Cardiovascular effects of anti-G suit inflation at 1 and 2 G

Montmerle, Stéphanie; Linnarsson, Dag

doi:10.1007/s00421-005-1331-6

Cited by 10 publications

(9 citation statements)

References 28 publications

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“…This device is similar to military anti-shock trousers that have been used previously during exercise (8). Antigravity suits have been shown to increase both cardiac preload and afterload, with little effect on Q (16). Before the experimental session, each subject was fitted with the suit such that, under the control condition, no pressure was exerted on the legs or abdomen; however, on inflation, the pressure was distributed around the entire lower body.…”

Section: Experimental Trialmentioning

confidence: 99%

Effect of acute increases in pulmonary vascular pressures on exercise pulmonary gas exchange

Stickland¹,

Welsh²,

Haykowsky³

et al. 2006

Journal of Applied Physiology

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The purpose of this study was to determine the effect of acute increases in pulmonary vascular pressures, caused by the application of lower-body positive pressure (LBPP), on exercise alveolar-to-arterial PO2 difference (A-aDO2), anatomical intrapulmonary (IP) shunt recruitment, and ventilation. Eight healthy men performed graded upright cycling to 90% maximal oxygen uptake under normal conditions and with 52 Torr (1 psi) of LBPP. Pulmonary arterial (PAP) and pulmonary artery wedge pressures (PAWP) were measured with a Swan-Ganz catheter. Arterial blood samples were obtained from a radial artery catheter, cardiac output was calculated by the direct Fick method, and anatomical IP shunt was determined by administering agitated saline during continuous two-dimensional echocardiography. LBPP increased both PAP and PAWP while upright at rest, and at all points during exercise (mean increase in PAP and PAWP 3.7 and 4.0 mmHg, respectively, P<0.05). There were no differences in exercise oxygen uptake or cardiac output between control and LBPP. Despite the increased PAP and PAWP with LBPP, A-aDO2 was not affected. In the upright resting position, there was no evidence of shunt in the control condition, whereas LBPP caused shunt in one subject. At the lowest exercise workload (75 W), shunt occurred in three subjects during control and in four subjects with LBPP. LBPP did not affect IP shunt recruitment during subsequent higher workloads. Minute ventilation and arterial PcO2 were not consistently affected by LBPP. Therefore, small acute increases in pulmonary vascular pressures do not widen exercise A-aDO2 or consistently affect IP shunt recruitment or ventilation.

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Section: Experimental Trialmentioning

confidence: 99%

Effect of acute increases in pulmonary vascular pressures on exercise pulmonary gas exchange

Stickland¹,

Welsh²,

Haykowsky³

et al. 2006

Journal of Applied Physiology

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“…The distance from VIPui to the right atrium determines the amount of blood available to the heart and thus the ability to maintain cardiac preload during orthostatic stress. For example inflation of MAST improves orthostatic tolerance (8,10,25,27,31), and this study demonstrates that the effect is explained, at least in part, by an upward shift of both HIP and VIPui, diminishing the gradient to the right atrium and thus facilitating filling of the heart (Fig. 4).…”

Section: Discussionmentioning

confidence: 58%

The hydrostatic pressure indifference point underestimates orthostatic redistribution of blood in humans

Petersen

Carlsen

Nielsen

et al. 2014

Journal of Applied Physiology

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The hydrostatic indifference point (HIP; where venous pressure is unaffected by posture) is located at the level of the diaphragm and is believed to indicate the orthostatic redistribution of blood, but it remains unknown whether HIP coincides with the indifference point for blood volume (VIP). During graded (± 20°) head-up (HUT) and head-down tilt (HDT) in 12 male volunteers, we determined HIP from central venous pressure and VIP from redistribution of both blood, using ultrasound imaging of the inferior caval vein (VIPui), and fluid volume, by regional electrical admittance (VIPadm). Furthermore, we evaluated whether inflation of medical antishock trousers (to 70 mmHg) affected HIP and VIP. Leaving cardiovascular variables unaffected by tilt, HIP was located 7 ± 4 cm (mean ± SD) below the 4th intercostal space (IC-4) during HUT and was similar (7 ± 3 cm) during HDT and higher (P < 0.0001) than both VIPui (HUT: 22 ± 16 cm; HDT: 13 ± 7 cm) and VIPadm (HUT: 29 ± 9 cm; HDT: 20 ± 9 cm below IC-4). During HUT antishock trousers elevated both HIP and VIPui [to 3 ± 5 cm (P = 0.028) and 17 ± 7 cm below IC-4 (P = 0.051), respectively], while VIPadm remained unaffected. By simultaneous recording of pressure and filling of the inferior caval vein as well as fluid distribution, we found HIP located corresponding to the diaphragm while VIP was placed low in the abdomen, and that medical antishock trousers elevated both HIP and VIP. The low indifference point for volume shows that the gravitational influence on distribution of blood is more profound than indicated by the indifference point for venous pressure.

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“…Photoplethysmography has been used occasionally in short-term and low level hypergravity (20–25 s) for ABP measurement [ 29 , 30 ] and SV determination [ 31 ]. Signal quality is not discussed in these studies.…”

Section: Discussionmentioning

confidence: 99%

“…In addition, the moderate jolt gave the baroreflex time to react and the backrest seat angle lowered +Gz by cos32°. Furthermore, anti-G trouser inflation increased preload, SV and afterload [ 7 , 29 , 41 ].…”

Section: Discussionmentioning

confidence: 99%

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Limitations of Stroke Volume Estimation by Non-Invasive Blood Pressure Monitoring in Hypergravity

Manen

Dussault²,

Sauvet

et al. 2015

PLoS ONE

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BackgroundAltitude and gravity changes during aeromedical evacuations induce exacerbated cardiovascular responses in unstable patients. Non-invasive cardiac output monitoring is difficult to perform in this environment with limited access to the patient. We evaluated the feasibility and accuracy of stroke volume estimation by finger photoplethysmography (SVp) in hypergravity.MethodsFinger arterial blood pressure (ABP) waveforms were recorded continuously in ten healthy subjects before, during and after exposure to +Gz accelerations in a human centrifuge. The protocol consisted of a 2-min and 8-min exposure up to +4 Gz. SVp was computed from ABP using Liljestrand, systolic area, and Windkessel algorithms, and compared with reference values measured by echocardiography (SVe) before and after the centrifuge runs.ResultsThe ABP signal could be used in 83.3% of cases. After calibration with echocardiography, SVp changes did not differ from SVe and values were linearly correlated (p<0.001). The three algorithms gave comparable SVp. Reproducibility between SVp and SVe was the best with the systolic area algorithm (limits of agreement −20.5 and +38.3 ml).ConclusionsNon-invasive ABP photoplethysmographic monitoring is an interesting technique to estimate relative stroke volume changes in moderate and sustained hypergravity. This method may aid physicians for aeronautic patient monitoring.

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Cardiovascular effects of anti-G suit inflation at 1 and 2 G

Cited by 10 publications

References 28 publications

Effect of acute increases in pulmonary vascular pressures on exercise pulmonary gas exchange

Effect of acute increases in pulmonary vascular pressures on exercise pulmonary gas exchange

The hydrostatic pressure indifference point underestimates orthostatic redistribution of blood in humans

Limitations of Stroke Volume Estimation by Non-Invasive Blood Pressure Monitoring in Hypergravity

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