Lower-body negative pressure restores leg bone microvascular flow to supine levels during head-down tilt

2015 ◽  
Vol 119 (2) ◽  
pp. 101-109 ◽  
Author(s):  
Jamila H. Siamwala ◽  
Paul C. Lee ◽  
Brandon R. Macias ◽  
Alan R. Hargens
Keyword(s):  
Negative Pressure ◽  
Repeated Measures ◽  
Simulated Microgravity ◽  
Near Infrared ◽  
Lower Body Negative Pressure ◽  
Lower Body ◽  
Calf Circumference ◽  
Fluid Shift ◽  
Microvascular Flow ◽  
Flow Head

Skeletal unloading and cephalic fluid shifts in microgravity may alter the bone microvascular flow and may be associated with the 1-2% bone loss per month during spaceflight. The purpose of this study was to determine if lower-body negative pressure (LBNP) can prevent microgravity-induced alterations of tibial microvascular flow. Head-down tilt (HDT) simulates the cephalad fluid shift and microvascular flow responses that may occur in microgravity. We hypothesized that LBNP prevents HDT-induced increases in tibial microvascular flow. Tibial bone microvascular flow, oxygenation, and calf circumference were measured during 5 min sitting, 5 min supine, 5 min 15° HDT, and 10 min 15° HDT with 25 mmHg LBNP using photoplethysmography (PPG), near-infrared spectroscopy (NIRS), and strain-gauge plethysmography (SGP). Measurements were made simultaneously. Tibial microvascular flow increased by 36% with 5 min 15° HDT [2.2 ± 1.1 V; repeated-measures ANOVA (RMANOVA) P < 0.0001] from supine (1.4 ± 0.8 V). After 10 min of LBNP in the 15° HDT position, tibial microvascular flow returned to supine levels (1.1 ± 0.5 V; RMANOVA P < 0.001). Tibial oxygenation did not change significantly during sitting, supine, HDT, or HDT with LBNP. However, calf circumference decreased with 5 min 15° HDT (−0.7 ± 0.4 V; RMANOVA P < 0.0001) from supine (−0.5 ± 0.4 V). However, with LBNP calf circumference returned to supine levels (−0.4 ± 0.1 V; RMANOVA P = 0.002). These data establish that simulated microgravity increases tibial microvascular flow and LBNP prevents these increases. The results suggest that LBNP may provide a suitable countermeasure to normalize the bone microvascular flow during spaceflight.

Daily generation of a footward fluid shift attenuates ocular changes associated with head-down tilt bed rest

2020 ◽  
Vol 129 (5) ◽  
pp. 1220-1231
Author(s):  
Justin S. Lawley ◽  
Gautam Babu ◽  
Sylvan L. J. E. Janssen ◽  
Lonnie G. Petersen ◽  
Christopher M. Hearon ◽  
...  
Keyword(s):  
Negative Pressure ◽  
Lower Body Negative Pressure ◽  
Bed Rest ◽  
Lower Body ◽  
Fluid Shift ◽  
Gravitational Gradients ◽  
Ocular Changes

Choroid measurements appear to be sensitive to changes in gravitational gradients, as well as periods of head-down tilt (HDT) bed rest, suggesting that they are potential indicators of early ocular remodeling and could serve to evaluate the efficacy of countermeasures for SANS. Eight hours of lower body negative pressure (LBNP) daily attenuates the choroid expansion associated with 3 days of strict −6° HDT bed rest, indicating that LBNP may be an effective countermeasure for SANS.

scholarly journals Nightly Sustained Lower Body Negative Pressure Attenuates Reductions in Cerebral Blood Flow Associated with Simulated Microgravity

2021 ◽  
Vol 35 (S1) ◽  
Author(s):  
Christopher Hearon ◽  
Katrin Dias ◽  
James Macnamara ◽  
John Marshall ◽  
James Leidner ◽  
...  
Keyword(s):  
Blood Flow ◽  
Cerebral Blood Flow ◽  
Negative Pressure ◽  
Simulated Microgravity ◽  
Lower Body Negative Pressure ◽  
Lower Body

Delayed vasoconstrictor response to venous pooling in the calf is associated with high orthostatic tolerance to LBNP

2010 ◽  
Vol 109 (4) ◽  
pp. 996-1001 ◽  
Author(s):  
T. Hachiya ◽  
M. L. Walsh ◽  
M. Saito ◽  
A. P. Blaber
Keyword(s):  
Blood Volume ◽  
Negative Pressure ◽  
Near Infrared ◽  
Lower Body Negative Pressure ◽  
Orthostatic Stress ◽  
Orthostatic Tolerance ◽  
Lower Body ◽  
High Tolerance ◽  
Venous Pooling ◽  
Vasoconstrictor Response

Central blood volume loss to venous pooling in the lower extremities and vasoconstrictor response are commonly viewed as key factors to distinguish between individuals with high and low tolerance to orthostatic stress. In this study, we analyzed calf vasoconstriction as a function of venous pooling during simulated orthostatic stress. We hypothesized that high orthostatic tolerance (OT) would be associated with greater vasoconstrictor responses to venous pooling compared with low OT. Nineteen participants underwent continuous stepped lower body negative pressure at −10, −20, −30, −40, −50, and −60 mmHg each for 5 min or until exhibiting signs of presyncope. Ten participants completed the lower body negative pressure procedure without presyncope and were categorized with high OT; the remaining nine were categorized as having low OT. Near-infrared spectroscopy measurements of vasoconstriction (Hachiya T, Blaber A, Saito M. Acta Physiologica 193: 117–127, 2008) in calf muscles, along with heart rate (HR) responses for each participant, were evaluated in relation to calf blood volume, estimated by plethysmography. The slopes of this relationship between vasoconstriction and blood volume were not different between the high- and low-tolerance groups. However, the onset of vasoconstriction in the high-tolerance group was delayed. Greater HR increments in the low-tolerance group were also observed as a function of lower limb blood pooling. The delayed vasoconstriction and slower HR increments in the high-tolerance group to similar venous pooling in the low group may suggest a greater vascular reserve and possible delayed reduction in venous return.

Association of sex and age with responses to lower-body negative pressure

1988 ◽  
Vol 65 (4) ◽  
pp. 1752-1756 ◽  
Author(s):  
M. A. Frey ◽  
G. W. Hoffler
Keyword(s):  
Heart Rate ◽  
Negative Pressure ◽  
Lower Body Negative Pressure ◽  
Peripheral Resistance ◽  
Older Men ◽  
Lower Body ◽  
Fluid Shift ◽  
Arterial Blood ◽  
Age Related ◽  
Older Subjects

Responses of 21 women and 29 men (29-56 yr of age) to -50 Torr lower body negative pressure (LBNP) were examined for differences due to sex or age. Responses to LBNP were normal, including fluid shift from thorax to lower body, increased heart rate and peripheral resistance, and decreased stroke volume, cardiac output, and Heather index of ventricular function. Mean arterial blood pressure did not change. Comparison of responses of the women to responses of an age-matched subset of the men (n = 26) indicated the men had larger relative increases in calf circumference and greater increases in peripheral resistance during LBNP than the women, whereas the women experienced greater increases in thoracic impedance and heart rate. Analyses of responses of the 29 men for age-related differences indicated older subjects had greater increases in peripheral resistance and less heart rate elevation in response to LBNP (P less than 0.05 for all differences, except sex-related heart rate difference, where P less than 0.10). Based on these data and the data of other investigators, we hypothesize the age-related circulatory differences in response to LBNP are due to a reduction in vagal response and a switch to predominant sympathetic nervous system influence in older men. We cannot exclude the possibility that diminished responsiveness in the afferent arm of the baroreceptor reflex also plays a role in the attenuated heart rate response of older men to LBNP.

scholarly journals Mobile Lower Body Negative Pressure Suit as an Integrative Countermeasure for Spaceflight

2019 ◽  
Vol 90 (12) ◽  
pp. 993-999 ◽  
Author(s):  
Lonnie G. Petersen ◽  
Alan Hargens ◽  
Elizabeth M. Bird ◽  
Neeki Ashari ◽  
Jordan Saalfeld ◽  
...  
Keyword(s):  
Mechanical Loading ◽  
Negative Pressure ◽  
Lower Body Negative Pressure ◽  
Cardiovascular Response ◽  
Axial Loading ◽  
The Body ◽  
Lower Body ◽  
Fluid Shift ◽  
Cross Sectional

BACKGROUND: Persistent headward fluid shift and mechanical unloading cause neuro-ocular, cardiovascular, and musculoskeletal deconditioning during long-term spaceflight. Lower body negative pressure (LBNP) reintroduces footward fluid shift and mechanical loading.METHODS: We designed, built, and tested a wearable, mobile, and flexible LBNP device (GravitySuit) consisting of pressurized trousers with built-in shoes to support ground reaction forces (GRF) and a thoracic vest to distribute load to the entire axial length of the body. In eight healthy subjects we recorded GRF under the feet and over the shoulders (Tekscan) while assessing cardiovascular response (Nexfin) and footward fluid shift from internal jugular venous cross-sectional area (IJVa) using ultrasound (Terason).RESULTS: Relative to normal bodyweight (BW) when standing upright, increments of 10 mmHg LBNP from 0 to 40 mmHg while supine induced axial loading corresponding to 0%, 13 ± 3%, 41 ± 5%, 75 ± 11%, and 125 ± 22% BW, respectively. Furthermore, LBNP reduced IJVa from 1.12 ± 0.3 cm2 to 0.67 ± 0.2, 0.50 ± 0.1, 0.35 ± 0.1, and 0.31 ± 0.1 cm2, respectively. LBNP of 30 and 40 mmHg reduced cardiac stroke volume and increased heart rate while cardiac output and mean arterial pressure were unaffected. During 2 h of supine rest at 20 mmHg LBNP, temperature and humidity inside the suit were unchanged (23 ± 1°C; 47 ± 3%, respectively).DISCUSSION: The flexible GravitySuit at 20 mmHg LBNP comfortably induced mechanical loading and desired fluid displacement while maintaining the mobility of hips and knee joints. The GravitySuit may provide a feasible method to apply low-level, long-term LBNP without interfering with daily activity during spaceflight to provide an integrative countermeasure.Petersen LG, Hargens A, Bird EM, Ashari N, Saalfeld J, Petersen JCG. Mobile lower body negative pressure suit as an integrative countermeasure for spaceflight. Aerosp Med Hum Perform. 2019; 90(12):993–999.

Sign in / Sign up

Export Citation Format

Share Document