Variations In Venous Return Research Articles

Baseline plethysmographic signal of arterial pulse during polysomnography: a potential insight into venous return and its clinical implications

Pulse oximetry is based on the technique of photoplethysmography. It is known that the pulsatile arterial component can provide a range of information, such as arterial blood oxygen saturation, the response to fluid infusion, and the nature of respiratory events during sleep. Until now, little importance has been given to the venous component of the plethysmographic signal, which is non-pulsatile but subject to volumetric variations in relation to changes in endopleuric pressure.Respiratory-induced intensity variations contained in the baseline of the photoplethysmographic signal have been well documented. We hypothesize that in polysomnography, variations in the baseline of the plethysmographic signal (referred to as the BPS, baseline plethysmographic signal) reflect variations in venous return induced by respiration, and that these variations present morphological aspects that could have clinical utility in the interpretation of polysomnographic signals, particularly regarding respiratory effort associated with respiratory events, their nature (central or obstructive), and the hemodynamic alterations associated with them.This article presents a selection of polysomnographic traces and images with physiopathological considerations that support our hypothesis.

Surgical implantation of the CardioWest Total Artificial Heart.

The CardioWest Total Artificial Heart (CW-TAH) is a pneumatically driven pump that completely replaces the patient’s native ventricles orthotopically. The device weighs 160 g and consists of two artificial ventricles, four Medtronic Hall tilting disk valves, two membranes, and two drivelines tunneled through the skin, which connect the ventricles to an external console generating pulsatile flow (1). At maximum stroke volume (close to 70 mL), it delivers a cardiac output between seven and nine litres per minute. Variations in cardiac output are determined by variations in venous return and peripheral resistance linked to the patient’s position and level of physical activity (2). The CW-TAH is indicated for use in patients with refractory cardiac failure as a bridge to transplantation, and when used for this indication, improves survival to transplant (3). Portable drivers have been approved in both Europe and the United States to allow stable patients to be discharged home while awaiting their transplant (4).

Functional haemodynamic monitoring.

Functional haemodynamic monitoring is the assessment of the dynamic interactions of haemodynamic variables in response to a defined perturbation. Fluid responsiveness can be predicted during positive pressure breathing by variations in venous return or left ventricular output using numerous surrogate markers, such as arterial pulse pressure variation (PPV), left ventricular stroke volume variation (SVV), aortic velocity variation, inferior and superior vena cavae diameter changes and pulse oximeter pleth signal variability. Similarly, dynamic changes in cardiac output to a passive leg raising manoeuvre can be used in any patient and measured invasively or noninvasively. However, volume responsiveness, though important, reflects only part of the overall spectrum of functional physiological variables that can be measured to define physiologic state and monitor response to therapy. The ratio of PPV to SVV defines central arterial elastance and can be used to identify those hypotensive patients who will not increase their blood pressure in response to a fluid challenge despite increasing cardiac output. Dynamic tissue O2 saturation (StO2) responses to complete stop flow conditions, as can be created by measuring hand StO2 and occluding flow with a blood pressure cuff, assesses cardiovascular sufficiency and micro-circulatory blood flow distribution. They can be used to identify those ventilator-dependent individuals who will fail a spontaneous breathing trial or trauma patients in need of life-saving interventions. Functional haemodynamic monitoring approaches are increasing in numbers, conditions in which they are useful and resuscitation protocol applications. This is a rapidly evolving field whose pluripotential is just now being realized.

Non-respiratory functions of the lung

The lung has an extremely distensible vasculature, which enables it to cope with large variations in venous return, especially during postural changes, exercise, and increased intravascular volume. The two mechanisms involved are recruitment and distension of the pulmonary vasculature. At resting cardiac output, the pulmonary vascular bed is not fully perfused. In the face of an increased cardiac output, underperfused areas of the pulmonary vasculature are ‘recruited’ to accommodate an increase in blood flow and to prevent an increase in pulmonary arterial pressures. The walls of the pulmonary vasculature are thin and contain relatively little smooth muscle, which make it compliant to increased blood volume. The pressure in the pulmonary circulation is approximately six times less than that of the systemic circulation and both arteries and veins increase in calibre with lung expansion. This ‘distension’ along with ‘recruitment’ helps in altering the lung blood volume by 500–1000 ml.

Experimental Right Atrial Ischemia and Its Response to Stimulation with Dobutamine.

In order to analyze the repercussion of experimental isolated selected right atrial ischemia on the hemodynamics of both ventricles, we investigated the response of atrial myocardium with administration of dobutamine and evaluated the utility of transesophageal echocardiography (TEE) with Doppler in the examination of alterations produced by atrial ischemia. Ten dogs were studied with normal, diminished, and increased cardiac output with ligation of the visible atrial branches of the right coronary artery. Right atrial wall movement and peak A wave velocity of tricuspid flow registered by TEE decreased (P < 0.05). The amplitude of the right atrial A wave decreased in hemodynamic recordings (P < 0.05). No significant modifications occurred in right ventricular wall movement nor in pressures registered in right or left ventricles or cardiac output. Seventy-five minutes after atrial ischemia was induced dobutamine was administered. In dogs with incomplete ligations of atrial circulation, right atrial wall movement improved (P < 0.001), and the amplitude of the peak A wave velocity of tricuspid flow increased. In dogs with complete coronary ligation, administration of the medication produced no improvement of these variables. The findings indicate that it is possible to produce selective right atrial ischemia manifested by diminished wall movement, a diminished atrial component of tricuspid flow in TEE, and decreased amplitude of the A wave in atrial pressure recordings. The localized hemodynamic changes produced by right atrial ischemia are not related to variations in venous return when right ventricular function is normal. Apparently isolated right atrial damage from ischemia does not affect ventricular function if these remain healthy. The recuperation of atrial contractility can be demonstrated with dobutamine. Transesophageal echocardiography is a very useful technique for studying right atrial ischemia and infarction.

Buffering of respiratory variations in venous return by right ventricle: a theoretical analysis

The role of the right ventricle (RV) in buffering systemic venous return, thereby dampening respiratory-induced variations, left ventricular (LV) stroke volume, and systemic arterial pressure variations was examined using a computer model of the cardiovascular system. Respiration was simulated by cyclical variations in intrathoracic and abdominal pressures (cycle time 5 heartbeats), causing a 43-ml fluctuation in venous return per heartbeat (mean 71 ml) compared with fluctuations of 19 ml in RV stroke volume, 6 ml in pulmonary venous flow, and only 3 ml in LV stroke volume. On a percentage basis, the RV provided 56% of the total buffering of systemic venous return, the lungs another 30%, whereas the LV only 7%. A 10-fold increase in RV diastolic compliance increased the RV stroke volume variations from 26 to 57% of the venous return variations; a 10-fold increase in RV elastance increased them from 24 to 60%, whereas decreasing pulmonary arterial pressure from 28 to 10 mmHg increased them from 28 to 56%. The results also suggest that an underrecognized function of the RV is to buffer systemic venous return and thereby keep LV stroke volume relatively constant.

Mechanosensitive fibroblasts in the sino-atrial node region of rat heart: interaction with cardiomyocytes and possible role.

The positive chronotropic response of the heart to stretch of the right atrium is one of the major mechanisms adjusting the heart rate to variations in venous return on a beat-by-beat basis. The precise pathway of this mechano-electric feedback and its cellular basis are uncertain. In this study, a possible contribution of mechanosensitive fibroblasts, abundant in the sino-atrial node region, was investigated using a mathematical model of the electrical interaction of a mechanosensitive fibroblast and a sino-atrial pacemaker cell. Electrophysiological evidence for a bio-electrical interaction of mechanosensitive fibroblasts with surrounding cardiomyocytes has been studied in (i) the isolated spontaneously beating atrium of rat hearts, and (ii) cell cultures of the neonatal rat heart. These investigations were performed using (i) double-barrelled floating microelectrodes for intracellular potential registrations, and (ii) the double whole cell patch-clamp technique. It was shown that cardiac fibroblasts and surrounding cardiomyocytes can be either electrically well isolated from each other, or coupled both capacitively and electrotonically. The electrophysiological data obtained were incorporated into the OXSOFT HEART program. Assuming that equivalent coupling may occur between mechanosensitive fibroblasts and sino-atrial pacemaker cells, a heterologous cell pair consisting of one fibroblast and one sino-atrial node myocyte connected by ten to thirty single gap junctional channels with a conductance of 30 pS was modelled. The model of the electrotonic interaction of these cells showed that stretch of the fibroblast during atrial diastole, simulating increased atrial wall tension during atrial filling, can raise the spontaneous depolarization rate of the pacemaker cell in a stretch-dependent manner by up to 24%. These results show that cardiac mechanosensitive fibroblasts could form a cellular basis for the positive chronotropic response of the heart to stretch of the right atrium.

Venous collapse and the respiratory variability in systemic venous return.

Venous collapse limits systemic venous return, but its effects on beat to beat respiratory venous return variations are less well known. The aim of this study was to investigate the effects of venous collapse on respiratory variations in venous return. A model of venous collapse which included both an increase in haemodynamic resistance to flow and an increase in vessel compliance was incorporated in a previously described cardiovascular model. Respiration was simulated by 5 mm Hg swings of intrathoracic pressure (PTH) at different mean pressures such that the abdominal vena cava and jugular vein were either fully collapsed (mean PTH -11 mm Hg), in the transition zone between collapse and distension (mean PTH -6 mm Hg), or fully distended (mean PTH 9 mm Hg). The mean and standard deviations over each respiratory cycle of the venous return volume (flow integral over heart cycle) and the abdominal vena caval volume were recorded. Different venous return volume variabilities in the three operating zones of the vena cava were identified: (1) reduced variability in the collapsed zone associated with the increased haemodynamic resistance [venous return 93(SD 6) ml, abdominal vena caval volume 30(3) ml. absolute right atrial pressure -6.3(1.1) mm Hg]; (2) increased variability in the transition zone [venous return 86(24) ml, abdominal vena caval volume 81(15) ml, right atrial pressure -2.2(0.8) mm Hg]; (3) low variability in the distended zone [venous return 42(11) ml, abdominal vena caval volume 120(2) ml, right atrial pressure 10.1(1.1) mm Hg]. The greater the change in compliance with collapse the greater the increase in flow variability in the transition zone; with no change in compliance there was no increased flow variability in the transition zone. The results suggest that venous collapse increases the respiratory variations in venous return in the transition zone. As venous return variations contribute to arterial pressure variations, the collapsible nature of the great veins may influence respiratory variations in systemic arterial pressure.

Paradoxical Pulse in Constrictive Pericarditis-Reply

In Reply.— Paradoxical pulse undoubtedly does occur in some instances of inactive chronic constrictive pericarditis. Dr Sasse makes an interesting and useful point that analysis of the respiratory changes in timing of A2and P2may show correlations with various degrees of paradoxical pulse. The relationship of inspiratory variations in venous return to paradoxical pulse in various types of pericardial disease is not completely elucidated and should be studied further, perhaps with Doppler flow-pattern studies and with echocardiographic studies of cardiac dimensions.

Venous pulsations in the upper arm studied with plethysmographic technique.

A plethysmographic method for studies of venous flow and volume pulsations in a limb was developed. The venous volume pulsations showed good agreement with the venous pressure pulsations. The venous pulsations were shown to be propagated from the heart. Respiratory variations in venous return from a limb could be demonstrated. The venous pulsations could be eliminated by a slight stasis proximal to the plethysmograph or by elevation of the limb above heart level.

Plethysmographic techniques for the measurement of phasic variations in venous return.

ArticlePlethysmographic techniques for the measurement of phasic variations in venous return.I F Mackay, and P Van LoonI F Mackay, and P Van LoonPublished Online:01 Jan 1968https://doi.org/10.1152/jappl.1968.24.1.124MoreSectionsPDF (975 KB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInWeChat Previous Back to Top Download PDF FiguresReferencesRelatedInformation Cited ByHemodynamic measurements in peripheral vascular diseaseCurrent Problems in Surgery, Vol. 13, No. 8Venous Pulsations in the Upper Arm Studied with Plethysmographic Technique8 July 2009 | Scandinavian Journal of Clinical and Laboratory Investigation, Vol. 24, No. 2 More from this issue > Volume 24Issue 1January 1968Pages 124-8 https://doi.org/10.1152/jappl.1968.24.1.124PubMed5635763History Published online 1 January 1968 Published in print 1 January 1968 Metrics

Rapid changes in human right heart blood temperature at variations in venous return.

ted in the temperature of the blood in the right auricle. The present experimental data coccerning right heart blood temperature are given with special reference to the amplitude and duration of changes in this temperature induced by pooling blood in the lower limbs.

Cardiac variations in venous return studied with a new bristle flowmeter.

Cardiac variations in venous return studied with a new bristle flowmeter.