Improved technique for estimating pleural pressure from esophageal balloons

Esophageal pressure has been measured in eight healthy men during breath holding (glottis open) at various fixed lung volumes with a rubber balloon (length: 10 cm; perimeter: 3.5 cm; wall thickness: ca. 0.06 mm) containing various volumes of air. The tip of the balloon was placed at a constant distance of 45 cm from the nares. Esophageal pressure was found to increase with balloon volume at all lung volumes but not uniformly, the effect of balloon volume being greatest at both extremes of the vital capacity. As a result, lung volume-pressure curves obtained from balloons containing volumes of gas such as are commonly used are distorted. One can avoid these distortions by repeating measurements at different balloon volumes and extrapolating esophageal pressure to zero balloon volume, or by making measurements at very small balloon volumes. A close approximation of the extrapolated pressures was obtained with the present balloon containing 0.2 ml air. The esophageal pressures at or near zero balloon volume probably reflect closely local absolute pleural pressures over the full vital capacity range in some subjects and above 20% of the vital capacity in most subjects. lung volume-pressure curves Submitted on August 13, 1963