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Biomedical subjects

J O Parker

Publications and source records attributed to J O Parker.

At least 19 recordsLinked to original sources
PubMed1992

Neurohormonal activation during nitrate therapy: a possible mechanism for tolerance.

The hemodynamic and antianginal effects of the organic nitrates are greatly reduced during therapy designed to provide 24-hour protection throughout each day. Although the mechanisms of tolerance are not clearly understood, it is likely that tolerance is related to a combination of reduced sulfhydryl groups in vascular smooth muscle and neurohormonal activation. These changes would reduce nitrate-induced vasodilation and induce sodium and water retention with an increase in plasma volume. These reflex neurohormonal changes would reduce the hemodynamic effect of any given degree of nitrate-induced vasodilation. Although preliminary studies suggest that diuretic therapy or the use of converting enzyme inhibitors may reduce or abolish tolerance, further clinical studies are required to confirm these findings.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1992

Effects of diuretic therapy on the development of tolerance during continuous therapy with nitroglycerin.

OBJECTIVES: This study examined the effects of concurrent diuretic therapy on the hemodynamic responses to short-term and sustained therapy with transdermal nitroglycerin. BACKGROUND: Sodium retention and plasma volume expansion occur during therapy with nitroglycerin and may play a role in the loss of nitroglycerin effects during sustained therapy. METHODS: Twenty-two normal male volunteers were treated for 1 week with either hydrochlorothiazide and amiloride (50 + 5 mg) (n = 11) or placebo (n = 11) in a randomized, double-blind fashion. All 22 subjects then received continuous transdermal nitroglycerin (19 +/- 1 mg/24 h) for 5 to 7 days. RESULTS: On the first and last day of transdermal nitroglycerin therapy, standing heart rate, systolic blood pressure and hematocrit values were assessed at 8, 9 and 10 AM and 12 noon. Heart rate and blood pressure responses to sublingual nitroglycerin (0.6 mg) were also evaluated before and after sustained transdermal nitroglycerin therapy. A significant loss of the hemodynamic effects of transdermal and sublingual nitroglycerin occurred during sustained therapy in both the diuretic and placebo therapy groups. In both groups, transdermal nitroglycerin therapy was associated with a significant decrease in hematocrit that persisted for the entire treatment period. CONCLUSIONS: These results suggest that diuretic therapy does not prevent plasma volume expansion or the loss of hemodynamic effects during sustained transdermal nitroglycerin therapy. The persistent decrease in hematocrit suggests that plasma volume expansion plays a role in the attenuation of nitrate effects. It also provides evidence of continued vascular activity of nitroglycerin despite loss of systemic hemodynamic effects.

Administration, Cutaneous↗
PubMed1979

Propranolol in angina pectoris: duration of improved exercise tolerance and circulatory effects after acute oral administration.

The duration of the effects of single oral doses of 80 and 160 mg of propranolol was studied in 11 patients with stable, exercise-induced angina pectoris. After administration of both doses, plasma propranolol levels peaked at 2 hours in 8 of the 11 patients and thereafter declined exponentially with an average plasma half-life of 3.98 hours (range 1.4 to 4.3) after the 80 mg dose and 4.28 hours (range 1.9 to 5.4) after the 160 mg dose. There was wide interindividual variation in plasma propranolol concentration at any given time after each dose. Treadmill walking time to the onset of angina, the total duration of exercise and the total external work performed were significantly greater by 1 hour after each dose of propranolol than after placebo. This improvement in exercise tolerance persisted unchanged for 8 hours (P less than 0.001) and was still significant although less marked at 12 hours (P less than 0.05). Improvement in exercise tolerance after propranolol was associated with a significant reduction in S-T segment depression during exercise. Both at rest and during exercise, heart rate, systolic blood pressure and rate-pressure product decreased after propranolol, and these circulatory effects persisted for 12 hours. Changes in walking time, heart rate and systolic blood pressure were similar after 80 and 160 mg of propranolol. Despite the increase in exercise duration and in total work performed after propranolol, the rate-pressure product at the onset of angina was lower after propranolol. In view of the prolonged effects of single oral doses of 80 and 160 mg of propranolol, it is suggested that administration of propranolol twice daily should be adequate in treating patients with stable angina pectoris. These studies also demonstrate that routine measurement of plasma propranolol levels is of little practical value in the management of patients with angina pectoris.

Administration, Oral↗
PubMed1979

Effects of glucose-insulin-potassium infusion on the angina response during treadmill exercise.

The effects of glucose-insulin-potassium (GIK) and placebo normal saline (S) infusion on treadmill-walking time to angina, ST depression, heart rate (HR), systolic blood pressure (SBP), rate pressure product (RPP), blood glucose (G), lactate (L) and free fatty acids (FFA) were studied in 14 non diabetic patients with exertional angina. For the whole group, the post-GIK walking time to angina (393 +/- 33 sec, mean +/- SEM) was greater than the values during control GIK (319 +/- 20 sec, p less than 0.02) and post-S infusion (334 +/- sec, p less than 0.05), but circulatory and ST responses were similar in post-GIK and post-S studies. 7 of the 14 patients experienced significantly greater improvement in exercise tolerance following GIK (467 +/- 39 sec) in comparison to control GIK (313 +/- 29 sec, p less than 0.001) and post-S infusion (334 +/- 32 sec, p less than 0.005) and exercised to a higher HR, SBP and RPP after GIK than after S infusion. At the onset of angina these patients had similar ST-segment depression before and after GIK but when ST segments were assessed after GIK at the same exercise duration when angina had occurred during the control and post-S studies, there was significantly less ST depression (p less than 0.01). Of the remaining 7 patients exercise tolerance following GIK deteriorated in 3, remained unchanged in 2 and increased by 12 and 48 sec in 2 patients in comparison to post-S values. Comparison of post-GUK and post-S values for G, L and FFA for the whole group showed significantly lower resting values of FFA and post-exercise values of G following GIK infusion. The differences in clinical and circulatory responses between patients who improved and those who did not improve following GIK were not related to the angiographically determined severity of coronary artery disease or to GIK-induced metabolic changes. Results suggest that some patients with angina pectoris do benefit from GIK infusion but the response in a given patient to this therapeutic modality is unpredictable.

Adult↗
PubMed1979

Normal left ventricular function.

The Starling relationship in the normal human ventricle may be different than usually portrayed. In normal, resting, supine man the ventricular function curve is at its peak at a left ventricular end-diastolic pressure of approximately 10 mm Hg. Below this point is a strong direct relation between filling pressure and stroke work, while at higher filling pressures, a plateau occurs. Limitation of ventricular response is related to a sharply rising ventricular pressure-volume curve at a normal level of filling pressure. Thus, in the supine position, the normal heart is not on the active portion of the ventricular function curve, but is in a unique position in which cardiac output is probably controlled by factors other than ventricular filling pressure. In ventricular failure, the peak of the ventricular function curve is displaced to a higher level.

Blood Pressure Determination↗
PubMed1979

Measurement of cardiac output by carbon dioxide rebreathing.

Twenty patients were studied on a bicycle ergometer at rest and at varying workloads to compare methods of measuring cardiac output. In nine patients, a comparison of carbon dioxide rebreathing and dye dilution techniques for measuring cardiac output were made. In eleven patients, comparisons between carbon dioxide rebreathing, dye dilution, and direct oxygen Fick techniques were made. The cardiac output measured by carbon dioxide rebreathing was reproducible and compared well with both the dye dilution and direct oxygen Fick. The correlation coefficient for the relationship between carbon dioxide rebreathing and direct oxygen Fick cardiac outputs was 0.80 and between carbon dioxide rebreathing and dye dilution cardiac outputs was 0.75. The relationship between dye dilution and direct oxygen Fick cardiac output was 0.71. The carbon dioxide rebreathing technique is a safe, non-invasive and reproducible method to measure cardiac output. The results compare well with the cardiac output measured by either the direct oxygen Fick or dye dilution technique.

Adult↗
PubMed1978

Aortic root motion determined by ultrasound: relation to cardiac performance in man.

The purpose of this study was to determine if aortic root systolic anteroposterior excursion measured ultrasonically is related to cardiac performance. Aortic motion was 9 +/- 1.5 mm (mean +/- SD) in 30 normal subjects (range 7-12 mm). Ten patients with coronary artery disease and congestive failure and 10 with congestive cardiomyopathy had significantly smaller values of 4 +/- 1.2 and 5 +/- 1.7 mm, respectively (P less than 0.001). In 28 subjects undergoing cardiac catheterization, aortic root motion correlated positively with stroke volume (r = 0.59), but did not correlate significantly with ejection fraction. By increasing heart rate in 14 subjects from 75 to 174 beats/min with atrial pacing, stroke volume decreased from 81 +/- 22 to 34 +/- 14 ml/beat and aortic excursion from 10 +/- 1.6 to 5 +/- 1.5 mm (P less than 0.001). This study has shown: 1) Aortic root motion less than or equal to 6 mm indicates left ventricular dysfunction; 2) stroke volume correlates positively with, but cannot be accurately predicted from, root motion.

Adult↗
PubMed1978

Effects of dextran infusion on left ventricular volume and pressure in man.

The purpose of this investigation was to quantitate the changes in left ventricular volume and end-diastolic pressure that occur with rapid infusion of 500 ml of low molecular weight dextran, and thus to study left ventricular pressure-volume relationships. Left ventricular pressure and echocardiographic dimensions were recorded before, during, and following dextran infusion in eight patients with normal left ventricular function. With the infusion of dextran, left ventricular end-diastolic pressure rose progressively from 10 +/- 3 mmHg (mean +/- SD) to 24 +/- 5 mmHg, whereas end-diastolic volume increased from 95 +/- 23 ml to 118 +/- 26 ml (24%). These results serve to emphasize the steepness of the left ventricular pressure-volume relationship at end-diastole in subjects with normal ventricular function when in the supine position.

Adult↗
PubMed1978

Echocardiography: pericardial tickening and constrictive pericarditis.

To evaluate the relation between mitral valve motion and left ventricular end-diastolic pressure, the PR-AC interval, an index derived from the electrocardiogram and mitral echogram, and the left ventricular endodiastolic pressure were determined simultaneously in 22 patients undergoing diagnostic cardiac catheterization. Intravenous infusion of dextran or administration of nitroglycerin was used to alter left ventricular end-diastolic pressure to determine if there was a predictive relation between this pressure and the PR-AC interval during acute hemodynamic manipulations. There was a weak negative correlation (r = -0.33, P less than 0.01) between this pressure and the PR-AC interval. At rest a PR-AC interval greater than 0.06 second correctly predicted a left ventricular end-diastolic pressure of less than 20 mm Hg in 15 of 16 subjects. However, in four of six subjects with a PR-AC interval of 0.06 second or less, the end-diastolic pressure was less than 20 mm Hg. After interventions that varied left ventricular end-diastolic pressure by a factor of 2, the PR-AC interval changed slightly or not at all. These data suggest that the PR-AC interval is of limited value in predicting abnormal values or serial changes in left ventricular end-diastolic pressure.

Adult↗
PubMed1978

Submitral annular left ventricular aneurysm--unusual echocardiographic and angiographic features.

A submitral annular left ventricular aneurysm in a Nigerian patient is described. The features consisted of an abnormal bulge on the left heart border with curvilinear calcification, an echo-free space behind the posterior left ventricular wall, and unusual angiographic appearance of the left circumflex coronary artery. The diagnosis was confirmed by pulmonary artery and left ventricular angiography. The patient underwent open heart surgery and a multiloculated submitral annular left ventricular aneurysm which was adherent to the pericardium was successfully resected.

Adult↗