STATIC AND DYNAMIC PULMONARY COMPLIANCE DURING UPRIGHT IMMERSION

Elastic properties of the lung are typically assessed using the static pressure-volume relaxation manoeuvre. Although dynamic methods have p roduced equivalent results in normal healthy subjects, their use under obstructive pulmonary disease states and during certain conditions ha s been questioned. Static (C-st(1)) and dynamic (C-dyn(1)) pulmonary c ompliance were measured in eight subjects in air (control) and during C-dyn(1) decreased from 2.94 to 1.61 1 kPa(-1) following immersion, du ring which subjects breathed air supplied at mouth pressure (P < 0.05) , while C-st(1) remained approximately equivalent (3.16 and 4.07 1 kPa (-1) respectively, P > 0.05). When immersed subjects were supplied wit h breathing gas at lung centroid pressure (P-LC), C-dyn(1) returned to control status (2.89 1 kPa(-1); P > 0.05), while C-dynm(1) remained s table at 3.60 1 kPa(-1) (P > 0.05). The difference between C-st(1) and C-dynm(1) may imply that flow-resistive properties are included withi n the latter measurement. It is recommended that C-dyn(1), under these conditions, be interpreted as an indes of peripheral airway patency, rather than as an assessment of lung elasticity.