Changes In Tissue Blood Volume Research Articles

Insights for Blood Flow Restriction and Hypoxia in Leg Versus Arm Submaximal Exercise

To assess tissue oxygenation, along with metabolic and physiological responses during blood flow restriction (BFR, bilateral vascular occlusion) and systemic hypoxia conditions during submaximal leg- versus arm-cycling exercise. In both legs and arms, 4 randomized sessions were performed (normoxia 400m, fraction of inspired oxygen [FIO2] 20.9% and normobaric hypoxia 3800m, FIO2 13.1% [0.1%]; combined with BFR at 0% and 45% of resting pulse elimination pressure). During each session, a single 6-minute steady-state submaximal exercise was performed to measure physiological changes and oxygenation (near-infrared spectroscopy) of the muscle tissue in both the vastus lateralis (legs) and biceps brachii (arms). Total hemoglobin concentration ([tHb]) was 65% higher (P < .001) in arms versus legs, suggesting that arms had a greater blood perfusion capacity than legs. Furthermore, there were greater changes in tissue blood volume [tHb] during BFR compared with control conditions (P = .017, F = 5.45). The arms elicited 7% lower tissue saturation (P < .001) and were thus more sensitive to the hypoxia-induced reduction in oxygen supply than legs, no matter the condition. This indicates that legs and arms may elicit different regulatory hemodynamic mechanisms (ie,greater blood flow in arms) for limiting the decreased oxygen delivery during exercise with altered arterial oxygen content. The combination of BFR and/or hypoxia led to increased [tHb] in both limbs likely due to greater vascular resistance; further, arms were more responsive than legs. This possibly influences the maintenance of oxygen delivery and enhances perfusion pressure, suggesting greater vascular reactivity in arms than in legs.

Broadband NIRS Cerebral Evaluation of the Hemodynamic and Oxidative State of Cytochrome-c-Oxidase Responses to +Gz Acceleration in Healthy Volunteers.

We used a miniature broadband NIRS system to monitor concentration changes in brain oxygenation (oxy- and deoxy- haemoglobin [HbO2], [HHb]) and oxidised cytochrome-c-oxidase ([oxCCO]) during a high +Gz acceleration, induced by a human centrifuge, on two healthy experienced volunteers (2 male, 34 and 37 years). We performed a sequence of several +Gz exposures that were terminated at the onset of visual symptoms (loss of peripheral vision). Systemic parameters were recorded (i.e. heart rate, blood pressure and arterial saturation), and brain tissue blood volume changes ([HbT] = [HbO2] + [HHb]) and oxygen delivery ([HbDiff] = [HbO2] - [HHb]) were calculated. Volunteer 1 demonstrated a decrease in [HbT] of −3.49 ± 0.02 μMol and [HbDiff] of −3.23 ± 0.44 μMol, and an increase of [oxCCO] of 0.42 ± 0.01μMol. Volunteer 2 demonstrated a decrease in [HbDiff] of −4.37 ± 0.23 μMol, and no significant change in [HbT] (0.53 ± 0.06 μMol) and [oxCCO] (0.09 ± 0.06 μMol). The variability of the brain metabolic response was related to the level of ischaemia, suggesting that suppression of metabolism was due to lack of glucose substrate delivery rather than oxygen availability.

Leg- vs arm-cycling repeated sprints with blood flow restriction and systemic hypoxia.

The aim was to compare changes in peripheral and cerebral oxygenation, as well as metabolic and performance responses during conditions of blood flow restriction (BFR, bilateral vascular occlusion at 0% vs. 45% of resting pulse elimination pressure) and systemic hypoxia (~ 400m, FIO2 20.9% vs. ~ 3800m normobaric hypoxia, FIO2 13.1 ± 0.1%) during repeated sprint tests to exhaustion (RST) between leg- and arm-cycling exercises. Seven participants (26.6 ± 2.9years old; 74.0 ± 13.1kg; 1.76 ± 0.09m) performed four sessions of RST (10-s maximal sprints with 20-s recovery until exhaustion) during both leg and arm cycling to measure power output and metabolic equivalents as well as oxygenation (near-infrared spectroscopy) of the muscle tissue and prefrontal cortex. Mean power output was lower in arms than legs (316 ± 118 vs. 543 ± 127W; p < 0.001) and there were no differences between conditions for a given limb. Arms demonstrated greater changes in concentration of deoxyhemoglobin (∆[HHb], - 9.1 ± 6.1 vs. - 6.5 ± 5.6μm) and total hemoglobin concentration (∆[tHb], 15.0 ± 10.8 vs. 11.9 ± 7.9μm), as well as the absolute maximum tissue saturation index (TSI, 62.0 ± 8.3 vs. 59.3 ± 8.1%) than legs, respectively (p < 0.001), demonstrating a greater capacity for oxygen extraction. Further, there were greater changes in tissue blood volume [tHb] during BFR only compared to all other conditions (p < 0.01 for all). The combination of BFR and/or hypoxia led to increased changes in [HHb] and [tHb] likely due to greater vascular resistance, to which arms were more responsive than legs.

Identifying individual sleep apnea/hypoapnea epochs using smartphone-based pulse oximetry.

Sleep apnea, characterized by frequent pauses in breathing during sleep, poses a serious threat to the healthy growth and development of children. Polysomnography (PSG), the gold standard for sleep apnea diagnosis, is resource intensive and confined to sleep laboratories, thus reducing its accessibility. Pulse oximetry alone, providing blood oxygen saturation (SpO2) and blood volume changes in tissue (PPG), has the potential to identify children with sleep apnea. Thus, we aim to develop a tool for at-home sleep apnea screening that provides a detailed and automated 30 sec epoch-by-epoch sleep apnea analysis. We propose to extract features characterizing pulse oximetry (SpO2 and pulse rate variability [PRV], a surrogate measure of heart rate variability) to create a multivariate logistic regression model that identifies epochs containing apnea/hypoapnea events. Overnight pulse oximetry was collected using a smartphone-based pulse oximeter, simultaneously with standard PSG from 160 children at the British Columbia Children's hospital. The sleep technician manually scored all apnea/hypoapnea events during the PSG study. Based on these scores we labeled each epoch as containing or not containing apnea/hypoapnea. We randomly divided the subjects into training data (40%), used to develop the model applying the LASSO method, and testing data (60%), used to validate the model. The developed model was assessed epoch-by-epoch for each subject. The test dataset had a median area under the receiver operating characteristic (ROC) curve of 81%; the model provided a median accuracy of 74% sensitivity of 75%, and specificity of 73% when using a risk threshold similar to the percentage of apnea/hypopnea epochs. Thus, providing a detailed epoch-by-epoch analysis with at-home pulse oximetry alone is feasible with accuracy, sensitivity and specificity values above 73% However, the performance might decrease when analyzing subjects with a low number of apnea/hypoapnea events.

Do Two Tissue Blood Volume Parameters Measured by Different Near-Infrared Spectroscopy Methods Show the Same Dynamics During Incremental Running?

Both the change in total hemoglobin concentration (cHb), assessed by near-infrared continuous-wave spectroscopy (NIR-CWS), and the normalized tissue hemoglobin index (nTHI), assessed by NIR spatially resolved spectroscopy (NIR-SRS), were used to quantify changes in tissue blood volume. However, it is possible that these parameters may show different changes because of the different measurement systems. The present study aimed to compare changes in cHb and nTHI in working muscles, which were selected for measurement because the parameters changed dynamically. After a standing rest, seven male runners (age 24±3 years, mean±S.D.) performed an incremental running exercise test on a treadmill (inclination=1%) from 180 to 300 m min(-1). During the tests, cHb and nTHI were monitored from the vastus lateralis (VL) and medial gastrocnemius (GM) muscles. These parameters were relatively evaluated from the minimal to maximal values through the test. When the exercise began, cHb and nTHI quickly decreased and then gradually increased during running. In comparison with both VL and GM, there was significant interaction between cHb and nTHI. The present results suggest that cHb and nTHI in working muscles are not always synchronized, particularly at the onset of exercise and at high intensities. Although cHb was previously used as the change of tissue blood volume, it is implied that tissue blood volume assessed by cHb is overestimated.

Two Tissue Blood Volume Parameters Show Different Dynamics During Prolonged Exercise

In previous studies, total hemoglobin changes (cHb), which were calculated by adding the oxygenated and deoxygenated hemoglobin, measured by near-infrared continuous-wave spectroscopy (NIR-CWS), are used as tissue blood volume changes (BV). During moderate to high intensity cycling exercise, cHb decreases temporarily at the onset of exercise, and then increases gradually. However, since NIR-CWS parameters, especially oxygenated hemoglobin, are affected by skin blood flow changes, it was hypothesized that BV assessed by cHb was overestimated, especially during prolonged exercise. On the other hand, it was reported that tissue oxygen saturation and a normalized tissue hemoglobin index (nTHI), monitored by NIR spatially-resolved spectroscopy (NIR-SRS), were less influenced. PURPOSE:The aim of this study was to compare the two BV parameters, cHb and nTHI, in the working muscle during prolonged cycling exercise. METHODS :Seven active male subjects (age, 22 ± 3 yr.) performed a 60-min cycling exercise test at 65 to 70% of the peak of pulmonary oxygen uptake (162 ± 25 W). Two BV parameters, cHb and nTHI, from the vastus lateralis muscle were continuously monitored by the commercially available NIR device. The values of the two parameters were relatively evaluated; 100% of BV was taken as the resting value and 0% of BV was taken as the minimum value for 30 s after the onset of exercise. All data are represented as mean ± SE. RESULTS::Both cHb and nTHI decreased acutely at the onset of exercise, and then increased. The relative values of cHb at the 10th, 30th, and 60th minutes were 230 ± 70%, 277 ± 74%, and 291 ± 56%, respectively. On the other hand, those of nTHI were 173 ± 37%, 177 ± 39%, and 170 ± 45%, respectively. There was significant interaction between the two parameters (p < 0.01). The maximal values in cHb and nTHI were 321 ± 76% and 235 ± 36% (N.S.), and the timing at the maximal value in cHb was significantly increased compared to nTHI (53.4 ± 5.1 min vs. 22.5 ± 19.6 min, p < 0.01). CONCLUSION: These results suggest that BV assessed by cHb during exercise is overestimated. Hence, it is likely that BV within the working muscle might be little changed or slightly decreased during prolonged exercise.

Inexpensive diffuse reflectance spectroscopy system for measuring changes in tissue optical properties.

The measurement of changes in blood volume in tissue is important for monitoring the effects of a wide range of therapeutic interventions, from radiation therapy to skin-flap transplants. Many systems available for purchase are either expensive or difficult to use, limiting their utility in the clinical setting. A low-cost system, capable of measuring changes in tissue blood volume via diffuse reflectance spectroscopy is presented. The system consists of an integrating sphere coupled via optical fibers to a broadband light source and a spectrometer. Validation data are presented to illustrate the accuracy and reproducibility of the system. The validity and utility of this in vivo system were demonstrated in a skin blanching/reddening experiment using epinephrine and lidocaine, and in a study measuring the severity of radiation-induced erythema during radiation therapy.

Respiratory‐induced vasoconstriction measured by light transmission and by laser Doppler signal

Changes in finger tissue blood volume (TBV) measured by light transmission and in laser Doppler flow (LDF) were obtained during long breathing (of 12 s period) and associated with the respiratory phases, inspiration and expiration. For fifteen out of sixteen subjects TBV and LDF started to decrease 0-2 s after the start of expiration and increased during inspiration but the start of increase occurred before the start of inspiration, showing that the respiratory-induced changes in TBV and LDF are mainly associated with the expiration. Decrease of TBV and LDF after expiration was also found during the inspiratory gasps

Comparison of respiratory-induced variations in photoplethysmographic signals

Photoplethysmography (PPG) is an optical method for detecting blood volume changes in tissue. Respiratory-induced intensity, frequency and amplitude variations are contained in the PPG signal; thus, an understanding of the relationships between all of these variations and respiration is essential to advancing respiration monitoring based on PPG. This study investigated correlations between respiratory-induced variations extracted from PPG and simultaneous respiratory signals. PPG signals were recorded from 28 healthy subjects under eight different conditions. Six respiratory-induced variations, i.e. the period of the systole, diastole and pulse, the amplitude of the systole and diastole, and the intensity variation, were determined from the PPG signal. The results indicate that, compared with the period of the pulse, the period of the systole and diastole correlates weakly with respiration; the amplitude of the diastole has a stronger correlation with respiration than the amplitude of the systole. For men, when the respiratory rate is less than 10 breaths min−1, the period of the pulse has the strongest correlation with respiration, whereas up to or above 15 breaths min−1, the intensity variation becomes strongest in the sitting posture, while the amplitude of the diastole is strongest in the supine posture. For women, compared with the other variations, the period of the pulse has nearly the strongest correlation with respiration, independent of respiratory rate or posture.

Full-field laser–Doppler imaging and its physiological significance for tissue blood perfusion

Using Monte Carlo simulations for a semi-infinite medium representing a skeletal muscle tissue, it is demonstrated that the zero- and first-order moments of the power spectrum for a representative pixel of a full-field laser–Doppler imager behave differently from classical laser–Doppler flowmetry. In particular, the zero-order moment has a very low sensitivity to tissue blood volume changes, and it becomes completely insensitive if the probability for a photon to interact with a moving red blood cell is above 0.05. It is shown that the loss in sensitivity is due to the strong forward scatter of the propagating photons in biological tissues (i.e., anisotropy factor g = 0.9). The first-order moment is linearly related to the root mean square of the red blood cell velocity (the Brownian component), and there is also a positive relationship with tissue blood volume. The most common physiological interpretation of the first-order moment is as tissue blood volume times expectation of the blood velocity (in probabilistic terms). In this sense, the use of the first-order moment appears to be a reasonable approach for qualitative real-time blood flow monitoring, but it does not allow us to obtain information on blood velocity or volume independently. Finally, it is shown that the spatial and temporal resolution trade-off imposed by the CMOS detectors, used in full-field laser–Doppler hardware, may lead to measurements that vary oppositely with the underlying physiological quantities. Further improvements on detectors' sampling rate will overcome this limitation.

Photoplethysmographic Assessment of Hemodynamic Variations Using Pulsatile Tissue Blood Volume

Sympathetic responses to provocative tests have shown to provide an early prognosis of abnormalities in the human autonomic nervous system. Photoplethysmographic signal characteristics have been studied to identify vascular diseases. However, knowledge about the pulse-added arterial volume of the photoplethysmographic waveforms during these clinical investigations is limited. In all, 16 normotensive adults (9 men) were recruited to perform 3 provocative test (2 postural changes and 1 resistive breathing) activities with photoplethysmographic signals being monitored on the upper and lower peripheries using customized devices. In all, 4 parameters derived from the photoplethysmographic waveforms that related to the pulsatile tissue blood volume changes were then assessed. The results obtained showed that amplitude-related parameters during these activities showed significant changes (>9.63%; P < .05). However, comparison of pulse-added arterial volume showed insignificant changes (<5.56%; P > .05) for all test settings. Hence, the findings herein suggest that there is clinical potential in using this aspect of the photoplethysmographic waveform.

Respiration-induced changes in tissue blood volume distal to occluded artery, measured by photoplethysmography

Photoplethysmography (PPG) measures the cardiac-induced fluctuations and other changes in tissue blood volume by light transmission measurement. In the current study, light transmission was simultaneously measured in the two index fingers of healthy subjects, while the brachial artery in the left arm was occluded by a pressure cuff, so that no PPG signal appeared in the left finger. Correlated respiratory-induced changes in the PPG baseline in the right hand and in the light transmission in the left hand were found, indicating respiratory-induced blood volume changes in the finger distal to the occluded artery. The blood volume changes under the PPG probe distal to the occluded artery are interpreted as transition of blood volume from small arteries into big veins, mediated by the sympathetic nervous system.

Right-left correlation of the sympathetically induced fluctuations of photoplethysmographic signal in diabetic and non-diabetic subjects

Photoplethysmography (PPG) records the cardiac-induced changes in tissue blood volume by light-transmission measurements. The baseline and amplitude of the PPG signal show very low-frequency (VLF) spontaneous fluctuations, which are mediated by the sympathetic nervous system, and high correlation between right and left extremities of healthy subjects. As sympathetic neuropathy is one of the diabetic complications, the right-left correlation of the PPG fluctuations was examined in diabetic patients. The PPG signal was simultaneously measured in the two index fingers and the two second toes of 35 diabetic patients and 33 non-diabetic subjects. For each PPG pulse, the baseline and amplitude were determined, and the right-left correlation coefficients of the VLF fluctuations in the baseline and amplitude were derived. The VLF fluctuations in the baseline showed high right-left correlation, both for fingers (0.93 +/- 0.05) and toes (0.93 +/- 0.06), for the non-diabetic subjects, and significantly lower correlation (0.78 +/- 0.22 and 0.84 +/- 0.17, respectively) for the diabetic patients. Similar results were obtained for the amplitude VLF fluctuations. The right-left correlation coefficients for diabetic patients decreased with the disease duration for the toe baseline and toe amplitude fluctuations and correlated with heart rate response to deep breathing for the finger baseline and toe amplitude fluctuations. The right-left correlation coefficients of the PPG fluctuations provide a simple and convenient means for assessing the adequacy of the sympathetic nervous system function.

Relationship between the thickness and hemodynamics of the erector spinae muscles in various lumbar curvatures

Background. There is little information about the relationship between the changes of hemodynamics and the morphologic changes of the erector spinae muscle. Methods. Fifty healthy male volunteers participated. Ultrasonography was used to measure muscle thickness, and near-infrared spectroscopy was used to measure tissue blood volume and its oxygenation in the erector spinae muscle at L3 in six different relaxed trunk postures (flexed 20°, flexed 40°, flexed maximum, neutral posture, extended 20°, and extended maximum of the lumbar spine). We also evaluated the reproducibility of the near-infrared spectroscopy measurements. Findings. Near-infrared spectroscopy gave highly reproducible measurements. The thickness of the erector spinae muscle and the total and oxygenated hemoglobin were simultaneously increased during relaxed extension and decreased during relaxed flexion. Changes in the thickness of the erector spinae muscle with various lumbar curvature were similar in pattern to the changes in tissue blood volume and its oxygenation. Interpretation. The erector spinae muscles’ thickness, tissue blood volume, and its oxygenation are simultaneously increased during relaxed extension and decreased during relaxed flexion, as demonstrated by non-invasive near-infrared spectroscopy and ultrasonography. These findings might afford a better understanding of the pathomechanics of posture-related back symptoms. Relevance The erector spinae muscles’ thickness, tissue blood volume, and its oxygenation are simultaneously increased during relaxed extension and decreased during relaxed flexion, as shown by non-invasive near-infrared spectroscopy and ultrasonography. Changes in hemodynamics and morphology of the erector spinae muscles in asymptomatic subjects are given for further research on the pathomechanism of back pain.

Influence of thoracic sympathectomy on cardiac induced oscillations in tissue blood volume.

The photoplethysmographic (PPG) signal, which measures cardiac-induced changes in tissue blood volume by light transmission measurements, shows spontaneous fluctuations. In this study, PPG was simultaneously measured in the right and left index fingers of 16 patients undergoing thoracic sympathectomy, and, from each PPG pulse, the amplitude of the pulse (AM) and its maximum (BL) were determined. The parameter AM/BL is proportional to the cardiac-induced blood volume increase, which depends on the arterial wall compliance. AM/BL increased after the thoracic sympathectomy treatment (for male patients, from 2.60+/-1.49% to 4.81+/-1.21%), as sympathetic denervation decreases arterial tonus in skin. The very low-frequency (VLF) fluctuations of BL or AM showed high correlation (0.90+/-0.11 and 0.92+/-0.07, respectively) between the right and left hands before the thoracic sympathectomy, and a significant decrease in the right-left correlation coefficient (to 0.54+/-0.22 and 0.76+/-0.20, respectively) after the operation. The standard deviation of the BL or AM VLF fluctuations also reduced after the treatment, indicating sympathetic mediation of the VLF PPG fluctuations. The study also shows that the analysis of the PPG signal and the VLF fluctuations of the PPG parameters enable the assessment of the change in sympathetic nervous system activity after thoracic sympathectomy.

Assessment of nasal mucosa blood supply by quantitative endoscopic imaging of the back-scattered light

In this article we present a method for the objective assessment and monitoring of tissue blood supply using a specially developed endoscopic imaging colorimeter that enables quantitative color modeling of the back-scattered light during endoscopic examination. Tissue blood volume changes in the nasal mucosa, induced by xylometazoline hydrochloride nasal spray, were evaluated with this method. It was found that quantitative imaging provides sensitive, reproducible, and reliable means for the monitoring and mapping of tissue blood supply and is easy to use routinely. The results showed that saturation decreases with time, being the most sensitive color parameter to the vasoconstriction procedure. It appears that objective indexes for optical tissue characterization and analysis may be promising in the understanding of the pathophysiology of tissue changes and in the objective evaluation of their response to different therapeutic schemes. (Otolaryngol Head Neck Surg 1999;121:307-12.)

Effect of cardiac flow on gradient recalled echo images of the canine heart

The effect of coronary flow on the signal intensity of gradient recalled echo (GRE) MR images of the canine heart was evaluated at 4 T. Using a fully instrumented canine model, hyperfusion (local adenosine infusion) and ischemia (local occlusion) were evaluated while coronary blood flow and venous oxygen tension were monitored. These studies demonstrated an increase in GRE signal intensity with increases in coronary blood flow and venous oxygenation. A local occlusion resulted in a small decrease in signal intensity in the affected area of the heart. The dependence of the signal changes on TE and TR indicated that the effects of high flow were associated with changes in the apparent T2 and T1. Both relaxation effects could reflect changes in tissue blood volume associated with the conditions studied. In addition, the apparent T2 changes were consistent with alterations in total tissue deoxyhemoglobin concentration and the changes in apparent T1 were consistent with inflow effects.

Determination of cerebral cortical capillary blood volume from mean transit time analysis.

A full understanding of the delivery of oxygen to a tissue cannot be attained by study of the blood flow to that tissue alone. An important component of the delivery system is the particular spatial arrangement of the capillaries supplying the tissue. This is especially critical in capillary networks that function through dynamic control of local tissue perfusion by regulating the number of open and closed capillaries. This form of vascular regulation has been generally known as ‘capillary recruitment’ and this concept implies that there are dynamic changes in tissue blood volume in response to changes in tissue metabolic demand. Capillary recruitment has long been suspected of being an integral part of cerebrovascular function, but until recently, experimental evidence for significant participation has been lacking (Weis et al., 1982; Pardridge and Fierer, 1985).KeywordsCerebral Blood FlowCerebral Blood VolumeMean Transit TimeStrip Chart RecorderCapillary RecruitmentThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Noninvasive, Infrared Monitoring of Cerebral and Myocardial Oxygen Sufficiency and Circulatory Parameters

The relatively good transparency of biological materials in the near infrared region of the spectrum permits sufficient photon transmission through organs in situ for the monitoring of cellular events. Observations by infrared transillumination in the exposed heart and in the brain in cephalo without surgical intervention show that oxygen sufficiency for cytochrome a,a3, function, changes in tissue blood volume, and the average hemoglobin-oxyhemoglobin equilibrium can be recorded effectively and in continuous fashion for research and clinical purposes. The copper atom associated with heme a3 did not respond to anoxia and may be reduced under normoxic conditions, whereas the heme-a copper was at least partially reducible.

Blood flow and volume measurements in the radiation depopulated testis of the rat.

The testis of the rat has been used as an experimental model for measuring blood flow and blood volume changes in tissue depopulated by X-rays. The results show that for single doses of X-ray up to 600 rads the blood flow per unit weight remains constant during the depopulation phase, while the blood volume per unit weight of tissue is increased.