The Measurement of Inspiratory Muscle Strength by Sniff Esophageal, Nasopharyngeal, and Mouth Pressures

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Abstract
Sniff esophageal pressure (Pes) is a useful measurement of global inspiratory muscle strength, although it does require passage of an esophageal balloon. We investigated the relationship between nasopharyngeal pressure (Pnp) or pressure within the mouth (Pmo) and Pes during a maximal sniff from FRC without a noseclip. We measured Pes, Pnp, and Pmo simultaneously in 10 normal volunteers, and in 12 patients with inspiratory muscle weakness. In both groups, Pnp and Pmo were slightly less but very close to Pes. In normal volunteers, the mean ratio Pnp/Pes was 0.92 .+-. 0.0005 (mean .+-. SE) and Pmo/Pes was 0.95 .+-. 0.006. Regression analysis showed Pes = 4.57 + 1.05 Pnp (r = 0.995, p < 0.001) and Pes = 0.74 + 1.05 Pmo (r = 0.994, p < 0.001). Similar relationships between Pnp, Pmo, and Pes were found over a wide range of pressures generated by submaximal sniffs in normal subjects. In patients, the mean ratio Pnp/Pes was 0.90 .+-. 0.02 and Pmo/Pes was 0.87 .+-. 0.03. Regression analysis showed Pes = 5.12 + 1.0 Pnp (r = 0.949, p < 0.001) and Pes = 11.2 + 0.882 Pmo (r = 0.036, p < 0.001). We conclude that Pnp and Pmo predict Pes during a maximal sniff in both normal subjects and in patients with inspiratory muscle weakness. Sniff Pnp and/or Pmo may provide a useful and less invesive method of measuring maximal inspiratory pressures during a sniff.