Lower Esophageal Sphincter Pressure Levels Research Articles

Influence of tidal volume on the distribution of gas between the lungs and stomach in the nonintubated patient receiving positive-pressure ventilation.

When ventilating a nonintubated patient in cardiac arrest, the European Resuscitation Council has recently recommended a decrease in the tidal volume from 0.8 to 1.2 L to 0.5 L, partly in an effort to decrease peak flow rate, and therefore, to minimize stomach inflation. The purpose of the present study was to examine the validity of the European Resuscitation Council's recommendation in terms of gas distribution between lungs and stomach in a bench model that simulates ventilation of a nonintubated patient with a self-inflatable bag representing tidal volumes of 0.5 and 0.75 L. A bench model of a patient with a nonintubated airway was used consisting of face mask, manikin head, training lung (lung compliance, 50 mL/cm H2O; airway resistance, 5 cm H2O/L/sec), adjustable lower esophageal sphincter pressure (LESP) and simulated stomach. University hospital laboratory. Thirty healthcare professionals. Healthcare professionals performed 1-min bag-mask ventilation at each LESP level of 5, 10, and 15 cm H2O at a rate of 12 breaths/min, using an adult and pediatric self-inflating bag, respectively. Volunteers were blinded to the LESP, which was randomly varied. Both types of self-inflating bags induced stomach inflation, with higher stomach and lower lung tidal volumes when the LESP was decreased. Lung tidal volume with the pediatric bag was significantly (p < .05) lower at all LESP levels when compared with the adult bag, and ranged between 240 mL at an LESP of 15 cm H2O and 120 mL at an LESP of 5 cm H2O. Stomach tidal volume with the adult bag ranged between 250 mL at an LESP of 15 cm H2O and increased to 550 mL at an LESP of 5 cm H2O. Stomach tidal volume with the pediatric bag was significantly lower (p < .05) at all LESP levels when compared with the adult bag and ranged between 70 mL at an LESP of 15 cm H2O and 300 mL at an LESP of 5 cm H2O. Our data support the recommendation of the European Resuscitation Council to decrease tidal volumes to 0.5 L when ventilating a cardiac arrest victim with an unprotected airway. A small tidal volume may be a better trade-off in the basic life support phase, as this may provide reasonable ventilation while avoiding massive stomach inflation.

Modulation of lower esophageal sphincter relaxation in the opossum.

The relationship of lower esophageal sphincter (LES) relaxation and sphincter pressure was studied in the basal state and after neurohumoral stimulation in the anesthetized opossum. LES relaxation was induced by electrical vagal stimulation, balloon distension, and swallowing, whereas LES pressure was increased by infusions of gastrin I, histamine, phenylephrine, or bethanechol. Each agent was selected to give an approximately twofold increase in LES pressure, at the highest dosage. The lower dosage gave a submaximal increase in LES pressure. Neither gastrin nor histamine modified sphincter relaxation as induced by vagal stimulation, esophageal distension, or swallowing. Phenylephrine or bethanechol made the LES less sensitive to vagal stimulation or esophageal distension without reducing maximal LES relaxation. Only bethanechol significantly decreased sphincter relaxation in response to swallowing (P less than 0.05). The results of this study suggest that LES relaxation is not a fixed response simply dependent on the inhibitory stimulus or the resting tonic level of LES pressure, but may be modulated by both alpha-adrenergic and cholinergic drugs.

Lower Esophageal Sphincter Dysfunction in Achalasia

In patients with achalasia, lower esophageal sphincter (LES) dysfunction plays an important role in the impairment of esophageal emptying. To evaluate this dysfunction, the manometric characteristics of the LES were recorded for 20 normals and for 16 patients with achalasia, both before and after pneumatic dilation. Before dilation, patients with achalasia have two abnormalities in LES function: (1) LES pressure at rest is twice that recorded in normals; and (2) the LES does not relax to the level of gastric pressure during swallowing. Therefore, a residual LES pressure is always present in patients with achalasia. Following clinically successful pneumatic dilation, the resting LES pressure is significantly reduced, but, as before dilation, the LES does not relax completely upon swallowing. The residual pressure at the LES in patients with achalasia is therefore a function of the resting LES pressure at which swallowing is initiated. Accordingly, the clinical status of each patient with achalasia is related inversely to the level of LES pressure. In normals, the LES relaxation always approximates the level of gastric pressure. Thus, a significant residual pressure never exists. This study suggests that the residual pressure at the LES, present only in patients with achalasia, results in an obstruction to esophageal emptying. The magnitude of this obstruction is a direct function of resting LES pressure.