Gender differences in tibial microvascular flow responses to head down tilt and lower body negative pressure.

Jamila H Siamwala,Paul C Lee,Brandon R Macias,Alan R Hargens

doi:10.14814/phy2.13143

Jamila H Siamwala, Paul C Lee + Show 2 more

Open Access

https://doi.org/10.14814/phy2.13143

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Journal: Physiological Reports	Publication Date: Feb 1, 2017
Citations: 8	License type: CC BY 4.0

Affiliation: University of California, San Diego

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; ANOVA P < 0.05) in men but there is no significant difference between supine and HDT in women. Ten minutes of LBNP during 15o HDT restored tibial bone microvascular flows to supine levels, (from 2.2V±1.0 HDT to 1.1V ± 0.7 supine; ANOVA P < 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.

Highlights

Bone loss during long-term space missions is a major concern for fracture risk (LeBlanc et al 2000)
The average heart rate (HR) and blood pressure (BP) did not change during all test conditions
The supine systolic blood pressure (SBP) and Diastolic blood pressure (DBP) were lower by 10 mmHg in women compared to men

Summary

Introduction

Bone loss during long-term space missions is a major concern for fracture risk (LeBlanc et al 2000). The probabilities of osteoporotic fractures due to bone loss is 3.5–31% higher in women compared to 2.8–15% in men (Kanis et al 2008). Women are more susceptible to bone loss and fractures compared to men as they start with a lower peak bone mass and reach osteoporotic stage faster than men (Vogt et al 1997). Recent countermeasures such as artificial gravity measures designed to counteract microgravity effects are ineffective and may not take the gender into consideration (Ploutz-Snyder et al 2014)

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