Hello everyone,
There are so many physiological events happening in your body during exercise such as energy metabolism, buffering, gas exchange… etc. CPET which is cardiopulmonary exercise test is a test to examine gasses you inhale and exhale. The gasses can tell you a lot of things, so I am gonna only focus on VT1, VT2, and VO2max in this blog.
Procedure
1, Import data
I inserted my CPET data on this blog below, so you can download and import it into MATLAB or other programing language.
2, Plot Wasserman 9 panel
The Wasserman 9 panel is 9 plots which are useful for physiological event detection. The panel is below…
Panel 1: Ventilation over time
Ventilation is Breath volume (TV) * frequency, and its unit is L / min
Panel 2: Heart rate over time
Heart rate is a number of beats in a minute, and its unit is beat / min
Panel 3: VO2 and VCO2 over time
VO2 and VCO2 are oxygen uptake and carbon dioxide exhalation, respectively, and their unit is L / min
Panel 4: Ventilation and VCO2 at each breath
Panel 5: VO2 and VCO2 at each breath
Panel 6: Ratios between ventilation and VO2 as well as VCO2 over time
Panel 7: Breath volume and ventilation at each breath
Panel 8: Respiratory gas exchange (RER) over time
RER is a ratio between VCO2 and VO2
Panel 9: PETO2 and PETCO2 over time
PETO2 and PETCO2 are partial pressure of oxygen and carbon dioxide, respectively, and their unit is mmHg
3, Find deflection point
Deflection points are eventually the points where VT1 and VT2 happened. VT1 stands for ventilation threshold 1. At this point, blood acidity is compensated by lactate metabolism and bicarbonate buffering system. Therefore, you can keep exercising at this pace for long time. VT2 stands for ventilation threshold 2, lactate threshold, or anaerobic threshold. At this point, the compensation is no longer in line with increase of blood acidity. Therefore, you cannot exercise for long time.
Let’s find a sign of VT1 first!
The sign of VT1 is the point where a ratio between ventilation and VO2 starts increasing, but a ratio between ventilation and VCO2 stays flat or decreases. This phenomenon happens because ventilation and carbon dioxide exhalation increase as intensity of exercise increases although oxygen uptake does not increase as much. As I mentioned above, the buffering system increases the CO2 production. The point is observable in panel 6 which is below …
Red circles are a candidate VT1 point. Then, we can check the points in panel 5 which is below …
A red circle is a point which is the second red circle in panel 6. Obviously, there is no time component, so you have to check the index of data and find corresponding data point in panel 5. I am explaining how to do that on my YouTube video (Its link is in the last section of this blog). As you can see on the panel 5, increment of VCO2 increases more than VO2 increment from the point at the red circle.
Let’s find VT2!
A sign of VT2 is the point where the ratio between ventilation and VCO2 starts increasing linearly with the ratio between ventilation and VO2. As intensity of exercise increases, ventilation further increases. However, VCO2 exhalation is no catching up with the pace although it is still increasing. As you may guess, the blue circles are the candidate point for VT2 on the panel 6.
We check the points on panel 4 and 5. The panel 4 is below …
The red circle is the second blue circle on panel 6. Again, there is no time point on this panel, so you have to take the index of data. Let’s see it on panel 5.
The black circle is the corresponding data point to the second blue point on panel 6. Usually, panel 4 is more obvious to find deflection point for VT2, but in this case, panel 5 shows more obvious deflection point.
4, Plot trend line
We find VT1 and VT2, so let’s draw a trend line !! The plot is below…
It is nothing special, but you can see a slope of the line gets sharper from the beginning of the exercise to the end of the exercise.
5, Find VO2max
Fortunately, there is VO2max data in my CPET data, so you just need to find its maximal value. However, just in case you have only VO2 data, the VO2max formula is below…
VO2max = max(VO2) * 1000 / Body Weight in kg
Since a unit of the VO2 is L / min, you have to convert it to ml / min. Then, you take its relative value which means dividing by your body weight.
There are ways to predict VO2 if you do not have VO2 data. One way is …
VO2max = (max(W)/65)*10.791+7
W is work load in Watt during exercise, and you take its maximal value. Another way is …
VO2max = 50.72 – (0.372*Age in year)
6, Find HRmax
It is just the maximal heart rate during exercise. You can also predict the maximal heart rate you would be able to reach during the maximal exercise test.
- Fox method: HRmax = 220 – Age in year
- Tanaka method: HRmax = 208 – (0.7*Age in year)
- Nikolaidis method: HRmax = 223 – (1.44*Age in year)
Also, by using VT1 and VT2 indices, you can find your heart rate at VT1 and VT2. The heart rate can be used to control your training. For example, if you want to conduct long slow distance training, you can keep your pace where your heart rate is around your VT1. If you want to train your aerobic capacity, you may train around your VT2 heart rate.
My YouTube video
I am explaining how to analyze CPET data on my YouTube video, so please check it out!!
MATLAB code and CPET data
Enjoy!!
I enjoy the knowledge on your web site. Thanks a ton. Jayne Jessee Osyth