Assessing the Effect of Spaceflight on the Propensity for Astronauts to Develop Disk Herniation

• Activity Number: 271
• Type: Contributed
• Date/Time: Monday, August 10, 2015 : 3:05 PM to 3:50 PM
• Sponsor: Biometrics Section
• Author(s): Alan Feiveson* and Claudia Mendez and Jeffrey T. Somers
• Companies: NASA Johnson Space Center and MEI Technologies and Wyle Science
• Keywords: NASA ; astronauts ; survival ; competing-risks ; hazard functions ; herniated disk

Abstract

A previous study reported that the risk of developing a Herniated Nucleus Pulposus (HNP) was higher in astronauts who had flown at least one mission, as compared with those in the astronaut corps who had not yet flown. However, the study did not account for the cumulative effect of multiple missions. While many HNPs occurred well into astronauts' careers or in some cases years after retirement, the higher incidence of HNPs relatively soon after completion of space missions suggests the possibility that these missions have increased the risk of HNP. To investigate this conjecture, we used a competing-risks survival model to analyze reports and dates of HNP occurrences from 330 US astronauts taking part in 789 space missions over 55 years. In this model, the outcome of interest, time from selection as an astronaut to report of HNP, is modeled as the minimum of several event times: one following each space mission, plus one influenced by astronaut training and general lifestyle irrespective of participation in actual missions. Spaceflight hazard functions have a finite integrals, thus allowing for the possibility that some astronauts might never develop mission-related HNPs.