Post-reperfusion Coagulopathy Hyperventilation-induced Unconsciousness during Labour

Sir,—In commenting on our paper [1], Kardos, Rudas and Simon described their own use of the analysis of short-term heart rate variability to assess the effect of varying posture on cardiac autonomic control. Essentially they have confirmed that head-up tilt causes sympathetic activation (as evidenced by an increase in the low frequency variability) in comparison with supine and head-down positions. This phenomenon is well described [2, 3]. Their letter also indicates that increased parasympathetic tone was found when their subjects went from head-up tilt ( + 70°) to head-down tilt ( — 30°). However, they give no indication of any comparison between the supine and head-down positions, which is the finding in which we were interested. Without this comparison we cannot comment further on their letter as their results seem consistent with our own. We would be very happy to reply to the letter of Kardos, Rudas and Simon if a statistical comparison can be given between the flat supine position and head-down tilt (with exclusion of order bias).