{'fraction_non_alphanumeric': 0.049706039551042226, 'fraction_numerical': 0.03580972741849278, 'mean_word_length': 5.36734693877551, 'pattern_counts': {'":': 0, '<': 1, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Lower Body Negative Pressure Counters Internal Jugular Vein Engorgement during Simulated Microgravity

Recent ophthalmic evaluations of seven astronauts after six‐month missions to International Space Station (ISS) show unexpected vision problems. A microgravity induced cephalad fluid shift during long‐duration ISS missions may result in cephalic venous congestion. We hypothesized that simulated microgravity would cause internal jugular vein (IJV) engorgement but application of lower‐body negative pressure (LBNP) would mitigate this response. Six normal healthy subjects volunteered for this study (mean age: 23 years) after IRB review. Cross‐sectional area (CSA) of IJV was measured using standard ultrasound procedures. Heart rate and blood pressure were measured using an automatic blood pressure device. Data were collected during the last min of each of the following conditions: sitting (5mins), supine (5mins), head‐down‐tilt (HDT) (5mins), and HDT+LBNP (10mins with LBNP of 25 mmHg). Standard onboard ultrasound software was used to calculate IJV CSA. Data are presented as mean ± SD. RMANOVA was used to determine statistical significance with p<0.05. The IJV CSA significantly increased from the sitting (0.074±0.028 cm2) to the supine (0.602±0.189 cm2) posture, p=0.001. IJV CSA further increased when the subjects were positioned in the HDT position (1.034±0.263 cm2), p=0.002. However, when LBNP was activated during HDT, IJV CSA decreased (0.714±0.289 cm2) and was not significantly different from supine levels (p=0.259). Mean blood pressure and heart rate did not change significantly across all conditions. In conclusion, LBNP during simulated microgravity may reduce cephalad venous congestion. This project was supported by APS Frontiers in Physiology Fellowship (to SLB), NSBRI through NASA NCC 9‐58 (to BRM), and NASA grant NNX13AJ12G (to ARH).