Changes In Buffering Capacity Research Articles

Utilization of Matrix Effect for Enhancing Resolution in Cation Exchange Chromatography.

In ion chromatography studies, the matrix effect of other inorganic ions present in the sample is a well-known phenomenon. In this work, the behavior of inorganic and organic ions was studied in a system overloaded with ammonium ions. The ammonium ions came from a solution of ammonium hydroxide in various concentrations (0.25-1.25%). In this system, which was significantly overloaded with ammonium ions, the behavior of three ions were tested (lithium, tris, and sodium cations). The measurements were performed at different eluent concentrations (6-17 mM), chromatographic column temperatures (25-40 °C), and injected volumes (15-40 µL). The retention times of sodium and lithium ions increased with increasing amounts of injected ammonium, while tris remained essentially unchanged, indicating that the resolution of these ions can be influenced by varying the concentration of the matrix. The results suggested that the observed effect was due to a combination of the pH change caused by the injected matrix, the dissociation of tris ions, the dissociation of the carbocylic ion-exchange groups of stationary phase, the change in buffer capacity, and the amount of ammonium ion introduced. It has been shown that in a well-designed experiment, the addition of ammonium hydroxide to the sample at concentrations greater than 1% can improve the efficiency of organic and inorganic cation separation. It was found that 8 mM methanesulfonic acid eluent, 30 °C, 1% ammonium hydroxide matrix concentration, and 25 µL injection were optimal for the baseline separation of tris and sodium ions on the high-capacity Dionex CS16 column. These ions could not be separated on this column without the presence of the ammonium matrix.

Oxidation affects pH buffering capacity of myofibrillar proteins via modification of histidine residue and structure of myofibrillar proteins

The pH buffering capacity is an important functionality of muscle proteins, and muscle foods are susceptible to being oxidized during storage and processing. In order to study the effect of oxidation on the pH buffering capacity of myofibrillar proteins, myofibrils extracted from snakehead fish (Channa argus) were oxidized with H2O2. Results showed that increased oxidation led to loss of free sulfhydryl groups, formation of carbonyl groups, increased surface hydrophobicity, and aggregation of myofibrillar proteins. In addition, there was a significant reduction in the content of histidine in oxidized myofibrillar proteins. The pH buffering capacity of myofibrillar proteins significantly decreased from 3.14 ± 0.03 mM H+/(mL × ΔpH) down to 2.55 ± 0.03 mM H+/(mL × ΔpH) after oxidation with 50 mM H2O2. Both oxidized myofibrillar proteins and histidine showed a high pH buffering capacity at pH near 5.8, which is the histidine pKa value. Here, we hypothesize that oxidation-induced changes in the pH buffering capacity of myofibrillar proteins were driven by oxidative modification of histidine and structural changes of myofibrillar proteins. The significance of this study to food industry may be the awareness that protein oxidation may affect pH through changes in buffering capacity. And the use of antioxidants, especially those targeting at histidine will be promising in addressing this issue.

Water inflow and endogenous factors drove the changes in the buffering capacity of biogenic elements in Erhai Lake, China

Buffering capacity could provide a comprehensive view to recognize the response between external loads and water quality and help address the significant challenges associated with the reduction of lake pollution. However, quantification of the dynamic change in the holistic buffering capacity of biogenic elements in lakes and its driving mechanisms has not been fully understood. Taking Erhai Lake in China as an example, this study quantified the long-term (2000–2019) dynamic changes in buffering capacity and revealed key driving forces for the changes in buffering capacity. The results showed that nitrogen buffering capacity (NBC) and organic buffering capacity (CODBC) decreased during the past 20 years, while phosphorus buffering capacity (PBC) did not change significantly. Endogenous factors are the main controlling factors of buffering capacity. Specifically, algal biomass drove the change in NBC (interpretation rate of 62.2%); the adsorption and sedimentation effects of sediments maintained the relative stability of PBC (56.30%) while algal biomass indirectly impacted the PBC (1.69% only) by affecting the redox environment of the sediments; and algae-derived organic matter and refractory organic matter accumulation dominated the change in CODBC (61.4% and 32.8%, respectively). Water inflow is another controlling factor for NBC and CODBC due to dilution of lake water. This study indicated that the accumulation of endogenous loads and a decrease in water inflow drove the decrease in the lake's buffering capacity (mainly NBC and CODBC), which could help explain why the decrease in external loads in Erhai Lake has not yet reversed the trend of water quality decline. Our study highlights the importance of comprehensive buffering capacity improvement instead of simple external load control to optimize lake environmental management. In the future, attention should be given to controlling endogenous loads, especially preventing algal blooms, and to optimizing hydrodynamic conditions to cope with the decrease in water inflow.

Arterial carbon dioxide and bicarbonate rather than pH regulate cerebral blood flow in the setting of acute experimental metabolic alkalosis.

We investigated the influence of arterial ( ) with and without acutely elevated arterial pH and bicarbonate ([HCO3- ]) on cerebral blood flow (CBF) regulation in the internal carotid artery and vertebral artery. We assessed stepwise iso-oxic alterations in (i.e. cerebrovascular CO2 reactivity) prior to and following i.v. sodium bicarbonate infusion (NaHCO3- ) to acutely elevate arterial pH and [HCO3- ]. Total CBF was unchanged irrespective of a higher arterial pH at each matched stage of , indicating that CBF is acutely regulated by rather than arterial pH. The cerebrovascular responses to changes in arterial H+ /pH were altered in keeping with the altered relationship between and H+ /pH following NaHCO3- infusion (i.e. changes in buffering capacity). Total CBF was ∼7% higher following NaHCO3- infusion during isocapnic breathing providing initial evidence for a direct vasodilatory influence of HCO3- independent of levels. Cerebral blood flow (CBF) regulation is dependent on the integrative relationship between arterial ( ), pH and cerebrovascular tone; however, pre-clinical studies indicate that intrinsic sensitivity to pH, independent of changes in or intravascular bicarbonate ([HCO3- ]), principally influences cerebrovascular tone. Eleven healthy males completed a standardized cerebrovascular CO2 reactivity (CVR) test utilizing radial artery catheterization and Duplex ultrasound (CBF); consisting of matched stepwise iso-oxic alterations in (hypocapnia: -5, -10mmHg; hypercapnia: +5, +10 mmHg) prior to and following i.v. sodium bicarbonate (NaHCO3- ; 8.4%, 50 mEq50mL-1 ) to elevate pH (7.408±0.020 vs. 7.461±0.030; P<0.001) and [HCO3- ] (26.1±1.4 vs. 29.3±0.9 mEqL-1 ; P<0.001). Absolute CBF was not different at each stage of CO2 reactivity (P=0.629) following NaHCO3- , irrespective of a higher pH (P<0.001) at each matched stage of (P=0.927). Neither hypocapnic (3.44±0.92 vs. 3.44±1.05% permmHg ; P=0.499), nor hypercapnic (7.45±1.85 vs. 6.37±2.23% permmHg ; P=0.151) reactivity to were altered pre- to post-NaHCO3- . When indexed against arterial [H+ ], the relative hypocapnic CVR was higher (P=0.019) and hypercapnic CVR was lower (P=0.025) following NaHCO3- , respectively. These changes in reactivity to [H+ ] were, however, explained by alterations in buffering between and arterial H+ /pH consequent to NaHCO3- . Lastly, CBF was higher (688±105 vs. 732±89 mLmin-1 , 7%±12%; P=0.047) following NaHCO3- during isocapnic breathing providing support for a direct influence of HCO3- on cerebrovascular tone independent of . These data indicate that in the setting of acute metabolic alkalosis, CBF is regulated by rather than arterial pH.

Lanthanum chloride-induced conformational changes of bovine liver catalase: A computational and biophysical study

We have investigated the effects of lanthanum chloride (LaCl3) on catalytic activity and conformation of bovine liver catalase (BLC) in different buffer solutions in vitro at 25 °C. Higher concentration of the salt caused decrease in catalase activity in the following order, HEPES > MOPS > Tris > Phosphate buffer. Results obtained from circular dichroism, fluorescence and absorption spectroscopy and from computational docking studies indicate that reduction in activity of BLC by LaCl3 is due to induction of conformational changes. Lanthanum-induced reduced BLC activity in MOPS, HEPES and Tris buffer is characterized by a significant loss in native fluorescence and increase in absorbance spectra of BLC. Nevertheless, the change in secondary conformation of BLC was maximum in HEPES and MOPS followed by Tris and least in Phosphate buffer. Therefore, the significant loss of BLC activity in phosphate buffer at higher molar concentration of lanthanum is attributed to the change in buffering capacity of the buffer. The conformational transition of BLC by LaCl3 was followed as a function of concentration. Therefore, the reduced BLC activity is directly controlled by lanthanum-induced conformational change of BLC in HEPES, MOPS and Tris buffer and indirectly controlled by the change in buffering capacity of the phosphate buffer.

Impact of water drawdown and rewetting on sediment nutrient-dynamics in a constructed delta-lake system (Oostvaardersplassen, The Netherlands): A mesocosm study

In densely populated delta regions, many freshwater shallow lakes constructed on top of marine deposits and their water tables are maintained at a fixed level. Reintroducing water table fluctuations in such lakes will stimulate emergent vegetation development, but potential alterations in nutrient fluxes are still largely unknown. In a mesocosm study, we investigated element fluxes between sediment and pore-water during water drawdown and over the sediment-water interface during subsequent rewetting using sediments from the Oostvaardersplassen (The Netherlands). Desiccation of lake sediment resulted in a decline in pore-water phosphate concentrations (up to 90%), while this was not observed for shore sediments with a desiccation history. Rewetting induced a strong flux of released sulphate and calcium over the sediment-water interface, while expected fluxes of phosphate and nitrogen to the surface water remained limited. In shore sediment, lower element fluxes were observed compared to lake sediments. While water drawdown in delta lakes on marine clay resulted in vegetation development, it can also induce in changes in buffering capacity of the sediment. This should be taken into account when applying water drawdown as a cyclic measure to regenerate emergent vegetation in constructed delta lakes.

Augmentation of bacterial homeostasis by regulating in situ buffer capacity: Significance of total dissolved salts over acidogenic metabolism

During anaerobic fermentation, consequent accumulation of acidic fermented products leads to the failure of pH homeostasis. The present study aimed to comprehend the changes in buffering capacity with addition of sodium salts of hydroxide, bicarbonate and phosphate. The results showed notable augmentation in buffer capacity and cumulative hydrogen production (CHP) compared to control. The influential factor is the amount of undissociated volatile fatty acids released that affected the cell metabolism and consequently biohydrogen generation. It is inferred that among the tested salts, sodium bicarbonate has substantial buffering capacity (β, 0.035± mol) ensuing maximum CHP (468± mL). Besides, bioelectrochemical analysis revealed variations in redox currents that aligned with biohydrogen production. The study provides valuable information on the role of inorganic dissolved salts that would be required to regulate H2 generation and acidogenesis in the aspects of acid–gas phase system.

Impact of Physical Stress on Salivary Buffering Capacity

Background: Saliva has many properties and the buffering capacity is important for the neutralization of oral fluids. It is unclear whether stressful conditions directly affect salivary buffering capacity, and we investigated the impact of physical stress on salivary buffering capacity. Methods: Twelve participants were subjected to the physical stress of jogging and running. The salivary buffering capacity and flow rate of the participants were measured before and after exposure to stressful conditions. Salivary α-amylase activity was measured as a quantitative index of stress. Results: No change in buffering capacity was detected among each time point during the whole course under physically stressful conditions. Next, we examined the change in buffering capacity after jogging compared to baseline. Six participants showed an increase in buffering capacity (Group A), while the other six participants showed a decrease or no change (Group B) after jogging. Group B showed a decrease in flow rate and increases in α-amylase activity and protein level after jogging, whereas Group A showed no changes in these properties. Conclusions: The results suggest that salivary buffering capacity changes following exposure to physically stressful conditions, and that the changes are dependent on the stress susceptibility of individuals.

Seasonal variability of chlorophyll content and the changes of the acidity and buffer capacity in the needles of Larix decidua and Larix leptolepis grown in different air pollution conditions

The needles of &lt;i&gt;Larix decidua&lt;/i&gt; Mili. and &lt;i&gt;Larix leptolepis&lt;/i&gt; showed different pattern of seasonal chlorophyll variability, the level of pigments in &lt;i&gt;L. decidua&lt;/i&gt; was more influenced by zinc-plant emissions than that in &lt;i&gt;L. leptolepis&lt;/i&gt;. The concentrations of chlorophyll a and b and their changes were markedly different from those estimated for the non-deciduous species. The seasonal variability of acidity of aqueous homogenates of the consdered larch needles appeared to be less characterisitic for the species and also for the pollution influence than the changes in buffer capacity.

Effects of chronic and periodic exposures to ammonia on the eye health in juvenile Atlantic halibut (Hippoglossus hippoglossus)

The effects of chronic and periodic peaks of un-ionised ammonia (UIA-N) exposure on eye health and cataract formation in juvenile Atlantic halibut, Hippoglossus hippoglossus, were examined. Fish with mean initial weight 51.7 g (SD 13.2) were exposed to five treatments consisting of control group and three groups (ChronicLow, ChronicMedium and ChronicHigh,) chronically exposed with UIA-N of 0.06, 0.12 to 0.17 mg/l, respectively, for 62 days at 11.9°C, pH 8.0 and salinity 34‰. Furthermore, a fifth group (HighPulse) was exposed to the same high levels as ChronicHigh for a short daily period (peak of 15 mg/l 30 min after exposure, 10 mg/l 1 h after exposure and 1.2 mg/l 3 h after exposure). In the subsequent period of the experimental study (from day 63 until day 100), no ammonia was added to the water. Mean weights were significantly lower in groups exposed to chronically high ambient ammonia concentrations compared to corresponding control group throughout the experimental period. The sampled fish exhibited signs of mild cataract formation, although the results showed no clear evidence that the ammonia treatments contributed to differences. Minor differences were found in measured muscle free amino acids, which could be used to explain potential changes in buffering capacity. The eye histidine status differed significantly at day 62, and osmotic differences in the eye lenses (measured as differences in N-acetyl histidine) were found in all group exposed to chronic levels of ammonia.

The Effect of Hyperbaric Oxygenation on Postradiation Xerostomia and Saliva in Patients with Head and Neck Tumours

The study was designed to evaluate the influence of hyperbaric oxygenation (HBO) therapy on salivary gland function and the growth of salivary Streptococcus mutans,Lactobacillus and Candida albicans in patients with head and neck tumours who had undergone radiation therapy. Sixteen patients were included, with radiation doses from 58 to 70 Gy. The first examination was performed at baseline before the first HBO therapy (33.7 ± 9 months after radiation therapy), and the second after 20 daily HBO therapies in a hyperbaric chamber at 2.5 ATA (absolute atmospheres), where patients breathed 100% oxygen for 90 min each day. Measurements of salivary flow, buffer capacity, saliva pH and colony density of S. mutans,Lactobacillus and C. albicans in stimulated saliva were conducted, and xerostomia grade was assessed. Salivary flow increased from 0.20 ± 0.1 to 0.39 ± 0.2 ml/min at the end of HBO therapy (p < 0.001). Salivary pH also increased from 6.0 ± 0.2 to 6.5 ± 0.1 (p < 0.05). The colony density decreased from the time at baseline to the end of HBO therapy for S. mutans (p < 0.001), Lactobacillus (p < 0.05) and the fungus C. albicans (p < 0.05). The xerostomia grade decreased from 2.63 ± 0.2 to 1.94 ± 0.2 after HBO (p < 0.001). There was no significant change in buffer capacity. The increased salivary secretion rate and salivary pH, and decreased S. mutans and Lactobacillus colony density that were observed after HBO therapy may reduce caries progression in those patients.

Effects of Oral Health Care on Salivary Flow Rate in Patients With Type 2 Diabetes

The purpose of this study is to evaluate the effects of the authors' oral health care program on the stimulated whole salivary flow rate and buffer capacity before and after a 6-month intervention. The authors conducted the intervention study among 25 participants with diabetes. The salivary flow rate and buffer capacity were evaluated before and after this intervention. Overall, the results showed a significant increase in salivary flow rate and no significant change in buffer capacity. Also, it was likely that salivary flow rate significantly increased among patients with more than 20 remaining teeth and patients with well-controlled diabetes. The findings suggest that this program for type 2 diabetes led to an increase in the stimulated whole salivary flow rate.

The effects of 10 weeks of resistance training combined with β-alanine supplementation on whole body strength, force production, muscular endurance and body composition

Carnosine (Carn) occurs in high concentrations in skeletal muscle is a potent physico-chemical buffer of H+ over the physiological range. Recent research has demonstrated that 6.4 g x day(-1) of beta-alanine (beta-ala) can significantly increase skeletal muscle Carn concentrations (M-[Carn]) whilst the resultant change in buffering capacity has been shown to be paralleled by significant improvements in anaerobic and aerobic measures of exercise performance. Muscle carnosine increase has also been linked to increased work done during resistance training. Prior research has suggested that strength training may also increase M-[Carn] although this is disputed by other studies. The aim of this investigation is to assess the effect of 10 weeks resistance training on M-[Carn], and, secondly, to investigate if increased M-[Carn] brought about through beta-ala supplementation had a positive effect on training responses. Twenty-six Vietnamese sports science students completed the study. The subjects completed a 10-week resistance-training program whilst consuming 6.4 g x day(-1) of beta-ala (beta-ALG) or a matched dose of a placebo (PLG). Subjects were assessed prior to and after training for whole body strength, isokinetic force production, muscular endurance, body composition. beta-Alanine supplemented subjects increased M-[Carn] by 12.81 +/- 7.97 mmol x kg(-1) dry muscle whilst there was no change in PLG subjects. There was no significant effect of beta-ala supplementation on any of the exercise parameters measured, mass or % body fat. In conclusion, 10 weeks of resistance training alone did not change M-[Carn].

A Novel Environmental Quality Criterion for Acidification in Swedish Lakes – An Application of Studies on the Relationship Between Biota and Water Chemistry

The recovery from acidification has led to the demand for more precise criteria for classification of acidification. The Swedish Environmental Protection Agency has revised Sweden’s Ecological Quality Criteria for acidification to improve the correlation between the chemical acidification criteria and biological effects. This paper summarises the most relevant findings from several of the studies commissioned for this revision. The studies included data on water chemistry in 74 reference lakes in southern Sweden with data on fish in 61 of the lakes, as well as data on littoral fauna in 48 lakes. We found that the acidity variable most strongly correlated to the biota was the median pH from the current year. Our results probably do not reflect the mechanisms behind the negative effects of acidity on the biota, but are fully relevant for evaluation of monitoring data. The biogeochemical models used for predicting acidification reference conditions generate a pre-industrial buffering capacity. In order to get an ecologically more relevant criteria for acidification based on pH, we transferred the estimated change in buffering capacity into a corresponding change in pH. A change of 0.4 units was defined as the threshold for acidification. With this criterion a considerably lower number of Swedish lakes were classified as acidified when compared with the present Ecological Quality Criteria.

Modification of Phosphate Uptake Model Considering Changing Buffering Capacity of Soil and Release Threshold Limit of Phosphorus in Soil due to Rhizosphere Effect#

To study the effect of root-secreted organic acids on phosphorus (P) uptake by wheat and rice and for better understanding and predictability of phosphorus uptake model, a series of green house and laboratory experiments was conducted in three different types of soils: Alfisol, Vertisol, and Inceptisol. Root length density and phosphorus uptake were estimated from pot culture experiments. Phosphorus desorption isotherms were determined by equilibrating soil with organic acids mostly found in rice and wheat rhizosphere. Considering the change in buffering capacity of soils in the presence of organic acids, introducing the concept of phosphorus release threshold level a phosphorus uptake model was modified. Buffering capacities of soils are greatly influenced by organic acids. The desorption isotherm was used instead of adsorption isotherm of P for estimating buffering capacity and P release threshold level. Release of nonlabile P was more in the presence of organic acids. Maximum root influx rate (I max) decreased with plant age, but Michaelis-Menten constant (K m ) was independent of plant age. The model was run by taking into account interroot competition for prediction of phosphorus uptake by crops. The model outputs were used for comparison of P uptake in pot culture experiments. The observed and predicted values agreed well as tested by χ 2 analysis. #The work was done in the Division of Soil Science and Agricultural Chemistry, Indian Agricultural Research Institute (IARI), New Delhi, India.

Derivative Estimation for Buffer Capacity of Continuous Transfer Lines Subject to Operation-Dependent Failures

We derive estimators of throughput sensitivity to changes in buffer capacity for continuous flow models of a transfer line comprising two machines separated by a buffer of finite capacity, where machines are subject to operation-dependent failures, i.e., a machine cannot fail when it is idle. Both repair times and failure times may be general, i.e., they need not be exponentially distributed. The system is hybrid in the sense that it has both continuous dynamics—as a result of continuous material flow—and discrete events: failures and repairs. The combination of operation-dependent failures and buffer capacity as the parameter of interest make the derivative estimation problem difficult, in that unlike previous work on continuous flow models, careful use of conditional expectation (i.e., smoothed perturbation analysis) is required to obtain unbiased estimators.

Modeling landscape functions and effects: a network approach

Landscape functions, including sediment and nutrient trapping, pollutant degradation, and flood control, are often adversely affected by human activities. Tools are needed for assessing the effects of human activities at the landscape scale. An approach is presented that addresses this goal. Spatially-explicit ecosystem units and their connections are used to define a transport network. A linear transport model is a tractable approach to landscape analysis for assessment purposes. The ability of each unit to provide ecosystem goods and services is considered explicitly in terms of its place in the network. Based on this simple model, landscape-level effects of impacts to the functioning of a given ecosystem unit can be calculated. Effects of changes in network structure (due to changes in the flow regime) can also be assessed. The model allows several useful concepts to be defined, including change in buffer capacity, free capacity, an ordinal ranking of the relative importance of ecosystem units to overall landscape functioning, and differentiation of cumulative versus synergistic effects. Utility functions for valuation of landscape function are also defined. The framework developed here should provide a foundation for the development of analytic tools that can be applied to assessment and permitting activities.

Flash-induced changes in buffering capacity of reaction centers from photosynthetic bacteria reveal complex interaction between quinone pockets

A novel method was applied to determine light-induced protonation in reaction centers from photosynthetic purple bacteria. Changes in buffering capacities upon flash excitation were detected in (0.03% Triton X-100) detergent solution of reaction centers from Rhodobacter ( Rb.) sphaeroides and Rb. capsulatus wild type and mutant strains with empty or occupied secondary quinone (Q B) binding sites in the presence of an external electron donor. The light-induced differences in buffering capacities between pH 4 and 11 were analyzed in terms of protonatable residues. Due to its differential nature, this method is more sensitive to the position and shift of p K a of the individual groups than the direct method based on proton uptake measurements. Out of the four different ionizable residues which were used to fit the curves, the two groups with apparent (dark) p K a values between 8.4–8.8 and 9.5–10.0 (depending on the species and conditions) disappeared when the native ubiquinone 10 was replaced by menadione at the primary quinone (Q A) binding site of Rb. sphaeroides or when the key protonatable residues (L212Glu and L213Asp) were replaced by non-protonatable alanines in the Q B binding site of the AA+M43D mutant from Rb. capsulatus. The experimentally observed acidic and neutral residues remained unchanged. These results obtained from modifications in both quinone sites reveal the origin of the alkaline pH groups: they reflect the interaction of Q A − and the cluster of ionizable residues around L212Glu in the Q B binding pocket. The involvement of two residues with close p K a values reflects the complex titration of the cluster. The interaction between the quinone pockets is best described qualitatively as a network of ionizable residues extending from the Q A site to the Q B site.

Regulation of B-type intercalated cell apical anion exchange activity by CO2/HCO3-.

The cortical collecting duct (CCD) B cell possesses an apical anion exchanger dissimilar to AE1, AE2, and AE3. The purpose of these studies was to characterize this transporter more fully by examining its regulation by CO2 and HCO3. We measured intracellular pH (pHi) in single intercalated cells of in vitro microperfused CCD using the fluorescent, pH-sensitive dye, 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF). In the absence of extracellular CO2/HCO3, luminal Cl removal caused reversible intracellular alkalinization, identifying this transporter as a Cl/base exchanger able to transport bases other than HCO3. Adding extracellular CO2/HCO3 decreased B cell pHi while simultaneously increasing Cl/base exchange activity. Since intracellular acidification inhibits AE1, AE2, and AE3, we examined mechanisms other than pHi by which the stimulation occurred. These studies showed that B cell apical anion exchange activity was CO2 stimulated and carbonic anhydrase dependent. Moreover, the stimulation was independent of luminal bicarbonate, luminal pH or pHi, and changes in buffer capacity. We conclude that the B cell possesses an apical Cl/base exchanger whose activity is regulated by CO2-stimulated, carbonic anhydrase-dependent cytoplasmic HCO3 formation.

The Effect of Duration of Exposure on Sulfuric Acid-Induced Pulmonary Function Changes in Asthmatic Adolescent Subjects: A Dose-Response Study

To evaluate the pulmonary effects of varying doses of sulfuric acid, adolescent subjects with asthma were exposed to 35 or 70 micrograms/m3 sulfuric acid for 45 or 90 min. Exposure was carried out during intermittent moderate exercise. The pulmonary functions measured before and after exposure were FEV1, FVC, and total respiratory resistance. The 45 min exposures were associated with larger decreases in FEV1 (-6% or -3%) than the 90 min exposures (-1% or +2%). Analysis of variance of the change in FEV1 among the exposures revealed that the 45 min exposure to 35 micrograms/m3 was significant (p = 0.03). The p value for 45 min exposure to 70 micrograms/m3 was not significant (p = 0.08). Using analysis of variance, neither of the 90 min exposures was associated with a significant decrease in FEV1 compared to air exposure. Also, none of the changes in FVC or RT was significant. When baseline to post-exposure changes were compared for each of the five test atmospheres using paired t tests, both of the 45 min exposures were associated with statistical significance (p < 0.001 for 35 micrograms/m3 and p < 0.005 for 70 micrograms/m3). This baseline to post exposure change was not statistically significant for the 90 min exposures. The reason for the lesser effect on pulmonary function at increased exposure duration is not known; it may be due to changes in either varying deposition patterns or changes in buffering capacity of the cells lining the airways. With respect to individual sensitivities to H2SO4, the data showed a significant consistency across test atmospheres.