2007, Piran, Slovenia

Gravitational Physiology
CARDIOVASCULAR RESPONSES TO LOWER BODY
NEGATIVE PRESSURE IN ATHLETES AND NON-ATHLETES
Masami Hirashita 1 , Yoko Kajiwara 2 , Saburo Yokokura 3 and Shigeru Okada 1
1 Department of Social Welfare, Kinjyo University, Japan
2 The Faculty of Education, Bunkyo University, Japan
3 School of Science and Engineering, Meisei University, Japan.
Contact person: masami12@po.incl.ne.jp
INTRODUCTION
During exercise and heat exposure, cutaneous blood flow increases in response to
centrally-mediated thermoregulatory drive. However, even during such states,
cutaneous vasoconstriction, mediated by the baroreceptor reflex, can occur when
various stimuli lower blood pressure. Indeed, this is a rather strong reflex (6) , which is
also powerfully induced when the blood volume is lowered following extended
sweating. Conversely, following regular endurance training, the blood and plasma
volumes are increased as part of the adaptation process. This is similar to that seen
with heat acclimatisation, and is associated with a significant and repeated increase in
intramuscular heat production, which also elevates body temperature. The
corresponding increase in blood volume acts to buffer blood pressure reductions, and
reduce the effect of the baroreceptor reflex on peripheral resistance vessels.
During endurance exercise that produces an elevation in body temperature, finger
blood flow increases, particularly at sites with well developed arteriovenous
anastomoses, thereby promoting heat dissipation (3,4) . It is believed that during such
exercise, two conflicting cutaneous vascular responses take place simultaneously.
First, there is cutaneous vasodilation caused by rise in body temperature. Second,
there is cutaneous vasoconstriction due to non-thermal factors (e.g. baroreflex). There
is an antagonism between this vasodilation and vasoconstriction, which lasts for some
time, and it resembles the cardiovascular response to lower body negative pressure
(LBNP) when body temperature is rising.
The adaptation effects following endurance training (i.e. increased blood volume and
cardiac output), may result in a better defence of blood pressure during an exercise
tolerance test. Therefore, there is a possibility for the baroreflex to be less powerfully
activated, even during training, and this reflex may thus become weakened. There are
two opposing views on this within the literature. One view is that endurance training
results is a less powerful baroreflex when LBNP is applied at rest (7) . The other view is
that endurance training has no influence on the baroreflex (5) . These differences of
opinion may be attributed to variations in the form of exercise and ambient
temperature during testing. However, the biggest factor seems to lie in different
interpretations of muscle blood flow and cutaneous blood flow. For instance, finger
blood flow, measured using venous occlusion plethysmography, reflects cutaneous
blood flow, while forearm blood flow, measured in the same manner, reflects muscle
blood flow. However, if the forearm blood flow serves for cutaneous blood flow, or if
it is measured by laser Doppler flowmetry, cutaneous vasoconstriction may not appear
clearly in response to the baroreceptor reflex. In our study, forearm blood flow was
simultaneously measured using laser Doppler flowmetry and venous occlusion
plethysmography, while finger blood flow was measured using plethysmography.
LBNP was applied, and we examined how endurance training influences peripheral
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