Healthy Volunteers Breathing Research Articles

Effects of Apnea-Induced Hypoxia on Hypoalgesia in Healthy Subjects

Introduction: Exercise-induced hypoalgesia is a phenomenon in which exercise bouts induce a reduction in pain sensitivity. Apnea training involves similar characteristics that could potentially induce hypoalgesia. Objectives: The objectives of this study are to explore the effect of apnea training on hypoalgesia; assess the correlation between conditioned pain modulation (CPM) response and apnea-induced hypoalgesia; and examine the association between hypoalgesia with hypoxemia, and heart rate (HR) during apnea. Methods: A randomized controlled trial was conducted comparing a walking protocol employing intermittent apnea compared with normal breathing in healthy volunteers. Hypoalgesia was tested with pressure pain thresholds (PPTs) and CPM. Oxygen saturation (SpO2) and HR were also tested. Results: Relevant but not significant changes were detected in the thumb (MD = 0.678 kg/cm2), and tibialis (MD = 0.718 kg/cm2) in favor of the apnea group. No significant differences were detected in CPM. The apnea group presented lower SpO2, but HR values similar to those of the control group during the intervention. Basal CPM and intrasession hypoxemia significantly correlated with the PPT response. However, HR did not correlate with the PPT response. Conclusions: The current results suggest a trend, though not statistically significant, toward an improvement in the PPT in favor of apnea training compared to normal breathing. Nevertheless, subjects who presented greater basal CPM and lower oxygen saturation during the session presented a greater PPT response, suggesting the possibility of mediators of response. Future investigations should clarify this phenomenon.

An Individual Barrier Enclosure Actively Removing Aerosols for Airborne Isolation: A Vacuum Tent.

Aerosol barrier enclosure systems have been designed to prevent airborne contamination, but their safety has been questioned. A vacuum tent was designed with active continuous suctioning to minimize risks of aerosol dispersion. We tested its efficacy, risk of rebreathing, and usability on a bench, in healthy volunteers, and in an ergonomic clinical assessment study. First, a manikin with airway connected to a breathing simulator was placed inside the vacuum tent to generate active breathing, cough, and CO2 production; high-flow nasal cannula (HFNC) was applied in the manikin's nares. Negative pressure was applied in the vacuum tent's apex port using wall suction. Fluorescent microparticles were aerosolized in the vacuum tent for qualitative assessment. To quantify particles inside and around vacuum tent (aerosol retention), an airtight aerosol chamber with aerosolized latex microparticles was used. The vacuum tent was tested on healthy volunteers breathing with and without HFNC. Last, its usability was assessed in 5 subjects by 5 different anesthesiologists for delivery of full anesthesia, including intubation and extubation. The vacuum tent was adjusted until no leak was visualized using fluorescent particles. The efficacy in retaining microparticles was confirmed quantitatively. CO2 accumulation inside the vacuum tent showed an inverse correlation with the suction flow in all conditions (normal breathing and HFNC 30 or 60 L/min) in bench and healthy volunteers. Particle removal efficacy and safe breathing conditions (CO2, temperature) were reached when suctioning was at least 60 L/min or 20 L/min > HFNC flow. Five subjects were successfully intubated and anesthetized without ergonomic difficulties and with minimal interference with workflow and an excellent overall assessment by the anesthesiologists. The vacuum tent effectively minimized aerosol dispersion. Its continuous suction system set at a high suction flow was crucial to avoid the spread of aerosol particles and CO2 rebreathing.

Hypoxic pulmonary vasoconstriction does not limit maximal exercise capacity in healthy volunteers breathing 12% oxygen at sea level.

Maximal exercise capacity is reduced at altitude or during hypoxia at sea level. It has been suggested that this might reflect increased right ventricular afterload due to hypoxic pulmonary vasoconstriction. We have shown previously that the pulmonary vascular sensitivity to hypoxia is enhanced by sustained isocapnic hypoxia, and inhibited by intravenous iron. In this study, we tested the hypothesis that elevated pulmonary artery pressure contributes to exercise limitation during acute hypoxia. Twelve healthy volunteers performed incremental exercise tests to exhaustion breathing 12% oxygen, before and after sustained (8-h) isocapnic hypoxia at sea level. Intravenous iron sucrose (n = 6) or saline placebo (n = 6) was administered immediately before the sustained hypoxia. In the placebo group, there was a substantial (12.6 ± 1.5 mmHg) rise in systolic pulmonary artery pressure (SPAP) during sustained hypoxia, but no associated fall in maximal exercise capacity breathing 12% oxygen. In the iron group, the rise in SPAP during sustained hypoxia was markedly reduced (3.4 ± 1.0 mmHg). There was a small rise in maximal exercise capacity following sustained hypoxia within the iron group, but no overall effect of iron, compared with saline. These results do not support the hypothesis that elevated SPAP inhibits maximal exercise capacity during acute hypoxia in healthy volunteers.

Effect of acetazolamide on obstructive sleep apnoea in highlanders: protocol for a randomised, placebo-controlled, double-blinded crossover trial

IntroductionObstructive sleep apnoea (OSA) is a highly prevalent disease that causing systemic hypertension. Furthermore, altitude-dependent hypobaric hypoxic condition and Tibetan ethnicity have been associated with systemic hypertension independent of OSA,...

Ni-Based Tantalate Sensing Electrode for Fast and Low Detection Limit of Acetone Sensor Combining Stabilized Zirconia

Introduction Acetone (CH3COCH3) is a colorless transparent liquid with a special pungent smell, which is categorized as important member of volatile organic compounds (VOCs). It offers many important information in early medical diagnosis of diabetes. In exhaled breath of healthy human, the average concentration of acetone is 0.3-0.9 ppm, which is far below lowest detection limit of 1.8 ppm in exhaled breath of diabetes patients. Taking into consideration of the practical detection demand for healthy medical diagnosis, the highly performance gas sensor is to be expected. Here, a stabilized zirconia (YSZ) based acetone sensor based on mixed potential sensing mechanism was fabricated using NiTa2O6 sensing electrode (SE) calcinated at 1000 °C. The NiTa2O6 sensing material was characterized by TG/DSC, XRD, SEM, Raman and XPS measurement. The gas sensing performance of developed sensing device demonstrated that the sensor based on NiTa2O6-SE displayed low detection limit of 200 ppb acetone and rapid response and recovery times of 9 s and 18 s to 2 ppm acetone at 600 °C. Between the response value to wide concentration range of 0.2-200 ppm acetone and the acetone concentration logarithm for the developed sensor presented piecewise linear function. The fabricated acetone sensor also possessed good wet fastness, reproducibility and stability of 20 days, portending great potential in aspect of low and high acetone concentration detection. More importantly, the solid electrolyte type acetone sensor utilizing NiTa2O6-SE open up a new possibility for noninvasive diagnosis of diabetes through detecting exhaled breath of healthy people and diabetes patients. Results and Conclusions The operating temperature affects the activation degree for the electrochemical reaction and adsorption and desorption process of sensing electrode, which results in the change of gas sensing performance for the fabricated sensor. Thus, the response and recovery curves of the sensor utilizing NiTa2O6-SE sintered at 1000 °C to 50 ppm acetone at temperature range of 475-650 °C are tested. Accordingly, 600 °C was selected as the optimal operating temperature to investigate the corresponding sensing characteristics of present device. In the acetone concentration range of 0.2-200 ppm, the sensor exhibited good response and recovery characteristics and the response signal increased gradually with the increase of acetone concentration. Notably, a spike appears at larger tested gas concentration, which is also observed by other reported works [1, 2, 3, 4]. Therefore, to avoid disturbance of the spike and to render certain the accuracy of sensing performance, the exposed time of 2.5 min in acetone gas and exposed time of 3.5 min in air is performed. The potential values at the last second were used for calculation of the response. The low detection limit of the sensor was 200 ppb acetone and the response and recovery times to 2 ppm acetone were 9 s and 18 s, respectively. The ΔV of the sensor to 0.2–2 ppm and 2-200 ppm acetone and concentration logarithm of acetone displayed linear relationship at 600 °C and the sensitivity of the sensor to 0.2-2 ppm and 2-200 ppm acetone were -11 and -27 mV/decade, which demonstrated the good acetone detection ability in aspects of lower and higher concentration. Comparison of the acetone sensing performances of developed sensor in this work and those of solid electrolyte sensing devices reported in literatures. More importantly, the present sensor attached with NiTa2O6-SE possessed significant advantages of low detection limit of acetone and response or recovery speeds in the lower acetone concentration, indicating the good potential alternative device for effectively monitoring acetone.To evaluate the possibility of the present sensor to be a practical acetone device, clinical detection for acetone biomarker in real exhaled breath of healthy volunteers and diabetes is further performed based on the sensor attached with NiTa2O6-SE. Here, the exhaled breath samples are taken from three healthy volunteers and diabetes patients. The blood ketone level of three diabetes patients is 0.6 mmol/L, 2.0 mmol/L and 6.3 mmol/L. The sensor exhibited low response signal and relatively good consistence to exhaled breath of three healthy volunteers. However, the response signal of the sensor to exhaled breath of three diabetes patients apparently higher than that of healthy peoples. Furthermore, the response value of the sensing device enhanced gradually with the increase of blood ketone levels of three diabetes patients. In this case, the difference in response value between diabetes and healthy people becomes more obvious, namely, the sensor can well distinguish between diabetic patients and healthy people. Accordingly, the developed acetone sensor attached with NiTa2O6-SE possessed good possibility to diagnosis diabetes.

Evidence of variations of endogenous halogenated volatile organic compounds in alveolar breath after mental exercise-induced oxidative stress

The effect of oxygen on markers of oxidative stress has not been totally elucidated because previous studies have yielded conflicting results. A method for the collection and gas chromatography-mass spectrometry of the halogenated volatile organic compounds in human alveolar breath is described. A transportable apparatus sampled specifically alveolar breath; the volatile organic compounds were captured in a thermal desorption tube, Carbotrap 200®. The sample was thermally desorbed from the trap in an automated gas chromatography with mass spectrometry detection and peak fragmentation. Compounds were identified by reference to a computer-based library of mass spectra. Trichlorotrifluoroethane, tetrafluoroethane, dichlorodifluoromethane were identified in alveolar breath of healthy volunteers after mental exercise-induced oxidative stress. The effects of halogenated alkanes were investigated on electron transport chain activity. These agents impaired the NADH oxidation suggesting an inhibition of the complex I (NADH: ubiquinone oxidoreductase) of the electron transport chain. These inhibitory effects are suspected likely to fight against oxidative stress deleterious reactions. Chemical inhibition of the oxidative burst in human body trough these halogenated inhibitors is a new concept of significant practical, medical, biological and scientific interest.

Plasma from Volunteers Breathing Helium Reduces Hypoxia-Induced Cell Damage in Human Endothelial Cells\u2014Mechanisms of Remote Protection Against Hypoxia by Helium

PurposeRemote ischemic preconditioning protects peripheral organs against prolonged ischemia/reperfusion injury via circulating protective factors. Preconditioning with helium protected healthy volunteers against postischemic endothelial dysfunction. We investigated whether plasma from helium-treated volunteers can protect human umbilical vein endothelial cells (HUVECs) against hypoxia in vitro through release of circulating of factors.MethodsHealthy male volunteers inhaled heliox (79% helium, 21% oxygen) or air for 30 min. Plasma was collected at baseline, directly after inhalation, 6 h and 24 h after start of the experiment. HUVECs were incubated with either 5% or 10% of the plasma for 1 or 2 h and subjected to enzymatically induced hypoxia. Cell damage was measured by LDH content. Furthermore, caveolin 1 (Cav-1), hypoxia-inducible factor (HIF1α), extracellular signal-regulated kinase (ERK)1/2, signal transducer and activator of transcription (STAT3) and endothelial nitric oxide synthase (eNOS) were determined.ResultsPrehypoxic exposure to 10% plasma obtained 6 h after helium inhalation decreased hypoxia-induced cell damage in HUVEC. Cav-1 knockdown in HUVEC abolished this effect.ConclusionsPlasma of healthy volunteers breathing helium protects HUVEC against hypoxic cell damage, possibly involving circulating Cav-1.

Supra-threshold inspiratory loads elicit respiratory related evoked potentials in healthy subjects

Objectives Respiratory-related evoked potential (RREP) are well-established cerebral correlates of respiratory perceptions. The early components N1/P1 reflect first-order sensory processing of afferent respiratory signals in brain sensorimotor regions while the late ones P2/P3 involve higher-order cognitive processing [1] . The current stimuli used to elicited RREP are short occlusions at the onset of an inspiration or a transiant interruption of the inspiration [1] . Durations of the inspiratory occlusion do not affect RREP components [3] while there is a linear relationship between inspiratory loads and RREP components amplitudes. Moreover, an inspiration load needs to reach some threshold value to elicit RREP [1] , [2] . Here, we investigated whether supra-threshold load inspiration could induce RREP without occlusion. Methods EEG was synchronously recorded with the respiratory signals in 11 healthy volunteers breathing into a mouthpiece connected to a non-rebreathing valve. Four consecutives inspiration loads were produced by a pressure-threshold device connected to the non-rebreathing valve: no_Load, 10, 20 and 30 cmH2O/L/sec. Each load was presented during 5 minutes and there is a 3-min resting time between two consecutives loads presentations. Magnitude estimation (ME) for each load was scored with the A1 subscale of the Multi-dimensional profile of dyspnea. Inspiration onset time locked EEG epochs were averaged for each breathing conditions and examined for presence of RREP components. Results The no_load condition did not elicit any peak of RREP, but 10, 20 and 30 cmH2O/L/sec produced N1 and P3 RREP components with amplitudes correlating with the loads as well as the loads’ magnitude estimation. Mean amplitudes of the N1 and P3 RREP components for 10, 20 and 30 cmH2O/L/sec were respectively 3.6 ± 0.5, 5.6 ± 0.9, 3.8 ± 1.3 and −4.5 ± 1.3, −11.4 ± 2.4, −7.6 ± 2.2 μV. Conclusion Supra-threshold load inspiration could induce RREP without occlusion. This method should be compared with the standard inspiration occlusion method.

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.

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.

High-Pressure Photon Ionization Source for TOFMS and Its Application for Online Breath Analysis.

Photon ionization mass spectrometry (PI-MS) is a widely used technique for the online detection of trace substances in complex matrices. In this work, a new high-pressure photon ionization (HPPI) ion source based on a vacuum ultraviolet (VUV) Kr lamp was developed for time-of-flight mass spectrometry (TOFMS). The detection sensitivity was improved by elevating the ion source pressure to about 700 Pa. A radio frequency (RF)-only quadrupole was employed as the ion guide system following the HPPI source to achieve high ion transmission efficiency. In-source collision induced dissociation (CID) was conducted for accurate chemical identification by varying the voltage between the ion source and the ion guide. The high humidity of the breath air can promote the detection of some compounds with higher ionization potentials (IPs) that could not be well detected by single photon ionization (SPI) at low pressure. Under 100% relative humidity (37 °C), the limits of detection down to 0.015 ppbv (parts per billion by volume) for aliphatic and aromatic hydrocarbons were obtained. This HPPI-TOFMS system was preliminarily applied for online investigations of the exhaled breath from both healthy nonsmoker and smoker subjects, demonstrating its analytical capacity for complicated gases analysis. Subsequently, several frequently reported VOCs in the breath of healthy volunteers, i.e., acetone, isoprene, 2-butanone, ethanol, acetic acid, and isopropanol, were successfully identified and quantified.

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.

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.

Raising the standard of care for oxygen delivery with nasal high flow in high-acuity areas—a controlled study

Nasal high-flow therapy and dispersion of nasal aerosols in an experimental setting Sally Roberts, N. Kabaliuk, Cjt Spence, Jane O'Donnell, Z. Zulkhairi Abidin, R. Dougherty, S. Roberts, Y. Jiang, Mc Jermy University of Canterbury, New Zealand Fisher & Paykel Healthcare, New Zealand University of KS, USA Auckland District Health Board, New Zealand University of Auckland, New Zealand Background/Purpose: Nasal high-flow (NHF) therapy delivers flows of heated and humidified gases up to 60 L/min via a nasal cannula. NHF is widely used to support patients, including those who may be infectious. It is thought that NHF gas flow velocities may increase cross-infection risk. Methods: Aerosols within the exhaled breath of healthy volunteers were imaged. Experimental breathing conditions deemed as typical patient breathing conditions were tested: at rest, with a violent exhalation (snorting), both with and without NHF, at flows of 30 and 60 L/min, and for both separate nostrils. The number, diameter, evaporation rates, and velocity of exhaled aerosols were collected. Results: The numbers of aerosols measured were greatest during a violent exhalation without NHF and reduced with NHF. The numbers of aerosols were higher at 60 than 30 L/min, suggesting that higher gas flow rates may be associated with increased aerosol production; however, the numbers were on average 43% and 56% less than without NHF, respectively. During breathing at rest, no differences were imaged between with and without NHF, except at 60 L/min where numbers of aerosols produced were equivalent to 10% of a violent exhalation. Aerosol trajectory and evaporation rates observed both with and without NHF predicted that aerosols between 25 and 250 μm may travel up to 4.4 m and remain airborne for 43 seconds. Conclusions: NHF use does not increase the risk of dispersing infectious aerosols above the risk of typical patient breathing with violent exhalation, which is the worst-case clinical scenario; therefore, standard risk control measures should apply.

Nasal high-flow therapy and dispersion of nasal aerosols in an experimental setting

Nasal high-flow therapy and dispersion of nasal aerosols in an experimental setting Sally Roberts, N. Kabaliuk, Cjt Spence, Jane O'Donnell, Z. Zulkhairi Abidin, R. Dougherty, S. Roberts, Y. Jiang, Mc Jermy University of Canterbury, New Zealand Fisher & Paykel Healthcare, New Zealand University of KS, USA Auckland District Health Board, New Zealand University of Auckland, New Zealand Background/Purpose: Nasal high-flow (NHF) therapy delivers flows of heated and humidified gases up to 60 L/min via a nasal cannula. NHF is widely used to support patients, including those who may be infectious. It is thought that NHF gas flow velocities may increase cross-infection risk. Methods: Aerosols within the exhaled breath of healthy volunteers were imaged. Experimental breathing conditions deemed as typical patient breathing conditions were tested: at rest, with a violent exhalation (snorting), both with and without NHF, at flows of 30 and 60 L/min, and for both separate nostrils. The number, diameter, evaporation rates, and velocity of exhaled aerosols were collected. Results: The numbers of aerosols measured were greatest during a violent exhalation without NHF and reduced with NHF. The numbers of aerosols were higher at 60 than 30 L/min, suggesting that higher gas flow rates may be associated with increased aerosol production; however, the numbers were on average 43% and 56% less than without NHF, respectively. During breathing at rest, no differences were imaged between with and without NHF, except at 60 L/min where numbers of aerosols produced were equivalent to 10% of a violent exhalation. Aerosol trajectory and evaporation rates observed both with and without NHF predicted that aerosols between 25 and 250 μm may travel up to 4.4 m and remain airborne for 43 seconds. Conclusions: NHF use does not increase the risk of dispersing infectious aerosols above the risk of typical patient breathing with violent exhalation, which is the worst-case clinical scenario; therefore, standard risk control measures should apply.

Investigation of C3–C10 aldehydes in the exhaled breath of healthy subjects using selected ion flow tube-mass spectrometry (SIFT-MS)

Aldehydes have attracted great scientific and clinical interest as potential disease biomarkers. We have investigated selected ion flow tube-mass spectrometry (SIFT-MS) in detecting and quantifying C3 to C10 saturated aldehydes (propanal, butanal, pentanal, hexanal, heptanal, octanal, nonanal and decanal) from the exhaled breath of 26 healthy human volunteers. To assess the reliability of the Nalophan® bag sampling method employed, the water level in the breath sample was measured up to 4 h after collection and showed no significant degradation. Propanal was found to be the most abundant aldehyde in the exhaled breath of healthy volunteers. For the C4–C10 aldehydes, their median concentrations were all less than 3 ppbv, demonstrating only trace quantities are present in the exhaled breath of the 26 healthy volunteers.

Association of intraoperative tissue oxygenation with suspected risk factors for tissue hypoxia

Tissue hypoxia may cause organ dysfunction, but not much is known about tissue oxygenation in the intraoperative setting. We studied microcirculatory tissue oxygen saturation (StO₂) to determine representative values for anesthetized patients undergoing urological surgery and to test the hypothesis that StO₂ is associated with known perioperative risk factors for morbidity and mortality, conventionally monitored variables, and hypotension requiring norepinephrine. Using near-infrared spectroscopy, we measured StO₂ on the thenar eminence in 160 patients undergoing open urological surgery under general anesthesia (FiO2 0.35-0.4), and calculated its correlations with age, risk level for general perioperative complications and mortality (high if age ≥70 and procedure is radical cystectomy), mean arterial pressure (MAP), hemoglobin concentration (Hb), central venous oxygen saturation (ScvO₂), and norepinephrine use. The time averaged StO₂ was 86 ± 6 % (mean ± SD). In the multivariate analysis, Hb [standardized coefficient (SC) 0.21, p = 0.003], ScvO₂ (SC 0.53, p < 0.001) and high risk level (SC 0.06, p = 0.03) were significant independent variables correlated with StO₂. SStO₂ was partly dependent on MAP only when this was below 65 mmHg (lowest MAP SC 0.20, p = 0.006, MAP area under the curve <65 mmHg SC 0.03, p = 0.02). Finally, StO₂ was slightly lower in patients requiring norepinephrine (85 ± 6 vs. 89 ± 6 %, p = 0.001). Intraoperative StO₂ in urological patients was comparable to that of healthy volunteers breathing room air as reported in the literature and correlated with known perioperative risk factors. Further research should investigate its association with outcome and the effect of interventions aimed at optimizing StO₂.

Myocardial velocity mapping for the right ventricle in pulmonary arterial hypertension using a novel image-based respiratory self-navigation from a golden-angle spiral acquisition

Background CMR is a recognized method of assessing global RV function in patients with pulmonary arterial hypertension (PAH). Unfortunately, assessment of regional myocardial motion with MRI remains challenging due to the thin RV wall. One solution may be tissue phase mapping (TPM) in which motion can be encoded at a higher spatial resolution. However, one problem is the need for respiratory navigation due to long scan times. We have therefore implemented a novel self-gated golden-angle spiral TPM technique that can acquire high-resolution data efficiently during free breathing in healthy volunteers and in patients with PAH. Methods

Exhaled Breath Biomonitoring Using Laser Spectroscopy

Biological monitoring usually relies on the collection of blood and urine samples. Although being non-invasive and providing an inextinguishable sampling pool, the analysis of exhaled breath is not well established. A gas phase measurement is, however, inherently simpler than the analysis of complex biological fluids, and modern methods have identified hundreds of volatile compounds in the breath of persons exposed to normal environmental concentrations. The most commonly deployed analytical techniques in breath analysis are gas chromatography combined with mass spectrometry (GC/MS) and other MS-based methods. Lately, also laser-based optical methods, such as cavity ring-down spectroscopy (CRDS), have emerged in the field. With such instruments, it is possible to accurately quantify the concentrations of volatiles in exhaled breath down to below part-per-billion (ppb) levels with sub-second time resolution. Laser spectroscopy thereby enables real-time investigations during and after exposure to exogenous chemicals. In general, depending on the sampling approach used, the measured levels of the breath compounds may vary significantly. It is therefore of importance to systematically study and account for the phenomena affecting the recorded concentrations, and subsequently select an appropriate sampling and measurement strategy. In Helsinki, we have used CRDS to study the background levels of hydrogen cyanide (HCN), ammonia (NH3) and acetylene (C2H2) in the exhaled breath of healthy volunteers. Different sampling techniques have been employed in an effort to standardize the breath sampling event. The realtime elimination kinetics of breath C2H2 after smoking has also been studied. Keywords: Acetylene, ammonia, biomonitoring, breath analysis, cavity ring-down spectroscopy, hydrogen cyanide, laser spectroscopy, toxicokinetics

Using Time-Frequency Analysis of the Photoplethysmographic Waveform to Detect the Withdrawal of 900 mL of Blood

We designed this study to determine if 900 mL of blood withdrawal during spontaneous breathing in healthy volunteers could be detected by examining the time-varying spectral amplitude of the photoplethysmographic (PPG) waveform in the heart rate frequency band and/or in the breathing rate frequency band before significant changes occurred in heart rate or arterial blood pressure. We also identified the best PPG probe site for early detection of blood volume loss by testing ear, finger, and forehead sites. Eight subjects had 900 mL of blood withdrawn followed by reinfusion of 900 mL of blood. Physiological monitoring included PPG waveforms from ear, finger, and forehead probe sites, standard electrocardiogram, and standard blood pressure cuff measurements. The time-varying amplitude sequences in the heart rate frequency band and breathing rate frequency band present in the PPG waveform were extracted from high-resolution time-frequency spectra. These amplitudes were used as a parameter for blood loss detection. Heart rate and arterial blood pressure did not significantly change during the protocol. Using time-frequency analysis of the PPG waveform from ear, finger, and forehead probe sites, the amplitude signal extracted at the frequency corresponding to the heart rate significantly decreased when 900 mL of blood was withdrawn, relative to baseline (all P < 0.05); for the ear, the corresponding signal decreased when only 300 mL of blood was withdrawn. The mean percent decrease in the amplitude of the heart rate component at 900 mL blood loss relative to baseline was 45.2% (38.2%), 42.0% (29.2%), and 42.3% (30.5%) for ear, finger, and forehead probe sites, respectively, with the lower 95% confidence limit shown in parentheses. After 900 mL blood reinfusion, the amplitude signal at the heart rate frequency showed a recovery towards baseline. There was a clear separation of amplitude values at the heart rate frequency between baseline and 900 mL blood withdrawal. Specificity and sensitivity were both found to be 87.5% with 95% confidence intervals (47.4%, 99.7%) for ear PPG signals for a chosen threshold value that was optimized to separate the 2 clusters of amplitude values (baseline and blood loss) at the heart rate frequency. Meanwhile, no significant changes in the spectral amplitude in the frequency band corresponding to respiration were found. A time-frequency spectral method detected blood loss in spontaneously breathing subjects before the onset of significant changes in heart rate or blood pressure. Spectral amplitudes at the heart rate frequency band were found to significantly decrease during blood loss in spontaneously breathing subjects, whereas those at the breathing rate frequency band did not significantly change. This technique may serve as a valuable tool in intraoperative and trauma settings to detect and monitor hemorrhage.