TABLE 1.

Comparison of the effects of spaceflight and head-down bedrest (HDBR) on blood volume (+: increased, −: decreased). Adapted and modified from Diedrich et al. (2007).

	Spaceflight	HDBR
Headward fluid shift	+	+
Hunger	−	+/-
Thirst	−	+/-
Diuresis	+/-, (explained above)	+
Renal response to fluid & salt	Reset	Preserved
Salt retention	+	Unknown
Atrial natriuretic peptide	Reset to lower levels	+
Mechanical compression of thorax	−	Maintained
Central venous pressure	−	Transiently increased
Radiation	+	NA