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PubMed1982

The effect of respiratory and metabolic acid-base changes on ionized calcium concentration: in vivo and in vitro experiments in man and rat.

Correlation of ionized calcium concentration, [Ca2+] and blood pH has long been recognized. So far no distinction of the acid-base changes, i.e. respiratory changes or metabolic changes seemed necessary. The present study, with the use of a recently developed system for in vivo analysis of [Ca2+], and with in vitro experiments reinvestigates this question. In a first series respiratory and metabolic changes were induced in rats. Changes of [Ca2+] (delta [Ca2+]) and of plasma pH (delta pH) were recorded continuously in vivo, plasma bicarbonate, [HCO-3] was measured in vitro. In a second series respiratory and metabolic changes were induced in sixteen volunteers and, separately, in vitro in plasma and modified Ringer solution, and the same parameters were determined. In all experiments delta [Ca2+] correlates negatively with delta pH. However, the correlation in respiratory changes was significantly less as compared to that in metabolic changes. As expected, delta [HCO-3] correlates positively with pH in metabolic and negatively in respiratory changes. We conclude from these experiments that in metabolic changes the effects of calcium-albumin interaction and calcium complexation with bicarbonate are additive, whereas both effects oppose each other in respiratory changes. This might explain the blunted effect of pH changes on [Ca2+] in respiratory changes.

Acidosis↗
PubMed1996

Effects of hypoxic pulmonary vasoconstriction on pulmonary gas exchange.

Several reports have suggested that hypoxic pulmonary vasoconstriction (HPV) might result in deterioration of pulmonary gas exchange in severe hypoxia. We therefore investigated the effects of HPV on gas exchange in normal and diseased lungs. We incorporated a biphasic HPV stimulus-response curve observed in intact dogs (S. Brimioulle, and R. Lejeune, J.L. Vachièry, M. Delcroix, R. Hallemans, and R. Naeije, J. Appl. Physiol. 77: 476-480, 1994) into a 50-compartment lung model (J.B. West, Respir. Physiol. 7: 88-110, 1969) to control the amount of blood flow directed to each lung compartment according to the local hypoxic stimulus. The resulting model accurately reproduced the blood gas modifications caused by HPV changes in dogs with acute lung injury. In single lung units, HPV had a moderate protective effect on alveolar oxygenation, which was maximal at near-normal alveolar PO2 (75-80 Torr), mixed venous PO2 (35 Torr), and PO2 at which hemoglobin is 50% saturated (24 Torr). In simulated diseased lungs associated with 40-60 Torr arterial PO2, however, HPV increased arterial PO2 by 15-20 Torr. We conclude that HPV can improve arterial oxygenation substantially in respiratory failure.

Acidosis, Respiratory↗
PubMedDate not supplied

The mixed acid-base disturbances of severe canine babesiosis.

Thirty-four dogs suffering from severe babesiosis caused by Babesia canis rossi were included in this study to evaluate acid-base imbalances with the quantitative clinical approach proposed by Stewart. All but 3 dogs were severely anemic (hematocrit <12%). Arterial pH varied from severe acidemia to alkalemia. Most animals (31 of 34; 91%) had inappropriate hypocapnia with the partial pressure of CO2 < 10 mm Hg in 12 of 34 dogs (35%). All dogs had a negative base excess (BE; mean of - 16.5 mEq/L) and it was below the lower normal limit in 25. Hypoxemia was present in 3 dogs. Most dogs (28 of 34; 82%) were hyperlactatemic. Seventy percent of dogs (23 of 33) were hypoalbuminemic. Anion gap (AG) was widely distributed, being high in 15, low in 12, and normal in 6 of the 33 dogs. The strong ion difference (SID; difference between the sodium and chloride concentrations) was low in 20 of 33 dogs, chiefly because of hyperchloremia. Dilutional acidosis was present in 23 of 34 dogs. Hypoalbuminemic alkalosis was present in all dogs. Increase in unmeasured strong anions resulted in a negative BE in all dogs. Concurrent metabolic acidosis and respiratory alkalosis was identified in 31 of 34 dogs. A high AG metabolic acidosis was present in 15 of 33 dogs. The lack of an AG increase in the remaining dogs was attributed to concurrent hypoalbuminemia, which is common in this disease. Significant contributors to BE were the SID, free water abnormalities, and AG (all with P < .01). Mixed metabolic and respiratory acid-base imbalances are common in severe canine babesiosis, and resemble imbalances described in canine endotoxemia and human malaria.

Acid-Base Imbalance↗
PubMed1984

Effects of aminophylline on diaphragmatic fatigue during acute respiratory failure.

The effects of aminophylline on diaphragmatic fatigue and recovery in the face of hypoxemia and hypercapnic acidosis were studied in anesthetized, spontaneously breathing, dogs. The phrenic nerves were stimulated supramaximally at 10, 20, 50, and 100 Hz during 2 s with electrodes placed around the fifth roots, and the resulting transdiaphragmatic pressure (Pdi) was measured with balloon catheters. The dogs were occluded before the stimulations at functional residual capacity. The latter was monitored by measuring the end-expiratory transpulmonary pressure, which remained constant throughout the experiment. Diaphragmatic fatigue was produced by resistive loaded breathing. At the end of the runs, which lasted 15 +/- 2 min, all the dogs were severely hypoxemic (30 +/- 5 mmHg), hypercapnic (65 +/- 4 mmHg), and acidotic (7.1 +/- 0.05). During the fatigue runs, phrenic stimulation resulted in a marked decrease in Pdi, which amounted at 20 Hz to 70 +/- 8% and 45 +/- 12% of the control values 5 min after the onset of the fatigue runs and at the end, respectively. After recovery (3 h), Pdi and arterial blood gas determinations returned to control values. Identical fatigue runs were repeated with aminophylline infusion (loading dose, 6 mg/kg in 10 min and maintenance dose, 1 mg/kg/h), leading to a plasmatic concentration of 16.4 +/- 2 mg/l. Aminophylline protected the diaphragm against fatigue, and despite the presence of hypoxemia and hypercapnic acidosis, the Pdi generated for a 20 Hz stimulation of the phrenic nerves at identical times of the preceding run amounting to 100 +/- 15% and 85 +/- 10% of control values, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Acidosis, Respiratory↗