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Biomedical subjects

O S Randall

Publications and source records attributed to O S Randall.

34 records · Page 2Linked to original sources
PubMed1984

Stroke volume--pulse pressure relationships in borderline hypertension: a possible indicator of decreased arterial compliance.

Resting invasive haemodynamic measurements were performed on 354 volunteers, 168 normals, and 186 with borderline hypertension. To test the hypothesis that patients with borderline hypertension would have a decrease in the compliance of their arterial system, the relationship of stroke volume (SV) and stroke volume index (SVI) to pulse pressure (PP) in the two groups was examined. Theoretically, as compliance decreases, there should have been a stronger relationship between SV or SVI and PP. In the sample studied, SV and SVI were significantly related to PP in borderline hypertensive patients (P less than 0.005), but not in normotensive patients. When the samples were divided into tertiles of low, middle, and high SV, the borderline hypertensive patients had higher PP with higher SV (P less than 0.01), while the normals did not. It is concluded that there appear to be significant differences between normals and patients with borderline hypertension in the relationship of SV and SVI to PP. This can be interpreted as evidence to support the existence of an abnormality in arterial compliance in borderline hypertension.

Adult↗
PubMed1982

Pulse wave reflection: can it explain the differences between systemic and pulmonary pressure and flow waves? A study in dogs.

We have studied the effect of changes in pulse wave reflection on the configurations of pressure and flow in systemic and pulmonary circulation. Electromagnetic flow transducers, atrial catheters, and pacing leads were implanted in 10 dogs. In four animals, the flow transducer was placed on the pulmonary artery, in another four on the ascending aorta, and in two additional dogs on both vessels. One week later, ascending aortic and/or pulmonary artery flow and pressure (catheter tip manometer) were measured under general anesthesia (Nembutal, 30 mg/kg, iv). When the pulmonary circulation was studied (six dogs), measurements were made before and during serotonin infusion (0.5-0.75 mg/min). When the systemic circulation was studied (six dogs), measurements were made before and during nitroprusside infusion (50-200 micrograms/min). To quantify the arterial load, we calculated pulmonary and systemic input impedances. To estimate the amount of reflection, we used a reflection index which we defined as the amplitude ratio of reflected and forward wave. Nitroprusside decreased total peripheral resistance, increased total arterial compliance, and decreased the reflection index; similarity between aortic pressure and flow wave shapes increased, and they looked more like their pulmonary counterparts. Serotonin increased pulmonary vascular resistance, decreased pulmonary arterial compliance, and increased the reflection index. Resemblance of pressure and flow waves decreased. The differences in wave shapes can thus be explained by the amount of reflection: the less reflection the more pressure and flow resemble each other.

Animals↗
PubMed1982

Effect of arterial compliance on systolic blood pressure and cardiac function.

To study the effects of arterial compliance on blood pressure and ventricular performance, 33 patients undergoing diagnostic cardiac catheterization who were found to be free of significant cardiac disease were selected. Since blood pressure is a continuous variable, a specific cutting point was not used as a criterion for selection, although 12 patients were classified as hypertensive. The interrelationships between blood pressure, peripheral resistance, arterial compliance, and stroke volume index were investigated by determining the linear correlation between any two desired variables; and by employing partial correlative analysis to determine whether an observed relationship was dependent upon or independent of the influence of a third variable. Peripheral resistance was observed to be independently related to diastolic pressure (r = 0.59, p less than 0.01); while arterial compliance was not only related to stroke volume index (r = 0.67, p less than 0.01) but was also independently related to systolic pressure (r = -0.63, p less than 0.01). Thus, these observations suggest that arterial compliance is a common hemodynamic variable related to both the level of systolic pressure and ventricular performance.

Adult↗
PubMed1981

Reliability of echocardiography in assessing cardiac output. A comparative study with a dye dilution technique.

Because of the potential benefits froma noninvasive technique in assessing cardiac output, we compared cardiac output estimates from left ventricular echocardiograms with results obtained simultaneously by a standard technique, dye dilution in 10 healthy normal volunteers. During rest, cardiac outputs by echocardiographic and dye dilution techniques were reproducible and not significantly different. Increases in cardiac output produced by intravenous infusion of isoproterenol (15 ng/kg/min for 4 min) were accurately estimated by echocardiography in subjects whose stroke volume increased less than 40%, but were significantly underestimated when stroke volume increased more than 40%. Decreased cardiac output produced by intravenous propranolol (0.2 mg/kg) was comparable by both methods. Although echocardiography accurately estimated mean cardiac output for the group it over- or underestimated cardiac output in individual subjects. We propose that echocardiography can reliably estimate cardiac output in groups at rest and when stroke volume changes less than 40%.

Cardiac Output↗
PubMed1981

Production of chronic heart block in closed-chest dogs: an improved technique.

Chronic complete heart block was produced in 38 closed-chest anesthetized dogs with a special cannula introduced via a jugular vein. A Formalin mixture (0.2-1.0 ml, consisting of equal amounts of 40% Formalin and radiopaque material) was injected through this cannula into the His bundle, which was located with a His-bundle catheter. The entire procedure took approximately 30 min and was successful in 90% of the cases.

Animals↗
PubMed1980

The arterial system characterised in the time domain.

When an impulse of flow is applied to the arterial system then the resulting pressure, the impulse response, is a characterisation of the arterial tree. The impulse is generated by means of an occluder around the ascending aorta. The impulse response shows an initial sharp peak followed by an exponential decay with two peaks superimposed on it. The exponential decay is due to diffuse reflection and is linked to the windkessel properties of the arterial tree. The superimposed peaks arise from two distinct reflection sites in the arterial tree. By means of the pulse wave velocity the location of these reflection sites may be calculated; one is found in the bed distal to the brachiocephalic and subclavian arteries and the other in the bed distal to the descending aorta. The distinct reflections are linked to the reflection sites in the asymmetric T-model of the arterial tree. Vasodilatation (nitroprusside) and vasoconstriction (angiotensin) mainly influence the diffuse reflections, while the locations of the distinct reflection sites appear to be unchanged. Inflation of a balloon in the descending aorta shows up as a sharp peak in the impulse response function. The results obtained are compared with the impulse response function computed from pressure and flow waves in the steady-state.

Animals↗
PubMed1980

Ventricular wall thickness: a predictor of response to vasodilators in cardiomyopathy.

The effect of chronic adjunctive vasodilator therapy was assessed in 14 symptomatic patients with idiopathic cardiomyopathy. Thirteen of the 14 patients improved by one or more in the New York Heart Association functional class, one remained unchanged. Three became asymptomatic (class I). Noninvasive and invasive (hemodynamic) parameters before and after vasodilators were assessed. The echocardiographic findings of septal and posterior wall thickness of 1.2 cm or greater were the best predictors of good response in our patients who subsequently became asymptomatic.

Administration, Oral↗
PubMed1979

The protective effects of dietary fish oil on focal cerebral infarction.

The protective effect of the (n-3) fatty acids in menhaden fish oil on acute cerebral ischemia was investigated in cats. Cerebral ischemia was produced by ligation of the left middle cerebral artery of cats fed either a basal diet of feline cat chow or the basal diet supplemented with 8% of the calories as menhaden oil for 18-24 days. Fatty acids esters of 20:5 (n-3) were increased and the 18:2 (n-6) decreased in the heart and liver of cats fed supplemental fish oil, but the brain lipid showed no effect of the diet. We found that the neurological deficit and the volume of brain infarction in the group treated with fish oil was less than that of the control group. The present findings suggest that moderate dietary supplements of fish oil may be beneficial in the prophylactic treatment of ischemic cerebral vascular disease.

Animals↗
PubMed1976

Relationship of age and blood pressure to baroreflex sensitivity and arterial compliance in man.

1. The relationship between baroreflex sensitivity (BRS) and arterial compliance index (ACI) has been investigated (a) in paired subjects matched in one instance for systolic blood pressure with differing ages, and (b) in another instance matched for age with differing systolic blood pressures. 2. There was a significant negative correlation between BRS and age and between ACI and age in the twelve systolic blood pressure-matched subjects. 3. A significant negative correlation of systolic blood pressure with both BRS and ACI was observed in the fourteen age-matched subjects. 4. Both BRS and ACI appear to decrease with increasing age and systolic blood pressure. This decrease in BRS is probably due at least in part to the observed reduction in arterial distensibility.

Adult↗
PubMed1975

Relation of renin status to neurogenic vascular resistance in borderline hypertension.

The relation of renin-angiotensin status to general hemodynamics and to neurogenic vascular resistance was studied in patients with border-line hypertension. Plasma renin activity during standing was referred to a standard renin-urinary sodium nomogram derived from 18 normal subjects. Among 22 patients with borderline hypertension the renin level was high in 8, low in 4 and within normal limits in the remaining 10. In patients with borderline hypertension and high or normal levels of plasma renin activity, the blood pressure elevation was due to increased total peripheral vascular resistance. In contrast, in patients with low renin borderline hypertension, total peripheral resistance was not significantly elevated; the blood pressure elevation reflected a cardiac index 12 percent higher than that in normal subjects. The neurogenic contribution to total peripheral vascular resistance was assessed by studying the effects of alpha adrenergic blockade with phentolamine, after prior autonomic blockade of the heart with atropine (0.04 mg/kg body weight) and propranolol (0.2 mg/kg). Phentolamine (15 mg) produced an immediate reduction in total peripheral resistance of 12.0 +/- 6.7 percent in patients with high renin borderline hypertension (P less than 0.01) but no change in normal subjects or those with borderline hypertension and normal or low renin levels. Normalization of the blood pressure followed "total" autonomic blockade with atropine, propranolol or phentolamine only in patients with high renin borderline hypertension. It is concluded from these preliminary data that in high renin borderline hypertension the blood pressure elevation is sustained by neurogenic mechanisms. The elevated renin level in these patients is probably an expression of increased sympathetic nervous activity. Although the elevated plasma renin level may possibly be contributing to the generation of higher sympathetic tone, or data do not support a direct role of circulating angiotensin in the maintenance of the elevated vascular resistance.

Adolescent↗
PubMed1975

Role of the autonomic nervous system in mild human hypertension.

1. Some of the haemodynamic abnormalities in mild (borderline) human hypertension appear to be neurogenic, since they can be completely abolished by pharmacological autonomic blockade. 2. The cardiac output is elevated in 30% of patients through increased sympathetic drive and decreased parasympathetic inhibition. 3. In the remainder, the higher blood pressure is maintained by increased total peripheral vascular resistance. 4. In approximately 30% of this latter group, the higher vascular resistance is maintained solely by increased alpha-adrenergic tone. 5. Elevated plasma renin activities in a proportion of cases are probably due to generalized increase in sympathetic nervous activity. 6. Patients with mild hypertension thus show increased sympathetic drive to the heart and arterioles as well as decreased cardiac parasympathetic inhibition. It is presumed that the increased plasma renin is also neurogenic. 7. Such a widespread distribution of altered autonomic tone suggests aberration of the function of the integrative centres of cardiovascular control. 8. Evidence is presented of a possible psychosomatic origin of these changes in some cases.

Adolescent↗
PubMed1975

Altered cardiac responsiveness and regulation in the normal cardiac output type of borderline hypertension.

Of 145 patients with borderline hypertension, 30% had increased resting cardiac index (QI), whereas the remainder had normal values. The specific aim of this study was to investigate cardiac regulation in patients who had normal resting QI. Eighty-five control subjects were used for comparison. At rest, patients with normal QI showed evidence of decreased parasympathetic inhibition; the QI after injection of atropine increased less than in control subjects. After complete cardiac autonomic blockade with propranolol and atropine, QI and stroke volume were significantly lower in patients than in control subjects. The mechanism of this low QI was further analyzed. Central blood volume, which strongly correlates with stroke volume, was used as an estimate of the cardiac venous filling. After blockade, stroke volume was decreased in patients, but central blood volume was normal. Patients also showed a decreased heart rate and QI response to infusion of isoproterenol. It is therefore postulated that two components may be responsible for the low QI in the "denervated" heart: patients exhibit a decreased responsiveness to sympathetic stimulation, and they may also be less responsive to venous filling. Behind the facade of cardiac normality in these borderline hypertensive patients with normal cardiac output, there is evidence of altered autonomic control of the heart (decreased vagal inhibition) and of changed cardiac response to sympathetic stimulation and possibly to venous filling.

Adult↗
PubMedDate not supplied

Can risk factor modification reduce cardiovascular morbidity and mortality in minority populations?

It appears that landmark epidemiological studies have shown that certain conditions and/or environmental factors to increased risk for developing certain diseases, in this instance cardiovascular diseases. These conditions have been labeled risk factors, so it appears that many of the variables, i.e., risk factors, which lead to diseases have been identified. Since many of them are alterable, they could be altered in a favorable direction. Thus, the future should consist of education and dissemination of information/knowledge which could result in a reduction in the risk for the development of cardiovascular diseases as well as a decrease in its incidence and prevalence in minority populations. Special techniques should be used so that the information is available to citizens of all socioeconomic and ethnic backgrounds. Education may be the best way to approach this complex issue, e.g., obesity as a risk factor for diabetes and hypertension. Obesity is an alterable risk factor and perhaps not an independent one. It is probably interrelated with socioeconomic and cultural factors, which would make it a product of multiple factors which have led it to being considered an independent risk factor. It is, therefore, necessary to develop special techniques to investigate methods to identify the contribution of various components to the development of a risk factor. This could enable us to develop a solution for either improving or removing the factors that lead to the development of a risk factor. One example of this would be to become knowledgeable about the correct types of food to eat, the proper preparation and consumption of these foods, and the level of exercise or activity needed to burn appropriate calories in order to prevent obesity. It is not the obesity per se that is the etiology for a specific condition or disease, it is a combination of the influence of the environmental, cultural, and socioeconomic factors in conjunction with the resultant end product, obesity, that is the etiology for the conditions or diseases associated with it. Senators and other government agents should strongly encourage people to employ techniques to reduce risk factors for cardiovascular diseases, i.e., insurance companies should pay for training, educational sessions, and participation in activities/programs which are aimed at informing or instructing the public on how to reduce risk factors. This would be a preventive approach for medical conditions and would be much better than waiting until conditions requiring pharmacological or surgical intervention develop. The health care reform bill should have a built-in component to promote techniques and methodologies to reduce the probability of developing medical conditions.

Black People↗