Retrograde arterial leg blood flow during tilt-back from a head-up posture: importance of capacitive flows when arterial pressure changes

Sheriff, Don D.; Nådland, Inger Helene; Toska, Karin

doi:10.1152/japplphysiol.01184.2009

Cited by 3 publications

(2 citation statements)

References 8 publications

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“…The initial tilt-induced fluctuations of AP are dependent on 1) the reference point of AP in relation to the hydrostatic indifference point (11), 2) capacitive flows with AP changes (22), and 3) changed efficiency of the venous muscle pump between postures during dynamic leg exercise (9,15). The return of AP to a new steady state follows reflexive changes in HR and vascular tone.…”

Section: Discussionmentioning

confidence: 99%

Time courses of central hemodynamics during rapid changes in posture

Sundblad

Spaak

Kaijser

2014

Journal of Applied Physiology

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Changes in posture cause blood volume redistribution, affecting cardiac filling and stroke volume (SV). We hypothesized that the time courses of ventricular filling would differ between the right and left ventricle during a rapid (2 s) tilt and that changes in right ventricular filling pressure would be more swift because of the direct coupling to the systemic circulation. We further hypothesized that the transient imbalance between right and left ventricular filling pressure would influence left ventricular SV changes. Right atrial pressure (RAP), pulmonary capillary wedge pressure (PCWP), left ventricular stroke volume, heart rate, and arterial pressure were recorded beat-by-beat during rapid tilts from supine to upright positions and back again, during rest and dynamic 100-W leg exercise. RAP changes had a faster time course than PCWP during down-tilts, both during rest and exercise (1 ± 1 vs. 6 ± 2 s and 2 ± 2 vs. 6 ± 2 s, respectively; P < 0.05). This discrepancy caused a transient decrease in the end-diastolic pressure difference between the right and left ventricle. The decreased pressure difference in diastole impeded left ventricular filling because of ventricular interdependence, causing SV to fall transiently. The mechanisms of ventricular interdependence were also involved in reverse during up-tilt, where SV was maintained for 2-3 s despite falling PCWP. Furthermore, the decrease in RAP during up-tilt in the resting condition was biphasic with an initial fast and a second slower component, which might suggest the effect of venous valves. This was not seen during dynamic leg exercise where blood pooling is prevented by the venous muscle pump.

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Section: Discussionmentioning

confidence: 99%

Time courses of central hemodynamics during rapid changes in posture

Sundblad

Spaak

Kaijser

2014

Journal of Applied Physiology

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“…a push-pull effect occurs 7 . The literature explains this increased regulatory response through the significant contribution of sympathetic activity 8 . A list of states deviating from the Earthly gravity is complemented by weightlessness and microgravity, i.e.…”

Section: Introductionmentioning

confidence: 99%

Development and evaluation of a novel system for inducing orthostatic challenge by tilt tests and lower body negative pressure

Dziuda

Krej

Śmietanowski

et al. 2018

Sci Rep

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Lower body negative pressure (LBNP) is a method derived from space medicine, which in recent years has been increasingly used by clinicians to assess the efficiency of the cardiovascular regulatory mechanisms. LBNP with combined tilt testing is considered as an effective form of training to prevent orthostatic intolerance. We have developed a prototype system comprising a tilt table and LBNP chamber, and tested it in the context of the feasibility of the device for assessing the pilots’ efficiency. The table allows for controlled tilting in the range from −45 to +80° at the maximum change rate of 45°/s. The LBNP value can smoothly be adjusted down to −100 mmHg at up to 20 mmHg/s. 17 subjects took part in the pilot study. A 24-minute scenario included −100 mmHg supine LBNP, head up tilt (HUT) and −60 mmHg LBNP associated with HUT, separated by resting phases. The most noticeable changes were observed in stroke volume (SV). During supine LBNP, HUT and the combined stimulus, a decrease of the SV value by 20%, 40% and below 50%, respectively, were detected. The proposed system can map any pre-programed tilt and LBNP profiles, and the pilot study confirmed the efficiency of performing experimental procedures.

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Effect of an acute increase in central blood volume on cerebral hemodynamics

Ogoh

Hirasawa

Raven

et al. 2015

American Journal of Physiology-Regulatory, Integrative and Comp

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Systemic blood distribution is an important factor involved in regulating cerebral blood flow (CBF). However, the effect of an acute change in central blood volume (CBV) on CBF regulation remains unclear. To address our question, we sought to examine the CBF and systemic hemodynamic responses to microgravity during parabolic flight. Twelve healthy subjects were seated upright and exposed to microgravity during parabolic flight. During the brief periods of microgravity, mean arterial pressure was decreased (-26 ± 1%, P < 0.001), despite an increase in cardiac output (+21 ± 6%, P < 0.001). During microgravity, central arterial pulse pressure and estimated carotid sinus pressure increased rapidly. In addition, this increase in central arterial pulse pressure was associated with an arterial baroreflex-mediated decrease in heart rate (r = -0.888, P < 0.0001) and an increase in total vascular conductance (r = 0.711, P < 0.001). The middle cerebral artery mean blood velocity (MCA Vmean) remained unchanged throughout parabolic flight (P = 0.30). During microgravity the contribution of cardiac output to MCA Vmean was gradually reduced (P < 0.05), and its contribution was negatively correlated with an increase in total vascular conductance (r = -0.683, P < 0.0001). These findings suggest that the acute loading of the arterial and cardiopulmonary baroreceptors by increases in CBV during microgravity results in acute and marked systemic vasodilation. Furthermore, we conclude that this marked systemic vasodilation decreases the contribution of cardiac output to CBF. These findings suggest that the arterial and cardiopulmonary baroreflex-mediated peripheral vasodilation along with dynamic cerebral autoregulation counteracts a cerebral overperfusion, which otherwise would occur during acute increases in CBV.

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Retrograde arterial leg blood flow during tilt-back from a head-up posture: importance of capacitive flows when arterial pressure changes

Cited by 3 publications

References 8 publications

Time courses of central hemodynamics during rapid changes in posture

Time courses of central hemodynamics during rapid changes in posture

Development and evaluation of a novel system for inducing orthostatic challenge by tilt tests and lower body negative pressure

Effect of an acute increase in central blood volume on cerebral hemodynamics

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