Table 1. The impact of‘respiratory’ variability in intrathoracic pressure and central haemodynamics on cerebral blood flow velocity during the struggle phase.

	Input
	(%)	Direct	Indirect	Total
ITP	5.5±0.8	–	0.366	0.366
HR	3.3±0.4	–	0.219	0.219
LVSV	5.9±0.5	–	0.474	0.474
CO	7.6±0.5	–	0.536	0.536
MAP	1.8±0.2	0.901	–	0.901

Values represent standardised ß-coefficients obtained from the ‘reduced-fit’ model depicted in Figure 2 . : mean variability (coefficient of variation in percent) observed in the corresponding parameter during the struggle phase of breath holding; ITP: intrathoracic pressure; HR: heart rate; LVSV: left ventricular stroke volume; CO: cardiac output; MAP: mean arterial blood pressure; CBFV: cerebral blood flow velocity. ^aThe standard deviation of ITP is presented here as a measure of respiratory variability in place of the coefficient of variation (see Methods). The group-average for used in the above Path analysis was 2.2±0.1%.