Venous Partial Pressure Of CO2 Research Articles

Prospective randomized evaluation of transcutaneous carbon dioxide monitoring during complex electrophysiological procedures under deep sedation: the TRACES trial.

The field of interventional electrophysiology is rapidly growing. For safe and efficient procedures sedation is needed for patient comfort and immobility. However, sedative and analgesic agents can induce respiratory depression, risking hypercapnia, hypoxia, and hypotension. This study evaluates the impact of adding transcutaneous carbon-dioxide (CO2) monitoring to standard monitoring practices in electrophysiological procedures under deep sedation. This prospective, randomized study at Ulm University Heart Center included 726 patients undergoing treatment under deep sedation between August 2019 and October 2023. Patients were randomly assigned to standard monitoring or standard monitoring with continuous transcutaneous CO2 monitoring (TCM-group). Standard monitoring involved non-invasive blood pressure, oxygen saturation (SpO2), and frequent peripheral venous blood gas analysis. The primary composite endpoint was SpO2 dips below 90% and pathological changes in venous blood gas analysis. The TCM-group included 357 patients, and the standard group had 348. The primary composite endpoint was reached by 195 patients (54.8%) in the TCM-group and 195 patients (56.5%) in the standard group (p = 0.642). However, peripheral venous CO2 partial pressure increased by more than 30% from baseline more often in the standard group than in the TCM-group (p = 0.005). Additionally, a venous pH below 7.25 was more common in the standard group (p = 0.047). While transcutaneous CO2 monitoring offers no significant benefit for the primary combined endpoint over standard monitoring during electrophysiological procedures, it helps mitigate significant CO2 elevations and respiratory acidosis. ClinicalTrials.gov, NCT04038476, 29 July 2019.

Diagnostic utility of capnography in emergency department triage for screening acidemia: a pilot study

BackgroundCapnography is a quantitative and reliable method of determining the ventilatory status of patients. We describe the test characteristics of capnography obtained during Emergency Department triage for screening acidemia.ResultsWe performed an observational, pilot study of adult patients presenting to Emergency Department (ED) triage. The primary outcome was acidemia, as determined by the basic metabolic panel and/or blood gas during the ED visit. Secondary outcomes include comparison of estimated and measured respiratory rates (RR), relationships between end-tidal CO2 (EtCO2) and venous partial pressure of CO2, admission disposition, in-hospital mortality during admission, and capnogram waveform analysis. A total of 100 adult ED encounters were included in the study and acidemia (\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\left[HC{O}_{3}^{-}\\right]\\le 22 \ ext{mEq/L}$$\\end{document} or \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ pH< 7.35$$\\end{document}) was identified in 28 patients. The measured respiratory rate (20.3 ± 6.4 breaths/min) was significantly different from the estimated rate (18.4 ± 1.6 breaths/min), and its area under the receiver operating curve (c-statistic) to predict acidemia was only 0.60 (95% CI 0.51–0.75, p = 0.03). A low end-tidal CO2 (EtCO2 < 32 mmHg) had positive (LR+) and negative (LR−) likelihood ratios of 4.68 (95% CI 2.59–8.45) and 0.34 (95% CI 0.19–0.61) for acidemia, respectively—corresponding to sensitivity 71.4% (95% CI 51.3–86.8) and specificity 84.7% (95% CI 74.3–92.1). The c-statistic for EtCO2 was 0.849 (95% CI 0.76–0.94, p = 0.00). Waveform analysis further revealed characteristically abnormal capnograms that were associated with underlying pathophysiology.ConclusionsCapnography is a quantitative method of screening acidemia in patients and can be implemented feasibly in Emergency Department triage as an adjunct to vital signs. While it was shown to have only modest ability to predict acidemia, triage capnography has wide generalizability to screen other life-threatening disease processes such as sepsis or can serve as an early indicator of clinical deterioration.

Comparison of Blood Gas and Acid–Base Measurement in Arterial and Venous Blood Samples in Patients with Diabetic Ketoacidosis

Background Diabetic ketoacidosis (DKA) is one of the most severe complications of diabetes mellitus (DM). Arterial blood gas analysis (ABGA) has been used as a conclusive diagnostic test for DKA. However, ABGA sampling is technically challenging, painful and may cause multiple complications. Venous blood gas analysis (VBGA) is a minimally invasive alternative for ABGA; however, the correlation between ABGA and VBGA has been controversial. Thus, the correlation between arterial and venous pH, partial pressure of CO2 (PCO2), and bicarbonate (HCO3) was studied. Objective To determine whether VBGA can replace ABGA in the evaluation of patients presenting with DKA. Material and Methods The present observational study was carried out in 76 patients with DKA. Two samples for ABGA and VBGA were obtained from each patient as close to each other as possible and were immediately sent to the laboratory. Data analysis was done using Pearson’s correlation coefficient (R) and Bland and Altman plots. Results The Bland and Altman plots and Pearson’s correlation coefficient depicted excellent agreement between arterial and venous pH (R = 0.69) and acceptably good agreement between arterial and venous PCO2 (R = 0.93) and HCO3 (R = 0.82). Conclusion Thus, VBGA can be used in the initial diagnosis and evaluation of DKA, allowing the utilisation of a minimally invasive, safer option to ABGA.

High venous to arterial CO2 gap is related to cardiovascular death in cardiogenic shock

Abstract Funding Acknowledgements Type of funding sources: None. Background Venous to arterial CO2 gap (CO2gap) is calculated by subtracting partial pressure of arterial CO2 to central venous partial pressure of CO2 (ScvCO2). This marker has been studied in septic shock and indicates hypoperfusion when exceeds 6mmHg. Its kinetics and applicability in cardiogenic shock (CS) are unclear, being mixed/central venous saturation and lactate more commonly used. Purpose The objective of the study is to describe CO2gap kinetics in patients with CS. Secondary objective is to analyze if CO2gap is as marker of prognosis in CS. Methods Prospective observational study that included patients admitted for CS in the Acute Cardiovascular Care Unit of a tertiary hospital. Gasometric samples were obtained at admission, 6, 12, 24 and 48 hours from the onset of shock. In-hospital mortality was registered. Results We included 40 patients with CS during 1 year. Most patients were male (80%), average age was 68 years. There was a high incidence of cardiac arrest (58%), most frequent cause of CS was STEMI (45%), in-hospital mortality was 45%, most cases from non-cardiovascular causes (61%). Refractory shock was frequent (28%). Average lactate peak was 6.02 mmol / L. CO2gap kinetics consisted in a peak at admission (8.8mmHg), a valley 6h (7.7mmHg), new peak at 12h (8.5mmHg) and progressive decrease at at 24 (6.8mmHg) and 48h (5.7 mmHg). Significantly, higher CO2gap values at admission (10.97mmHg vs 8.16mmHg, p = 0.007) was predictor of cardiovascular mortality. Lactate values at 6, 12 and 48 hours were also predictors of cardiovascular mortality, as well as ScvO2 at admission. Conclusions Patients with CS present with high CO2gap values during first hours of admission. The kinetics of this marker consists in two peaks at admission and 12 hours from CS onset, a valley at 6 hours and a progressive decrease at 24 and 48 hours. Its determination at admission is associated with cardiovascular mortality. We suggest the potential benefit of combining this marker, along with lactate and ScvO2 values, to guide management of patients with CS. Abstract Figure. CO2 gap and cardiovascular mortality

Paramètres dérivés du CO2 pour évaluer l’état hémodynamique chez le malade de réanimation

Le dioxyde de carbone (CO2) constitue le produit de dégradation final du métabolisme cellulaire. Plusieurs gradients de CO2, obtenus grâce à la mesure de la pression partielle de CO2 (PCO2) dans différents compartiments, sont utilisés afin d’évaluer l’état circulatoire des patients de réanimation. Au cours d’un état de choc, l’augmentation de la PCO2 veineuse et tissulaire est principalement la conséquence d’une hypoperfusion tissulaire et non d’une hypoxémie, reflétant ainsi une anomalie macro et/ou microcirculatoire. Un gradient veino-artériel de PCO2 (Pv-aCO2) ≥ 6 mmHg peut suggérer une inadéquation du débit cardiaque. À l’échelle locale, un gradient tissu-artériel en PCO2 (Pt-aCO2) élevé malgré un Pv-aCO2 normal (&lt; 6 mmHg) peut faire évoquer une atteinte de la microcirculation locale. Enfin, un indice combiné des paramètres dérivés du CO2 et de l’O2, comme le rapport entre le Pv-aCO2 et la différence des contenus artériel et veineux en oxygène (Pv-aCO2 / CaO2 – CvO2), suggère une hypoxie tissulaire lorsqu’il dépasse 1,4. Chez les patients de réanimation en insuffisance circulatoire, les paramètres dérivés du CO2 doivent toutefois s’intégrer dans une approche multiparamétrique (examen clinique, marqueurs biologiques, échocardiographie et autres outils hémodynamiques).

Efficacy of Noninvasive Positive Pressure Ventilation for Improving the Respiratory Function, Use of Accessory Respiratory Muscles, Quality of Sleep and Nutrition of Cystic Fibrosis Patients

Background: Respiratory failure secondary to recurrent respiratory infections is the most common cause of death in Cystic fibrosis (CF). Objectives: To assess the efficacy of noninvasive positive pressure ventilation (NIPPV) on respiratory function, use of accessory respiratory muscles, ease of physiotherapy for respiratory clearance, quality of sleep and nutritional status in CF patients with respiratory failure. Methods: All CF patients admitted to the pediatric department of Masih Daneshvari hospital, Tehran from March 2015 to January 2016 were studied. The inclusion criteria were clinical evidence of respiratory distress and signs of respiratory acidosis. The exclusion criteria were nausea and vomiting, not tolerating NIPPV, need for intubation, pneumothorax, presence of giant bullous emphysema or decreased level of consciousness. Baseline spirometry and venous blood gas (VBG) was obtained before and after NIPPV. A simple questionnaire was filled out for the nutritional status, sleep quality, ease of physiotherapy for airway clearance and the volume of secretions after NIPPV compared to baseline. Paired samples t-test and Wilcoxon Signed Rank test in SPSS version 16 were used for the before and after comparison of numerical and ordinal variables, respectively. Results: Out of a total of 53 CF hospitalized patients 17 met the inclusion criteria. There were 10 (58.8%) males and 7 (41.1%) females with a mean age of 11 ± 4.57 (10 - 25) years, mean weight of 31.85 ± 10.11 (13 - 48) kg and mean BMI of 14.16 ± 2.71 (5.9 - 18). The mean Saturation of peripheral oxygen (SPO2), respiratory rate (RR) and mean partial pressure of CO2 (PCO2) of patients before the intervention were 75 ± 13.25% (52 - 90%), 32 ± 11.17 (22 - 55) mmHg and 55.20 ± 17.62 (30.3 - 108), mmHg respectively. A significant difference was noted after the intervention in SPO2, venous PCO2 and RR compared to baseline (P < 0.05). The change in sleep quality (P = 0.001), nutritional status (P = 0.001) and ease of physiotherapy for respiratory clearance (P = 0.008) after NIPPV was statistically significant while the change in use of accessory respiratory muscles (P = 0.785) and the volume of secretions (P = 0.1) was not significant. Conclusions: NIPPV in CF patients with respiratory failure can improve the respiratory function, sleep quality and nutritional status of patients. Also, NIPPV enhances airway clearance during respiratory physiotherapy.

The Importance of Acid-base Analysis in Dogs Whit Orthopedic Procedures Under General Anesthesia (P)

Venous blood gases analysis provides information on acid-base status and ventilation (venous partial pressure of CO2) (Reiss A.2009). General anaesthesia reduces the oxygenation degree of blood (Grimm K.A. 2010), and SpO2 analysis by trans cutaneous monitor does not approximate correctly the level of oxygenation from the patient’s body (Linda S.Barter 2011).

Use of a medetomidine-ketamine combination for anesthesia in captive common hippopotami (Hippopotamus amphibius)

To establish an anesthetic protocol suitable for surgical interventions in hippopotami (Hippopotamus amphibius). Prospective case series. 10 adult male hippopotami undergoing castration. A combination of medetomidine (60 to 80 mg/kg [27.3 to 36.4 mg/lb]) and ketamine (1 mg/kg [0.45 mg/lb]) was administered IM on the basis of mean estimated weights of 1,330 ± 333 kg (2,926 ± 733 lb; median, 1,350 kg [2,790 lb]; range, 900 to 2,000 kg [1,980 to 4,400 lb]). Monitoring included sequential blood gas analyses, pulse oximetry, and capnography. Reversal of anesthesia with atipamezole (0.34 ± 0.06 mg/kg [0.15 ± 0.027 mg/lb]; median, 0.33 mg/kg [0.15 mg/lb]; range, 300 to 500 mg total dose]) was uneventful and rapid in all cases. Complete immobilization and a surgical anesthetic plane were achieved 27 ± 11.8 minutes (median, 24.5 minutes [range, 14 to 44 minutes]) after initial injection. Anesthesia (97.3 ± 35.3 minutes; median, 95 minutes [range, 57 to 188 minutes]) was maintained with 3.4 ± 2.2 (median, 3) additional doses of ketamine (0.1 to 0.4 mg/kg [0.045 to 0.18 mg/lb]). Transitory apnea of 4.71 ± 2.87 minutes (median, 4 minutes [range, 1 to 9 minutes]) was documented in 5 animals. Apnea during anesthesia was viewed as a physiologic condition in this semiaquatic mammal because related vital parameters (heart rate, pH, peripheral hemoglobin oxygen saturation as measured by pulse oximetry, venous partial pressure of CO(2), and lactate and HCO(3) concentrations) remained unchanged and did not differ significantly than those parameters for the 5 animals with continuous respiration. Both in captivity and in the wild, common hippopotami are difficult to anesthetize. The combination of medetomidine and ketamine provided an excellent surgical plane of anesthesia and a self-limiting dive response.

Tidal breathing model describing end-tidal, alveolar, arterial and mixed venous CO2 and O2

Thermodilution is the current standard for determination of cardiac output. The method is invasive and constitutes a risk for the patient. As an alternative CO2 rebreathing allows non-invasive cardiac output estimation using Ficks principle. The method relies on estimation of arterial CO2 partial pressure from end-tidal CO2 pressure and estimation of mixed venous CO2 partial pressure from end-tidal CO2 during rebreathing. Presumably the oxygenation of blood in the lung capillaries increases lung capillary CO2 pressure due to the Haldane effect, which during rebreathing may result in overestimation of the mixed venous CO2 pressure. However, the Haldane effect is not discussed in the current litterature describing cardiac output estimation using CO2 rebreathing. The purpose of this study is to construct and verify a compartmental tidal breathing lung model to investigate the physiological mechanisms that influence the CO2 rebreathing technique. The model simulations show agreement with previous studies describing end-tidal to arterial differences in CO2 pressure and rebreathing with high and low O2 fractions in the rebreathing bag. In conclusion the simulations show that caution has to be taken when using end-tidal measurements to estimate CO2 pressures, especially during rebreathing where the Haldane effect causes an overestimated mixed venous CO2 partial pressure.

Dietary sodium bicarbonate, cool temperatures, and feed withdrawal: impact on arterial and venous blood-gas values in broilers

Sodium bicarbonate (NaHCO3) has been used successfully in mammals and birds to alleviate pulmonary hypertension. Experiment 1 was designed to provide measurements of arterial and venous blood-gas values from unanesthetized male broilers subjected to a cool temperature (16 degrees C) challenge and fed either a control diet or the same diet alkalinized by dilution with 1% NaHCO3. The incidences of pulmonary hypertension syndrome (PHS, ascites) for broilers fed the control or bicarbonate diets were 15.5 and 10.5%, respectively (P = 0.36, NS). Non-ascitic broilers fed the control diet were heavier than those fed the bicarbonate diet on d 49 (2,671 vs. 2,484 g, respectively); however, other comparisons failed to reveal diet-related differences in heart weight, pulse oximetry values, electrocardiogram amplitudes, or blood-gas values (P > 0.05). When the data were resorted into categories based on right:total ventricular weight ratios (RV:TV) indicative of normal (RV:TV < 0.28) or elevated (RV:TV > or = 0.28) pulmonary arterial pressures, broilers with elevated RV:TV ratios had poorly oxygenated arterial blood that was more acidic, had high partial pressure of CO2 (PCO2), and had higher HCO3 concentrations when compared with broilers with normal RV:TV ratios. Experiment 2 was conducted to determine if metabolic variations associated with differences in feed intake or environmental temperature potentially could mask an impact of diet composition on blood-gas values. Male broilers maintained at thermoneutral temperature (24 degrees C) either received feed ad libitum or had the feed withdrawn > or = 12 h prior to blood sampling. Broilers fed ad libitum had lower venous saturation of hemoglobin with O2, higher venous PCO2, and higher arterial HCO3 concentrations than broilers subjected to feed withdrawal. Broilers in experiment 2 fed ad libitum and exposed to cool temperatures (16 degrees C) had lower arterial partial pressure of O2 and higher venous PCO2 than broilers fed ad libitum and maintained at 24 degrees C. Overall, these results demonstrate that changes in diet composition (control vs. 1% NaHCO3 diets) had minimal impact on arterial and venous blood-gas variables when compared with the more dramatic differences associated with feed intake (ad libitum vs. > or = 12 h withdrawal), environmental temperature (24 vs. 16 degrees C), and the pathogenesis associated with PHS (RV:TV < 0.28 vs. > or = 0.28).

Effects of CO2 anaesthesia on central nervous system activity in swine.

The objective of the study was to examine the changes in central nervous system (CNS) activity and physical behaviour during induction and awakening from CO2 anaesthesia. Two studies, each using pigs immersed into 90% CO2 gas for a period of 60 s were performed. In study 1, we monitored middle latency auditory evoked potentials (changes in latencies, amplitudes and a depth of anaesthesia index), electroencephalographic parameters (delta, theta, alpha and beta electroencephalographic power and 95% spectral edge frequency) and heart rate; and in study 2, we monitored body movements and arterial and venous partial pressure of CO2 and O2. No behavioural signs of distress were observed during the early part of the induction. The swine exhibited muscular activity from 13-30 s after induction-start as well as during awakening from anaesthesia, possibly because of a transitory weaker suppression of the brain stem than of the cortex. The CNS and blood gas parameters started to change from the very start of induction. The CNS suppression lasted only approximately one minute after the end of the induction period. The two studies indicated a good temporal relationship between changes in amplitude, depth of anaesthesia index, spectral edge frequency, and arterial PCO2 during the induction period.

Effect of twin-to-twin delivery interval on umbilical cord blood gas in the second twins.

To examine the effect of twin-to-twin delivery interval on the umbilical cord blood gas status of the second twin following vaginal delivery. A retrospective study. The department of obstetrics and gynaecology in a university teaching hospital. Twin deliveries at or beyond 34 weeks of gestation over a period of five years, with the first twin delivered vaginally. Twins with any antepartum complications including discordant growth, intrauterine growth restriction, intrauterine death, fetal malformations and pre-eclampsia were excluded. The correlation between the twin-to-twin delivery interval, and both the umbilical arterial and venous blood gas parameters of the second twin, including pH, partial pressure of CO2 and base excess, were studied. A total of 118 cases were reviewed. The mean gestation at delivery was 37.1 weeks. The median twin-to-twin delivery interval was 16.5 minutes. There were significant negative correlations between twin-to-twin delivery interval and both the umbilical cord arterial and venous pH and base excess of the second twin (P <0.05). There were also significant positive correlations between both arterial and venous partial pressure of CO2 and the delivery interval (P <0.05). Similar changes were found even if the analyses were limited to those who had normal vaginal deliveries. The umbilical arterial pH of Twin 2 was <7.00 in none of the cases delivered within 15 minutes of the birth of Twin 1, 5.9% if within 16-30 minutes, and 27% if more than 30 minutes. Among those with an inter-twin delivery interval of more than 30 minutes, 73% had cardiotocographic evidence of fetal distress which required operative delivery. Umbilical cord arterial and venous values of pH, partial pressure of CO2 and base excess of the second twin deteriorate with increasing twin-to-twin delivery interval. Risks of fetal distress and acidosis in the second twin are high when the twin-to-twin delivery interval is beyond 30 minutes.

A NOVEL HOLLOW FIBER MEMBRANE

The efficacy of a new polymethylpentene (PMP) hollow fiber membrane (inner diameter of 200μm and wall thickness of 90μm) was tested with an intravenous oxygenator and carbon dioxide removal prototype. The prototypes consisted of a polyurethane potted bundle of crimped hollow fibers with a membrane surface area of 0.38m2. The prototypes (two groups of n=3) gas transfer performance was tested using a buffered cristalloyd solution (pH=7.4) in a completely automated in vitro system. Each one was placed in a plexyglass chamber (inner diameter of 20mm) as host vessel. Oxygen and carbon dioxide transfer values (VO2, VCO2) were calculated and displayed continuosly at different liquid flow rates through the chamber (Qb=1; 2; 3; 5l/min) and gas flow rates (Qg=1; 3; 51/min). Permissive hypercapnia was modelized increasing venous CO2 partial pressure (pCO2=45; 60; 90mmHg). Liquid pressure drop in the chamber was also measured (ΔP mmHg). Gas transfer values were compared at the same conditions, with three other prototypes (with identical membrane surface area) made with polypropylene (PP) hollow fibers (inner diameter of 240μm and wall thickness of 30μm). Maximal and minimal gas transfer mean values are resumed in the following table:TableMaximal mean ΔP (for Qb= 5 l/min) for PP prototypes is 17.3±2.5mmHg and ΔP=28.71±6.1mmHg for those made with PMP. These results demonstrate a better performance of PMP fibers for O2 transfer. Besides, experiments showed an adequate capacity for CO2 transfer. Their smaller inner diameter and the higher hollow fiber densitiy in the chamber (derived from their bigger outer diameter) are effective ways to increase O2 transfer.

An evaluation of exercise cardiac output using the CO2 rebreathing extrapolation technique.

We investigated the reproducibility of the carbon dioxide (CO2) rebreathing extrapolation technique of Defares to determine the mixed venous partial pressure of CO2 (PvCO2) using a direct, rather than the commonly used indirect, extrapolation method. The PvCO2 determinations were made five times a day on four subjects who exercised for 4 h daily on a bicycle ergometer over a period of 13 days. The concentration of CO2 in the rebreathing bag was monitored continuously using a rapid-response infrared capnograph. The mean standard deviation was 1.56 mmHg (0.21 kPa) for a mean PvCO2 of 47.6 mmHg (6.3 kPa), giving a mean coefficient of variation of 3.3%. This level of reproducibility agrees favourably with the reliability of direct measurements of pulmonary arterial partial pressure of CO2. We conclude that the CO2 rebreathing extrapolation technique can give reproducible PvCO2 values when a direct method of extrapolation is used.

Influence of stimulation parameters on the release of adenosine, lactate and CO2 from contracting dog gracilis muscle.

1. The addition of adenosine, CO2 and lactate to the venous blood draining an isolated constant-flow perfused gracilis muscle was studied in anaesthetized and artificially ventilated dogs during twitch and tetanic contractions. 2. Venous adenosine concentration increased from 154 +/- 33 nM (mean +/- S.E.M.) to 279 +/- 121 or 280 +/- 125 nM after 10 min of 1.5 or 3 Hz twitch contractions and to 240 +/- 120 or 276 +/- 139 nM after 10 min of 1 or 5 s tetani occurring at 0.1 Hz. Twitch contractions at 0.1 or 0.5 Hz for 10 min did not significantly elevate venous adenosine. 3. Venous lactate concentration was significantly increased after 10 min of 1.5 or 3 Hz twitches or 5 s tetani at 0.1 Hz. There was a good correlation (r = 0.70; P < 0.001) between venous adenosine and lactate concentrations. 4. Venous partial pressure of CO2 (PCO2) was significantly elevated after 10 min of 1.5 or 3 Hz twitch contractions or 1 or 5 s tetani at 0.1 Hz. There was also a good correlation (r = 0.58; P < 0.001) between venous adenosine concentration and PCO2. 5. Venous partial pressure of O2 (PO2) decreased during all contractions except those at 0.1 Hz, but the oxygen cost per unit of tension x time was similar during every pattern of stimulation, and the percentage of the total energy production achieved by anaerobic means during muscle contractions did not exceed that at rest, indicating that there had been no limitation to the oxygen supply. Venous PO2 was poorly correlated with venous adenosine concentration (r = 0.28), but quite well correlated with venous lactate concentration (r = 0.53; P < 0.001). If the indirect influence of PO2 on venous adenosine concentration via an increase in lactate concentration was eliminated by partial correlation, then the coefficient for the relationship between venous adenosine concentration and venous PO2 became 0.15. 6. There was a significant correlation between the venous adenosine concentration and the venous pH (r = 0.53; P < 0.001). If the influence of oxygenation on venous adenosine and pH was eliminated by partial correlation, the coefficient for the relationship between venous adenosine and pH increased to 0.95.(ABSTRACT TRUNCATED AT 400 WORDS)

Halothane-sensitivity gene and muscle contractile properties in malignant hyperthermia.

Malignant hyperthermia (MH) results from the presence of the halothane-sensitivity gene and is characterized by abnormalities in muscle function. Populations of genetically defined pigs were used to determine the in vivo and in vitro expression of this gene in both the homozygous and the heterozygous condition. On exposure to halothane, isolated muscle bundles from the homozygous halothane-sensitive pigs exhibited decreased tetanus tension and increased tetanus half-relaxation time and contracture and were clearly distinguished from homozygous normal muscles. The heterozygous and homozygous normal muscles were similar in contractile responses except for the occurrence of halothane-induced contractures in the heterozygotes. The heterozygous halothane-negative pigs did not exhibit the characteristic signs of an MH episode in response to halothane succinylcholine, although some metabolic responses were significantly altered (e.g., increased venous partial pressure of CO2 and arterial and venous K+ concentration). Thus the heterozygous pigs were not MH susceptible but did represent a phenotype distinct from the homozygous normal pigs both in vitro and in vivo. These data provide the first convincing evidence for the expression of the halothane-sensitivity gene in heterozygotes.

Arterial and Mixed Venous Blood Gas Status during Apnoea of Intubation — Proof of the Christiansen-Douglas-Haldane Effect in Vivo

The Christiansen-Douglas-Haldane effect, in short the Haldane effect, describes the dependence of the CO2 binding of blood on the degree of oxygenation of haemoglobin. Under the physiological conditions of an 'open' system between blood and alveoli the partial pressure of arterial CO2 (PaCO2), must be less than that of mixed venous blood (PvCO2). During the unphysiological conditions of a 'closed' system, e.g. hyperoxic apnoea, i.e. continuous oxygen uptake without CO2 delivery by the lungs, the PaCO2 will not only approximate the PvCO2 but will even exceed it. Without the Haldane effect, rapid adjustment of PaCO2 to PvCO2 would be expected during apnoea due to the lack of CO2 excretion. If, however, as undertaken in this study, ongoing oxygenation (high alveolar PO2 (PACO2) with concomitant lack of CO2 delivery (apnoea, i.e. the CO2 concentration remains constant) lead to a continuing sufficient oxygenation of blood during its passage through the lung capillaries, then this leads to a rightwards shift of the CO2 binding curve--the Haldane effect. The resulting increase in PCO2 as shown here actually leads to an arterial-mixed venous CO2 partial pressure difference (avDPCO2) of 2.8 +/- 1.8 mmHg. The results described substantiate for the first time the existence of the Haldane effect under clinical conditions.

The relationship between the ventilation and lactate thresholds following normal, low and high carbohydrate diets.

Five men performed an incremental exercise test following a normal, low and high carbohydrate dietary regimen over a 7-day period, to examine the influence of an altered carbohydrate energy intake on the relationship between the ventilation (VET) and lactate (LaT) thresholds. VET and LaT were determined from the ventilatory equivalents for O2 (VE.VO2(-1) and CO2 (VE.VCO2(-1) and the log-log transformation of the lactate (La) to power output relationship, respectively. The total duration of the incremental exercise test, carbon dioxide output (VCO2), respiratory exchange ratio, blood La values and arterialized venous partial pressure of CO2 (PCO2) were reduced, and VE.VCO2(-1), the slope of the VE-VCO2 relationship, blood beta-hydroxybutyrate and pH were increased during the low carbohydrate trial compared with the other conditions. Total plasma protein and Na+, K+, and Cl- were similar across conditions. LaT and VET were unaffected by the altered proportions of carbohydrate in the diets and occurred at a similar oxygen consumption (mean VO2 across trials was 1.98 L.min-1 for VET and 2.01 L.min-1 for LaT). A significant relationship (r = 0.86) was observed for the VO2 that represented individual VET and LaT values. The increased VE.VCO2(-1) and slope of the VE-VCO2 relationship could be accounted for by the lower PCO2. It is concluded that alterations in carbohydrate energy intake do not produce an uncoupling of VET and LaT as has been reported previously.

Cardiorespiratory responses to hypoxia in intact and bilaterally vagotomized pigeons.

Bilateral, cervical vagotomy in birds denervates, among other receptors, the carotid bodies. To test whether such neural section removes sensitivity to hypoxia, we measured respiratory, cardiovascular, and blood gas responses to hypoxia at 84-, 70-, and 49-Torr inspiratory O2 partial pressure (PIO2) in five pigeons with intact vagi and in five bilaterally, cervically vagotomized pigeons. Normoxic respiratory frequency (fresp) and expiratory flow rate (VE) were decreased after vagotomy. Intact pigeons showed large increases in VE in response to hypoxia, effected mostly by increases in fresp. VE also increased greatly in response to hypoxia in vagotomized pigeons, but increases were largely the result of tidal volume. O2 consumption, CO2 production, and respiratory exchange ratio increased slightly in all pigeons during hypoxia. Normoxic heart rate was greater after vagotomy; cardiac output increased in all pigeons in response to hypoxia, but stroke volume increased only in intact pigeons. During normoxia, arterial and mixed venous O2 partial pressure, O2 concentration, and pH were lower and arterial and mixed venous CO2 partial pressure was higher, after vagotomy. In all pigeons during hypoxia, arterial and mixed venous O2 and CO2 partial pressure and O2 concentration decreased and arterial and mixed venous pH increased; changes were roughly parallel in intact and vagotomized pigeons. The arteriovenous O2 concentration differences during normoxia and hypoxia were similar in all pigeons. We conclude that bilateral, cervical vagotomy in the pigeon causes hypoventilation and tachycardia during normoxia, but strong respiratory and cardiovascular responses to hypoxia are still present.

Plasma volume and proteins in voluntary hyperventilation

In a controlled study the changes of the plasma volume and plasma proteins induced by voluntary hyperventilation (HV) were investigated in nine splenectomized volunteers. The plasma volume changes were calculated from the changes of the hemoglobin and hematocrit. After 20 min of HV in supine position, which lead to a decrease of the venous CO2 partial pressure by 19 Torr and to an increase of plasma epinephrine and norepinephrine levels, the plasma volume was reduced by 12.9%. The intravascular masses of total protein, albumin, and several other proteins decreased during HV but a similar decrease of these proteins was also observed during the control study (C), i.e., rest in supine position without HV. The differences between changes during HV and C were not significant, indicating that the loss of protein was not due to HV. It is concluded that acute HV leads to a rapidly reversible loss of a virtually protein-free solution from the vascular space. The red cell compartment participated in fluid shifts in that the mean red cell volume decreased by 2.2% (P less than 0.02 compared with C). Comparison with earlier work shows that addition of erythrocytes from the normal spleen does not play a part in the HV-induced increase of hemoglobin and hematocrit.