Regional pleural surface expansile forces in intact dogs by wick catheters

Hoffman and co-workers (J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 55: 935-948, 1983) using a technique based on distances between percutaneously inserted X-ray opaque apical and basal lung-parenchymal markers (LPM) calibrated to known transpulmonary pressures in dogs studied without thoracotomy found that apical values measured in the head-up position were more negative than values measured simultaneously by liquid-filled catheters. This finding prompted comparison of pleural pressures (Ppl) measured simultaneously by apical and basal pairs of identical percutaneously inserted liquid-filled catheters, one open ended (OE) and the other wick tipped (WT). Simultaneously OE and WT values were always closely similar in dependent regions of the thorax and usually also in nondependent regions independent of body position and the orientation of the external segment of the wick relative to the catheter tip. However, in some instances in head-up dogs when the wick was extended distal to the catheter tip, apical WT values were 10-15 cm more negative than simultaneous OE measurements. The latter observations agree with the more negative values obtained previously by the LPM technique and support the possibility that apical expansile forces in head-up dogs may be greater than indicated by Ppl measured by liquid-filled catheters and considerably greater than indicated by usually accepted balloon techniques.