Human Spaceflight Research

Our space medical team are carrying out research into the effects of human spaceflight on the body. A summary of their recent research is below.

This is an executive summary document of a full report submitted to the UK Civil Aviation Authority on the 30th June 2023 from the Mathematical Modelling in Medicine research group in the Division of Clinical Medicine, University of Sheffield, UK entitled Modelling the effects of gravitational forces on cardiovascular pathophysiology: the potential role of electrical analogue models. This summary document was prepared by Prof Ian Halliday and Dr Paul Morris in January 2024.

Modelling the effects of gravitational forces on cardiovascular pathophysiology: the potential role of electrical analogue models

Executive summary

Commercial sub-orbital spaceflight (CSOS) is becoming a realistic proposition. Typically, flights are relatively brief but involve exposure to significant Gx and Gz profiles. There is an appropriate concern that many individuals will be of average fitness or below and may have pathology that would exclude participation given traditional selection processes (e.g. astronaut or pilot cohorts). Such pre-existing conditions may either impair their experience or pose a health risk. The data regarding the effects of high G in this population are sparse. Computational modelling provides a mechanism to understand the association between subject parameters, including disease, and physiological changes of pressure and flow under transient gravitational loading profiles, and to predict these changes both on average for a cohort and, in principle, for an individual. Modelling is complementary to an experimental programme in which physiological parameters are measured in appropriate cohorts, and indeed such studies are important for the validation of the model.

Cardiovascular function underlies issues experienced due to poor tolerance of hyper-gravity (e.g. syncope) and disease of the cardiovascular system is common in the general population. This report provides a review of relevant literature and makes recommendations for computational model development to support the development of understanding of the influence of pathology on physiological changes due to gravitational loads to assist regulators in the construction of appropriate guidelines, and to assist individuals contemplating CSOS to make an informed decision. Preliminary feasibility studies are undertaken to demonstrate application of models towards the reporting of modification of cardiovascular risk due to the combined effect of existing pathology and medication with exposure to hyper-gravity conditions.

Topics covered by the review include principles of fundamental fluid dynamics and of model content and construction and their application to the study of cardiovascular conditions, including the regulation of the circulation associated with homeostatic mechanisms. Significantly, the use of models to consider combined effects of Gz and Gx on the cardiovascular system has not yet been addressed in the literature.

The preliminary data reported here, initially considering “healthy” subjects, demonstrates the capability of the modelling approach to extend existing frameworks to incorporate blood volume shifts due to both Gx and Gz profiles, facilitating future research to consider impairment of oxygen transfer in the pulmonary vasculature. The form of the model is illustrated in Figure 1, with compartments representing each of the four chambers of the heart and regions of the vasculature, including the systemic and pulmonary circulations. The systemic circulation is resolved into upper body, thoracic, abdominal and lower limb elements to capture the fluid shifts and pressure changes associated with the gravitational loads. The model is able to describe the variation of pressure, flow and volume within each compartment, as well as system parameters such as heart rate and cardiac output. The plots in the figure illustrate, for an average healthy subject, the predicted temporal variation of heart rate, mean arterial pressure and cardiac output over a period of ninety seconds under the application of a launch profile typical of a particular class of spacecraft.

Model outcomes are consistent with other studies reported in the literature for published load cases, including tilt table experiments. Examples of the application of a model to consider the influence of both pathology (coronary artery disease and impaired cardiac function) and a pre-existing medication regimen (diuretics) on the response to gravitational stress are included in the report.

This work has demonstrated the feasibility of applying existing modelling approaches to deliver haemodynamic outcomes appropriate for risk stratification based on clinical characterisation of individuals wishing to participate in CSOS.