Spirometry follows airflow and exhaled volume during controlled breathing maneuvers, whereas body plethysmography uses pressure changes produced while a person breathes inside an enclosed chamber. This distinction allows the two approaches to provide complementary information: spirometry describes how air moves out, while plethysmography estimates the total amount of air the lungs can contain, including air that remains after exhalation.
Total lung capacity indicates the maximum volume the lungs can contain, while residual volume reflects air retained after exhalation. Measuring these quantities adds information that cannot be obtained from exhaled volume alone. Their inclusion helps clinicians assess how fully the lungs expand and empty, which is important when investigating abnormal respiratory function or unexplained breathlessness.
The pattern of measured airflow and lung volumes helps separate obstructive from restrictive respiratory disease. Obstructive conditions are evaluated in relation to difficulty moving air out, whereas restrictive conditions are considered in relation to reduced ability of the lungs to expand. Using the measurements together provides a broader physiological picture than examining airflow or volume in isolation.
A person performs controlled breathing maneuvers while the system records airflow and exhaled volume for spirometry. When body plethysmography is needed, the person breathes inside an enclosed chamber so the equipment can detect pressure changes and estimate total lung capacity and residual volume. The resulting measurements are then considered as indicators of how effectively the lungs expand and empty.
Clinicians may request these measurements to investigate unexplained breathlessness, distinguish obstructive from restrictive lung disease, or monitor changes in respiratory disease over time. Testing can also show whether lung function changes after treatment. By quantifying expansion and emptying, the results support a more structured assessment than symptoms alone and can help follow a patient's respiratory status.
The measurements support preoperative evaluation by providing information about respiratory function before an operation. They also contribute to physiological research, where quantified lung expansion, emptying, and retained air help investigators characterize breathing performance. In clinical care, repeated assessments can document disease progression or treatment response, making the technique useful for both decision-making and longitudinal monitoring.