Hardworking Hearts

2 MIN READ TAGS  ScatterPloteCharts

The Reddit Dataviz Data Battle for August 2019 presented a small but interesting dataset comparing the heart rates, mass, and longevity of select animals.

In this data, resting heart rate is inversely related to mass or body size. You can explore the range of heart rates from 20 to 450 beats per minute (BPM) using the interactive legend in the below viz.

Given the longevity values in the data, the number of heart beats over the animals' lifetimes can be estimated - humans come out on top closely followed by chicken (the only bird among the mammals in the dataset).

Creating this simple viz to emphasize the relationship between resting heart rate and lifespan turned out to be a learning experience in more ways than one. Check out the Heart Project at the Public Science Lab to explore this fascinating field further and become a citizen scientist as well, if so inclined!

The science seems to indicate that most mammals have a lifespan of around a billion heartbeats. So the faster your heart beats, the sooner you will hit the 1 billion mark and your expiry date. Thus, the hamster, with a heart rate of 450 beats per minute, races to the end of its life in 3 years. The shrew’s tiny heart works at double this rate, giving it only 14 months of life. At the other end of the spectrum, a whale’s heart manages only about 20 beats in a minute or 0.8 billion beats over its lifetime of ~80 years. At 60 beats per minute, we humans are a lot faster and in fact lead the race, achieving about 2.2 billion heartbeats over a similar lifespan. Given that we are constantly searching for ways to prolong our lives, perhaps we need to consider slowing down, literally? On that note, studies do link heart rate and lifespan and overall heart health.

The chicken was the odd man - or bird - out in the otherwise mammalian dataset and it managed to come in a close second in the hardworking hearts series: 2.17 billion heartbeats over its 15 years lifespan. 20 bpm increase in heart rate associated with 30-50% increase in mortality.

Calculating the lifetime heartbeats (Y-axis), rather than plotting the longevity data directly, best highlighted whose heart works the hardest over a lifetime. The viz uses the echarts library to animate the heart icons for some fun, but it would have been a lot cooler to have the icons animated proportional to the actual heart rate. A couple of other entries in the contest did manage this using React+d3.js and p5.js so thanks to them for the useful learning!

The other fact that showed up from the data was the inverse relationship between the resting heart rate and mass or body size - the smaller the animal, the higher the rate and lesser the lifespan (compare the hamster’s 60g and the whale’s 12 * 10^7 g).

This extreme difference prompted the choice of using the logarithmic scale to depict mass on the X-axis, resulting in a much better spread of the data.

Generally, heart rates are associated with the body’s metabolic or energy expenditure rate by governing oxygen consumption.


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