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Hypothesis The changes reported with pulse oximetry after the injection of isosulfan blue for sentinel lymph node identification in patients with breast cancer are consistent and predictable. Design Retrospective study. Setting University hospital. Patients and Methods The complete anesthesia records of 92 patients who underwent sentinel lymph node biopsy with intraparenchymal injection of isosulfan blue were reviewed. The study extended from January 1999 to February 2000. The operations were all performed after the patient received general anesthesia. We injected 5 mL of isosulfan blue into the breast tissue surrounding the tumor. The data reviewed included preinjection pulse oximeter saturation readings and postinjection values continuing until the readings returned to baseline levels in the postanesthesia care unit. Main Outcome Measures Changes in oxygen saturation readings with the pulse oximeter before and after injection of isosulfan blue. Results Isosulfan blue injection interfered with pulse oximeter measurements for a substantial time—as much as 195 minutes. The mean time to the maximum change in the pulse oximeter reading was 35 minutes. The median decrease in oxygen saturation was 5%. The maximum decrease in the pulse oximeter reading was 11%. Conclusions Although the changes in pulse oximeter readings can be substantial, their course appears to be predictable, and therefore in most otherwise healthy patients with normal pulmonary function, invasive monitoring is not necessary.

In recent years there has been a great deal of progress in understanding the homeostasis of different tissue microenvironments, and this has been particularly true of the hematopoietic system. Insights into the interaction of the microenvironmental stromal cells of the bone marrow with the blood

SUMMARY The influence of cardiac output on the correlation between central venous oxygen saturation and mixed venous oxygen saturation was assessed in 51 patients who had both a pulmonary artery catheter and separate central venous catheter in situ. Seventy-six paired samples were taken from the catheters and oxygen saturation measured immediately in a Ciba Corning 2500 Co-oximeter. Cardiac output was measured using a standard thermodilution technique. The data were separated into groups with low cardiac index ( −1 m −2 ; n=20). medium cardiac index (2.5–4.0 litre min −1 m −2 ; n=36) and high cardiac index (> 4.0 litre min −1 m −2 ; n=20). The correlation coefficients of the three groups were: low cardiac index 0.95, medium cardiac index 0.88 and high cardiac index 0.95 (P

Unlabelled Near-infrared spectroscopy has been used to monitor cerebral oxygen saturation during cerebral circulatory arrest and carotid clamping. However, its utility has not been demonstrated in more complex situations, such as in patients with head injuries. The authors tested this method during conditions that may alter the arteriovenous partition of cerebral blood in different ways. Methods The authors compared changes in measured cerebral oxygen saturation and other hemodynamic parameters, including jugular venous oxygen saturation, in nine patients with severe closed head injury during manipulation of arterial carbon dioxide partial pressure and after mean arterial pressure was altered by vasopressors. Results The Bland and Altman representation of cerebral oxygen saturation versus jugular oxygen saturation showed a uniform scatter. Values for changing arterial carbon dioxide partial pressure were: bias = 1.1%, 2 SD = +/-21%, absolute value; and those for alterations in mean arterial pressure: bias = 3.7%, 2 SD = +/-24%, absolute value. However, a Bland and Altman plot of changes in cerebral oxygen saturation versus changes in jugular oxygen saturation had a negative slope (alteration in arterial carbon dioxide partial pressure: bias = 2.4%, 2 SD = +/-17%, absolute value; alteration in mean arterial pressure: bias = -4.9%, 2 SD = +/-31%, absolute value). Regression analysis showed that changes in cerebral oxygen saturation were positively correlated with changes in jugular venous oxygen saturation during the carbon dioxide challenge, whereas correlation was negative during the arterial pressure challenge. Conclusions Cerebral oxygen saturation assessed by near-infrared spectroscopy does not adequately reflect changes in jugular venous oxygen saturation in patients with severe head injury. Changes in arteriovenous partitioning, infrared-spectroscopy contamination by extracerebral signal, algorithm errors, and dissimilar tissue sampling may explain these findings.

This study was designed to determine the extent of coupling between regional myocardial segment work and corresponding regional oxygen consumption, and to examine whether tachycardia induced changes in regional work are translated into corresponding changes in external cardiac work. In the open chest anaesthetised dog, the heart was paced at frequencies of 120-270 beats.min-1. Global and regional myocardial O2 supply, consumption, and balance were evaluated at each heart rate, and correlated with corresponding functional changes. Global cardiac function was evaluated from aortic flow, blood pressure, and left ventricular pressure. Coronary sinus flow and O2 saturation were used to calculate O2 consumption. The integrated multiple of myocardial shortening (ultrasonic dimension crystals) by corresponding force (strain gauge arch) during an averaged beat was used to express regional segment work. Regional coronary blood flow was measured with radioactive microspheres, and microspectrophotometry was used to evaluate O2 saturation in small arteries and veins. These indices were used to calculate regional myocardial oxygen consumption. NADH redox levels were recorded by surface fluorometry, and were found to increase with heart rate by up to 67%. Increasing heart rate from 120 to 180 beats.min-1 increased regional work from 3040(SEM 220) to a peak of 4290(280) mm.g-1.min-1, whereas external cardiac work did not increase [67.0(2.6) to 65.3(4.4) mm Hg.litre-1.min-1] and fell further at the highest rates. Regional oxygen consumption increased from 6.16(0.47) to 8.29(0.53) ml O2.min-1.100 g-1 and was linearly related to regional work at all heart rates (r = 0.971, p less than 0.05). External cardiac work fell by about 26% whereas global myocardial oxygen consumption increased by 49% during tachycardia. It is concluded that myocardial oxygen consumption is more closely related to regional segment work than to external work, and that tachycardia significantly raises the oxygen cost of external work of the heart.

A study of the estimated hepatic blood flow (EHBF) using a colloidal gold technique in 28 patients undergoing saphenous vein stripping, showed that the EHBF decreased to 68% of its initial value during the period of halothane anaeshtesia and operation. When enteral oxygen was added EHBF increased to 82% of its initial value. An investigation in 14 other patients under going upper abdominal operations showed that enteral oxygen administration caused the oxygen saturation of the portal blood to increase from 55+/-7.2% (mean +/- SEM) to 80+/-6.2% and, by producing a concomitant decrease in portal pressure, led to a reduction in the portocaval pressure gradient from 74+/-12.5 to 38+/-8.7 mm H2O. It is suggested that the oxygen content of the portal blood per se influences the tone of hepatic presinusoidal sphincters. It is concluded that enteral oxygen administration may minimize disturbances in the hepatic circulation occurring during halothane anaesthesia and surgical operations.

Arterial hypoxemia may contribute to morbidity during cardiac catheterization. Therefore, we measured arterial hemoglobin oxygen saturation (SaO2) continuously using pulse oximetry in 29 patients (age range, 21 to 83 years) undergoing cardiac catheterization. Baseline SaO2 was 96 +/- 0.4 percent. All patients had a decrease in SaO2 at some time during the procedure. Eleven patients (38 percent) had episodes of arterial hypoxemia, defined as a decrease in SaO2 below 90 percent. In these 11 patients, the mean number of episodes of hypoxemia was 16 +/- 7, and the mean duration of each episode was 53 +/- 25 seconds. Multiple stepwise regression analysis showed that the minimum SaO2 during catheterization for any patient was significantly associated with the baseline SaO2, duration of the procedure, and end-diastolic volume (EDV) as described by the following regression equation: minimum SaO2 = 46.8 - 0.0580 (duration of procedure in minutes) + 0.5362 (baseline SaO2) - 0.0159 (EDV). Based on our finding of arterial hypoxemia in greater than one third of our patients, we would consider continuous SaO2 monitoring or supplemental oxygen during cardiac catheterization, especially for those patients with poor ventricular function or low resting SaO2 or those expected to have long procedures.

Two denitrifying bacteria ( Pseudomonas chlororaphis and P. aureofaciens ) and a plant (barley, Hordeum vulgare ) were used to study the effect of O2 concentration on denitrification and NO3− uptake by roots under well-defined aeration conditions. Bacterial cells in the early stationary phase were kept in a chemostat vessel with vigorous stirring and thus a uniform O2 concentration in the solution. Both Pseudomonads lacked N2O reductase and so total denitrification could be directly measured as N2O production. Denitrification decreased to 6–13% of the anaerobic rate at 0.01% O2 saturation (0.14 μM O2) and was totally inhibited at 0.04% O2 saturation (0.56 μM O2). In this well-mixed system denitrification was 10-times more oxygen sensitive than stated in earlier reports. Uptake of nitrate by plants was measured in the same system under light. The NO3− uptake rate decreased gradually from a maximum in 21% O2-saturated medium (air saturated) to zero at 1.6% O2 saturation (22.4 μM O2). Owing to the very different non-overlapping oxygen requirements of the two processes, direct competition for nitrate between plant roots and denitrifying bacteria cannot occur.

At sea level, it appears that oxygen desaturation does not occur in normal children at night and that the desaturation that occurs in moderately severe asthmatic children with therapeutic levels of theophylline does not approach dangerously low levels.

We have developed a computerized analysis of respiratory and body movements (static charge sensitive bed [SCSB]), oxygen saturation (pulse oximeter), and airflow (thermistor) for the evaluation of sleep related apneas. The cumulative distribution of oxygen saturation, the number and distribution of desaturation events, and the duration and type of apneas are assessed. Analysis is performed separately during the total recording time and during the time when the patient sleeps on his back. We have compared the automatic analysis with the results obtained on simultaneous daytime polysomnograph naps in 55 subjects (snorers or obstructive sleep apnea syndrome [OSAS] patients). The compressed graphs obtained automatically demonstrated a periodic breathing pattern in all 22 patients who presented sleep-related apneas at polygraphic recording. The cumulative distribution of oxygen saturation was not as steep in the apnea patients as in patients not showing apneas; in 19 of the 22 OSAS patients, the value was outside our normal limits (80 percent of the recording time inside 3.6 percent SaO2 variation band). The apnea index (AI) was 26.4 in manual and 23.3 in automatic analysis. Using the automatic method diere were three false negative cases in the analysis of desaturations; in these patients periodic breathing was present in output graphs indicating need for further polygraphic assessment. The duration of apneas in the automatic analysis was shorter than in manual analysis, but the agreement was sufficient for screening purposes (mean error less than 3 s, mean duration of apneas 20.1 s). The automatic method is presently used in clinical routine for screening purposes, for assessment of the severity of the disorder and the type of treatment that a subject may need, in epidemiologic investigation and follow-up of the treatment. (Chest 1989; 96:255–61)

The strong absorbance of indocyanine green in a broad band around lambda = 800 nm invalidates the usual spectrophotometric two-wavelength methods for measuring oxygen saturation operating in the red and near infrared region. By proper wavelength selection, however, the effect of the dye can be eliminated. With the two-wavelength method utilising lambda = 660 and 860 nm oxygen saturation is measured virtually independent of the presence of indocyanine green.

Venous blood from the dorsal surface of the hot hand of 23 conscious patients was analyzed by micromethods. The pH, Pco2, Po2 and derived oxygen saturation were compared with those of blood taken from the radial artery; significant differences were found. Arterialized venous blood may be regarded as arterial blood with a venous admixture which in this series averaged about 11 per cent of the total flow through the hand. For clinical measurements of Pco2 and pH, arterialized venous blood may provide an adequate estimate. It appears to be of little use as a measure of arterial Po2 or oxygen saturation.

SUMMARY Studies were made to test the effects in mice exposed to halothane of various percentages of oxygen in the anaesthetic vehicle were on induction and survival times. Over all, increaing oxygen concentrations in the vechicle were associated with longer induction times with 4 per cent and 10 per cent halothane and with longer survival times with 10 per cent halothane. It is not possible from the results to define accurately the respective roles which haemoglobin, oxygen saturation, and the carriage of oxygen in solution in the plasma, play in prolonging induction and survival times.

ANAESTHETISTS have long bees in the habit of administering oxygen-rich gas mixtures. Some administer almost pure oxygen (Johnstone, 1959) and when pulmonary ventilation is allowed to become grossly deficient this is undoubtedly necessary if anoxia is to be avoided. Others take the view that an adequate minute volume should be ensured, and that it is therefore unnecessary to administer more than 20 per cent oxygen (for example, ordinary room air) except in occasional circumstances. In Oxford this latter view is held (Parkhouse and Simpson, 1959) and a clinical trial has been concluded recently, in which 1,250 cases were anaesthetized with volatile agents vaporized in room air. Although this method of anaesthesia is quite satisfactory from the clinical point of view the writers are aware that there is doubt in some anaesthetists' minds as to whether the patient's colour is always a reliable guide to the adequacy of his arterial oxygen saturation. Accordingly it was decided to make a full investigation of blood oxygen levels during anaesthesia with volatile agents vaporized in room air. PREVIOUS INVESTIGATIONS

1. Injection of a suspension of potato starch cells into the left branch of the pulmonary artery, in quantity sufficient ordinarily to give rise to markedly accelerated respirations, resulted in no change in respiratory rate. 2. A method for injecting substances into the pulmonary artery or its branches without interfering with the blood flow to the lungs has been described. 3. Injection of similar material into one lung when the other is excluded from the circulation either by ligation or by temporary clamping does give rise to rapid and shallow breathing (from a rate of 10 to 15 per minute to one of 60 or over) identical in character to that brought about by introducing emboli into both lungs. 4. A method for clamping and releasing the pulmonary artery or its branches in a dog breathing normally with closed thorax has been devised. This is described in detail in another paper. 5. After rapid breathing has been initiated by the effect of emboli lodged in the arterioles and capillaries of the right lung, reestablishing the circulation in the other lung by releasing the clamp on its artery may or may not restore the respiratory rate to its original, normal level. 6. This discrepancy in results has not been correlated with any difference in oxygen saturation of the arterial blood, or in carbon dioxide tension or pH of its plasma. 7. It is, however, believed to be related to the gross and microscopic anatomy of the lung of which the artery has been temporarily clamped. Photomicrographs are published, showing in one dog (No. 3), in which the respiratory rate returned to normal, a normal histological picture of the left lung, and in another dog (No. 4), in which the rate remained rapid after release of the clamp, a picture characterized by congestion and dilatation of arterioles and capillaries. 8. The fact that accelerated respirations result from emboli in the pulmonary capillaries and arterioles only after a certain quantity of material has been introduced, and the fact that emboli in one lung do not occasion accelerated respirations unless the circulation through the other lung is occluded or abnormal, leads us to the conclusion that the phenomenon is not an irritative stimulus due to foreign bodies, but is in some manner related to (a) diminution of the pulmonary vascular bed, (b) resistance to the blood flow through the lungs or (c) congestion or dilatation of the arterioles and capillaries of the lungs.

SUMMARY A consecutive series of patients undergoing cardiac surgery for valve replacement was divided into two groups. The first underwent postoperative artificial ventilation using the oxygen-driven Bird ventilator. The inspiratory oxygen concentration was 83%. In the second group a Bird ventilator was also used but with an oxygen concentration of 40%. In the first group the intrapulmonary right-to-left shunt rose to an average of 17% during the first two postoperative daysand in the second group to an average of 9%. The study supports the view that the inspiratory oxygen concentration should only be kept high enough to achieve a normal oxygen saturation of arterial blood.

Using a double-beam stopped-flow apparatus estimations were made of the velocity constant for the initial uptake of oxygen by fully reduced erythrocytes (k'(c)). Mammalian cells were studied with volumes varying from 20 micro(3) (goat) to 90 micro(3) (man), as were bullfrog cells (680 micro(3)). Measurements were made under physiological conditions of pH, P(CO2), and temperature. In man k'(c) was 80 mM(-1) sec(-1) and in other species smaller cells generally had a greater value for k'(c) than did the larger cells. In the goat it was 1.8 times as great as the human value; in the bullfrog it was only one-fifth as great. These differences could not be accounted for by interspecific differences in hemoglobin kinetics. The differences probably represent a true effect of size conferring some biological advantage on the species with the smaller cells. The cell membrane offered resistance to oxygen passage. Using the usual red cell model of an infinite sheet of reduced hemoglobin, membrane permeability appeared to differ among mammals. If, as is likely, the effective cell halfthickness differs among mammals, actual membrane permeability differences may be less. A method for measurement of oxygen saturation of dilute cell suspensions is also described.

Objectives : to evaluate the oxygen saturation of the calf muscle measured by means of spatially resolved spectroscopy (SRS) in claudicants. Methods : a total of 150 legs in 84 consecutive patients with calf claudication were studied by SRS. Oxygen saturation (SmO 2 ) and the relative changes in oxygenated haemoglobin (HbO 2 ) and deoxygenated haemoglobin (Hb) of the gastrocnemius muscle were measured during a treadmill walking test (2.4km/h, 12%, 5min) Results : exercise was associated with a decrease in HbO 2 and an increase in Hb. There was no difference in SmO 2 at rest among all groups. The decrease oxygen saturation correlated well with the severity of symptoms of IC. Conclusion : muscle oxygen saturation measurement by SRS can be used clinically to provide objective information regarding the severity of IC.

We have studied the effect of sedation with midazolam on arterial oxygen saturation during spinal anaesthesia in two groups of patients: one group received supplementary oxygen, the other group breathed room air. A significant reduction in oxygen saturation was observed in patients not receiving supplementary oxygen; six of 15 patients in this group developed hypoxaemia or severe hypoxaemia which was corrected immediately by administration of oxygen. There were no episodes of hypoxaemia in any patient in the group receiving supplementary oxygen. It is concluded that oxygen should be administered routinely to patients receiving sedatives during spinal anaesthesia.

The linearity and repeatability of measurements of total haemoglobin concentration ([Hb]) and oxygen saturation (So2) by the OSM2 oximeter have been studied. Standard deviations (SD) of measurements from linearity were as follows: [Hb], 4.2 g . litre-1; So2, 1.14 to 1.08% between zero and 100% saturation. Reproducibility by a single operator was within SD 1.1 g . litre-1 for [Hb] and 0.32% for So2, and between operators the means of 5 measurements had SD 0.42 g . litre-1 for [Hb] and 0.19% for So2, suggesting little if any extra variation from one operator to another. Foetal haemoglobin behaved as adult haemoglobin, but carboxyhaemoglobin caused a systematic and reproducible error in So2 measurement, from which HbCO concentration can be derived.

The rate of fall in oxygen saturation is said to be greater during obstructive apneas than during breath-holding in wakefulness. Using an ear oximeter, a face mask and flowmeter, and measurements of thoracoabdominal motion, we determined in six healthy subjects the rate of fall in arterial oxygen saturation (SaO2) during breath-holding which simulated obstructive and nonobstructive apneas. Breath-holding maneuvers were performed during progressive isocapnic hypoxia and were initiated at the same end-expiratory thoracoabdominal configuration. We found that at any given initial SaO2 the rate of fall in SaO2 was similar during simulated obstructive (y = 5.5-0.06 x; r = 0.83) and nonobstructive (y = 6.8-0.07 x; r = 0.92) apneas. In two healthy subjects and 13 patients with obstructive and nonobstructive apneas during sleep, the rate of fall in SaO2 at any initial SaO2 was similar to that found in healthy subjects during breath-holding in wakefulness. We conclude that during wakefulness the presence or absence of respiratory efforts does not affect the rate of fall in SaO2 during breath-holding and that the rate of fall of SaO2 during sleep apnea is largely dependent on the initial SaO2 at the onset of apnea.

Because central venous O2 saturation (superior vena cava, ScvO2) can be monitored with less patient risk than mixed venous O2 saturation (pulmonary artery, SvO2), we examined the correlations between SvO2 and ScvO2 over a broad range of cardiorespiratory conditions, including hypoxia, hemorrhage, and resuscitation in anesthetized dogs. The correlation coefficient (r) between SvO2 and ScvO2 in 179 simultaneously drawn blood samples from 22 dogs was 0.97. In another nine dogs, the two sites were continuously and simultaneously monitored with fiberoptic catheters; r was 0.96 with a mean difference of 3.7 +/- 2.9 percent (SD) saturation. In each dog the changes in ScvO2 closely paralleled the changes in SvO2. Although absolute values of ScvO2 are not sufficiently identical to SvO2 to calculate O2 uptake or pulmonary shunt precisely, close tracking of changes in the two sites across a wide range of hemodynamic conditions warrant further consideration of ScvO2 for patient monitoring of trends in O2 supply/demand.

Pulse oximeters (Biox III, Nellcor N-100) and a transmittance oximeter [Hewlett-Packard 47201A (HP)] were compared for SaO2 measurement and responsiveness during dynamic changes in arterial oxygen saturation and heart rate. Five sleep apnea syndrome patients were studied because they had large oscillations in SaO2 and heart rate in sleep. During sleep, each patient exhibited a series of rapid (18.0 +/- 8.3 s, mean +/- SD) oscillations in oxygen saturation (92.1 +/- 2.6% to 74.2 +/- 7.7%). Oxygen saturation measurements were sampled simultaneously from each oximeter by computer (at 2 Hz). Accuracy was assessed by comparing pulse and transmittance oxygen saturation measurements at the peak and trough of each apnea-related oscillation. Oximeter response was defined in terms of the "delay" or absolute time difference between the pulse oximeters and the transmittance oximeter for the determination of the peak and trough saturations. Linear regression analysis was used to establish accuracy and response relationships between pulse oximeter sensors (reusable ear, reusable digit, disposable digit, and disposable nasal sensors) and the transmittance oximeter sensor (reusable ear sensor). Pulse oximeter response delay was highly correlated with heart rate. Pulse oximeter SaO2 measurement and response characteristics varied considerably with sensor type (disposable, reusable) and sensor location (ear, nose, and digit). One must be aware of these differences in clinical and research application.

The mortality of diabetic patients with autonomic neuropathy (DAN) is higher than that in those without autonomic neuropathy (DM). To test the hypothesis that this may be due to respiratory rather than cardiac dysfunction, we evaluated ventilatory responses to isocapnic-hypoxic and hyperoxic-hypercapnic conditions in 14 diabetic patients (8 DAN and 6 DM) and compared the results with those in 8 normal subjects. In all groups tested there was a significant linear correlation between end-tidal CO2 and minute ventilation and between end-tidal CO2 and mouth occlusion pressure (p100), as an index of the drive to breathe. There were no significant differences between the slopes and intercepts in the groups tested. A significant linear correlation was found between the O2 saturation and both minute ventilation and p100. There were no significant differences in the relationship between minute ventilation and O2 saturation, but the slopes and the intercepts of the regression lines of p100 vs. O2 saturation were significantly different in the DAN compared with those in normal subjects and DM. Additionally, five of eight patients with DAN lost their ventilatory drive and ventilatory responses to hypoxemia compared with only one of six DM. These findings suggest that a disorder in the ventilatory response to hypoxemia exists in some DAN.

SUMMARY The frequency with which blood of differing oxygen saturation in syringes may be distinguished from a fully saturated sample of the same blood was examined using both anaemic and normal blood. It is suggested that under suitable lighting conditions the examination of arterial blood in a syringe may provide a more reliable guide to the state of arterial oxygenation than the presence or absence of cyanosis.

Central body temperature measurements were made and the incidence of postoperative shivering noted in sixty patients. There was a marked difference in the incidence of shivering between male and female patients. A relationship between the fall in central body temperature and postoperative shivering was noted. In thirty cases postoperative oxygen saturation levels were measured, severe falls in oxygen saturation being associated with the postoperative shivering. It is suggested that the patients who fall into the poor risk category should, as a routine, receive oxygen during the initial two to three hours after operation when they might be considered to be at greatest risk.

A two photocell assembly has been used to measure the light reflection of blood conducted by fibre optics. Fibre optic reflection spectra of oxygenated and reduced blood samples show an isobestic region around 850 nm. Non-specific variations of the light reflection from a mirror do not affect the ratio of detecting and compensating photocell outputs, whereas the ratio is not independent of variations in blood flow and haemoglobin concentration. The relation of log R640/R800 and the oxygen saturation is linear. The relation of R900/R800 and indocyanine green dye concentration is linear up to 20 mg/l.

The polarographic current of whole blood is in excess of that given by plasma at the same oxygen tension. The magnitude of this difference depends on (a) the oxygen content of the sample and thus is determined by the red blood cell content and by the state of oxygen saturation of hemoglobin, and (b) on the rate of dissociation of oxyhemoglobin and therefore is influenced by changes in pH, pCO2, and temperature. The total current at 37°C. is proportional to the oxygen content of the sample and can be used to determine the latter. The theoretical basis of the studied phenomena is discussed in detail.

Purpose Reduced perfusion of the retinal parapapillary tissue is well documented in glaucoma patients. Whether or not this is a cause or result of the disease is however unknown. Studying the correlation of this perfusion and the retinal vascular oxygen saturation (O2S) could give clues to the retinal O2 consumption/demand and provide an answer to this question. Methods Seventeen eyes of 17 healthy controls and 32 eyes of 32 patients with primary open angle glaucoma were prospectively recruited. Global and sectoral nerve fiber layer (NFL) thickness was measured with optical coherence tomography (OCT); parapapillary OCT-angiography was performed and quantified into vascular density (VD) and perfusion density (PD). Retinal vascular O2S was measured. Results Global and sectoral NFL thickness, VD, PD (except for temporal sector of VD), and arteriovenous difference of O2S (AV-D) were lower in glaucomatous eyes compared with controls (P < 0.05 for all). A significant inverse correlation of venous O2S with global VD (r = -0.37, P = 0.04) and PD (r = -0.37, P = 0.04) and a direct correlation of the AV-D with global VD (r = 0.50, P = 0.004) and PD (r = 0.49, P = 0.004) were observed. In sector analysis, the strongest correlation of AV-D with VD and PD was seen in inferior (VD: r = 0.52, P = 0.001; PD: r = 0.55, P = 0.002) and superior (VD: r = 0.454, P = 0.009; PD: r = 0.46, P = 0.008) segments. Conclusions In glaucomatous eyes, there exists a direct correlation of the AV-D to the VD and PD with the strongest correlation being in superior and inferior segments where typically tissue loss occurs. This could possibly be explained by the loss of tissue being followed by the reduced density.

Purpose To investigate the age-dependence of total retinal blood flow and total retinal oxygen extraction in healthy subjects and determine their possible correlations with structural optical coherence tomography (OCT) parameters. Methods This observational cross-sectional study consisted of 68 healthy subjects (mean ± SD age, 45.6 ± 16.3 years; 47% female). Total retinal oxygen extraction was calculated based on measurement of total retinal blood flow using bi-directional Doppler OCT and measurement of oxygen saturation using spectroscopic reflectometry. Retinal nerve fiber layer thickness was measured using OCT, and the total number of retinal ganglion cells was estimated based on a previous published model. Correlation of these parameters with age was studied and the association between structural OCT parameters and hemodynamic vascular parameters was calculated. Results Both structural and vascular parameters showed a significant decline with increasing age. The correlation coefficients were between r = -0.25 and r = -0.41. Furthermore, structural and vascular parameters were significantly correlated with each other. The strongest association was found between the level of total retinal oxygen extraction and the number of retinal ganglion cells (r = 0.75, P < 0.001). Conclusions We showed that there was an age-related decline of retinal oxygen extraction. Levels of retinal oxygen extraction are correlated to retinal nerve fiber layer thickness and number of retinal ganglion cells. Our data partially explain the wide inter-individual variability in retinal blood flow values in healthy subjects. Longitudinal studies are required to study the time course of vascular and neuronal loss in humans.

Background. As a part of a multicenter, observational study in determining the prevalence and risk factors of elevated tricuspid regurgitant jet velocity (TRV) in children, oxygen desaturation correlated with TRV. We further investigated the risk factors and clinical associations of oxygen desaturation at rest and after execrcise in children at steady state. Methods. 310 children and adolescents with sickle cell disease were studied under basal conditions. Pulse oximetry was determined at rest and after a six minute walk test. The relationships of oxygen saturation at rest and desaturation during exercise to the available clinical and laboratory variables were investigated. Results. Among 300 patients with available baseline oxygen saturations, 30 (10%) had saturation 98 percent. Twenty-three (9%) of 244 patients had >3 percentage point reduction in oxygen saturation during a six minute walk; the median (interquartile range) baseline saturation was 96 (95– 99) percent among these patients versus 98 (97–100) percent among those with less or no reduction in saturation during the walk (P = 0.0009). Hemoglobin (p3 percentage points during the walk while a hemolytic index (p3 percentage points. Conclusion. Markers of hemolysis, low hemoglobin, PIEDV, LVMI, LVIDD z score, lower TLC, and elevated TRV velocities are associated with ≥3% reduction in oxygen desaturation during six minute walk in children and adolescents with sickle cell disease. A high degree of oxygen desaturation during the six minute walk in sickle cell disease patients might serve as an early biomarker for pulmonary hypertension. Exercise induced changes in oxygen saturation in sickle cell disease children may provide insight into the development of pulmonary hypertension as adults.