# LabVIEW

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## Plotting blood pressure

When plotting blood pressure, I want to make the time (X-axis) start at zero with each new cycle, like at a min point. Each cycle is about 0.8 seconds long, and the time being plotted is absolute time. As we plot multiple cycles over about 5 seconds, we only get the PC's time. We would like to have each cycle have its own time values.  We are exporting these to excel, and would like to streamline the process.

Any ideas?

Thanks!

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## Re: Plotting blood pressure

I am unsure what you want to do.  Are you sampling Blood Pressure at a fixed rate?  How fast?  What, exactly, do you want to save?  What's wrong with, say, sampling continuously for, say, 5 minutes at, say, 100 Hz, saving all the data, and then analyzing it to find the peaks and valleys, frequencies of beats, etc.?  Once you get an algorithm to do this "off-line", you can consider revising your code to analyze your data "on the fly".

Bob Schor

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## Re: Plotting blood pressure

We are reading Blood Pressure. We currently sample continuously for 5 seconds, sampling at 100Hz, and then analyze the peaks and valleys. The only issue is that after we export, the time stamp options aren't suitable, neither absolute nor relative time, because the units are not small enough. Each cycle can run about 0.8 seconds so we need increments of 0.01 seconds. We measure pressure at multiple points simultaneously and export them to excel. Ideally, these exports would allow us to measure time on the X-axis starting with 0 at each minimum (Essentially, the start/end of a cycle). When we export now, we have to make adjustments by manually finding the minimum, start of each cycle.

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## Re: Plotting blood pressure

Here's an example of what we are plotting. I guess we are looking for better ways to plot and export the data to excel. We would like to have the time start at the beginning of a cycle.

We are also open to suggestions. If there's a better way, we'd try it.

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## Re: Plotting blood pressure

Hi MagnusJ,

I think this KB can help you in setting the timestamp to zero. https://knowledge.ni.com/KnowledgeArticleDetails?id=kA00Z0000019KZrSAM&l=en-US

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## Re: Plotting blood pressure

TCChun,

Thanks for your response. I will look into the VI. I wonder if it is possible to have the plot act like a Blood Pressure monitor. Where the X-axis scale stays in place, while the waveform is plotted from 0-Inf.

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## Re: Plotting blood pressure

Hi MagnusJ,

As I've never seen a blood pressure monitor that plot before, so I do not know how it plot. This is what I understand from the description.

For the x-scale to be constant, the autoscale function needs to be disabled through right-click menu or via Create>Property Node>X Scale>Scale Fit and write zero (do not autoscale) into it. The chart will automatically scroll to the right when plotting.

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## Re: Plotting blood pressure

@MagnusJ wrote:

Thanks for your response. I will look into the VI. I wonder if it is possible to have the plot act like a Blood Pressure monitor. Where the X-axis scale stays in place, while the waveform is plotted from 0-Inf.

You failed to attach your VI (no pictures, please, attach the actual LabVIEW .VI file(s)), so we cannot tell if you are plotting using a Chart or a Graph.  I'm going to "guess" you are using a Chart.

Charts plot a finite number of points (I think, by default, they plot 100 points, but you can increase this by a factor of 10 or more).  Once they hit this limit, they can respond in three ways:

• Strip Chart.  The chart "scrolls to the left", as though it is paper being produced by a pen writing on paper moving to the left (with the pen writing on the right-hand end).  Note that, initially, the "paper" stays stationary and the "pen" moves to the right.
• Scope Chart.  This looks like an oscilloscope, the "pen" moving left-to-right, erasing ("blanking") the plot when the pen reaches the right edge and starting the next "sweep" on the left.
• Sweep Chart.  This is like the Scope Chart, except there is no "blanking" when the pen reaches the right edge.  Instead, the old point is erased and the new point is plotted.

You can set the Chart to either of these modes (default is Strip Chart) by changing its Update Mode property.

Bob Schor

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## Re: Plotting blood pressure

We currently use the "Scope Chart" option. Plots start at the left and move to the right for 5 seconds. Shown in the picture below.

What we are hoping for is to have the plot being at the minimum on the waveform which will coincide with 0 on the X-Axis. My VI is attached. Please be nice, I didn't design it, it's just what I have to work with. Thanks for your help.

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