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1. Carbon dioxide titration curves were determined in vivo in dog and man at various degrees of acute non-respiratory acidaemia and alkalaemia. 2. The slope of the CO2 titration curve (?log Pco2/?pH) was found to increase with the severity of the acute non-respiratory acidaemia. In states of acute non-respiratory alkalaemia the slope (?log Pco2/?pH) tended towards unity. 3. A simple scheme based on the CO2 titration curves determined in vivo has been proposed for the assessment of acute acid-base disturbances in man. 4. Carbon dioxide titration curves were also determined in vivo in patients with chronic respiratory and non-respiratory acidaemia and it was found that these curves were not significantly different from those obtained in states of acute acid-base disturbances. It is therefore suggested that the scheme described in this paper is applicable to all acid-base disturbances.

1. Nifedipine is used in patients with stable angina of effort and any resulting change in symptoms is attributed to several effects of nifedipine. However, there have been indications in such patients that one effect of nifedipine could be an increase in the severity of myocardial ischaemia, and the present report involves a trial the results of which could explain this effect. 2. In the present trial, the effect of nifedipine on myocardial ischaemia was assessed by using the maximal ST/heart rate slope. This slope was used as an index of myocardial ischaemia because, in our hands in patients with angina, an increase or a decrease in the value of the slope respectively indicated an increase or a decrease in the severity of myocardial ischaemia as assessed by coronary arteriography. 3. The maximal ST/heart rate slope was obtained at least twice in each of 23 patients with stable angina, with and without nifedipine; two patients were examined twice and three other patients were examined after an increased dose. Nifedipine resulted in an increase in the slope in 24 of the 28 comparisons, no change in three and a decrease in one comparison; there was a statistically significant (P < 0.005; n = 28; paired t-test) increase in the maximal ST/heart rate slope. A further increase in the slope was obtained by increasing the dose of nifedipine in two out of three patients. 4. The increase in the maximal ST/heart rate slope occurred in the absence of any effect of nifedipine on the initial level of the ST segment. 5. It is concluded that nifedipine therapy in the patients with stable angina caused increases in the maximal ST/heart rate slope, suggesting an increase in the severity of myocardial ischaemia.

1. Stimulation of atrial receptors by distension of a balloon in the left atrium of anaesthetized dogs results in a reflex diuresis mediated by a humoral agent of unknown identity. 2. In previous investigations, a substance was recovered in a low molecular weight fraction from Bio-Gel P-2 (100-1800 daltons) and shown to be related to the reflex diuresis. 3. In this investigation, the active Bio-Gel P-2 fraction was partitioned with ethyl acetate at pH 11.0, with subsequent partition of the aqueous phase with ethyl acetate at pH 7.4; the activity of the humoral agent was soluble in ethyl acetate at pH 7.4. 4. These investigations suggest that the humoral agent is a low molecular weight, lipophilic and weakly acidic substance. 5. The substance is not antidiuretic hormone (ADH) as vasopressin is insoluble in ethyl acetate at pH 7.4.

1. Simultaneous CO2 titration curves of arterial and mixed venous blood were determined in both dog and man in vivo. 2. The slopes of the CO2 titration curves of mixed venous blood were significantly less than those of the corresponding arterial curves. 3. The non-respiratory pH values of the CO2 titration curves of mixed venous blood were significantly greater than those of the corresponding arterial curves. 4. The theoretical explanations of these differences have been discussed.

1. CO2 titration curves in vivo were determined at various degrees of acute non-respiratory acidaemia in man. 2. The slope of the CO2 titration curve was found to increase as the severity of the acute non-respiratory acidaemia increased. 3. A simple scheme based on the CO2 titration curves in vivo has been proposed for the assessment of acute acidaemia in man.

1. The existing methods for assessing states of acidosis are discussed with particular reference to non-respiratory acidosis. Most of these methods are based either on the Henderson—Hasselbalch equation or on the direct extrapolation of in vitro studies on blood to the whole animal. The evidence available shows that these methods cannot be used to obtain an accurate assessment of disturbances of acid-base balance in the whole animal. 2. The experiments were designed to investigate the acid-base parameters of an animal when a respiratory acidosis was superimposed on a non-respiratory acidosis caused by the infusion of n HCl; from these experiments it was possible to construct CO2 titration curves at various levels of non-respiratory acidosis. 3. A scheme which is based upon the CO2 titration curves, has been proposed for assessing an acute acid-base disturbance in terms of its respiratory and non-respiratory components. 4. The use of sodium bicarbonate to correct a non-respiratory acidosis was investigated, and it was shown that the amount of sodium bicarbonate required varied with the rate of infusion. No firm predictions could be made regarding the dose of bicarbonate required, but from the results of the present experiments an infusion rate of 0·1 mEq kg-1 min-1 is recommended in dogs.

1. An open-circuit method for the measurement of oxygen consumption in children which is suitable for use during cardiac catheterization has been described. 2. Since it has been previously shown that there is no systematic error in this method, the accuracy of the method is described by the random error (i.e. reproducibility). The reproducibility of the method has been determined by the repeated measurement of oxygen consumption in children with congenital diseases of the heart under specified ‘standard’ conditions. 3. A simple method of predicting the oxygen consumption in these children was devised by subjecting the data to a multivariate regression analysis. 4. It is concluded that the accuracy of these predictions, although considerably better than that in the published literature, is not good enough to merit its use in the routine haemodynamic assessment.