Arterial Carbon Dioxide Concentration Research Articles

Ventilatory targets following brain injury.

Recent studies have focused on identifying optimal targets and strategies of mechanical ventilation in patients with acute brain injury (ABI). The present review will summarize these findings and provide practical guidance to titrate ventilatory settings at the bedside, with a focus on managing potential brain-lung conflicts. Physiologic studies have elucidated the impact of low tidal volume ventilation and varying levels of positive end expiratory pressure on intracranial pressure and cerebral perfusion. Epidemiologic studies have reported the association of different thresholds of tidal volume, plateau pressure, driving pressure, mechanical power, and arterial oxygen and carbon dioxide concentrations with mortality and neurologic outcomes in patients with ABI. The data collectively make clear that injurious ventilation in this population is associated with worse outcomes; however, optimal ventilatory targets remain poorly defined. Although direct data to guide mechanical ventilation in brain-injured patients is accumulating, the current evidence base remains limited. Ventilatory considerations in this population should be extrapolated from high-quality evidence in patients without brain injury - keeping in mind relevant effects on intracranial pressure and cerebral perfusion in patients with ABI and individualizing the chosen strategy to manage brain-lung conflicts where necessary.

Haemodynamics and Arterial Blood Gases in Smokers versus Non Smokers During General Anaesthesia for Abdominal Surgeries: An Analytical Study

Introduction: Tobacco smoking is a worldwide accepted health hazard and its effect on cardiopulmonary system is a wellknown fact. In a long run, it results in to gross derangements in haemodynamics and arterial blood gases which can lead to further complications during general anaesthesia. Aim: To evaluate the effect of smoking on cardiopulmonary system, and also to compare its effects on haemodynamics and arterial blood gases during general anaesthesia for abdominal surgeries in smokers and non smokers. Materials and Methods: This analytical study was conducted in the Department of Anaesthesiology, Mahatma Gandhi Memorial Medical Colledge, Indore, Madhya Pradesh, India, from May 2020 to April 2021. The study included 74 male patients of American Society of Anaesthesiologist (ASA) grade I and II, aged 20-70 years, undergoing elective abdominal surgeries. The patients were divided into two groups, smokers and non smokers, depending on their smoking status. Haemodynamic monitoring was done from preinduction time till 48 hours after extubation, and arterial blood gas analysis was also done before induction and 2 hours after extubation in both the groups. T-test and Mann-whitney test were applied according to the requirement. A p-value < 0.05 was taken as statistically significant. The statistical software Statistical Package for Social Sciences (SPSS) version 20.0 and Medcalc 19.5 were used for the analysis. Results: Significant increase in Heart Rate (HR) and Mean Arterial Pressure (MAP) was observed in smokers as compared to non smokers at all time intervals (p-value<0.001). End-tidal carbon dioxide concentration (EtCO2 ) values were found to be significantly higher in smokers (37.77±2.63 mmHg) than non smokers (32.99±2.83 mmHg) (p-value<0.001). Regarding arterial blood gas analysis significant difference was observed in preoperative and postoperative arterial carbon dioxide concentration (PaCO2 ) (p-value<0.0001), and pH levels (p-value<0.0001) in both the groups. A significant difference was also seen in preoperative and postoperative PaCO2 levels of the smokers (p-value= 0.0004) with a corresponding change in their pH levels also (p-value=0.0012). Peak Expiratory Flow Rate (PEFR) was lower in smokers in comparison to non smokers (p-value<0.0001). Conclusion: Smoking has significant effects on haemodynamic status and arterial blood gases of smokers which can be aggravated during general anaesthesia.

P0323 / #365: EFFECTS OF INHALED NITRIC OXIDE ON HEMODYNAMICS AND GAS EXCHANGE IN CHILDREN AFTER HAVING UNDERGONE CARDIAC SURGERY UTILIZING CARDIOPULMONARY BYPASS

Aims & Objectives: For congenital heart defect patients undergoing corrective surgery utilizing cardiopulmonary bypass, post-operative inhaled nitric oxide has been administered to alleviate pulmonary hypertension. We performed a systematic review and meta-analyses to determine the effect of inhaled nitric oxide on hemodynamics, gas exchange, and hospitalization characteristics in children immediately after cardiopulmonary bypass. Methods: A systematic review of the literature was performed to identify full text manuscripts in English. PubMed, EMBASE, and the Cochrane databases from 1980 to 2018. The following search terms were used individually and various combinations to query these databases: “inhaled nitric oxide”, “cardiopulmonary bypass”, “cardiac surgery”, “pediatric”, “congenital heart disease”, “hemodynamics”, “gas exchange”. Results: There were significant differences with decreases in mean pulmonary artery pressure of -6.82mmHg, left atrial pressure of -1.16mmHg, arteriovenous oxygen difference of -1.63, arterial carbon dioxide concentration of -2.41 mmHg, mechanical ventilation duration of -8.56 hours, and length of cardiac intensive care unit stay duration of -0.91 days. All significant variables achieved p<0.001. Conclusions: Inhaled nitric oxide in children immediately after cardiopulmonary bypass decreases mean pulmonary artery pressure significantly and decreases the arterial carbon dioxide concentration significantly without significantly altering other hemodynamic parameters. This results in a statistically shorter duration of mechanical ventilation and cardiac intensive care unit length of stay without altering overall hospital length of stay.

Effects of inhaled nitric oxide on haemodynamics and gas exchange in children after having undergone cardiac surgery utilising cardiopulmonary bypass.

For CHD patients undergoing corrective surgery utilising cardiopulmonary bypass, post-operative inhaled nitric oxide has been administered to alleviate pulmonary hypertension. We performed a systematic review and meta-analyses to determine the effect of inhaled nitric oxide on haemodynamics, gas exchange, and hospitalisation characteristics in children immediately after cardiopulmonary bypass. A systematic review of the literature was performed to identify full-text manuscripts in English. PubMed, EMBASE, and the Cochrane databases were queried. Once manuscripts were identified for inclusion, a list of all the endpoints in each manuscript was created. Endpoints with data present from two or more studies were then kept for pooled analyses. All endpoints included were continuous variables and so mean and standard deviation were utilised as the effect data for comparison. A total of eight studies were deemed appropriate for inclusion. There were significant differences with decreases in mean pulmonary artery pressure of -6.82mmHg, left atrial pressure of -1.16mmHg, arteriovenous oxygen difference of -1.63, arterial carbon dioxide concentration of -2.41mmHg, mechanical ventilation duration of -8.56 hours, and length of cardiac ICU stay duration of -0.91 days. All significant variables achieved p < 0.001. Inhaled nitric oxide in children immediately after cardiopulmonary bypass decreases mean pulmonary artery pressure significantly and decreases the arterial carbon dioxide concentration significantly without significantly altering other haemodynamic parameters. This results in a statistically shorter duration of mechanical ventilation and cardiac ICU length of stay without altering overall hospital length of stay.

Principles, Utility and Limitations of Pulse Oximetry in Management of COVID-19

Pulse oximetry is an essential component of the standard care of COVID-19 patients. In the context of the spreading COVID-19 pandemic for which no targeted therapy or vaccines are yet available, early identification of the severe cases or cases with high risk of severe disease and appropriate supportive treatment are of paramount importance to save lives. Pulse oximetry is a cheap, fast, easy to use, noninvasive, painless and accurate tool that allows real-time monitoring of hypoxemia. As the primary target of the disease is the respiratory system pulse oximetry provides an unparalleled way to assess the severity of the disease, guide supportive therapies and monitor the clinical status and response to treatment with greater benefits in the low-resource settings. All settings from the quarantine facilities at the ground level to the ICUs in the highest level hospitals can utilize it to achieve their goals. To get the best of this tool, it needs to be used properly and the findings interpreted carefully. Role of basic understanding of the physiological principles and technology behind its use and awareness of its limitations cannot be overemphasized. The pulse oximetry readings are interpreted in the context of blood hemoglobin concentration, tissue perfusion, arterial blood carbon dioxide concentration and oxygen supplementation status.

Interaction between the respiratory system and cerebral blood flow regulation.

This review summarizes the interaction between the regulatory system of respiration and cerebral vasculature. Some clinical reports provide evidence for the association between these two physiological regulatory systems. Physiologically, arterial carbon dioxide concentration is mainly regulated by two feedback control systems: respiration and cerebral blood flow. In other words, both of these systems are sensitive to the same mediator, i.e., carbon dioxide, at a set point. In addition, respiratory dysfunction alters various physiological factors that affect the cerebral vasculature. Therefore, it is physiologically plausible that these systems are closely linked. The regulation of arterial carbon dioxide concentration affected by respiration and cerebral blood flow may be a key factor for a rise in the risk of brain disease in the patients with respiratory dysfunction. For example, the management of respiratory disease (e.g., patients with chronic obstructive pulmonary disease) and the use of prophylactic therapy are essential to reduce the risk of stroke.

High‐flow nasal therapy – modelling the mechanism

High‐flow nasal therapy – modelling the mechanism

Assessment of cerebral hemodynamic parameters using pulsatile versus non-pulsatile cerebral blood outflow models.

Prior methods evaluating the changes in cerebral arterial blood volume (∆CaBV) assumed that brain blood transport distal to big cerebral arteries can be approximated with a non-pulsatile flow (CFF) model. In this study, a modified ∆CaBV calculation that accounts for pulsatile blood flow forward (PFF) from large cerebral arteries to resistive arterioles was investigated. The aim was to assess cerebral hemodynamic indices estimated by both CFF and PFF models while changing arterial blood carbon dioxide concentration (EtCO2) in healthy volunteers. Continuous recordings of non-invasive arterial blood pressure (ABP), transcranial Doppler blood flow velocity (CBFVa), and EtCO2 were performed in 53 young volunteers at baseline and during both hypo- and hypercapnia. The time constant of the cerebral arterial bed (τ) and critical closing pressure (CrCP) were estimated using mathematical transformations of the pulse waveforms of ABP and CBFVa, and with both pulsatile and non-pulsatile models of ∆CaBV estimation. Results are presented as median values ± interquartile range. Both CrCP and τ gave significantly lower values with the PFF model when compared with the CFF model (p ≪ 0.001 for both). In comparison to normocapnia, both CrCP and τ determined with the PFF model increased during hypocapnia [CrCPPFF (mmHg): 5.52 ± 8.78 vs. 14.36 ± 14.47, p = 0.00006; τPFF (ms): 47.4 ± 53.9 vs. 72.8 ± 45.7, p = 0.002] and decreased during hypercapnia [CrCPPFF (mmHg): 5.52 ± 8.78 vs. 2.36 ± 7.05, p = 0.0001; τPFF (ms): 47.4 ± 53.9 vs. 29.0 ± 31.3, p = 0.0003]. When the CFF model was applied, no changes were found for CrCP during hypercapnia or in τ during hypocapnia. Our results suggest that the pulsatile flow forward model better reflects changes in CrCP and in τ induced by controlled alterations in EtCO2.

Arterial Chemoreflex Protective Effect on Left Ventricle Energetics and Changes after Myocardial Infarct

The Arterial Chemoreflex negative feedback mechanism regulates the cardiovascular responses to arterial oxygen and carbon dioxide concentrations as sensed by carotid chemoreceptors. Whenever the arterial pressure of oxygen chnages the Autonomic Nervous System madulates heart rate and arterial blood pressure. As the Arterial Chemoreflex influences cardiac output to compensate for changes in oxygen arterial pressure, we hypothesized that it must influence the mechanical interaction between the left ventricle and the arterial tree, as well as cardiac energy consumption and efficiency during Myocardial Infarct. The Arterial Chemoreflex was provoked by the application of lobeline in the left-carotid sinus of 11 rabbits anesthetized, paralyzed and artificially ventilated; an intraventricular impedance catheter was used to measure simultaneously ventricular pressure and volume. All experiments were performed according to national laws and international guidelines. We designed a custom software to compute beat by beat left-ventricle end-systolic elastance (Ees), arterial elastance (Ea) and the ventriculo arteral coupling ratio (Ea/Ees); from this data we calculated left-ventricular stroke work (SW), total energy expenditure (PVA), ratio of the SW to its theoretical maximum (Qload) and cardiac energetic efficiency (CEE=SW/PVA). Under Basal Conditions and after Myocardial Infarct the Arterial Chemoreflex increased Ees and Ea in paralell, without any change in Ees/Ea. SW and PVA both decreased, without any change of Qload or CEE (Table). Ventriculo-arterial coupling was maintained in the interval of optimal cardiac mechanical and energetic efficiency. In conclusion, the Arterial Chemoreflex is a control mechanism of the cardiovascular system that exerts a feedback modulation on cardiovascular responses through an increase in both left ventricle contractility and arterial elastance, in such a balanced way that ventriculo-arterial coupling is mantained, mechanical and energetic efficiency are maintained at optimal values. Most remarckably the increase in ventricular and arterial elastance is acomplished decreasing the SW and PVA(equivalent to myocardial oxygen demand), therefore emphasizing the protective effect of the Arterial Chemoreflex the myocardial oxygen comnsumption is ischemic conditions. Support or Funding Information PHYSIOMAT - Modelação Matemática e Computacional da Fisiologia Humana (2013) Fundação para a Ciência e Tecnologia EXCL/MAT-NAN/0114/2012 This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Perturbation treadmill training improves clinical rating of the motor symptoms gait and postural stability, and sensor-based gait parameters in Parkinson’s disease

Although deep neuromuscular block (post-tetanic-count 1-2 twitches) improves surgical conditions during laparoscopic retroperitoneal surgery compared with standard block (train-of-four 1-2 twitches), the quality of surgical conditions varies widely, often related to diaphragmatic contractions. Hypocapnia may improve surgical conditions. Therefore we studied the effect of changes in arterial carbon dioxide concentrations on surgical conditions in patients undergoing laparoscopic surgery under general anaesthesia and deep neuromuscular block.Forty patients undergoing elective laparoscopic surgery for prostatectomy or nephrectomy received propofol/remifentanil anaesthesia and deep neuromuscular block with rocuronium. Patients were randomized to surgery under hypocapnic or hypercapnic conditions. During surgery, the surgical conditions were evaluated using the 5-point Leiden-Surgical Rating Scale (L-SRS) ranging from 1 (extremely poor conditions) to 5 (optimal conditions) by the surgeon, who was blinded to group.Mean (sd) arterial carbon dioxide concentrations were 4.5 (0.6) [range: 3.8–5.6] kPa under hypocapnic and 6.9 (0.6) [6.1–8.1] kPa under hypercapnic conditions. The L-SRS did not differ between groups: 4.84 (0.4) [4-5] in hypocapnia and 4.77 (0.4) [3.9–5] in hypercapnia. Ninety-nine percent of ratings were good or excellent irrespective of treatment.Deep neuromuscular block provides good to optimal surgical conditions in laparoscopic retroperitoneal urological surgery, independent of the level of arterial PCO2.NCT01968447.

Influence of variations in arterial PCO2 on surgical conditions during laparoscopic retroperitoneal surgery

BackgroundAlthough deep neuromuscular block (post-tetanic-count 1-2 twitches) improves surgical conditions during laparoscopic retroperitoneal surgery compared with standard block (train-of-four 1-2 twitches), the quality of surgical conditions varies widely, often related to diaphragmatic contractions. Hypocapnia may improve surgical conditions. Therefore we studied the effect of changes in arterial carbon dioxide concentrations on surgical conditions in patients undergoing laparoscopic surgery under general anaesthesia and deep neuromuscular block. MethodsForty patients undergoing elective laparoscopic surgery for prostatectomy or nephrectomy received propofol/remifentanil anaesthesia and deep neuromuscular block with rocuronium. Patients were randomized to surgery under hypocapnic or hypercapnic conditions. During surgery, the surgical conditions were evaluated using the 5-point Leiden-Surgical Rating Scale (L-SRS) ranging from 1 (extremely poor conditions) to 5 (optimal conditions) by the surgeon, who was blinded to group. ResultsMean (sd) arterial carbon dioxide concentrations were 4.5 (0.6) [range: 3.8–5.6] kPa under hypocapnic and 6.9 (0.6) [6.1–8.1] kPa under hypercapnic conditions. The L-SRS did not differ between groups: 4.84 (0.4) [4-5] in hypocapnia and 4.77 (0.4) [3.9–5] in hypercapnia. Ninety-nine percent of ratings were good or excellent irrespective of treatment. ConclusionsDeep neuromuscular block provides good to optimal surgical conditions in laparoscopic retroperitoneal urological surgery, independent of the level of arterial PCO2. Clinical trial registrationNCT01968447.

Respiratory challenge MRI: Practical aspects.

Respiratory challenge MRI is the modification of arterial oxygen (PaO2) and/or carbon dioxide (PaCO2) concentration to induce a change in cerebral function or metabolism which is then measured by MRI. Alterations in arterial gas concentrations can lead to profound changes in cerebral haemodynamics which can be studied using a variety of MRI sequences. Whilst such experiments may provide a wealth of information, conducting them can be complex and challenging. In this paper we review the rationale for respiratory challenge MRI including the effects of oxygen and carbon dioxide on the cerebral circulation. We also discuss the planning, equipment, monitoring and techniques that have been used to undertake these experiments. We finally propose some recommendations in this evolving area for conducting these experiments to enhance data quality and comparison between techniques.

Associations of arterial carbon dioxide and arterial oxygen concentrations with hospital mortality after resuscitation from cardiac arrest.

IntroductionArterial concentrations of carbon dioxide (PaCO2) and oxygen (PaO2) during admission to the intensive care unit (ICU) may substantially affect organ perfusion and outcome after cardiac arrest. Our aim was to investigate the independent and synergistic effects of both parameters on hospital mortality.MethodsThis was a cohort study using data from mechanically ventilated cardiac arrest patients in the Dutch National Intensive Care Evaluation (NICE) registry between 2007 and 2012. PaCO2 and PaO2 levels from arterial blood gas analyses corresponding to the worst oxygenation in the first 24 h of ICU stay were retrieved for analyses. Logistic regression analyses were performed to assess the relationship between hospital mortality and both categorized groups and a spline-based transformation of the continuous values of PaCO2 and PaO2.ResultsIn total, 5,258 cardiac arrest patients admitted to 82 ICUs in the Netherlands were included. In the first 24 h of ICU admission, hypocapnia was encountered in 22 %, and hypercapnia in 35 % of included cases. Hypoxia and hyperoxia were observed in 8 % and 3 % of the patients, respectively. Both PaCO2 and PaO2 had an independent U-shaped relationship with hospital mortality and after adjustment for confounders, hypocapnia and hypoxia were significant predictors of hospital mortality: OR 1.37 (95 % CI 1.17–1.61) and OR 1.34 (95 % CI 1.08–1.66). A synergistic effect of concurrent derangements of PaCO2 and PaO2 was not observed (P = 0.75).ConclusionsThe effects of aberrant arterial carbon dioxide and arterial oxygen concentrations were independently but not synergistically associated with hospital mortality after cardiac arrest.Electronic supplementary materialThe online version of this article (doi:10.1186/s13054-015-1067-6) contains supplementary material, which is available to authorized users.

Ultrasonographic Optic Nerve Sheath Diameter Is Correlated With Arterial Carbon Dioxide Concentration During Reperfusion in Liver Transplant Recipients

BackgroundCerebral blood flow and intracranial pressure (ICP) has been known to be increased after graft reperfusion during liver transplantation, which was correlated with arterial carbon dioxide concentration (PaCO2). Ultrasonographic measurement of optic nerve sheath diameter (ONSD) is a simple and noninvasive method for evaluating ICP. We investigated the correlation between ONSD and the PaCO2 during reperfusion in liver transplant recipients. MethodsTwenty liver transplant recipients with end-stage liver disease were enrolled. We measured ONSD and PaCO2 at 6 time points: preinduction, preanhepatic phase, anhepatic phase, 5 minutes after reperfusion, 30 minutes after reperfusion, and neohepatic phase. Pearson correlation analysis and receiver operating characteristics (ROC) curve analysis were performed. ResultsONSD measured 5 minutes after reperfusion was significantly higher compared with the other time points. Differences in ONSD between the anhepatic phase and 5 minutes after reperfusion demonstrated significant correlations with both PaCO2 at the anhepatic phase and 5 minutes after reperfusion (both P < .001). On the ROC curve analysis, PaCO2 of 35 mm Hg at the anhepatic phase could be used to indicate ≥20% changes in ONSD after reperfusion. There were significant increases in ONSD after graft reperfusion in liver transplant recipients with PaCO2 ≥ 35 mm Hg at the anhepatic phase (P = .004). ConclusionONSD was increased just after reperfusion, which demonstrated good correlation with PaCO2 during reperfusion in liver transplant recipients. This finding suggests that the carbon dioxide can play a key role in increasing ONSD during hepatic graft reperfusion.

Malignant Hyperthermia or Not Malignant Hyperthermia

In an acute event, the diagnosis of malignant hyperthermia (MH) in patients in the ICU can be challenging. Initial presentation may be attributed to a gamut of causes, making the diagnosis complicated. This example is the case of a 46-year-old African American man who was admitted to the Stroke Service and intubated for respiratory distress. To facilitate intubation, he was given etomidate and succinylcholine. Within an hour, a sustained increase in arterial carbon dioxide concentration, rhabdomyolysis, and later on, hyperthermia, developed. He was started on broad-spectrum antibiotics, aggressive fluid hydration, and mechanical ventilation. He had had one previous uneventful anesthesia exposure and he denied having any family member having anesthesia complications. With a very convoluted presentation, a high degree of suspicion for MH warranted appropriate treatment to avoid significant morbidity and/or mortality. Moreover, until the diagnosis is confirmed, education regarding the disease process to patients and their family members is as vital as the treatment itself. The main objective of this case is to present a diagnostic dilemma in a probable MH patient who is in a state of shock in the ICU.

Effects of High Altitude on Sleep and Respiratory System and Theirs Adaptations

High-altitude (HA) environments have adverse effects on the normal functioning body of people accustomed to living at low altitudes because of the change in barometric pressure which causes decrease in the amount of oxygen leading to hypobaric hypoxia. Sustained exposure to hypoxia has adverse effects on body weight, muscle structure and exercise capacity, mental functioning, and sleep quality. The most important step of acclimatization is the hyperventilation which is achieved by hypoxic ventilatory response of the peripheral chemoreceptors. Hyperventilation results in increase in arterial carbondioxide concentration. Altitude also affects sleep and cardiac output, which is the other determinant of oxygen delivery. Upon initial exposure to HA, the resting pulse rate increases rapidly, but with acclimatization, heart rate and cardiac output tend to fall. Another important component that leads to decrease in cardiac output is the reduction in the stroke volume with acclimatization. During sleep at HA, the levels of CO2 in the blood can drop very low and this can switch off the drive to breathe. Only after the body senses a further drop in O2 levels breathing is started again. Periodic breathing is thought to result from instability in the control system through the hypoxic drive or the response to CO2.

Intratesticular lidocaine reduces the response to surgical castration in dogs

ObjectiveTo investigate whether intratesticular injection of lidocaine pre-surgery would reduce the intraoperative responses to elective castration in dogs. Study designDouble-blinded, randomized, controlled, prospective clinical study. AnimalsForty-two client-owned dogs weighing 2.2–38.4 kg and aged between 4.5 and 56 months. MethodsGroup L dogs received an intratesticular injection of 2% lidocaine (2 mg kg−1) and Group S an identical volume of saline prior to surgery. Premedication was with acepromazine and morphine intramuscularly. Anaesthesia was induced with propofol intravenously and maintained with isoflurane vaporized in oxygen. Heart rate (HR), mean arterial pressure (MAP), respiratory rate (fR), end-tidal isoflurane (Fe′ISO) and carbon dioxide concentrations, oxygen saturation and ECG were monitored during surgery. Fe′ISO was maintained at 1.0 ± 0.1%. Supplemental propofol was given in response to gross movement. ResultsGroup L had significantly lower maximum values for both HR and MAP. Group L displayed significantly smaller increases in HR during exteriorization of the first testis than Group S. There was an overall significant difference in MAP between groups during all surgical events (p = 0.041) and time points (p = 0.002). In univariate analysis, Group L showed significantly less changes in MAP during skin incision, exteriorization of the first testis and clamping of both spermatic cords. Group S reached its highest fR significantly earlier. Group L (eight dogs) required additional propofol 33 ± 18 minutes after the start of surgery and Group S (seven dogs) at 19 ± 17 minutes; this difference was not statistically significant. Seven dogs in Group L and 12 dogs in Group S required rescue analgesia with morphine (GCMPS-SF score ≥6); this difference was not statistically significant. No adverse effects were reported postoperatively. Conclusions and clinical relevanceBased on this study, the authors recommend the use of intratesticular lidocaine for surgical castration in dogs.

The effect of partial acclimatization to high altitude on loop gain and central sleep apnoea severity

Loop gain is an engineering term that predicts the stability of a feedback control system, such as the control of breathing. Based on earlier studies at lower altitudes, it was hypothesized that acclimatization to high altitude would lead to a reduction in loop gain and thus central sleep apnoea (CSA) severity. This study used exposure to very high altitude to induce CSA in healthy subjects to investigate the effect of partial acclimatization on loop gain and CSA severity. Measurements were made on 12 subjects (age 30 ± 10 years, body mass index 22.8 ± 1.9, eight males, four females) at an altitude of 5050 m over a 2-week period upon initial arrival (days 2-4) and following partial acclimatization (days 12-14). Sleep was studied by full polysomnography, and resting arterial blood gases were measured. Loop gain was measured by the 'duty cycle' method (duration of hyperpnoea/cycle length). Partial acclimatization to high-altitude exposure was associated with both an increase in loop gain (duty cycle fell from 0.60 ± 0.05 to 0.55 ± 0.06 (P = 0.03)) and severity of CSA (apnoea-hypopnoea index increased from 76.8 ± 48.8 to 115.9 ± 20.2 (P = 0.01)), while partial arterial carbon dioxide concentration fell from 29 ± 3 to 26 ± 2 (P = 0.01). Contrary to the results at lower altitudes, at high-altitude loop gain and severity of CSA increased.

Obesity hypoventilation syndrome: From sleep‐disordered breathing to systemic comorbidities and the need to offer combined treatment strategies

Obesity hypoventilation syndrome (OHS) is defined as a combination of obesity (body mass index ≥ 30 kg/m(2)), daytime hypercapnia (partial arterial carbon dioxide concentration ≥45 mm Hg) and sleep-disordered breathing after ruling out other disorders that may cause alveolar hypoventilation. Through the prism of the International Classification of Functioning, OHS is a chronic condition associated with respiratory, metabolic, hormonal and cardiovascular impairments, leading to a decrease in daily life activities, a lack of social participation and high risk of hospitalization and death. Despite its severity, OHS is largely underdiagnosed and the health-related costs are higher than those of apnoeic or obese eucapnic patients. The present review discusses the definition, epidemiology, physiopathology and treatment modalities of OHS. Although nocturnal positive airway pressure therapies represent first-line treatment and are effective in improving patient outcomes, there is a need to offer combined treatment strategies and to assess the effect of multimodal therapeutic strategies on morbidity and mortality.

Observations on the Study of Second Gas Effects

Observations on the Study of Second Gas Effects