Pleural manometry-historical background, rationale for use and methods of measurement

Subatmospheric pleural pressure (Ppl), which is approximately -3 to -5 cmH₂O at functional residual capacity (FRC) makes pleura a unique organ in the human body. The negative Ppl is critical for maintaining the lungs in a properly inflated state and for proper blood circulation within the thorax. Significant and sudden pleural pressure changes associated with major pleural pathologies, as well as therapeutic interventions may be associated with life-threatening complications. The pleural pressure may show two different values depending on the measurement method applied. These are called pleural liquid pressure and pleural surface pressure. It should also be realized that there are significant differences in pleural pressure distribution in pneumothorax and pleural effusion. In pneumothorax, the pressure is the same throughout the pleural space, while in pleural effusion there is a vertical gradient of approximately 1 cm H₂O/cm in the pleural pressure associated with the hydrostatic pressure of the fluid column. Currently, two main methods of pleural pressure measurement are used: simple water manometers and electronic systems. The water manometers are conceptually simple, cheap and user-friendly but they only allow the estimation of the mean values of pleural pressure. The electronic systems for pleural pressure measurement are based on pressure transducers. Their major advantages include precise measurements of instantaneous pleural pressure and the ability to display and to store a large amount of data. The paper presents principles and details of pleural pressure measurement as well as the rationale for its use.