The thoracic index, a measurement used in the healthcare field to assess lung function, is spelled /θəˈræsɪk ˈɪndeks/. The initial sound /θ/ is a voiceless dental fricative, followed by the unstressed syllable /ə/ with a schwa vowel. The second syllable contains the stressed vowel /æ/ followed by the voiceless alveolar fricative /s/. The final two syllables contain the unstressed vowels /ɪ/ and /ɛ/ respectively, followed by the voiceless fricative /ks/ spelled as "x". Together, these sounds create the spelling of "thoracic index".
The thoracic index is a term used in anatomy and anthropometry to measure and describe the shape and proportions of the human thorax, specifically in relation to the ribcage and the spine. It is defined as the ratio between the transverse diameter and the anteroposterior diameter of the thorax, usually expressed as a percentage.
To calculate the thoracic index, the transverse diameter (the widest distance between the lateral edges of the ribcage) is divided by the anteroposterior diameter (the distance between the anterior surface of the sternum and the posterior surface of the spine) and then multiplied by 100. The resulting value indicates the shape and width of the thorax.
A lower thoracic index signifies a more cylindrical or "barrel-shaped" thorax, typically seen in individuals with certain medical conditions like emphysema or obesity. Conversely, a higher thoracic index indicates a narrower and elongated thorax, often observed in individuals with a slim build or marfanoid habitus.
The thoracic index is significant in anthropological studies as it relates to variation in human body types, genetics, and population groups. Additionally, it may have clinical implications when evaluating patients for certain respiratory conditions and thoracic anomalies. However, it is essential to interpret the thoracic index in conjunction with other physical parameters to obtain a comprehensive understanding of an individual's thoracic structure.
The ratio of the anteroposterior to the transverse diameter of the thorax.
A practical medical dictionary. By Stedman, Thomas Lathrop. Published 1920.
The word "thoracic index" combines two key terms: "thoracic" and "index".
The term "thoracic" refers to the thorax, which is the region of the body between the neck and the abdomen, including the chest cavity. It is derived from the Latin word "thorax", which means "chest" or "breastplate".
On the other hand, the term "index" is derived from the Latin word "index", which means "pointer", "indicator", or "list". In this context, it refers to a measurement or ratio used as an indicator or reference.
Therefore, the etymology of "thoracic index" can be understood as a reference to a measurement or ratio related to the thorax or chest cavity.