Hypotension induced by haemorrhage impairs lower oesophageal sphincter function.

The effect of haemorrhage-induced hypotension on lower oesophageal sphincter (LOS) tone was studied in 11 adult mongrel dogs. Mean(s.e.m.) blood loss of 760(66) ml, corresponding to 42 per cent of estimated blood volume, was associated with a significant fall in LOS tone (14.2(1.0) versus 7.2(0.6) sphinctometer units, P < 0.002). This was associated with a reduction in mean(s.e.m.) arterial blood pressure (99(7) versus 53(3) mmHg, P < 0.002) and heart rate (113(6) versus 106(5) beats per min, P = 0.06). Group 1 animals (n = 6) received autotransfusion, restoring LOS tone to prehaemorrhage values. Dogs in group 2 (n = 5) were given intravenous erythromycin 4 mg/kg, which also restored LOS tone. This effect was transient, lasting a mean(s.e.m.) of only 67(7) min. Infusion of an equivalent volume of 0.9 per cent saline following cessation of the erythromycin effect restored LOS tone to control values although the animals remained hypotensive. Reduction in LOS tone with haemorrhage may be part of a vagal reflex mediated by myocardial afferent C fibres and may explain the high incidence of pulmonary aspiration in shocked patients.