‘Transport in Humans’ is a chapter most students enjoy learning. Learning about how our own system works seems to ignite an interest in many. However, despite their interest, many students are still stumped upon seeing a question with a graph as shown below….

Compared to other questions from the chapter, heart pressure-time graph questions are ‘complicated’, ‘illogical’ and even ‘unsolvable’. I’ve even encountered some students who give up solving the question upon seeing the graph.

Are you one of them?

Between points W and X, are the following valves open or closed?

If you are still struggling to solve questions like this, do not fret! Today, you will learn to overcome the mystery of the pressure-time graph with 4 simple steps! This 4-step strategy can be used to solve 90% of heart pressure-time graph questions. The only thing you will need prior to this is basic knowledge of the heart structure.

Here are the four steps to master such questions:

1)      Draw line

2)      Compare pressure

3)      Determine blood flow direction

4)      Determine if valve closes or opens

Once you are ready to learn how to use the four steps, take out a trusty ruler… And here we go!

1)      Use ruler to draw a vertical line down the area you want to measure, as shown below.

2)      Use the line to help you compare the pressure of atrium vs ventricle and the pressure of aorta vs ventricle

From the graph, we can see that between W and X pressure of atrium is lower than pressure of ventricle while pressure of aorta is higher than the pressure of ventricle.

3)      Determine blood flow.

Blood always flows from an area of higher pressure to an area of lower pressure. Assuming that all valves are open, blood should flow from the ventricle to atrium (which is abnormal) and from the aorta to ventricle (which is also abnormal).

4)      Determine if valve opens or closes

Now here’s the final part. Normally, blood ALWAYS flows from atrium to ventricle and from ventricle to aorta. But as we see in step 3, this is not the case. Therefore, the atrio-ventricular valve must close to prevent backflow of blood from ventricle to atrium and the semilunar valve must close to prevent backflow of blood from aorta to ventricle.

From these four steps, we can see that the answer to the question is… A! Easy!

This strategy can also be used to answer structured questions. A typical answer will go something like this, “As the pressure in the left ventricle is higher than the pressure in the left atrium, the biscuspid valve must close in order to prevent backflow of blood from the left ventricle to the left atrium.” The keywords underlined can be found using the four steps shown. Simple!

So now you’ve learnt to decipher the mystery of the heart pressure-time graph, stay tuned for more Biology tips and strategies coming your way!