all peaks for plotting purposes
plt.title(“Detected peaks in signal”)
plt.xlim(0,2500)
plt.plot(dataset.hart, alpha=0.5, color=’blue’) #Plot semi-transparent HR
plt.plot(mov_avg, color =’green’) #Plot moving average
plt.scatter(peaklist, ybeat, color=’red’) #Plot detected peaks
plt.show()
***
i did this it says window in mov_avg = pd.rolling_mean(dataset.hart, int(window=(hrw*fs)))
TypeError: ‘window’ is an invalid keyword argument for this function
please help im new to python but i need to code for learning purposes i tried my best.
Paul van Gent
November 8, 2017Hi Meredith, what version of pandas are you using? I believe the “rolling_mean()” function was planned to change to “rolling()” in newer versions.
Paul van Gent
November 11, 2017If you’re using the VS command prompt, make sure you use the correct instruction set. Use the 64-bit VS prompt if you’re trying to build a 64-bit library, etc.
meredith
November 10, 2017hi paul thanks for replying my pandas version is ‘0.18.1’
Paul van Gent
November 11, 2017Try calling rolling() in stead of rolling_mean.
– Paul
meredith
November 13, 2017it says module pandas has no attribute rolling…..so it does not contain the function?
thanks paul
amrita
June 28, 2018hey did you solve the rolling problem ?
palkab
June 28, 2018I’ve updated to code to reflect a possible solution using pandas. Also take a look at the repo since I dropped the dependency on pandas completely during development.
– Paul
ann
November 15, 2017hi paul,
in 2nd code i just changed hrw= any integer without fractions and i get the output otherwise no, why does this happen?
Paul van Gent
December 4, 2017Hi Ann. This is an issue with the current implementation. As soon as my paper about the algorithm is published, I’ll update everything (and put part 4 online). For now use floor division (“//” in stead of “/”), or wrap the division in int(). It doesn’t work because the rolling window function expects an integer.
Sree
November 20, 2017Hi,
Great Tutorial!
How would I modify this code to read in input from audio source (say I have a heart sound recording).
Could I use:
from scipy.io import wavfile as wav
rate, data = wav.read(‘heart_sound.wav’)
In this case would my data be equivalent to dataset.hart?
Thanks again for the great tutorial!
Paul van Gent
December 4, 2017Hi Sree, We talked on Github. I will try to implement a quick fix for you asap.
anu
November 21, 2017can i please have your mail paul cause i could send screenshots of the signals i have cause there’s a question i have
Paul van Gent
December 4, 2017Hi Anu, info@paulvangent.com
Samer
December 3, 2017Hi Paul!
I am loading an already recorded raw ECG signal and filtering it:
x = []
with open(‘C:/Users/PC/Downloads/SamirECG(Win).txt’,’r’) as csvfile:
dat = csv.reader(open(‘C:/Users/PC/Downloads/SamirECG(Win).txt’,’r’))
for row in dat:
x.append(float(row[0]))
x = np.transpose(x)
dataset = x[50:2000]
f2 = np.convolve(dataset, np.ones((7,)) / 7, mode = ‘valid’)
Things are working well regarding this issue, but when I try to run the first part of your code, which does the moving average calculation:
hrw = 0.75 #One-sided window size, as proportion of the sampling frequency
fs =500 #The example dataset was recorded at 100Hz
mov_avg = pd.rolling_mean(f2.hart, window=(hrw*fs))
I keep getting the following error:
AttributeError: ‘numpy.ndarray’ object has no attribute ‘hart’
Could you please help me fix this problem?
Your help is appreciated,
thanks!
Paul van Gent
December 4, 2017Hi Samer. The implementation on this site uses Pandas DataFrame objects as data handlers. These, unlike numpy arrays that you’re using, can use named data retrieval. In the case of pandas: f2.hart, or similarly, f2[‘hart’].values, would return the values in the column with the header ‘hart’.
The quickest way for you to get moving is to clone the numpy-based code from my github (https://github.com/paulvangentcom/heartrate_analysis_python). This code natively handles numpy arrays. Alternatively, you can open your csv using pandas and put the ECG data in a column named ‘hart’.
Note that if you’re using raw ECG values, you need to transpose the entire signal up so that there are no negative values. This is addressed in the final part of the tutorial which will go online early 2018.
– Paul
John
December 15, 2017Hi Paul:
(Please, see my thanks for your work on the comments section of part 2!)
Many reading your code have been complaining about an integer error on parameter ‘window’ in pandas.rolling_mean. There seems to be a glitch of some sort. I was getting the error too.
Here is what I’ve noticed:
1. forcing window=int(hrw*fs) gives the same error
2. typing “mov_avg = pd.rolling_mean(dataset.hart, window=int(hrw*fs))” on ipython works. Same goes for “mov_avg=dataset[‘hart’].rolling(window=75,center=False).mean()”
3. calling the functions from the main body of heartbeat.py also works fine when window=int(hrw*fs).
My recommendation to ones having this problem is calling the functions like this:
>>import heartbeat
>>dataset=get_data(‘data.csv’)
>>process(dataset,0.75,100)
>>bpm=measures[‘bpm’]
>>print measures.keys()
I’m using Python2.7 and tested the above on Spyder 3.1.4 under Anaconda2 distribution.
I’m not really sure where the heart of the problem is. Just seem to have found a workaround.
Thank you (and any reading),
John
Paul van Gent
December 16, 2017Thanks. I hop others will benefit from this as well. Pretty soon I hope my software paper about this is published and I can release part 4, which contains many changes including dropping pandas. You can sneak peak in my github for few changes.
– Paul
Nat
January 22, 2018Hi, Paul. loving this tutorial. It’s really good. Can you eyeball the timeframe until possible pip install? I’m also wondering why is “dropping dependencies on pandas ” on your to do? I’m curious about the reasoning behind it 🙂 Keep up the good work!
Paul van Gent
January 25, 2018Hi Nat. Thanks for the comment. I’m dropping pandas by default because I want to reduce dependencies as much as possible and make the package more versatile. Not everyone might have pandas, want to use it, or need to use it. Right now the github version defaults to Numpy, but of course you can also pass it data from a dataframe.
The pip install timeframe will likely be mid-2018. As you may have read in some of my other comments here I’m working on a paper and project integration of the software, after which I’ll have more time for these kinds of things (and then I can finally release part 4). Sometimes developing these open source things within a scientific project can take a lot more time than you’d like, but then again I’m thankful the opportunity is here to keep the package open source.
p.s. a full version in embedded C (Arduino!) is now in the final testing phase and will come online soon as well, in case you’re planning wearable projects.
– Paul
Namrata
January 31, 2018Hi Paul..
could you please provide the information about the device from which you took the readings.. and did you convert the input audio files into csv format?
Paul van Gent
January 31, 2018Hi Namrata. I’ve used a PPG sensor (optical), there’s plenty out there you can use. I’ve not used audio recordings. There’s multiple heart sounds per cardiac cycle, analysing heart reate by audio is less trivial because of this. There is some experimental code on my github for this, but use it sparingly: it needs to be tuned much further.
Thibault
February 25, 2018Hi,
I study the sensor max30101. I found your tutorial, and he really help me to understand how exploit raw data to get Bpm.
1- In my case, I receive 1 data every 1ms. I took arround 1k5 data to be precise as much as possible. I found that, the distance betweens two peaks is arround 30ms and do this calcul to get bpm : 1(min) / 30e-3(ms convert to min). Is that right ?
2- I can’t understand this line : ms_dist = ((RR_interval / fs) * 1000.0)
why you multiple all by 1000?
Thank you for your tutorial, and your time !
Paul van Gent
February 26, 2018Hi Thibault.
1 – distance between two peaks of 30 ms seems very low. This implies a heart rate of 2000 bpm. Your calculation is correct, it is “time units in minute / average R-R interval in same time units”. I use “60000 / mean(R-R) in ms” to get it in ms.
2 – What I do is rescale the R-R intervals to be in ms-units. I divide the RR_interval by the sample rate (in Hz) to get R-R in seconds, then multiply by 1000.0 to get it in ms.
– Paul
Thibault
February 26, 2018Hi Paul.
1- It’s clearly too slow… I don’t know if it’s my measures which are false or my units when I determine distance between each peaks.
2- Great ! it’s much clear now !
Thank you for your explanations !
Paul van Gent
February 26, 2018Can you send me a sample recording of 1 or 2 minutes from your data set? You can send it to info@paulvangent.com
– Paul
Priyanka
March 28, 2018Hey
I need to convert my raw ECG waveform into a data set or a text file. How do I do it?
I am using Python on Debian.
Paul van Gent
March 28, 2018What is a ‘raw ECG waveform’? What data format is it, how is it collected, etc?
Priyanka
March 29, 2018It is obtained directly from ECG cable connected to patient’s body. I need to use the waveform on Raspberry PI hence I want to convert it to .txt or .csv file
Paul van Gent
March 29, 2018That depends on how you read the sensor values. How is it hooked up to the Raspberry? What type of sensor is it?
Priyanka
April 6, 2018We have designed a breakout board for ECG using analog front end modules. It is an ECG sensor from Analog Devices. I need to display it on raspberry pi through spi port.
Paul van Gent
April 11, 2018This should get you started with SPI communication. Important to keep in mind is to pull your chip select pin high when you want to transfer data. I’m abroad on holiday these weeks so I cannot make and test something for you as I don’t have any equipment with me.
You can also look at ‘WiringPi’ to talk over SPI with a sensor.
Plotting the data should be straightforward with matplotlib. Real-time plotting is difficult in python on raspberry, I wouldn’t put too much effort into that. You could make something that updates once or twice a second, for example.
– Paul
Preyanka
April 18, 2018Thank you for your code…it helped me a lot in doing my project and i hope could you please help me to find the P and T wave from the above dataset
Paul van Gent
April 23, 2018Hi Preyanka. I’ll add some details to the first part. There are no P and T waves in the PPG signal (technically there are no Q-R-S waves either). The signal consists of a systolic and diasystolic peak, separated by a dicrotic notch.
If you’re using ECG data, take a look at some other algorithms out there that are for QRS (Pan-Tompkins) and P-T detection.
– Paul
ccnalu
June 15, 2018for Basic analysis example@GitHub heartrate_analysis_python, run the validate pipeline code as following,
import heartbeat as hb
data = hb.get_data(‘data.csv’)
fs = 100.0 #example file ‘data.csv’ is sampled at 100.0 Hz
measures = hb.process(data, fs)
print(measures[‘bpm’]) #returns BPM value
print(measures[‘lf/hf’] # returns LF:HF ratio
#Alternatively, use dictionary stored in module:
print(hb.measures[‘bpm’]) #returns BPM value
print(hb.measures[‘lf/hf’] # returns LF:HF ratio
#You can also use Pandas if you so desire
import pandas as pd
df = pd.read_csv(“data.csv”)
measures = hb.process(df[‘hr’].values, fs)
print(“measures[‘bpm’])
print(“measures[‘lf/hf’])
then get the result as
KeyError: ‘lf’
please help me how to fix it, thanks.
Paul van Gent
June 20, 2018Hi ccnalu. You need to run the
process()function withcalc_fft=Trueif you want to be able to access the frequency-domain measures. Note that at this stage they are not super reliable yet.– Paul
Arjun
June 20, 2018Hi Paul,
Much thanks for the code.
I’m trying to detect Blood Pressure from PPG Signal as part of my project.
Is there a way I could extract features from the PPG signal (Time domain…15fps) using Python libraries?
Paul van Gent
June 22, 2018Hi Arjun. There is not an easy way to extract blood pressure from a PPG without calibrated sensors or a standardised measurement site. The relationship depends heavily on vascular properties which vary with the measurement site. The best thing you can do is buy a commercially available finger cuff for BP.
– Paul
BruceLee
July 2, 2018http://www.paulvangent.com/wp-content/uploads/2016/03/data.csv
I cant find the heart sounds data by this website(404).
palkab
July 4, 2018Should be fixed now, BruceLee!
rsr
October 4, 2018I am getting an error stating that series object has no attribute rolling in the line
mov_avg = dataset[‘hart’].rolling(int(hrw*fs)).mean()
in the code
palkab
October 5, 2018Hi Rsr. You are using an older version of Pandas. Either change rolling() to rolling_mean(), or (preferably) update your pandas.
– Paul
sesha
October 7, 2018sir can I have the algorithm for r – peak detection of ECG signal??
palkab
October 8, 2018It’s in the tutorial. Also take a look at the GitHub