PMID- 10102731
OWN - NLM
STAT- MEDLINE
DCOM- 19990506
LR  - 20061115
IS  - 0095-6562 (Print)
IS  - 0095-6562 (Linking)
VI  - 70
IP  - 3 Pt 1
DP  - 1999 Mar
TI  - The heart is not necessarily empty at syncope.
PG  - 213-9
AB  - BACKGROUND: Although extensively investigated, the mechanism(s) of 
      post-spaceflight orthostatic intolerance has not been elucidated. Several 
      researchers have proposed that the "trigger" for syncope is an empty ventricle, 
      initiated when a hypercontractile state, possibly due to a sudden surge in 
      epinephrine, causes the walls of the left ventricle to touch leading to a 
      profound sympatho-inhibition and intense vagal stimulation. HYPOTHESIS: A 
      markedly reduced left ventricular end systolic volume (LVESV) achieved during 
      progressive, presyncopal-limited lower body negative pressure (LBNP) is the 
      trigger for syncope. METHODS: Eight healthy men, age 25.1+/-1.3 yr, volunteered 
      for the study. Changes in left ventricular end-diastolic volume and LVESV were 
      measured, using two-dimensional echocardiography, at each stage of LBNP from rest 
      up to presyncope (PS). Plasma venous catecholamine concentrations were measured 
      at the end of each stage by high performance liquid chromatography (HPLC) with 
      electrochemical detection. RESULTS: All subjects reached PS. Three men became 
      bradycardic at presyncope while five remained tachycardic. LVESV decreased by 28% 
      at PS with no evidence of ventricular cavity obliteration. Norepinephrine 
      increased by 44% from rest to PS, but no epinephrine surge was detected (35% 
      increase from rest to PS). CONCLUSION: These data indicate that it is possible to 
      initiate syncope with only a 28% decrease in LVESV, and that sympatho-inhibition 
      and bradycardia are not required elements for syncope to occur.
FAU - Davrath, L R
AU  - Davrath LR
AD  - Colorado State University, Department of Physiology, Fort Collins 80523, USA.
FAU - Gotshall, R W
AU  - Gotshall RW
FAU - Tucker, A
AU  - Tucker A
FAU - Sadeh, W Z
AU  - Sadeh WZ
FAU - Luckasen, G J
AU  - Luckasen GJ
FAU - Downes, T R
AU  - Downes TR
FAU - Coonts, C C
AU  - Coonts CC
LA  - eng
PT  - Journal Article
PT  - Research Support, U.S. Gov't, Non-P.H.S.
PL  - United States
TA  - Aviat Space Environ Med
JT  - Aviation, space, and environmental medicine
JID - 7501714
RN  - 0 (Catecholamines)
SB  - IM
MH  - Adult
MH  - Blood Pressure
MH  - Cardiac Output
MH  - Cardiac Volume
MH  - Catecholamines/blood
MH  - Echocardiography
MH  - Heart/*physiopathology
MH  - Heart Rate
MH  - Humans
MH  - Lower Body Negative Pressure
MH  - Male
MH  - Posture
MH  - Space Flight
MH  - Stroke Volume
MH  - Syncope/*physiopathology
MH  - Vascular Resistance
MH  - Ventricular Function, Left
OTO - NASA
OT  - NASA Discipline Cardiopulmonary
OT  - Non-NASA Center
FIR - Davrath, L R
IR  - Davrath LR
IRAD- CO St U, Ft Collins
EDAT- 1999/04/02 00:00
MHDA- 1999/04/02 00:01
CRDT- 1999/04/02 00:00
PHST- 1999/04/02 00:00 [pubmed]
PHST- 1999/04/02 00:01 [medline]
PHST- 1999/04/02 00:00 [entrez]
PST - ppublish
SO  - Aviat Space Environ Med. 1999 Mar;70(3 Pt 1):213-9.