Thoracic Index

Definition Ratio of the anteroposterior diameter of the chest to the lateral diameter (chest width) multiplied by 100.

Landmarks Anteroposterior diameter is measured (Fig. 9.8a) from the sternum, at the level of the nipples, to the vertebrae, at the same level, while at rest. Lateral diameter is measured between the midaxillary lines at the level of the nipples (Fig. 9.8b)

Instruments Calipers.

Position The patient should be standing with the arms hanging loosely at the sides; the measurement is made during mid-expiration.

Alternative If calipers are not available, the patient can be placed against a wall, facing sideways and forward for each measurement, respectively, while the boundaries of the thoracic cage, at the nipple level, are marked on the wall. The marks are then measured with a measuring tape.

Remarks Timing of respiration is important for accuracy of this measurement. Mid-expiration is the position of rest (prior to forced expiration). Ideally each measurement should be obtained twice. Thoracic diameters anteroposterior and lateral are shown in Fig 9.9, and values for the thoracic index in Fig. 9.10.

Figure 9.8 Measuring anteroposterior (a) and lateral (b) chest diameters.

Figure 9.8 Measuring anteroposterior (a) and lateral (b) chest diameters.

Lateral Diameter Chest

Pitfalls Variation in the body chest cage will distort the thoracic index. Pectus carinatum, or the barrel chest of an asthmatic, will lead to an increased value. Pectus excavatum will reduce the value. Hypotonia will also produce a reduced anteroposterior diameter.

In women the position of the nipples is extremely variable. This is less important in a ratio than in an absolute measurement. The fourth intercostal space can be used as an alternative landmark, or one can measure 10 cm down from the clavicles.

Figure 9.9 Thoracic diameters, both sexes, birth to 16 years. From Pryor (1966), by permission.

Figure 9.9 Thoracic diameters, both sexes, birth to 16 years. From Pryor (1966), by permission.

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Responses

  • Corey
    How to measure Barrel chest?
    3 years ago
  • MICHAEL
    How to meadure lateral diameter pf chest?
    2 years ago
  • manuela
    How to measure lateral diameter of chest?
    1 year ago

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