This study had the following specific aims:
The Braslet SDTO used multiple modes of ultrasound imaging and measurements, in combination with short-term application of Braslet-M occlusive cuffs and cardiopulmonary maneuvers using both Valsalva and Mueller techniques to demonstrate and to evaluate the degree of changes in the circulating volume on orbit. This was accomplished by performing echocardiographic examinations in multiple modes, including tissue Doppler mode and ultrasound measurements of jugular and lower extremity venous vasculature. Responses to Braslet-M device under nominal conditions and also during cardiopulmonary Mueller and Valsalva maneuvers were recorded and analyzed. Identical measurements were repeated without and with Braslet-M applied and a subset of data were collected during release of the occlusion device.
A directed cardiac examination was performed to acquire the four chamber view of the heart. The primary cardiac window used for volume and Doppler was the apical four-chamber; when this view did not yield satisfactory images, the subcostal four chamber window was used. The remote guidance team made real-time decisions on what view should be used based on the limitations from each subject‘s physiology. The window that yielded the best view of all four chambers of the heart was eventually chosen. The probe was remotely guided by voice commands to achieve the desired images. Examination completeness was evaluated initially by the ground-based Braslet team consisting of two expert sonographers by viewing the real-time downlinked ultrasound video stream.
Modified Valsalva and Mueller maneuvers were performed to initiate responses throughout the protocol. These maneuvers induced increased and decreased intrathoracic pressure, and initiated physiological changes as demonstrated by changes in the cross section areas of the veins, chamber sizes of the heart, and blood flow patterns. Respiratory maneuvers were performed using an ISS drinking straw to limit extreme pressures that might be caused by exerting against a closed glottis; this approach was taken as a safety measure. The straw effectively metered the air and allowed the crewmember to time the inhalation or expiration of air across the maneuver to roughly gauge the extent of the maneuver. Participants were asked to inhale or exhale through the straw for approximately 10 seconds, starting from a moderate lung volume. These respiratory maneuvers altered the cardiac loading in manner similar to changing posture in a gravity environment.
Findings conclude that the Braslet device acutely reduced the effective circulating volume by sequestering fluid in the lower extremities, as directly observed by vascular ultrasound and supported by the reduced preload indexes measured by echocardiography. Vascular ultrasound confirmed reduced distention of the jugular venous system and increased sensitivity of the jugular vein area to thoracic maneuvers. These findings combined with subjective comments from crewmembers, suggest that the relative cranial venous insufficiency caused by microgravity is partially alleviated by the Braslet device.
These respiratory maneuvers were shown to cause statistically significant hemodynamic effects. A statistically significant reduction in jugular venous (IJV) filling was also observed during Braslet application, which coupled with negative airway pressure to consistently collapse the IJV.
Remotely guided ultrasound provided an effective and objective means of measuring the physiological effects of the Braslet and produced data quality that was superior to previous investigations in space. Fourteen of eighty-one conditions (27 parameters measured at baseline, Valsalva, and Mueller maneuver) were significantly different when the Braslet-M cuff was applied. Seven of twenty-seven parameters were found to respond differently to respiratory maneuvers depending on the presence or absence of thigh compression. The Valsalva and Mueller maneuvers appeared to enhance the ability at the microgravity bedside to determine volume status.
|Mission||Launch/Start Date||Landing/End Date||Duration|
|Expedition 16||10/10/2007||04/19/2008||192 days|
|Expedition 18||10/12/2008||04/17/2009||187 days|
|Expedition 19||03/26/2009||10/11/2009||199 days|