Respiratory excursion refers to the total range of movement of the chest wall during the breathing cycle. It quantifies how much the lungs can fill with and expel air, providing insight into overall respiratory function. A greater excursion indicates a larger change in lung volume with each breath, contributing to efficient air exchange.
How the Lungs and Diaphragm Move
Quiet breathing involves a coordinated effort of several muscles to facilitate air movement. The primary muscle involved in inspiration is the diaphragm, a dome-shaped muscle located at the base of the lungs. When the diaphragm contracts, it flattens and moves downward into the abdominal cavity, increasing the vertical dimension of the thoracic cavity.
Simultaneously, the external intercostal muscles, located between the ribs, contract. This action pulls the ribs upward and outward, expanding the rib cage and increasing the chest cavity’s front-to-back and side-to-side dimensions. These combined movements create a negative pressure within the thoracic cavity, drawing air into the lungs.
During quiet exhalation, these muscles relax. The diaphragm moves upward, and the rib cage returns to its resting position due to the natural elasticity of the lung tissue and chest wall. This passive recoil reduces the volume of the thoracic cavity, increasing the pressure inside the lungs and passively expelling air.
Measuring Respiratory Excursion
Respiratory excursion can be assessed using simple, non-invasive methods. A common approach involves using a tape measure to quantify the change in chest circumference. This measurement is performed at two points: at the xiphoid process (bottom tip of the sternum) and at the axillary line (armpit level).
To measure, the patient exhales fully, and the chest circumference is noted. Then, the patient takes a maximal deep breath, and the circumference is measured again. The difference between these two measurements represents the respiratory excursion. Normal diaphragmatic excursion is between 3 to 5 centimeters in healthy adults. While tape measurement provides a general assessment, more advanced techniques like spirometry can offer detailed insights into lung volumes and capacities.
Factors Affecting Respiratory Excursion
Several non-pathological factors can influence respiratory excursion in healthy individuals. Age can play a role, as the elasticity of lung tissue and the flexibility of the chest wall may decrease with advancing years, potentially leading to a slightly reduced excursion. An individual’s physical activity level also has an impact; people who engage in regular aerobic exercise often exhibit greater respiratory excursion due to enhanced respiratory muscle strength and lung capacity.
Posture significantly affects breathing mechanics, with an upright, open posture allowing for fuller chest expansion compared to a slumped or restrictive position. General physical fitness, encompassing muscle strength and flexibility, contributes to the efficiency of breathing movements. Temporary factors can also cause variations, such as pain from an injury or surgery, which might limit deep breathing due to discomfort. Similarly, abdominal distension, such as after a large meal, can impede the downward movement of the diaphragm, transiently reducing excursion.
What Abnormal Excursion Indicates
Abnormal respiratory excursion can indicate various underlying health conditions affecting the lungs, muscles, or chest cavity. Restrictive lung diseases, such as pulmonary fibrosis, cause the lung tissue to become stiff and less elastic, directly limiting how much the lungs can expand. This stiffness reduces the overall change in chest volume during breathing.
Neuromuscular disorders, like amyotrophic lateral sclerosis (ALS), can weaken the muscles responsible for breathing, including the diaphragm and intercostal muscles. When these muscles are compromised, their ability to contract and relax effectively is impaired, leading to a diminished respiratory excursion. Severe pain, especially in the chest or abdomen, can cause individuals to take shallow breaths to avoid discomfort, thereby restricting chest wall movement.
Conditions that accumulate fluid or air in the space between the lungs and the chest wall also reduce excursion. Pleural effusions, which are collections of fluid, and pneumothorax, the presence of air, compress the lung and prevent its full expansion. Obesity can also restrict respiratory excursion due to the mechanical burden of excess weight on the chest wall and abdomen, hindering diaphragmatic movement.
While less common, an increased respiratory excursion can be observed. This might occur in conditions where the lungs are chronically overinflated, such as severe emphysema, as the body attempts to compensate for impaired gas exchange. However, consistently abnormal excursion, whether reduced or increased, suggests a need for professional medical evaluation to determine the underlying cause and appropriate management.