Trans-thoracic fluid shifts and endocrine responses to 6 degrees head-down tilt
Grundy, D.; Reid, K.; Mcardle, F.J.; Brown, B.H.; Barber, D.C.; Deacon, C.F.; Henderson, I.W.
Aviation Space and Environmental Medicine 62(10): 923-929
1991
ISSN/ISBN: 0095-6562 PMID: 1837213 Document Number: 380992
A tomographic method of measuring electrical impedance known as Applied Potential Tomography (APT) has been used to image the impedance changes within the thoraxes of 8 healthy volunteers (4 male, 4 female) during 4-h priods of 6.degree. head-down tilt (HDT). A large decrease in impedance, reflecting an increase in thoracic fluid, was apparent within 1 min of tilting, peaked after 45 min, and was maintained throughout, although during the 4 h there was an 8% return towards baseline resistitviity. Resistivity changes were most obvious in the region of the lungs. Simultaneous measurements of the key fluid regulating hormones revealed a significant increase in atrial natriuretic peptide (ANP) and a significant decrease in angiotensin II (AII) and aldosterone. There was no significant difference in plasma antidiuretic hormone level. These results illustrate the dynamic nature of fluid shifts during HDT, the spatial distribution of the fluid within the thorax and the associated endocrine responses.