Relation between resting spleen volume and apnea-induced increases in hemoglobin mass.

Introduction: Indigenous populations renowned for apneic diving have comparatively large spleen volumes. It has been proposed that a larger spleen translates to heightened apnea-induced splenic contraction and elevations in circulating hemoglobin mass (Hbmass), which, in theory, improves O2 carrying and/or CO2/pH buffering capacities. However, the relation between resting spleen volume and apnea- induced increases in Hbmass is unknown. Therefore, we tested the hypothesis that resting spleen volume is positively related to apnea-induced increases in total Hbmass. Methods: Fourteen healthy adults (six women; 29 ± 5 years) completed a two-minute carbon monoxide rebreathe procedure to measure pre-apneas Hbmass and blood volume. Spleen length, width, and thickness were measured pre-and post-five maximal apneas via ultrasound. Spleen volume was calculated via the Pilström equation (test-retest CV:2 ± 2%). Hemoglobin concentration ([Hb]; g/dl) and hematocrit (%) were measured pre- and post-apneas via capillary blood samples. Post-apneas Hbmass was estimated as post-apnea [Hb] x pre-apnea blood volume. Data are presented as mean ± SD. Results: Spleen volume decreased from pre- (247 ± 95 mL) to post- (200 ± 82 mL, p<0.01) apneas. [Hb] (14.6 ± 1.2 vs. 14.9 ± 1.2 g/dL, p<0.01), hematocrit (44 ± 3 vs. 45 ± 3%, p=0.04), and Hbmass (1025 ± 322 vs. 1046 ± 339 g, p=0.03) increased from pre- to post-apneas. Pre-apneas spleen volume was unrelated to post-apneas increases in Hbmass (r=-0.02, p=0.47). O2 (+28 ± 31 mL, p<0.01) and CO2 (+31 ± 35 mL, p<0.01) carrying capacities increased post-apneas. Conclusion: Larger spleen volume is not associated with a greater rise in apneas-induced increases in Hbmass in non-apnea-trained healthy adults.

Prognostic implications of volume status assessed by blood volume analysis in ambulatory heart failure.

The prognostic implications of intravascular volume status assessed by blood volume analysis (BVA) in ambulatory heart failure (HF) remain uncertain. The incremental benefits of assessing volume status, beyond the well-established filling pressures, in predicting HF outcomes are unknown.

Blood volume phenotypes and patient sex in resistant hypertension.

The relationship of blood volume (BV) to systemic blood pressure (BP) is not well defined in resistant hypertension (RH). The goal of this study was to examine the extent to which systemic BP stratified by patient sex would impact BV phenotypes. A retrospective analysis of clinical and quantitative BV data was undertaken in a cohort of ambulatory patients with a history of controlled and uncontrolled RH. We analyzed 253 unique BVs with 54% of patients above goal BP of <150 mmHg. BV phenotypes were highly variable but no correlation of systolic BP to absolute BV or percentage deviation from normal volume was identified in either sex. Males demonstrated overall larger absolute BVs with higher prevalence of large plasma volume (PV) expansion; females were overall more hypovolemic by total BV but with a higher frequency of normal PV than males. Females trended towards more RBC mass deficit (true anemia) (49% vs. 38%. P  = 0.084) while more males demonstrated RBC mass excess (erythrocythemia) (21% vs. 11%, P  = 0.029). Importantly, a significant portion (52%) of patients with true anemia identified by BVA would go undetected by hemoglobin measurement alone. BV phenotypes are highly diverse in patients with RH. However, absolute BV or variability in BV phenotypes even when stratified by patient sex did not demonstrate an association with systemic BP. BV phenotyping provides a key to optimizing clinical management by identifying RBC mass profiles particularly distinguishing true anemia, dilutional anemia, and erythrocythemia and the contribution of PV expansion. Findings support the clinical utility of BV phenotyping in RH.

Ultrasound findings and specific intrinsic blood volume expansion therapy for neonatal capillary leak syndrome: report from a multicenter prospective self-control study.

OBJECTIVE: Capillary leak syndrome (CLS) is characterized by severe systemic edema without specific treatment, resulting in a high mortality rate. This study investigated whether there is organ edema in neonatal CLS patients and specific treatment strategies to improve patient prognosis. METHODS: Thirty-seven newborns diagnosed with CLS were included in this study. (1) Routine point-of-care ultrasound (POCUS) was used to identify whether the patients had visceral edema or fluid collection. (2) All patients were treated with 3% NaCl intravenously, and the clinical manifestations, laboratory indices and outcomes were compared before and after treatment. RESULTS: (1) Diffuse severe edema was found in 92.0% of the patients. (2) The POCUS examination revealed that CLS patients exhibited significant visceral edema in addition to diffuse severe edema, which included pulmonary edema in 67.6%, cerebral edema in 37.8%, severe intestinal edema in 24.3%, severe myocardial edema in 8.1%, pericardial effusion in 5.4%, pleural effusion in 29.7% and peritoneal effusion in 18.9%. Two patients (5.45%) had only myocardial edema without other manifestations. (3) Before and after the intravenous injection of 3% NaCl, there were no significant differences in the serum sodium or potassium levels of CLS patients, while the hemoglobin and hematocrit levels were significantly lower after treatment (p < 0.01). Her plasma ALB concentration and arterial pressure returned to normal levels after the treatment was completed. (4) All the patients survived, and no side effects or complications were observed during or after treatment with 3% NaCl. CONCLUSIONS: (1) In addition to diffuse severe edema, visceral edema and effusion are common and important clinical manifestations of neonatal CLS and need to be detected by routine POCUS. (2) The intravenous injection of 3% NaCl is a safe, effective and specific treatment strategy for neonatal CLS, with a survival rate of 100% and no adverse effects.

Regional pulmonary perfusion, blood volume, and their relationship change in experimental early ARDS.

Regional pulmonary perfusion (Q) has been investigated using blood volume (Fb) imaging as an easier-to-measure surrogate. However, it is unclear if changing pulmonary conditions could affect their relationship. We hypothesized that vascular changes in early acute respiratory distress syndrome (ARDS) affect Q and Fb differently. Five sheep were anesthetized and received lung protective mechanical ventilation for 20 h while endotoxin was continuously infused. Using dynamic 18F-FDG and 13NN Positron Emission Tomography (PET), regional Fb and Q were analysed in 30 regions of interest (ROIs) and normalized by tissue content (Fbn and Qn, respectively). After 20 h, the lung injury showed characteristics of early ARDS, including gas exchange and lung mechanics. PET images of Fbn and Qn showed substantial differences between baseline and lung injury. Lung injury caused a significant change in the Fbn-Qn relationship compared to baseline (p < 0.001). The best models at baseline and lung injury were Fbn = 0.32 + 0.690Qn and Fbn = 1.684Qn-0.538Qn2, respectively. Endotoxine-associated early ARDS changed the relationship between Fb and Q, shifting from linear to curvilinear. Effects of endotoxin exposure on the vasoactive blood flow regulation were most likely the key factor for this change limiting the quantitative accuracy of Fb imaging as a surrogate for regional Q.

The effect of chronic habitual exercise on oxygen carrying capacity and blood compartment volumes in older adults.

Absolute total hemoglobin mass (tHbmass) and blood compartment volumes are often considered to be higher in endurance athletes compared with nonathletes, yet little data support a fitness effect in older age. Therefore, we measured tHbmass and blood compartment volumes (carbon monoxide rebreathing) in 77 healthy individuals (23% female; aged, 60-87 yr). Participants were recruited into groups based upon their lifelong (>25 yr) exercise "dose": 1) 15 sedentary individuals, <2 sessions/wk; 2) 25 casual exercisers, 2-3 sessions/wk; 3) 24 committed exercisers, 4-5 sessions/wk; and 4) 13 competitive Masters athletes, 6-7 sessions/wk, plus regular competitions. Absolute (L/min) and relative (mL/kg/min) V̇o2peak were higher with increasing exercise "dose" (P = 0.0005 and P < 0.0001, respectively). Hemoglobin concentration, hematocrit, and absolute tHbmass and blood compartment volumes were not significantly different between groups (all, P > 0.1328). When scaled to body mass, tHbmass (Sedentary, 9.2 ± 1.7 mL/kg; Casual, 9.2 ± 1.3; Committed, 10.2 ± 1.4; Competitive, 11.5 ± 1.4, ANOVA P < 0.0001) and blood volume were significantly different between groups [Sedentary, 63.4 (59.2-68.5) mL/kg; Casual, 67.3 (64.4-72.6); Committed, 73.5 (67.5-80.2); Competitive, 83.4 (78.9-88.6), ANOVA P < 0.0001], whereby all values were highest in Masters athletes. However, when scaled to fat-free mass (FFM), tHbmass and blood compartment volumes were greater in Competitive compared with Casual exercisers (all, P < 0.0340) and tHbmass and erythrocyte volume were also higher in Committed compared with Casual exercisers (both, P < 0.0134). In conclusion, absolute tHbmass and blood compartment volumes are not different between groups, with dose-dependent differences only among exercisers when scaled for FFM, with the highest tHbmass and blood compartment volumes in competitive Masters athletes.NEW & NOTEWORTHY We observed that absolute oxygen carrying capacity (total hemoglobin mass, tHbmass) and blood compartment volumes were not associated with lifelong exercise dose. However, hematological adaptations associated with lifelong habitual exercise are only present among exercisers, whereby competitive Masters athletes have a greater oxygen carrying capacity (tHbmass) and expanded blood compartment volumes when scaled to fat-free mass.

Blood volume and hemodynamics during treatment of major hemorrhage with Ringer solution, 5% albumin, and 20% albumin: a single-center randomized controlled trial.

BACKGROUND: Volume replacement with crystalloid fluid is the conventional treatment of hemorrhage. We challenged whether a standardized amount of 5% or 20% albumin could be a viable option to maintain the blood volume during surgery associated with major hemorrhage. Therefore, the aim of this study was to quantify and compare the plasma volume expansion properties of 5% albumin, 20% albumin, and Ringer-lactate, when infused during major surgery. METHODS: In this single-center randomized controlled trial, fluid replacement therapy to combat hypovolemia during the hemorrhagic phase of cystectomy was randomly allocated in 42 patients to receive either 5% albumin (12 mL/kg) or 20% albumin (3 mL/kg) over 30 min at the beginning of the hemorrhagic phase, both completed by a Ringer-lactate replacing blood loss in a 1:1 ratio, or Ringer-lactate alone to replace blood loss in a 3:1 ratio. Measurements of blood hemoglobin over 5 h were used to estimate the effectiveness of each fluid to expand the blood volume using the following regression equation: blood loss plus blood volume expansion = factor + volume of infused albumin + volume of infused Ringer-lactate. RESULTS: The median hemorrhage was 848 mL [IQR: 615-1145]. The regression equation showed that the Ringer-lactate solution expanded the plasma volume by 0.18 times the infused volume while the corresponding power of 5% and 20% albumin was 0.74 and 2.09, respectively. The Ringer-lactate only fluid program resulted in slight hypovolemia (mean, - 313 mL). The 5% and 20% albumin programs were more effective in filling the vascular system; this was evidenced by blood volume changes of only + 63 mL and - 44 mL, respectively, by long-lasting plasma volume expansion with median half time of 5.5 h and 4.8 h, respectively, and by an increase in the central venous pressure. CONCLUSION: The power to expand the plasma volume was 4 and almost 12 times greater for 5% albumin and 20% albumin than for Ringer-lactate, and the effect was sustained over 5 h. The clinical efficacy of albumin during major hemorrhage was quite similar to previous studies with no hemorrhage. TRIAL REGISTRATION: ClinicalTrials.gov NCT05391607, date of registration May 26, 2022.

Role of splanchnic circulation in the pathogenesis of heart failure: State-of-the-art review.

A hallmark of heart failure (HF), whether it presents itself during rest or periods of physical exertion, is the excessive elevation of intracardiac filling pressures at rest or with exercise. Many mechanisms contribute to the elevated intracardiac filling pressures, and notably, the concept of volume redistribution has gained attention as a cause of the elevated intracardiac filling pressures in patients with HF, particularly HF with preserved ejection fraction, who often present without symptoms at rest, with shortness of breath and fatigue appearing only during exertion. This phenomenon suggests cardiopulmonary system non-compliance and inappropriate volume distribution between the stressed and unstressed blood volume components. A substantial proportion of the intravascular blood volume is in the splanchnic vascular compartment in the abdomen. Preclinical and clinical investigations support the critical role of the sympathetic nervous system in modulating the capacitance and compliance of the splanchnic vascular bed via modulation of the greater splanchnic nerve (GSN). The GSN activation by stressors such as exercise causes excessive splanchnic vasoconstriction, which may contribute to the decompensation of chronic HF via volume redistribution from the splanchnic vascular bed to the central compartment. Accordingly, for example, GSN ablation for volume management has been proposed as a potential therapeutic intervention to increase unstressed blood volume. Here we provide a comprehensive review of the role of splanchnic circulation in the pathogenesis of HF and potential novel treatment options for redistributing blood volume to improve symptoms and prognosis in patients with HF.

Remote Heart Rate Estimation Based on Transformer with Multi-Skip Connection Decoder: Method and Evaluation in the Wild.

Heart rate is an essential vital sign to evaluate human health. Remote heart monitoring using cheaply available devices has become a necessity in the twenty-first century to prevent any unfortunate situation caused by the hectic pace of life. In this paper, we propose a new method based on the transformer architecture with a multi-skip connection biLSTM decoder to estimate heart rate remotely from videos. Our method is based on the skin color variation caused by the change in blood volume in its surface. The presented heart rate estimation framework consists of three main steps: (1) the segmentation of the facial region of interest (ROI) based on the landmarks obtained by 3DDFA; (2) the extraction of the spatial and global features; and (3) the estimation of the heart rate value from the obtained features based on the proposed method. This paper investigates which feature extractor performs better by captioning the change in skin color related to the heart rate as well as the optimal number of frames needed to achieve better accuracy. Experiments were conducted using two publicly available datasets (LGI-PPGI and Vision for Vitals) and our own in-the-wild dataset (12 videos collected by four drivers). The experiments showed that our approach achieved better results than the previously published methods, making it the new state of the art on these datasets.

Effect of using smaller blood volume tubes and closed blood collection devices on total blood loss in patients undergoing major cardiac and vascular surgery.

BACKGROUND: Diagnostic laboratory tests are an integral part of managing hospitalized patients. In particular, patients in the intensive care units (ICUs) can experience a concerning amount of blood loss due to diagnostic testing, which can increase the risk developing iatrogenic anemia. Several interventions exist to curtail avoidable blood loss, for example computerized decision support, smaller phlebotomy tubes, and other blood conservation devices. Nevertheless, use of these interventions is not standardized. Therefore, the objective of our study was to quantify the daily phlebotomy volume taken from patients who had undergone major cardiac or vascular surgery. METHODS: We estimated the number of blood analyses and volumes of drawn blood of 400 consecutive patients (≥ 18 yr) undergoing major cardiac or vascular surgery. The amount of blood saved using small-volume tubes and in combination with blood conservation device rather than standard-volume tubes was estimated for serum chemistry (serum), ethylenediaminetetraacetic acid (EDTA) tubes, sodium citrate coagulation (SCC) tubes, and arterial blood gas (ABG) analysis. RESULTS: The mean total blood loss due to phlebotomy drawing using standard-volume tubes during hospitalization was 167.9 mL (95% confidence interval [CI], 158.0 to 177.8), 255.6 mL (95% CI, 226.5 to 284.6), and 695.3 mL (95% CI, 544.1 to 846.4) for patients undergoing cardiac surgery with a hospital length of stay (LOS) of 0-10, 11-20, and ≥ 21 days, respectively. The mean total blood loss due to phlebotomy during hospitalization was 80.5 mL (95% CI, 70.5 to 90.6), 225.0 mL (95% CI, 135.1 to 314.8 mL) and 470.3 mL (95% CI, 333.5 to 607.1) for vascular surgery patients with LOS 0-10, 11-20, and ≥ 21 days, respectively. Patients with at least a two-day stay at the ICU had a mean blood loss of 146.6 mL (95% CI, 134.6 to 158.6 mL) and those with ≥ 11 days incurred a loss of 1,428 mL (95% CI, 1,117.8 to 1,739.2). The use of closed blood collection device and small-volume tubes (serum, EDTA, SCC, and ABG) reduced blood loss by 82.8 mL for patients with an ICU stay of 2 days and up to 824.0 mL for patients with a ICU stay of ≥ 11 days. CONCLUSION: Diagnostic laboratory tests are associated with significant patient blood loss, but are a modifiable risk factor. The use of small-volume tubes and closed blood collection devices decreases the volume of patient blood drawn for analysis and prevents blood waste.

RéSUMé: CONTEXTE: Les tests diagnostiques de laboratoire font partie intégrante de la prise en charge des personnes hospitalisées. Plus spécifiquement, la patientèle des unités de soins intensifs (USI) peut perdre une quantité inquiétante de sang en raison des tests de diagnostic, ce qui peut augmenter le risque d'anémie iatrogène. Plusieurs interventions existent pour réduire les pertes de sang évitables, par exemple une aide à la décision informatisée, des tubes de phlébotomie plus petits et d'autres dispositifs de conservation du sang. Néanmoins, le recours à ces interventions n'est pas normalisé. Par conséquent, l'objectif de notre étude était de quantifier le volume quotidien de phlébotomie prélevée chez des patient·es ayant bénéficié d'une chirurgie cardiaque ou vasculaire majeure. MéTHODE: Nous avons estimé le nombre d'analyses sanguines et les volumes de sang prélevés de 400 personnes consécutives (≥ 18 ans) bénéficiant d'une chirurgie cardiaque ou vasculaire majeure. La quantité de sang économisée à l'aide de tubes de petit volume et en combinaison avec un dispositif de conservation du sang plutôt que des tubes de volume standard a été estimée pour la chimie sérique (sérum), les tubes d'acide éthylène-diamine-tétra-acétique (EDTA), les tubes de coagulation au citrate de sodium (CCS) et l'analyse des gaz du sang artériel (GSA). RéSULTATS: La perte sanguine totale moyenne due au prélèvement de phlébotomie à l'aide de tubes de volume standard pendant l'hospitalisation était de 167,9 mL (intervalle de confiance [IC] à 95 %, 158,0 à 177,8), 255,6 mL (IC 95 %, 226,5 à 284,6) et 695,3 mL (IC 95 %, 544,1 à 846,4) chez les patient·es bénéficiant d'une chirurgie cardiaque avec une durée de séjour à l'hôpital de 0 à 10, 11 à 20, et ≥ 21 jours, respectivement. La perte sanguine totale moyenne due à la phlébotomie pendant l'hospitalisation était de 80,5 mL (IC 95 %, 70,5 à 90,6), 225,0 mL (IC 95 %, 135,1 à 314,8 mL) et 470,3 mL (IC 95 %, 333,5 à 607,1) chez les patient·es ayant bénéficié d'une chirurgie vasculaire avec des durées de séjour de 0-10, 11-20 et ≥ 21 jours, respectivement. Les patient·es ayant séjourné au moins deux jours à l'USI ont eu une perte de sang moyenne de 146,6 mL (IC 95 %, 134,6 à 158,6 mL) et celles et ceux ayant séjourné ≥ 11 jours ont subi une perte de 1428 mL (IC 95 %, 1117,8 à 1739,2). L'utilisation d'un dispositif de prélèvement sanguin fermé et de tubes de petit volume (sérum, EDTA, SCC et gsa) a réduit la perte de sang de 82,8 mL pour les patient·es ayant séjourné à l'USI 2 jours et jusqu'à 824,0 mL pour les patient·es ayant séjourné en USI ≥ 11 jours. CONCLUSION: Les tests de laboratoire diagnostiques sont associés à une perte de sang importante chez les patient·es, mais constituent un facteur de risque modifiable. L'utilisation de tubes de petit volume et de dispositifs fermés de prélèvement sanguin diminue le volume de sang prélevé pour analyse et prévient le gaspillage de sang.

Arterial stiffness assessment using PPG feature extraction and significance testing in an in vitro cardiovascular system.

Cardiovascular diseases (CVDs) remain the leading cause of global mortality, therefore understanding arterial stiffness is essential to developing innovative technologies to detect, monitor and treat them. The ubiquitous spread of photoplethysmography (PPG), a completely non-invasive blood-volume sensing technology suitable for all ages, highlights immense potential for arterial stiffness assessment in the wider healthcare setting outside specialist clinics, for example during routine visits to a General Practitioner or even at home with the use of mobile and wearable health devices. This study employs a custom-manufactured in vitro cardiovascular system with vessels of varying stiffness to test the hypothesis that PPG signals may be used to detect and assess the level of arterial stiffness under controlled conditions. Analysis of various morphological features demonstrated significant (p < 0.05) correlations with vessel stiffness. Particularly, area related features were closely linked to stiffness in red PPG signals, while for infrared PPG signals the most correlated features were related to pulse-width. This study demonstrates the utility of custom vessels and in vitro investigations to work towards non-invasive cardiovascular assessment using PPG, a valuable tool with applications in clinical healthcare, wearable health devices and beyond.

Evaluation of an Association Between Enoxaparin Dose per Estimated Blood Volume and Clinically Relevant Bleeding in Low-Weight Trauma Patients.

BACKGROUND: The optimal dosing for enoxaparin venous thromboembolism (VTE) prophylaxis in low-weight trauma patients is unknown. Estimated blood volume (EBV) has shown promise as a dose modifier. OBJECTIVE: To characterize the association of enoxaparin dose per EBV with the prevalence of VTE and bleeding in low-weight trauma patients. METHODS: This was a retrospective study of trauma patients admitted over a 4-year period. Included patients were adults weighing <60 kg who received a minimum of 3 consecutive doses of enoxaparin. The primary endpoint was a comparison of enoxaparin dose per EBV in patients experiencing bleeding and VTE. Secondary endpoints included comparisons of dose per body mass index (BMI) and total body weight (TBW) and the ability of dose per EBV to predict clinical endpoints. Subgroup analyses for patients weighing <50 kg were performed for all endpoints. RESULTS: A total of 189 patients were included. Statistical comparisons for VTE were not performed because of low prevalence. The dose of enoxaparin per EBV was not statistically different between patients who did and did not bleed in all analyses. Doses per BMI and TBW were also not statistically different between the groups. In patients weighing <50 kg, numerically higher doses per EBV, BMI, and TBW were noted in patients that bled versus those that did not. Enoxaparin dose per EBV was not a statistically significant predictor of bleeding in logistic regression models. CONCLUSION AND RELEVANCE: No significant associations between enoxaparin dose per EBV, BMI, or TBW and bleeding were noted in the study. Future analyses of EBV and other dose modifiers should consider inclusion of patients weighing <50 kg.

Techniques to Assess the Effect of Sodium-Glucose Cotransporter 2 Inhibitors on Blood Volume in Patients with Diabetic Kidney Disease.

BACKGROUND: Sodium-glucose cotransporter 2 (SGLT2) inhibitors exert a kidney protective effect in patients with diabetic kidney disease. Several mechanisms have been proposed, but why precisely SGLT2 inhibition has a kidney protective effect is incompletely understood. Clinical trials using SGLT2 inhibitors have found them to induce a rapid weight loss likely due to loss of sodium and subsequently fluid. While SGLT2 inhibitors are reported to increase hematocrit, it remains unknown whether the natriuretic and aquaretic effect reduces patient's blood volume and whether this could partly explain its kidney protective effects. A blood volume reduction could induce several beneficial effects with reduction in arterial and venous blood pressure as two central mechanisms. The aim of this paper was to review current techniques for assessing patient blood volume that could enhance our understanding of SGLT2 inhibitors' physiological effects. SUMMARY: Changes induced by SGLT2 inhibitors on erythrocyte volume and plasma volume can be assessed by tracer dilution techniques that include radioisotopes, indocyanine green (ICG) dye, or carbon monoxide (CO). Techniques with radioisotopes can provide direct estimates of both erythrocyte volume and plasma volume but are cumbersome procedures and the radiation exposure is a limitation for repeated measures in clinical studies. Methods more suitable for repeated assessment of erythrocyte and plasma volume include dilution of injected ICG dye or dilution of inhaled CO. ICG dye requires higher precision with timed blood samples and provides only a direct estimate of plasma volume wherefrom erythrocyte volume is estimated. Inhalation of CO is a time-effective and automated method that provides measure of the total hemoglobin mass wherefrom erythrocyte and plasma volumes are estimated. KEY MESSAGES: A kidney protective effect has been observed in clinical trials with SGLT2 inhibitors, but the underlying mechanisms are not fully understood. Significant weight loss within weeks has been reported in the SGLT2 inhibitor trials and could be related to a reduction in blood volume secondary to increased natriuresis and aquaresis. Alterations in blood volume compartments can be quantified by tracer dilution techniques and further improve our understanding of kidney protection from SGLT2 inhibitors.

Intravascular volumes and the influence on anemia assessed by a carbon monoxide rebreathing method in patients undergoing maintenance hemodialysis.

INTRODUCTION: Fluid overload is a major challenge in hemodialysis patients and might cause hypervolemia. We speculated that hemodialysis patients reaching dry weight could have undetected hypervolemia and low hemoglobin (Hb) concentration (g/dL) due to hemodilution. METHODS: The study included hemodialysis patients (n = 22) and matched healthy controls (n = 22). Blood volume, plasma volume, red blood cell volume, and total Hb mass were determined using a carbon monoxide (CO)-rebreathing method in hemodialysis patients reaching dry weight and controls. Blood volume measurements were also obtained by a dual-isotope labeling technique in a subgroup for validation purposes. FINDINGS: In the hemodialysis group, the median specific blood volume was 89.3 mL/kg (interquartile range [IQR]: 76.7-95.4 mL/kg) and was higher than in the control group (79.9 mL/kg [IQR: 70.4-88.0 mL/kg]; p < 0.037). The median specific plasma volume was 54.7 mL/kg (IQR: 47.1-61.0 mL/kg) and 44.0 mL/kg (IQR: 38.7-49.5 mL/kg) in the hemodialysis and control groups, respectively (p < 0.001). Hb concentration was lower in hemodialysis patients (p < 0.001), whereas no difference in total Hb mass was observed between groups (p = 0.11). A correlation was found between blood volume measured by the CO-rebreathing test and the dual-isotope labeling technique in the control group (r = 0.83, p = 0.015), but not the hemodialysis group (r = 0.25, p = 0.60). DISCUSSION: The hemodialysis group had increased specific blood volume at dry weight due to high plasma volume, suggesting a hypervolemic state. However, correlation was not established against the dual-isotope labeling technique underlining that the precision of the CO-rebreathing test should be further validated. The total Hb mass was similar between hemodialysis patients and controls, unlike Hb concentration, which emphasizes that Hb concentration is an inaccurate marker of anemia among hemodialysis patients.

Low- and high-volume blood-flow restriction treadmill walking both improve maximal aerobic capacity independently of blood volume.

AIM: Assess the effect of low- and high-volume blood flow restriction training (BFR) on maximal aerobic capacity (VO2 max) and determine if alteration in VO2 max is mediated through changes in hemoglobin mass (Hbmass) and blood volume. METHODS: Participants' Hbmass (CO-rebreathe), single, and double-leg VO2 max and blood volume regulating hormonal responses (renin and copeptin) were measured before and after BFR training. Training consisted of treadmill walking either (1) twice-daily for 4week (CON and BFRHV ) or (2) twice-weekly for 6week (BFRLV ). Each session consisted of five intervals (3 min, 5% incline, 5 km/h, 100% of lowest occlusion pressure), with 1 min of standing rest between sets. RESULTS: VO2 max increased using both training exposures, in as quickly as 2-weeks (BFRLV baseline to 4week: +315 ± 241 mL (8.7%), p = 0.02; BFRHV baseline to 2week: +360 ± 261 mL (7.9%), p < 0.01), for the BFRLV and BFRHV groups, with no change in CON. Single- and double-leg VO2 max improved proportionately (single/double-leg VO2 max ratio: BFRLV 78 ± 4.9-78 ± 5.8%, BFRHV 79 ± 6.5-77 ± 6.5%), suggesting that the mechanism for increased VO2 max is not solely limited to central or peripheral adaptations. Hbmass remained unchanged across groups (CON: +10.2 ± 34 g, BFRLV : +6.6 ± 42 g, BFRHV : +3.2 ± 44 g; p = 0.9), despite a significant release of blood volume regulating hormones after initial BFR exposure (renin +20.8 ± 21.9 ng/L, p < 0.01; copeptin +22.0 ± 23.8 pmol/L, p < 0.01), which was blunted following BFRHV training (renin: +13.4 ± 12.4 ng/L, p = 0.09; copeptin: +1.9 ± 1.7 pmol/L, p = 0.98). CONCLUSION: BFR treadmill walking increases VO2 max irrespective of changes in Hbmass or blood volume despite a large release of blood volume regulating hormones in response to BFR treadmill walking.