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Fig. 5. Sample of data collected when both pressure probes were placed within the
lower esophageal sphincter (LES). The top and second trace are recordings of
the pH and ventilation, respectively. Ventilation begins with an exhalation
(positive voltage) and ends with an inspiration. Thus, the apnea consists of a
breath-hold. The third and fourth traces give the pressure from the most
proximal (cranial) probe with a gross and fine pressure scale, respectively.
Note that peak pressures during ventilation increased dramatically, in this
case from a baseline of 
1.3 kPa to a peak of nearly 26.7 kPa. The small
regular spikes in pressure seen in the fine scale are caused by the heartbeat.
The fifth and sixth traces are the pressure recordings from the distal
(caudal) probe with two pressure scales. The expanded pressure scale of the
sixth trace shows most clearly the relaxation in pressure that occurred in the
LES during a wet swallow (the arrow indicates the time a 2 ml bolus of water
was given). This response to wet swallows was observed in all animals studied
(N=5).
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