pletysmografialla

Plethysmography is a family of noninvasive methods for measuring changes in volume within a body part or the entire body. The techniques infer flow, volume, or tissue perfusion by detecting signals that accompany blood or air volume changes, using optical, electrical, or pressure-based sensors.

Photoplethysmography (PPG) uses light to detect blood volume changes in tissue, a basis for pulse oximetry and heart-rate monitoring. Impedance plethysmography measures changes in electrical impedance due to circulating blood, useful for assessing limb vascular status. Air or volumetric plethysmography uses sealed chambers or cuffs to track volume changes in a limb or in the thorax, enabling limb edema assessment and measurements of lung volumes. Whole-body plethysmography places the subject in a sealed chamber to infer thoracic gas volume and airway resistance from pressure changes during breathing.

Applications span cardiology, pulmonology, vascular medicine, and physiology research. Clinically, plethysmography aids evaluation of venous insufficiency, edema, arterial disease, and obstructive or restrictive lung conditions. In research, it supports studies of perfusion, hemodynamics, and responses to interventions.

Advantages include noninvasiveness, relative simplicity, and the ability to provide functional information. Limitations involve susceptibility to movement and volume- or posture-related artifacts, calibration needs, and reliance on surrogate signals rather than direct volume measurements.

See also: Photoplethysmography, Impedance plethysmography, Body plethysmography, Lung volume measurement, Venous plethysmography.