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Biomedical subjects

D O Williams

Publications and source records attributed to D O Williams.

At least 145 records · Page 8Linked to original sources
PubMed1976

Selective versus non-selective His bundle pacing.

His bundle pacing was achieved in 10 anaesthetized open chest dogs by stimulation from bipolar electrode catheters positioned in the aortic root and right heart. Recordings were taken directly through plunge wires from the right atrium, high ventricular septum, and epicardial sites on the right and left ventricles. Six types of response were seen during A-V junctional stimulation: (1) low atrial pacing; (2) combined atrial and His bundle pacing; (3) His bundle pacing; (4) combined atrial, ventricular septal, and His bundle pacing; (5) combined septal and His bundle pacing; and (6) ventricular pacing. Pacing of the His bundle in combination with the atrium and/or ventricular septum is designated as non-selective, whereas stimulation of the His bundle alone is considered selective pacing. Non-selective His bundle pacing can be recognized from the surface leads by changes in onset and amplitude of the QRS with appreciable T-wave alterations. Although electrode position was an important determinant of the type of pacing achieved, a variety of patterns of stimulation resulted from variation in the modalities of the pacing stimulus, ie, polarity, intensity, and duration. Unless these factors are considered, selective His bundle pacing may not be achieved.

Animals↗
PubMed1976

Muscle potentials simulating pacemaker malfunction.

Interference spikes were noted on the electrocardiogram of a patient with an implanted demand pacemaker. Runaway malfunction was suspected and the generator replaced. Subsequent investigation showec that the interference originated from fasciculation in the left leg caused by underlying neuromuscular disease. Skeletal muscle potentials can produce an electrocardiographic appearance closely resembling 'runaway' pacemaker. Such abnormalities should prompt a search for occult neuromuscular disease.

Action Potentials↗
PubMed1976

Pharmacological mechanisms for left ventricular unloading in clinical congestive heart failure. Differential effects of nitroprusside, phentolamine, and nitroglycerin on cardiac function and peripheral circulation.

We compared cardiocirculatory actions of the commonly employed systemic vasodilators, intravenous (iv) nitroprusside (NP), iv phentolamine (PH), and sublingual nitroglycerin (NTG), causing left ventricular (LV) unloading in 29 chronic coronary subjects with congestive failure to determine whether they produce disparate responses in LV function by different relaxing actions on systemic resistance and capacitance beds. Each drug equally lowered systemic arterial pressures to a small extent, whereas heart rate rose slightly with NTG. Cardiac catheterization showed a decline in end-diastolic pressure with NTG (19 to 8 mm Hg) which was greater (P less than 0.05) than with NP and PH (21 to 11). Cardiac index increased (P less than 0.05) during NP (2.68 to 2.93 liters/min per m2) and PH (2.60 to 3.02) but was unchanged (2.83) by NTG. Stroke work increased with PH, ejection fraction rose with NP and PH, and mean ejection rate increased with each, whereas pressure-time per minute fell and end-diastolic volume decreased with each agent. Total systemic vascular resistance declined (P less than 0.001) during NP and PH (1,475 to 1,200 dynes sec cm-5) but was unchanged (1,487) by NTG. Plethysmographically, forearm vascular resistance (FVR) decreased (P less than 0.01) with NP and PH (61.6 to 39.1 mm Hg/ml per 100 g/min) but not (52.4) by NTG. The decreases in venous tone (VT) with NTG (18.2 to 9.3 mm Hg/ml) and NP (18.5 to 9.8) were greater (P less than 0.05) than with PH (18.8 to 13.1) FVR/VT percent changes of 0.96, 1.62, and 0.53 with NP, PH, and NTG indicated balanced systemic arteriolovenous relaxation by iv NP, greater arteriolar dilation with iv PH, and predominant venous dilation by sublingual NTG. Thus, vasodilators produce disparate modifications of LV function by their differing alterations of preload and impedance, which are dependent upon relative extents of relaxation of systemic resistance and capacitance vessels characteristic of each agent as used clinically.

Adult↗
PubMed1975

Hemodynamic effects of nitroglycerin in acute myocardial infarction.

Nitroglycerin (NTG) has recently been suggested to decrease myocardial ischemia and enhance cardiac pump function during acute myocardial infarction (AMI). To evaluate the sublingual agnet in this condition, the hemodynamic effects of 0.4 mg NTG administered to 16 supine patients during the first 72 hours of AMI were determined serially 5, 10 to 15, and 20 to 30 minutes post-NTG. Data were evaluated for the entire group, as well as for six patients with normal pulmonary artery wedge pressure (PAW) (less than or equal to 12 mm Hg; mean 7) who formed group I and for ten patients with elevated PAW (greater than 12 MM Hg; mean 19) who comprised group II. In the 16 patients, NTG resulted in significant decreases in PAW (14 TO 7 MM Hg; P less than .01), mean systemic arterial pressure (MAP) (95 TO 82 MM Hg; P less than .01), cardiac index (CI) (1.79 TO 1.46 L/min/m-2; P less than .02), stroke index (SI) (24 TO 18 CC/M-2; P less than .01) and stroke work index (SWI) (27 TO 20 GM TIMES M/M-2; P less than .01). These alterations were significant in both subgroups, with the decline in PAW greater (P less than .05), while there was no change in group II. There was no significant change in total peripheral vascular resistance (TPVR) for the entire group or in the two subgroups. This study demonstrates that, regardless of initial left ventricular filling pressure, sublingual NTG given in the acute phase of AMI results in rapid fall in PAW, concomitant with decreases in systemic blood pressure, cardiac output and SWI, without changes in TPVR and with little or no effect on heart rate. Since TPVR was unaltered, the decline in MAP was due to fall in cardiac output. Thus, the principal action of sublingual NTG in AMI appears to be systemic venodilation with consequent reduction of ventricular preload. This effect is translated into decline ofpump output even in patients with high initial filling pressures. Although NTG may rapidly relieve pulmonary congestion and lower myocardial oxygen consumption, use of the agent sublingually is limited in AMI because these salutary effects are accomppanied by potentially deleterious fall in cardiac output and systemic blood pressure.

Aged↗
PubMed1970

Combined axillary plexus block and basal sedation for cardiac catheterization in young children.

A technique for the management of cardiac catheterization in children is described which combines axillary plexus block with basal sedation. The technique offers a quiet still arm with pronounced vasodilatation, permitting the use of larger catheters than usual, making sampling easier, and giving undamped pressure records. These factors, together with the absence of venospasm, make catheterization of an arm vein in young chīldren a feasible proposition; in addition arterial sampling via the brachial artery may be performed without further inconvenience to the child.

Anesthesia, Conduction↗
PubMedDate not supplied

Oestrone sulphate measurement in bovine serum during late pregnancy and its relationship with the number of calves born.

A radioimmunoassay developed for the measurement of oestrone sulphate in bovine serum was used to determine levels of hormone in cows. The cows were sampled as part of an embryo transfer programme designed to investigate the production of twin calves. The concentration of oestrone sulphate in serum was higher in cows carrying twin calves, but the difference did not become significant until around 220 days' gestation. The predictive value of the test could be used as a guide to increase feeding of cows pregnant with more than one calf.

Animals↗
PubMedDate not supplied

A trial of the calcium antagonist nisoldipine in hypertensive non-insulin-dependent diabetic patients.

The antihypertensive and metabolic effects of a new calcium antagonist nisoldipine (10 to 20 mg at night) were investigated in 14 mild to moderately hypertensive non-insulin-dependent diabetic patients (median age 62, range 50-70 years). In a 12-week placebo controlled single blind study, sitting and standing blood pressure were significantly lowered (p less than 0.001). Heart rate was unchanged as were blood urea, creatinine, bilirubin, mmol/l (mean +/- SEM) and uric acid concentrations. Plasma sodium levels fell during active therapy (142 +/- 0.5 mmol/l (mean +/- SEM) versus 139 +/- 0.5 (p less than 0.001) and remained lower during the washout period. Plasma calcium concentrations increased during nisoldipine therapy (2.41 +/- 0.02 versus 2.51 +/- 0.03 mmol/l, p less than 0.001) and returned towards baseline during the washout period. Plasma ionized calcium concentrations showed similar changes but plasma sodium and calcium remained within the normal laboratory ranges in all patients at all times. Serum triglyceride concentrations fell (placebo 1.9 +/- 0.02 mmol/l vs nisoldipine 1.6 +/- 0.2, p less than 0.05), but fasting cholesterol was unchanged. Fasting blood glucose, and the blood glucose response to oral glucose challenge (75 g) showed no differences though HbA1 concentrations fell (10.6 +/- 0.7 versus 9.2 +/- 0.05%, p less than 0.05) and tended to rise when the drug was withdrawn. Haemoglobin concentrations also fell during active therapy (14.7 +/- 0.4 vs 14 +/- 0.32 g/dl p less than 0.001) and also remained lower after the washout period (13.9 +/- 0.03 g/dl).(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗