7 Comparing the heart rates of animals and human beings

Is a person’s life expectancy greater or less than an animal’s life expectancy? In Figure 11 you can see that a human’s life expectancy is longer. This graph is a ‘logarithmic–linear’ scale, so you need to be careful when you read values from the scales. On the heart rate scale (the vertical one on the left), the values go up in tens from 20 to 50 and then in hundreds from 100 to 1000. This helps to fit the data on a more manageable graph. The life expectancy scale increases linearly, from 0 to 90 in equal increments of 10.

Figure 11 Heart rate (beats per minute, bpm) and life expectancy (years) of animals and humans.

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This image is a graph where the vertical axis is labelled with heart rate in beats per minute (bpm) on a logarithmic scale, starting at zero bpm running through values of 20bpm, 50 bpm, 100 bpm, 200 bpm, 500 bpm and 1,000 bpm. The horizontal axis is labelled with life expectancy in terms of years on a linear scale, starting at zero years running through values from 10 years to 90 years in units of 10 years. Various animals are labelled on this graph; starting from the top left with a mouse (500 bpm, less than 10 years) next to a hamster and rat with similar values; then a marmot and monkey (200 bpm, 20 years); then a cat and dog (100-200 bpm, 30 years); then a giraffe, tiger and ass (50-100 bpm, 30-40 years); then a horse, lion and elephant (30-50 bpm, 55-60 years); then a whale (20 bpm, 60 years); finally a human (100 bpm, 80 years). A line of negative gradient is drawn from the mouse to the whale indicating a correlation between the faster the bpm the shorter the life expectancy or conversely, the shorter the bpm, the longer the life expectancy.

Figure 11 Heart rate (beats per minute, bpm) and life expectancy (years) of animals and humans.

Human beings are incredibly adaptable. For example, free-divers can slow down their heart rates substantially and can dive to incredible depths (Figure 12). Every 10 metres down in the water adds another atmospheric pressure (about 100 000 newtons per square metre). So, the pressure at great depths quickly becomes very dangerous. This contrasts with the pressure when you are at an increased height. This pressure reduces, which you experience when your ears ‘pop’ and you need to swallow to equalise the pressure.

Figure 12 Free-divers in the Caribbean.

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This image is a colour photograph of two divers coming to the surface.

Figure 12 Free-divers in the Caribbean.

Everyone is aware of the dangers of heart attacks. You may have seen a defibrillator (Figure 13). This life-saving device can help to save human lives by stopping and then restarting a heart that is fibrillating or in cardiac arrest. There are portable versions, which can be used by paramedics, and community ones are also now available in public places such as shopping centres and airports.

You have seen how your heart rate can be compared with an astronaut’s; clearly your heart is a measure of your overall health. When placing astronauts into physically challenging situations, their hearts are working incredibly hard. Indeed many of us will experience heart racing situations; it’s reassuring to know that defibrillators are more available now in the event of an emergency!

Figure 13 A portable defibrillator used to treat heart attacks.

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This image is a colour photograph of a defibrillator.

Figure 13 A portable defibrillator used to treat heart attacks.

You will now move on to your next practical activity, growing mold on bread.