1. Fainting is a common phenomenon in young subjects, but the final events before the actual faint are not well known. The aim of the present study was to study the inter-individual variability of haemodynamic events associated with near-fainting in children and teenagers.
2. Sixty-eight healthy subjects (aged 6–16 years) performed a 70° tilt-up test with intravascular instrumentation for 5 min. Responses in 29 near-fainting subjects were analysed and compared with 39 non-fainting subjects. Arterial pressure was measured by Finapres. Left ventricular stroke volume was computed from the pressure pulsation waveform.
3. Inability to maintain vasomotor tone was the mechanism underlying near-fainting in the vast majority of near-fainting subjects. The three classical haemodynamic responses (vasovagal, vasodepressor and vagal) could be recognized, but large individual differences were found. After tilt back, blood pressure in near-fainters showed a mirror response to the stage before tilt-back; blood pressure gradually increased and was normal at 1 min after tilt-back.
4. The variability in haemodynamic responses on approach of an orthostatic faint is wide in the young.