Oxygen transport and 2,3-diphosphoglycerate (DPG)

Relative anemia and perioperative stroke in children with moyamoya

OBJECTIVES

Surgical revascularization for moyamoya arteriopathy decreases long-term stroke risk but carries a risk of perioperative ischemic complications. We aimed to evaluate modifiable stroke risk factors in children undergoing surgical revascularization for moyamoya.

MATERIALS AND METHODS

In this exploratory, single-center, retrospective cohort study, medical records of pediatric patients undergoing surgical revascularization for moyamoya arteriopathy at our center between 2003 and 2021 were reviewed. Candidate modifiable risk factors were analyzed for association with perioperative stroke, defined as ischemic stroke ≤7 days after surgery.

RESULTS

We analyzed 53 surgeries, consisting of 39 individual patients undergoing indirect surgical revascularization of 74 hemispheres. Perioperative ischemic stroke occurred following five surgeries (9.4%). There were no instances of hemorrhagic stroke. Larger pre-to-postoperative decreases in hemoglobin (OR 3.90, p=0.017), hematocrit (OR 1.69, p=0.012) and blood urea nitrogen (OR 1.83, p=0.010) were associated with increased risk of perioperative ischemic stroke. Weight-adjusted intraoperative blood loss was not associated with risk of perioperative ischemic stroke (OR 0.94, p=0.796). Among children with sickle cell disease, all of whom underwent exchange transfusion within one week prior to surgery, none experienced perioperative stroke.

CONCLUSIONS

Decreases in hemoglobin, hematocrit, and blood urea nitrogen between the preoperative and postoperative periods are associated with increased risk of perioperative stroke. These novel findings suggest that dilutional anemia, possibly due to standardly administered hyperhydration, may increase the risk of perioperative stroke in some children with moyamoya. Further work optimizing both mean arterial pressure and oxygen-carrying capacity in these patients, including consideration of alternative blood transfusion thresholds, is necessary.

Erythrocytes Functionality in SARS-CoV-2 Infection: Potential Link with Alzheimer's Disease

Coronavirus disease 2019 (COVID-19) is a rapidly spreading acute respiratory infection caused by SARS-CoV-2. The pathogenesis of the disease remains unclear. Recently, several hypotheses have emerged to explain the mechanism of interaction between SARS-CoV-2 and erythrocytes, and its negative effect on the oxygen-transport function that depends on erythrocyte metabolism, which is responsible for hemoglobin-oxygen affinity (Hb-O2 affinity). In clinical settings, the modulators of the Hb-O2 affinity are not currently measured to assess tissue oxygenation, thereby providing inadequate evaluation of erythrocyte dysfunction in the integrated oxygen-transport system. To discover more about hypoxemia/hypoxia in COVID-19 patients, this review highlights the need for further investigation of the relationship between biochemical aberrations in erythrocytes and oxygen-transport efficiency. Furthermore, patients with severe COVID-19 experience symptoms similar to Alzheimer's, suggesting that their brains have been altered in ways that increase the likelihood of Alzheimer's. Mindful of the partly assessed role of structural, metabolic abnormalities that underlie erythrocyte dysfunction in the pathophysiology of Alzheimer's disease (AD), we further summarize the available data showing that COVID-19 neurocognitive impairments most probably share similar patterns with known mechanisms of brain dysfunctions in AD. Identification of parameters responsible for erythrocyte function that vary under SARS-CoV-2 may contribute to the search for additional components of progressive and irreversible failure in the integrated oxygen-transport system leading to tissue hypoperfusion. This is particularly relevant for the older generation who experience age-related disorders of erythrocyte metabolism and are prone to AD, and provide an opportunity for new personalized therapies to control this deadly infection.

Determinants of oxygen delivery and hemoglobin saturation during incremental exercise in horses

OBJECTIVE

To determine components of the increase in oxygen consumption (VO2) and evaluate determinants of hemoglobin saturation (SO2) during incremental treadmill exercise in unfit horses.

ANIMALS

7 unfit adult mares.

PROCEDURES

Horses performed 1 preliminary exercise test (EXT) and 2 experimental EXT. Arterial and mixed venous blood samples and hemodynamic measurements were taken during the last 30 seconds of each step of the GXT to measure PO2, hemoglobin concentration ([Hb]), SO2, and determinants of acid-base state (protein, electrolytes, and PCO2).

RESULTS

Increased VO2 during exercise was facilitated by significant increases in cardiac output (CO), [Hb], and widening of the arteriovenous difference in O2. Arterial and venous pH, PaO2, and PvO2 decreased during exercise. Arterial PCO2, bicarbonate ([HCO3-])a, and [HCO3-] decreased significantly, whereas PVCO2 and increased. Arterial and venous sodium concentration, potassium concentration, strong ion difference, and venous lactate concentration all increased significantly during exercise.

CONCLUSIONS AND CLINICAL RELEVANCE

Increases in CO, [Hb], and O2 extraction contributed equally to increased VO2 during exercise. Higher PCO2 did not provide an independent contribution to shift in the oxyhemoglobin dissociation curve (OCD) in venous blood. However, lower PaCO2 shifted the curve leftward, facilitating O2 loading. The shift of ODC resulted in minimal effect on O2 extraction because of convergence of the ODC at lower values of PO2. Decreased pH appeared responsible for the rightward shift of the ODC, which may be necessary to allow maximal O2 extraction at high blood flows achieved during exercise.

Arterial hypoxemia and performance during intense exercise

In order to determine the level of hypoxemia which is sufficient to impair maximal performance, seven well-trained male cyclists [maximum oxygen consumption (VO2max) > or = 5 l.min-1 or 60 ml.kg-1.min-1] performed a 5-min performance cycle test to exhaustion at maximal intensity as controlled by the subject, under three experimental conditions: normoxemia [percentage of arterial oxyhemoglobin saturation (%SaO2) > 94%], and artificially induced mild (%SaO2 = 90 +/- 1%) and moderate (% SaO2 = 87 +/- 1%) hypoxemia. Performance, evaluated as the total work output (Worktot) performed in the 5-min cycle test, progressively decreased with decreasing % SaO2 [mean (SE) Worktot = 107.40 (4.5) kJ, 104.07 (5.6) kJ, and 102.52 (4.7) kJ, under normoxemia, mild, and moderate hypoxemia, respectively]. However, only performance in the moderate hypoxemia condition was significantly different than in normoxemia (P = 0.02). Mean oxygen consumption and heart rate were similar in the three conditions (P = 0.18 and P = 0.95, respectively). End-tidal partial pressure of CO2 was significantly lower (P = 0.005) during moderate hypoxemia compared with normoxemia, and ventilatory equivalent of CO2 was significantly higher (P = 0.005) in both hypoxemic conditions when compared with normoxemia. It is concluded that maximal performance capacity is significantly impaired in highly trained cyclists working under an % SaO2 level of 87% but not under a milder desaturation level of 90%.

Respiratory failure due to choriocarcinoma: a study of 103 dyspneic patients

Treatment of choriocarcinoma is mostly successful but there is still appreciable mortality from early respiratory failure. A series of 135 patients with choriocarcinoma presenting with dyspnea between 1960 and 1988 was studied to find prognostic factors for early respiratory death and to identify how mortality may be further reduced. Mortality with respect to early respiratory death (ERD) was 11% and was significantly associated with WHO prognostic score, chest X-ray appearance, central cyanosis, tachycardia, anemia, and clinical evidence of pulmonary hypertension. Indicators on chest X ray of high risk of ERD were the presence of more than 10 opacities, extensive opacification of lung fields, size of metastases, and hazy background obscuring the vascular pattern. Intensity of initial treatment was not correlated with this outcome. A set of criteria has been derived which will predict ERD with 100% sensitivity and 38% positive predictive value. These are opacification of lung fields on chest X ray of more than 50%, OR initial plasma hCG level greater than 10(5) when there is anemia and a history of chest pain. Patients presenting with choriocarcinoma and dyspnea who fulfill these criteria should be considered for extracorporeal perfusion techniques. As respiratory failure in this condition is characterized by hypoxemia and right-to-left shunting, extracorporeal perfusion should be effective. Ventilation should be avoided as no patient survived mechanical ventilation.

Effects of the dipyridamol-dihydroergotoxine methane sulphonate associations on pO2 and its incidence in brain tissue

Several groups of rats were treated with dipyridamol and dihydroergotoxine methane sulphonate and their association. Their clinical constants were then monitored and their brain tissue examined by optical microscopy. This study indicates that the association has a remarkable effect on the pO2, maintaining the level of 2,3-diphosphoglycerate concentration, and moreover a vasodilatory action, facilitating a better supply of oxygen to the cerebral cells. The results show the advantage of these drugs in treating cerebral vascular disease.

The effect of hemodialysis on oxygen transport in chronic uremics

Previous studies from our laboratory suggested a decrease in tissue oxygen delivered during hemodialysis of chronic uremic patients due to an increase in hemoglobin-oxygen affinity, i.e. decrease in P50. This current study was designed to determine whether the changes in cardiac index and/or tissue oxygen extraction could compensate for increases in hemoglobin-oxygen affinity previously observed, so that total tissue delivery was unchanged during hemodialysis. This study demonstrated in patients during a 6-hour hemodialysis that: 1) no change occurs in hemoglobin-oxygen affinity expressed as P50, with unchanging plasma inorganic phosphate and red blood cell pH; 2) increased extraction of oxygen from tissue, measured via (A-V) O2 difference compensates for decreased oxygen delivery due to decreased cardiac output, and although there was no demonstrable change in hemoglobin-oxygen affinity, it would appear that increased tissue extraction of oxygen via other mechanisms should be easily able to compensate for previously reported changes in P50.

Hemodynamic predictors of myocardial oxygen consumption during static and dynamic exercise

Hemodynamic predictors of myocardial oxygen consumption (MVO 2 ) during static and dynamic exercise were examined in ten normal subjects. Studies were done under the following circumstances: 1) during upright bicycle exercise at an average heart rate of 147 beats/min, 2) during static exercise with an isometric load in the left hand equal to 17% of the maximal voluntary contraction (MVC), and 3) during combined dynamic exercise (average heart rate 147 beats/min) and static exercise using 17% MVC of the left hand. Mean myocardial blood flow (MBF) was 181 ml/100 gm LV/min during dynamic exercise, 98 ml/100 gm LV/min during static exercise, and 201 ml/100 gm LV/min during combined static and dynamic exercise. Addition of a static load to the dynamic load resulted in a higher blood pressure (average 12 mm Hg), MVO 2 and MBF than during dynamic exercise alone. MVO 2 correlated best with products of heart rate and blood pressure regardless of whether the blood pressure was obtained by a central aortic catheter ( r = 0.88) or by a blood pressure cuff ( r = 0.85).

When the current data were combined with previous data, 82 determinations of MVO 2 and MBF in 29 normal subjects during several levels of upright exercise were available for analysis. Forty-four determinations were done during dynamic upright exercise, 18 during exercise after propranolol, ten during combined static and dynamic work, and ten during static work alone. MVO 2 correlated best with the product of heart rate and blood pressure ( r = 0.86). Heart rate alone correlated better with MVO 2 ( r = 0.82) than did the tension time index ( r = 0.65) or the product of systolic blood pressure, heart rate, and ejection time ( r = 0.68). The readily measured variables of heart rate and of heart rate x blood pressure correlated well with MVO 2 in normal young men during exercise under a wide variety of circumstances.