Posted in Psychology & Medicine

Heartbeat Hypothesis

When you compare the lifespans of mammals, it is common to see that larger animals live longer than smaller animals. Another observation is that smaller mammals almost always have a much higher basal heart rate. For example, a mouse has a basal heart rate of about 600 beats per minute (bpm), but only lives 3 years on average. An elephant has a basal heart rate of 30bpm, but lives up to 60 years. If you do the maths, it turns out that the total heartbeats per lifespan is surprisingly similar between the two species (0.94 billion beats). It has been noted that amongst mammals, there is a clear inverse correlation between heart rate and lifespan.

This observation led to the popularisation of a factoid that the heart can only beat a limited number of time before it eventually fails.

Unfortunately, there has been very limited evidence to support this theory. It is medically true that a heart under more strain for a long period of time, such as with high blood pressure, has a tendency to develop more diseases such as cardiomyopathy and heart failure. However, there are too many other variables to consider. For example, exercise temporarily raises your heart rate but improves your overall cardiovascular health and lowers your basal heart rate.

It is much more likely that death from aging is related to the basal metabolic rate. Metabolism produces free radicals, which are elements with free electrons that can damage cells. Therefore, the higher the metabolic rate (such as in mice), the faster the damage accumulates and results in death.

That being said, consider the other implication of the so-called heartbeat hypothesis. Our hearts beat faster in response to many stimuli: exercise, excitement, fear, anxiety, fun and love. If the hypothesis is true, that would mean that intense emotions could make our hearts tire out faster and hasten our inevitable demise.

Could falling in love be detrimental to our physical health? Thankfully, this has never been shown to be true, with many studies showing that happily married couples tend to outlive single people.

Even if it were true, would you give up on the idea of love to live a few more years? What kind of life would be worth living without any highs or lows? Perhaps when we fall in love, experience heartache or become overwhelmed with happiness, we are making the voluntary choice of quality, not quantity, of life.

Posted in Psychology & Medicine

Viscera: Heart

(Learn more about the organs of the human bodies in other posts in the Viscera series here:

Out of the numerous organs found in the human body, the heart is perhaps the most well-known. This is probably because since the dawn of time, man has put his hand on his chest and felt the rhythmic pounding of his heart – a reminder that he is alive. The function of the heart is to pump oxygenated blood from the lungs to the rest of the body via the circuit of blood vessels (vascular system).

The heart relies on electricity to pump blood in a rhythmic, autonomous way. Because of this property, a heart will beat on its own even if you took it out of the human body. Every muscle in the human body requires an electrical impulse for it to contract. This is also the case in the heart, but unlike the skeletal muscle in other parts of the body which receive their impulses from the brain and spinal cord, the heart has its own source of electricity.

The heart has a small group of pacemaker cells in the right atrium called the sinoatrial node, which always fires electrical impulses at a set rate and rhythm (sinus rhythm). The SA node will do this without any instruction from the brain. The impulse from the SA node spreads throughout the atria of the heart, causing the atrial muscles to contract simultaneously to squeeze blood into the ventricles. The impulses then reach the atrioventricular node, which filters the signals and sends a stream of electricity through a wiring system known as the Purkinje fibres. These fibres act like a high-speed internet cables running down the centre of the heart, sending rapid signals through out the ventricles to induce a strong, cooridnated contraction in both ventricles. This causes blood to be forcefully squeezed out through the two outlet vessels of the heart: the pulmonary artery (to the lungs) and the aorta (to the rest of the body).


Although the SA node is completely autonomous, it can be controlled using hormones, nerve signals and medications. For example, adrenaline will speed up the rate the heart beats at while massaging the carotid arteries in the neck will slow the heart down.

One thing people wonder about is what the doctors listen to when they put a stethoscope to a patient’s chest. Everyone knows the heart makes a rhythmic “lub dub” sound as it beats away, but what information could that give away? A doctor can gain much information about the heart from a cardiac examination by taking the pulse and blood pressure, but listening to the heart (auscultation) may reveal a medical sign known as a murmur. A murmur is any added sound other than the normal “lub dub” sound of the heart. For example, a heart with aortic stenosis may give the sound “shhhhhhh” as if it was giving off static. This sound is produced when blood flow in the heart is turbulent and not smooth. This may be for a number of reasons but the most common reason is because the valves of the heart are not functioning properly. For example, the valve between the left atrium and left ventricle may be leaky (mitral regurgitation) or the valve at the start of the aorta may be stiff and narrowed (aortic stenosis).

By carefully listening to the sound the heart makes, an experienced doctor may pick up on such structural abnormalities even without the use of fancy medical imaging technologies.

Posted in Psychology & Medicine


Blood, which supplies all the cells in the human body with nutrients and oxygen, flows through the vessels due to the pumping of the heart. Thus, blood flow directly transmits the force generated by every heartbeat. As the blood ejected by the heart causes the arteries to “pulse” by stretching and relaxing. As some pulses can be felt over the skin, they are very useful in patient examinations, especially a clinical exam of the cardiovascular system. Although people commonly know how to take a pulse from the wrist or neck, there are many more places a pulse can be taken from.

  • Radial pulse: Taken from the inside of the wrist on the side of the thumb.
  • Brachial pulse: Taken from the inside of the elbow.
  • Carotid pulse: Taken from where the neck meets the jawline, or 2~3cm either side of the Adam’s apple to be precise.
  • Apex beat: This measures the heartbeats directly, taken on the left chest between the 4th and 6th ribs (around the left nipple).
  • Abdominal pulse: Taken from above the belly button of a lying patient, may be able to see the pulse.
  • Femoral pulse: Taken from the middle of the groin. 
  • Popliteal pulse: Taken from the inside of the knee.
  • Posterior tibial pulse: Taken from the inside of the ankle behind the bone.
  • Dorsalis pedis pulse: Taken from the back (upper side) of the foot along the middle.

When taking a pulse, you use your second and third fingers (and the fourth if you want) and press lightly on the pulse point. If you press too hard, you may stop the blood flow and obliterate the pulse. As a pulse is measured per-minute, it is often taken for 10 or 15 seconds and multiplied by 6 or 4 respectively. Also, it should be noted whether the pulse has a regular rhythm, and if it is irregular, whether it is regularly irregular or irregularly irregular. If the pulse is over 100 beats per minute, it is called tachycardia, while less than 60 beats per minute is referred to as bradycardia. If it is irregular, it is called an arrhythmia.

An experienced doctor can diagnose different conditions such as an aortic stenosis or atrial fibrillation just from taking the pulse of the patient. Taking a pulse is also a crucial diagnostic tool in traditional Korean and Chinese medicine.


Posted in Psychology & Medicine

Love And Heartbeats

A thumping heart is often quoted as the first sign of love – a way of your body telling you that the girl or boy in front of you is what you desire.
But does love come first or does your heartbeat come first?

Although most people believe that their heart is beating faster because they’re in love, science proves that it is in fact the opposite.
An experiment was designed where male subjects were asked to answer a questionnaire given out by an attractive woman. One group had to cross a very long suspension bridge first, the control group had to cross the same distance on flat, solid ground. It was found that men from the first group were more likely to complete the questionnaire, give answers that were more romantic and sexual, and even call the survey girl afterwards.

Similarly, a group of men were shown four women while being connected to headphones that played back their own heart sounds. They were then asked to rate which girl was the most attractive.
After the experiment, it was found that the third girl received a landslide win, despite the different tastes of each man in the group. When asked, the subjects all replied that they heard their heart speeding up, thus believed that they found her the most attractive.
The twist was, when the third girl was shown, the audio was changed from the subject’s heartbeat to a pre-recorded heartbeat that beat faster than normal. Therefore, the men were fooled into thinking that the girl was more attractive by “increasing” their heart rate. This phenomenon was found in women also.

The answer to the question is that dopamine and serotonin, neurotransmitters secreted when a person is in love, also has the effect of increasing one’s heart rate. The brain therefore can misinterpret an increased heart rate as the effect of love through false association.
This effect is quite well known in dating tips as people are encouraged to go to places that invoke fear or excitement, such as an amusement park, horror movie, or high place to gain the best response from the opposite sex.
Ergo, science does play a role in love and just like anything else, it can be easily manipulated.