Bohr Effect

Knol Authors: Jennifer and Russell Stark

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Jennifer and Russell Stark: authors of the book The Carbon Dioxide Syndrome
The Bohr effect means that in spite of the oxygen content in the blood being normal, when more air is breathed than is required, tissue cells are starved of oxygen.

Bohr Effect

Content Authors: Jennifer and Russell Stark

Introduction

It is common knowledge that eating too much food does not mean good nutrition and this principle applies to breathing. Breathing too much air does not mean good breathing, nor does it even mean that extra oxygen is delivered to the tissues, because the amount of oxygen carried by the blood largely depends on haemoglobin content and the availability of oxygen rather than the depth of breathing. Providing the person is not anaemic and has healthy red blood cells there is no problem with haemoglobin, and unless the lungs are damaged, oxygen is readily available to the blood. Breathing calmly almost completely (98%) fills each haemoglobin cell with oxygen, so in theory it would only be possible to make a 2% improvement. However, since haemoglobin is constantly releasing oxygen, in reality it cannot be 100% saturated. Therefore breathing deeper is going to make virtually no improvement to the collection of oxygen by the haemoglobin.

Even when oxygen pressure dips from the average 104 mm Hg in the lungs to 60 mm Hg, haemoglobin is still 90% saturated with oxygen (Guyton 1982), so getting oxygen into the bloodstream is not usually the problem. Getting haemoglobin to release it is more of a challenge, because once haemoglobin and oxygen are joined, they form a tight bond and conditions need to be ideal in order for them to separate. This can be compared to four postage stamps joined together. It is always hard to tear off the first stamp, but once it has been removed, the other stamps come apart easily.

Figure 2:15. Haemoglobin and oxygen cling together like postage stamps.

In the early 20th century, Danish scientist Christian Bohr

In the early 20th century, Danish scientist Christian Bohr discovered that carbon dioxide pressure affects the ability of haemoglobin to carry oxygen (Lumb 2000). This is called the ‘Bohr effect’. Low pressure of carbon dioxide means that oxygen is retained by haemoglobin and high pressure means that more oxygen is released to tissue cells. Temperature and low oxygen pressure in tissue cells also drive oxygen off haemoglobin. The body is like a well-balanced machine – when it is working hard and the tissue cells need extra oxygen, it is simultaneously making an abundance of carbon dioxide and heat, thus ensuring a steady flow of oxygen to the tissues.

A problem can occur (retaining oxygen instead of releasing it)

A problem can occur however, when breathing is increased to the level where too much carbon dioxide is exhaled. This compels blood to become more alkaline than normal (Respiratory Alkalosis) and haemoglobin becomes ‘stickier’, retaining oxygen instead of releasing it. This creates a vicious circle, because less oxygen reaching tissues means that less carbon dioxide is being produced.

Figure 2:16 The production of carbon dioxide and the release of oxygen are dependent on each other.

The graph below of the Bohr effect shows the connection between oxygen release and carbon dioxide pressure.

Figure 2:17 The Bohr effect and its consequence on oxygen tension. When blood is less alkaline, more oxygen is released from haemoglobin and received by the tissues.

The Reality of the Bohr Effect

On a basic and practical level the Bohr effect means that in spite of oxygen content in the blood being normal, when more air is breathed than is required tissue cells are starved of oxygen.

Breathing quietly and steadily actually means better oxygenation because adequate supplies of both oxygen and carbon dioxide are maintained. This scientific fact is totally the opposite from the way the person feels when short of breath.

Figure 2:18 When the person breathes calmly sufficient oxygen both reaches the lungs and is released to tissues. Not breathing enough or breathing too much will cause a problem.

It is accepted that when smoking a cigarette less oxygen is available to tissues and this is one of the reasons that smokers generally have older looking skin than nonsmokers. Because of the Bohr effect, breathing more air than is required for metabolism is also going to mean that less oxygen is released to tissues and this might be done for several hours a day, if not continuously. So for a lengthy time each day, just like a cigarette smoker, slightly less oxygen will be reaching tissues. When tissues do not receive sufficient oxygen, lactic acid is produced by and accumulates in the tissue (Fried 1993), which makes them ache and tire quickly. It also makes the whole body feel tired and lacking in energy. One more factor to consider is that everyone has an organ or tissues that are genetically weaker than they should be and these are likely to show the first sign of wear and tear, or to suffer the most from a lack of oxygen. This may help to explain why there is such a wide range of symptoms associated with hyperventilation .

References

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Fried R. The Psychology and Physiology of Breathing. Plenum Press. New York 1993. p104 Grippi M. Pulmonary Pathophysiology. J.B. Lippincott Company. Philadelphia. 1995. p287

Guyton. AC. Human Physiology and Mechanisms of Disease. W.B. Saunders Co. Philadelphia. 1982. pp279-280, 285, 300, 306, 320-323

Henderson. Y. Cyclopedia of Medicine. 1940

Hickling KG, Walsh J, Henderson S, Jackson R. Low mortality rate in adult respiratory distress syndrome using low-volume, pressure-limited ventilation with permissive hypercapnia: a prospective study. Critical Care Medicine. 1994. 22. pp1568-1578

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Laffey JG, Kavanagh BP. Carbon dioxide and the critically ill – too little of a good thing? Lancet. 1999. 354(9186). pp1283-1286

Lum LC. Respiratory Alkalosis and Hypocarbia. The roles of carbon dioxide in the body economy. Chest, Heart & Stroke. Winter 1978/79. 3(4). pp31-34

Lumb AB. Nunn’s Applied Respiratory Physiology. Reed. London. 2000. pp 3-12, 237, 267, 321, 362

Naifeh K. Behavioural and Psychological Approaches to Breathing Disorders. Ed. B.H. Timmons & R Ley. Plenum. New York. 1994. p17

Piper AJ, Parker S, Torzillo PJ et al. Nocturnal nasal IPPV stabilizes patients with CF and hypercapnic respiratory failure. Chest 1992. 102. pp846-850

Tortora GJ, Anagnostakos NP. Principles of Anatomy and Physiology, Harper & Row, New York. 1984. pp562 563, 564, 570, 587, 693

Thank you to Jennifer and Russell Stark for giving permmision to use this excerpt from their book:

The Carbon Dioxide Syndrome .

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