Cardiovascular
and Hormonal Changes with Different Angles of
Head-up Tilt in Men
Z. LÁSZLÓ, A. RÖSSLER, H. G. HINGHOFER-SZALKAY1
Volume Regulation and Space Medicine Research
Group, Department of Physiology, School of
Medicine, Karl-Franzens University and 1Institute
for Adaptational and Spaceflight Physiology,
Austrian Society for Aerospace Medicine and Life
Sciences, Graz, AustriaReceived April
5, 2000
Accepted May 19, 2000
Summary
The
purpose of this study was to assess the endocrine
status, thoracic impedance, blood concentration,
and hemodynamic dose-responses using different
angles of passive head-up tilt (HUT) ranging from
12° to 70° in the same subjects. Measurements
were performed during 20 min supine position
(pre-HUT), 30 min upright (HUT12, HUT30, HUT53,
or HUT70), and 20 min supine (post-HUT); subjects
70 min in the supine position only (HUT0) served
as resting controls. Norepinephrine increased
above resting control values by 19, 44, 80, and
102 %; epinephrine by 30, 41, 64, and 68 %;
aldosterone by 29, 62, 139, and 165 %; plasma
renin activity n. s., 41, 91, and 89 %;
vasopressin n.s., 27, 47, and 59 %; thoracic
bioimpedance n. s., 8, 13, and 16 %; heart rate
n. s., 5, 26, and 45 %, and mean arterial
pressure n. s., 5, 7, and 10 %; at min 27 of
HUT12, HUT30, HUT53, and HUT70, respectively.
Pulse pressure decreased with HUT53 and HUT70 by
4 and 10 %. Hematocrit increased by 0.2, 1.7,
6.3, and 7.2 %, respectively. Blood density
increased by 2.3 and 3.0 g/l, plasma density by
1.7 and 1.8 g/l with HUT53 and HUT70. After
finishing HUT, heart rate fell to values which
stayed below pre-HUT, and also below resting
control levels for ł 5 min
("post-orthostatic bradycardia") even
after the lowest orthostatic load (HUT12).
Thoracic impedance and arterial pressure remained
increased after terminating HUT30, HUT53, and
HUT70. In conclusion, passive orthostatic loading
of different extent produces specific
dose-responses of different magnitude in the
endocrine system, blood composition, thoracic
impedance, and hemodynamic variables. The heart
rate is depressed even after HUT12, while
arterial blood pressure and thoracic impedance
exceed pre-stimulus levels after greater head-up
tilt, indicating altered cardiovascular response
after passive orthostasis.
Key
words
Cardiopulmonary
baroreceptors · Thoracic electrical bioimpedance
· Blood volume · Catecholamines · Arginine
vasopressin (AVP)
Reprint
requests
Z.
László, Weiss Manfréd Hospital, Department of
Internal Medicine, Cardiology, Déli u. 11,
H-1211 Budapest, Hungary, fax: +36-1-276-1767
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