Value of Intraoral Pressure as a Measure of Intrapleural Pressure

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Abstract
In 6 patients with artificial (therapeutic) pneumothorax, intrapleural pressure was found to be consistently lower than intraoral pressure. During a Valsalva-like maneuver (which is described), intraoral pressure averaged 6.7 mm. Hg higher than intrapleural pressure, and the difference between the 2 was linear during all phases of the maneuver. During quiet respiration the differences between avg. peak intraoral and intrapleural pressure on inspiration and expiration were smaller than on forced expiration but of the same order of magnitude. A lag of intrapleural pressure behind intraoral pressure was noted and was probably due to the varying alveolo-tracheal pressure gradient during different phases of respiration. Resistance to respiration introduced by the Robinson valve used cannot be excluded as a contributory factor. It is concluded that intraoral pressure can be substituted for intrapleural pressure in calculating net blood pressure during a Valsalva-like maneuver, providing the glottis remains open, and a correction factor of 6 to 7 mm. Hg is introduced.

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