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At least 685 records · Page 38Linked to original sources
PubMed1993

Effects of carbonic anhydrase inhibition on ventilation-perfusion matching in the dog lung.

Lung carbonic anhydrase (CA) permits rapid pH responses when changes in regional ventilation or perfusion alter airway and alveolar PCO2. These pH changes affect airway and vascular resistances and lung compliance to optimize the balance of regional ventilation (VA) and perfusion (Q) in the lung. To test the hypothesis that these or other CA-dependent mechanisms contribute to VA/Q matching, we administered acetazolamide (25 mg/kg intravenously) to six anesthetized and paralyzed dogs and measured VA/Q relationships before and after CA inhibition by the multiple inert gas elimination technique. Four other groups of dogs were studied to control for possible confounding effects of time under anesthesia and nonselective CA inhibition by acetazolamide: (a) saline placebo as a control for duration of anesthesia, (b) 4% CO2 inhalation to mimic systemic CO2 retention, (c) 1 mg/kg benzolamide (a selective renal CA inhibitor) or 0.5 meq/kg HCl to mimic systemic metabolic acidosis, and (d) 500 mg/kg 4,4'-dinitrostilbene-2,2'-disulfonate (an inhibitor of red cell band 3 protein) to mimic the respiratory acidosis arising from an intracapillary block to rapid mobilization of plasma HCO3- in CO2 exchange. Acetazolamide increased VA/Q mismatch and reduced arterial PO2 measured at equilibrium but these did not occur in the control group. There was no deterioration in VA/Q matching when systemic respiratory acidosis produced either by CO2 inhalation or 4,4'-dinitrostilbene-2,2'-disulfonate or metabolic acidosis (benzolamide or HCl) were imposed to mimic the effects of acetazolamide apart from its inhibition of lung CA. These results support the concept that lung CA subserves VA/Q matching in the normal lung.

Acetazolamide↗
PubMed2002

Influence of acidosis and hypoxia on liver ischemia and reperfusion injury in an in vivo rat model.

The contribution of acidosis to the development of reperfusion injury is controversial. In this study, we examined the effects of respiratory acidosis and hypoxia in a frequently used in vivo liver ischemia and reperfusion (I/R) injury rat model. Rats were anesthetized with intraperitoneal anesthetics and subjected to partial liver ischemia (70%) for 60 min and subsequent reperfusion for 90 min under the following conditions: 1) no acidosis and normoxia, maintained by controlled ventilation; 2) acidosis and normoxia, maintained by passive supply with oxygen; 3) no acidosis and hypoxia, maintained by bicarbonate administration without respiratory support; and 4) acidosis and hypoxia, i.e., without respiratory support or pH correction. Changes in plasma aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels were measured as parameters of hepatocellular injury, and bile secretion was monitored. AST and ALT levels were lowest in the ventilated rats and highest in the bicarbonate-treated rats. No differences in bile secretion were found between groups. Our results suggest that respiratory acidosis significantly enhanced liver I/R injury under normoxic conditions, whereas respiratory acidosis significantly reduced liver I/R injury under hypoxic conditions.

Acidosis↗
PubMedDate not supplied

Restoration of the phosphaturic effect of parathyroid hormone in lithium-treated rats.

The purpose of this study was to clarify the means by which lithium induced a greatly diminished phosphaturic response to parathyroid hormone (PTH). Acutely thyroparathyroidectomized lithium-treated rats did not respond to PTH whereas similarly prepared animals in the presence of metabolic or respiratory acidosis exhibited a large phosphaturic response. Respiratory alkalosis significantly decreased fractional phosphate excretion and blocked the phosphaturic effect of PTH whereas PTH induced increases in cyclic AMP excretion in these animals. Lithium increased urinary excretion of oxoglutarate and citrate. In metabolic acidosis the restoration of PTH-dependent phosphaturia is accompanied by decreased organic acid excretion. No significant decrease of urinary citrate and oxoglutarate excretion occurred in respiratory acidosis in lithium-treated rats. It is suggested that PTH-dependent phosphate transport is mediated by intracellular pH but the increased excretion of citrate and oxoglutarate may reflect high intracellular levels of bicarbonate.

Acidosis↗
PubMed1992

Acid-base regulation during exercise and recovery in humans.

Arterial pH, PCO2, standard bicarbonate, lactate, and ventilation were measured with a high sampling density during rest, exercise, and recovery in normal subjects performing upright cycle ergometer exercise. Three 6-min constant-work exercise tests (moderate, heavy, and very heavy) were performed by each subject. We found a small respiratory acidosis during the moderate-intensity exercise and an early respiratory acidosis followed by a metabolic acidosis for the heavy- and very-heavy-intensity exercise. During recovery, arterial pH rapidly returned to the preexercise value for the moderate-intensity work. However, arterial pH decreased further during the first 2 min of recovery for the heavy- and very-heavy-intensity work, before a slower return toward the resting values. We conclude that arterial acidosis is the consistent arterial pH reaction for moderate-, heavy-, and very-heavy-intensity cycle ergometer exercise in humans and that this acidosis is blunted but not eliminated by the ventilatory response. During recovery, the return to resting arterial pH and PCO2 and standard bicarbonate appears to be determined by the rate of lactate decline.

Acid-Base Equilibrium↗
PubMed1982

Effects of acute acid-base disturbances on K+ delivery to the juxtamedullary end-descending limb.

Effects of acute-base disturbances on fractional delivery of potassium to the juxtamedullary end-descending limb were examined by micropuncture in the rat to test the hypothesis that potassium is reabsorbed from the collecting duct and is secreted in juxtamedullary pars recta or descending limb in the renal medulla. In metabolic acidosis, fractional potassium delivery was only slightly reduced compared with control values and was a function of potassium excretion, as the hypothesis predicts. Fractional potassium delivery was sharply reduced both in respiratory acidosis and metabolic alkalosis and was no longer a function of potassium excretion. Although seemingly inconsistent with the recycling hypothesis, the latter finding may be reconciled by the following observations. In respiratory acidosis, vasa recta blood flow nearly doubled, which would lead to vascular washout of interstitial potassium. In metabolic alkalosis, flow rate in the pars recta or descending limb was reduced by 28%, which would limit transepithelial potassium addition. The results indicate complex effects of acid-base disturbances on fractional potassium delivery to the end-descending limb, which can be unified by postulated changes in transepithelial potassium concentration differences across the juxtamedullary pars recta or descending limb. An unexpected observation emerged--fractional delivery of water to the end-descending limb declined as a function of plasma bicarbonate concentration when all groups were combined.

Acid-Base Imbalance↗
PubMed1996

Effects of serosal-side acidosis on cell pH (pHi) and membrane electrical properties in gastric mucosa.

Acute gastric mucosal injury and bleeding occur in the settings of both respiratory acidosis or metabolic acidosis secondary to systemic sepsis or shock. Respiratory acidosis, however, is more predictably associated with acute injury than metabolic acidosis. We hypothesized that the gastric surface epithelial cells are more susceptible to acute increases in PCO2 than to acute decreases in HCO3-, even for the same level of extracellular acidification. To evaluate this hypothesis, we used intracellular microelectrodes to measure pHi, cell membrane potential (Vc), as well as ion conductances of the apical (Ga) and basolateral (Gb) membranes and the paracellular pathway (Gs) in gastric mucosal cells during acute changes in serosal PCO2 or HCO3-. Necturus antral mucosae were mounted in Ussing chambers, perfused on both sides by Ringer solution (40 mmHg PCO2, 18 mM HCO3-, pH 7.3). Measurements were performed before and during increases in PCO2 (80 mmHg, pH 7.0) or decreases in HCO3- (7.2 mM, pH 6.8 or 2.4 mM, pH 6.4). Both forms of acidosis acidified pHi, depolarized membrane potentials, and decreased ion conductances across apical and basolateral membranes, but not the paracellular pathways. For the same level of extracellular acidification, increases in PCO2 were more effective than acute decreases in HCO3- in acidifying pHi and eliciting disturbances in voltage-generating and ion permeability properties of the cell membranes. These findings suggest that pH-buffering mechanisms in gastric surface cells respond less effectively to high PCO2 than low HCO3.

Acidosis↗
PubMed1976

[The acid-base equilibrium during mouse lymphoblastic leukemia].

In transplantable and in spontaneous lymphoblastic mouse leukemia blood pH, PCO2, TCO2 and BB were examined. Spontaneous Gross-leukemia in AKR mice was found to develop in its final phase respiratory acidosis. Transplantable (TAL) leukemia of AKR mice presents from the onset a tendency toward respiratory acidosis. "L-1210"-leukemia, on the contrary, was shown to alcalise the recipients during the first 8 days after inoculation, later on it can bring about an acidosis. The pH-deviations in "L-1210"-leukemia display a respiratory character in syngeneic DBA/2J recipients, whereas in semiallogeneic recipients the observed changes are metabolic or mixt in nature. This finding strongly argues for the importance of histocompatibility. Intranodally inoculated animals distinctly differ in their parameters in comparison to intravenously and intraperitoneally recipients, hence, an important role of the tissular-milieu which is put first in contact with the leukemic factor must be concluded.

AKR murine leukemia virus↗
PubMed1991

[Hypo- and hyperventilation: consequences for acid-base balance].

Deviations of the alveolar ventilation rate from normality induce respiratory acid-base disturbances. Alveolar hyperventilation leads to hypocapnia and thus respiratory alkalosis whereas alveolar hypoventilation induces hypercapnia leading to respiratory acidosis. The changes in CO2 induce compensatory alterations of renal bicarbonate transport: Hypercapnia stimulates renal reabsorption of bicarbonate whereas hypocapnia enhances urinary bicarbonates. The plasma bicarbonate concentration rises in response to hypercapnia and falls following hypocapnia. Renal regulation of plasma bicarbonate results in a characteristic dependence on systemic PCO2 permitting the formation of diagnostic criteria for respiratory imbalance of acid-base homeostasis. In chronic respiratory acidosis plasma bicarbonate should rise by 0.35 mmol/l per mmHg increase in PCO2. In chronic respiratory alkalosis, on the other hand, plasma bicarbonate should fall by 0.4 mmol/l for every mmHg decrease in PCO2. If the measured bicarbonate values do not fall into this expected range, acute respiratory or mixed (respiratory and metabolic) acid-base disturbances should be suspected. The clinical significance and application of these diagnostic criteria are illustrated by examples.

Acid-Base Equilibrium↗
PubMed2003

Ventilating the patient with severe asthma: nonconventional therapy.

Conventional pharmacotherapy of severe asthma and status asthmaticus includes beta2-sympathomimetics, theophylline, corticosteroids and occasionally topical anticholinergics (ipratropium bromide). Since hypoxemia is the most severe phenomenon in status asthmaticus the administration of oxygen is mandatory. However, if the bronchodilating therapy fails and hypoxemia continues, usually respiratory failure develops due to progressive respiratory muscle failure. An increasing PaCO(2) and respiratory acidosis are indications for mechanical ventilatory support to unload the failing respiratory pump. Nowadays, there is increasing consensus that ventilatory support should be administered primarily as non-invasive ventilation (NIV) via a face mask1. However, in a significant number of patients with severe asthma NIV is either contraindicated or insufficient. In this case usually the patient must be endotracheally intubated and mechanically ventilated "invasively". Intubation and ventilation of patients with severe asthma or status asthmaticus is associated with a high incidence of complications compared to patients ventilated for other causes of respiratory failure2,3. Therefore the risks of invasive mechanical ventilation have to be weighted carefully to ongoing conservative therapy and NIV. Cardiopulmonary arrest and severe hypoxemia in spite of O2 supplement and NIV are absolute criteria for intubation and ventilation. Mostly deterioration in mental status and exhaustion are the clinical findings leading to mechanical ventilation. Decision is guided rather by the course of the deterioration (how fast the patient's condition is worsening) than by pathological values alone. An increased PaCO(2) with moderate respiratory acidosis alone is not per se an indication for mechanical ventilation. However, a continuously rising PaCO(2) or the development of a severe metabolic acidosis after 1 hour of NIV is a strong argument for invasive mechanical ventilation. Other criteria are evidence of cardiac failure with fall in pulse volume and dysrhythmias, pneumomediastinum or pneumothorax (which has to be drained before mechanical ventilation!).

Anesthetics, Inhalation↗
PubMed1998

Repercussions of acidosis on postnatal erythrocyte deformability in term and preterm newborns.

Erythrocyte deformability in newborns, a determining factor in neonatal blood hyperviscosity, is also often responsible for decreased blood flow in the microcirculation of several organs, such as the brain, kidneys, and digestive tract. In 70 neonates classified by gestational age and by the presence or absence of acidosis, we analyzed the filterability of erythrocytes in suspension through 5 polycarbonate membranes and its relation with gasometric determinations, Anion-GAP, plasma viscosity, plasma osmolality, erythrocyte volumes, and plasma lipids. Using a logistic regression analysis, controlling gestational age (p = 0.17), mean corpuscular volume (MCV) (p = 0.63), and mean corpuscular hemoglobin concentration (MCHC) (p = 0.21), the presence of acidosis (p = 0.0049, odds ratio: 3.60) is a risk factor for an increased rigidity index in newborns. Metabolic and respiratory acidosis were significantly related with lower erythrocyte deformability in the early neonatal period (below 5 days of age). Decreased plasma bicarbonate and increased Anion-GAP (even in compensated metabolic acidosis), as well as increased pCO2 in respiratory acidosis, were significantly related with decreased erythrocyte filterability. In newborns under 32 weeks of gestational age the increase in erythrocyte rigidity index is more related to the low gestational age and increased MCV than to the presence of acidosis. These factors can produce changes in the microcirculation of these patients.

Acidosis↗
PubMed1988

Acidosis, hypoxia and stress hormone release in response to one-minute inhalation of 80% CO2 in swine.

The study pertains to a series of investigations on the effects of CO2 inhalation as used for pre-slaughter anaesthesia in swine. Acid/base parameters, blood oxygen tension, plasma Na, K, Ca and stress hormone concentrations were monitored in Yorkshire swine before, during, and for 10 min after the animals were descended for 1 min into 80% CO2 in air. Severe respiratory acidosis (PaCO2 approximately 50 kPa, arterial pH approximately 6.6) and hypoxia (PaO2 approximately 4kPa) had developed after 45 s of the CO2 inhalation. The corresponding changes in venous blood were less drastic (PvCO2 approximately 17 kPa, pH 7.1, PvO2 approximately 4 kPa). Readjustment to PaCO2 approximately II kPa, arterial pH 7.2, and PaO2 approximately 13 kPa had occurred at 1 min post CO2. Four minutes later the respiratory acidosis had become converted into metabolic acidosis subjected to partial respiratory compensation (arterial pH 7.3 in the presence of moderate hypocapnia and hyperoxaemia). The cause of this metabolic acidosis (present also at 10 min post CO2) was apparently hypoxia-induced anaerobic metabolism (= lactic acid production). Apparently due to hydrogen ion transport into the cells in exchange for other cations, hyperkalaemia (K approximately 6.6 mmol l-1), and a 7 mmol l-1 increase in plasma Na had developed at 1.5 min later. The CO2 inhalation did not change the total plasma Ca significantly. The transport of the swine from the stable to the immediate pre-experimental situation induced a 3-fold increase in plasma cortisol concentration (PC, to approximately 130 mmol l-1). No further increase in PC occurred in response to the CO2 inhalation. It indicates that no additional emotional strain was imposed upon the animals during the CO2 exposure.(ABSTRACT TRUNCATED AT 250 WORDS)

Acidosis, Respiratory↗
PubMed1993

Depth profiles of pH and PO2 in the isolated brain stem-spinal cord of the neonatal rat.

We have measured depth profiles of extracellular pH (pHECR) and PO2 (PtO2) as well as the kinetics of changes of pHECR in the isolated brain stem-spinal cord preparation of the neonatal rat using pH and PO2 microelectrodes that entered from the ventral surface. When the preparation was superfused with control mock cerebrospinal fluid (Control mock CSF; pH = 7.5, PO2 = 630 Torr, PCO2 = 28 Torr, at 27 degrees C), the pH in the medulla diminished with a nearly constant gradient from the surface to a depth of about 1000 microns, the slope being about 0.1 pH unit per 100 microns. A similar gradient in the 200 to 300 microns of the CSF above the surface suggested existence of unstirred layers despite continuously flowing superfusate. The pH gradient in the spinal cord was somewhat smaller than that in the medulla. The PO2 gradients in both medulla and spinal cord were about 100 Torr per 100 microns from 200 microns above to 100 to 200 microns below the surface; PO2 reached zero at about 450 (medulla) to 600 microns (spinal cord). Although the preparation was anoxic and acidic except for a small layer below the surface, respiratory activity was recorded for several hours in C4 phrenic roots. The kinetics of changes in pHECF were recorded at 100 and 200 microns depth while rapidly replacing the control mock CSF by more acidic CSF, either with increased PCO2 ("Respiratory acidosis") or by adding fixed acid ("Metabolic acidosis"). The changes in pHECF were smaller than those in pHCSF, particularly during respiratory acidosis, as a result of the buffering of the brain tissue. Our results show the importance of superficial layers of the ventral medulla in producing respiratory rhythmicity; they further suggest that somewhat alkaline CSF (pH about 7.8) should be used in this preparation to ensure physiologic surface pH values despite unstirred surface layers.

Animals↗
PubMed1967

Acid-base alterations and renal gluconeogenesis: effect of pH, bicarbonate concentration, and PCO2.

In previous studies it was found that renal cortical slices from rats with induced metabolic acidosis have an increased capacity to produce glucose, whereas cortical slices from rats with metabolic alkalosis manifest decreased gluconeogenesis. To evaluate the relative influence of extracellular fluid pH, [HCO(3) (-)], and carbon dioxide tension on renal gluconeogenesis, we observed glucose production by cortex from rats with induced respiratory acidosis, and by cortex taken from normal animals and incubated in acid and alkaline media. We found glucose production to be increased in cortex from rats with respiratory acidosis, as is the case in metabolic acidosis. Glucose production by slices from normal rats was increased in media made acidic by reducing [HCO(3) (-)], and decreased in media made alkaline by raising [HCO(3) (-)]. These effects were evident whether the gluconeogenic substrate employed was glutamine, glutamate, alpha-ketoglutarate, or oxalacetate. Glucose production was also increased in media made acidic by raising CO(2) tension and decreased in media made alkaline by reducing CO(2) tension. These data indicate that both in vivo and in vitro, pH, rather than CO(2) tension or [HCO(3) (-)], is the most important acid-base variable affecting renal gluconeogenesis. The findings suggest that a decrease in extracellular fluid pH enhances renal gluconeogenesis through direct stimulation of one of the rate-limiting reactions involved in the conversion of oxalacetate to glucose. We hypothesize that the resultant increase in the rate of removal of glutamate, a precursor of oxalacetate, may constitute an important step in the mechanism by which acidosis increases renal ammonia production.

Acidosis, Respiratory↗
PubMed1980

[The dependence of acid-base balance in the aqueous humor on carbon dioxide and oxygen diffusion through the cornea (author's transl)].

In 20 rabbits the effect of, gas exchange, between the aqueous humor and surrounding air through the cornea, on the acid-base balance in the aqueous was investigated. It was found that tight eye closure leads to a decrease of oxygen partial pressure in the aqueous humor. A concurrent displacement of the acid-base balance in the form of a mixed acidosis (respiratory and metabolic acidosis) was demonstrated.

Acid-Base Equilibrium↗
PubMed1998

The role of adenosine in rat coronary flow regulation during respiratory and metabolic acidosis.

The role of adenosine in rat coronary flow regulation during acidosis was evaluated in isolated, perfused, Langendorff rat heart preparations exposed to brief periods of hypercapnic or metabolic acidosis. Acidosis resulted in increases in coronary flow rate, in conjunction with decreases in ventricular contractile tensions. Heart rates were non-significantly increased. Two non-selective adenosine antagonists, caffeine and 8-phenyltheophylline, markedly attenuated the increases in coronary flow during hypercapnic acidosis without affecting the decline in contractile tension or the heart rate. ZM 241385 (4-(2-[7-amino-2-(2-furyl)[1,2,4]triazolo[2,3-a]triazin-5-ylami no]ethyl)phenol), a selective adenosine A2A receptor antagonist, also blocked hypercapnic acidosis-evoked coronary flow rate increases. The adenosine A1 selective antagonist, 8-cyclopentyl-1,3-dipropylxanthine, did not affect flow rate increases during hypercapnic acidosis. SCH 58261 (5-amino-7-(2-phenyl ethyl)-2-(2-furyl)pyrazolo-[4,3-e]-1,2,4-triazolo[1,5-c] pyrimidine, a selective adenosine A2A receptor antagonist, blocked the increases in coronary flow rate evoked by metabolic acidosis. An adenosine transport inhibitor, dipyridamole, doubled coronary flow rates during hypercapnic acidosis. When taken in conjunction with previous reports that acidosis enhances adenosine release from cardiac preparations, these results suggest that adenosine is a significant contributor to acidosis-evoked increases in coronary flow.

Acidosis↗