Sleep disruption is a common and important problem in space flight. There are a wide range of environmental and therapeutic interventions which could ameliorate the negative effects of space flight on sleep, and several new interventions are being investigated. However, the current reality is that we are unable to adequately assess these countermeasures. CASPER (Cardiac Adapted Sleep Parameters Electrocardiogram Recorder) provides a simple and accurate means of detecting sleep parameters and disturbance by assessing cardiac autonomic activity from an electrocardiogram (ECG). CASPER will provide an efficient method of monitoring and cataloging incidents of disturbance during an astronauts sleep period, based primarily upon the ECG activity, while being augmented by other physiological parameters. These measurements will be provided by existing hardware in the form of a fitted, adaptable and available physiological monitoring system. In tandem with a specialised “sleep diary” and diagnostic programme, these individual tools provide the clinician with both objective and subjective data. This culminates in an ideally practical, portable and non-invasive system called CASPER which will monitor and record sleep disruption, which is specially adapted for the microgravity and space flight environment.
Since sleep disruption has been identified as a problem in space flight, on some shuttle missions, up to 50% of the crew take hypnotic medication for several days inflight, suggesting that insomnia is a prevalent symptom among astronauts. The results of previous research on both short and long duration missions suggests that approximately 25% of crew members experience dramatic impairment in the quantity and/or quality of sleep. Astronauts average 6 hours of sleep per night in orbit. They must also endure an orbital dawn every 90 minutes. These and other factors, which affect the sleep and circadian rhythm of orbiting astronauts, have been studied on previous missions. There is currently obvious disruption to sleep on a routine basis in space flight, both on long and short duration missions. Several studies agree that it merits routine monitoring, both to study the mechanisms involved in sleep disruption in microgravity and the need for a method of monitoring the effect of interventions to try and solve the problems. However, in reality at the moment it is difficult to assess the efficacy of any given intervention. Current methodology for monitoring sleep requires complex and dedicated polysomnographic equipment as was used on the NASA-Mir Increment missions and Neurolab. It simply cannot be used as a routine part of biomedical monitoring inflight. Future countermeasures will need to be based and developed on the basis of evidence-based intervention, which current methods don’t support, to collect the data required.
The objective of this project is to trial and test a novel and accurate method of monitoring sleep disturbance and future countermeasures and interventions. It combines several different aspects, both objective physiological data and subjective input, which will lead to the development of a monitoring system called CASPER. It is designed to eliminate the limits of previous orbital sleep studies by removing the need for the presence of full polysomnographic equipment, by instead relying upon an assessment of cardiac autonomic activity from an ECG. The adoption of a single-lead ECG has also been verified as a useful diagnostic tool in the detection of sleep pathology in the domestic medical community. The equipment and necessary software for the development of this project is already available and has proven valuable in other clinical settings. The objective also takes significant steps towards addressing one of the primary needs identified by NASA in their critical path roadmap for the advancement of long term human space flight including the need for a “portable and non-intrusive” system capable of monitoring sleep disruption, loss and subsequent interventions.
In developing the necessary hardware for the experiment, it was decided to use off the shelf commercial technology for several reasons, including international safety accreditation (which should maximize the compliance for the system to be used in the space station environment), development time and ergonomic ease of use. The primary system chosen is the Lifeshirt by Viviometrics. This is a continuous ambulatory monitoring system (FDA and CE approved) that enables the analyzing and reporting of health data. The garment is a fitted lightweight shirt with embedded sensors. Respiratory function can be measured through sensor bands integrated into the shirt around the patient’s chest and abdomen. This will enable the clinician to gain even more physiological data from the astronaut during sleep. A three-lead, single channel ECG will monitor cardiac activity and an accelerometer will record patient posture and activity level. This system also offers the potential of attaching optional peripheral devices to measure blood pressure and oxygen saturation. The attached PDA will then efficiently store the astronaut’s physiologic data on a compact flash memory card. The flight surgeon will subsequently be able to correlate subjective astronaut input with objectively measured physiologic parameters on a PC laptop. |
PROJECT C.A.S.P.E.R