Carbon Dioxide Breathing Research Articles

Diagnosis and Severity Assessment of COPD Using a Novel Fast-Response Capnometer and Interpretable Machine Learning

Introduction Spirometry is the gold standard for COPD diagnosis and severity determination, but is technique-dependent, nonspecific, and requires administration by a trained healthcare professional. There is a need for a fast, reliable, and precise alternative diagnostic test. This study’s aim was to use interpretable machine learning to diagnose COPD and assess severity using 75-second carbon dioxide (CO2) breath records captured with TidalSense’s N-TidalTM capnometer. Method For COPD diagnosis, machine learning algorithms were trained and evaluated on 294 COPD (including GOLD stages 1–4) and 705 non-COPD participants. A logistic regression model was also trained to distinguish GOLD 1 from GOLD 4 COPD with the output probability used as an index of severity. Results The best diagnostic model achieved an AUROC of 0.890, sensitivity of 0.771, specificity of 0.850 and positive predictive value (PPV) of 0.834. Evaluating performance on all test capnograms that were confidently ruled in or out yielded PPV of 0.930 and NPV of 0.890. The severity determination model yielded an AUROC of 0.980, sensitivity of 0.958, specificity of 0.961 and PPV of 0.958 in distinguishing GOLD 1 from GOLD 4. Output probabilities from the severity determination model produced a correlation of 0.71 with percentage predicted FEV1. Conclusion The N-TidalTM device could be used alongside interpretable machine learning as an accurate, point-of-care diagnostic test for COPD, particularly in primary care as a rapid rule-in or rule-out test. N-TidalTM also could be effective in monitoring disease progression, providing a possible alternative to spirometry for disease monitoring.

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.

Investigation of Air Change Rate in a Single Room Using Multiple Carbon Dioxide Breathing Models in China: Verification by Field Measurement

It is difficult to accurately measure the air exchange rate (AER) in residential and office buildings during occupation via on-site field measurement. The tracer gas method was widely applied to estimate the AER in these buildings, and human metabolic carbon dioxide (CO2) was often used as a tracer gas in different models. This study introduced three models (the ASHRAE model, the ASHRAE China-specific modified model, and the BMR model), which were proposed to estimate the AER based on exhaled CO2. We verified these models by comparing the exhaled CO2-based AER with AER from field measurements using sulfur hexafluoride (SF6) as a tracer gas. We also analyzed the potential factors that could affect the uniformity of the indoor tracer gas distribution. Our results indicate that the ASHRAE China-specific modified model has the best performance with an average deviation of −6.67% and a maximum deviation of −14.6% with multiple measurement points, a stable personnel activity, and proper Parameter settings in a single room in China.

Exposure to acute noxious heat evokes a cardiorespiratory shock response in humans

Background: Noxious acute cold stimuli cause cold shock via the sympathetic nervous system. However, no studies have investigated respiratory “heat shock” in response to noxious acute heat stimuli (≥ 42 °C). Methods: In the present study, we examined whether short-duration whole-body immersion (for 5 min) in noxious hot water (45 °C) is a sufficient stimulus to induce a respiratory acute shock response. Results and conclusion: Our results indicate that short-duration whole-body immersion in noxious 45 °C water produces a significantly greater body temperature, heart rate, and perceptual and respiratory strain than immersion in innocuous warm 37 °C water (p < .05). The initial first minute of hot water immersion (HWI) at 45 °C (vs. immersion at 37 °C) caused a cardiorespiratory shock response, which manifested as acute hyperventilation, and increased ventilatory tidal volume, respiratory exchange ratio, and heart rate (p < .05). Adjustment to this initial respiratory heat shock response within the first minute of immersion was observed as compared with remaining HWI time (1–5 min). Intriguingly, the time-course kinetics of breathing frequency, oxygen uptake, and carbon dioxide washout did not differ between whole-body immersion at 37 °C and immersion at 45 °C, but were higher than in control thermoneutral conditions of an empty bath (p < .05). This may be because of events initiated not only by the water temperature but also by the change in the hydrostatic pressure acting upon the body when immersed in the water bath.

Incremental and decremental cardiopulmonary exercise testing protocols produce similar maximum oxygen uptake in athletes

The aim of the study was to evaluate and compare the maximal oxygen uptake (dot{mathrm{V}}O2max) achieved during incremental and decremental protocols in highly trained athletes. Nineteen moderate trained runners and rowers completed, on separate days, (i) an initial incremental dot{mathrm{V}}O2max test (INC) on a treadmill, followed by a verification phase (VER); (ii) a familiarization of a decremental test (DEC); (iii) a tailored DEC; (iv) a test with decremental and incremental phases (DEC-INC); (v) and a repeated incremental test (INCF). During each test dot{mathrm{V}}O2, carbon dioxide production, ventilation, heart and breath rates and ratings of perceived exertion were measured. No differences were observed in dot{mathrm{V}}O2max between INC (61.3 ± 5.2 ml kg−1 min−1) and DEC (61.1 ± 5.1 ml kg−1 min−1; average difference of ~ 11.58 ml min−1; p = 0.831), between INC and DEC-INC (60.9 ± 5.3 ml kg−1 min−1; average difference of ~ 4.8 ml min−1; p = 0.942) or between INC and INCF (60.7 ± 4.4 ml kg−1 min−1; p = 0.394). dot{mathrm{V}}O2max during VER (59.8 ± 5.1 ml kg−1 min−1) was 1.50 ± 2.20 ml kg−1 min−1 lower (~ 2.45%; p = 0.008) compared with values measured during INC. The typical error in the test-to-test changes for evaluating dot{mathrm{V}}O2max over the five tests was 2.4 ml kg−1 min−1 (95% CI 1.4–3.4 ml kg−1 min−1). Decremental tests do not elicit higher dot{mathrm{V}}O2max than incremental tests in trained runners and rowers, suggesting that a plateau in dot{mathrm{V}}O2 during the classic incremental and verification tests represents the maximum ceiling of aerobic power.

Roles of periodic breathing and isocapnic buffering period during exercise in heart failure.

In heart failure, exercise – induced periodic breathing and end tidal carbon dioxide pressure value during the isocapnic buffering period are two features identified at cardiopulmonary exercise testing strictly related to sympathetic activation. In the present review we analysed the physiology behind periodic breathing and the isocapnic buffering period and present the relevant prognostic value of both periodic breathing and the presence/absence of the identifiable isocapnic buffering period.

Market Surveillance of Filtering Facepiece (FFP)of Respirator Protective Equipment (RPE): Malaysian Perspectives

Filtering Facepieces (FFPs) are commonly use as personal protective equipment (PPE). It is disposable Respiratory Protective Equipment (RPE). Basically it is used for protection against dusts, particles and aerosols. Available in 3 classes FFP1, FFP2 and FFP3. Various Respiratory Protective Equipment (RPE) offered in Malaysia’s market today are not being controlled and monitored by expert bodies and authorities. This has led to various perceptions among the users, especially on the quality and safety and health features of the products offered by different companies. This situation also makes it difficult for users to decide appropriate RPE based on quality and standard compliance. The tendency of consumers to choose RPE is mainly based on the price but not the technical aspect of RPE. Hence, the RPE they purchased not necessary enhance user protection, as there is no guidance available to assist user before they purchase the most appropriate RPE. This study describes market surveillance testing of FFP2 respirator from 30 different brand in Malaysia. The objective is to determine performance requirements required by the Malaysia standard. 3 types of testing were used on this study Filter Penetration, Breathing Resistance and Carbon Dioxide Content. All testing was carried out based on Malaysia Standard; MS 2323:2010 and MS2553:2014.All 30 sample were passed the breathing resistance and carbon dioxide content except 10 brand was failed the filter penetration testing. It is noticed that the user and consumer should aware with their PPE basic requirement.

Cerebrovascular reactivity to carbon dioxide is not influenced by variability in the ventilatory sensitivity to carbon dioxide.

What is the central question of this study? Do differing magnitudes of ventilation influence cerebrovascular CO2 reactivity and the cerebral blood flow response to increases in arterial carbon dioxide? What is the main finding and its importance? While a greater ventilation, through voluntary hyperventilation, is associated with a higher anterior cerebral blood flow during carbon dioxide breathing, this elevated cerebral blood flow is due to a higher blood pressure and not ventilation per se. A greater ventilation, through voluntary hyperventilation, does not influence global or posterior cerebral blood flow during carbon dioxide breathing. Cerebrovascular reactivity to carbon dioxide is not influenced by an individual's ventilatory sensitivity to carbon dioxide. Recent work demonstrated an influence of ventilation on cerebrovascular reactivity to CO2 ; however, the concomitant influence of changes in mean arterial blood pressure (MAP) on ventilation-induced differences in cerebral blood flow (CBF) has yet to be examined in this context. Healthy participants (n=15; 25±3years of age; 179±6cm height; 74±10kg weight; 3 female) underwent end-tidal forcing to increase their partial pressure of end-tidal CO2 by +3, +6 and +9mmHg above baseline in 5-min sequential steps while maintaining iso-oxia. This protocol was then repeated twice, with participants hyperventilating and hypoventilating by ∼30% compared to the first trial. Intra-cranial and extra-cranial CBF were measured using ultrasound. The MAP (finger photo-plethysmography) was higher during the hyperventilation and hypoventilation trials compared to normal ventilation (main effects, P<0.05 for both). While internal carotid artery blood flow was higher during the hyperventilation trial compared to normal ventilation (P=0.01), this was due to a higher MAP, as indicated by analysis of conductance values (P=0.68) or inclusion of MAP in covariate analysis (P=0.11). Global CBF (P=0.11) and vertebral artery blood flow (P=0.93) were unaffected by the magnitude of ventilation. Further, CO2 reactivity was not affected by the different breathing trials (P>0.05 for all). Retrospective analysis of a larger data set (n=53) confirmed these observations and demonstrated no relationships between the ventilatory and global CBF response to hypercapnia (r2 =0.04; P=0.14). Therefore, when differences in MAP are accounted for, cerebrovascular CO2 reactivity (assessed via end-tidal forcing) is independent of the magnitude of ventilation.

Examining the Association between Trait Mindfulness and Distress in Response to a Repeated CO2 Challenge

The present research examined the degree to which facets of trait mindfulness were associated with level and changes in psychological distress in response to a repeated carbon dioxide (CO2) breathing challenge. Undergraduate students (N = 93) completed a self-report measure of mindfulness and underwent two 7.5% CO2 challenges, spaced 1 week apart. Subjective distress, physical/fear symptoms, and threat cognitions were assessed at multiple times throughout each administration. A pattern emerged such that although mindfulness facets were not reliably associated with distress at either administration separately, a low (but not high) level of mindfulness was associated with a significant decrease in distress across administrations, likely indicative of habituation, for the facets Describing (β = − 0.25, p < − 0.01), Acting with Awareness (β = − 0.27, p < .01), and Observing (β = − 0.25, p < 0.01). This suggests that those components of mindfulness tied to noticing/attending to the present moment may at times interfere with typical habituation processes. In contrast, those high in components of mindfulness tied to not evaluating—Non-judging (β = − 0.23, p < 0.01) and Non-reacting (β = − 0.12, p < 0.01)—tended to report less distress, as expected. Findings suggest that the relation between trait mindfulness and stress response is more complex and nuanced than previously thought and that focusing on both mindfulness facets and repeated exposure to stressors may help elucidate this relationship.

Cognitive Bias Modification to Enhance Resilience to a Panic Challenge

This study tested an intervention to enhance resilience among people at risk for developing panic disorder. Participants (N = 50) high in anxiety sensitivity (fear of anxiety symptoms) were randomly assigned to either four sessions of resilience-enhancing interpretation bias modification (CBM-I) or a control (Sham) condition. Following the intervention, participants engaged in a 7.5 % steady state carbon dioxide (CO2) breathing challenge, an established panic stressor. In line with hypotheses, CBM-I resulted in an increase in resilience-congruent interpretations (though no change for general panic interpretation bias) at post-training, and a trend for a greater reduction in anxiety sensitivity at 2-month follow-up. Additionally, CBM-I resulted in less intense cognitive symptoms of panic during the CO2 challenge, though not less intense physical or total panic symptoms. These results, though somewhat mixed, provide preliminary support for the value of training resilience using CBM-I.

Abstract 1796: Targeting the microenvironment and vasculature of tumors to improve response to radiation administered using a dose and schedule equivalent to those of a stereotactic radiation treatment

Abstract Purpose: The vasculature and microenvironment of tumors play significant roles in influencing tumor response to radiation. Applying approaches that target these tumor parameters can effectively enhance radiation response when using large single doses or a conventional fractionated schedule. This pre-clinical study was designed to use such vascular and microenvironmental modifiers to improve tumor response to radiation administered in a schedule equivalent to a stereotactic radiation treatment. Materials and methods: C3H mammary carcinomas, grown in the right rear foot of female CFD1 mice, were treated when at 200 cubic mm in size. Tumors were locally irradiated in restrained, non-anesthetized mice with 3×15 Gy during a 1-week period, followed 3-days later by a clamped top-up dose to produce a dose-response curve; the endpoint being tumor control at 90 days. Following logit analysis of the radiation dose-response curve, the TCD50 values (radiation dose that controlled 50% of tumors) were calculated. Statistical analysis was achieved using a Chi-squared test (p&amp;lt;0.05). The radiation modifiers were nimorazole (200 mg/kg), injected intraperitoneally (i.p.) 30 minutes before irradiating; nicotinamide (120 mg/kg; injected i.p. 20 minutes before irradiation) and carbogen (95% oxygen + 5% carbon dioxide) breathing (started 5 minutes before and continued during the irradiation period); OXi4503 (10 mg/kg; injected i.p. 1-hour after irradiating); and hyperthermia (41.5 degrees C for 1-hour started 4-hours after irradiating). Results: The clamped TCD50 dose following 3×15 Gy was 30 Gy. Giving nimorazole or nicotinamide+carbogen prior to the final 15 Gy irradiation non-significantly reduced this TCD50 to 20-23 Gy; when administered with each 3×15 Gy irradiation these values were significantly reduced to 2.5 Gy or below. Injecting OXi4503 or heating significantly reduced the TCD50 to 9-12 Gy regardless of whether administered with one or all three 15 Gy treatments. Combining OXi4503 and heat with the final 15 Gy irradiation had a significantly larger effect (TCD50 = 2 Gy). Conclusions: Clinically relevant modifiers of the vasculature or microenvironment of a tumor effectively enhanced radiation given in a stereotactic equivalent schedule. But, different effects were obtained with the various agents, which may be related to the different mechanisms of action. This latter issue is under investigation. Supported by grants from the Danish Cancer Society and the Danish Council for Independent Research: Medical Sciences. Citation Format: Michael R. Horsman, Thomas R. Wittenborn. Targeting the microenvironment and vasculature of tumors to improve response to radiation administered using a dose and schedule equivalent to those of a stereotactic radiation treatment. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1796. doi:10.1158/1538-7445.AM2015-1796

Muscular contraction mode differently affects autonomic control during heart rate matched exercise.

The precise contributions of afferent feedback to cardiovascular and respiratory responses to exercise are still unclear. The aim of this crossover study was to assess whether and how autonomic cardiovascular and respiratory control differed in response to dynamic (DYN) and isometric contractions (ISO) at a similar, low heart rate (HR) level. Therefore, 22 healthy males (26.7 ± 3.6 yrs) performed two kinds of voluntary exercises at similar HR: ISO and DYN of the right quadriceps femoris muscle. Although HR was eqivalent (82 ± 8 bpm for DYN and ISO, respectively), rating of exertion, blood pressures, and rate pressure product were higher, whereas breathing frequency, minute ventilation, oxygen uptake and carbon dioxide output were significantly lower during ISO. Tidal volume, end-tidal partial pressures of O2 and CO2, respiratory exchange ratio and capillary blood lactate concentration were comparable between both contraction modes. Heart rate variability (HRV) indicators, SDNN, HF-Power and LF-Power, representing both vagal and sympathetic influences, were significantly higher during ISO. Sample entropy, a non-linear measure of HRV was also significantly affected by contraction mode. It can be concluded that, despite the same net effect on HR, the quality of cardiovascular control during low intensity exercise is significantly different between DYN and ISO. HRV analysis indicated a sympatho-vagal coactivation during ISO. Whether mechanoreceptor feedback alone, a change in central command, or the interaction of both mechanisms is the main contributor of the distinct autonomic responses to the different exercise modes remains to be elucidated.

Co-Activation vs. Reciprocal Antagonism

The model of a two-dimensional autonomic space, where equivalent heart rates (HR) can be considered as an end product achieved by different autonomic modes, such as reciprocal behavior or sympathovagal co-activation, has been introduced in the early 1990s (1). Findings of exercise physiologists question the traditional view of the interplay between both autonomic branches as a reciprocal antagonism, with a reduction of vagal efferent activity at the beginning or during low intensity exercise to a minimum at HRs around 100 bpm and a subsequent rise in sympathetic activity during higher exercise intensities (2-4). PURPOSE: To elucidate the mechanisms of autonomic cardiac control during low intensity isometric (ISO) vs. dynamic exercise (DYN). METHODS: Twenty healthy males performed two kinds of voluntary exercises at similar HR: ISO and DYN of the right quadriceps femoris muscle (randomized, cross-over design). RESULTS: Although HR was equivalent (82 ± 8 bpm for DYN and ISO, respectively, p = 0.489), heart rate variability (HRV) indicators representing dual autonomic and sympathetic influences were significantly higher during ISO. Rating of perceived exertion and blood pressure were higher, while breathing frequency, minute ventilation, oxygen uptake and carbon dioxide output were significantly lower during ISO. Tidal volume, end-tidal partial pressures of O2 and CO2, respiratory exchange ratio and capillary blood lactate concentration were comparable between both contraction modes. CONCLUSION: Low intensity ISO seems to contribute to a sympathovagal co-activation. Results support the model of a two-dimensional autonomic space and help to explain mechanisms of autonomic cardiovascular control under low intensity exercise. REFERENCES 1. Berntson GG, Cacioppo JT, Quigley KS. Cardiac psychophysiology and autonomic space in humans: empirical perspectives and conceptual implications. Psychol Bull. 1993;114(2):296-322. 2. Fisher JP. Autonomic control of the heart during exercise in humans: role of skeletal muscle afferents. Experimental Physiology. 2014;99(2):300-5. 3. Weippert M, Behrens K, Rieger A, Stoll R, Kreuzfeld S. Heart Rate Variability and Blood Pressure during Dynamic and Static Exercise at Similar Heart Rate Levels. PLoS One. 2013;8(12). 4. White DW, Raven PB. Autonomic neural control of heart rate during dynamic exercise: revisited. J Physiol. 2014;592(Pt 12):2491-500.

Breathing Carbon Dioxide (4% for 1-Hour) Slows Response Selection, Not Stimulus Encoding

This experiment sought to determine whether breathing carbon dioxide (CO2), a toxic environmental stressor known to impair reaction time, slows human information processing in the stimulus encoding or response selection stage, or both, and whether this effect is influenced by time-on-task and exposure duration. In a 2 X 2 X 2 X 4 (Gas X Degradation X Compatibility X Time-on-Task) within-participants design, six highly practiced (more than 10,000 trials) healthy young male participants performed a serial choice reaction time (SCRT) task while breathing either 4% CO2 (with 50% O2) or room air (0.03% CO2 and 21% O2) for 60 minutes. Task variables manipulated were stimulus degradation (intact vs. degraded) and stimulus-response compatibility (high vs. low). Data from each 20-min SCRT test were subdivided into 5-min and 2-min intervals to determine the effects of time-on-task (and exposure duration). There were significant increases in SCRT from breathing carbon dioxide (p =.004), degrading the stimulus (p &lt;.001), lowering compatibility (p =.004), and increasing time-on-task (p =.020). Lowering compatibility served to exaggerate the impairment produced by carbon dioxide inhalation (p =.038). Time-on-task (and exposure duration), however, did not interact with gas, degradation, or compatibility. Thus, SCRT, analyzed according to the Additive Factors Method (Sternberg, 1969, 1998), (1) was sensitive to the degrading effects of breathing CO2 at an undetectable concentration that did not produce clinical symptoms, (2) determined the locus of this effect was associated with the response selection stage of processing, (3) demonstrated that the progressive deterioration in performance due to increases in time-on-task (and exposure duration) affects both the stimulus encoding and response selection stages in a similar manner, and (4) ruled out alternative explanations by showing the results did not vary with distribution analyses, data trimming, error analyses, and analyses for tradeoffs of speed-accuracy, SCRT-DT, and other performance operating characteristics.

The Relationship Between Pulse Count and Energy Expenditure at Submaximal Work Under Different Ambient Temperatures

Studies were carried out in on six soldiers to evaluate the energy expenditure submaximal work under three environmental temperatures of 22 degree C, 30 Degree C. The subjects were given a standard graded exercise of varying work loads from 200 to 600 kgm/mim on a bicycle ergometer. Pulse count, pulmonary ventilation, oxygen consumption, carbon dioxide elimination and breathing frequency were measured during rest and at each work load. Results indicated that oxygen consumption was not influenced by environment, whereas. pulse count was significantly influenced by environment, being highest for subjects at 37 degree C (P<0.01). The findings of the present study assess the likely effect of variation in environmental temperatures between 22 Degree C and 30 degree C, 22 degree C and 37 Degree C and 30 Degree C and 37 Degree C on the physiological respones to the submaximal type of exercise.

Preliminary results of a miniaturized respiratory sensor system used under hypergravity conditions up to 9 gz

Respiratory gas analyses are used to explore the influence of increased gravity on the physiology of breathing. Due to the mass, size and intricacy of standard measurement systems, previous studies were limited to a maximum acceleration of + 5 gz (head-to-foot direction). Furthermore, no in situ mainstream measurements of oxygen and carbon dioxide concentration were possible under hypergravity conditions so far. This paper shows a first study which demonstrates a respiratory sensor system developed at the Institute for Aerospace Engineering at TU Dresden. This system is suitable for an in situ measurement of respiratory changes up to + 9 gz (maximum acceleration of jet pilots) and therefore provides a possibility for detailed physiological analyses in future. Three jet pilots were equipped with this system and accelerated under a defined profile up to 7, 8 and + 9 gz. The breathing air flow, oxygen and carbon dioxide concentration were recorded with our miniaturized solid state electrolyte gas sensors, which are also described in this paper. The analysed data show significant changes of the measured respiratory parameters depending on the G-level, the acceleration rate (G-rate of onset [g s−1]) and the examination time.

Cardiac output monitoring

Minimally invasive and non-invasive methods of estimation of cardiac output (CO) were developed to overcome the limitations of invasive nature of pulmonary artery catheterization (PAC) and direct Fick method used for the measurement of stroke volume (SV). The important minimally invasive techniques available are: oesophageal Doppler monitoring (ODM), the derivative Fick method (using partial carbon dioxide (CO2 ) breathing), transpulmonary thermodilution, lithium indicator dilution, pulse contour and pulse power analysis. Impedance cardiography is probably the only non-invasive technique in true sense. It provides information about haemodynamic status without the risk, cost and skill associated with the other invasive or minimally invasive techniques. It is important to understand what is really being measured and what assumptions and calculations have been incorporated with respect to a monitoring device. Understanding the basic principles of the above techniques as well as their advantages and limitations may be useful. In addition, the clinical validation of new techniques is necessary to convince that these new tools provide reliable measurements. In this review the physics behind the working of ODM, partial CO2 breathing, transpulmonary thermodilution and lithium dilution techniques are dealt with. The physical and the physiological aspects underlying the pulse contour and pulse power analyses, various pulse contour techniques, their development, advantages and limitations are also covered. The principle of thoracic bioimpedance along with computation of CO from changes in thoracic impedance is explained. The purpose of the review is to help us minimize the dogmatic nature of practice favouring one technique or the other.

How quick is soon? Early response to continuous positive airway pressure: a randomized controlled trial

Numerous studies have confirmed that using non-invasive continuous positive airway pressure (nCPAP) for chronic obstructive pulmonary disease and congestive heart failure improves the respiratory rate, heart rate (HR), and work of breathing. We hypothesize that early application of nCPAP with concomitant medical therapy to patients with acute undifferentiated shortness of breath (SOB) will improve objective measures of respiratory distress. Specifically, early application of nCPAP can improve the tidal volume (TV), end-tidal carbon dioxide (EtCO2) and Rapid Shallow Breathing Index (RSBI), and reduce intubations over the standard of treatment alone in 15 minutes or less.

Breathing patterns, oxygen and carbon dioxide levels during infancy

Breathing patterns, oxygen and carbon dioxide levels during infancy

End expiratory oxygen concentrations to predict central venous oxygen saturation: an observational pilot study

BackgroundA non-invasive surrogate measurement for central venous oxygen saturation (ScVO2) would be useful in the ED for assessing therapeutic interventions in critically ill patients. We hypothesized that either linear or nonlinear mathematical manipulation of the partial pressure of oxygen in breath at end expiration (EtO2) would accurately predict ScVO2.MethodsProspective observational study of a convenience sample of hemodialysis patients age > 17 years with existing upper extremity central venous catheters were enrolled. Using a portable respiratory device, we collected both tidal breathing and end expiratory oxygen and carbon dioxide concentrations, volume and flow on each patient. Simultaneous ScVO2 measurements were obtained via blood samples collected from the hemodialysis catheter. Two models were used to predict ScVO2: 1) Best-fit multivariate linear regression equation incorporating all respiratory variables; 2) MathCAD to model the decay curve of EtO2 versus expiratory volume using the least squares method to estimate the pO2 that would occur at <20% of total lung capacity.ResultsFrom 21 patients, the correlation between EtO2 and measured ScVO2 yielded R2 = 0.11. The best fit multivariate equation included EtCO2 and EtO2 and when solved for ScVO2, the equation yielded a mean absolute difference from the measured ScVO2 of 8 ± 6% (range -18 to +17%). The predicted ScVO2 value was within 10% of the actual value for 57% of the patients. Modeling of the EtO2 curve did not accurately predict ScVO2 at any lung volume.ConclusionWe found no significant correlation between EtO2 and ScVO2. A linear equation incorporating EtCO2 and EtO2 had at best modest predictive accuracy for ScVO2.