Electrical admittance for filling of the heart during lower body negative pressure in humans

Cai, Yan; Holm, Søren; Jenstrup, M; Strømstad, M.; Eigtved, Annika; Warberg, Jørgen; Højgaard, Liselotte; Friberg, Lars; Secher, Niels H.

doi:10.1152/jappl.2000.89.4.1569

Cited by 62 publications

(94 citation statements)

References 22 publications

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“…To evaluate the volume within the thoracic region, including the central vessels and the heart, electrodes are positioned at the right side of the neck and as high as possible in the left mid-axillary line with an approximate 5 cm distance between each pair. With this arrangement of the electrodes, high correlations (r > 0.9) are derived to changes in the thoracic blood volume 10,60,67 and near perfectly matching values are obtained in experimental haemorrhage studies (Fig. 3).…”

Section: Electrical Admittancesupporting

confidence: 70%

“…Changes in the distribution of red cells are illustrated either by placement of a collimator 10 or, more elegantly, by a beta camera or positron emission tomography. 67 With such a determination and appropriate definition of regions of interest, separate values are obtained for different parts of the lung or for the lungs as a whole. Equally, the amount of blood within the heart can be quantified, although it may be difficult to make a clear distinction between the heart and the liver.…”

Section: Imaging Techniquesmentioning

confidence: 99%

“…For instance, during HUT 10 and LBNP, 67 changes in CBV are reflected accurately by changes in electrical admittance. The delicate changes in the distribution of blood following exercise can also be followed.…”

Section: Electrical Admittancementioning

confidence: 99%

“…over the legs) during HUT and it is demonstrated that the fluid accumulating in the legs is recruited from the thoracic region. 10,67 A direct evaluation of the electrical properties of the thorax is made during thoracocentesis, where the change in fluid volume is known. The correlation coefficient between changes in thoracic impedance and the amount of fluid withdrawn is close to perfect (r = 0.97).…”

Section: Electrical Admittancementioning

confidence: 99%

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Normovolaemia defined by central blood volume and venous oxygen saturation

Secher

Lieshout

2005

Clin Exp Pharma Physio

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Section: Electrical Admittancesupporting

confidence: 70%

Section: Imaging Techniquesmentioning

confidence: 99%

Section: Electrical Admittancementioning

confidence: 99%

Section: Electrical Admittancementioning

confidence: 99%

See 2 more Smart Citations

Normovolaemia defined by central blood volume and venous oxygen saturation

Secher

Lieshout

2005

Clin Exp Pharma Physio

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“…Total vascular conductance (TVC) was calculated as Q divided by MAP. To assess changes in the CBV during HUT, electrical thoracic admittance (TA) was measured using 200 µA at 1.5 kHz (C-guard, Danmeter, Odense, Denmark) [15,16]. A malleable lead neck collar that encircled the anterior 2/3 of the neck of each subject was used for the application of NP and NS [1,17].…”

Section: Methodsmentioning

confidence: 99%

Carotid-Cardiac Baroreflex Function Does Not Influence Blood Pressure Regulation during Head-Up Tilt in Humans

et al. 2006

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Abstract:The influence of the carotid-cardiac baroreflex on blood pressure regulation was evaluated during supine rest and 40° head-up tilt (HUT) in 9 healthy young subjects with and without full cardiac vagal blockade. The carotid baroreflex responsiveness, or maximal gain (G MAX ), was assessed from the beatto-beat changes in heart rate (HR) and mean arterial pressure (MAP) by the variable neck pressure and suction technique ranging in pressure from +40 to -80 Torr, with and without glycopyrrolate (12.0 ± 1.0 µg/kg body weight; mean ± SE). In the supine position, glycopyrrolate increased the HR to 91 ± 3 bpm, from 54 ± 3; MAP to 89 ± 2 mmHg, from 76 ± 2; and cardiac output to 6.8 ± 0.3 l·min -1 , from 4.9 ± 0.3 (P < 0.05). The G MAX of the carotid baroreflex control of HR was reduced to -0.06 ± 0.01 bpm·mmHg -1 , from -0.30 ± 0.02 (P < 0.05) with no significant effect on the G MAX of the carotid baroreflex control of MAP. During HUT the carotid baroreflex control of MAP was unchanged, though the G MAX of the carotid baroreflex control of HR was increased (P < 0.05). During HUT, central blood volume, assessed by electrical thoracic admittance, and total vascular conductance were decreased with and without glycopyrrolate. Furthermore, glycopyrrolate reduced G MAX of the carotid baroreflex control of HR during HUT (P < 0.05) with no significant effect on G MAX of the carotid baroreflex control of MAP. These data suggest that during supine rest and HUT-induced decreases in central blood volume, the carotid baroreflex control of HR is mediated primarily via parasympathetic activity. Furthermore, the maintenance of arterial blood pressure during postural stress is primarily mediated by arterial and cardiopulmonary reflex regulation of sympathetic activity and its effects on the systemic vasculature.Key words: arterial blood pressure, baroreflex, central blood volume, heart rate.The balance between the contribution of the carotid-cardiac and the carotid-vasomotor reflex arms to the carotid baroreflex (CBR) responses to changes in arterial pressure is altered during upright seating compared to the supine position [1]. This change in balance identified that the major adjustment to changes in posture primarily involved the carotid-vasomotor arm of the reflex [1]. This finding confirmed earlier work involving reflex adjustments to reductions in central blood volume (CBV) induced by lower body negative pressure (LBNP) [2]. Furthermore, in average healthy and fit young adults the maximal gains (G MAX ) of the carotid-cardiac and the carotid-vasomotor arms of the CBR were augmented during decreases in CBV [3,4] induced by head-up tilt (HUT) or LBNP [5,6].However, patients who exhibit parasympathetic dysfunction during an orthostatic challenge also exhibit decreased vasomotor responsiveness [7][8][9], indicating that a dysfunction of the carotid-vasomotor arm may be the underlying mechanism of the postural syncope despite the parasympathetic dysfunction. These findings raise the question of whether parasympathetic dysfunctio...

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Techniques of cardiac output measurement during liver transplantation: Arterial pulse wave versus thermodilution

et al. 2009

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In this study, we compared continuous cardiac output (CO) obtained from the femoral arterial pressure by simulation of an aortic input impedance model [model-simulated cardiac output (MCO)] to thermodilution cardiac output (TDCO) determined by bolus injection during liver transplantation. Both variables were measured in 39 adult patients (13 females) every 10th minute during liver transplant surgery. Paired measurements were compared during the 4 phases of surgery-dissection, anhepatic phase, early reperfusion (the first 15 minutes after reperfusion), and late reperfusion (15-60 minutes after reperfusion)-without the detection of any significant difference between the 2 estimates of CO. TDCO ranged from 2.3 to 17.2 L/minute, and the bias (the mean difference between MCO and TDCO) prior to calibration was Ϫ0.4 Ϯ 1.6 L/minute (mean Ϯ standard deviation; 1309 paired measurements; 95% limits of agreement: Ϫ3.4 to 2.6 L/minute). After calibration of the first determined MCO by the simultaneously determined TDCO, the bias was 0.1 Ϯ 1.5 L/minute, with 57% (n ϭ 744) of the comparisons being less than 1 L/minute and 35% (n ϭ 453) being less than 0.5 L/minute; this was independent of the level of CO, and the mutual correlation coefficient was 0.812 (P Ͻ 0.001). This study indicates that during liver transplantation surgery, MCO reflects TDCO throughout the operation. Thus, for CO, this less invasive method appears to provide a reliable uninterrupted measurement during orthotopic liver transplantation. The preparation of liver transplant patients for general anesthesia involves thorough monitoring of respiratory and circulatory variables. In particular, during the hepatectomy and reperfusion phases of the operation, the circulation is vulnerable because of potentially rapid changes in the central blood volume and total peripheral resistance. For the determination of cardiac output (CO), techniques that make use of dye or thermodilution, 1 rebreathing of inert gas or CO 2 , 2,3 and Fick's equation 4 have in common that the hemodynamic values obtained are averages over a period of time, so changes in the left ventricular stroke volume (SV) or CO cannot be assessed with a high time resolution. Also, the inhomogeneous washout temperature of the transplant effluent renders a thermodilution-based continuous determination 1,5 and even a bolus determination of CO [thermodilution cardiac output (TDCO)] 1,5-9 unreliable during early reperfusion of the liver.Several alternative continuous methods have been introduced for the determination of CO, including arterial pulse contour analysis, Most of these methods appear, however, to suffer from Abbreviations: CO, cardiac output; HR, heart rate; MAP, mean arterial pressure; MCO, model-simulated cardiac output; SD, standard deviation; SV, stroke volume; S v O 2 , mixed venous oxygen saturation; TDCO, thermodilution cardiac output; TOE, transesophageal echocardiography. The abstract of this article was presented as a poster at the

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Electrical admittance for filling of the heart during lower body negative pressure in humans

Cited by 62 publications

References 22 publications

Normovolaemia defined by central blood volume and venous oxygen saturation

Normovolaemia defined by central blood volume and venous oxygen saturation

Carotid-Cardiac Baroreflex Function Does Not Influence Blood Pressure Regulation during Head-Up Tilt in Humans

Techniques of cardiac output measurement during liver transplantation: Arterial pulse wave versus thermodilution

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