The effect of normobaric hyperoxia on cardiac index in healthy awake volunteers

Fifteen healthy volunteers were exposed to a stepwise increase in FIO2 between 0.21 and 1.0, and their haemodynamic responses were measured with a non-invasive transthoracic bio-impedance monitor. There was mean reduction in cardiac index from 3.44 to 3.08 l.min(-1).m(-2) (10.7%, p<0.001). The mean reduction in heart rate was from 77.3 to 69.1 beats.min(-1) (10.5%, p<0.001) and the mean systemic vascular index increased from 2062 to 2221 dyne.s(-1).cm(-5).m(-2) (7.7%, p<0.025). There were no significant changes in stroke index or mean arterial pressure. These changes are similar quantitatively and qualitatively to those previously reported by dye dilution techniques.