, 2009). Signals of flow, volume, pressure (Paw) and end-tidal partial pressure of carbon dioxide (PETCO2) were recorded at the mouth. Esophageal (Pes) and gastric pressures (Pga) were measured with balloon-tipped catheters ( Laghi et al., 1996). Crural diaphragm electrical activity (EAdi) was recorded with 9 stainless-steel electrodes mounted on a polyurethane tube positioned across the gastroesophageal junction and wired as 8 trans-isomer overlapping bipolar pairs ( Beck et al., 2009). Bilateral surface electrodes recorded compound diaphragmatic action

potentials (CDAPs) elicited by phrenic nerve stimulation ( Laghi et al., 1996). Two pairs of surface electrodes (lower abdomen and rectus abdominis) recorded abdominal muscle recruitment ( Fig. 1) ( Strohl et al., 1981). Cross-sectional area of upper and lower abdomen was monitored with respiratory inductive plethysmography (RIP) bands placed 2–3 cm

above and 2–3 cm below the umbilicus. All signals were recorded continuously. The purpose of this experiment, conducted in 17 subjects, was threefold: to examine diaphragmatic neuromechanical coupling during threshold loading; to measure extent of diaphragmatic recruitment at task failure (central fatigue); and to explore whether changes in diaphragmatic neuromechanical coupling during loading Wortmannin chemical structure resolve after task failure. After placement of transducers, subjects performed at least three inspiratory capacity (IC) maneuvers (Hussain et al., 2011) to determine maximum voluntary diaphragmatic activation (maximum EAdi) (Fig. 2) (Sinderby et al., 1998 and Juan et al., 1984). Thereafter, subjects sustained an incremental inspiratory threshold load until task failure (Eastwood et al., 1994 and Laghi et al., 2005). At the start of loading, a 200-g weight was placed on a platform connected to a one-way plunger valve. Every minute, the inspiratory load was increased by 100 g (Laghi et al., 2005). Loading was

terminated when a subject was unable to sustain the breathing task despite strong encouragement (task failure). No instructions were given to the subjects regarding what ASK1 breathing pattern to adopt (Laghi et al., 2005 and Eastwood et al., 1994). Immediately after task failure, subjects were asked whether they stopped because of unbearable breathing effort (defined as “sensation of excessive respiratory muscle contraction to breathe in”), unbearable air hunger (defined as “the unbearable discomfort when asked to hold your breath longer than what you could”) or other reasons ( Laghi et al., 1998). Immediately before and immediately after task failure, and 5 and 15 mintes later, subjects breathed through a small, constant inspiratory threshold load set at −20 cm H2O for at least 1 min (Fig. 2).