What are normal human physiology values?

• Blood pressure (BP): between 90/60 mmHg and 130/80 mmHg
• Pulse (heart) rate: 60 to 100 beats per minute
• Breathing (respiratory rate): 12 to 20 breaths per minute
• Temperature (core): average 37°C (36.5°C to 37.3°C)
• Blood pH (acid-base balance): average pH 7.40 (7.35 to 7.45)
• Glomerular filtration rate (GFR): 120 ml/min (70-120 ml/min; aged 18-24 years, non-diseased white males and females; see below)
• Total blood volume: average 5 L (4.5-5.7 L)
• Cardiac output: average 5 L/min (4-8 L/min): 1.5 L/min to liver/GI tract; 1.3L/min to kidneys (25%); 1L/min to brain).

In fact these biomedical variables are also not true (anything in medicine or science that is ‘too neat’ is rarely true). They are just currently accepted normal ranges, for most people, most of the time.

So where do these averages come from?

They are usually calculated by measuring the parameter in large numbers of (usually younger) people; then using 2 standard deviations from the mean, as the upper and lower limits of ‘normal’.

In other words, there will be plenty of normal well people with:

• A BP of 145/95
• A pulse rate of 40 bpm and
• A core temperature of 35.7 C.

And these people do not have a disease.

Normal (or Gaussian) distribution

This is because they are biomedical variables that follow a Normal (or Gaussian) distribution, like weight or height – as shown in the following graph. And people who are 154cm and 196 cm (3 SDs from the mean) are not ill. That graph would be the same shape (with the same inferences) for blood pressure, heart or respiratory rate, temperature and pH.

Graph of average human height

Effects of age and gender

Most of the variables above are affected by age and gender (and usually ethnicity too). A good example as GFR as shown by the following graphs (Wetzels, 2007)

Note 1. Whether age/gender really affects GFR is another issue. The patterns above (and ‘decline’ over time) may reflect muscle mass and other factors
Note 2. The CKD/GFR classification states that GFR is 90-120 ml/min. This is clearly far to neat and made up. But it is approximately correct according to the study by Wetzels above. 70-120 ml/min (for a younger person) and 60-90 ml/min (for mid-life) and 40-90 ml/min (for an older person) would be better normal ranges according to that study.

Conclusion

There is no such thing as normal human physiology values. There is an average human being with average physiological variables at an average age, all of which are average ranges. But even that has little meaning.

Other resource

Review article: Kanap, 2020