It reflects intravascular depletion, usually from blood loss. Yet, this may also occur in normovolemia.
Moreover, it has a sensitivity of only 9% for blood loss of 450–630 mL. Hence, it is not particularly useful--
and definitely much less useful than the postural heart rate response
Moreover, it has a sensitivity of only 9% for blood loss of 450–630 mL. Hence, it is not particularly useful--
and definitely much less useful than the postural heart rate response