Inspired Carbon Dioxide Research Articles

Impact of personal protective equipment on wearer's health indicators using multi-parameter physiological monitoring

Previous studies have primarily focused on thermal discomfort-related problems arising from wearing personal protective equipment (PPE) in hot environments. However, PPE is also extensively utilized under comfortable thermal conditions, where health-related problems may become particularly important due to hypoxia and inhalation of self-emitted bio-effluents. To evaluate the impact of wearing PPE on the health outcomes of individuals under comfortable thermal conditions, ten physiological parameters were measured under three conditions (sitting without PPE, sitting with PPE, and walking with PPE). Under light intensity activity, wearing PPE significantly increased end-tidal carbon dioxide pressure (17.9 ± 6.3 mm Hg vs 22.0 ± 5.7 mm Hg, P < 0.001) when compared to wearing no PPE, while negligible (although statistically significant) changes were observed for tympanic membrane temperature and blood oxygen saturation. It did not affect significantly respiratory frequency (RF), inspiratory carbon dioxide pressure (PICO2), heart rate (HR), pulse rate (PR), systolic/diastolic blood pressure (SBP/DBP), and potential of ST-segment (ST) in electrocardiogram. It suggests that short-term PPE use is safe under comfortable conditions. The physiological parameters of PPE wearers were more affected by the increase in activity intensity than the presence of PPE. Larger body mass index was associated with decreased RF and increased PICO2. Higher age was associated with increased HR and PR and decreased ST. Males had a lower SpO2 but a higher SBP. The data obtained improves our understanding of the health outcomes associated with wearing PPE and assists in improving PPE, thus contributing to better occupational health.

Evaluation of a portable, lightweight modular system to deliver high inspired oxygen to trauma casualties without the use of pressurised cylinders

IntroductionAdministering supplemental oxygen is a standard of care for trauma casualties to minimise the deleterious effects of hypoxaemia. Forward deployment of oxygen using pressurised cylinders is challenging, for example, logistics...

Breathing 5% carbon dioxide for 1 minute increases cerebral blood flow during lower body negative pressure

Objective: Lower body negative pressure (LBNP) is an established surrogate of hypergravity to investigate responses to central hypovolemia, including the reduction in cerebral blood flow. Increased inspired carbon dioxide (CO2) causes cerebrovascular dilation and increases cerebral blood flow. We aimed to determine whether breathing 5% CO2 for 1 minute increased cerebral blood flow during LBNP. We hypothesized 5% inspired CO2 would increase cerebral blood flow during LBNP. Methods: We collected data from 15 (9 M/6 F, 31±8 yr, 25.6±3.2 kg/m2) healthy individuals. Subjects breathed room air or a mix of 5% CO2, 21% oxygen, balance nitrogen gas for 1 minute prior to initiation of 2 minutes of -60 mmHg LBNP and throughout the duration of LBNP. We allowed a 2-minute wash-out between trials. We measured middle cerebral artery velocity (MCAv) with transcranial Doppler ultrasound and continuous, non-invasive blood pressure (MAP) with a finger plethysmograph. We corrected MCAv for MAP and present it as cerebrovascular conductance index (CVCi). We also measure ventilation and gas exchange with a pneumotachometer and gas analyzer. Results: All measured variables were similar prior to the initiation of room air and 5% CO2 prebreathe ( p &gt; 0.05). Inspired (1±1 vs. 36±1 mmHg) and end-tidal (38±4 vs. 47±3 mmHg) CO2 were greater during the 5% inspired CO2 trial ( p &lt; 0.05, main effect of gas). LBNP caused an increase in heart rate, decrease in stroke volume, decrease in cardiac output, and an increase in total peripheral resistance ( p &lt; 0.05, main effect of LBNP). These variables were similar regardless of inspiratory gas. MCAv (40±16 vs. 53±19 cm/s), MAP (94±10 vs. 99±11 mmHg), and CVCi (0.46±0.22 vs 0.56±0.24 cm/s/mmHg) were all greater during the 5% inspired CO2 trials ( p &lt; 0.05, main effect of gas). Discussion: Breathing a mixture of 5% CO2 for 1 minute increased cerebral blood flow and blood pressure during a mimic of hypergravity stress. Despite technical challenges of integration into high-performance aircraft, increasing inspired CO2 could contribute to better tolerance to hypergravity stress. Funding was provided by the Air Force Offce of Scientific Research and King’s College London. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Baroreflex sensitivity is blunted in hypoxia independently of changes in inspired carbon dioxide pressure in prematurely born male adults.

Premature birth may result in specific cardiovascular responses to hypoxia and hypercapnia, that might hamper high-altitude acclimatization. This study investigated the consequences of premature birth on baroreflex sensitivity (BRS) under hypoxic, hypobaric and hypercapnic conditions. Seventeen preterm born males (gestational age, 29 ± 1 weeks), and 17 age-matched term born adults (40 ± 0 weeks) underwent consecutive 6-min stages breathing different oxygen and carbon dioxide concentrations at both sea-level and high-altitude (3375 m). Continuous blood pressure and ventilatory parameters were recorded in normobaric normoxia (NNx), normobaric normoxic hypercapnia (NNx + CO2 ), hypobaric hypoxia (HHx), hypobaric normoxia (HNx), hypobaric normoxia hypercapnia (HNx + CO2 ), and hypobaric hypoxia with end-tidal CO2 clamped at NNx value (HHx + clamp). BRS was assessed using the sequence method. Across all conditions, BRS was lower in term born compared to preterm (13.0 ± 7.5 vs. 21.2 ± 8.8 ms⋅mmHg-1 , main group effect: p < 0.01) participants. BRS was lower in HHx compared to NNx in term born (10.5 ± 4.9 vs. 16.0 ± 6.0 ms⋅mmHg-1 , p = 0.05), but not in preterm (27.3 ± 15.7 vs. 17.6 ± 8.3 ms⋅mmHg-1 , p = 0.43) participants, leading to a lower BRS in HHx in term born compared to preterm (p < 0.01). In conclusion, this study reports a blunted response of BRS during acute high-altitude exposure without any influence of changes in inspired CO2 in healthy prematurely born adults.

Comparative Effectiveness of an Artificial Air Pocket Device to Delay Asphyxiation in Supine Individuals Critically Buried in Avalanche Debris

Approximately 70% of individuals critically buried in avalanche debris die within 35 minutes as a result of asphyxial cardiac arrest. An artificial air-pocket device (AAPD) that separates inhaled air from exhaled air may delay the onset of severe hypoxemia and eventual asphyxia during snow burial. To investigate the efficacy of a new AAPD during snow burial in a supine position. This comparative effectiveness trial was performed in winter 2016 with data analysis in November 2016 and November 2022. Each trial used a simulated critical avalanche burial scenario, in which a trough was dug in a snow pile and an additional air pocket of 0.5 L volume was punched into the lateral wall for each control trial. All participants were buried in a supine position. Trials could be voluntarily terminated at any time, with a maximum length of 60 minutes; trials were automatically terminated if the participant's peripheral oxygen saturation (Spo2) dropped to less than 84%. Each participant conducted 2 trials, one in which they breathed into the AAPD (intervention trial) and the other in which they breathed into the prepared air pocket (control trial). Measurements included Spo2, cerebral oxygenation, ventilatory parameters, respiratory gas concentrations, and visual-analogue scales. Kaplan-Meier survival curves and rank test for matched survival data were used to analyze the total burial time in each trial. A total of 13 volunteers (9 men; mean [SD] age, 33 [8] years) were exposed to the intervention and control trials. Intervention trials were terminated less often (2 of 13 trials) as a result of hypoxemia than control trials (11 of 12 trials). Similarly, survival curves showed a longer duration of burial in the intervention compared with the control trials for the time to reach an Spo2 less than 84% (rank test for matched survival data: P = .003). The intervention trials, compared with the control trials, also had slower rates of decrease in fraction of inspired oxygen (mean [SD] rate, -0.8 [0.4] %/min vs -2.2 [1.2] %/min) and of increase in fraction of inspired carbon dioxide (mean [SD] rate, 0.5 [0.3] %/min vs 1.4 [0.6] %/min) and expired ventilation per minute (mean [SD] rate, 0.5 [1.0] L/min2 vs 3.9 [2.6] L/min2). This comparative effectiveness trial found that the new AAPD was associated with delaying the development of hypoxemia and hypercapnia in supine participants in a critical burial scenario. Use of the AAPD may allow a longer burial time before asphyxial cardiac arrest, which might allow longer times for successful rescue by companions or by prehospital emergency medical services.

Effects of wearing different face masks on cardiopulmonary performance at rest and exercise in a partially double-blinded randomized cross-over study

The use of face masks became mandatory during SARS-CoV-2 pandemic. Wearing masks may lead to complaints about laboured breathing and stress. The influence of different masks on cardiopulmonary performance was investigated in a partially double-blinded randomized cross-over design. Forty subjects (19–65 years) underwent body plethysmography, ergometry, cardiopulmonary exercise test and a 4-h wearing period without a mask, with a surgical mask (SM), a community mask (CM), and an FFP2 respirator (FFP2). Cardiopulmonary, physical, capnometric, and blood gas related parameters were recorded. Breathing resistance and work of breathing were significantly increased while wearing a mask. During exercise the increase in minute ventilation tended to be lower and breathing time was significantly longer with mask than without mask. Wearing a mask caused significant minimal decreases in blood oxygen pressure, oxygen saturation, an initial increase in blood and inspiratory carbon dioxide pressure, and a higher perceived physical exertion and temperature and humidity behind the mask under very heavy exercise. All effects were stronger when wearing an FFP2. Wearing face masks at rest and under exercise, changed breathing patterns in the sense of physiological compensation without representing a health risk. Wearing a mask for 4-h during light work had no effect on blood gases.

Evaluation of respiratory exchange ratio (RER) for predicting postoperative outcomes in elderly patients undergoing oncological resection for gastrointestinal malignancies - A prospective cohort study.

Predicting complications after major oncosurgery is particularly daunting in the elderly subcategory of patients owing to factors like preexisting age-related immune cellular senescence and a significant imbalance of oxygen delivery (DO2) and consumption (VO2) characteristic of major oncological surgeries. The respiratory exchange ratio (RER) indicates DO2-VO2 balance and onset of anaerobic metabolism. We evaluated the ability of RER in predicting the occurrence of postoperative complications following geriatric oncosurgery. In the study, we enrolled 96 patients aged 65 years and above undergoing definitive surgery for gastrointestinal malignancy. The RER was calculated at predefined time points by a non-volumetric method from the respiratory parameters as RER = (end-tidal fractional carbon dioxide [FetCO2] - fraction of inspired carbon dioxide [FiCO2]/fraction of inspired oxygen [FiO2] - end-tidal fractional oxygen [FetO2]). Other indices of tissue perfusion, like central venous oxygen saturation and lactate levels, were also recorded. The patients were followed up for postsurgical complications. The predictive value of RER and other perfusion parameters was assessed and compared by appropriate statistical methods. The patients who sustained major complications had a higher RER than the patients who did not sustain complications (1.47 ± 0.99 vs. 0.90 ± 0.31, P = 0.001). An intraoperative cutoff value of RER ≥0.89 was found to best predict postoperative complications at a specificity and sensitivity rate of 81.2% and 76%, respectively. End-operative partial pressure of carbon dioxide (pCO2) gap of >5.2 mm and elevated arterial lactate could also predict postsurgical complications in this age group. The RER can serve as a noninvasive, real-time and sensitive indicator of tissue hypoperfusion and postoperative complications in geriatric gastrointestinal oncosurgery.

Increased Carbon Dioxide Respiration Prevents the Effects of Acceleration/Deceleration Elicited Mild Traumatic Brain Injury

Acceleration/deceleration forces are a common component of various causes of mild traumatic brain injury (mTBI) and result in strain and shear forces on brain tissue. A small quantifiable volume dubbed the compensatory reserve volume (CRV) permits energy transmission to brain tissue during acceleration/deceleration events. The CRV is principally regulated by cerebral blood flow (CBF) and CBF is primarily determined by the concentration of inspired carbon dioxide (CO2). We hypothesized that experimental hypercapnia (i.e. increased inspired concentration of CO2) may act to prevent and mitigate the actions of acceleration/deceleration-induced TBI. To determine these effects C57Bl/6 mice underwent experimental hypercapnia whereby they were exposed to medical-grade atmospheric air or 5% CO2 immediately prior to an acceleration/deceleration-induced mTBI paradigm. mTBI results in significant increases in righting reflex time (RRT), reductions in core body temperature, and reductions in general locomotor activity-three hours post injury (hpi). Experimental hypercapnia immediately preceding mTBI was found to prevent mTBI-induced increases in RRT and reductions in core body temperature and general locomotor activity. Ribonucleic acid (RNA) sequencing conducted four hpi revealed that CO2 exposure prevented mTBI-induced transcriptional alterations of several targets related to oxidative stress, immune, and inflammatory signaling. Quantitative real-time PCR analysis confirmed the prevention of mTBI-induced increases in mitogen-activated protein kinase kinase kinase 6 and metallothionein-2. These initial proof of concept studies reveal that increases in inspired CO2 mitigate the detrimental contributions of acceleration/deceleration events in mTBI and may feasibly be translated in the future to humans using a medical device seeking to prevent mTBI among high-risk groups.

Influence of graded hypercapnia on endurance exercise performance in healthy humans.

Military and/or emergency services personnel may be required to perform high-intensity physical activity during exposure to elevated inspired carbon dioxide (CO2). Although many of the physiological consequences of hypercapnia are well characterized, the effects of graded increases in inspired CO2 on self-paced endurance performance have not been determined. The aim of this study was to compare the effects of 0%, 2%, and 4% inspired CO2 on 2-mile run performance, as well as physiological and perceptual responses during time trial exercise. Twelve physically active volunteers (peak oxygen uptake = 49 ± 5 mL·kg-1·min-1; 3 women) performed three experimental trials in a randomized, single-blind, crossover manner, breathing 21% oxygen with either 0%, 2%, or 4% CO2. During each trial, participants completed 10 min of walking at ∼40% peak oxygen uptake followed by a self-paced 2-mile treadmill time trial. One participant was unable to complete the 4% CO2 trial due to lightheadedness during the run. Compared with the 0% CO2 trial, run performance was 5 ± 3% and 7 ± 3% slower in the 2% and 4% CO2 trials, respectively (both P < 0.001). Run performance was significantly slower with 4% versus 2% CO2 (P = 0.046). The dose-dependent performance impairments were accompanied by stepwise increases in mean ventilation, despite significant reductions in running speed. Dyspnea and headache were significantly elevated during the 4% CO2 trial compared with both the 0% and 2% trials. Overall, our findings show that graded increases in inspired CO2 impair endurance performance in a stepwise manner in healthy humans.

The effect of trait self-control on dyspnoea and tolerance to a CO2 rebreathing challenge in healthy males and females

BackgroundHigh trait self-control is associated with greater tolerance of unpleasant sensations including effort and pain. Dyspnoea and pain have several commonalities and this study aimed to investigate for the first time whether trait self-control influences responses to a hypercapnic rebreathing challenge designed to induce dyspnoea. As sex also influences tolerance to dyspnoea, we also sought to investigate whether this moderated the role of trait self-control. MethodsParticipants (n = 65, 32 females) scoring high or low for trait self-control, performed a standardised rebreathing challenge, in which inspired carbon dioxide (CO2) gradually increased over a period of 6 min or until an intolerable level of dyspnoea. Air hunger (AH) intensity – a distinctive quality of dyspnoea, was measured every 30 s. The multidimensional dyspnoea profile (MDP) was completed after the rebreathing challenge for a more complete overview of breathing discomfort. ResultsMales high in trait self-control (SCHIGH) (302 ± 42 s), tolerated the rebreathing challenge for longer than males low in self-control (SCLOW) (252 ± 66 s, P = 0.021), experienced slower increases in AH intensity during the rebreathing challenge (0.03 ± 0.01 cm.s − 1 vs. 0.04 ± 0.01 cm.s − 1,P = 0.045) and reported lower perceived mental effort on the MDP (4.94 ± 2.46 vs. 7.06 ± 1.60, P = 0.007). There was no difference between SCHIGH and SCLOW females for challenge duration. However, SCHIGH females (9.29 ± 0.66 cm) reported greater air hunger at the end of the challenge than SCLOW females (7.75 ± 1.75 cm, P = 0.003). It is possible that SCLOW females were unwilling to tolerate the same perceptual intensity of AH as the SCHIGH females. ConclusionsThese results indicate that individuals high in trait self-control are more tolerant of dyspnoea during a CO2 rebreathing challenge than low self-control individuals. Tolerance of the stimulus was moderated by the sex of the participant, presenting an interesting opportunity for future research.

Assessing central and peripheral respiratory chemoreceptor interaction in humans.

What is the central question of this study? We investigated the interaction between central and peripheral respiratory chemoreceptors in healthy, awake human participants by using a background of step increases in steady-state normoxic fraction of inspired carbon dioxide to alter central chemoreceptor activation and by using the transient hypoxia test to target the peripheral chemoreceptors. What is the main finding and its importance? Our data suggest that the interaction between central and peripheral respiratory chemoreceptors is additive in minute ventilation and respiratory rate, but hypo-additive in tidal volume. Our study adds important new data in reconciling chemoreceptor interaction in awake healthy humans and is consistent with previous reports of simple addition in intact rodents and humans. Arterial blood gas levels are maintained through respiratory chemoreflexes, mediated by central chemoreceptors in the CNS and peripheral chemoreceptors located in the carotid bodies. The interaction between central and peripheral chemoreceptors is controversial, and few studies have investigated this interaction in awake, healthy humans, owing, in part, to methodological challenges. We investigated the interaction between the central and peripheral chemoreceptors in healthy humans using a transient hypoxia test (three consecutive breaths of 100% N2 ; TT-HVR), which targets the temporal domain and stimulus specificity of the peripheral chemoreceptors. The TT-HVRs were superimposed upon three randomized background levels of steady-state inspired fraction of normoxic CO2 ( ; 0, 0.02 and 0.04). Chemostimuli [calculated oxygen saturation ( )] and respiratory variable responses [respiratory rate (RR ), inspired tidal volume (VTI ) and ventilation ( )] were averaged from all three TT-HVR trials at each level. Responses were assessed as: (1) a change (∆) from baseline; and (2) indexed against . Aside from a significantly lower ∆VTI response in 0.04 (P=0.01), the hypoxic rate responses (∆RR or ∆RR / ; P=0.46 and P=0.81), hypoxic tidal volume response ( ; P=0.08) and the hypoxic ventilatory responses ( and ; P=0.09 and P=0.31) were not significantly different across trials. Our data suggest simple addition between central and peripheral chemoreceptors in , which is mediated through simple addition in RR responses, but hypo-addition in VTI responses. Our study adds important new data in reconciling chemoreceptor interaction in awake, healthy humans and is consistent with previous reports of simple addition in intact rodents and humans.

Potential rebreathing of carbon dioxide during noninvasive ventilation provided by critical care ventilator

BackgroundCritical care ventilators are frequently used to provide noninvasive ventilation (NIV) support to critically ill patients. Questions remain regarding carbon dioxide (CO2) clearance while using a critical care ventilator and dual limb circuit with various patient interfaces. The purpose of this study is to determine the positive end expiratory pressure (PEEP) level required to effectively washout CO2 for full-face and oronasal masks when using a dual limb circuit.MethodThis randomized crossover trial was conducted at an academic medical center in the Midwest United States. After obtaining informed consent, eight healthy volunteers were placed on a 980 Puritan Bennett (Medtronic, Minneapolis, MN) ventilator operating in the NIV mode. All subjects performed 20 min of breathing on four levels of PEEP (0, 2, 4, and 5 cm H2O) and pressure support of 5 cm H2O. NIV settings were applied to four masks (two oronasal and two full-face masks) that were randomly selected with a 5-min washout period between each mask. The fraction of inspired carbon dioxide (FICO2) was sampled/monitored with a nasal cannula using a Capnostream 20p monitor (Medtronic, Minneapolis, MN) and reported as percentages. A Kruskal–Wallis test was used to reveal significant differences across PEEP levels. Pairwise comparisons of the groups were made using Mann–Whitney tests with a family-wise error correction.ResultsMedian (IQR) FICO2 was significantly lower 0.0% (0%–0.92%) at PEEP of 5 compared to 1.83% (0.66%–4.0%; p < 0.001) at PEEP of 0 or 1.0% (0.33%–2.66%; p = 0.002) at PEEP of 2. FICO2 was significantly lower 0.5% (0%–1.92%) at PEEP of 4 compared to PEEP of 0 (p = 0.001).ConclusionA PEEP level of at least 5 cm H2O associated with the reported leak was required to minimize the likelihood of CO2 rebreathing while using a critical care ventilator to provide NIV with a double limb circuit and full-face or oronasal masks.

Cardiorespiratory Response and Power Output During Submaximal Exercise in Normobaric Versus Hypobaric Hypoxia: A Pilot Study Using a Specific Chamber that Controls Environmental Factors

2021.—Many previous studies have examined hypoxia-induced physiological responses using various conditions, e.g., artificially reduced atmospheric oxygen concentration [normobaric hypoxia (NH) condition] or low barometric pressure at a mountain [hypobaric hypoxia (HH) condition]. However, when comparing the results from these previous studies conducted in artificial NH and HH including real high altitude, we must consider the possibility that environmental factors, such as temperature, humidity, and fraction of inspired carbon dioxide, might affect the physiological responses. Therefore, we examined cardiorespiratory responses and exercise performances during low- to high-intensity exercise at a fixed heart rate (HR) in both NH and HH using a specific chamber where atmospheric oxygen concentration and barometric pressure as well as the abovementioned environmental factors were precisely controlled. Ten well-trained university students (eight males and two females) performed the exercise test consisting of two 20-minute submaximal pedaling at the intensity corresponding to 50% (low) and 70% (high) of their HR reserve, under three conditions [NH (fraction of inspired oxygen, 0.135; barometric pressure, 754 mmHg), HH (fraction of inspired oxygen, 0.209; barometric pressure, 504 mmHg), and normobaric normoxia (NN; fraction of inspired oxygen, 0.209; barometric pressure, 754 mmHg)]. Peripheral oxygen saturation (SpO2) to estimate arterial oxygen saturation and partial pressure of end-tidal carbon dioxide (PETCO2) were monitored throughout the experiment. SpO2, PETCO2, and power output at fixed HRs (i.e., pedaling efficiency) in NH and HH were all significantly lower than those in NN. Moreover, high-intensity exercise in HH induced greater decreases in SpO2 and power output than did high-intensity exercise in NH (NH vs. HH; SpO2, 78.2% - 5.0% vs. 75.1% - 7.1%; power output, 120.7 - 24.9 W vs. 112.4 - 23.2 W, both p &lt; 0.05). However, high-intensity exercise in HH induced greater increases in PETCO2 than did high-intensity exercise in NH (NH vs. HH; 54.2 - 5.9mmHg vs. 57.2 - 3.4 mmHg, p &lt; 0.01). These results suggest that physiological responses and power output at a fixed HR during hypoxic exposure might depend on the method used to generate the hypoxic condition.

Arterial baroreflex regulation of muscle sympathetic nerve activity during hypoxia and hypercapnia in healthy young men and women

Background In hypertension augmented vasoconstrictor sympathetic nerve activity (SNA) responses to both hypoxia and hypercapnia have been identified. The arterial baroreflex (ABR) normally restrains SNA, but whether ABR-SNA sensitivity is modified by peripheral, central or combined chemoreflex stimulation (i.e. hypoxia, hypercapnia and hypercapnic hypoxia) in young men and women is incompletely understood. We tested the hypothesis that ABR-SNA sensitivity is attenuated by hypoxia, hypercapnia and combined hypercapnic hypoxia thereby allowing SNA to rise. The existence of sex-differences in ABR-SNA sensitivity was also examined. Methods Ten (5 males) healthy individuals (aged 27±4 yr and BMI 24.2±2.7 kg/m2) volunteered to participate in the study. Muscle SNA (microneurography), ventilation and blood pressure were measured during randomized 5-min breathing trials; room-air, isocapnic hypoxia [10% inspired oxygen (O2)], hypercapnic hyperoxia [7% inspired carbon dioxide (CO2), 50%O2] and hypercapnic hypoxia (7%CO2, 10%O2). ABR-SNA sensitivity was determined as the slope of the linear relationship between SNA burst incidence (i.e., bursts/100 heart beats) and diastolic blood pressure. Results Compared to room-air, isocapnic hypoxia, hypercapnic hyperoxia and hypercapnic hypoxia elevated both muscle SNA (16±5, 20±6, 27±7 and 31±8 bursts/100 heart beats, respectively, p<0.001) and ventilation (7.3±2.5, 9.9±3.6, 21.4±4.3 and 31.1±5.5 L/min, respectively, p<0.001). No between-trial differences were observed in mean blood pressure (p=0.32). ABR-SNA slope was not different during room air, isocapnic hypoxia, hypercapnic hyperoxia and hypercapnic hypoxia (-3.76±1.12, -2.95±1.03, -3.97±2.08 and -2.53±2.24 bursts/100 heart beats/mmHg, respectively, p=0.67). No sex-differences in muscle SNA, ventilation, mean blood pressure and ABR-SNA slope were observed. Discussion These preliminary findings suggest that sympatho-excitation evoked by hypoxia, hypercapnia and hypercapnic hypoxia are similar between men and women and are not attributable to a concurrent reduction in ABR-SNA sensitivity. Thus, elevated SNA evoked by peripheral and central chemoreflexes reflects a primary reflex response of chemoreceptor origin.

An unusual cause of intraoperative hypercarbia: Who's the boss:- Machine or The Man behind the machine?

Sir, Modern integrated anaesthesia workstations provide comprehensive facilities for patient ventilation, gas delivery and agent vapourisation, and allow seamless integration of patient monitoring and recording with anaesthesia information systems. American Society of Anesthesiologists (ASA) 2008 recommendations for pre-anaesthesia checkout advocate pre-use testing of anaesthesia machine before the conduct of anaesthesia.[1] Modern anaesthesia workstations including Dräger Perseus® A500 (Dräger, Germany) have integrated automatic self-testing to circumvent human errors and ensure administration of safe anaesthesia.[2] A 5 year-old boy with left hydrocele was posted for elective open herniotomy. Dräger Perseus® A500 anaesthesia workstation (Dräger, Germany) which had already passed an automated self-test was used to administer general anaesthesia with controlled ventilation using i-gel® supraglottic airway device (Intersurgical Limited, Wokingham) in-situ with ultrasound-guided left ilioinguinal and iliohypogastric nerve block. After obtaining valid informed parental consent, the child was pre-medicated with oral midazolam 0.5 mg/kg and wheeled into the operating room (OR). Standard ASA monitors were attached and incremental induction with sevoflurane (2-8%) was done. On achieving jaw relaxation and loss of purposeful movement, size 2 i-gel® was inserted and controlled ventilation using volume control auto-flow mode initiated. Anaesthesia was maintained using air-oxygen (50:50) and sevoflurane titrated to maintain age-adjusted minimum alveolar concentration (MAC) -1, with fresh gas flows (FGF) of 0.5 L/min. Following this, ultrasound-guided left-sided ilioinguinal and iliohypogastric nerve block using 0.15 ml/kg of 0.25% bupivacaine was given. A few minutes later, end-tidal carbon dioxide (ETCO2) and fraction of inspired carbon dioxide (FiCO2) values were observed to have risen from baseline values of 34 to 62 and 0 to 16 respectively. Switching over to the manual controlled mode of ventilation showed no increase in airway resistance (peak airway pressure <15 cm H2O) with bilaterally equal breath sounds. However, ETCO2 values continued to rise. At this point, we switched over to Jackson Rees (JR) circuit, to rule out the possibility of a faulty closed circuit. Simultaneously, a quick survey of the machine revealed an empty absorbent canister. The same was immediately refilled, following which ETCO2 values gradually normalised. Increased ETCO2 under anaesthesia is either due to decreased excretion or increased production [Table 1].[34] In accordance with our OR standard operating procedure (SOP), the canisters are refilled as required, which is usually on completion of the last case of the day. Visual inspection for exhausted carbon dioxide absorbent is a standard practice in the ASA checklist. We failed to identify the empty canister on visual inspection prior to beginning the case, which was a gross error irrespective of the high-end anaesthesia workstation. However, the machine passed the automated self-test and did not alert us regarding the same. Dräger Perseus® A500 workstation (Dräger, Germany) has two functional tools to support the safe conduct of low flow anaesthesia viz. the Low Flow Wizard and the Econometer.[5] Low Flow Wizard enables real-time analysis of data like patient uptake, breathing system leakage and the volume of carbon dioxide absorbed by the absorbent and compares the sum of these values with the actual FGF.[5] Econometer displays the FGF in a colour-coded bar graph based on filling of the manual breathing bag with each delivered breath, thus enabling a judicious and economical FGF set-up.[5] However, none of these tools are designed to identify the presence of an empty absorbent canister per se or indicate the time to complete exhaustion.Table 1: Causes of increased end-tidal carbon dioxide[4]We recommend that automated self-tests should include testing for presence of the absorbent to ensure patient safety. This assumes greater importance particularly in the context of increasing practice of paediatric low flow anaesthesia. Furthermore, an in-built alarm indicating the absorbent's functional capacity should be incorporated into the anaesthesia workstation to avert human errors and avoid hypercarbia. The advancements of the century may be leading us to an era of robotic anaesthesia and hi-tech workstations; nonetheless, “it is not the machine, but the man behind it that matters.” Declaration of patient consent The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.

Cardiorespiratory Response and Power Output During Submaximal Exercise in Normobaric Versus Hypobaric Hypoxia: A Pilot Study Using a Specific Chamber that Controls Environmental Factors.

Takezawa, Toshihiro, Shohei Dobashi, and Katsuhiro Koyama. Cardiorespiratory response and power output during submaximal exercise in normobaric versus hypobaric hypoxia: a pilot study using a specific chamber that controls environmental factors. High Alt Med Biol. 22: 201-208, 2021. Background: Many previous studies have examined hypoxia-induced physiological responses using various conditions, e.g., artificially reduced atmospheric oxygen concentration [normobaric hypoxia (NH) condition] or low barometric pressure at a mountain [hypobaric hypoxia (HH) condition]. However, when comparing the results from these previous studies conducted in artificial NH and HH including real high altitude, we must consider the possibility that environmental factors, such as temperature, humidity, and fraction of inspired carbon dioxide, might affect the physiological responses. Therefore, we examined cardiorespiratory responses and exercise performances during low- to high-intensity exercise at a fixed heart rate (HR) in both NH and HH using a specific chamber where atmospheric oxygen concentration and barometric pressure as well as the abovementioned environmental factors were precisely controlled. Methods: Ten well-trained university students (eight males and two females) performed the exercise test consisting of two 20-minute submaximal pedaling at the intensity corresponding to 50% (low) and 70% (high) of their HR reserve, under three conditions [NH (fraction of inspired oxygen, 0.135; barometric pressure, 754 mmHg), HH (fraction of inspired oxygen, 0.209; barometric pressure, 504 mmHg), and normobaric normoxia (NN; fraction of inspired oxygen, 0.209; barometric pressure, 754 mmHg)]. Peripheral oxygen saturation (SpO2) to estimate arterial oxygen saturation and partial pressure of end-tidal carbon dioxide (PETCO2) were monitored throughout the experiment. Results: SpO2, PETCO2, and power output at fixed HRs (i.e., pedaling efficiency) in NH and HH were all significantly lower than those in NN. Moreover, high-intensity exercise in HH induced greater decreases in SpO2 and power output than did high-intensity exercise in NH (NH vs. HH; SpO2, 78.2% ± 5.0% vs. 75.1% ± 7.1%; power output, 120.7 ± 24.9 W vs. 112.4 ± 23.2 W, both p < 0.05). However, high-intensity exercise in HH induced greater increases in PETCO2 than did high-intensity exercise in NH (NH vs. HH; 54.2 ± 5.9 mmHg vs. 57.2 ± 3.4 mmHg, p < 0.01). Conclusions: These results suggest that physiological responses and power output at a fixed HR during hypoxic exposure might depend on the method used to generate the hypoxic condition.

Effect of wearing a face mask on fMRI BOLD contrast

International spread of the coronavirus SARS-CoV-2 has prompted many MRI scanning facilities to require scan subjects to wear a facial covering (“mask”) during scanning as a precaution against transmission of the virus. Because wearing a mask mixes expired air with the subject's inspired air stream, the concentration of inspired carbon dioxide [CO2] is elevated, resulting in mild hypercapnia. Changes in the inspired gas mixture have been demonstrated to alter R2*-weighted Blood Oxygen Dependent (BOLD) contrast. In this study, we investigate a potential for face masking to alter BOLD contrast during a sensory-motor task designed to activate visual, auditory, and sensorimotor cortices in 8 subjects. We utilize a nasal cannula to supply air to the subject wearing a surgical mask in on-off blocks of 90s to displace expired CO2, while the subject performs the sensory-motor task. While only a small fraction (2.5%) of the sensory-motor task activation is related to nasal air modulation, a 30.0% change in gray matter BOLD signal baseline is found due to air modulation. Repeating the scan with mask removed produces a small subject-specific bias in BOLD baseline signal from nasal air supply, which may be due to cognitive influence of airflow or cannula-induced hypoxia. Measurements with capnography demonstrate wearing a mask induces an average increase in ETCO2 of 7.4%. Altogether, these results demonstrate that wearing a face mask during gradient-echo fMRI can alter BOLD baseline signal but minimally affects task activation.

The Partial Pressure of Inspired Carbon Dioxide Exposure Levels in the Extravehicular Mobility Unit.

BACKGROUND: NASA has been making efforts to assess the carbon dioxide (CO₂) washout capability of spacesuits using a standard CO₂ sampling protocol. This study established the methodology for determining the partial pressure of inspired CO₂ (PIco₂) in a pressurized spacesuit. We applied the methodology to characterize PIco₂ for the extravehicular mobility unit (EMU).METHODS: We suggested an automated and mathematical algorithm to find the end-tidal CO₂ and the end of inspiration. We provided objective and standardized guidelines to identify acceptable breath traces, which are essential to accurate and reproducible calculation of the in-suit inhaled and exhaled partial pressure of CO₂ (Pco₂). The mouth guard-based method for measurement of inhaled and exhaled dry-gas Pco₂ was described. We calculated all individual concentrations of PIco₂ inhaled by 19 healthy subjects classified into 3 fitness groups. The transcutaneous Pco₂ was monitored as a secondary measure to validate washout performance.RESULTS: Mean and standard deviation values for the data collection performance and the CO₂ metrics were presented (e.g., minimum time weighted average Pco₂ at suited workloads of resting, 1000, 2000, and 3000 (BTU h1) were 4.75 1.03, 8.09 1.39, 11.39 1.26, and 14.36 1.29 (mmHg s1). All CO₂ metrics had a statistically significant association and all positive slopes with increasing metabolic rate. No significant differences in CO₂ metrics were found between the three fitness groups.DISCUSSION: A standardized and automated methodology to calculate PIco₂ exposure level is presented and applied to characterize CO₂ washout in the EMU. The EMU has been operated successfully in over 400 extravehicular activities (EVAs) and is considered to provide acceptable CO₂ washout performance. Results provide a basis for establishing verifiable Pco₂ requirements for current and future EVA spacesuits.Kim KJ, Bekdash OS, Norcross JR, Conkin J, Garbino A, Fricker J, Young M, Abercromby AFJ. The partial pressure of inspired carbon dioxide exposure levels in the extravehicular mobility unit. Aerosp Med Hum Perform. 2020; 91(12):923931.

Anesthesiologist behavior and anesthesia machine use in the operating room during the COVID-19 pandemic: awareness and changes to cope with the risk of infection transmission.

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) disease [coronavirus disease 2019 (COVID-19) infection] first appeared in December 2019 in China and is now spreading worldwide. Because SARS-CoV-2 can be transmitted via aerosols and surface contaminations of the environment, appropriate use of anesthesia machines and appropriate behavior in the operation room (OR) are required specifically in relation to this disease. The use of high-performance hydrophobic filters with a high rate of virus rejection is recommended as the type of viral filter, and surgical team behaviors that result in aerosol splashes should be avoided. Appropriate hand hygiene by the anesthesiologist is crucial to prevent unexpected environmental contamination. When the anesthesia machine is used instead of an intensive care unit ventilator, it is important to keep the fresh gas flow at least equal to the minute ventilation to prevent excessive humidity in the circuit and to monitor condensation in the circuit and inspiratory carbon dioxide pressure. In addition, both the surgical smoke inherent in thermal tissue destruction and the surgical team’s shoe soles may be factors for the presence of SARS-CoV-2 in the operating room. Ensuring social distancing—even with a mask in the OR—may be beneficial because healthcare providers may be asymptomatic carriers. After the acute crisis period of COVID-19, the number of cases of essential but nonurgent surgeries for waiting patients is likely to increase; therefore, optimization of OR scheduling will be an important topic. Anesthesiologists will benefit from new standard practices focusing on the prevention of COVID-19 infection.

Standardizing the cerebrovascular response to hypercapnia - increasing the flow of data!

Standardizing the cerebrovascular response to hypercapnia - increasing the flow of data!