Voluntary Breathing Research Articles

Влияние произвольного гиповентиляционного дыхания на функциональное состояние и физическую работоспособность человека при различных по интенсивности режимах физической нагрузки до отказа

Влияние произвольного гиповентиляционного дыхания на функциональное состояние и физическую работоспособность человека при различных по интенсивности режимах физической нагрузки до отказа

Respiratory variation in left ventricular cardiac function with 3D double golden-angle whole-heart cine imaging.

To develop a 3-dimensional free-breathing cardiovascular MR technique for quantifying the variation in left ventricular end-diastolic volume (LVEDV) during the respiratory cycle. A 3-dimensional radial trajectory with double golden-angle ordering was used for free-running data acquisition during free breathing in healthy volunteers (N = 8). A respiratory self-gating signal was extracted from the center of k-space, and data were retrospectively binned into eight respiratory phases in end-diastole. Three-dimensional image volumes with 2-mm isotropic spatial resolution were reconstructed with conjugate-gradient sensitivity encoding for acquisition durations of 4.5, 9, and 25 min. The LVEDV was manually segmented for each respiratory phase and acquisition duration. Respiratory-induced variation expressed as minimum LVEDV (during mid-inspiration) relative to maximum LVEDV (during mid-expiration) was 5.9 ± 0.3% for 4.5 min, 5.3 ± 0.4% for 9 min (P = 0.64 versus 4.5 min), and 5.0 ± 0.4% for 25 min (P = 0.25 versus 4.5 min, and P = 1.00 versus 9 min). The proposed technique enables high spatial-resolution quantification of the respiratory variation in LVEDV during free breathing in under 5 min, and was found to be 5 to 6% for healthy volunteers. Magn Reson Med 79:2693-2701, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

The relationship between minute ventilation and end tidal CO2 in intubated and spontaneously breathing patients undergoing procedural sedation.

BackgroundMonitoring respiratory status using end tidal CO2 (EtCO2), which reliably reflects arterial PaCO2 in intubated patients under general anesthesia, has often proven both inaccurate and inadequate when monitoring non-intubated and spontaneously breathing patients. This is particularly important in patients undergoing procedural sedation (e.g., endoscopy, colonoscopy). This can be undertaken in the operating theater, but is also often delivered outside the operating room by non-anesthesia providers. In this study we evaluated the ability for conventional EtCO2 monitoring to reflect changes in ventilation in non-intubated surgical patients undergoing monitored anesthesia care and compared and contrasted these findings to both intubated patients under general anesthesia and spontaneously breathing volunteers.MethodsMinute Ventilation (MV), tidal volume (TV), and respiratory rate (RR) were continuously collected from an impedance-based Respiratory Volume Monitor (RVM) simultaneously with capnography data in 160 patients from three patient groups: non-intubated surgical patients managed using spinal anesthesia and Procedural Sedation (n = 58); intubated surgical patients under General Anesthesia (n = 54); and spontaneously breathing Awake Volunteers (n = 48). EtCO2 instrument sensitivity was calculated for each patient as the slope of a Deming regression between corresponding measurements of EtCO2 and MV and expressed as angle from the x-axis (θ). All data are presented as mean ± SD unless otherwise indicated.ResultsWhile, as expected, EtCO2 and MV measurements were negatively correlated in most patients, we found gross systematic differences across the three cohorts. In the General Anesthesia patients, small changes in MV resulted in large changes in EtCO2 (high sensitivity, θ = -83.6 ± 9.9°). In contrast, in the Awake Volunteers patients, large changes in MV resulted in insignificant changes in EtCO2 (low sensitivity, θ = -24.7 ± 19.7°, p < 0.0001 vs General Anesthesia). In the Procedural Sedation patients, EtCO2 sensitivity showed a bimodal distribution, with an approximately even split between patients showing high EtCO2 instrument sensitivity, similar to those under General Anesthesia, and patients with low EtCO2 instrument sensitivity, similar to the Awake Volunteers.ConclusionsWhen monitoring non-intubated patients undergoing procedural sedation, EtCO2 often provides inadequate instrument sensitivity when detecting changes in ventilation. This suggests that augmenting standard patient care with EtCO2 monitoring is a less than optimal solution for detecting changes in respiratory status in non-intubated patients. Instead, adding direct monitoring of MV with an RVM may be preferable for continuous assessment of adequacy of ventilation in non-intubated patients.

A pulse wave monitoring system based on a respiratory pacemaker

We constructed a reasonable healthcare monitoring system with pulse wave and respiratory analysis to assess blood vessel conditions and the autonomic function in daily life. Filter circuits with an infrared sensor were carefully designed to complete the peripheral pulse wave measurement and analysis, considering individual differences to a pulse sensor and the potential for the system to be used as wearable devices and applications. The analyzer for our system is capable of predicting arterial states and stiffness. A user interface with a respiratory pacemaker can assist voluntary breathing, visualize pulse wave features, and regulate them in real time. The user interface software is widely compatible and could be easily applied to mobile healthcare devices. We also evaluated how respiration control reflected pulse rate variability [i.e., fluctuations in peak-to-peak intervals (PPI)] associated with the autonomic nervous system. An experimental study under various breathing rates was performed using the created user interface with a respiratory pacemaker. The transfer gain of the PPI caused resonance at the respiratory rate of 0.1 Hz (p < 0.5), corresponding to the sufficiently stimulated vagal tone of the heart. A simulation study revealed that the fuzzy inference indicates the robustness of respiratory regulation to maximize the amplitude of PPI oscillations under the inclusion of individual difference and unexpected response. As future perspective, the respiratory pacemaker used to regulate the pulse wave feature could be applied to an effective recovery support system especially under blunted autonomic function such as during mental stress and hypoxia.

Internal jugular vein blood flow in the upright position during external compression and increased central venous pressure: an ultrasound study in healthy volunteers.

External compression of the jugular veins is an effective method to increase intracranial blood volume and brain stiffness in rats and healthy volunteers. It has been reported that, on assuming an upright posture, cerebral venous drainage is distributed away from the internal jugular veins (IJVs) to the cervical venous plexus, causing complete collapse of the IJV. If so, it is not clear why external IJV compression would increase intracranial blood volume, but the latter is frequently observed in neurosurgery in the sitting position. The aim of this study was to observe the effect of external IJV compression and the Valsalva maneuver on the change in IJV cross-sectional area and IJV flow in volunteers in the upright posture. After Research Ethics Board approval, we used ultrasound to evaluate both IJV cross-sectional areas and peak velocities in ten healthy volunteers in the sitting position. With the volunteers breathing normally at rest, we applied the Valsalva maneuver along with circumferential supraclavicular compression of 15 mmHg. Imaging was performed at the level of the cricoid cartilage and at the most superior level under the mandible. The IJV flow was calculated using the product of Doppler velocity and IJV cross-sectional area. Flow was detected in both IJVs of all subjects. The median [interquartile range] cross-sectional area for the right IJV at the level of the cricoid was 0.04 [0.03-0.08] cm2 (baseline), with collar 0.4 [0.2-0.6] cm2 (P=0.003 compared with baseline). There were no significant changes in the median blood flow. Compression of the internal jugular veins or an increase in intrathoracic pressure does not reduce venous drainage but actually may increase intracranial venous volume.

Changes in acute pulmonary vascular responsiveness to hypoxia during a progressive ascent to high altitude (5300m).

What is the central question of this study? Do the pulmonary vascular responses to hypoxia change during progressive exposure to high altitude and can alterations in these responses be related to changes in concentrations of circulating biomarkers that affect the pulmonary circulation? What is the main finding and its importance? In our field study with healthy volunteers, we demonstrate changes in pulmonary artery pressure suggestive of remodelling in the pulmonary circulation, but find no changes in the acute responsiveness of the pulmonary circulation to changes in oxygenation during 2 weeks of exposure to progressive hypoxia. Pulmonary artery pressure changes were associated with changes in erythropoietin, 8-isoprostane, nitrite and guanosine 3',5'-cyclic monophosphate. We sought to determine whether changes in pulmonary artery pressure responses to hypoxia suggestive of vascular remodelling occur during progressive exposure to high altitude and whether such alterations are related to changes in concentrations of circulating biomarkers with known or suspected actions on the pulmonary vasculature during ascent. We measured tricuspid valve transvalvular pressure gradients (TVPG) in healthy volunteers breathing air at sea level (London, UK) and in hypoxic conditions simulating the inspired O2 partial pressures at two locations in Nepal, Namche Bazaar (NB, elevation 3500m) and Everest Base Camp (EBC, elevation 5300m). During a subsequent 13day trek, TVPG was measured at NB and EBC while volunteers breathed air and hyperoxic or hypoxic mixtures simulating the inspired O2 partial pressures at the other locations. For each location, we determined the slope of the relationship between TVPG and arterial oxygen saturation (SaO2) to estimate the pulmonary vascular response to hypoxia. Mean TVPG breathing air was higher at any SaO2 at EBC than at sea level or NB, but there was no change in the slope of the relationship between SaO2 and TVPG between locations. Nitric oxide availability remained unchanged despite increases in oxidative stress (elevated 8-isoprostane). Erythropoietin, pro-atrial natriuretic peptide and interleukin-18 levels progressively increased on ascent. Associations with TVPG were observed only with erythropoietin, 8-isoprostane, nitrite and guanosine 3',5'-cyclic monophosphate. Although the increased TVPG for any given SaO2 at EBC suggests that pulmonary vascular remodelling might occur during 2weeks of progressive hypoxia, the lack of change in the slope of the relationship between TVPG and SaO2 indicates that the acute pulmonary vascular responsiveness to changes in oxygenation does not vary within this time frame.

Meta-Analysis of Effects of Voluntary Slow Breathing Exercises for Control of Heart Rate and Blood Pressure in Patients With Cardiovascular Diseases

Rising heart rate (HR) and elevated blood pressure (BP) cause a greater frequency of cardiovascular events. Many patients cannot maintain target HR and BP using pharmacological therapies. To evaluate the effectiveness of voluntary slow breathing exercises in reducing resting HR and BP, we searched Embase (1974 to April 2016), PubMed (1966 to April 2016), the Cochrane Central Register of Controlled Trials (issue 4, April 2016), and PEDro (www.pedro.org.au; 1999 to April 2016). The primary outcome was the mean change in HR at rest. Secondary outcomes included changes in systolic blood pressure (SBP) and diastolic blood pressure (DBP) as well as compliance with the breathing training. Finally, we included 6 studies consisting of 269 subjects. Practice of the breathing exercises resulted in statistically significant HR reduction (mean difference:-1.72 beats/min, 95% CI-2.70 to-0.75). Reductions were seen in SBP (mean difference:-6.36mm Hg, 95% CI-10.32 to-2.39) and DBP (mean difference:-6.39mm Hg, 95% CI-7.30 to-5.49) compared with the controls. Trial durations ranged from 2weeks to 6months. In conclusion, theexisting evidence from randomized controlled trails demonstrates that short-term voluntary slow breathing exercises can reduce resting HR, SBP, and DBP for patients with cardiovascular diseases.

The Application of Biphasic Extrathoracic Cuirass-Assisted Ventilation in Normal Subjects Wearing Chemical-Biological-Radiological-Nuclear (CBRN) Gas Masks.

Mobile RTX (MRTX), a portable light-weighted ventilator, provides noninvasive respiratory support using biphasic extrathoracic cuirass-assisted ventilation. Despite the effectiveness of chemical-biological-radiological-nuclear (CBRN) gas masks, they cause respiratory loading as a result of added dead space and resistance. This prospective comparative pilot study was conducted to investigate the safety and efficacy of assisted ventilation provided by MRTX in healthy adult volunteers wearing CBRN gas masks at rest. Cardiorespiratory parameters were monitored in 11 healthy adult volunteers breathing spontaneously or with assisted ventilation provided by MRTX, freely or with the mask on. Comparisons were made by single-factor analysis of variance. AV significantly increased minute ventilation (p < 0.001). MRTX increased minute ventilation by 6.4 L/min (mean, 95% confidence interval: 3.1, 9.8; p < 0.005) and by 4.7 L/min (1.8, 7.5; p < 0.01) during spontaneous breathing and with the mask on, respectively. Simultaneously, end-tidal carbon dioxide partial pressure decreased by 3.6 mmHg (2.2, 5.1; p < 0.001) and by 6.5 mmHg (3.8, 9.1; p < 0.001). Biphasic extrathoracic cuirass assisted ventilation provided by MRTX is safe and effective in supporting adequate needs at rest even when wearing protective masks. MRTX should be further assessed as a possible adjunct to currently used field ventilation in CBRN scenarios.

Sedation with Dexmedetomidine or Propofol Impairs Hypoxic Control of Breathing in Healthy Male Volunteers: A Nonblinded, Randomized Crossover Study: Erratum

Sedation with Dexmedetomidine or Propofol Impairs Hypoxic Control of Breathing in Healthy Male Volunteers: A Nonblinded, Randomized Crossover Study: Erratum

Clinical Update: The Risk of Opioid Toxicity and Naloxone Use in Operational K9s.

The increasing use of opioids (e.g., fentanyl, carfentanil) for illicit drug manufacturing poses a potential life-threatening hazard to law enforcement officers and first responders (e.g., EMS, fire and rescue) who may unknowingly come into contact with these drugs during the course of their daily activities. Similarly, Operational canines (OpK9s) of all disciplines-detection (drug, explosive, accelerant), patrol, tracking, search and rescue, and others-are at risk for accidental illicit opioid exposure. The most serious adverse effect of opioid exposure is respiratory depression leading to slow, shallow breathing or complete cessation of voluntary breathing (respiratory arrest). Naloxone, an opioid antagonist, is the antidote for reversing the effects of an opioid overdose in both humans and OpK9s. This clinical update describes the potential risks associated with opioid exposure as well as the use of naloxone as it pertains to the OpK9.

ОСТРАЯ ДЫХАТЕЛЬНАЯ НЕДОСТАТОЧНОСТЬ ПРИ ПОРАЖЕНИИ НЕРВНОЙ СИСТЕМЫ

Objective: The analysis of clinical physiology of acute respiratory failure, depending on the localization of the process in the nervous system in various diseases of it and the setting of indications for artificial ventilation of lungs (AVL). Methods: Traced 26 patients with serious diseases of the nervous system, who needed to the AVL, and which were in aftercare in the Resuscitation Department of the National Medical Center. Results: Depending on the lesion of the nervous system, the patients were divided into 2 groups. 18 (69%) of patients (group I) received central nervous system damage (strokes, encephalitis), which caused of acute respiratory failure (ARF). In 8 (31%) of patients (group II), the cause of ARF was the pareses and stethoparalyses (polyradiculoneuropathy, myasthenia). Conclusion: Clinical syndromes in lesions of the central regulation of respiratory system are the partial or complete loss of voluntary breathing and coughing as well as pathological forms of respiratory movements. The assessment of respiratory failure is based on the degrees of liquation of PO2, the diffusive capability of the lungs, an increase in the ventilation-perfusion ratio, and an increase in the physiological dead space by a factor of 1.5. Keywords: Acute respiratory failure, artificial ventilation of lungs (AVL), violation of ventilation-perfusion ratio.

Irregular amplitude and frequency of respiratory movements in hemispheric stroke

Objectives: The aims of the study were to investigate respiratory movement patterns among patients with right versus left hemispheric stroke with emphasis on regularity of respiratory frequency and amplitude of movements during both quiet and voluntary deep breathing and to compare the results with reference values.Materials and methods: Eighteen patients with severe stroke were measured with the Respiratory Movement Measuring Instrument. Respiratory frequencies, movements, regularity of amplitude and frequency were compared with individuals with no neurological disease.Results: The demographics and physical performance were comparable for 8 left and 10 right hemispheric stroke. Deep respiratory movements were significantly decreased (p < 0.001) and frequency significantly increased (p < 0.03 for quiet and p = 0.002 for deep breathing), for the group (n = 18) compared with reference values. Fifty-six percent of our stroke patients had irregular amplitude of deep respiratory movements (p = 0.003), and 33% had irregular frequency (p = 0.058), but none of the individuals with no neurological diseases (p = 0.003). Seventy percent of RHS patients had irregular amplitude of deep respiratory movements, compared with 38% of LHS patients (p = 0.34).Conclusion: Results show significantly decreased amplitude of deep breathing in hemispheric stroke and indicate a possible effect on regularity of range and frequency of respiratory movements.

Sedation with Dexmedetomidine or Propofol Impairs Hypoxic Control of Breathing in Healthy Male Volunteers

In contrast to general anesthetics such as propofol, dexmedetomidine when used for sedation has been put forward as a drug with minimal effects on respiration. To obtain a more comprehensive understanding of the regulation of breathing during sedation with dexmedetomidine, the authors compared ventilatory responses to hypoxia and hypercapnia during sedation with dexmedetomidine and propofol. Eleven healthy male volunteers entered this randomized crossover study. Sedation was administered as an intravenous bolus followed by an infusion and monitored by Observer's Assessment of Alertness/Sedation (OAA/S) scale, Richmond Agitation Sedation Scale, and Bispectral Index Score. Hypoxic and hypercapnic ventilatory responses were measured at rest, during sedation (OAA/S 2 to 4), and after recovery. Drug exposure was verified with concentration analysis in plasma. Ten subjects completed the study. The OAA/S at the sedation goal was 3 (3 to 4) (median [minimum to maximum]) for both drugs. Bispectral Index Score was 82 ± 8 and 75 ± 3, and the drug concentrations in plasma at the sedation target were 0.66 ± 0.14 and 1.26 ± 0.36 μg/ml for dexmedetomidine and propofol, respectively. Compared with baseline, sedation reduced hypoxic ventilation to 59 and 53% and the hypercapnic ventilation to 82 and 86% for dexmedetomidine and propofol, respectively. In addition, some volunteers displayed upper airway obstruction and episodes of apnea during sedation. Dexmedetomidine-induced sedation reduces ventilatory responses to hypoxia and hypercapnia to a similar extent as sedation with propofol. This finding implies that sedation with dexmedetomidine interacts with both peripheral and central control of breathing.

Effects of Depth of Propofol and Sevoflurane Anesthesia on Upper Airway Collapsibility, Respiratory Genioglossus Activation, and Breathing in Healthy Volunteers.

Volatile anesthetics and propofol impair upper airway stability and possibly respiratory upper airway dilator muscle activity. The magnitudes of these effects have not been compared at equivalent anesthetic doses. We hypothesized that upper airway closing pressure is less negative and genioglossus activity is lower during deep compared with shallow anesthesia. In a randomized controlled crossover study of 12 volunteers, anesthesia with propofol or sevoflurane was titrated using a pain stimulus to identify the threshold for suppression of motor response to electrical stimulation. Measurements included bispectral index, genioglossus electromyography, ventilation, hypopharyngeal pressure, upper airway closing pressure, and change in end-expiratory lung volume during mask pressure drops. A total of 393 attempted breaths during occlusion maneuvers were analyzed. Upper airway closing pressure was significantly less negative at deep versus shallow anesthesia (-10.8 ± 4.5 vs. -11.3 ± 4.4 cm H2O, respectively [mean ± SD]) and correlated with the bispectral index (P < 0.001), indicating a more collapsible airway at deep anesthesia. Respiratory genioglossus activity during airway occlusion was significantly lower at deep compared with light anesthesia (26 ± 21 vs. 35 ± 24% of maximal genioglossus activation, respectively; P < 0.001) and correlated with bispectral index (P < 0.001). Upper airway closing pressure and genioglossus activity during airway occlusion did not differ between sevoflurane and propofol anesthesia. Propofol and sevoflurane anesthesia increased upper airway collapsibility in a dose-dependent fashion with no difference at equivalent anesthetic concentrations. These effects can in part be explained by a dose-dependent inhibiting effect of anesthetics on respiratory genioglossus activity.

Electrical impedance tomography as possible guidance for individual positioning of patients with multiple lung injury.

Electrical Impedance Tomography (EIT) is a tomographic, radiation-free technique based on the injection of a harmless alternating current. As electrical impedance strictly correlates with the variation of air content, EIT delivers highly dynamic information about global and regional ventilation. We want to demonstrate the potential of EIT individualizing ventilation by positioning. Gravity-dependent EIT findings were analyzed retrospectively in a critically ill mechanically ventilated pediatric patient with cystic fibrosis and coincident lung diseases. To further evaluate gravity-dependent changes in ventilation, six adult healthy and spontaneously breathing volunteers were investigated during simultaneous detection of EIT, breathing patterns, tidal volume (VT) and breathing frequency (BF). EIT findings in healthy lungs in five positions showed gravity-dependent effects of ventilation with overall ventilation of predominantly the right lung (except during left-side positioning) and with the ventral lung in supine, prone and upright position. These EIT-derived observations are in line with pathophysiological mechanisms and earlier EIT studies. Unexpectedly, the patient with cystic fibrosis and lobectomy of the right upper and middle lobe one year earlier, showed improvement of global and regional ventilation in the right position despite reduced lung volume and overinflation of this side. This resulted in individualized positioning and improvement of ventilation. Although therapeutic recommendations are available for gravitational influences of lung ventilation, they can be contradictory depending on the underlying lung disease. EIT has the potential to guide therapists in the positioning of patients according to their individual condition and disease, especially in case of multiple lung injury.

Oxygen dependence of endothelium-dependent vasodilation: importance in chronic obstructive pulmonary disease.

IntroductionEpidemiological studies have shown increased morbidity and mortality in patients with coronary artery disease (CAD) and chronic obstructive pulmonary disease (COPD). We aimed to characterize the oxygen dependence of endothelial function in patients with CAD and coexisting COPD.Material and methodsIn CAD patients with and without COPD (n = 33), we non-invasively measured flow-mediated dilation (FMD) and intima-media thickness (IMT) of the brachial artery (BA), forearm blood flow (FBF), and perfusion of the cutaneous microcirculation with laser Doppler perfusion imaging (LDPI). In an experimental setup, vascular function was assessed in healthy volunteers (n = 5) breathing 12% oxygen or 100% oxygen in comparison to room air.ResultsCOPD was associated with impaired FMD (3.4 ±0.5 vs. 4.2 ±0.6%; p < 0.001) and increased IMT (0.49 ±0.04 vs. 0.44 ±0.04 mm; p <0.01), indicating functional and structural alterations of the BA in COPD. Forearm blood flow and LDPI were comparable between the groups. Flow-mediated dilation correlated with capillary oxygen pressure (pO2, r = 0.608). Subgroup analysis in COPD patients with pO2 > 65 mm Hg and pO2 ≤ 65 mm Hg revealed even lower FMD in patients with lower pO2 (3.0 ±0.5 vs. 3.7 ±0.4%; p < 0.01). Multivariate analysis showed that pO2 was a predictor of FMD independent of the forced expiratory volume and pack years. Exposure to hypoxic air led to an acute decrease in FMD, whereby exposure to 100% oxygen did not change vascular function.ConclusionsOur data suggest that in CAD patients with COPD, decreased systemic oxygen levels lead to endothelial dysfunction, underlining the relevance of cardiopulmonary interaction and the potential importance of pulmonary treatment in secondary prevention of vascular disease.

Detecting gas-induced vasomotor changes via blood oxygenation level-dependent contrast in healthy breast parenchyma and breast carcinoma.

PurposeTo evaluate blood oxygenation level‐dependent (BOLD) contrast changes in healthy breast parenchyma and breast carcinoma during administration of vasoactive gas stimuli.Materials and MethodsMagnetic resonance imaging (MRI) was performed at 3T in 19 healthy premenopausal female volunteers using a single‐shot fast spin echo sequence to acquire dynamic T 2‐weighted images. 2% (n = 9) and 5% (n = 10) carbogen gas mixtures were interleaved with either medical air or oxygen in 2‐minute blocks, for four complete cycles. A 12‐minute medical air breathing period was used to determine background physiological modulation. Pixel‐wise correlation analysis was applied to evaluate response to the stimuli in breast parenchyma and these results were compared to the all‐air control. The relative BOLD effect size was compared between two groups of volunteers scanned in different phases of the menstrual cycle. The optimal stimulus design was evaluated in five breast cancer patients.ResultsOf the four stimulus combinations tested, oxygen vs. 5% carbogen produced a response that was significantly stronger (P < 0.05) than air‐only breathing in volunteers. Subjects imaged during the follicular phase of their cycle when estrogen levels typically peak exhibited a significantly smaller BOLD response (P = 0.01). Results in malignant tissue were variable, with three out of five lesions exhibiting a diminished response to the gas stimulus.ConclusionOxygen vs. 5% carbogen is the most robust stimulus for inducing BOLD contrast, consistent with the opposing vasomotor effects of these two gases. Measurements may be confounded by background physiological fluctuations and menstrual cycle changes. J. Magn. Reson. Imaging 2016;44:335–345.

The "Abdominal Circulatory Pump": An Auxiliary Heart during Exercise?

Apart from its role as a flow generator for ventilation the diaphragm has a circulatory role. The cyclical abdominal pressure variations from its contractions cause swings in venous return from the splanchnic venous circulation. During exercise the action of the abdominal muscles may enhance this circulatory function of the diaphragm. Eleven healthy subjects (25 ± 7 year, 70 ± 11 kg, 1.78 ± 0.1 m, 3 F) performed plantar flexion exercise at ~4 METs. Changes in body volume (ΔVb) and trunk volume (ΔVtr) were measured simultaneously by double body plethysmography. Volume of blood shifts between trunk and extremities (Vbs) was determined non-invasively as ΔVtr-ΔVb. Three types of breathing were studied: spontaneous (SE), rib cage (RCE, voluntary emphasized inspiratory rib cage breathing), and abdominal (ABE, voluntary active abdominal expiration breathing). During SE and RCE blood was displaced from the extremities into the trunk (on average 0.16 ± 0.33 L and 0.48 ± 0.55 L, p < 0.05 SE vs. RCE), while during ABE it was displaced from the trunk to the extremities (0.22 ± 0.20 L p < 0.001, p < 0.05 RCE and SE vs. ABE respectively). At baseline, Vbs swings (maximum to minimum amplitude) were bimodal and averaged 0.13 ± 0.08 L. During exercise, Vbs swings consistently increased (0.42 ± 0.34 L, 0.40 ± 0.26 L, 0.46 ± 0.21 L, for SE, RCE and ABE respectively, all p < 0.01 vs. baseline). It follows that during leg exercise significant bi-directional blood shifting occurs between the trunk and the extremities. The dynamics and partitioning of these blood shifts strongly depend on the relative predominance of the action of the diaphragm, the rib cage and the abdominal muscles. Depending on the partitioning between respiratory muscles for the act of breathing, the distribution of blood between trunk and extremities can vary by up to 1 L. We conclude that during exercise the abdominal muscles and the diaphragm might play a role of an “auxiliary heart.”

Effects of profound hypoxemia on coagulation & fibrinolysis in normal individuals.

Hypoxia has been proposed to enhance, diminish, or have no effect on laboratory measures of coagulation or clinical thrombosis. Further, there usually are significant pathological or environmental factors concurrently present with hypoxia. Thus, the goal of the present investigation was to determine whether whole blood or plasmatic coagulation and fibrinolytic kinetics would change in response to progressive hypoxia to a systemic oxygenation (SpO2) of 70%. Healthy, conscious volunteers (n = 9) breathing a hypoxic mixture of gases during an in-vivo validation of noninvasive cerebral oximetry had blood samples collected and assessed with thrombelastography at normoxia and after SpO2 of 70%. A mild release of endogenous heparin-like activity occurred that diminished plasmatic coagulation, and a mild increase in clot lysis time also was noted. Further investigation to determine whether these phenomena occur in more chronic, less hypoxic states as sources of hypocoagulation or thrombophilia is needed.

Use of retinal oximetry in estimating cerebral tissue oxygenation

PurposeTo investigate the correlation between cerebral tissue oxygenation (SctO2) and retinal vessel oxygen saturation (SO2) using non‐invasive spectroscopy in healthy individuals.MethodsRetinal and cerebral oxygen saturations were measured in dark‐adapted, healthy volunteers breathing ambient air in a seated position using dual wavelength retinal oximetry and transcranial near‐infrared spectroscopy (NIRS) respectively. Correlations between SO2 and SctO2 were analyzed using Pearson correlation coefficients. Multivariate analysis was performed to determine the relative contribution of the arterial and venous vessels to SctO2. Using this model, SctO2 was estimated based on retinal arterial and venous oxygen saturation. Pearson correlation coefficients, paired sample t‐test and Bland‐Altman analysis were used to assess the agreement between the measured and the predicted SctO2.ResultsTwenty‐one young healthy individuals aged 26.4 ± 2.2 years were analyzed. SctO2 showed a significant positive correlation with both arterial and venous SO2 (r = 0.442, P = 0.045 and r = 0.434 P = 0.049 respectively). In multivariate analysis, the relative contribution of arterial and venous SO2 to SctO2 was significantly correlated with diastolic blood pressure, retinal venous oxygen saturation and retinal venous diameter (R2=0.60, P &lt; 0.001). The measured SctO2 (72.2 ± 3.5%, range 67.3–80.1) correlated well with estimated SctO2 (72.2 ± 2.6%, range 67.6–77.5) (r = 0.774, P &lt; 0.001). Bland–Altman plots showed 95% agreement within ±6.8%.ConclusionsIn this pilot study, retinal oximetry showed promising as an estimate of cerebral tissue oxygenation as measured by NIRS.