title: Gender differences in tibial microvascular flow responses to head down tilt and lower body negative pressure.
abstract: The purpose of the investigation was to study lower body negative pressure recovery in response to head down tilt position in men and women. The study examined the primary hypothesis that tibial bone microvascular flow responses to HDT and lower body negative pressure (LBNP) differ in women and men. Nine women and nine men between 20 to 30 years of age participated in the study. Tibial microvascular flow, head and tibial oxygenation and calf circumference were measured using photoplethysmography (PPG), near-infrared spectroscopy (NIRS) and strain gauge plethysmography (SGP), respectively, during sitting (control baseline), supine, 15° HDT, and 15° HDT with 25 mmHg LBNP Tibial microvascular flow with HDT increased by 57% from supine position (from 1.4V ± 0.7 to 2.2V ± 1.0 HDT; ANOVAP< 0.05) in men but there is no significant difference between supine and HDT in women. Ten minutes of LBNP during 15oHDT restored tibial bone microvascular flows to supine levels, (from 2.2V±1.0 HDT to 1.1V ± 0.7 supine; ANOVAP< 0.05) in men but not in women. These data support the concept that there are gender specific microvascular responses to a fluid-shift countermeasure such as LBNP Thus, gender differences should be considered while developing future countermeasure strategies to headward fluid shifts in microgravity.
authors.affiliation: Department of Orthopedic Surgery, University of California, San Diego, California jsiamwala@ucsd.edu.
authors.forename: Jamila H
authors.identifier: http://orcid.org/0000-0001-9482-9183
authors.initials: JH
authors.lastname: Siamwala
authors.affiliation: Department of Orthopedic Surgery, University of California, San Diego, California.
authors.forename: Brandon R
authors.initials: BR
authors.lastname: Macias
authors.affiliation: Department of Orthopedic Surgery, University of California, San Diego, California.
authors.forename: Paul C
authors.initials: PC
authors.lastname: Lee
authors.affiliation: Department of Orthopedic Surgery, University of California, San Diego, California.
authors.forename: Alan R
authors.initials: AR
authors.lastname: Hargens
mesh_terms: D000328:Adult; D001794:Blood Pressure / Q000502:physiology; D005260:Female; D018475:Head-Down Tilt; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D008150:Lower Body Negative Pressure; D008297:Male; D055806:Microvessels / Q000502:physiology*; D017156:Photoplethysmography; D012039:Regional Blood Flow / Q000502:physiology*; D012727:Sex Characteristics; D019265:Spectroscopy, Near-Infrared; D013977:Tibia / Q000098:blood supply*; D055815:Young Adult
keywords: Bone microvascular flow; head down tilt; limb girth; lower body negative pressure; oxygenation; photoplethysmography; spaceflight