Redistribution Of Blood Volume Research Articles

Thermoregulation and Haematological Responses to Induced Acute Haemorrhage in Adult Nubian Goats

Background and Objectives: Acute haemorrhage is a major cause of morbidity and mortality in surgery and trauma due to ischaemic lesions followed by multiple organ dysfunction. After haemorrhage, compensatory redistribution of blood volume may occur to more vital and survival organs. The objective of the study was evaluation of thermoregulation and haematological responses to acute haemorrhage in Nubian goats.
 Materials and Methods: The study used 6 female mature goats, weighing 18.0 kg on average. The goats were subjected to 40% bleeding. The rectal temperature (Tr), respiration rate (RR) and heart rate (HR) were monitored before bleeding and then immediately after bleeding and at 1,2,3,4,5,6,24 hrs post-bleeding. Venous blood samples were collected before and then immediately after bleeding and at 6, 24, 48, 72 hrs post-bleeding. The haemoglobin concentration (Hb), packed cell volume (PCV), total leukocyte count(TLC), differential leukocyte count (DLC), serum total protein, albumin, and concentrations of sodium (Na) were determined.
 Results: The post-bleeding values of Tr, RR and HR were significantly higher compared to the pre-bleeding values. The post-bleeding values of PCV, Hb concentration, erythrocyte count and TLC were lower compared to prebleeding values. The ratios of lymphocytes, monocytes and eosinophils decreased, whereas the neutrophil ratio increased post-bleeding. The values of serum total protein, albumin and serum Na concentrations decreased post-bleeding.
 Conclusion: The studies indicate that the goat can be adopted as a valid research model in investigations of experimental haemorrhage. The findings have implications in the fields of veterinary haematology and surgery and comparative medicine.

Systolic Blood Pressure Response to Orthostasis after Concussion is Related to ADRA2A Gene Receptor Subtypes

Orthostasis causes a gravity-dependent redistribution of blood volume to the lower extremities. The baroreflex coordinates effector organs of the cardiovascular autonomic nervous system (CV-ANS) to produce a proportional response to mitigate an aberrant change in systolic blood pressure (SBP). In autonomic dysfunction (AD), there may be a lag or impaired accommodation leading to dramatic changes in SBP. Growing evidence indicates that AD is a part of the post-injury period after concussion. The impact of genetic variability of CV-ANS receptors including that of alpha-2 adrenoceptor (ADRA2A) gene polymorphisms remains undefined. PURPOSE: To evaluate the effect of ADRA2A gene variants on SBP responses to orthostasis in recently concussed athletes. METHODS: A prospective study was performed in 13 concussed college athletes (gender: 10 female, 3 male; age: 20±1 yrs; height: 1.70±0.11 m; weight: 74±17 kg). Beat-to-beat SBP was assessed digitally at rest for 10 minutes in the supine (SUP) position and then for 3 minutes in the standing (STND) position within 48 hours (48H) of concussion; SBP was averaged and a change score computed (ΔSBP = STND SBP - SUP SBP). Fast-Fourier transform was performed and power calculated for the low frequency (LF) spectra in each position (e.g., SUP LF-SBP, STND LF-SBP); the variables were log10 transformed for parametric analyses. A saliva sample was obtained from each participant and a commercial laboratory identified the ADRA2A single nucleotide polymorphism (rs1800544) using PMR-array. RESULTS: Data are presented as group mean (±SD). There were no ADRA2A [C/C: n=5; C/G: n=5, G/G: n=3) group differences for demographics, SUP and STND SBP or LF-SBP. A significant group main effect (p<0.05) was observed for ΔSBP and post-hoc tests revealed that the G/G [-21(±3)] response was significantly (p<0.05) lower than the C/G [7(±18)] group. A 3 X 2 RMANOVA for LF-SBP was performed. A significant group, position and interaction effect (p<0.05) was observed; post-hoc tests were not significant, but trending for an effect in the G/G group. CONCLUSION: The ADRA2A receptor, whose activation is known to inhibit the release of norepinephrine and reduce peripheral vasoconstriction, contributed to a blunted SBP response to orthostasis in G/G homozygotes compared to other variants within 48H of concussion.

Development and practical implementation of organ preservation surgery in case of placenta accreta in patients with a scar on the uterus

Comparative analysis of methods for preventing/stopping intraoperative hemorrhage during surgical delivery of patients with placenta accreta (temporary balloon-assisted occlusion of common iliac arteries, internal iliac artery ligation; uterine artery embolization - UAE) has shown that internal iliac artery ligation is not effective. UAE and especially balloon-assisted occlusion of common iliac arteries have demonstrated a significantly greater effect due to the temporary 'devascularization' of the uterine corpus. It has been proved that an innovative surgical technique - a lower segment Caesarean section (LSCS) significantly reduces intraoperative blood loss. The main purpose of an alternative uterus cut - anterior placenta previa preserving and bleeding absence before the child removal - has been achieved within all observations. LSCS has caused a significantly smaller (by 1.6 times) amount of intraoperative blood loss than the corporal one. Another innovative surgical technique is metroplasty. It entails removing placenta accreta areas from the uterus with subsequent restoration of the organ integrity. The authors have proved the necessity of autologous advance blood donation and hemodilution strategy, which was first implemented in Moscow Center for Family Planning and Reproduction, and after 2006 was used in all obstetric institutions in Moscow. This allowed reducing the number of blood donations up to 85% and additionally decreased transfusiological risks which is economically valuable as well. Improvement of diagnostic methods, operating techniques, hemostasis, blood volume redistribution and creating an algorithm on its basis has proved the possibility of implementing an organ-, life, health- and fertility preserving approach in cases of placenta accreta in patients with a scar on the uterus after cesarean section. The introduction of the enhanced principles of patient management with placenta accreta has significantly reduced the number of hysterectomies in Moscow (from 48 in 2007 to 8 in 2016), and during the last 2 years no patient with this complication has had a hysterectomy. 12 out of 85 patients who had deliveries in accordance with the developed algorithm, have realized their subsequent fertility.

Classic Papers Revisited: My Love Affair with the Venous System.

The Pathophysiology of Aortic Cross-clamping and Unclamping. By Gelman S. ANESTHESIOLOGY 1995; 82:1026-60. Reprinted with permission.Aortic cross-clamping (AoX) and unclamping are associated with severe hemodynamic disturbances in virtually all organs and systems. The main hemodynamic changes induced by AoX result from an increase in impedance to aortic flow, an increase in systemic vascular resistance and afterload, blood volume redistribution caused by collapse and constriction of venous vasculature distal to the aortic clamp, and a subsequent increase in preload. Preload may not increase if the aorta is clamped distal to the celiac artery; in that case, blood volume from distal venous vasculature may be redistributed to the splanchnic vasculature without associated increases in preload. Increases in afterload and preload demand an increase in contractility, which results in an autoregulatory increase in coronary blood flow. Without increases in coronary blood flow and myocardial contractility, decompensation may occur. Aortic cross-clamping is associated with the formation and release of many mediators which constitute a double-edged sword: they may mitigate or aggravate the harmful hemodynamic effects of AoX and unclamping. Injuries to the lungs, kidneys, spinal cord, or abdominal viscera are caused mainly by ischemia and reperfusion of organs distal to aortic cross-clamping. A clear understanding of the pathophysiologic mechanisms involved in these processes should help to promote rational, well-focused, and effective measures to prevent and treat homeostatic disturbances occurring during AoX and unclamping.

Measurements of Inferior Vena Cava Diameter for Prediction of Hypotension and Bradycardia during Spinal Anesthesia in Spontaneously Breathing Patients during Elective Knee Joint Replacement Surgery

Background and objective: Hypotension and bradycardia are the most common hemodynamic disorders and side effects of spinal anesthesia (SA) on the cardiovascular system. SA-induced sympathetic denervation causes peripheral vasodilatation and redistribution of central blood volume that may lead to decreased venous return to the heart. The aim of the study was to evaluate the changes of inferior vena cava collapsibility index (IVC-CI) during SA in spontaneously breathing patients during elective knee joint replacement surgery to prognose manifestation of intraoperative hypotension and bradycardia. Materials and methods: 60 patients (American Society of Anesthesiologists (ASA) physical status I or II, no clinically significant cardiovascular pathology) of both sexes undergoing elective knee joint replacement surgery under SA were included in the prospective study. Inspiratory and expiratory inferior vena cava (IVCin, IVCex) diameters were measured using an ultrasound device in supine position before and immediately after SA, then 15 min, 30 min, and 45 min after SA was performed. The heart rate, along with systolic, diastolic, and mean arterial blood pressures were collected. The parameters were measured at the baseline and at the next four time points. Results: There were no significant changes in IVCin, IVCex, and IVC-CI compared to baseline and other time point measurements in hypotensive versus nonhypotensive and bradycardic versus nonbradycardic patients (p > 0.05). Changes in IVC diameter do not prognose hypotension and/or bradycardia during SA: the area under the curve (AUC) of the receiver operating characteristic (ROC) curve for IVC-CI at all measuring points was <0.7, p > 0.05. Conclusions: Reduction in IVC diameters and increase in IVC-CI do not predict hypotension and bradycardia during SA in spontaneously breathing patients undergoing elective knee joint replacement surgery.

Hemodynamic changes lead to alterations in aortic diameters and may challenge further stent graft sizing in acute aortic syndrome.

Precise stent graft sizing in Thoracic endovascular aortic repair (TEVAR) is crucial to receive optimal long-term results. Computed tomography (CT), as the current standard in assessing aortic diameters (ADs), is often performed at initial diagnosis. Since several acute aortic diseases are associated with blood loss and/or volume re-distribution, assessed AD might be influenced by impaired hemodynamic conditions. Intravascular ultrasound (IVUS) offers real-time assessment, especially after hemodynamic restoration, and might help for stent graft choice. We investigated the correlation between CT and later IVUS measurements in elective (n=83) and emergency patients (n=32) at the level distal to the left subclavian artery (LSA), a frequent proximal landing zone in TEVAR. Patients were grouped depending on their shock index (heart rate/systolic blood pressure): emergency patients with diagnosis of acute aortic syndrome, urgently required treatment after admission and had a shock index >1, otherwise were grouped as elective. Basic hemodynamics were assessed for both groups at admission and at definite IVUS-procedure. At time of admission the emergency group showed lower blood pressure (99±19.8 vs. 141±24 mmHg; P=0.001) and higher heart rate (98±13 vs. 70±12 bpm; P=0.001) compared to elective patients. By hemodynamic stabilization comparable blood pressure and heart rate were achieved in both groups at time of IVUS. In the emergency group, we found a significantly increase in AD after hemodynamic stabilization, whereas the diameters did not change in the elective group (IVUSmeanvs. CTmean: 5.1±1.0 vs. 0.4±2.2 mm; P=0.001 and IVUSminvs. CTmean: 3.9±1.3 vs. -0.3±2.2 mm; P=0.011). IVUS for stent graft sizing is a valuable approach during TEVAR, especially in the light of emergency treatment by offering real-time assistance. Impaired hemodynamic conditions might lead to relevant changes in AD and may strongly influence stent graft choice. In these cases, careful stent graft selection might contribute to avoidance of stent graft related complication.

Predicting Cardiovascular Hemodynamics in Cold and Warm Environments at Rest with Skin and Core Temperature

Many occupations require workers to be exposed to extreme heat or cold. During prolonged exposure to extreme environments, the cardiovascular system plays a critical role in thermal homeostasis, by adjusting blood flow in peripheral and central vascular beds. Importantly, exposure to either environment, and the concordant blood‐volume redistribution, increases morbidity and mortality from the additional [and often significant] stress on the cardiovascular system. To gain insight on how to predict cardiovascular stress during exposure to extreme environments at rest, this study attempted to build a regression model to examine the influence of progressive, whole‐body skin and core cooling and heating on cardiovascular hemodynamics. Seventeen participants (12 males, 22.9 ± 3.58 years, 174.2 cm ± 7.85 cm, 12.8 ± 6.20 kg fat mass, and 59.3 ± 9.49 kg fat free mass) wearing shorts and a t‐shirt participated in two laboratory sessions: i) progressive heating (22°C to 40°C); and ii) progressive cooling (22°C to 5°C); each aimed to independently influence skin and core temperatures. Cardiovascular hemodynamics data was collected via thoracic electrical bioimpedance, while metabolic and cardiorespiratory variables were assessed via indirect calorimetry. Mean weighted skin (Tsk) and core (Tc) temperature were measured via portable data loggers and a thermocouple, respectively. Mean weighted skin temperatures ranged from 22.7°C to 37.4°C and Tc ranged from 35.5°C to 37.9°C. A stepwise multiple linear regression analysis was conducted using Tsk, Tc, fat free mass, fat mass, sex and age as predictors for cardiovascular hemodynamics changes under thermal stress. The present model explained 24.4% of changes in stroke volume, 27.9% of heart rate, 15.9% of cardiac output and 49.5% of oxygen consumption. Although changes in Tsk and Tc temperature induced by whole‐body cooling and heating at rest accounted for changes in cardiovascular hemodynamics in the model, a significant portion of the variation remained unexplained. Further research is needed to develop a more accurate model to represent changes in cardiovascular hemodynamics under thermal stress.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Cerebral blood volume redistribution during hypercapnia

Cerebral blood volume redistribution during hypercapnia

Investigation of cerebral venous outflow in microgravity

Objective: The gravitational gradient is the major component to face when considering the physiology of venous return, and there is a growing interest in understanding the mechanisms ensuring the heart filling, in the absence of gravity, for astronauts who perform long-term space missions. Approach: The purpose of the Drain Brain project was to monitor the cerebral venous outflow of a crew member during an experiment on the International Space Station (ISS), so as to study the compensatory mechanisms that facilitate this essential physiological action in subjects living in a microgravity environment. Such venous function has been characterized by means of a novel application of strain-gauge plethysmography which uses a capacitive sensor. Main results: In this contribution, preliminary results of our investigation have been presented. In particular, comparison of plethysmography data confirmed that long duration spaceflights lead to a redistribution of venous blood volume, and showed interesting differences in the amplitude of cardiac oscillations measured at the level of the neck veins. Significance: The success of the experiment has also demonstrated that thanks to its easy portability, non-invasiveness, and non-operator dependence, the proposed device can be considered as a novel tool for use aboard the ISS. Further trials are now under way to complete the investigation on the drainage function of the neck veins in microgravity.

Cardiopulmonary physiology: why the heart and lungs are inextricably linked.

Because the heart and lungs are confined within the thoracic cavity, understanding their interactions is integral for studying each system. Such interactions include changes in external constraint to the heart, blood volume redistribution (venous return), direct ventricular interaction (DVI), and left ventricular (LV) afterload. During mechanical ventilation, these interactions can be amplified and result in reduced cardiac output. For example, increased intrathoracic pressure associated with mechanical ventilation can increase external constraint and limit ventricular diastolic filling and, therefore, output. Similarly, high intrathoracic pressures can alter blood volume distribution and limit diastolic filling of both ventricles while concomitantly increasing pulmonary vascular resistance, leading to increased DVI, which may further limit LV filling. While LV afterload is generally considered to decrease with increased intrathoracic pressure, the question arises if the reduced LV afterload is primarily a consequence of a reduced LV preload. A thorough understanding of the interaction between the heart and lungs can be complicated but is essential for clinicians and health science students alike. In this teaching review, we have attempted to highlight the present understanding of certain salient aspects of cardiopulmonary physiology and pathophysiology, as well as provide a resource for multidisciplined health science educators and students.

Vascular Reactivity during Cardiopulmonary Bypass in Patients at Punjab Institute of Cardiology &amp; Shalamar Hospital Lahore, Pakistan

Background: The operative treatment of cardiac diseases remains associated with systemic inflammation and a suboptimal outcome in many patients. These inflammatory changes are manifested by systemic hypotension, myocardial failure, increased vascular permeability and consequent dysfunction of organs such as the lungs, gut and brain. In general terms, sympathetic innervations of the small arteries and arterioles allows vasoconstriction, thereby increasing resistance to blood flow, whereas innervations of the large arteries and veins decreases the volume in these vessels, resulting in the redistribution of blood volume. This study was conducted to determine the effect of vasodilator drugs on duration of vasodilatation in patients undergoing coronary artery bypass grafting (CABG) with Cardiopulmonary bypass (CPB).Methods: We evaluated prospectively the effect of vasodilator medications before CABG surgery on hemodynamic variables and use of vasoactive drugs. We studied 30 patients with good left ventricular function allocated randomly to continue vasodilator drugs before cardiac surgery. Arterial pressure, Cardiac output, systemic vascular resistance and use of vasoactive drugs were recorded during anaesthesia, perioperative and in the early postoperative period.Results: Patients who using vasodilator drugs before cardiac surgery had not significant relationship between vasodilator drugs and vessels reactivity (vasoconstriction &amp; vasodilatation). However, these patients required more vasodilator drugs to control hypertension after CPB and in the early postoperative period.Conclusion: There was no difference in hypotension at the onset of CPB or in the use of vasodilator drugs before cardiac surgery. We conclude that vasodilator drugs before cardiac surgery did not have sufficient effect to be recommended routinely.

Variability of skin microcirculation in case of arterial hypertension from the view of distributional responses of blood flow

The aim of the study. To evaluate individual variability of skin microcirculation (MC) in patients with arterial hypertension (AH) and characteristics of microvascular (MV) reaction to hypotensive impact from the view of blood distribution. Material and methods. Microcirculation of forearm skin in 176 patients with AH stage 2 was studied by laser doppler flowmetry (LDF). All the patients were divided into 2 groups: 1 - with low (n=46) value of MV resistance and 2 - with high (n=130) value of MV resistance. 90 patients out of the total amount (also divided into the same 2 groups - 25 people in the first group and 65 people in the second) had another study of MC after sublingual taking of 20 mg of corinfar. Results. The results revealed controversial MC skin picture with high blood filling of MV canal and reduced MV tone in the first group and high value of MV tone with hemoperfusion limitation in the second group in patients with AH and the same blood pressure (BP). Reduction in the first group can be caused by redistribution of a minute blood volume kept on a high level in the condition of elevated total peripheral resistance (TPR) (the so called central blood bypass). In this case the skin where a part of a cardiac output goes to serves as a depot. Increase of intravascular resistance in the skin of patients from the second group is caused by prevalence of TPR in hemodynamic mechanisms of BP elevation. Whereas constriction of microcirculation vessel is observed not only in the abdominal vessel area (which is the main area responsible for TPR formation) but also in the other areas, particularly in the skin. Corresponding BP decrease in groups of patients under the influence of corinfar was accompanied by bidirectional shifts of MC values: vasodilation in the second group and vasoconstriction in the first group of patients. It happens due to more balanced bloodflow distribution in the vessel areas more responsible for TPR formation as a result of vasodilation under the influence of corinfar.

Transient pressure changes in the vertebral canal during whiplash motion – A hydrodynamic modeling approach

In vehicle collisions, the occupant׳s torso is accelerated in a given direction while the unsupported head tends to lag behind. This mechanism results in whiplash motion to the neck. In whiplash experiments conducted for animals, pressure transients have been recorded in the spinal canal. It was hypothesized that the transients caused dorsal root ganglion dysfunction. Neck motion introduces volume changes inside the vertebral canal. The changes require an adaptation which is likely achieved by redistribution of blood volume in the internal vertebral venous plexus (IVVP). Pressure transients then arise from the rapid redistribution. The present study aimed to explore the hypothesis theoretically and analytically. Further, the objectives were to quantify the effect of the neck motion on the pressure generation and to identify the physical factors involved. We developed a hydrodynamic system of tubes that represent the IVVP and its lateral intervertebral vein connections. An analytical model was developed for an anatomical geometrical relation that the venous blood volume changes with respect to the vertebral angular displacement. This model was adopted in the hydrodynamic tube system so that the system can predict the pressure transients on the basis of the neck vertebral motion data from a whiplash experiment. The predicted pressure transients were in good agreement with the earlier experimental data. A parametric study was conducted and showed that the system can be used to assess the influences of anatomical geometrical properties and vehicle collision severity on the pressure generation.

Photoplethysmography-Based Algorithm for Detection of Cardiogenic Output During Cardiopulmonary Resuscitation

Detecting return of spontaneous circulation (ROSC) during cardiopulmonary resuscitation (CPR) is challenging, time consuming, and requires interrupting chest compressions. Based on automated-CPR porcine data, we have developed an algorithm to support ROSC detection, which detects cardiogenic output during chest compressions via a photoplethysmography (PPG) signal. The algorithm can detect palpable and impalpable spontaneous pulses. A compression-free PPG signal which estimates the spontaneous pulse waveform, was obtained by subtracting the compression component, modeled by a harmonic series. The fundamental frequency of this series was the compression rate derived from the transthoracic impedance signal measured between the defibrillation pads. The amplitudes of the harmonic components were obtained via a least mean-square algorithm. The frequency spectrum of the compression-free PPG signal was estimated via an autoregressive model, and the relationship between the spectral peaks was analyzed to identify the pulse rate (PR). Resumed cardiogenic output could also be detected from a decrease in the baseline of the PPG signal, presumably caused by a redistribution of blood volume to the periphery. The algorithm indicated cardiogenic output when a PR or a redistribution of blood volume was detected. The algorithm indicated cardiogenic output with 94% specificity and 69% sensitivity compared to the retrospective ROSC detection of nine clinicians. Results showed that ROSC detection can be supported by combining the compression-free PPG signal with an indicator based on the detected PR and redistribution of blood volume.

Time courses of central hemodynamics during rapid changes in posture

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.

Trigemino‐Cardiac Reflex as Lethal Mechanism in a Suicidal Fire Death Case

In the vast majority of immediate fire deaths, the mechanism of death is inhalation of toxic gases (especially carbon monoxide), direct thermal injury, or neurogenic shock due to the redistribution of the body's blood volume produced by surface heat on the skin. We present a suicidal case that is unusual because the mechanism of immediate fire death could arguably be explained in terms of a primitive autonomic reflex/the trigemino-cardiac reflex. Although this reflex is well known to surgeons and anesthetists, with possible lethal consequences in the course of invasive surgical procedures on the head and neck region, it is much less familiar to forensic pathologists.

Up-regulation of ryanodine receptor expression increases the calcium-induced calcium release and spontaneous calcium signals in cerebral arteries from hindlimb unloaded rats

Microgravity induces a redistribution of blood volume. Consequently, astronauts' body pressure is modified so that the upright blood pressure gradient is abolished, thereby inducing a modification in cerebral blood pressure. This effect is mimicked in the hindlimb unloaded rat model. After a duration of 8 days of unloading, Ca2+ signals activated by depolarization and inositol-1,4,5-trisphosphate intracellular release were increased in cerebral arteries. In the presence of ryanodine and thapsigargin, the depolarization-induced Ca2+ signals remained increased in hindlimb suspended animals, indicating that Ca2+ influx and Ca2+-induced Ca2+ release mechanism were both increased. Spontaneous Ca2+ waves and localized Ca2+ events were also investigated. Increases in both amplitude and frequency of spontaneous Ca2+ waves were measured in hindlimb suspension conditions. After pharmacological segregation of Ca2+ sparks and Ca2+ sparklets, their kinetic parameters were characterized. Hindlimb suspension induced an increase in the frequencies of both Ca2+ localized events, suggesting an increase of excitability. Labeling with bodipy compounds suggested that voltage-dependent Ca2+ channels and ryanodine receptor expressions were increased. Finally, the expression of the ryanodine receptor subtype 1 (RyR1) was increased in hindlimb unloading conditions. Taken together, these results suggest that RyR1 expression and voltage-dependent Ca2+ channels activity are the focal points of the regulation of Ca2+ signals activated by vasoconstriction in rat cerebral arteries with an increase of the voltage-dependent Ca2+ influx.

Common Syndromes of Orthostatic Intolerance

The autonomic nervous system, adequate blood volume, and intact skeletal and respiratory muscle pumps are essential components for rapid cardiovascular adjustments to upright posture (orthostasis). Patients lacking sufficient blood volume or having defective sympathetic adrenergic vasoconstriction develop orthostatic hypotension (OH), prohibiting effective upright activities. OH is one form of orthostatic intolerance (OI) defined by signs, such as hypotension, and symptoms, such as lightheadedness, that occur when upright and are relieved by recumbence. Mild OI is commonly experienced during intercurrent illnesses and when standing up rapidly. The latter is denoted "initial OH" and represents a normal cardiovascular adjustment to the blood volume shifts during standing. Some people experience episodic acute OI, such as postural vasovagal syncope (fainting), or chronic OI, such as postural tachycardia syndrome, which can significantly reduce quality of life. The lifetime incidence of ≥1 fainting episodes is ∼40%. For the most part, these episodes are benign and self-limited, although frequent syncope episodes can be debilitating, and injury may occur from sudden falls. In this article, mechanisms for OI having components of adrenergic hypofunction, adrenergic hyperfunction, hyperpnea, and regional blood volume redistribution are discussed. Therapeutic strategies to cope with OI are proposed.

Changes in cerebral oxygenation during parabolic flight

Assessing changes in brain activity under extreme conditions like weightlessness is a desirable, but difficult undertaking. Results from previous studies report specific changes in brain activity connected to an increase or decrease in gravity forces. Nevertheless, so far it remains unclear (1) whether this is connected to a redistribution of blood volume during micro- or hypergravity and (2) whether this redistribution might account for neurocognitive alterations. This study aimed to display changes in brain oxygenation caused by altered gravity conditions during parabolic flight. It was hypothesized that an increase in gravity would be accompanied by a decrease in brain oxygenation, whereas microgravity would lead to an increase in brain oxygenation. Oxygenized and deoxygenized haemoglobin were measured using two near infrared spectroscopy (NIRS) probes on the left and right prefrontal cortex throughout ten parabolas in nine subjects. Results show a decrease of 1.44 μmol/l in oxygenized haemoglobin with the onset of hypergravity, followed by a considerable increase during microgravity (up to 5.34 μmol/l). In contrast, deoxygenized haemoglobin was not altered during the first but only during the second hypergravity phase and showed only minor changes during microgravity. Changes in oxygenized and deoxygenized haemoglobin indicate an increase in arterial flow to the brain and a decrease in venous outflow during microgravity.

Blood Volume Redistribution During Hypovolemia

The goal of this study was to investigate the contribution of splanchnic volume redistribution and lower limb vasoconstriction in the maintenance of blood pressure during progressive central hypovolemia induced by graded lower body negative pressure (LBNP). It was hypothesized that splanchnic blood volume loss during LBNP would buffer decreases in thoracic blood volume. There were 15 healthy subjects (8 men, 7 women) who participated in the study. We used LBNP of -10, -20, -30, and -40 mmHg with segmental impedance analysis to determine central and splanchnic volume changes, and near infrared spectroscopy (NIRS) to assess calf venous volume changes and vasoconstrictor tone. In relation to baseline, LBNP to -40 mmHg resulted in a 57% increase in deoxygenated blood in the calf, indicating venous pooling in the lower limbs. These events led to a decrease in venous return and a 28% decline in cardiac output. Total upper body impedance increased by 6.6% with a 2.4% change in thoracic and a 13.1% increase in splanchnic impedance with progressive LBNP. Splanchnic blood volume contributed to more than 50% of the volume redistribution to the thoracic compartment during hypovolemia. Both men and women increased their heart rate, but only men vasoconstricted (4.4%) with increasing LBNP. The net result of these events was the maintenance of mean arterial blood pressure with no presyncopal symptoms in these subjects. Our results suggest that splanchnic blood volume redistribution--rather than leg vasoconstriction--plays an important role in blood pressure regulation during central hypovolemia.