What factors can affect pulse and respiratory rates?

Being able to take an accurate pulse and respiratory rate is a core skill for first aiders. There are a number of factors which can affect pulse and respiratory rates, we’ll take a look at some of these in this blog post.

Pulse rate

Radial PulseWhen the heart contracts and pumps blood round the body, the vessels the blood runs through (the arteries) expand as the wave of blood passes.

We can feel this ‘pulse’ where the arteries pass over a solid structure like bone – the wrist is a good example. The pulse – its rate (the number of times per minute we can feel the pulse), its strength (whether it’s full and ‘bounding’ or weak and ‘thready’) and its rhythm (regular or irregular) – can tell us a lot about a casualty.

The pulse rate can be affected by:

  • Age – young children commonly have a higher pulse rate, in the elderly it may be slower.
  • Exercise – taking part in exercise will raise the pulse rate. Trained athletes may have a slower ‘resting heart rate’.
  • Disease – illness places pressure on the body, leading to an increased heart rate
  • Drugs – depending on the drug, it can speed up or slow down the heart rate
  • Body Temperature – cold will initially raise the pulse rate, before slowing dramatically. Fever (pyrexia) will cause an increase in pulse rate.
  • Posture – a patient lying flat will have a slower heart rate than when sat or stood.
  • Stress – stress increases the heart rate due to adrenaline/epinephrine release.

Respiratory rate

The rate and character of the respirations gives us important insights into people’s general health status. In addition, breathlessness is a very distressing symptom for many people, and it’s important that to identify problems early and deal with them.

A number of factors can influence the respiration rate, such as:

  • Age – younger children generally have higher oxygen demands and therefore breath faster
  • Pain – pain will cause an increase in respiration rate
  • Emotion – emotion will cause an increase in respiration rate
  • Resistance from air passages – increased resistance (e.g. in asthma) prevents as much air entering the lungs during each cycle. The demand for oxygen will then increase, increasing the respiration rate.
  • Fever – fever increases the body’s demand for oxygen, increasing the respiration rate
  • Elasticity of the lungs – the less elastic the lungs, the less air can enter the lungs each cycle, increasing the respiration rate. Chemical changes – chemical changes in the body, caused by hypoxia, metabolic disorders or medications / drugs, can cause the respiration rate to increase or decrease, depending on the stimulus

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