ABSTRACT
In a mechanical apparatus such as the respiratory system, where motion is transduced into volume, forces are expressed in terms of pressure. Contraction of respiratory muscles essentially causes pressures in the respiratory system to change, and consequently lung volume to alter. Pressures thus produce the mechanical outcome of respiratory muscle contraction and are, in combination with volume and flow, commonly used to estimate the mechanical properties of the respiratory system (I ,2). Several pressures may be measured. First, the pressure across the whole respiratory system, transrespiratory pressure cPrs), is measured as the pressure at the airway opening (P 80) relative to that at the surface of the body. The former is measured through measurement of mouth pressures (3--13), nasal pressure, or nasopharyngeal pressure (II ,14).
