The hydrostatic pressure indifference point underestimates orthostatic redistribution of blood in humans.
J Appl Physiol (1985)
; 116(7): 730-5, 2014 Apr 01.
Article
in En
| MEDLINE
| ID: mdl-24481962
ABSTRACT
The hydrostatic indifference point (HIP; where venous pressure is unaffected by posture) is located at the level of the diaphragm and is believed to indicate the orthostatic redistribution of blood, but it remains unknown whether HIP coincides with the indifference point for blood volume (VIP). During graded (± 20°) head-up (HUT) and head-down tilt (HDT) in 12 male volunteers, we determined HIP from central venous pressure and VIP from redistribution of both blood, using ultrasound imaging of the inferior caval vein (VIPui), and fluid volume, by regional electrical admittance (VIPadm). Furthermore, we evaluated whether inflation of medical antishock trousers (to 70 mmHg) affected HIP and VIP. Leaving cardiovascular variables unaffected by tilt, HIP was located 7 ± 4 cm (mean ± SD) below the 4th intercostal space (IC-4) during HUT and was similar (7 ± 3 cm) during HDT and higher (P < 0.0001) than both VIPui (HUT 22 ± 16 cm; HDT 13 ± 7 cm) and VIPadm (HUT 29 ± 9 cm; HDT 20 ± 9 cm below IC-4). During HUT antishock trousers elevated both HIP and VIPui [to 3 ± 5 cm (P = 0.028) and 17 ± 7 cm below IC-4 (P = 0.051), respectively], while VIPadm remained unaffected. By simultaneous recording of pressure and filling of the inferior caval vein as well as fluid distribution, we found HIP located corresponding to the diaphragm while VIP was placed low in the abdomen, and that medical antishock trousers elevated both HIP and VIP. The low indifference point for volume shows that the gravitational influence on distribution of blood is more profound than indicated by the indifference point for venous pressure.
Key words
Full text:
1
Collection:
01-internacional
Database:
MEDLINE
Main subject:
Posture
/
Vena Cava, Inferior
/
Blood Volume
/
Diaphragm
/
Central Venous Pressure
/
Dizziness
Type of study:
Clinical_trials
/
Diagnostic_studies
Limits:
Adult
/
Humans
/
Male
Language:
En
Journal:
J Appl Physiol (1985)
Journal subject:
FISIOLOGIA
Year:
2014
Document type:
Article