Continuous pH Measurements Research Articles

Maintenance and regulation of the pH microclimate at the luminal surface of the distal colon of guinea-pig.

1. The fluorescent dye 5-N-hexadecanoyl-aminofluorescein (HAF) was used to study the mechanisms involved in maintaining a relatively constant luminal surface pH (pHs) in the distal colon of the guinea-pig. The fatty acyl chain of the HAF molecule inserts into the apical membrane of epithelial cells. This allows a continuous measurement of the surface pH for several hours. 2. The localization of HAF was confirmed by confocal laser-scanning microscopy and by using monoclonal antibodies against fluorescein. The insertion of HAF into the apical membrane of the colonocytes did not change the transepithelial conductance or the short-circuit current of the epithelium. 3. With the HAF method a pH microclimate was confirmed at the colonic surface. Although the pH of the bulk luminal solution was decreased in bicarbonate-containing solution from 7.4 to 6.4 the pHs changed only in the range 7.54-6.98. 4. In the absence of bicarbonate pHs almost followed changes of bulk luminal pH. In the presence of bicarbonate there was a decrease in pHs after removal of chloride from the luminal side and an increase in pHs after addition of butyrate to the luminal solution. This suggests the involvement of a bicarbonate-anion exchange in bicarbonate secretion: a Cl--HCO3- as well as a short-chain fatty acid--HCO3- exchange. 5. The apical K+-H+-ATPase in the distal colon of guinea-pig has little influence on pHs in the presence of physiological buffer concentrations. 6. Our findings indicate that bicarbonate plays a major role in maintaining the pH microclimate at the colonic surface.

Continuous measurement of gut pH with near-infrared spectroscopy during hemorrhagic shock.

The rate and magnitude of pH changes in the bowel during hemorrhagic shock are greater than those in the stomach, implying that gastric intramucosal pH may not be a reliable indicator of gut perfusion. Here, we evaluate near-infrared spectroscopy (NIRS) to assess bowel pH in a swine shock model. Laparotomy was performed to place flow probes, pH microelectrodes, and NIRS probes. Shock was maintained for 45 minutes at a blood pressure of 45 mm Hg, and resuscitation was achieved with shed blood and lactated Ringer's solution to baseline over 60 minutes. Hemodynamic measurements were significantly reduced during shock. Lactic acid peaked during resuscitation and remained elevated. NIRS-measured pH was correlated to electrode-measured pH (R2 = 0.903 [ischemia] and R2 = 0.889 [reperfusion]). Estimated measurement accuracy after subject-specific offset correction was 0.083 pH units during ischemia and 0.076 pH units during reperfusion. NIRS determination of small-bowel pH may be a good tool to monitor the adequacy of resuscitation.

Automatic control of pH in industrial processes, using a tungsten electrode‐based device

This article presents a self-made device used for continuous determination of pH in hard-working industrial conditions: mining and sugar industries. The device consists of a pH detector and a specific pH meter. The tungsten (W) based pH electrode and the mechanical cleaner of the electrode surface are the main parts of the pH detector. The continuous cleaning of the electrode surface ensures the high accuracy (±0.15 pH) of the continuous pH measurements. © 1999 John Wiley & Sons, Inc. Lab Robotics and Automation 11: 147–150, 1999

Automatic control of pH in industrial processes, using a tungsten electrode-based device

This article presents a self-made device used for continuous determination of pH in hard-working industrial conditions: mining and sugar industries. The device consists of a pH detector and a specific pH meter. The tungsten (W) based pH electrode and the mechanical cleaner of the electrode surface are the main parts of the pH detector. The continuous cleaning of the electrode surface ensures the high accuracy (±0.15 pH) of the continuous pH measurements. © 1999 John Wiley & Sons, Inc. Lab Robotics and Automation 11: 147–150, 1999

Clinical Evaluation of a New In-Line Continuous Blood Gas Monitor

Two methodologies for obtaining accurate blood gas and electrolyte values during cardiopulmonary bypass (CPB) are traditional laboratory analyzers, which use an electrochemical technology, and continuous in-line monitoring systems, which use a fluorometric and/or spectrophotometric technology. The purpose of the present study was to evaluate the accuracy of a new continuous in-line monitor, the 3M™ CDI™ Blood Parameter Monitoring System 500, which provides continuous in-line measurements of pH, PCO2, PO2, potassium (K+), oxygen saturation, hematocrit, hemoglobin, and temperature, during partial or complete CPB. Study parameters included arterial pH, PCO2, PO2 , and K+ values. Overall performance was analyzed by calculating the mean difference (expressed as the bias) between the CDI system 500 and the laboratory analyzer for each parameter. The accuracy of the arterial pH, PCO2, and K+ values provided by the CDI system 500 was then evaluated using target values established in the acceptable performance standards for laboratory analyzers from the Clinical Laboratory Improvement Act of 1988 (CLIA '88). The accuracy of the PO2 value provided by the CDI system 500 was evaluated using a target value of ± 10% of the reference, or laboratory analyzer, value. A prospective multi-center trial was conducted following Institutional Review Board approval. A total of 75 cases was included in the analyses, with over 200 data points from 4 clinicallocations. Results for pH, PCO2 , and K+ were within the target values established by CLIA '88. pH bias was 0.00 ± 0.02 pH units. PCO2 bias was −0.3 ± 3.3 mm Hg. K+ bias was approximately + 0.12 ± 0.31 mmole/l. Results for PO2 were within 10% of the reference value. PO2 bias was 7.5 ± 13.8 mm Hg. The results of this clinical trial show that the CDI System 500 continuous in-line monitoring system provides values that meet the accuracy standards for laboratory analyzers for arterial pH, PCO2, PO2, and K+.

Dissolved carbon dioxide and oxygen in the River Thames: Spring–summer 1997

Data on excess carbon dioxide partial pressures (EpCO 2) and oxygen saturations in the River Thames 3 km upstream of Wallingford, Oxfordshire, are presented and related to general water quality. The data, which cover the period for the spring and summer of 1997, relate to: (1) weekly-spot sampling for determination of major, minor and trace elements, pH and alkalinity; and (2) continuous measurements of pH linked to the weekly alkalinity data. (Throughout the period major cation, major anion and alkalinity concentrations are relatively constant and the greatest changes in water quality are determined by the biological fluctuations changing the pH and dissolved oxygen levels). Large variations in EpCO 2 occur, ranging between 0.3 and 11.5 times the atmospheric value. During April–May time, relatively high pH (8.7–9.4) and oversaturation with respect to dissolved oxygen (100–175% saturation) and relatively low EpCO 2 of 0.3 to 2 times the atmospheric value, and low dissolved silica concentrations of <0.5 mg-Si/l occurs. This probably reflects a period of high photosynthetic activity. Later in the year, pH is about 0.7 lower and the water is approximately saturated with respect to dissolved oxygen (80–120%) and this probably reflects a period of lower photosynthetic activity. pH shows a negative relationship with EpCO 2 and strong diurnal fluctuations in pH, dissolved oxygen and EpCO 2 occur throughout the spring and summer as the balance between photosynthesis and respiration changes under differing light conditions. pH shows the highest and dissolved oxygen the lowest levels during the day and the opposite pattern is observed during the night in line with the changeover from net photosynthesis to net respiration. The largest variations occur during the spring period when photosynthetic activity is at its highest. The biological activity in combination with aeration not only determines the EpCO 2 level but the pH as well and EpCO 2 is directly proportional to the hydrogen ion activity. Thermodynamic analysis of the water quality data reveals that the waters vary between oversaturation and undersaturation with respect to the mineral calcite (CaCO 3) although there is no evidence for active precipitation or dissolution. There is an approximate transition from undersaturation to oversaturation with respect to calcite around pH 8 and EpCO 2 of seven times the atmospheric value with oversaturation occurring at higher pH and lower EpCO 2. On a daily basis, EpCO 2 is negatively and linearly correlated with the percentage of dissolved oxygen saturation in line with changing patterns of CO 2 and O 2 gaseous exchange during photosynthesis, respiration and transfers to and exchange with the atmosphere. EpCO 2 and pH averages and ranges lie between those observed for the more pristine and the industrially polluted eastern UK rivers. The values are similar to those for eastern UK catchments with low but significant sewage inputs.

Acid-induced duodenal mucosal nitric oxide output parallels bicarbonate secretion in the anaesthetized pig.

We recently showed the involvement of the L-arginine/nitric oxide (NO) pathway in acid-induced duodenal mucosal bicarbonate secretion in rats. The aim of the present study was to confirm this observation in pigs by direct measurements of NO production. Experiments were performed on 16 anaesthetized pigs of both sexes treated with guanethidine (6 mg kg-1, intravenously). A duodenal segment, devoid of pancreaticobiliary influxes, was perfused with saline and the duodenal mucosal bicarbonate secretion was calculated from continuous measurements of pH and PCO2. The perfusate contents of NO and its oxidative product nitrite were determined by chemiluminescence, after reduction of nitrite to NO. Luminal acidification with 30 mM hydrochloric acid increased the output of bicarbonate as well as NO to the perfusate, by 195 +/- 45% and 106 +/- 10%, respectively. These responses to acid were markedly inhibited by adding the NO synthase inhibitor NG-monomethyl-L-arginine (L-NMMA, 0.3 mM) to the perfusate. The inhibitory effect of L-NMMA could be reversed by administration of L-arginine (3 mM). The study presents simultaneous measurements of bicarbonate and NO outputs to a duodenal luminal perfusate. The results strongly support the view that the L-arginine/NO pathway is involved in the acid-induced duodenal mucosal bicarbonate secretory response.

Continuous hypopharyngeal pH measurements in spontaneously breathing anesthetized outpatients: Laryngeal mask airway versus tracheal intubation.

Continuous hypopharyngeal pH measurements in spontaneously breathing anesthetized outpatients: Laryngeal mask airway versus tracheal intubation.

An Evaluation of In-Situ Measurements of Water Temperature Specific Conductance, and pH in Low Ionic Strength Streams

The performance of minimonitors used by the U.S. Geological Survey for continuous measurement of water temperature, specific conductance, and pH in four low ionic strength streams in the Catskill Mountains of New York was evaluated through a calculation of their bias, precision, and accuracy and by comparison with laboratory measurements of specific conductance and pH on samples collected concurrently. Results indicate that the mini-monitor measurements of specific conductance and pH in an acidic stream (acid-neutralizing capacity always less than 0) agreed with laboratory measurements well enough that the minimonitors can be used to supplement laboratory measurements (mean difference in pH was 0.02 pH unit and mean difference in specific conductance was 0.72 μS cm−1. This mean difference was 0.32 μS cm−1 if the minimonitor data were adjusted by the bias). In less acidic streams (two streams in which the acid-neutralizing capacity was always greater than 0 and one in which the acid-neutralizing capacity was greater than 0 except during high flows), there was poor agreement between laboratory and minimonitor measurements of specific conductance at high flows and pH at all flows. The water-temperature probes measured with sufficiently small bias (–0.1 °C) and adequate precision (±0.70 °C) for use with most applications.

Continuous hypopharyngeal pH measurements in spontaneously breathing anesthetized outpatients: Laryngeal mask airway versus tracheal intubation.

Continuous hypopharyngeal pH measurements in spontaneously breathing anesthetized outpatients: Laryngeal mask airway versus tracheal intubation.

Continuous pH, electrical conductivity and temperature measurement at Plynlimon: towards an integrated, reliable and low maintenance instrument system

Abstract. Water quality data for the Nant Tanilwyth stream, Plynlimon (an acidic upland stream, the waters of which are of such low ionic strength that measurement is difficult), has been recorded using a new integrated field instrument system. The negligible drift of the pH electrode allows the system to operate for extended periods (months) without re-calibration, whilst maintaining a standard deviation of 0.19 pH units between its readings and laboratory reference measurements. Conductivity measurements, although within the sensor manufacturer's specification, did not provide meaningful readings at conductivities below 50 μS cm-1. Using the pH data as a surrogate tracer, a high temporal resolution estimate of the stream dynamics, in terms of the contributions of groundwater and soil-water is presented; the dependence of these relative proportions on instantaneous flow and antecedent conditions is shown. It is concluded that, whilst improvements in instrumentation have been made, greater accuracy is still desirable for some scientific applications and ways forward are described.

Mast cell histamine in gastric secretion--a study on the isolated portion of a guinea pig stomach.

The effects of an H3-agonist, R-alpha-methylhistamine (0.1 and 1 microM), on gastric acid secretion and on mast cell histamine release was studied on the isolated portion of guinea pig stomach. Secretion, induced by calcium ionophore, A23187 (1 microM), and by vagal stimulation was determined by continuous pH measurement, mast cell degranulation was examined histologically. Secretory effects were not significantly changed by H3-agonist. Mast cell degranulation, elicited by vagal stimulation, was not influenced by R-alpha-methylhistamine, but the degranulating effect of A23187 was clearly augmented by the H3-agonist. The results support the view that H3-receptors could influence the release of mast cell histamine in the guinea pig stomach.

Differential Effects of Adenosine Preconditioning on the Postischemic Rat Myocardium

Ischemic preconditioning describes the phenomenon of endogenous myocardial protection against sustained ischemia-reperfusion injury (I/R). Although the complex stimulus of transient ischemia induces global myocardial protection against acidosis, infarction, and stunning, it is unknown whether select components of transient ischemia (e.g., adenosine) are responsible for different aspects of protection. To study this, isolated rat hearts were treated with adenosine (125 μMcoronary concentration) or vehicle 10 min prior (preconditioning) to global myocardial I/R (20 min/40 min; 37°C). To determine whether adenosine affects stunning, continuous functional data (rate pressure product and coronary flow) were obtained. To determine whether adenosine affects necrosis, creatine kinase (CK) loss into the coronary effluent was determined during postischemic reflow. To determine whether adenosine affects pH, continuous pH measurements were made using NMR. Results indicate that adenosine protects against stunning but provides only minimal protection against acidosis. Adenosine's protection of function occurs despite severe acidosis. Adenosine does not limit CK loss. We conclude that (1) adenosine preconditioning, a component of ischemic preconditioning, protects myocardial function following I/R, but does not provide global myocardial protection against I/R in the rat; (2) protection of function can occur despite severe ischemic acidosis; and (3) protection of function occurs despite equivalent postischemic CK loss. These results suggest that pharmacologic preconditioning may require multiple agents in order to provide global myocardial protection.

48-Hour Continuous Intragastric pH Fluctuation During Lansoprazole Administration Every Other Day

The inhibitory effect on acid secretion of lansoprazole administered every other day in comparison with cimetidine was investigated in this study. Drugs and dosages were assigned to patients with peptic ulcer as follows: cimetidine 800 and 400mg daily; lansoprazole 30mg every other day. The patients’ intragastric pH was continuously measured, and the time at or above pH 4 (pH 4 holding time) was assessed. Total measurement time and night-time pH 4 holding times were 48.4 ± 3.7% and 56.1 ± 5.7%, respectively, with cimetidine 800mg; 33.7 ± 4.9% and 51.1 ± 7.3%, respectively, with cimetidine 400mg; and 66.1 ±6.1 % and 67.9 ± 5.6%, respectively, with lansoprazole every other day, revealing a significantly more powerful acid suppression in the lansoprazole than in the cimetidine groups. In addition, according to continuous 48-hour intragastric pH measurements, the pH 4 holding time during lansoprazole treatment days was significantly longer than on nontreatment days. Changes in patients’ blood gastrin levels over 48 hours while taking lansoprazole every other day revealed slightly higher values, depending on the time period, but 86% of the patients had fasting gastrin levels of 160 ng/L or less. When lansoprazole was administered every other day, the pH 4 holding time differed between the two days, and gastrin elevation was smaller. We suggest that lansoprazole every other day seems to be pharmacologically capable of being used just for peptic ulcer maintenance therapy.

Continuous intra-arterial blood gas monitoring during cardiopulmonary resuscitation

Continuous intra-arterial blood gas monitoring is becoming more common in Intensive Care practice. Several trials have been undertaken to evaluate their performance in critically ill patients and varying degrees of accuracy have been reported [l-S]. No published trial to date has addressed the question of their utility in clinical practice, though there are anecdotal reports of their usefulness in various clinical situations. We report a case of a patient with a continuous intra-arterial sensor, who suffered a cardiac arrest and required cardiopulmonary resuscitation (CPR). Continuous blood gas monitoring during CPR has been reported before [6-81 using transcutaneous and transconjunctival oxygen electrodes and was shown to be useful in guiding therapy; continuous Pco2 monitoring was used in one study. To our knowledge, continuous pH monitoring during CPR has not been reported before. The Paratrend 7 (Biomedical Sensors, UK) is a multiparameter intravascular sensor for on-line, continuous measurements of pH, Pco2, PO* and temperature. It comprises an electrochemical oxygen sensor [9], optode-based Pco2 and pH sensors [lo] and a thermocouple for the determination of temperature. Preliminary evaluation of its use in Intensive Care patients and during anaesthesia has shown an acceptable level of accuracy over a wide range of pH, Pc02 and Pot measurements [ll-131.

Supplemental Oxygen and Gastric pH in Unfed Preterm Infants

Hypoxia has been associated with decreased gastric acidity in infants and children. In neonates, an inverse relationship between gestational age and gastric acidity may confound this association. To assess the relationship between oxygen supplementation and gastric acidity in premature neonates, mean 24-hour continuous measurements of gastric pH, obtained by an indwelling flexible gastric pH probe, were compared in infants requiring and not requiring oxygen. Patients were < 36 weeks' gestational age and were unfed before and during the assessment period. The gestational age of infants who required oxygen was less than that of infants who did not (30.5 +/- 3.0 vs 32.9 +/- 1.5 weeks, respectively). Other comparison variables were not different. The mean pH for infants requiring oxygen (4.4 +/- 1.7) was significantly greater than that of those not needing oxygen (2.7 +/- 1.2). After controlling for population characteristics and gestational age, we found that infants requiring oxygen still had significantly reduced gastric acidity.

Continuous Intra-Arterial Blood Gas Monitoring

Arterial blood gas analysis is necessary for the optimal management and treatment of many critically ill patients. Currently, arterial blood gases (ABG) are measured intermittently. Continuous measurement of PO2, PCO2, and pH in arterial blood would be a major medical advance for the intensivist. Certain patient populations in the intensive care unit (ICU) would clearly benefit from continuous intra-arterial blood gas monitoring (CIABGM). CIABGM would not be expected to totally replace intermittent ABG sampling and periodic calibration of a CIABGM device may also be necessary.

The pH/PCO2 method for continuous determination of human gastric acid and bicarbonate secretion. A validation study.

The present paper describes and evaluates a methodologic approach for registration of the fast, interdigestive, motility-related changes in gastric acid and bicarbonate outputs seen in man. The technique is based on continuous gastric luminal perfusion and measurements of pH and PCO2 in gastric effluent and concomitant intragastric/duodenal manometry. Fourteen healthy volunteers participated. Direct acid secretory estimations from pH recordings, corrected for hydrogen ion activity, correlated closely with values obtained by conventional titration. After intragastric infusion of bicarbonate, 96 +/- 5% of the newly measured steady-state value was registered virtually instantaneously provided that corrections for the PCO2 electrode time constant and the perfusion/aspiration time were made. In the neutral pH range (pH 5-7), practically full quantitative recovery of intragastrically infused bicarbonate was obtained. In the acid pH interval (pH 2-5) the recovery was significantly lower (53 +/- 6%; p < 0.01). With an aspirate without air admixture and during high perfusion rates (31 and 46 ml/min), full recovery of bicarbonate was obtained also at an acid pH, whereas a reduced perfusion rate (16 ml/min) significantly (p < 0.05) reduced the recovery rate. With the pH/PCO2 technique both acid and bicarbonate assessments have a close to on-line time resolution. Acid output is measured accurately, but the method potentially underestimates actual bicarbonate levels in the acid pH range, a combined effect of diffusion of CO2 into air bubbles in the aspirate and into the gastric mucosa from the lumen. A high gastric perfusion rate minimizes this source of error. The pH/PCO2 technique is well suited for studies of the interaction between secretion and motility in the human stomach.

Effects of wine on lower oesophageal sphincter pressure and oesophageal pH*

Abstract Eleven volunteers received 300 ml white wine, an ethanol solution and tap water to compare the effects of these beverages on lower oesophageal sphincter pressure and gastro‐oesophageal reflux. A continuous measurement of sphincter pressure and oesophageal pH was performed one hour before and after ingestion. A significant increase in fraction of time pH&lt;4 (P &lt; 0.01 vs ethanol, P &lt; 0.001 vs water) coincident with a significant decrease in sphincter pressure (P &lt; 0.01) was observed after the intake of wine, The duration of transient sphincter relaxations (P &lt; 0.05) as well as the duration of reflux episodes (P &lt; 0.001) were significantly prolonged, its frequencies were not significantly enhanced. Reflux occurred almost exclusively during complete sphincter relaxations after the intake of ethanol and water, whereas an increase in ‘stress reflux’ and the occurrence of ‘free reflux’ was observed after ingestion of wine (P &lt; 0.001). It is concluded that this change in reflux pattern is related to the depressive effect of wine on lower oesophageal sphincter pressure. Pure ethanol is not responsible for the effects of wine.

Simplified dual-lumen catheter design for simultaneous potentiometric monitoring of carbon dioxide and pH.

A novel dual-lumen catheter electrode design suitable for the simultaneous measurement of PCO2 (partial pressure of carbon dioxide) and pH in flowing blood is described. The probe is fabricated from a single segment of dual-lumen silicone rubber or polyurethane tubing that is impregnated with the proton ionophore tridodecylamine. The impregnation step imparts H+ permselectivity to both inner and outer walls of the tubing. By filling each lumen with a suitable buffer/electrolyte solution and Ag/AgCl reference electrode wire, simultaneous potentiometric detection of both PCO2 and pH is achieved. Careful optimization of incorporated proton carrier (tridodecylamine), plasticizer (o-nitrophenyl octyl ether), and lipophilic counteranion sites (tetrakis[3,5-bis(trifluoromethyl)phenyl]borate) within the tubing walls yields catheter electrodes with resistance values of 10-20 M omega and relatively high stability in flowing blood. Results from continuous measurements of PCO2 and pH during long-term 30-65-h blood loop experiments demonstrate that, after an initial conditioning period, the catheter exhibits low drift rates (PCO2, 4.7 +/- 1.7 mV/30 h; pH, 1.4 +/- 0.5 mV/30 h) and yields continuously measured values in good agreement with those obtained on discrete samples with a commercial blood gas analyzer (PCO2, r2 = 0.997; pH, r2 = 0.915). In vivo evaluation of the catheter sensors, performed by implanting silicone rubber dual-lumen probes in the arteries of anesthetized dogs, indicates that the proposed catheter design can closely follow PCO2/pH changes induced in the animals during 6-13 h of continuous monitoring.