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Biomedical subjects

S M Cobbe

Publications and source records attributed to S M Cobbe.

At least 181 records · Page 10Linked to original sources
PubMed1983

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 Mean plasma free haemoglobin was very low (1.6 mg/dl), indicating minimal haemolysis of the blood withdrawn past the electrode.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.

Animals↗
PubMed1983

Action of sotalol on potential reentrant pathways and ventricular tachyarrhythmias in conscious dogs in the late postmyocardial infarction phase.

Sotalol is a beta-adrenergic blocker that also prolongs action potential duration and myocardial refractoriness over the short term (class III effect). Its short-term antiarrhythmic effects were compared with those of metoprolol, which has neither short-term class III nor membrane-stabilizing action, on reentrant ventricular arrhythmias produced by programmed stimulation in 17 conscious dogs 3 to 8 days after myocardial infarction. Ventricular arrhythmias were prevented or significantly slowed by sotalol in 11 of 19 studies (58%) compared with in one of 14 (7%) studies with metoprolol. Sotalol prolonged refractoriness in the infarct zone, measured from an implanted "composite" electrode, by 41 +/- 45% (mean +/- SD, p less than .01), which was significantly greater than the increases it produced in effective refractory period of the normal ventricle (14.0 +/- 5.5%) or QT interval (12.5 +/- 7.8%). Metoprolol had no effect on infarct-zone refractoriness. Sotalol differentially increases refractoriness in potential reentry circuits in ischemic myocardium. Its antiarrhythmic effect in this model is not due to beta-blockade, and is presumably related to prolongation of action potential duration.

Action Potentials↗
PubMed1982

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.

Animals↗
PubMed1982

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.

Adult↗
PubMed1980

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.

Acid-Base Equilibrium↗
PubMed1978

Continuous monitoring of mixed venous oxygen tension (PvO2) in cardiorespiratory disorders.

The development of a miniature polarographic electrode mounted in the tip of a double-lumen plastic catheter has made possible continuous in-vivo monitoring of oxygen tension. Inexpensive catheters of this type have already proved of value as a means of continuously monitoring arterial oxygen tension in the newborn. In 25 patients with acute respiratory failure we found that these catheters could be safely and easily flow-guided into the pulmonary artery. In this way continuous recordings of mixed venous oxygen tension (PvO2) could be made for a period of several days. In our experience a sustained fall of PvO2 below 40 mm Hg proved to be a reliable indicator of respiratory or cardiac deterioration not always obvious by observation. In the patients described, falls of this order were seen after reductions in inspired oxygen concentration, in acute respiratory failure, in accidental underventilation, and in hypovolaemia and cardiac arrythmias. In some very ill patients routine nursing care involving movement of the patient caused pronounced falls of PvO2. Although electrode drift was an occasional problem, this could be checked by intermittent blood-sampling and recalibration if necessary.

Aged↗
PubMed1978

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.

Action Potentials↗
PubMedDate not supplied

Efficacy of out of hospital defibrillation by ambulance technicians using automated external defibrillators. The Heartstart Scotland Project.

During the Heartstart Scotland project all 407 ambulances in Scotland were equipped with automated external defibrillators (AEDs). All cases of chest pain or collapse aged over 10 years were monitored and multiple 3-s rhythm strips recorded in a solid state memory module. A shockable rhythm was defined as an organised rhythm of > or = 180 beats/min or a disorganised rhythm of > or = 100 beats/min and amplitude > 0.1 mV. We analysed all the stored rhythm strips in two patient populations to determine the ability of the AED and ambulance crews to detect a shockable rhythm and to initiate appropriate defibrillation. The first population comprised 493 patients, all of whom had received shocks. A total of 4741 rhythm strips were analysed, of which 1461 were true positives, 33 false positives, 3161 true negatives and 86 false negatives. Overall sensitivity of the AED was 94.4% and specificity 99.0%. The second population comprised a random sample of 200 shocked and 200 non-shocked arrests. The combined group contained 4154 rhythm strips of which 562 were true positives, 12 false positives, 3460 true negatives and 120 false negatives. Overall sensitivity of the system (AED+crew) was 82.4% and specificity 99.7%. However, only 66 of the 120 false negatives were attributable to the AED giving a sensitivity of 90.3% for the AED. The sensitivity of the AED is dependent on the prevalence of shockable rhythms, but will be within the range 90.3-94.4% for most emergency medical services. We conclude that early management of potentially lethal arrhythmias by ambulance technicians using AEDs is practical with acceptable sensitivity and specificity.

Ambulances↗
PubMedDate not supplied

Approaches to experimental arrhythmias in heart failure.

Sudden cardiac death accounts for at least 50% of the mortality of patients with heart failure. Available clinical evidence suggests that lethal ventricular arrhythmias are responsible for the vast majority of cases of sudden death in heart failure. However, despite extensive clinical investigation over the last decade, there has been relatively little experimental study of the mechanisms underlying the development of lethal ventricular arrhythmias in heart failure. In addition to the original process leading to myocardium alterations, the role of other arrhythmogenic mechanisms such as ventricular overload and neuro endocrine activation remains to be elucidated. In ventricular hypertrophy both reentry and triggered activity may induce arrhythmias. Some studies on experimental models of heart failure did not provide consistent results concerning electrophysiological modifications and their relations with arrhythmias. Few studies in man in vivo are in favor of prolongation as well as increased dispersion of repolarisation in patients undergoing heart transplantation for idiopathic dilated cardio-myopathy. Further studies will need to be undertaken to clarify mechanisms underlying arrhythmias in heart failure.

Animals↗