Calcium out of control

The accumulation of calcium during myocardial hypoxia or ischaemia followed by reoxygenation or reperfusion is related to the development of cell necrosis and may be an important causal mechanism. Influx of calcium is a late event during hypoxia but occurs abruptly on reoxygenation or reperfusion. On reoxygenation calcium influx is not altered by nifedipine or quiescence but can be prevented by nickel (3 mM), cyanide (5 mM) or FCCP (10(-6) M). The extracellular marker 51Cr-EDTA does not enter the intracellular fluid on reoxygenation but can when the cell membrane is disrupted by a detergent, Brij'35, or the calcium paradox. The results suggest that the uptake of calcium on reoxygenation or reperfusion is related to the reintroduction of oxygen and caused by an increased calcium influx down the concentration gradient. The flux is not through the slow calcium channel and is not due to disruption of the membrane. The effects of CN- and FCCP and the unaltered calcium efflux suggest that the major part of the calcium uptake is stored in intracellular compartments and is not located in the intracellular fluid.

The role of digitalis in the future

Cardiac glycosides exert an acute positive inotropic effect on the normal and failing heart. Recent evidence establishes that the positive inotropic effect is maintained over several months in many patients. The effectiveness of long-term treatment with cardiac glycosides in relieving symptoms is less certain; only a small subset of patients benefits. An effect on mortality is not established. The use of digoxin in the treatment of mild heart failure is questionable since the drug has serious side-effects and the efficacy in patients already taking diuretics has not been established. The use of glycosides in the treatment of severe chronic heart failure is being challenged because of the availability of powerful diuretics, new vasodilators and alternative positive inotropes.

The calcium paradox in isolated frog heart: Ringer revisited

Restoration of a normal calcium concentration in the perfusate of isolated hearts after a short period of calcium-free perfusion may result in irreversible cell damage (calcium paradox). We have compared the calcium paradox in rat and frog hearts. Perfusion with zero calcium for 8 min at 37 degrees C predisposed the rat heart to the paradox. After the reintroduction of calcium to the perfusate resting tension rose, developed tension did not recover, ultrastructural changes occurred and enzyme loss was substantial. In the frog heart a calcium paradox did not occur after 8 min of calcium-free perfusion at 23 degrees C. Removal of both potassium and calcium caused a rise in resting tension on reintroduction of control solution, but the rise was only transient and absent if potassium was present during the perfusion with zero calcium. At 37 degrees C no complete calcium paradox occurred after 8 min calcium-free perfusion. Only a small rise in resting tension was apparent, and developed tension partially recovered. A calcium paradox could only be induced in the frog heart after calcium-free perfusion at 37 degrees C for 30 min. Ultrastructural changes were apparent and resting tension rose but even under these conditions the recovery of developed tension was not abolished. Release of creatine kinase was 161 +/- 55 IU/g dry tissue during the 15 min after reintroduction of calcium (n = 5). Calcium-free perfusion for 8 min resulted in a smaller release of creatine kinase over 15 min (39 +/- 11 IU/g dry tissue. n = 5).(ABSTRACT TRUNCATED AT 250 WORDS)

High potassium concentration in a parenteral preparation of glyceryl trinitrate. Need for caution if given by intracoronary injection

Glyceryl trinitrate (Tridil) was given by intracoronary injection to a patient who developed coronary artery spasm during angioplasty. Transient exacerbation of chest pain and electrocardiographic changes occurred. This formulation of the drug contains a high concentration of potassium ions and should not be given by this route.

Symptoms, haemodynamics, and exercise capacity during long term treatment of chronic heart failure. Experience with pirbuterol

An open study of long term treatment with an oral beta 2 agonist (pirbuterol 20 mg three times daily) was undertaken in 63 patients with severe chronic heart failure. During three months of treatment 20 (32%) patients died, of whom 16 were taking the drug at the time of death. Mortality was related to initial functional class (New York Heart Association classification: 23% in grade III and 75% in grade IV). Concomitant treatment with digoxin did not affect mortality. The drug was well tolerated by most patients but unwanted side effects necessitated withdrawal of the drug in six (10%). Thirty-five patients were continuing to take the drug after three months, of whom 22 reported symptomatic improvement and only four deterioration. There was a relation between symptomatic improvement and increase in exercise capacity. At initial haemodynamic assessment a single dose of pirbuterol increased the cardiac index by 34% and the stroke index by 21%. Left ventricular filling pressure fell by 23% and systemic vascular resistance by 22%. Haemodynamic reassessment after three months of continuous treatment in 29 patients showed maintained improvement in the group as a whole, although individual variation was considerable. There was no apparent relation between haemodynamic improvement and improvement in exercise duration and symptoms. Severe heart failure has a poor prognosis. Identification of those patients who may derive benefit from treatment with a particular drug is not yet possible.

Coronary sinus potassium concentration recorded during coronary angioplasty

Coronary sinus potassium concentration was measured continuously in two patients undergoing angioplasty of a significant stenosis of the left anterior descending coronary artery. After each coronary occlusion there was a transient rise in coronary sinus plasma potassium concentration caused by washout of potassium which had accumulated in the extracellular fluid during the short period of ischaemia. There were no significant changes in the surface electrocardiogram and the patients experienced no chest pain. Changes in coronary sinus potassium concentration provide a sensitive and early indication of myocardial ischaemia in man.

Measurement of pulmonary venous and arterial pH oscillations in dogs using catheter tip pH electrodes

Respiratory pH oscillations were studied in situ in the aorta and superior vena cava of rabbits, and in the pulmonary vein and aorta of open-chested dogs, using catheter tip pH electrodes. Preliminary experiments on two spontaneously breathing rabbits showed pH oscillations of 0.006-0.010 pH units in the ascending aorta at a respiratory rate of 40/min. No oscillations were apparent in the superior vena cava. In anaesthetized, ventilated dogs, the delay from the upstroke in airway pressure to the onset of the alkaline limb of the pH oscillation was 1.15 +/- 0.9 s in the pulmonary vein and 4.1 +/- 0.1 s in the descending aorta (mean + S.E. of mean, n = 28 tracings in four dogs). Pulmonary venous oscillations were equal to or larger in amplitude than those in the aorta. Aortic oscillations became proportionately smaller at shorter respiratory cycle lengths, although both were related to tidal volume. Stop flow experiments were performed using a pH electrode placed in situ in the left atrium inside a wide-bore tube. A small fall in pH occurred when flow was stopped (-0.0036 +/- 0.0012, mean +/- S.E. of mean, n = 22 recordings in four dogs). The findings were not dependent upon the phase of the oscillation at which flow was stopped. Mean plasma free haemoglobin was very low (1.6 mg/dl), indicating minimal haemolysis of the blood withdrawn past the electrode. It is concluded that the plasma CO2 hydration reaction is virtually at equilibrium by the time blood reaches the pulmonary vein.

Acute haemodynamic comparison of amrinone and pirbuterol in chronic heart failure. Additional effects of isosorbide dinitrate

A randomised, within patient comparison was made in patients with severe chronic heart failure, to study the acute haemodynamic effects of oral agents which have inotropic and vasodilator properties. A non-glycosidic non-adrenergic positive inotropic agent with vasodilator properties (amrinone) was compared with a beta-agonist which has vasodilator and positive inotropic effects (pirbuterol). To assess whether combined treatment with a venodilator might be advantageous, the effect of adding isosorbide dinitrate was studied. Oral amrinone or pirbuterol were given in random order to each of 13 patients, on successive days, and oral isosorbide dinitrate was added after two-and-a-half hours. Control values before amrinone or pirbuterol were similar, and both drugs increased cardiac index while reducing left ventricular filling pressure, right atrial pressure, and systemic vascular resistance. Heart rate and blood pressure were unchanged. The magnitude of the changes caused by amrinone and pirbuterol were not significantly different. The addition of isosorbide dinitrate caused further falls in left ventricular filling pressure and right atrial pressures, and a fall in heart rate with each drug. Other measurements remained unchanged. Although amrinone and pirbuterol have different pharmacological properties, their acute haemodynamic effects in patients with chronic heart failure are indistinguishable.

Continuous coronary sinus and arterial pH monitoring during pacing-induced ischaemia in coronary artery disease

Catheter tip pH electrodes were used for continuous recording of coronary sinus and arterial pH during atrial pacing in 20 patients undergoing coronary arteriography for chest pain. An ischaemic response to atrial pacing was identified by the onset of angina and/or electrocardiographic abnormalities. Technically satisfactory coronary sinus recordings were obtained in 18 patients. Mean coronary sinus pH at the peak pacing rate fell by 0.021 +/- 0.006 units (n = 9) in the ischaemic group, while there was no significant change in the non-ischaemic group. A larger fall in coronary sinus pH (-0.052 +/- 0.009) was found in the ischaemic group in the 30 seconds after the end of atrial pacing, the maximum change occurring after 16.1 +/- 1.5 seconds. A maximum fall of coronary sinus pH greater then 0.02 units identified patients with an ischaemic response. Changes in arterial pH did not account for these results. The sensitivity of coronary sinus pH recording for the detection of ischaemic heart disease is enhanced by sampling during the "washout" phase after the end of pacing.

The effects of verapamil, quiescence, and cardioplegia on calcium exchange and mechanical function in ischemic rabbit myocardium

The effects of verapamil (1 mg/liter, 2 x 10(-6) mol/liter), quiescence, and cardioplegia (K+ 16 mmol/liter, Mg2+ 16 mmol/liter) on calcium exchange and mechanical function during ischemia and reperfusion have been investigated in the rabbit interventricular septum at 32 degrees C. Calcium influx and efflux were recorded continuously with 47Ca2+ and 45Ca2+. After 60 minutes of total ischemia and reperfusion for 30 minutes, there was a net calcium gain of 4.9 mmol/kg dry tissue. Verapamil given before total ischemia reduced net calcium gain to 1.5 mmol/kg dry tissue (n = 5, P less than 0.03). When given only on reperfusion after total ischemia, or 10 minutes before reperfusion during low flow ischemia, verapamil did not affect calcium exchange. Cardioplegia begun 10 minutes before total ischemia reduced net calcium gain to 1.0 +/- 0.26 mmol/kg dry tissue (n = 6, P less than 0.001). Cardioplegia during the first 10 minutes of reperfusion, or lack of electrical stimulation during reperfusion, did not reduce calcium gain. Net calcium gain correlated with the maximum rise in resting tension and with the recovery of developed tension. In control experiments neither verapamil nor cardioplegia altered influx or efflux of slowly exchanging calcium. The cardioprotective effects of cardioplegia and the calcium channel blocker verapamil appear to be due to a reduction of myocardial work rather than to any specific direct action on calcium fluxes across the myocardial cell membrane.

Tissue and coronary venous pH in ischemic canine myocardium

The relationship between changes in myocardial tissue pH and local coronary venous pH during and after transient occlusion of the left anterior descending artery was investigated in 6 open chested anesthesized dogs. Tissue pH was recorded with a needle pH electrode, and coronary venous pH with a specially designed catheter tip pH electrode. Myocardial tissue pH fell steadily after coronary occlusion, and had fallen by 0.107 +/- 0.043 pH units (mean +/- SD, n = 12, occlusions) after 150 s. On reperfusion there was a further small fall in tissue pH to 0.138 +/- 0.035 units before tissue pH returned to control. In contrast, the fall of coronary venous pH during ischemia was small (0.15 +/- 0.027 after 150 s, n = 12 occlusions). Within 5 s of reperfusion, a large fall in venous pH occurred, reaching a maximum of 0.150 +/- 0.072 at 20-30 s after reperfusion. During ischemia changes in tissue pH are poorly represented by changes in coronary venous pH. The size of early change of venous pH during the reperfusion washout of retained metabolites is a better estimate of the fall of tissue pH. Measurement of metabolites in the coronary sinus of man during the washout after the end of an ischemic intervention such as a trial pacing is superior to measurements performed during pacing in providing biochemical evidence of myocardial ischemia.

Treatment of chronic heart failure with pirbuterol: acute haemodynamic responses

Fifty-nine patients with severe chronic heart failure were given pirbuterol, a beta agonist with vasodilator and positive inotropic properties. The acute haemodynamic responses to both single (20 patients) and incremental doses (39 patients) were measured. Pirbuterol increased cardiac index and reduced left ventricular filling pressure and systemic vascular resistance with only small changes in heart rate and blood pressure. Maximal effects were observed at an average of 170 minutes after a single oral dose of pirbuterol. In the incremental dose studies the plasma pirbuterol concentration was found to increase with increasing doses and was related to the magnitude of the haemodynamic response. Pirbuterol was well tolerated, and no drug-related side effects were recorded. Oral pirbuterol clearly improved pump performance in these patients, the haemodynamic changes being consistent with vasodilatation as the dominant mechanism rather than a direct inotropic effect.

Effects of thiopental on tension development, action potential, and exchange of calcium and potassium in rabbit ventricular myocardium

Thiopental in concentrations of 28 and 227 mumoles/liter reduced the tension developed by isolated rabbit ventricular myocardium by 50 and 80%, respectively. The effect was rapid, reversible, and independent of heart rate. Thiopental (227 mumoles/liter) inhibited influx and efflux of potassium to the same extent, so that no net gain or loss occurred. Calcium influx and efflux were also reduced, but calcium was not displaced from the myocardium in association with the decline of tension. The maximum rate of depolarization of the action potential and the time to 50% repolarization were decreased, but resting membrane potential, amplitude, and time to 90% depolarization were unchanged. The negative inotropic effect of thiopental appears to be due to reduced availability of calcium to the myofibrils.

Effects of ischaemia and reperfusion on calcium exchange and mechanical function in isolated rabbit myocardium

We have studied calcium exchanges and mechanical function in heart muscle during and after a period of ischaemia. The experimental preparation was the isolated but arterially perfused interventricular septum of the rabbit. Uptake of calcium was measured with 47Ca2+ and efflux with 45Ca2+. 51Cr-EDTA was used as a marker of the extracellular space. Ischaemia caused a rapid decline of developed tension followed by a rise in resting tension. Tissue counts of 47Ca2+ decreased due to a reduction in the extracellular space. On reperfusion after ischaemia developed tension partially recovered and resting tension increased further before returning towards control values. A large and prolonged uptake of 47Ca2+ occurred immediately on reperfusion while 45Ca2+ efflux rose transiently. The uptake of calcium was related to the severity and duration of ischaemia and to the degree of mechanical recovery. Calcium accumulation on reperfusion is due to an increased influx which is not related to gross disruption of the cell membrane but more probably to a specific abnormality of ionic channels.

Effects of acid-base changes on excitation--contraction coupling in guinea-pig and rabbit cardiac ventricular muscle

1. Respiratory and metabolic acid-base changes caused similar steady-state changes in the contractility of cardiac ventricular muscle, but the rate of response was more rapid with the former intervention. 2. Variations in extracellular pCO2 and [HCO3-] at constant pH caused only a transient change in contractility. 3. An intracellular pH change can describe the above events. 4. The changes in contractility caused by extracellular acid-base changes could be explained by competition between Ca2+ and H+ ions for a single process. 5. Assuming an electroneutral scheme whereby one extracellular Ca2+ ion or two intracellular H+ ions compete for a binding site, the interior of ventricular cells must be better buffered than the extracellular fluid. 6. H+ ions evoked a release of Ca2+ ions from a mitochondrial suspension with a time course similar to the partial recovery of tension observed during a respiratory acidosis. 7. Respiratory and metabolic acidosis depressed the action potential plateau and prolonged repolarization. 8. The resting potential and the maximum rate of depolarization were unaffected by the above acid-base changes. 9. An acidosis depressed Ca2+ influx through the slow inward channel by an amount sufficient to account for the observed contractility changes. 10. It is concluded that between pH 7.6 and 6.6 the major physiological effect of an acidosis is to depress the slow inward current as a result of an intracellular pH change.

R wave amplitude during exercise. Relation to left ventricular function and coronary artery disease

Change in R wave amplitude (mean delta R) was measured sequentially during and after 12 lead maximal treadmill exercise tests in 14 subjects with normal coronary arteries and 62 patients with coronary artery disease. In normal subjects mean delta R decreased maximally one minute after exercise and returned to control levels within three minutes. In contrast, mean delta R increased in patients with coronary artery disease, the greatest change occurring in patients with either triple vessel or left main disease or those with an akinetic region on the left ventriculogram. R wave amplitude returned to resting levels in five minutes. Increase in R wave amplitude was not directly related to changes in the ST segment. Changes in R wave amplitude during maximal treadmill exercise may improve the discrimination between patients with and without coronary artery disease and may help to identify those patients with abnormal left ventricular function.

Calcium exchange in rabbit myocardium during and after hypoxia: effect of temperature and substrate

Calcium influx and efflux were measured during hypoxia and on reoxygenation in the isolated arterially perfused septum of the rabbit heart. The uptake of 47Ca2+ was continuously followed with a NaI crystal and counter. The extracellular space (ECS) was measured in a similar manner with 51Cr-EDTA. Calcium efflux was recorded by collection of effluent drops after labelling with 45Ca2+. Hypoxia caused a rapid decline of developed tension followed by a rise in resting tension. The ECS increased initially but decreased as resting tension rose. 51Cr-EDTA did not have free access to the intracellular fluid. Calcium efflux did not change and calcium influx was either unchanged or reduced. On reoxygenation calcium influx increased immediately but efflux was unaltered and 51Cr-EDTA did not enter the cell. The effects of hypoxia were altered by manipulation of temperature and substrate. The recovery of mechanical function was related to the size of the calcium influx on reoxygenation. The experiments show that a rise of resting tension during hypoxia can occur in the absence of a net gain of calcium, calcium accumulation is closely associated with the extent of tissue damage, and that calcium influx on reoxygenation is probably due to a specific abnormality and not gross disruption of the cell membrane.

Salbutamol in cardiogenic shock complicating acute myocardial infarction

Intravenous salbutamol (13 microgram/min) has been given to 31 patients with cardiogenic shock complicating acute myocardial infarction. Haemodynamic measurements were made in nine of these patients. Salbutamol increased cardiac index by 41 per cent from 1.25 +/- 0.06 l/min per m2 to 1.76 +/- 0.19 l/min per m2 and decreased systemic vascular resistance by 16 per cent from 26.2 +/- 1.9 units to 21.9 +/- 2.1 units. Heart rate rose by 13 per cent from 95 +/- 4.5 beats/min to 106 +/- 6.0 beats/min. Pulmonary artery end-diastolic pressure fell from 20.6 +/- 1.7 mmHg to 16.9+/- 1.9 mmHg. Of the 31 patients, eight survived to leave hospital (27%). Five of the survivors had initial low heart rates and in these patients the clinical improvement was probably attributable to the positive chronotropic action of salbutamol. In the remaining three survivors clinical improvement was probably a result of salbutamol mediated afterload reduction. Salbutamol may be useful in the treatment of cardiogenic shock and pump failure complicating acute myocardial infarction.

Catheter tip pH electrodes for continuous intravascular recording

A small, flexible catheter-tip pH electrode has been developed for continuous measurement of intravascular pH in man and animals. The electrode utilises a pH sensitive polymer membrane rather than pH glass. The electrode passes through the lumen of a conventional cardiac catheter, by which it may be introduced to any desired site in the circulation. The electrode has no cross-sensitivity to other ions, to osmolality or oxygen tension. It is insensitive to flow and pressure. The response time is less than 300 ms, and the mean drift in vivo is 0.01 pH units/h. Continuous recordings of intravascular pH in animals have been made for up to 7h. The electrodes can be sterilised, and have been used in man.

Salbutamol in treatment of heart failure

The haemodynamic effects of oral and intravenous salbutamol were investigated in 22 patients with chronic heart failure. Intravenous salbutamol (13 micrograms/min) increased cardiac index by 53 per cent from 1.5 +/- 0.13 1/min per m2 to 2.3 +/- 0.23 1/min per m2 and decreased systemic vascular resistance by 28 per cent from 29.4 +/- 3.9 units to 21.2 +/- 2.5 units. Heart rate rose by 10 per cent from 101 +/- 3.5 beats per minute to 111 +/- 3.2 beats per minute and pulmonary artery end-diastolic pressure fell by 13 per cent from 26.3 +/- 1.8 mmHg to 22.8 +/- 2.1 mmHg. Similar results were obtained after oral salbutamol (8 mg). Cardiac index rose by 40 per cent and systemic vascular resistance fell by 30 per cent. There was a small rise in heart rate and a variable and not significant change in pulmonary artery end-diastolic pressure. Experiments on isolated rabbit papillary muscle showed that salbutamol, at the concentration which exists in patients, had no detectable positive inotropic effect. It is probable that the increase in cardiac output in patients is primarily the result of reduced afterload caused by vasodilatation. Salbutamol is a useful drug in the treatment of chronic heart failure.

Effect of ouabain in therapeutic concentrations on K+ exchange and contraction of human and rabbit myocardium

1. Experiments were undertakn on strips of human atrial and ventricular muscle, on right ventricular rabbit papillary muscles and on the rabbit interventricular septum. 2. In all preparations an increase of developed tension after 30 min exposure to ouabain was apparent only at or above a concentration of 10(-7) mol/l (73 micrograms/l). 3. In the rabbit septum there was a net loss of potassium on exposure to ouabain if the concentration was greater than 10(-7) mol/l. There was no net loss, or gain, of potassium at lower concentrations. Loss of potassium, indicating inhibition of the sodium pump, could not be dissociated from the positive inotropic effect of ouabain. 4. The greater sensitivity to ouabain of human myocardium in vivo (10(-8) mol/l) than in vitro (10(-7) mol/l) may be due to cellular changes occurring in isolated preparations.

Influence of contractile state on the size of the extracellular space in isolated ventricular myocardium

A method is described with which the extracellular space of isolated ventricular muscle can be measured accurately and continuously in the same muscle. The size of the extracellular space is shown to vary with the contractile state of the myocardium. Interventions such as quiescence, manganese and acidosis reduce myocardial contractility and increase the size of the extracellular space. Barium, ouabain and hypoxia cause contracture and reduce the size of the extracellular space. These changes should be taken into account when measuring intracellular electrolytes in isolated ventricular preparations.

Calcium overload and mechanical function in posthypoxic myocardium: biphasic effect of pH during hypoxia

Mechanical function and calcium accumulation in the myocardium during and after hypoxia were examined in the isolated but arterially perfused interventricular rabbit septum. The pH of the perfusate during hypoxia was varied from 7.4 to 6.6 by increase of the pCO2. All septa were reoxygenated for 30 min at pH 7.4. In the posthypoxic period the recovery of developed tension was greatest and the magnitude of contracture least in those septa perfused at pH 6.8 during hypoxia; calcium overload did not occur. By contrast, marked calcium overload (3.5 mumol/g wet wt) occurred in septa perfused at pH 7.4 during hypoxia. Reduction of pH to 6.6 during hypoxia did not result in a greater degree of recovery of developed tension or complete reversal of contracture in the posthypoxic period, and marked calcium overload was not prevented. These results indicate that: (1) partial recovery of mechanical function in the posthypoxic period can occur concurrent with a net gain of calcium; (2) the beneficial effects on recovery in the posthypoxic period in septa perfused at pH 6.8 during hypoxia may be in part released to prevention of calcium overload; (3) the beneficial effects of acidosis are lost when the perfusate pH is reduced to 6.6 during hypoxia.

Effects of acidosis on mechanical function and Ca2+ exchange in rabbit myocardium

The effects of acidosis on myocardial function and calcium exchange have been studied in the isolated but arterially perfused interventricular septum of the rabbit. Temperature was 28 degrees C and stimulation rate 48 beats/min. Acidosis was induced either by increase of the perfusate PCO2 (pH reduced from 7.35 to 6.68) or by decrease of the bicarbonate-chloride ratio (pH 7.35 to 6.72). The effect on calcium efflux was assessed by introduction of acidosis at different times during the washout of 45Ca2+ from the muscle. The uptake of 47Ca2+ was recorded directly with a NaI crystal and counter. An increase of perfusate PCO2 caused a rapid fall in developed tension. The efflux of slowly exchanging 45Ca2+ and the uptake of 47Ca2+ were inhibited. There was no rapid displacement of calcium from the muscle. Decrease of the bicarbonate-chloride ratio caused a slower fall of developed tension and neither the efflux nor uptake of calcium were altered. These results suggest that developed tension and calcium exchange in the myocardium are more responsive to acidosis within the cell or cell membrane than to extracellular acidosis.

Acute effects of diuretics on potassium exchange, mechanical function and the action potential in rabbit myocardium

1. We have studied the acute effects of frusemide, triamterene and amiloride on potassium exchange, the action potential and mechanical function of isolated rabbit myocardium. 2. Potassium exchange in the myocardium was unaltered by these diuretics. 3. Frusemide and amiloride did not affect the action potential of rabbit papillary muscles. Triamterene caused a transient shortening of the action potential. 4. Frusemide and triamterene did not alter myocardial mechanical function in rabbit papillary muscles or the interventricular septum. Amiloride caused a reduction of about 5% in developed tension in two out of three papillary muscles.

The effect of beta-adrenoceptor and Ca2+ antagonist drugs on the hypoxia-induced increased in resting tension

Using isolated, Langendorff-perfused, electrically-paced guinea-pig hearts, we have investigated the rise in resting tension that occurs when mammalian heart muscle becomes hypoxic. Substrate-depletion, tachycardia, hyperthyroidism, and inotropic interventions (ouabain, isoprenaline, and beta-receptor antagonists at concentrations which increase inotropic state) enhanced the rate of development of this increase in resting tension. 3.86 mumol.litre-1 propranolol, 0.22 to 2.20 mumol.litre-1 verapamil or removing Ca2+ from the extracellular phase at the start of the hypoxic episode prevented (or delayed) the rise in resting tension. Adding these same agents or removing Ca2+ from the extracellular phase after the hypoxia-induced rise in resting tension had started to develop failed to prevent its progression. These results provide some support for an hypothesis that the hypoxia-induced increase in resting tension is independent of an enhanced Ca2+ influx.

Use of electromagnetic flow probes to assess myocardial performance in man

Aortic blood flow was measured in 14 patients by means of an electromagnetic flow probe placed around the ascending aorta during cardiac surgery. High fidelity left ventricular pressure was monitored directly, 8 different indices of left ventricular function were derived from these measurements, and compared. Peak aortic blood flow correlated with the conventional indices of left ventricular function derived from left ventricular pressure, but better correlations were obtained for the maximum rate of change of power with respect to time. The clinical advantage of the derivation of this index is small and for clinical purposes peak aortic blood flow and the maximum rate of change of flow provide indices of myocardial performance which are directly available from the instrument.

Haemodynamic effects of salbutamol and nitroprusside after cardiac surgery

The haemodynamic effects of a continuous intravenous infusion of salbutamol (15 to 30 microgram/min) and nitroprusside (50 to 100 microgram/min) were compared in 9 patients after cardiac surgical operations. The mean falls in left atrial pressure and systemic vascular resistance were similar with the two drugs but salbutamol caused a greater increase in heart rate, maximum acceleration of aortic blood flow, and maximum rate of change of left ventricular power. Because these differences would cause greater myocardial oxygen consumption with salbutamol and because the infusion of salbutamol is less easily controlled, nitroprusside is the preferred drug after cardiac operations.