Low pCO2 Levels Research Articles

Analyses of pre-injection reservoir data for stable carbon isotope trend predictions in CO2 monitoring: preparing for CO2 injection

Baseline monitoring at the proposed enhanced gas recovery site in Altmark (Germany) was carried out in combination with theoretical and laboratory investigations to describe and predict the principles of expected stable carbon isotope and dissolved inorganic carbon (DIC) trends during CO2 injection in reservoirs. This provides fundamental data for site-specific characterisation for monitoring purposes. Baseline δ13C values at the Altmark site ranged between −1.8 and −11.5 ‰ and DIC values were about 2 mmol L−1. These baseline values form the basis for a theoretical study on the influences of the ambient reservoir conditions on the state of geochemical and isotope equilibrium of the reservoir fluids. Transferring this theoretical study to the Altmark site enables predictions on geochemical trends during potential injection. Assuming that CO2 would be injected at the Altmark site to pCO2 = 100 bar and with a δ13C of −30 ‰, at isotopic and geochemical equilibrium, δ13CDIC values would approach this end-member, and DIC concentrations of 1,000 mmol L−1 would be expected. Laboratory experiments were conducted at low pCO2 levels (4–35 bars) to mimic the approach of a CO2 plume at a monitoring well. These results support field investigations from other sites: that δ13CDIC is a sensitive tool for monitoring CO2 migration in the subsurface and simultaneously allows quantification of geochemical trapping of CO2.

Feeding lactate for CHO cell culture processes: Impact on culture metabolism and performance

Lactate has long been regarded as one of the key metabolites of mammalian cell cultures. High levels of lactate have clear negative impacts on cell culture processes, and therefore, a great amount of efforts have been made to reduce lactate accumulation and/or to induce lactate consumption in the later stage of cultures. However, there is virtually no report on the impact of lactate depletion after initial accumulation. In this work, we observed that glucose uptake rate dropped over 50% at the onset of lactate consumption, and that catabolism of alanine due to lactate depletion led to ammonium accumulation. We explored the impact of feeding lactate as well as pyruvate to the cultures. In particular, a strategy was employed where CO(2) was replaced by lactic acid for culture pH control, which enabled automatic lactate feeding. The results demonstrated that lactate or pyruvate can serve as an alternative or even preferred carbon source during certain stage of the culture in the presence of glucose, and that by feeding lactate or pyruvate, very low levels of ammonia can be achieved throughout the culture. In addition, low levels of pCO(2) were also maintained in these cultures. This was in strong contrast to the control cultures where lactate was depleted during the culture, and ammonia and pCO(2) build-up were significant. Culture growth and productivity were similar between the control and lactate-fed cultures, as well as various product quality attributes. To our knowledge, this work represents the first comprehensive study on lactate depletion and offers a simple yet effective strategy to overcome ammonia and pCO(2) accumulation that could arise in certain cultures due to early depletion of lactate.

Volume Limitation Reduces Early Significant Hypocarbia in Preterm Ventilated Infants in a Busy Tertiary Neonatal Setting

Background and Aims: Hypocarbia in preterm infants affects neurodevelopmental outcome. We showed by repeated audit that preterm ventilated infants were routinely running low CO2 ( 7.5). table Conclusions: Volume limitation successfully reduced the number of blood gases with very low levels of pCO2 where education had failed. This was achieved without any increase in gases with a high pCO2. This method has been easily understood by a team experienced only in pressure limited ventilation. Other units that currently pressure ventilate may like to consider this method of helping to achieve targeted CO2 values without the need to switch to volume ventilation.

Air—sea flux of CO2 in arctic coastal waters influenced by glacial melt water and sea ice

Annual air–sea exchange of CO2 inYoung Sound,NEGreenlandwas estimated using pCO2 surface-water measurements during summer (2006–2009) and during an ice-covered winter 2008. All surface pCO2 values were below atmospheric levels indicating an uptake of atmospheric CO2. During sea ice formation, dissolved inorganic carbon (DIC) content is reduced causing sea ice to be under saturated in CO2. Approximately 1% of the DIC forced out of growing sea ice was released into the atmosphere while the remaining 99% was exported to the underlying water column. Sea ice covered the fjord 9 months a year and thereby efficiently blocked air–sea CO2 exchange. During sea ice melt, dissolution of CaCO3 combined with primary production and strong stratification of the water column acted to lower surface-water pCO2 levels in the fjord. Also, a large input of glacial melt water containing geochemically reactive carbonate minerals may contribute to the low surface-water pCO2 levels. The average annual uptake of atmospheric CO2 was estimated at 2.7 mol CO2 m−2 yr−1 or 32 g C m−2 yr−1 for the study area, which is lower than estimates from the Greenland Sea. Variability in duration of sea ice cover caused significant year-to-year variation in annual gas exchange.

Variations in leatherback turtle nest environments: consequences for hatching success

Physical and biological conditions of nests in which sea turtle embryos develop can vary among and within nesting beaches. Monitoring these conditions and their effects on embryonic development should be considered when assessing conservation efforts to increase sea turtle hatch- ling production. Sandy Point National Wildlife Refuge (SPNWR), St. Croix, US Virgin Islands, hosts a leatherback turtle Dermochelys coriacea nesting colony that has increased exponentially in the past 2 decades, due in part to an ongoing egg relocation program. We characterized the influence of nest environment conditions (e.g. partial pressures of oxygen, pO2, and carbon dioxide, pCO2, and tem- perature) on hatching success of relocated eggs at 3 different sites at SPNWR to evaluate potential intra-beach variation in nest environment conditions and hatching success. Although nest conditions varied significantly among sites, hatching success did not vary significantly among relocation sites. Among all clutches and sites, hatching success varied significantly with minimum pO2, maximum pCO2, and maximum temperatures measured in leatherback nests. Thus, leatherback embryos col- lectively affected their nest environment (i.e. decreased pO2, increased pCO2, and temperature), and appeared to show developmental sensitivity to low pO2 and high levels of pCO2 and temperature in nests. Our study shows the importance of considering sea turtle nest environment conditions when designing and executing beach-based conservation strategies such as egg relocation programs.

Excitability of human motor and visual cortex before, during, and after hyperventilation

In humans, hyperventilation (HV) has various effects on systemic physiology and, in particular, on neuronal excitability and synaptic transmission. However, it is far from clear how the effects of HV are mediated at the cortical level. In this study we investigated the effects of HV-induced hypocapnia on primary motor (M1) and visual cortex (V1) excitability. We used 1) motor threshold (MT) and phosphene threshold (PT) and 2) stimulus-response (S-R) curves (i.e., recruitment curves) as measures of excitability. In the motor cortex, we additionally investigated 3) the intrinsic inhibitory and facilitatory neuronal circuits using a short-interval paired-pulse paradigm. Measurements were performed before, during, and after 10 min of HV (resulting in a minimum end-tidal Pco(2) of 15 Torr). HV significantly increased motor-evoked potential (MEP) amplitudes, particularly at lower transcranial magnetic stimulation (TMS) intensities. Paired-pulse stimulation indicated that HV decreases intracortical inhibition (ICI) without changing intracortical facilitation. The results suggestthat low Pco(2) levels modulate, in particular, the intrinsic neuronal circuits of ICI, which are largely mediated by neurons containing gamma-aminobutyric acid. Modulation of MT probably resulted from alterations of Na(+) channel conductances. A significant decrease of PT, together with higher intensity of phosphenes at low stimulus intensities, furthermore suggested that HV acts on the excitability of M1 and V1 in a comparable fashion. This finding implies that HV also affects other brain structures besides the corticospinal motor system. The further exploration of these physiological mechanisms may contribute to the understanding of the various HV-related clinical phenomenona.

Nasal Congestion and Hyperventilation Syndrome

This article evaluates the prevalence of hyperventilation syndrome (HVS) in patients who continue to complain of ongoing nasal congestion, despite an apparently adequate surgical result and appropriate medical management. Prospective case series of 14 patients from June 2002 to October 2003 was performed. Patients, who presented complaining of nasal congestion after previous nasal surgery and who appeared to have an adequate nasal airway with no evidence of nasal valve collapse, were evaluated for HVS. When appropriate, nasal steroids and oral antihistamines also had been tested without success. Three patients had end-tidal P(CO2) levels measured and five patients underwent breathing reeducation. All patients had an elevated respiratory rate (>18 breaths/minute) with an upper thoracic breathing pattern. Twelve of the 14 patients complaining of nasal obstruction had an elevated Nijmegen score indicative of HVS. An average number of 2.5 procedures had been performed on each patient. End-tidal P(CO2) levels were < or = 35 mmHg in the three patients who had expired P(CO2) levels measured. Breathing retraining was successful in correcting the nasal congestion in two of five patients. HVS should be included in the differential diagnosis of patients presenting with nasal congestion, particularly after failed nasal surgery. One possible explanation is increased nasal resistance secondary to low arterial P(CO2) levels. Another possible explanation is reduced alae nasae muscle activity secondary to the reduced activity of serotonin-containing raphe neurons. Additional surgery may not necessarily be the answer in HVS patients complaining of nasal congestion.

The Role of the Intrauterine and Perinatal Environment in Cerebral Palsy

Author Disclosure Drs Paneth, Korzeniewski, and Hong did not disclose any relationships relevant to this article. After completing this article, readers should be able to: 1. Discuss the prevalence of cerebral palsy (CP) in school-aged children. 2. Describe the role of neuroimaging in CP. 3. Describe the impact of ventilatory practices in low-birthweight infants on the risk of CP. 4. Delineate the role of infection and fetal inflammation in pregnancy in the development of CP. The special importance of CP to clinicians whose practices encompass pregnancy and the perinatal or neonatal period is that no other neurodevelopmental disorder bears as close a causal relationship to the hazards of intrauterine and perinatal life. Although the strength of that relationship has been exaggerated at times, especially in relation to obstetric trauma and birth asphyxia, there can be no serious doubt that adverse events in pregnancy and the perinatal period do occasionally damage the fetal or neonatal brain. A distinctive feature of brain damage produced between early gestation and infancy is destruction of cerebral white matter or extrapyramidal tracts, thereby producing a clinical syndrome in which disturbance of motor control is a prominent and probably a necessary feature. Depending on the nature and extent of the insult, the motor disorder may be predominantly spastic, dyskinetic, or ataxic and may involve all four limbs (quadriplegia), one side (hemiplegia), or be most prominent in the legs (diplegia). CP severe enough to be recognized as a disability is found in about 1 in 500 school-age children in most developed countries, with little variation between countries or over the past 30 years. (1) Because CP often is accompanied by other neurodevelopmental disabilities, particularly seizure disorders, varying degrees of mental retardation, blindness, or deafness, affected children constitute the single largest group of children in the population who have major disabilities. (2) More …

Carbon dioxide levels do not predict duration of home oxygen requirement: a retrospective study.

Knowing how long an infant with chronic lung disease (CLD) might require oxygen is a useful tool for counseling parents. We aimed to determine if carbon dioxide levels (PCO2) measured near term in newborn infants with CLD still requiring low flow oxygen would be useful in predicting their duration of oxygen requirement. A retrospective study was conducted on infants with CLD discharged from the neonatal unit on home oxygen treatment. The PCO2 levels of 64 infants measured by capillary gas after 34 weeks corrected gestation was correlated with duration of home oxygen requirement. We have shown that PCO2 levels measured near to term on a capillary gas sample in infants with chronic lung disease correlate with length of oxygen dependency (r = 0.55; p < 0.0001). However it was impossible to accurately predict the length of oxygen dependency in an individual case. We conclude that it would be unwise to predict an individual infant's duration of oxygen requirement using the PCO2 levels prior to discharge. However it might be possible to counsel parents in general that infants with lower PCO2 levels prior to discharge are likely to have their oxygen withdrawn more rapidly than those with higher PCO2.

Seasonal controls on surface pCO2 in the central and eastern Arabian Sea

The variability in partial pressure of carbon dioxide (pCO2) and its control by biological and physical processes in the mixed layer (ML) of the central and eastern Arabian Sea during inter-monsoon, northeast monsoon, and southwest monsoon seasons were studied. The ML varied from 80–120 m during NE monsoon, 60–80 m and 20–30 m during SW- and inter-monsoon seasons, respectively, and the variability resulted from different physical processes. Significant seasonal variability was found in pCO2 levels. During SW monsoon, coastal waters contain two contrasting regimes; (a) pCO2 levels of 520–685 μatm were observed in the SW coast of India, the highest found so far from this region, driven by intense upwelling and (b) low levels of pCO2 (266 μatm) were found associated with monsoonal fresh water influx. It varied in ranges of 416–527 μatm and 375–446 μatm during inter- and NE monsoon, respectively, in coastal waters with higher values occurring in the north. The central Arabian Sea pCO2 levels were 351–433, 379–475 and 385–432 μatm during NE-inter and SW monsoon seasons, respectively. The mixed layer pCO2 relations with temperature, oxygen, chlorophylla and primary production revealed that the former is largely regulated by physical processes during SW- and NE monsoon whereas both physical and biological processes are important in inter-monsoon. Application of Louanchiet al (1996) model revealed that the mixing effect is the dominant during monsoons, however, the biological effect is equally significant during SW monsoon whereas thermodynamics and fluxes influence during inter-monsoons.

Predicting Periventricular Leukomalacia (PVL): No support for “low pCO2” hypothesis † 1194

Background: Reports have correlated low pCO2 levels with PVL among very premature infants. We investigated the prevalence of low pCO2 and its association with PVL in a large multi-site data set.

A sink for atmospheric carbon dioxide in the northeast Indian Ocean

Intensive observations in the northeast Indian Ocean (Bay of Bengal) during the presouthwest and northeast monsoon seasons of 1991 reveal that freshwater discharge from rivers of the Indian subcontinent exerts the dominant control over total carbon dioxide (TCO2) and pCO2 distributions in surface waters. Low pCO2 levels occur within the low‐salinity zones, with a large area in the northwestern bay acting as a sink for atmospheric CO2. Only a part of the observed pCO2 variation can be accounted for by the effect of salinity, and biological production supported by external nutrient inputs in conjunction with strong thermohaline stratification may be more important in lowering surface water pCO2 by &gt;100 μatm relative to that in the atmosphere. The pCO2 distribution is seasonally variable and appears to be controlled by the spreading of fresher waters by the prevailing surface circulation.

Biological challenge manipulation of PCO2 levels: a test of Klein's (1993) suffocation alarm theory of panic.

D.F. Klein (1993) proposed that patients with panic disorder (PD) have a hypersensitive suffocation monitor that predisposes them to experience panic attacks under certain conditions. The suffocation alarm theory predicts differential emotional responding to biological challenges that affect arterial partial pressure of carbon dioxide (PCO2). These PD patients should exhibit (a) lower fear and less likelihood of panic in response to biological challenges that lower PCO2 levels (e.g., hyperventilation), and (b) increased fear and greater likelihood of panic in response to biological challenges that raise PCO2 levels (e.g., inhalation of 35% CO2 gas). The following indicators of the suffocation monitor were assessed: (a) severity of dyspnea symptoms, (b) frequency of dyspnea symptoms, (c) heightened respiration rate, and (d) lowered PCO2 levels. Ratings of physiological and subjective responding, as well as panic, were obtained during both a hyperventilation and a 35% CO2 challenge. None of the classification methods predicted differential emotional responding to hyperventilation versus 35% CO2 challenge.

Relationship Between Combined Fetal Biophysical Activities, Oligohydramnios, and Fetal Acid–Base Status

The purpose of this study was to determine the relationship between combined fetal biophysical activities, oligohydramnios, and fetal acid-base status at the time of testing. In a prospective study of 101 patients undergoing cesarean section before the onset of labor, a fetal biophysical profile was performed within 3 h before the cesarean section. Different combinations of fetal biophysical activities (fetal heart rate reactivity, fetal breathing movements, fetal body movements, and fetal tone) and oligohydramnios were correlated with umbilical cord blood gas and acid-base measurements (artery and vein). Fetal acidemia was defined as umbilical arterial blood pH <7.20. The group of fetuses with reactive nonstress test (NST) and/or fetal breathing present had significantly higher pH, pO2, bicarbonate, and base excess and significantly lower pCO2 levels compared with fetuses who had nonreactive NST, absent fetal breathing, and compromised or absent body movements and tone. These blood gas and acid-base diff...

Use of a chemical equilibrium model to understand soil chemical processes that influence soil solution and surface water alkalinity

A chemical equilibrium model was applied to soil chemistry data (Spodosols) collected from 30 and 21 forested watersheds in New York and Maine, respectively, during the EPA Pilot Soil Survey. Chemistry data were evaluated between states using lumped series and within New York using three series (Adams, Becket, and Canaan). All New York horizons had soil characteristics that tend to cause lower solution alkalinity in comparison to Maine horizons. Negative alkalinities were produced in all E horizons (− 69 to − 37 μmol LU−1) at each of the pCO2 levels used (0.3 to 2%). All B horizons had negative alkalinities at low PCO2 levels, which became positive at higher levels, except for the Canaan B and New York Bh horizons, which were negative at all pCO2 levels. C horizons generated positive alkalinities (1 to 67 μmol L−1) at most pCO2 levels. Results indicate the importance of water contact with different horizons and soil series in determining solution alkalinity. Because of degassing effects, solutions with a positive alkalinity will increase in pH after leaving the soil, whereas solutions with a negative alkalinity will remain at low pH (pH < 5.5) and cause the surface water to be acidic. Application of the model to soil chemistry data collected in the northeastern U.S. illustrates the importance of various factors such as pCO2, Al solubility, base saturation, and exchange coefficients in determining surface water chemistry.

Effects of bronchoconstriction on respiratory muscle activity during expiration.

The effect of methacholine-induced bronchoconstriction on the electrical activity of respiratory muscles during expiration was studied in 12 anesthetized spontaneously breathing dogs. Before and after aerosols of methacholine, diaphragm, parasternal intercostal, internal intercostal, and external oblique electromyograms were recorded during 100% O2 breathing and CO2 rebreathing. While breathing 100% O2, five dogs showed prolonged electrical activity of the diaphragm and parasternal intercostals in early expiration, postinspiratory inspiratory activity (PIIA). Aerosols of methacholine increased pulmonary resistance, decreased tidal volume, and elevated arterial PCO2. During bronchoconstriction, when PCO2 was varied by CO2 rebreathing, PIIA was shorter at low levels of PCO2, and external oblique and internal intercostal were higher at all levels of PCO2. Vagotomy shortened PIIA in dogs with prolonged PIIA. After vagotomy, methacholine had no effects on PIIA but continued to increase external oblique and internal intercostal activity at all levels of PCO2. These findings indicate that bronchoconstriction influences PIIA through a vagal reflex but augments expiratory activity, at least in part, by extravagal mechanisms.

Blood gas and acid-base balance during cardiopulmonary resuscitation by intrathoracic and abdominal pressure variations.

The blood gases and acid-base balance in a modified cardiopulmonary resuscitation (CPR) technique, based on intrathoracic and abdominal pressure variations by means of circumferential chest and abdominal balloon inflation, were examined in seven mongrel dogs. CPR proceeded for periods lasting 30 min or more and was monitored by measurements of aortic and right ventricular pressures and carotid blood flow during the compression (artificial systole) and the relaxation phase (artificial diastole). The carotid blood flow was 21.7 +/- 7.8 (mean +/- SD) ml/min, which was 0.18 +/- 0.6 (mean +/- SD) of the baseline mean carotid flow. Arterial blood was well oxygenated throughout the experiments, and low PCO2 levels (5-9 mm Hg) caused an initial severe alkalosis (pH = 7.94). However, a gradual decline in the pH was observed, reaching a value of 7.34 +/- 0.11 in the arterial blood after 30 min of CPR. The venous blood had a very low oxygen content (less than 25.5%) with a low PO2 and a normal PCO2 (43.7 +/- 7.3 mm Hg) throughout the experiment. A gradually developing metabolic acidosis was reflected in the pH values, and an increase in base deficit from 2.25 +/- 5.6 meq/1 prior to CPR to 16.7 +/- 3.2 meq/1 after 30 min of CPR was observed. High arteriovenous differences in oxygen content (greater than 66.4%) and CO2 tension (30.1-41.5 mm Hg) with a slowly developing metabolic acidosis were noted. Thus, CPR by thoracic and abdominal pressure variations is associated with a slowly developing metabolic acidosis which is the result of the combination of hyperventilation and a low perfusion state.

Within-breath PCO2 levels in the airways and at the pulmonary stretch receptor sites.

The discharge frequency of pulmonary stretch receptors (PSRs) shows an inverse responsiveness to the CO2 partial pressure (PCO2), which is limited to an extremely hypocapnic range. During inspiration extremely hypocapnic PCO2 levels are obtained in a large part of the respiratory tract due to the diffusion limited gas mixing. The question remains whether PSRs in combination with these low levels of PCO2 are involved in the regulation of breathing. As a necessary first step to be able to answer this question, this paper is devoted to the calculation of the within-breath PCO2 transients in the respiratory tract and the corresponding PCO2 oscillations in the superficial airway tissue. For PSRs located in the smooth muscles of large bronchi, the calculations predict a time delay of a few seconds to adapt their discharge frequency to a change in PCO2 in the airway lumen. The result is in good agreement with the observed time delay reported in the literature. For the PSRs located in the acini the calculated time constant of their discharge response to PCO2 variations in the lumen is much smaller than 250 ms. This implies a within-breath response to the oscillating luminal PCO2. Further, the calculations show that a CO2 diffusion front is established within the acini during early inspiration. This diffusion front penetrates further and further into the acini with increasing work load due to the concomitant increase in inspiratory flow. As a consequence, the discharge frequency vs. volume response curve of PSRs, especially those located in distal airways, may be modified by a flow-induced PCO2-related contribution.(ABSTRACT TRUNCATED AT 250 WORDS)

Acclimatization to high altitude in goats with ablated carotid bodies.

In awake goats with ablated carotid bodies, we studied resting pulmonary ventilation, CO2 production, composition of arterial blood and cerebrospinal fluid (CSF), and ventilatory responsiveness to hyperoxic CO2 rebreathing at sea level (SL) and after 3 days at simulated high altitude (HA) (PB 446 +/- 5 Torr, equivalent to 4,300 m). At HA, resting pulmonary ventilation was increased, resulting in marked hypocapnia with appropriate base deficit in blood plasma; CSF became more alkaline; CO2-response curves were shifted to lower PCO2 levels, and their slopes were steeper than at SL. Although these changes in regulation of respiration were not demonstrably different from those seen after normal acclimatization to HA with carotid bodies intact, the mechanisms of their initiation and development are probably different.

INDIRECT MEASUREMENT OF ARTERIAL BLOOD PRESSURE (BP) IN NEWBORNS (NBs) UTILIZING DOPPLER ULTRASOUND

The purpose of this study was to determine systolic blood pressure values in normal NBs as well as in distressed infants using an ultrasonic Doppler transducer and a newly designed sphygmomanometer cuff. To establish normal values, 100 full term and premature babies were studied during the first week of life. The values for systolic pressure (SP) in normal full term infants ranged between 45 & 65 mmHg in the first 2 days & 55 to 75 mmHg over the next 2 weeks. SP in prematures (weight 1500 to 2250 gms) ranged from 40 to 60 mmHg. The SP in prematures correlated better with weight and postnatal age than with gestational age. Significant hypertension was noted in 34 of 40 (85%) babies born of mothers receiving methadone treatment. SP ranged from 90 to 120 mmHg & remained elevated for up to 3 weeks. The elevated SP was not related to maternal BP, or to the babies symptoms or therapy. Hypertension was also noticed in some babies with low Apgar scores & elevated levels of PCO2, however, severe asphyxia neonatorum was associated with hypotension. Significant hypotension in the range of 30 mmHg was recorded in NBs with RDS, intracranial bleeding, sepsis, and maternal administration of Mg SO4 for eclampsia. Babies born of mothers with diabetes, essential hypertension, and eclampsia were normotensive. Our BP measurements have proven to be useful in clinical management of sick NBs and the technique currently employed is simple, accurate, and reliable.