MadSci Network: Anatomy

Re: Do different people's chests expand by the same amount during inhalation?

Date: Mon Jun 5 10:00:11 2006
Posted By: Keith Anderson, Staff, Vascular Research, Brigham & Womens Hospital
Area of science: Anatomy
ID: 1149043672.An

Q: Do different people’s chests expand by the same amount during inhalation?

The answer to your question is not actually a straightforward yes or no, hopefully I can explain below.

During normal or resting respiration, only a small amount of the lung’s capacity to hold air is used thus allowing ample capacity for when the body needs more air for increased oxygen uptake for energy, like during exercise. (It is interesting to note that the lungs are never empty, and even if removed and collapsed, enough air is trapped in the alveoli to allow the organ to float in water.) This normal amount of air that we breathe is called the tidal volume of air and is usually about 450-500 mL for a healthy adult. If one were to blow out all the air that they possibly can expire (known as vital capacity), that is about 4-5 liters. Total lung volume is usually about 6 liters. When one speaks, sneezes, laughs, exercises we move more air than the tidal volume.

A good summary of respiratory volumes can be found at or in any good biology/physiology textbook.

More related to your question, total lung capacity depends on a person’s age, weight, smoking history, and sex; these all vary slightly from person to person in a “normal, healthy” adult but do not vary wildly. For example, taller people tend to have larger lung capacity, males tend to have 10-20% greater capacity than females. In fact, there are a set of equations that one can use to approximate the capacity of a person’s lungs based on the surface area of that person’s body. Also, regular strenuous exercise does not dramatically increase one’s total lung capacity but simply seems to allow the process of breathing to occur more easily and the process of oxygen transfer to be more efficient. During inspiration, air moves into the lungs because of the contraction of the diaphragm at the base of the rib cage combined with the contraction of the intercostal muscles between the ribs. This causes the ribs to move up and out, thereby increasing chest volume and decreasing pressure causing air to move into the lungs.

An interesting paper from the Journal of Applied Physiology gets at your question even more directly. [1]
This work shows five different subjects seated and the motion of their chest cavity and abdominal cavity measured with sensors. What they show is that the chest cavity moves in three directions during tidal breathing and there is variation from subject to subject. Embedded in the data one can see that the amount of movement in any one direction does vary from person to person. However, the differences are on the order of millimeters, but can be 25% or more of the total distance moved.

Another very early paper from 1954 in the Journal of Physiology [2] tool=pubmed&pubmedid=13175123 shows that chest circumference expansion in all of the ten subjects studied is 1.2 cm when standing and 0.7 cm supine, however the standard deviation are 0.4 and 0.2cm respectively.

So it seems that in absolute numbers there is not much difference in chest expansion from person to person at rest and in fact is a fairly small measurement; however, when the variation is compared as a percentage of the total measured expansion, then it is actually a mathematically large variation. (To lend some perspective, from the 1954 study mentioned above, the circumference of the thoracic cavity increases 5-11 cm during deep respiration and shows that movement of the diaphragm is very important.)

Hope this answers your question.

Keith Anderson
Brigham & Women’s Hospital, Boston MA USA


[1] A. De Groote, M. Wantier, G. Cheron, M. Estenne, and M. Paiva. Chest wall motion during tidal breathing J Appl Physiol 83: 1531-1537, 199

[2] O. L. Wade Movements of the thoracic cage and diaphragm in respiration J Physiol. 1954 May 28; 124(2): 193–212.

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