Fig. 6. Sample of data collected when the proximal (cranial) and distal (caudal) transducers were located within the lower esophageal sphincter (LES) and stomach, respectively. The top portion of the graph shows a time span of approximately 15 min and illustrates large rises in LES (proximal) pressure with ventilation. The two spikes in pressure marked with an asterisk were due to vocalization and a general elevation of pressure in the thoraco-abdominal cavity. These spikes demonstrate that the increase in LES pressure associated with ventilation is independent of any thoraco-abdominal pressure changes and is intrinsic to the LES. Fluctuations in the ventilatory trace that are marked with daggers are caused by gular flutter, where air is taken in and out of the gular cavity. This serves an olfactory but not a gas exchange function (Farmer and Carrier, 2000b). Note that there is no rise in LES pressure associated with the gular flutter. The bottom part of the figure shows panels 1, 2 and 3 in more detail. Note that the scale for the gastric pressure on panel 2 is also expanded. Although ventilation generally caused LES pressure to increase, it caused gastric pressures to decrease. This is because the glottis is closed during apnea and the respiratory muscles are relaxed, thus elevating thoraco-abdominal pressure (Farmer and Carrier, 2000a). Panel 3 shows a bout of ventilation that was interrupted by a 2 ml bolus of water (indicated by arrow). Note that the wet-swallow reflex predominated over the LES pressure increase.