Untersuchung über Kreislaufregulation während der orthostatischen Anpassungsphase

Marées, H. de; Kunitsch, G; Barbey, K.

doi:10.1007/bf01905948

Cited by 6 publications

(3 citation statements)

References 14 publications

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“…With a posture change or with application of subatmospheric pressure to the lower part of the body [lower body negative pressure (LBNP)], the shift of blood from the chest to the lower parts of the body reduces central venous pressure and stroke volume (10,54), modifying arterial pulsatility and with concomitant activation of vestibulosympathetic reflexes (48). The posture-induced carotid baroreceptor unloading evokes an increase in efferent sympathetic vasoconstrictor activity.…”

Section: Discussionmentioning

confidence: 99%

Time course analysis of baroreflex sensitivity during postural stress

Westerhof¹,

Gisolf²,

Karemaker³

et al. 2006

American Journal of Physiology-Heart and Circulatory Physiology

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Postural stress requires immediate autonomic nervous action to maintain blood pressure. We determined time-domain cardiac baroreflex sensitivity (BRS) and time delay (tau) between systolic blood pressure and interbeat interval variations during stepwise changes in the angle of vertical body axis (alpha). The assumption was that with increasing postural stress, BRS becomes attenuated, accompanied by a shift in tau toward higher values. In 10 healthy young volunteers, alpha included 20 degrees head-down tilt (-20 degrees), supine (0 degree), 30 and 70 degrees head-up tilt (30 degrees, 70 degrees), and free standing (90 degrees). Noninvasive blood pressures were analyzed over 6-min periods before and after each change in alpha. The BRS was determined by frequency-domain analysis and with xBRS, a cross-correlation time-domain method. On average, between 28 (-20 degrees) to 45 (90 degrees) xBRS estimates per minute became available. Following a change in alpha, xBRS reached a different mean level in the first minute in 78% of the cases and in 93% after 6 min. With increasing alpha, BRS decreased: BRS = -10.1.sin(alpha) + 18.7 (r(2) = 0.99) with tight correlation between xBRS and cross-spectral gain (r(2) approximately 0.97). Delay tau shifted toward higher values. In conclusion, in healthy subjects the sensitivity of the cardiac baroreflex obtained from time domain decreases linearly with sin(alpha), and the start of baroreflex adaptation to a physiological perturbation like postural stress occurs rapidly. The decreases of BRS and reduction of short tau may be the result of reduced vagal activity with increasing alpha.

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Section: Discussionmentioning

confidence: 99%

Time course analysis of baroreflex sensitivity during postural stress

Westerhof¹,

Gisolf²,

Karemaker³

et al. 2006

American Journal of Physiology-Heart and Circulatory Physiology

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“…The first circulatory event upon assumption of the upright position, either passive or active, is a gravitational displacement of blood away from the thorax filling the veins of dependent regions of the body resulting in a fall in central venous return (Hill 1895 ; Amberson 1943 ; Matzen et al 1991 ). This shift in blood volume distribution is estimated to 300–800 ml (Blomqvist and Stone 1984 ) of which 50% takes place within the first few seconds (Brown et al 1949 ; De Marées et al 1973 ; Kirsch et al 1980 ; Smith and Ebert 1990 ). The central blood volume is further challenged by an estimated 10% or ~500 ml reduction after 5 min and 15–20% or ~750 ml reduction after 10 min (Lundvall et al 1996 ) reflecting a shift in the balance between transcapillary fluid loss and gain with distension of dependent veins (Thompson et al 1928 ; Tarazi et al 1970 ; Hagan et al 1978 ; Smith and Ebert 1990 ).…”

Section: Orthostatic Stressmentioning

confidence: 99%

A definition of normovolaemia and consequences for cardiovascular control during orthostatic and environmental stress

2010

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The Frank–Starling mechanism describes the relationship between stroke volume and preload to the heart, or the volume of blood that is available to the heart—the central blood volume. Understanding the role of the central blood volume for cardiovascular control has been complicated by the fact that a given central blood volume may be associated with markedly different central vascular pressures. The central blood volume varies with posture and, consequently, stroke volume and cardiac output () are affected, but with the increased central blood volume during head-down tilt, stroke volume and do not increase further indicating that in the supine resting position the heart operates on the plateau of the Frank–Starling curve which, therefore, may be taken as a functional definition of normovolaemia. Since the capacity of the vascular system surpasses the blood volume, orthostatic and environmental stress including bed rest/microgravity, exercise and training, thermal loading, illness, and trauma/haemorrhage is likely to restrict venous return and . Consequently the cardiovascular responses are determined primarily by their effect on the central blood volume. Thus during environmental stress, flow redistribution becomes dependent on sympathetic activation affecting not only skin and splanchnic blood flow, but also flow to skeletal muscles and the brain. This review addresses the hypothesis that deviations from normovolaemia significantly influence these cardiovascular responses.

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“…The immediate circulatory event upon assumption of the upright position, either passive or active, is a gravitational displacement of blood to dependent regions of the body and a fall in venous return (Hill, 1895; Matzen et al 1991). Between 300 and 800 ml of blood is shifted from the chest to lower parts of the body during orthostatic stress (Asmussen, 1943; Sjöstrand, 1952), and ∼50% of that shift takes place within the first few seconds (De Marées et al 1973; Kirsch et al 1980). Passive head‐up tilt (HUT) decreases activity of technetium‐labelled erythrocytes ( 99m Tc) over the thorax by ∼25%, whereas the 99m Tc activity over the thigh increases (Matzen et al 1991).…”

mentioning

confidence: 99%

Orthostatic leg blood volume changes assessed by near‐infrared spectroscopy

Truijen

Kim

Krediet

et al. 2012

Experimental Physiology

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Standing up shifts blood to dependent parts of the body, and blood vessels in the leg become filled. The orthostatic blood volume accumulation in the small vessels is relatively unknown, although these may contribute significantly. We hypothesized that in healthy humans exposed to the upright posture, volume accumulation in small blood vessels contributes significantly to the total fluid volume accumulated in the legs. Considering that near-infrared spectroscopy (

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Untersuchung über Kreislaufregulation während der orthostatischen Anpassungsphase

Cited by 6 publications

References 14 publications

Time course analysis of baroreflex sensitivity during postural stress

Time course analysis of baroreflex sensitivity during postural stress

A definition of normovolaemia and consequences for cardiovascular control during orthostatic and environmental stress

Orthostatic leg blood volume changes assessed by near‐infrared spectroscopy

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