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Biomedical subjects

A Ramirez

Publications and source records attributed to A Ramirez.

At least 91 records · Page 5Linked to original sources
PubMed1984

Role of cardiopulmonary receptors in reflex control of renin release in man.

Animal studies have shown that renin release is reflexly modulated by cardiopulmonary and arterial baroreceptors, and that during changes in posture the former receptors play a major role. This role has been challenged in man, however, by reflex modulation of renin secretion which has been claimed to take place only if arterial and cardiopulmonary receptor areas are engaged together. We studied 19 normotensive and essential hypertensive subjects in which plasma renin activity was assessed by radioimmunoassay during a mild 20 min increase and a mild 20 min reduction in central venous pressure (+1.1 +/- 0.2 mmHg and -2.6 +/- 0.4 mmHg). The increase and reduction in central venous pressure were accompanied by no change in systolic blood pressure, diastolic blood pressure and heart rate which indicated that the increased and reduced stimulus had involved only cardiopulmonary receptors and not arterial baroreceptors as well. During the increase in central venous pressure plasma renin activity showed a significant (P less than 0.01) reduction (-18 +/- 3%) whereas during the reduction in central venous pressure it showed a significant (P less than 0.01) and more marked increased (+64 +/- 17%). The plasma renin activity increase observed during lower body suction was not significantly different from that observed during a 20 min tilting, a manoeuvre that reduced central venous pressure to an extent similar to that observed during lower body suction, but that also deactivated carotid baroreceptors by positioning the carotid sinuses above the heart and reducing their transmural pressure. Thus in normotensive and hypertensive humans renin release can be reflexly modulated by selective engagement of cardiopulmonary receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1983

Mechanisms of antihypertensive action of beta-adrenergic blocking drugs: evidence against potentiation of baroreflexes.

A possibility that can be advanced to explain the antihypertensive effect of beta-blocking drugs is that they act through the baroreflex control of the cardiovascular system. In 38 essential hypertensive patients we measured 1) The lengthening and shortening in R-R interval caused by stimulation or deactivation of arterial baroreceptors (vasoactive drug technique); 2) The fall and rise in blood pressure caused by stimulation and deactivation of carotid baroreceptors (neck chamber); 3) The rise in forearm vascular resistance caused by deactivation of cardiopulmonary receptors (lower body suction). The study was made before and after 6-10 days' administration of nadolol (80-360 mg once a day) or acebutolol (200-600 mg t.i.d.). Nadolol and acebutolol similarly reduced blood pressure and heart rate. Either drug increased heart rate responses to arterial baroreceptor manipulation but the increase fell short of statistical significance. Blood pressure and vasomotor responses to carotid baroreceptor and cardiopulmonary receptor manipulation were also not significantly modified by beta blockade. The baroreceptor control of heart rate and blood pressure showed a modification, however, insofar as a resetting towards the lower blood pressure values occurred. These findings demonstrate that arterial baroreceptor and cardiopulmonary receptor control of circulation is not potentiated by beta-blocking drugs, and that therefore this mechanism cannot account for their antihypertensive effect. The resetting of the baroreflex that occurs during beta blockade may, however, contribute to maintain the hypotension obtained.

Adrenergic beta-Antagonists↗
PubMed1983

A comparative study on the effects of pindolol and propranolol on systemic and cardiac haemodynamics in hypertensive patients.

Eight out-patients with essential hypertension participated in a comparative, placebo-controlled study with a cross-over design. Pindolol and propranolol were administered orally in doses of 20.0 +/- 3.13 mg/d (mean +/- SEM) and 125.0 +/- 19.17 mg/d respectively. Pindolol reduced mean blood pressure by 11.9 mmHg; pre-ejection period index by 8.1 msec; total peripheral resistance by 3.1 mmHg min/L; and limb vascular resistance by 3.28 mmHg min 100 g/ml. Heart rate, cardiac output, plasma renin activity and urinary norepinephrine excretion rate were not altered by pindolol. Propranolol reduced mean blood pressure by 14.0 mmHg; heart rate by 9.1 beats/min; cardiac output by 0.57 L/min; limb blood flow by 1.06 ml/100 g.min; and plasma renin activity by 1.44 ng/ml/h; and increased pre-ejection period index by 8.7 msec. Total peripheral resistance, limb vascular resistance and urinary norepinephrine excretion rate were not altered by propranolol. It was concluded that: (1) the drugs, pindolol and propranolol, are equally effective as antihypertensive agents; (2) heart function and plasma renin activity are decreased by propranolol and unaltered by pindolol; (3) total peripheral resistance is decreased by pindolol and unaltered by propranolol; and (4) these findings may be explained by the intrinsic sympathomimetic activity exhibited by pindolol only.

Adult↗
PubMed1983

Reproducibility of laboratory tests evaluating neural cardiovascular regulation in man.

In 31 normotensive and hypertensive subjects with continuous intra-arterial blood pressure (BP) and heart rate (HR) monitoring, we examined the short term reproducibility of the haemodynamic responses to a number of tests commonly employed in studies on neural cardiovascular regulation: (1) hand-grip exercise and cold pressor tests that increase BP and HR through central and reflex mechanisms; (2) bolus injections of phenylephrine and trinitroglycerine that reflexly reduce and increase HR through stimulation and inhibition of arterial baroreceptors; (3) negative and positive pressure alterations within a neck chamber that reflexly reduce and increase BP through stimulation and inhibition of carotid baroreceptors. Each test was standardized and repeated at 30 min intervals six times in each subject. In the group as a whole the BP and HR responses to hand-grip showed a variability (mean variation coefficient, VC) of 22 and 25% respectively. BP and HR responses to cold pressor test showed a VC of 17 and 44% and HR responses to trinitroglycerine showed a VC of 28%. HR responses to phenylephrine were slightly less (19%) and BP responses to neck chamber considerably less variable (14 and 10%). The variability of the responses was not related to basal BP or HR or to the time sequence of the tests. Thus, tests commonly employed for studying neural cardiovascular control in man have a limited short-term reproducibility. This implies that caution should be used in interpreting results obtained by a single performance of any given test, and in comparing results in different states or groups such as normotensive and hypertensive subjects, unless a relatively large number of responses is available.

Adult↗
PubMed1982

Cerebral protection in carotid surgery.

We performed 956 carotid endarterectomies in 661 conscious patients who were under cervical block anesthesia and in whom the stroke rate was 2.5%. They were analyzed to determine the mechanisms of strokes and the risk factor for perioperative stroke. Twenty-three patients with perioperative strokes, regardless of severity, were analyzed as to the mechanism of cause. One half were due to technical problems, one quarter to intraoperative embolization, one sixth to intracerebral hemorrhage, and the remainder were not directly related to the operative procedures. Perioperative stroke rate varied by group from 0.6% to 28.4%, highest when the contralateral carotid was occluded, where there was a preoperative persistent neurologic deficit, and when the patient failed to tolerate carotid clamping. Regional block monitoring was accurate and no stroke could be ascribed to anesthetic technique. Standard reporting techniques should be used in classifying patients into appropriate risk groups to permit meaningful comparisons among groups using different techniques for cerebral protection.

Anesthesia, Conduction↗
PubMed1982

Pulmonary circulation of the llama at high and low altitudes.

We have studied the pulmonary circulation of three closely related animals, the llama, alpaca, and guanaco. The mean pulmonary arterial pressure of 12 llamas and one alpaca indigenous to high altitude in the Andes was found to be slightly but significantly higher than that of three llamas and three guanacos born and bred at low altitude in England. On the other hand, the medial thickness of the muscular pulmonary arteries and the relative weights of the two ventricles were the same in three llamas and one alpaca at high altitude as they were in one llama and two guanacos at low altitude. It is concluded that the pulmonary vasoconstrictive response to hypoxia, while present, is greatly reduced in this species and it is suggested that this may have taken place by evolutionary adaptation.

Altitude↗
PubMed1981

Effects of high-frequency harmonics on cardiac relaxation indices.

This study was designed to determine the degree to which the systematic distortions in the pressure curve due to recording and filtering systems influence the relaxation indices. The purposes are 1) to analyze the dependency on the high frequencies of the relaxation and contractility parameters, 2) to determine the degree to which the catheter recordings modify those parameters, and 3) to test the monoexponential hypothesis in which the T index is based (Weiss, Frederiksen, and Weisfeldt, J. Clin. Invest. 58: 751-760, 1976). In 17 open-chest dogs, the left ventricular pressure (LVP) was recorded in four different ways: 1) with a large-bored metal cannula, 2) with a catheter-tip manometer, 3) with a Cournand catheter, and 4) with a pigtail catheter. The ECG and LVP were digitized by a computer. A Fourier analysis was performed, and the LVP waves were resynthesized with different numbers of harmonics. We conclude that 1) the catheter recordings are not recommended to calculate relaxation indices, 2) relaxation parameters present more sources of errors than contractility parameters, 3) the monoexponential hypothesis of T is fulfilled if the isovolumic relaxation is considered to end at the time the LVP is 10 mmHg more than left ventricular end-diastolic pressure level, 4) the dependency on higher harmonics of T index and +dP/dtmax is similar, and 5) -dP/dtmax is much more high-frequency dependent than T index.

Animals↗
PubMed1980

Correlates and changes over time in drug and alcohol use within a barrio population.

Extent and determinants of use of alcohol, marijuana, inhalants, and PCP were explored in a group of 339 Mexican American youths from the East Los Angeles Housing projects. Results from this study were compared to those from a similar survey carried out in the same area 2 years ago. Use of inhalants has declined markedly compared with prevalence reported in the previous report. However, use of alcohol and marijuana have increased across all age and sex cohorts. Prevalence of PCP use, explored for the first time in this report, was shown to be extremely high. Use of all drugs was generally predicted by age, sex, and number of peers reporting use. Self-concept factors, especially one's self-evaluation with respect to others, were also significant predictors to use of marijuana, inhalants, and PCP. However, alcohol use was not related to any self-concept factors. Language (Spanish-English) used both in the home and with peers was related to use of all substances studied. Limitations in the generalization of this study as a result of sampling problems are discussed.

Adolescent↗
PubMed1980

Echocardiographic diagnosis of left ventricular thrombi.

Left ventricular thrombi have not been commonly recognized by M-mode or by cross-sectional echocardiographic techniques despite their frequency at postmortem examination in patients dying of cardiovascular disease. We discuss two patients, with left ventricular throbmi recognized echocardiographically and confirmed by pathologic and/or angiographic evaluation, whose M-mode and cross-sectional echocardiographic abnormalities add to the variable spectrum of appearance of left ventricularl thrombi. The sensitivity and specificity of echocardiographic techniques in the diagnosis of intracardiac thrombi are discussed.

Adult↗
PubMed1979

Ascending colon volvulus due to a vitelline duct remnant in an elderly patient.

A 77-year old female is presented with volvulus of the ascending colon due to torsion around a vitelline duct remnant. Symptoms were mild and intermittent. Roentgenograms are presented which demonstrated this lesion preoperatively. At surgery the ascending colon was found to be twisted around a fibrous band extending from the umbilicus to the ileum.

Aged↗
PubMed1978

[Regional variations and particle binding of free amino acids in the rat brain: effects of amphetamine and methaqualone].

Amphetamine and methaqualone affected aspartate level in various regions of Rat brain. Increased aspartate level in cerebral cortex of methaqualone treated Rats was produced in the aspartate fraction whose binding to subcellular particules was Na+ dependant. This work suggest that aspartate level was altered only in brain fraction implicated in the pharmacological effects of the drugs.

Alanine↗
PubMed1978

Double-blind evaluation of chemonucleolysis for herniated lumbar discs. Late results.

Sixty-six patients with symptomatic herniated lumbar discs refractory to the usual conservative management were allocated at random into one of two treatment groups according to a double-blind protocol: 31 received chymopapain intradiscally (chemonucleolysis) and 35 received a placebo intradiscally. Symptoms remained significantly improved 1 year or more after injection for 55% of those treated with chymopapain and for 46% of those treated with placebo. The difference is not statistically significant. However, to discard chemonucleolysis on the basis of this one small clinical trial may be premature. Since continuing controversy has re-established a climate in which another double-blind study of chemonucleolysis is ethically feasible and scientifically desirable, we favor additional clinical trials under a tightly controlled protocol to help resolve the issue.

Adult↗