The Reid Index is a mathematical relationship that exists in a human bronchus section observed under the

microscope A microscope () is a laboratory instrument used to examine objects that are too small to be seen by the naked eye. Microscopy is the science of investigating small objects and structures using a microscope. Microscopic means being invisibl ...

. It is defined as ratio between the thickness of the submucosal

mucus Mucus ( ) is a slippery aqueous secretion produced by, and covering, mucous membranes. It is typically produced from cells found in mucous glands, although it may also originate from mixed glands, which contain both serous and mucous cells. It is ...

secreting

gland In animals, a gland is a group of cells in an animal's body that synthesizes substances (such as hormones) for release into the bloodstream (endocrine gland) or into cavities inside the body or its outer surface (exocrine gland). Structure De ...

s and the thickness between the

epithelium Epithelium or epithelial tissue is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. It is a thin, continuous, protective layer of compactly packed cells with a little intercellul ...

and

cartilage Cartilage is a resilient and smooth type of connective tissue. In tetrapods, it covers and protects the ends of long bones at the joints as articular cartilage, and is a structural component of many body parts including the rib cage, the neck an ...

that covers the bronchi. The Reid index is not of diagnostic use ''in vivo'' since it requires a dissection of the airway tube, but it has value in ''post mortem'' evaluations and for research. The Reid Index was developed in the late 1950s from the work of Dr. Lynne McArthur Reid, M.D. who first described the relationship between hypertrophic bronchial mucous glands and the resultant narrowing of the airways seen in chronic bronchitis. In 1967, Dr. Reid became the first woman to achieve the rank of professor of experimental pathology in England and later became the first dean of the Cardiothoracic Institute at London University.

Calculation

\ RI = \frac

where: : RI is the Reid Index :''wall'' is the thickness of the airway wall between the

and the

perichondrium The perichondrium (from Greek el, περί, peri, around, label=none and el, χόνδρος, chondros, cartilage, label=none) is a layer of dense irregular connective tissue that surrounds the cartilage of developing bone. It consists of two sep ...

:''gland'' is the thickness of the mucus-producing gland at the location of inspection.

Interpretation

A normal Reid Index should be smaller than 0.4, the thickness of the wall is always more than double the thickness of the glands it contains. Chronic smoking causes submucosal gland hypertrophy and

hyperplasia Hyperplasia (from ancient Greek ὑπέρ ''huper'' 'over' + πλάσις ''plasis'' 'formation'), or hypergenesis, is an enlargement of an organ or tissue caused by an increase in the amount of organic tissue that results from cell proliferati ...

, leading to a Reid Index of >0.5 indicating chronic bronchitis.School of Medicine, Tulane University
/ref>

References

{{Eponymous medical signs for respiratory system Respiratory system