Levels of evidence for human system risk evaluation

NASA uses a continuous risk management process to seek out new knowledge of spaceflight-induced risk to human health and performance. The evidence base that informs the risk assessments in this domain is constantly changing as more information is gleaned from a continuous human presence in space and from ongoing research. However, the limitations of this evidence are difficult to characterize because fewer than 700 humans have ever flown in space, and information comes from a variety of sources that span disciplines, including engineering, medicine, food and nutrition, and many other life sciences. The Human System Risk Board (HSRB) at NASA is responsible for assessing risk to astronauts and communicating this risk to agency decision-makers. A critical part of that communication is conveying the uncertainty regarding the understanding of the changes that spaceflight induces in human processes and the complex interactions between humans and the spacecraft. Although the strength of evidence grades is common in the academic literature, these scores are often not useful for the problems of human spaceflight. The HSRB continues to update the processes used to report the levels of evidence. This paper describes recent updates to the methods used to assign the level of evidence scores to the official risk postures and to the causal diagrams used by the HSRB.

Causal diagramming for assessing human system risk in spaceflight

For over a decade, the National Aeronautics and Space Administration (NASA) has tracked and configuration-managed approximately 30 risks that affect astronaut health and performance before, during and after spaceflight. The Human System Risk Board (HSRB) at NASA Johnson Space Center is responsible for setting the official risk posture for each of the human system risks and determining-based on evaluation of the available evidence-when that risk posture changes. The ultimate purpose of tracking and researching these risks is to find ways to reduce spaceflight-induced risk to astronauts. The adverse effects of spaceflight begin at launch and continue throughout the duration of the mission, and in some cases, across the lifetime of the astronaut. Historically, research has been conducted in individual risk "silos" to characterize risk, however, astronauts are exposed to all risks simultaneously. In January of 2020, the HSRB at NASA began assessing the potential value of causal diagramming as a tool to facilitate understanding of the complex causes and effects that contribute to spaceflight-induced human system risk. Causal diagrams in the form of directed acyclic graphs (DAGs) are used to provide HSRB stakeholders with a shared mental model of the causal flow of risk. While primarily improving communication among those stakeholders, DAGs also allow a composite risk network to be created that can be tracked and configuration managed. This paper outlines the HSRB's pilot process for this effort, the lessons learned, and future goals for data-driven risk management approaches.

Optic nerve sheath diameter measurement techniques: examination using a novel ex-vivo porcine model

BACKGROUND

Ultrasound (U/S) and MRI measurements of the optic nerve sheath diameter (ONSD) have been proposed as intracranial pressure measurement surrogates, but these methods have not been fully evaluated or standardized. The purpose of this study was to develop an ex-vivo model for evaluating ONSD measurement techniques by comparing U/S and MRI measurements to physical measurements.

METHODS

The left eye of post mortem juvenile pigs (N = 3) was excised and the subdural space of the optic nerve cannulated. Caliper measurements and U/S imaging measurements of the ONSD were acquired at baseline and following 1 cc saline infusion into the sheath. The samples were then embedded in 0.5% agarose and imaged in a 7 Tesla (7T) MRI. The ONSD was subsequently measured with digital calipers at locations and directions matching the U/S and direct measurements.

RESULTS

Both MRI and sonographic measurements were in agreement with direct measurements. U/S data, especially axial images, exhibited a positive bias and more variance (bias: 1.318, 95% limit of agreement: 8.609) compared to MRI (bias: 0.3156, 95% limit of agreement: 2.773). In addition, U/S images were much more dependent on probe placement, distance between probe and target, and imaging plane.

CONCLUSIONS

This model appears to be a valid test-bed for continued scrutiny of ONSD measurement techniques. In this model, 7T MRI was accurate and potentially useful for in-vivo measurements where direct measurements are not available. Current limitations with ultrasound imaging for ONSD measurement associated with image acquisition technique and equipment necessitate further standardization to improve its clinical utility.

Individual patient data systematic review and meta-analysis of optic nerve sheath diameter ultrasonography for detecting raised intracranial pressure: protocol of the ONSD research group

BACKGROUND

The purpose of the optic nerve sheath diameter (ONSD) research group project is to establish an individual patient-level database from high quality studies of ONSD ultrasonography for the detection of raised intracranial pressure (ICP), and to perform a systematic review and an individual patient data meta-analysis (IPDMA), which will provide a cutoff value to help physicians making decisions and encourage further research. Previous meta-analyses were able to assess the diagnostic accuracy of ONSD ultrasonography in detecting raised ICP but failed to determine a precise cutoff value. Thus, the ONSD research group was founded to synthesize data from several recent studies on the subject and to provide evidence on the diagnostic accuracy of ONSD ultrasonography in detecting raised ICP.

METHODS

This IPDMA will be conducted in different phases. First, we will systematically search for eligible studies. To be eligible, studies must have compared ONSD ultrasonography to invasive intracranial devices, the current reference standard for diagnosing raised ICP. Subsequently, we will assess the quality of studies included based on the QUADAS-2 tool, and then collect and validate individual patient data. The objectives of the primary analyses will be to assess the diagnostic accuracy of ONSD ultrasonography and to determine a precise cutoff value for detecting raised ICP. Secondly, we will construct a logistic regression model to assess whether patient and study characteristics influence diagnostic accuracy.

DISCUSSION

We believe that this IPD MA will provide the most reliable basis for the assessment of diagnostic accuracy of ONSD ultrasonography for detecting raised ICP and to provide a cutoff value. We also hope that the creation of the ONSD research group will encourage further study.

TRIAL REGISTRATION

PROSPERO registration number: CRD42012003072.

Hormonal contraception and HIV disease progression

The majority of the 15.4 million human immunodeficiency virus (HIV)-infected women worldwide are of child-bearing age and need access to contraception. Hormonal methods of contraception are safe, acceptable, and effective in preventing unwanted pregnancies. Many published studies have examined the impact of hormonal contraception on HIV disease acquisition and transmissibility. Far fewer have investigated the relationship between hormonal contraception and HIV disease progression. This review examines available data on this relationship from clinical, animal, and immunological studies. Several clinical studies suggest an overall effect but are not definitive, and the mechanisms behind HIV disease progression are unclear. Animal and immunological data suggest that immunomodulation by hormonal contraceptive methods may affect the immune response to HIV infection. Additional work is needed in this area to elucidate the possible relationship between hormonal methods for birth control and progression to acquired immunodeficiency syndrome in HIV-infected women.

[Intraperitoneal sequestration of a radium loaded tube, following perforation of the uterus, and his surgical management (author's transl)]

The authors present a case of uterineperforation due to Radiumapplication and its surgical treatment: removal of the Radiumcontainer at laparotomy without postoperative complications.