The Value of Sniff Esophageal Pressures in the Assessment of Global Inspiratory Muscle Strength

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Abstract
Esophageal pressure generated during a maximal sniff (sniff Pes) was compared with mouth pressure generated during a maximal inspiration against a closed airway (Pimax) as a measure of global inspiratory muscle strength in 61 patients referred for investigation of respiratory muscle function. Transdiaphragmatic pressure (Pdi) was also measured during both maneuvers to compare maximal diaphragmatic strength. Sniff Pes (males, 68 .+-. 27 cm H2O; normal > 53; females, 66 .+-. 21; normal > 48) was greater than PImax (males, 45 .+-. 24 cm H2O; normal > 42; females, 42 .+-. 24; normal > 17) in 55 of the 61 patients, both in absolute values and as a percentage of normal. In 36 patients, PImax was and sniff Pes were both normal (mean .+-. 2SD), whereas in 13 patients they were both low. In 11 patients, PImax low, but sniff Pes was normal. One patient had a reduced sniff Pes but a Pimax at the lower limit of normal. In the 36 patients in whom both PImax and sniff Pes were normal, Pdi was also normal or only moderately reduced, and in the 13 patients in whom both Pimax and sniff Pes were reduced, Pdi was very low. However, in the group of 11 patients with a low PImax but a normal sniff Pes, Pdi was normal or only moderately reduced, suggesting that PImax was falsely low, perhaps because of difficulties with the technique. Conversely, in the single patient with a low sniff Pes but a PImax just within the normal range, Pdi was very low. We conclude that measurement of eosphageal pressure during a maximal sniff is a useful test of inspiratory muscle strength and overcomes the difficulty some patients have in carrying out the PImax maneuver.

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