Plethysmography - registration of change of volume of the organ or body part, usually used to assess the dynamics of their blood. Apply for the study of vascular tone and its regulation. In recent years, finds application plethysmography combined total body to evaluate the function of external respiration. Devices for plethysmography combined based on the principle of direct or registration of volume (mechanical plethysmography)or registration related to the dynamics of the blood supply to changes in the electrical properties of tissues (electroretinography, peoplesmart) or light transmission (photopletismography).

Plethysmography (from the Greek. plethysmos - filling, increase and grapho - write) is a method of continuous graphic registration of changes in the volume of peripheral organ or body part (leg, fingers, ears and other) to determine the fluctuations of the blood vessels of the investigated organ.
On obtained by plethysmography combined accounts - plethysmogram - in a healthy person can be detected quickly (pulse, breathing and slow variations in the volume of the authority related with the corresponding shifts his blood vessels.
In combination with synchronous registration of blood pressure plethysmography allows to judge about the regulation of vascular tone of the body under certain effects in the body. The combination P. with a number of functional tests can detect venous tone and other indices of peripheral blood circulation in the conditions of chronic experiment and clinical research.
In the clinic P. is used for analysis of development of pathological symptoms, and to clarify the extent of participation of peripheral vessels in hemodynamic disorders. A very widely used P. and for research disorders of the higher nervous activity, which is determined based on the study of vascular conditioned reflexes patients.
For plethysmography combined created special devices - plethysmography, which consist of: 1) the receptive part (calibrator volume); 2) the transmission system; 3) the Registrar; 4) the tape drive mechanism (with a timer and a validity period of stimuli).
In mechanical plethysmography perceiving part is camera with hard walls, in the cavity, which introduce the monitoring body. Then the cavity of the camera along with the air (in the air plethysmography) carefully seal or fill it with water (in the water and water-air plethysmography). If you increase the amount of authority the appropriate amount of water or air from the chamber of displaced and flows through the receiver of the transmission system to the Registrar. In the mobile part of the Registrar (diaphragm, piston and so on) are shifted; these shifts are recorded on a uniformly moving strip of paper in either mechanical (ink, removing soot)or photographed on a moving photo paper. For a photographic recording of plethysmogram mechanical plethysmograph in clinic conditions apply AIDS visiograph 068 and mechanochemical 063 with photographic N 106 sensitive pneumatic vibrators.
In recent years, developed electric (dielectric and impedance) and photovoltaic plethysmography. Electric plethysmography allow to investigate the blood vessels such broad areas as the trunk of the body (Central impedance plethysmography) and the head (brain P.). Photoelectrochemistry make it possible to determine the blood vessels of the skin of flat parts of the body, skin interdigital folds of the ear, etc., However, obtained by these methods of plethysmogram, unlike mechanical, does not allow accurate analysis of the blood supply to the body in volumetric units.
Cm. also Ecografia.