Study objectives: We sought to determine the adaptability and effectiveness of a new esophageal balloon technique to measure changes in esophageal pressure (Pes) as a reflection of pleural pressure with progressive incremental exercise testing in normal subjects.
Design: An 8F (0.9 cm) esophageal balloon catheter (Smart Cath; Allied Health Products; Riverside, Calif), a CP-100 pulmonary monitor (BiCore Monitoring Systems PC-100; Irvine, Calif), and a flow transducer (Var flex; Allied Health Products; Riverside, Calif) were connected to a breathing valve (model 2700; Hans-Rudolph Inc; Kansas City, Mo). This apparatus was then used to measure Pes during a graded cardiopulmonary exercise test (CPX) to symptom limitation.
Setting: University-affiliated Veterans Affairs Hospital.
Participants: Eight nonsmoking volunteers with normal results of pulmonary function tests.
Interventions: Plots of ΔPes against pressure time product (PTP), minute ventilation (VE), and oxygen consumption (VO2) were obtained. Pes at baseline, anaerobic threshold (AT), and maximum oxygen consumption (VO2max) were obtained by comparing the Pes measurements from the computer printout to the corresponding breath-by-breath measurements on the CPX.
Measurements and results: The flow transducer (Varflex) connection added only 20 mL of dead space to the standard mouthpiece apparatus. The mean maximum work performance was 203±32 W. The mean VO2max was 29±9 mL/kg/min. The Pes at AT was 16±3 cm H2O. The Pes at maximal exercise was 42±16 cm H2O.
Conclusion: The small esophageal balloon was well tolerated by all subjects. Plots of ΔPes vs PTP, VE, and VO2 demonstrated a linear correlation. This apparatus could be added to the standard CPX to assess the contribution of the diaphragm and respiratory muscles in patients with dyspnea.