Respiratory Dead Space Research Articles

Effects of the Use of N95 Masks on the Vital Signs of Healthy Healthcare Workers During the COVID-19 Pandemic: A Hospital-Based Cross-Sectional Study.

The N95 filtering facepiece respirator (FR) is the most commonly recommended respiratory protection used in healthcare settings. However, concerns have been raised about its use because it can increase respiratory resistance and dead space. The primary objective of this study was to determine the effect of wearing N95 masks on the vital signs, i.e., oxygen saturation, pulse rate, and respiratory rate, of the participant health workers. Our secondary objective was to assess the subjective feeling of discomfort when wearing N95 masks. The study participants were healthy healthcare workers taking care of coronavirus disease 2019 (COVID-19)-infected pediatric cases who did at least six hours of continuous shift duty in the pediatric COVID-19 ward at a tertiary care hospital in the eastern part of India. They were evaluated for vital signs at various time intervals while wearing N95 masks. Subjective discomfort at any point in time was also noted. We found a significant variation in the mean oxygen saturation (SpO2) and heart rate (HR) reduction across the four different points. The pair-wise comparison showed a small but significant decrease in the mean SpO2 of 98.3% (1.1)at six hoursas compared with a mean SpO2 of 98.7% (0.9) at three hours. Similarly, a significant increase was noted for a mean HR of 84.7bpm (11.2) at six hours compared with a baseline of 82.3bpm (9.2) and 83.2bpm (8.8) at three hours. The continuous use of an N95 mask leads to a mild increase in respiratory rate. However, heart rate and oxygen saturation vary significantly at different points in time after N95 mask use.

Non-invasive ventilation treatment for patients with chronic obstructive pulmonary disease.

Chronic obstructive pulmonary disease (COPD) affects the lives of millions of patients worldwide. Patients with advanced COPD may require non-invasive ventilation (NIV) to support the resultant deficiencies of the respiratory system. The purpose of this study was to evaluate the effects of varying the continuous positive airway pressure (CPAP) and oxygen supplementation components of NIV on simulated COPD patients by using an established and detailed model of the human respiratory system. The model used in the study simulates features of advanced COPD including the effects on the changes in ventilation control, increases in respiratory dead space and airway resistance, and the acid-base shifts in the blood seen in these patients over time. The results of the study have been compared with and found to be in general agreement with available clinical data. Our results demonstrate that under non-emergency conditions, low levels of oxygen supplementation combined with low levels of CPAP therapy seem to improve hypoxemia and hypercapnia in the model, whereas prolonged high-level CPAP and moderate-to-high levels of oxygen supplementation do not. The authors conclude that such modelling may be useful to help guide beneficial interventions for COPD patients using NIV.

Expert consensus on the diagnosis and treatment of severe and critical coronavirus disease 2019.

Expert consensus on the diagnosis and treatment of severe and critical coronavirus disease 2019.

Increased respiratory dead space could associate with coagulation activation and poor outcomes in COVID-19 ARDS.

PurposeTo determine whether VDPhys/VT is associated with coagulation activation and outcomes.Materials and methodsWe enrolled patients with COVID-19 pneumonia who were supported by invasive mechanical ventilation and were monitored using volumetric capnography. Measurements were performed during the first 24 h of mechanical ventilation. The primary endpoint was the likelihood of being discharge alive on day 28.ResultsSixty patients were enrolled, of which 25 (42%) had high VDPhys/VT (>57%). Patients with high vs. low VDPhys/VT had higher APACHE II (10[8-13] vs. 8[6-9] points, p = 0.002), lower static compliance of the respiratory system (35[24–46] mL/cmH2O vs. 42[37–45] mL/cmH2O, p = 0.005), and higher D-dimer levels (1246[1050–1594] ng FEU/mL vs. 792[538–1159] ng FEU/mL, p = 0.001), without differences in P/F ratio (157[112–226] vs. 168[136–226], p = 0.719). Additionally, D-dimer levels correlated with VDPhys/VT (r = 0.530, p < 0.001), but not with the P/F ratio (r = −0.103, p = 0.433). Patients with high VDPhys/VT were less likely to be discharged alive on day 28 (32% vs. 71%, aHR = 3.393[1.161–9.915], p = 0.026).ConclusionsIn critically ill COVID-19 patients, increased VDPhys/VT was associated with high D-dimer levels and a lower likelihood of being discharged alive. Dichotomic VDPhys/VT could help identify a high-risk subgroup of patients neglected by the P/F ratio.

Comparison of Pressure and Volume-Controlled Mechanical Ventilation in Laparoscopic Bariatric Surgery: A Randomized Crossover Trial.

BackgroundThe number of patients with obesity undergoing various surgeries is increasing annually, and ventilation problems are highly prevalent in these patients.ObjectivesWe aimed to evaluate ventilation effectiveness with pressure-controlled (PC) and volume-controlled (VC) ventilation modes during laparoscopic bariatric surgery.MethodsIn this open-label randomized crossover clinical trial, 40 adult patients with morbid obesity candidates for laparoscopic bariatric surgery were assigned to VC-PC or PC-VC groups. Each patient received both ventilation modes sequentially for 15 min during laparoscopic surgery in a random sequence. Every 5 min, exhaled tidal volume, peak and mean airway pressure, oxygen saturation, heart rate, mean arterial pressure, and end-tidal CO2 were recorded. Blood gas analysis was done at the end of 15 min. Dynamic compliance, PaO2/FiO2 ratio, P (A-a) O2 gradient, respiratory dead space, and PaCO2-ETCO2 gradient were calculated according to the obtained results.ResultsThe study included 40 patients with a mean age of 35.13 ± 9.06 years. There were no significant differences in peak and mean airway pressure, dynamic compliance, and hemodynamic parameters (P > 0.05). There was no significant difference between the two ventilation modes in pH, PaCO2, PaO2, PaO2/FIO2, dead space volume, and D (A-a) O2 at different time intervals (P > 0.05).ConclusionsIf low tidal volumes are used during adult laparoscopic bariatric surgery, mechanical ventilation with PC mode is not superior to VC mode.

Warm-Up With Added Respiratory Dead Space Volume Mask Improves the Performance of the Cycling Sprint Interval Exercise: Cross-Over Study.

Special breathing exercises performed during warm-up lead to hypercapnia and stimulation of mechanisms leading to increased exercise performance, but the effect of a device that increases the respiratory dead space volume (ARDSv) during warm-up has not been studied. The purpose of this study was to investigate the effect of 10 min warm-up with ARDSv on performance, physiological and biochemical responses during sprint interval cycling exercise (SIE). During four laboratory visits at least 72 h apart, they completed: (1) an incremental exercise test (IET) on a cycloergometer, (2) a familiarization session, and cross-over SIE sessions conducted in random order on visits (3) and (4). During one of them, 1200 mL of ARDSv was used for breathing over a 10-min warm-up. SIE consisted of 6 × 10-s all-out bouts with 4-min active recovery. Work capacity, cardiopulmonary parameters, body temperature, respiratory muscle strength, blood acid-base balance, lactate concentration, and rating of perceived exertion (RPE) were analyzed. After warm-up with ARDSv, PETCO2 was 45.0 ± 3.7 vs. 41.6 ± 2.5 (mm Hg) (p < 0.001). Body temperature was 0.6 (°C) higher after this form of warm-up (p < 0.05), bicarbonate concentration increased by 1.8 (mmol⋅L–1) (p < 0.01). As a result, work performed was 2.9% greater (p < 0.01) compared to the control condition. Respiratory muscle strength did not decreased. Warming up with added respiratory dead space volume mask prior to cycling SIE produces an ergogenic effect by increasing body temperature and buffering capacity.

Positive end-expiratory pressure in COVID-19 acute respiratory distress syndrome: the heterogeneous effects

BackgroundWe hypothesized that as CARDS may present different pathophysiological features than classic ARDS, the application of high levels of end-expiratory pressure is questionable. Our first aim was to investigate the effects of 5–15 cmH2O of PEEP on partitioned respiratory mechanics, gas exchange and dead space; secondly, we investigated whether respiratory system compliance and severity of hypoxemia could affect the response to PEEP on partitioned respiratory mechanics, gas exchange and dead space, dividing the population according to the median value of respiratory system compliance and oxygenation. Thirdly, we explored the effects of an additional PEEP selected according to the Empirical PEEP-FiO2 table of the EPVent-2 study on partitioned respiratory mechanics and gas exchange in a subgroup of patients.MethodsSixty-one paralyzed mechanically ventilated patients with a confirmed diagnosis of SARS-CoV-2 were enrolled (age 60 [54–67] years, PaO2/FiO2 113 [79–158] mmHg and PEEP 10 [10–10] cmH2O). Keeping constant tidal volume, respiratory rate and oxygen fraction, two PEEP levels (5 and 15 cmH2O) were selected. In a subgroup of patients an additional PEEP level was applied according to an Empirical PEEP-FiO2 table (empirical PEEP). At each PEEP level gas exchange, partitioned lung mechanics and hemodynamic were collected.ResultsAt 15 cmH2O of PEEP the lung elastance, lung stress and mechanical power were higher compared to 5 cmH2O. The PaO2/FiO2, arterial carbon dioxide and ventilatory ratio increased at 15 cmH2O of PEEP. The arterial–venous oxygen difference and central venous saturation were higher at 15 cmH2O of PEEP. Both the mechanics and gas exchange variables significantly increased although with high heterogeneity. By increasing the PEEP from 5 to 15 cmH2O, the changes in partitioned respiratory mechanics and mechanical power were not related to hypoxemia or respiratory compliance. The empirical PEEP was 18 ± 1 cmH2O. The empirical PEEP significantly increased the PaO2/FiO2 but also driving pressure, lung elastance, lung stress and mechanical power compared to 15 cmH2O of PEEP.ConclusionsIn COVID-19 ARDS during the early phase the effects of raising PEEP are highly variable and cannot easily be predicted by respiratory system characteristics, because of the heterogeneity of the disease.

Acute Effects of Using Added Respiratory Dead Space Volume in a Cycling Sprint Interval Exercise Protocol: A Cross-Over Study.

Background: The aim of the study was to compare acute physiological, biochemical, and perceptual responses during sprint interval exercise (SIE) with breathing through a device increasing added respiratory dead space volume (ARDSV) and without the device. Methods: The study involved 11 healthy, physically active men (mean maximal oxygen uptake: 52.6 ± 8.2 mL∙kg1∙min−1). During four visits to a laboratory with a minimum interval of 72 h, they participated in (1) an incremental test on a cycle ergometer; (2) a familiarization session; (3) and (4) cross-over SIE sessions. SIE consisted of 6 × 10-s all-out bouts with 4-min active recovery. During one of the sessions the participants breathed through a 1200-mL ARDSv (SIEARDS). Results: The work performed was significantly higher by 4.4% during SIEARDS, with no differences in the fatigue index. The mean respiratory ventilation was significantly higher by 13.2%, and the mean oxygen uptake was higher by 31.3% during SIEARDS. Respiratory muscle strength did not change after the two SIE sessions. In SIEARDS, the mean pH turned out significantly lower (7.26 vs. 7.29), and the mean HCO3– concentration was higher by 7.6%. Average La− and rating of perceived exertion (RPE) did not differ between the sessions. Conclusions: Using ARDSV during SIE provokes respiratory acidosis, causes stronger acute physiological responses, and does not increase RPE.

Influence of a Six-Week Swimming Training with Added Respiratory Dead Space on Respiratory Muscle Strength and Pulmonary Function in Recreational Swimmers.

The avoidance of respiratory muscle fatigue and its repercussions may play an important role in swimmers’ health and physical performance. Thus, the aim of this study was to investigate whether a six-week moderate-intensity swimming intervention with added respiratory dead space (ARDS) resulted in any differences in respiratory muscle variables and pulmonary function in recreational swimmers. A sample of 22 individuals (recreational swimmers) were divided into an experimental (E) and a control (C) group, observed for maximal oxygen uptake (VO2max). The intervention involved 50 min of front crawl swimming performed at 60% VO2max twice weekly for six weeks. Added respiratory dead space was induced via tube breathing (1000 mL) in group E during each intervention session. Respiratory muscle strength variables and pulmonary and respiratory variables were measured before and after the intervention. The training did not increase the inspiratory or expiratory muscle strength or improve spirometric parameters in any group. Only in group E, maximal tidal volume increased by 6.3% (p = 0.01). The ARDS volume of 1000 mL with the diameter of 2.5 cm applied in moderate-intensity swimming training constituted too weak a stimulus to develop respiratory muscles and lung function measured in the spirometry test.

Risks of N95 Face Mask Use in Subjects With COPD.

The N95 filtering facepiece respirator (FFR) is the most popular individual protective device to reduce exposure to particulate matter. However, concerns have been raised with regard to its use because it can increase respiratory resistance and dead space. Therefore, this study assessed the safety of N95 use in patients with COPD and air-flow limitation. This prospective study was performed at a tertiary hospital and enrolled 97 subjects with COPD. The subjects were monitored for symptoms and physiologic variables during a 10-min rest period and 6-min walking test while wearing an N95. Of the 97 subjects, 7 with COPD did not wear the N95 for the entire test duration. This mask-failure group showed higher British modified Medical Research Council dyspnea scale scores and lower FEV1 percent of predicted values than did the successful mask use group. A modified Medical Research Council dyspnea scale score ≥ 3 (odds ratio 167, 95% CI 8.4 to >999.9; P = .008) or a FEV1 < 30% predicted (odds ratio 163, 95% CI 7.4 to >999.9; P = .001) was associated with a risk of failure to wear the N95. Breathing frequency, blood oxygen saturation, and exhaled carbon dioxide levels also showed significant differences before and after N95 use. This study demonstrated that subjects with COPD who had modified Medical Research Council dyspnea scale scores ≥ 3 or FEV1 < 30% predicted wear N95s only with care.

In Vivo Measurements of Lung Volumes in Ringed Seals: Insights from Biomedical Imaging.

Marine mammals rely on oxygen stored in blood, muscle, and lungs to support breath-hold diving and foraging at sea. Here, we used biomedical imaging to examine lung oxygen stores and other key respiratory parameters in living ringed seals (Pusa hispida). Three-dimensional models created from computed tomography (CT) images were used to quantify total lung capacity (TLC), respiratory dead space, minimum air volume, and total body volume to improve assessments of lung oxygen storage capacity, scaling relationships, and buoyant force estimates. Results suggest that lung oxygen stores determined in vivo are smaller than those derived from postmortem measurements. We also demonstrate that-while established allometric relationships hold well for most pinnipeds-these relationships consistently overestimate TLC for the smallest phocid seal. Finally, measures of total body volume reveal differences in body density and net vertical forces in the water column that influence costs associated with diving and foraging in free-ranging seals.

Modes of Ventilation

Lung ventilation is required to maintain oxygenation and eliminate carbon dioxide. The basic parameters of ventilation—tidal volume, respiratory rate, airway resistance, and lung and thoracic compliance—all combine to affect the airway pressure. These parameters, in turn, can affect cardiac output and hemodynamic stability through their effect on intrathoracic pressure and on venous return to the heart. Since the 1950s, many machines have been designed to allow the physician to optimize ventilation. These designs have revolved around three physical variables: volume, pressure, and time. Volume is required to overcome the anatomic respiratory dead space and allows gas exchange in the alveoli. Pressure is required to inflate the elastic system comprising the lungs and thorax, but must also be limited to prevent tissue damage. Time not only determines the respiratory rate but also the rate of flow of gas in and out of the lungs. Many permutations of these basic parameters in anesthesia machines are available today. Knowledge of the common forms of ventilation and their advantages and disadvantages will guide the anesthesiologist in choosing from among these various complex systems. This review contains 5 figures, 3 tables, and 27 references. Key words: CPAP, HFOV, IMV, IPPV, jet ventilation, PEEP, pressure cycled, pulmonary ventilation, SIMV, spontaneous, volume cycled

Modes of Ventilation

Lung ventilation is required to maintain oxygenation and eliminate carbon dioxide. The basic parameters of ventilation—tidal volume, respiratory rate, airway resistance, and lung and thoracic compliance—all combine to affect the airway pressure. These parameters, in turn, can affect cardiac output and hemodynamic stability through their effect on intrathoracic pressure and on venous return to the heart. Since the 1950s, many machines have been designed to allow the physician to optimize ventilation. These designs have revolved around three physical variables: volume, pressure, and time. Volume is required to overcome the anatomic respiratory dead space and allows gas exchange in the alveoli. Pressure is required to inflate the elastic system comprising the lungs and thorax, but must also be limited to prevent tissue damage. Time not only determines the respiratory rate but also the rate of flow of gas in and out of the lungs. Many permutations of these basic parameters in anesthesia machines are available today. Knowledge of the common forms of ventilation and their advantages and disadvantages will guide the anesthesiologist in choosing from among these various complex systems. This review contains 5 figures, 3 tables, and 27 references. Key words: CPAP, HFOV, IMV, IPPV, jet ventilation, PEEP, pressure cycled, pulmonary ventilation, SIMV, spontaneous, volume cycled

An in vitro evaluation of the influence of neonatal endotracheal tube diameter and length on the work of breathing

Neonates, particularly premature babies, are often managed with endotracheal intubation and subsequent mechanical ventilation to maintain adequate pulmonary gas exchange. There is no consensus on the standard length of endotracheal tube. Although a short tube reduces resistance and respiratory dead space, it is believed to increase the risk of accidental extubation. There are not entirely coherent data regarding the effect of endotracheal tube length on work of breathing in infants. The aim of this study was to evaluate the impact of neonatal endotracheal tube diameter and length on the work of breathing using an infant in vitro lung model. We assessed the work of breathing index and mechanical ventilation settings with various endotracheal tube diameters and lengths using the JTR100 invitro infant lung model. The basic parameters of the model were breathing frequency of 20 per minutes, inspiratory-expiratory ratio of 1:3, and positive end-expiratory pressure of 5cmH2 O. In addition, the diaphragm driving pressure to maintain the set tidal volume was measured as the work of breathing index. The JTR100 was connected to the Babylog 8000plus through the endotracheal tube. Finally, we monitored the peak inspiratory pressure generated during assist-control volume guarantee mode with a targeted tidal volume of 10-30mL. The diaphragm driving pressure using a 2.0-mm inner diameter tube was twice as high as that using a 4.0-mm inner diameter tube. To maintain the targeted tidal volume, a shorter tube reduced both the diaphragm driving pressure and ventilator-generated peak inspiratory pressure. The difference in the generated peak inspiratory pressure between the shortest and longest tubes was 5cmH2 O. In our infant lung model, a shorter tube resulted in a lower work of breathing and lower ventilator-generated peak inspiratory pressure.

Effect of pressure-controlled inverse ratio ventilation on dead space during robot-assisted laparoscopic radical prostatectomy: A randomised crossover study of three different ventilator modes.

Pressure-controlled inverse inspiratory to expiratory ratio ventilation (PC-IRV) is thought to be beneficial for reducing the dead space volume. To investigate the effects of PC-IRV on the components of dead space during robot-assisted laparoscopic radical prostatectomy (RLRP). A randomised crossover study of three different ventilator modes. A single university hospital from September 2014 to April 2015. Twenty consecutive study participants undergoing RLRP. Patients were ventilated sequentially with three different modes in random order for 30 min: volume control ventilation (VCV; inspiratory to expiratory ratio 0.5), pressure control ventilation (PCV; inspiratory to expiratory ratio 0.5) and PC-IRV. Inverse inspiratory to expiratory ratio was adjusted individually by observing the expiratory flow-time wave to prevent the risk of dynamic pulmonary hyperinflation. The primary outcome included physiological dead space (VDphys), airway dead space (VDaw), alveolar dead space (VDalv) and shunt dead space (VDshunt). VDphys was calculated by Enghoff's method. We also analysed respiratory dead space (VDresp) and VDaw using a novel analytical method. Then, VDalv and VDshunt were calculated by VDalv = VDresp - VDaw and VDshunt = VDphys - VDresp, respectively. The VDphys/expired tidal volume (VTE) ratio in PC-IRV (29.2 ± 4.7%) was significantly reduced compared with that in VCV (43 ± 8.5%) and in PCV (35.9 ± 3.9%). The VDshunt/VTE in PC-IRV was significantly smaller than that in VCV and PCV. VDaw/VTE in PC-IRV was also significantly smaller than that in VCV but not that in PCV. There was no significant change in VDalv/VTE. PC-IRV with the inspiratory to expiratory ratio individually adjusted by the expiratory flow-time wave decreased VDphys/VTE in patients undergoing RLRP. University Hospital Medical Information Network in Japan 000014004.

Incremental exercise test performance with and without a respiratory gas collection system

Objective. Despite their widespread use in exercise testing, few data are available on the effect of wearing respiratory gas collection (RGC) systems on exercise test performance. Industrial-type mask wear is thought to impair exercise performance through increased respiratory dead space, flow resistance and/or discomfort when compared with RGC facemasks, but whether performance decrements exist for RGC facemask wear versus non-wear is unclear. The objective of this study was to evaluate the difference in incremental exercise test performance with and without a RGC system. Incremental exercise test performance with and without a respiratory gas collection system Design. Twenty moderately active males (age 21.0 ± 1.9 years; VO2peak 55.9 ± 3.0 ml∙kg-1∙min-1) performed two progressive treadmill tests to volitional exhaustion. In random order subjects ran with (MASK) or without (NO-MASK) a RGC facemask and flow sensor connected to a gas analyzer. Descriptive data (mean ± SD) were determined for all parameters. The Wilcoxon signed rank test for paired differences was used to assess mean differences between MASK and NO-MASK conditions. Results. Exercise time to exhaustion, peak treadmill speed, peak blood lactate concentration, peak heart rate and rating of perceived exertion (RPE) were not different (p&gt;0.05) between MASK and NO-MASK conditions. Conclusions. Incremental exercise test performance is not adversely affected by RGC and analysis equipment, at least in short duration progressive treadmill exercise. Respiratory gas analysis during exercise testing for diagnostic, performance assessment or training prescription purposes would appear to be unaffected by RGC systems.

Respiratory dynamics and dead space to tidal volume ratio of volume-controlled versus pressure-controlled ventilation during prolonged gynecological laparoscopic surgery.

Laparoscopic operations have become longer and more complex and applied to a broader patient population in the last decades. Prolonged gynecological laparoscopic surgeries require prolonged pneumoperitoneum and Trendelenburg position, which can influence respiratory dynamics and other measurements of pulmonary function. We investigated the differences between volume-controlled ventilation (VCV) and pressure-controlled ventilation (PCV) and tried to determine the more efficient ventilation mode during prolonged pneumoperitoneum in gynecological laparoscopy. Twenty-six patients scheduled for laparoscopic radical hysterectomy combined with or without laparoscopic pelvic lymphadenectomy were randomly allocated to be ventilated by either VCV or PCV. Standard anesthesic management and laparoscopic procedures were performed. Measurements of respiratory and hemodynamic dynamics were obtained after induction of anesthesia, at 10, 30, 60, and 120min after establishing pneumoperitoneum, and at 10min after return to supine lithotomy position and removal of carbon dioxide. The logistic regression model was applied to predict the corresponding critical value of duration of pneumoperitoneum when the Ppeak was higher than 40cmH2O. Prolonged pneumoperitoneum and Trendelenburg position produced significant and clinically relevant changes in dynamic compliance and respiratory mechanics in anesthetized patients under PCV and VCV ventilation. Patients under PCV ventilation had a similar increase of dead space/tidal volume ratio, but had a lower Ppeak increase compared with those under VCV ventilation. The critical value of duration of pneumoperitoneum was predicted to be 355min under VCV ventilation, corresponding to the risk of Ppeak higher than 40cmH2O. Both VCV and PCV can be safely applied to prolonged gynecological laparoscopic surgery. However, PCV may become the better choice of ventilation after ruling out of other reasons for Ppeak increasing.

Критические времена воздействия моноксида углерода на человека при пожаре в помещении

The aim of this work was to create the mathematical model for calculation of the carboxyhemoglobin concentration in the human blood in case of fire. Tests were conducted in conditions of variable CO density, typical for the initial stage of indoor fire, and increased pulmonary ventilation rate. It is offered the criteria for determination of the critical values of fire duration under the terms of safe evacuation and people rescue. The methods of theoretical analysis of the content of carboxyhemoglobin in the human blood and calculation of the carbon monoxide (CO) concentration, in conditions of fire in premises, were used during the experiment. The mathematical model was created taking into account the concentration of CO in the inhaled air, the mass of hemoglobin in the blood, the pulmonary ventilation rate, the volume of respiratory dead space and the CO exposure time. Critical time of safe evacuation for people under the effects of CO is accepted when the content of carboxyhemoglobin in the blood reaches the 20 % by mass (minor poisoning). Critical time from the initial stage of fire and until the moment when people, which stay in premises without protection means against CO (respirators, gas masks, self-rescuers, etc.), and, with high probability, are unable to leave the premises independently, is accepted when the concentration of carboxyhemoglobin in the blood reaches the 50 % by mass (moderate poisoning). The model premises were in the form of parallelepiped with dimensions (m): 4´5´3, 4´5´6 and 24´12´3. As combustible materials there were used the wood building materials, PVC sheath of cables and transformer oil. The results of numerical experiments on determination of the carboxyhemoglobin concentration using the analytical solution of the integral calculation model for the thermal and gas dynamics of fire are presented. The estimated values of CO exposure intervals prior to various degrees of human intoxication are obtained. The comparison of critical durations of fire (considering CO effects), obtained using proposed model and existing approach, is made. The critical duration of fire, obtained using proposed model, was significantly greater than the corresponding value determined by existing methods (for example, in case of burning of the transformer oil in the room with dimensions of 4´5´3 m). The main conclusion is that existing scientific and regulatory literature contains the calculation methods for critical duration of fire, considering CO effects, which may lead to qualitatively and quantitatively wrong results. The proposed criteria for determination of the critical values of CO exposure time and the calculation methods for the content of carboxyhemoglobin allow defining the time of safe evacuation and people rescue more reasonably than existing approach.

Case Studies in Physiology: The Case of the Giant Giraffe.

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Comparing the Effect of Adaptive Support Ventilation (ASV) and Synchronized Intermittent Mandatory Ventilation (SIMV) on Respiratory Parameters in Neurosurgical ICU Patients.

BackgroundVarious modes of mechanical ventilation have different effects on respiratory variables. Lack of patients’ neuro-ventilatory coordination and increasing the work of breathing are major disadvantages in mechanically ventilated patients.ObjectivesThis study is conducted to compare the respiratory parameters differences in Adaptive support ventilation (ASV) and synchronized intermittent mandatory ventilation (SIMV) modes in neurosurgical ICU patients.MethodsIn a crossover study, patients under mechanical ventilation in neurosurgical ICU were enrolled. The patients alternatively experienced two types of ventilations for 30 minutes (adaptive support ventilation and synchronized intermittent mandatory ventilation). The respiratory parameters (tidal volume, respiratory rate, airway pressure, lung compliance, end-tidal carbon dioxide, peripheral oxygenation and respiratory dead space), hemodynamic variables, every 10 minutes and arterial blood gas analysis at the end of each 30 minutes were recorded. Results were compared and analyzed with SPSS v.19.ResultsSixty patients were involved in this study. In ASV mode, values including peak airway pressure (P-peak), end-tidal carbon dioxide (EtCO2), tidal volume and respiratory dead space were significantly lower than SIMV mode. Although the mean value for dynamic compliance had no significant difference in the two types of ventilation, it was better in ASV mode.ConclusionsASV mode compared with SIMV mode can lead to improve lung compliance and respiratory dead space.