Development of a plethysmography system for its use on the International Space Station

Drain Brain (Space Dreams) is a project approved by the Italian Space Agency (ASI) and aims to develop a payload to be used by the European Space Agency (ESA) astronaut of Italian nationality Samantha Cristoforetti, during her mission on the International Space Station (ISS). Since the gravitational gradient is the major component to face when considering the physiology of venous return, there is a growing interest in understanding the mechanisms ensuring the heart filling in the absence of gravity for astronauts who perform long-term space missions. Our aim is to characterize the venous return by means of a novel application of strain-gauge plethysmography. Strain-gauge plethysmography is a non-invasive technique that measures variations in electrical parameters associated with changes in blood volume, recorded through a sensor encircling any cylindrical segment of the body. In our experiment aboard the ISS, the measurement of venous blood flow will be carried out by measuring the variation of the circumference of neck, calf of the leg, and forearm under different respiratory conditions via a three-channel plethysmography system. Basal spirometry will be used to change such respiratory conditions and some physical exercises will be also performed during the experimental session. Concerning spirometry, we will make use of the Pulmonary Function System (PFS), which is already available on the ISS. The plethysmography system uses a capacitive sensor for which the capacitance increases when stretched. The sensor will be electrically connected to a portable electronic unit (PEU) to record changes of blood volume over time (volume-time curves will be used to assess the physiology of venous return of the subject). The PEU is in a vented container and will be worn by a crew member during the experiment by means of a non removable Nomex® belt to be fixed around astronaut’s waist. Signal conditioning, data acquisition and storage is performed by a custom electronic board that has been developed by the University of Ferrara and the INFN (Istituto Nazionale di Fisica Nucleare), Italy. The PEU contains non-rechargeable Li-ion batteries to provide power supply to the instrument. Because of its easy portability, small footprint, and non-invasiveness, the proposed device is an ideal tool for use aboard the International Space Station.