Bertil Karlmark

The determination of bicarbonate in nanoliter samples.

Abstract A methodological system is described which permits the determination of bicarbonate ions in samples of a few nanoliters. The samples were collected anaerobically and were then equilibrated in oil of different CO2 tensions. The pH was measured with antimony microelectrodes after each equilibration. The pH log , PCO2 curve thus obtained represented the buffer curve. Using the intratubular pH measured in situ prior to the sampling, the corresponding PCO2 was obtained from the buffer curve. Using the Henderson-Hasselbalch equation, the bicarbonate concentration was calculated for that particular PCO2. Some theoretical and practical aspects on these determinations are discussed.

The determination of titratable acid and ammonium ions in picomole amounts

Abstract A methodological system mainly designed for the use on intratubular urine samples is described, which permits the determination of titratable acid and ammonium ions in samples of a few nanoliters. The pH measurements were performed by means of antimony micro electrodes, the construction of which are described in detail. The hydroxyl ions were added to the samples from a second antimony electrode system, by an electric current. The amount of hydroxyl ions liberated was equivalent to the amount of current used. The ammonium determinations were based upon the fact that hydrogen ions were liberated from the ammonium ions by formaldehyde. The hydrogen ions were titrated in the same manner as the titratable acid. The use of two electrode systems simultaneously inserted in the droplet permitted recordings of the titration curves. The magnitude of methodological errors of these ultramicro methods are the same as those of corresponding methods using milliliter volumes.

In vivo micropuncturePCO2 measurements

SummaryAn electrode is presented which permits in vivoPCO2 measurements using a micropuncture technique. The tip diameter of the electrode is only a few microns, the tip is specially designed for measuringPCO2 in small tissue compartements.

Acid—Base Status in Dogs during Long Term Anaesthesia

The acid-base status in dogs anaesthetized with chloralose or combinations of chloralose and barbiturates was studied. No surgical procedures were used to elucidate whether the anesthesia per se changes in the acid-base status. Irrespective of the anaesthetic used, a progressive metabolic acidosis developed after 2-3 hours. This progressed for several hours despite normal arterial blood pressure and pulse rate. A theoretical model, based on the results, is presented. Even the induction of anesthesia caused an impairment of the peripheral circulation. This impairment, in combination with rising body temperature, might be strong enough to cause a detectable metabolic acidosis. It is concluded that, as compared with blood pressure and pulse rate, the acid-base status of the blood is a reliable and early sign of the impairment of circulation during anesthesia.

An ultramicro method for the separate titration of hydrogen and ammonium ions

SummaryThe measurement of pH in biological fluids is a dubious method for determination of the total hydrogen ion content. This determination requires a titration procedure. The classical titration method with adding OH− ions gives large volumetric errors in nanoliter samples. The method presented here for ultramicro analyses consists of the liberation of OH− ions from metal oxide using a current. The amount of current used is a measure of the liberated OH− ions. This method permits titration of hydrogen ions with simultaneous recording of the titration curves. After adding formaldehyde, ammonium ions in the sample liberate equivalent amounts of hydrogen ions which can be titrated in the same way. The results are presented here as correlations between this ultramicro method and conventional macro methods, and indicate a high validity, reliability and sensitivity.

The antidiuretic hormone as an inhibitor of gastric secretion.

Male Heidenhain pouch dogs were used to evaluate the antidiuretic hormone as a physiological inhibitor of gastric acid secretion. The dogs were stimulated to a constant gastric secretion by food and 40-minute ADH infusions of different concentrations took place. The inhibition was expressed as a percentage and plotted against the dose of ADH. The physiological significance of these doses is discussed and evaluated against already published data on normal concentrations. In our experiments we found that 30 muU/kg min markedly influenced the gastric secretion, which means that this inhibition may well occur under physiological conditions.

CO2 PERMEABILITY OF THE NEPHRON IN RELATION TO THE NATURE OF LUMINAL FLUID ACIDIFICATION

If we take a nephron luminal fluid sample out of its natural site and measure the pH in vitro, we will probably get a value that is not identical to that measured in viva There are at least two explanations for this “in vivo-in vitro pH difference”: 1. The bicarbonate buffer system is not in chemical equilibrium in vivo, but has the time to become so when the in vitro measurement is performed. This condition of a chemical nonequilibrium is sometimes also named a chemical “disequilibrium.” 2. The in vitro measurement is made at the wrong pC02 , usually due to the fact that local p C 0 , values at cellular values are not easily obtained. In the rat kidney tubule it is now recognized that the intraluminal p C 0 , is not identical to that in systemic arterial blood.’, It is, however, not clear if the “in vivo-in vitro pH difference” noticed in the tubule during different physiological B , .I and pharmacological conditions 5 can fully be explained by a high p C 0 , or if, besides, a chemical nonequilibrium condition exists. Provided the in vivo bicarbonate activity is known and the constants in the Henderson-Hasselbalch equation are known for the particular fluid under study, a chemical nonequilibrium condition theoretically can be quantitatively translated into a ApCO, condition. Of course, both circumstances can occur simultaneously, a topic unfortunately discussed only infrequently in the literature. To distinguish between the two conditions in the kidney tubule, the measurement of local p C 0 , in vivo is a useful approach. The first measurements performed using microelectrodes2 showed a 17 mm Hg higher p C 0 , in the proximal convoluted tubule of the rat as compared to that in systemic arterial blood. An extension of this study 1 showed a somewhat higher figure, 26 mm Hg, under comparable conditions. In addition, in the distal tubule as well as in the star vessel, nearly identical values of 27 mm Hg and 25 mm Hg, respectively-higher values as compared to systemic arterial blood-were obtained. The interpretation in the later study 1 was a diffusion equilibrium for CO, all over the cortex, similar to what is proposed for NH,. Since, however, a net transport of CO, takes place from the lumen to the blood, a p C 0 , difference across the cell must exist. Accordingly, a 29 rnm Hg lumen to blood p C 0 , difference was found in the rat proximal cortical tubule,* in sharp contrast to the aforementioned finding of 1 mm Hg. A calculation was made for this difference on the basis of findings from the isolated rabbit proximal convoluted tubule and an estimation of this difference of, at best, 8.7 mm Hg was obtained.?

Kidney Function and Intrarenal Blood Flow Distribution After Bleeding and Infusions of Mannitol and Dextran

Investigations were carried out on the effect of hemorrhagic hypotension on the intrarenal blood flow distribution, as studied by internal monitoring of labelled red cells with beta‐detectors, and on the kidney function with respect to clearance and concentration ability and the blood acid‐base status, together with studies on the renal hemodynamics and kidney function during the infusion of mannitol and dextran. Moderate bleeding of 20 ml/kg was found to produce only slight changes in the variables under study; however, additional bleeding of 5–10 ml/kg, which produced an anuric condition, caused an increased cortical vascular resistance, whereas in the medullary circulation this remained essentially unchanged, thus indicating a different response to vasoconstrictor mechanisms in the two renal vascular beds. The degree of shock seemed to be faithfully reflected in the acid‐base status, especially in the base excess values. Mannitol infusion had almost no effect on the variables studied except for a rise in urine production and a fall in urine osmolality. Plasma expansion with dextran caused all values to return toward the control levels, and the acid‐base status was normalized, indicating a restitution of the oxygen supply to the tissues.

Gas Flow Measurements with a Gas Dilution Technique

A new method for gas flow measurements, based on a gas dilution technique, is described. A known amount of fresh room air is injected as a tracer gas into a carrier gas stream. The downstream concentration profile of the tracer gas is recorded with a portable mass‐spectrometer. The flow rate of the carrier gas is calculated from the area under the tracer gas curve as electronically integrated. The method was tested against precision spirometers, one of the rolling seal type and one of the fluidistor type. It was shown that any rapid gas analyser might be used for the analyses, either of the tracer gas or of the carrier gas. The applicability of this method during general Anaesthesia and in other clinical situations is discussed.