Institute of Adaptive & Spaceflight Physiology
Graz, Austria
Institut für Adaptive und Raumfahrtphysiologie
Automated Multi-Stimulation Test Device (AMSD)
 (a.k.a. 'Stargate')


>> AMSD performing head down tilt
Photo: © Karl Pilz


A test device, developed and built by IAP, for freely adjustable, automated, combined change of
 
     pitch (+70° head-up to -70° head-down tilt) and

     yaw (+30° to -30° sidewards slant).

In addition, a lower body pressure system allows for LBNP or LBPP simulated (anti-)orthostasis.
Transition between any possible combination of stimuli is reached smoothly via computer setting in <60s.

A special laser system allows for precisely reproducible positioning of electrodes for thoracic impedance monitoring. The setup has a master clock system for internal synchronization of stimulus setting and data recording, and external protocol elapsed time display for precise (blood) sample timing,

The resilience of the human cardiovascular system (blood pressure stability, orthostatic tolerance) can be studied using various techniques. Amongst those are centrifuge rides that expose humans to high G loads until they may reach a point where loss of consciousness (LOC) occurs.

Using our Automated Multi-Stimulation Test Device, we assess cardiovascular stability simply by using a combination of passive head up tilt and additional lower body suction (LBNP) of increasing magnitude, until a presyncopal point (status immediately preceding syncope, or LOC)  is reached.

Amongst the standard monitoring approaches used in these investigations are hemodynamic (blood pressure, cardiac output) and brain perfusion measurements (Doppler ultrasound a. cerebri media blood flow). 

We could show that individual tolerance times, and cardiovascular response patterns, are well reproducible. This test provides valuable information on human cardiovascular stability.

Visceral afferents influence the perception of body positioning, and vestibular stimuli alter cardiovascular regulation. In this way, investigations of regulatory aspects within a certain subsystem may be influenced by parallel changes within an intermeshed other subsystem, which may go unnoticed but potentially confound interpretation of the results - as altered baroreceptor sensitivity with adaptation to ‘weightless’ conditions  may be affected by parallel changes within vestibular, somatosensory, or visceral systems.

Our investigations are designed to define how cardiovascular effects of passive head down tilt positioning (i.e., simulated weightlessness) can be nullified by applying, at the same time, certain amounts of lower body ‚negative’ pressure.

LBNP is used to simulate  orthostasis by pooling blood in the lower extremities. Similar to upright positioning, it induces decreased cardiac preload and baroreceptor unloading as a direct hydrostatic effect.

This is followed by reflex effects: Heart rate and peripheral arterial resistance rise, and certain hormones try to stabilize the cardiovascular functioning. Increased filtration pressures in lower body parts lead to hemoconcentration, mirrored by a rise in hematocrit and plasma protein concentration and plasma mass density.

Studies have demonstrated stimulus 'dose responses'  for heart rate and dimensions, central venous pressure, stress dependent hormones, and body fluid shifts.

Antiorthostasis  (head down tilt) empties lower leg veins and causes opposed cardiovascular effects. LBNP and HDT can be applied in combination, therefore it is possible to investigate whether certain stimulus pairs's effects simply cancel out each other, given the right intensities.

Further, it is unknown if HDT / LBNP combinations produce no effect ­ i.e., balance each other ­ on cardiovascular and hormonal variables in humans.  We experimentally determine nullifying HDT-LBNP stimulus pairs to answer that question.
 
AMSD delivered to DLR
 
 
A new version of the AMST device has been built for DLR Cologne (Germany) as part of our scientific cooperation and delivered in 2009. Since then, numerous experiments were successfully carried out at DLR using this equipment.