Respiratory excursion reflects the maximum movement capacity of the chest wall during the breathing cycle. It is defined as the difference in chest circumference between maximal inhalation and complete, maximal exhalation. Evaluating this range provides a non-invasive indicator of overall respiratory health and the elasticity of the lungs and thoracic cage. A reduced excursion can signal a problem with the lungs, the muscles that drive breathing, or the flexibility of the bony structures enclosing the chest.
The Muscular Mechanics of Excursion
Respiratory excursion is generated by a coordinated sequence of muscle contractions and structural changes within the thoracic cavity. The primary muscle of quiet inspiration is the diaphragm, a dome-shaped sheet of muscle that separates the chest from the abdomen. When the diaphragm contracts, it flattens and moves downward, which increases the vertical dimension of the chest cavity and draws air into the lungs.
Simultaneously, the external intercostal muscles located between the ribs contract to lift the rib cage upward and outward. This action employs two distinct mechanical movements: the “pump handle” action of the upper ribs, which increases the anterior-posterior diameter of the chest, and the “bucket handle” action of the lower ribs, which increases the transverse diameter. These combined movements maximize the expansion of the chest wall during a forced breath.
Exhalation during a resting breath is mostly a passive process, relying on the elastic recoil of the lungs and chest wall as the inspiratory muscles relax. When a person forces a maximal exhalation, the abdominal muscles and the internal intercostal muscles become active. The abdominal muscles contract to push the diaphragm upward, while the internal intercostals pull the rib cage down and inward, forcefully decreasing the volume of the thoracic cavity.
Clinical Assessment and Normal Findings
Assessing respiratory excursion begins with visual inspection and palpation to check for symmetry and overall extent of movement. The examiner places their hands on the posterior chest wall, with their thumbs positioned at the midline over the tenth rib, to feel the chest expansion during a deep breath. Observing whether the thumbs separate equally provides an immediate indication of bilateral symmetry in lung and chest wall movement.
The most common method for quantifying excursion is a circumferential measurement using a flexible tape measure. This technique, often called thoracic expansion, measures the difference between the chest circumference at the end of maximal expiration and the circumference at the end of maximal inspiration. The measurement is typically taken at the level of the xiphoid process or the fourth intercostal space to capture the greatest range of movement.
For a healthy adult, a normal thoracic excursion measurement generally falls within the range of 5 to 10 centimeters, though values vary based on age, fitness level, and measurement location. A finding below this range suggests a restriction in movement. Conversely, an asymmetrical result points to a problem specific to one side of the chest.
Causes of Restricted or Unequal Movement
A reduced respiratory excursion restricted across both sides of the chest often suggests a global limitation on lung or chest wall expansion. Conditions like pulmonary fibrosis cause scarring within the lung tissue, making the lungs stiff and unable to fully inflate. Chronic obstructive pulmonary disease (COPD) also reduces chest wall mobility due to hyperinflation, which places the diaphragm in a flattened, less efficient position.
External factors can also cause bilateral restriction, such as severe obesity, where excess weight on the chest and abdomen physically impedes the downward movement of the diaphragm. Certain neuromuscular diseases, including amyotrophic lateral sclerosis (ALS) or muscular dystrophy, lead to generalized weakness in the diaphragm and intercostal muscles, directly reducing the force available for maximal inhalation. Chest wall deformities like severe kyphoscoliosis also mechanically restrict the space available for lung expansion.
An unequal or unilateral reduction in excursion indicates a localized problem affecting only one side of the thoracic cavity. A pneumothorax prevents the affected lung from expanding, resulting in minimal movement on that side. A pleural effusion, the accumulation of fluid surrounding the lung, physically compresses the lung and restricts its ability to inflate. Pain, such as that caused by fractured ribs or lobar pneumonia, can also lead to a unilateral reduction because the patient involuntarily guards the injured side to avoid discomfort.