Sniff esophageal and nasopharyngeal pressures and maximal relaxation rates in patients with respiratory dysfunction.

Sniff esophageal pressure (Pes) and maximal relaxation rate (MRR, percent pressure loss/10 ms) are useful measurements of inspiratory muscle performance, but they require the passage of an esophageal balloon. We have examined the relationship between sniff esophageal and nasopharyngeal pressures (sniff Pes, sniff Pnp) and maximal relaxation rates (Pes MRR, Pnp MRR) in 13 patients with chronic obstructive pulmonary disease (COPD), five with intrapulmonary fibrosis (IPF), and seven with the "shrinking lung syndrome" of systemic lupus erythematosus (SLE). The ratio sniff Pnp/Pes (mean +/- SD) was 0.65 +/- 0.15 in COPD, 0.76 +/- 0.18 in IPF, and 0.91 +/- 0.03 in SLE. The ratio Pnp/Pes MRR was 1.20 +/- 0.2 in COPD, 1.14 +/- 0.12 in IPF, and 1.07 +/- 0.13 in SLE. We confirm that the transmission of pleural pressure to the upper airways during brief dynamic maneuvers is impaired in the presence of airway obstruction and lung fibrosis. We conclude that measurements of sniff Pnp and Pnp MRR are of limited value in patients with abnormal lung mechanics.