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Biomedical subjects

F Miranda

Publications and source records attributed to F Miranda.

At least 19 recordsLinked to original sources
PubMed2005

Anatomical study of the gastrocnemius venous network and proposal for a classification of the veins.

OBJECTIVES: To present a detailed description of the gastrocnemius venous network. DESIGN: Anatomical study in cadavers. MATERIAL AND METHODS: Forty lower limbs from 20 adult male cadavers were studied. All gastrocnemius veins were dissected from the gastrocnemius muscle heads proximally toward their drainage site. RESULTS: Eighty heads of 40 gastrocnemius muscles showed 438 gastrocnemius veins. The number of veins per muscle head varied between 2 and 12. There were 221 gastrocnemius trunks distributed as 95 main gastrocnemius trunks, 81 axial and 45 collateral ones. From the 95 main gastrocnemius trunks, 83 (87%) drained into the popliteal vein. Direct observation of the gastrocnemius venous network allowed us to classify the anatomical distribution as four distinct types. CONCLUSIONS: The majority of main gastrocnemius venous trunks drain into the popliteal vein. There is wide variability in the number of gastrocnemius veins. We propose a classification of four distinct types of anatomical pattern.

Adult↗
PubMed2004

Prevalence of varicose veins and venous anatomy in patients without truncal saphenous reflux.

OBJECTIVES: To determine the prevalence and distribution of primary venous reflux in the lower limbs in patients without truncal saphenous reflux. DESIGN: Prospective cohort study. PATIENTS AND METHODS: One thousand and seven hundred and twelve patients with suspected venous disease were examined by duplex ultrasonography. Seven hundred and thirty-five patients had primary varicose veins with competent saphenous trunks. Limbs with truncal saphenous reflux, deep vein reflux or obstruction, previous injection sclerotherapy or vein surgery, arterial disease and inflammation of non-venous origin were excluded from further consideration. The CEAP classification system was used for clinical staging. Systematic duplex ultrasound examination was undertaken to assess the distribution of incompetent saphenous tributaries. RESULTS: The prevalence of primary reflux with competent saphenous trunks was 43%. Reflux of GSV calf tributaries was the most common. The majority of the limbs (96%) belonged to chronic venous disease classes C1 and C2 of the CEAP classification. CONCLUSIONS: Superficial venous reflux causing varicose veins in the presence competent saphenous trunks is very prevalent in this series in contrast to other studies, presumably reflecting differing patient populations. Our data clearly show that varicose veins may occur in any vein and do not depend on truncal saphenous incompetence. Careful duplex ultrasound evaluation allows the pattern of venous reflux to be established in this group of patient ensuring appropriate management of varices.

Adolescent↗
PubMed2003

Further evidence that the discriminative stimulus properties of indorenate are mediated by 5-HT 1A/1B/2C receptors.

Indorenate (5-methoxytryptamine beta-methylcarboxylate, INDO) is a serotonin (5-hydroxytryptamine, 5-HT) agonist that has affinity for 5-HT(1A/1B/2C) receptors. Unlike other anxiolytics such as 5-HT receptor agonists, INDO may not share tolerance or dependency with the benzodiazepine anxiolytics. It has been reported that the discriminative stimulus properties of 5-HT(1A/1B/2C) agonists, but not those of 5-HT(3/4) agonists, generalize to INDO. Therefore, the aim of the present study was to obtain further evidence on the differential involvement of 5-HT(1A/1B/2C) receptors in the discriminative stimulus properties of INDO by evaluating its interactions with antagonists of the 5-HT(1A), 5-HT(1B), 5-HT(2C), and 5-HT(3/4) receptor subtypes. Rats were trained to discriminate INDO from saline in a conditioned taste aversion paradigm. For Group D(+)S(-), administration of INDO signalled that saccharin flavour was followed by LiCl, while injection of vehicle signalled safe consumption of saccharin solution. Group D(-)S(+) had the contingencies reversed. After this training, rats had generalization tests where INDO administration was preceded by different doses of the following antagonists: WAY100635 (5-HT(1A)), NAN190 (5-HT(1A)), methiothepin (5-HT(1A/1B/2C)), GR127935 (5-HT(1B/1D)), ketanserin (5-HT(2A/2C)), ritanserin (5-HT(2C/2A)), mesulergine (5-HT(2C/2A)), metergoline (5-HT(2C/2A)), SB206553 (5-HT(2B/2C)), and tropisetron (5-HT(3/4)). In Group D(+)S(-), the order of potency to block the discriminative stimulus properties of INDO was WAY100635>ketanserin>ritanserin>GR127935>mesulergine congruent with SB206553>metergoline>methiothepin>NAN190, while in Group D(-)S(+), the order was WAY100635>GR127935>ketanserin>ritanserin>mesulergine congruent with SB206553>metergoline>methiothepin>NAN190. Tropisetron did not produce any alteration of the discriminative control by INDO. These results suggest that the discriminative signal of INDO is mediated by 5-HT(1A/2C/1B) receptors and that blockade of any of its components produces a degradation of its discriminative effects.

5-Methoxytryptamine↗
PubMed2003

Effects of a 5-HT2 receptor agonist, DOI (2,5-dimethoxy-4-iodoamphetamine), and antagonist, ketanserin, on the performance of rats on a free-operant timing schedule.

This experiment examined the effect of a 5-HT2 receptor agonist DOI (2,5-dimethoxy-4-iodoamphetamine), and antagonist, ketanserin, on temporal differentiation performance. Twelve rats were trained under the free-operant psychophysical procedure to press two levers (A and B) in 50-s trials in which sucrose reinforcement (0.6 mol/l, 50 microl) was provided intermittently for responding on A during the first half, and on B during the second half of the trial. Psychometric curves were derived from percent responding on B (%B), recorded in successive 5-s epochs of the trials; logistic functions were fitted to these data for the derivation of timing indices (T50 [time corresponding to %B=50%], epsilon [slope of the logistic curve], Weber fraction). Cumulative probability of switching in successive 5-s epochs was used to estimate the mean switching time, S50. DOI (0.0625, 0.125 and 0.25 mg/kg, s.c.) dose-dependently reduced T50 and S50. These effects of DOI (0.25 mg/kg) were antagonized by ketanserin (1.0 mg/kg). The results show that DOI alters temporal differentiation in the free-operant psychophysical procedure. The antagonistic effect of ketanserin indicates that the effect of DOI was probably mediated by 5-HT2A rather than 5-HT2C receptors, since ketanserin is relatively selective for 5-HT2A receptors. Comparison of these results with our previous findings with a 5-HT1A receptor agonist indicates that 5-HT1A and 5-HT2A receptors mediate qualitatively similar effects on temporal differentiation.

Amphetamines↗
PubMed2002

Hyperhomocysteinemia increases the risk of venous thrombosis independent of the C677T mutation of the methylenetetrahydrofolate reductase gene in selected Brazilian patients.

Fasting total homocysteine (tHcy) and the methylenetetrahydrofolate reductase (MTHFR) C677T mutation were evaluated in 91 patients with venous thromboembolism and without acquired thrombophilia, and in 91 age-matched and sex-matched controls. Hyperhomocysteinemia was detected in 11 patients (12.1%) and in two controls (2.2%), yielding an odds ratio (OR) for venous thrombosis of 6.1 [95% confidence interval (CI), 1.3-28.4]. After excluding 21 patients and four controls with other known genetic risk factors for venous thrombosis, the OR was not substantially changed (7.0; 95% CI, 1.5-33.1). The prevalence of the MTHFR 677TT genotype was not significantly different in patients (9.9%) and in controls (5.5%), with an OR for venous thrombosis of 1.8 (95% CI, 0.6-5.8). Subjects with the MTHFR 677TT genotype showed higher levels of tHcy compared with the 677CC genotype in patients (P = 0.010) and in controls (P = 0.030). In conclusion, we found that fasting hyperhomocysteinemia is a risk factor for venous thrombosis in patients without known acquired thrombophilia and other genetic risk factors for venous thrombosis. Although tHcy levels are significantly higher in those homozygous for the MTHFR C677T mutation, this genotype does not increase the thrombotic risk in our study population.

3' Untranslated Regions↗
PubMed2002

Full substitution of the discriminative cue of a 5-HT(1A/1B/2C) agonist with the combined administration of a 5-HT(1B/2C) and a 5-HT(1A) agonist.

The present study examined whether animals attend to the individual components of the cue produced by a drug that stimulates different 5-hydroxytryptamine (5-HT) receptor populations, using a drug discrimination task based on the conditioned taste aversion (CTA) procedure. The training drug was indorenate (5-methoxytryptamine beta-methylcarboxylate) (INDO) that has been described as a 5-HT(1A/2C/1B) agonist able to exert discriminative control in both operant and CTA procedures. The principal objective was to examine generalization with the combined administration of agonists for the different receptor sites that may mimic the mechanism of action of the training drug. Male Wistar rats, deprived of water, were trained to discriminate INDO from saline; during the drug trials, the administration of INDO preceded saccharin-LiCl pairings, while, during the saline trials, the administration of saline preceded the saccharin-saline pairings. In generalization tests, INDO, 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT, a 5-HT(1A) agonist), 1-(3-trifluoromethylphenyl)piperazine (TFMPP, a 5-HT(1B) agonist), alpha-methyl-5-HT (a 5-HT(2C) agonist) or 2-methyl-5-HT (a 5-HT(3) agonist), were administered alone or in combination. The results showed that 8-OH-DPAT, TFMPP and alpha-methyl-5-HT produced dose-dependent generalization, up to 88% in the case of 8-OH-DPAT. The combined administration of the following pairs of drugs, 8-OH-DPAT+TFMPP or 8-OH-DPAT+ alpha-methyl-5-HT, at doses that produced only 15-55% generalization when administered alone, produced greater than 80% generalization to INDO. However, the single administration of 2-methyl-5-HT produced only saline-like responding and its combined administration with 8-OH-DPAT did not modify the generalization produced by the single administration of 8-OH-DPAT. These results suggest that animals attend to the individual components of the drug cue; in the case of INDO, which has three elements, each mediated by a different receptor subpopulation (5-HT(1A), 5-HT(1B) and 5-HT(2C) ), the separate stimulation of at least two receptor subpopulations was 'interpreted' by the subject as the presence of the training drug.

5-Methoxytryptamine↗
PubMed2001

Discriminative stimulus properties of indorenate in a conditioned taste aversion paradigm.

Indorenate (5-methoxytryptamine beta-methylcarboxylate, INDO) is a serotonin (5-hydroxytryptamine, 5-HT) agonist that has affinity for 5-HT(1A/1B/2C) receptors. It possesses anxiolytic and antihypertensive actions mediated by 5-HT(1A) receptors and anorectic activity mediated by 5-HT(2C/1B) receptors. This study examined whether INDO may exert discriminative control using a conditioned taste aversion (CTA) paradigm, and whether differential participation of 5-HT receptor subtypes may be involved in its cue. Male Wistar rats trained to drink their daily water in a 30-min period were trained to discriminate INDO from saline. One group received the intraperitoneal administration of INDO (10.0 mg/kg) before saccharin-LiCl pairings; on alternate days, rats received saline before the saccharin-saline pairings (Group D(+)S(-)). The other group had the contingencies reversed (i.e., the administration of INDO preceded saccharin-saline pairings: Group D(-)S(+)). In two-bottle generalization tests (one bottle containing saccharin, the other plain water), the preference for saccharin was evaluated after different doses of INDO, [3H]-8-hydroxy-2-(di-N-propylamino)tetralin (8-OH-DPAT) (5-HT(1A)), buspirone (5-HT(1A)), RU24969 (5-HT(1A/1B)), TFMPP (5-HT(1B/2C)), MK212 (5-HT(2C)), alpha-Me-5-HT (5-HT(2C/2A)), 2-Me-5-HT (5-HT(3)) and cisapride (5-HT(4)). The results showed that INDO, RU24969, TFMPP, alpha-Me-5-HT and MK 212 produced a dose-dependent generalization; 8-OH-DPAT and buspirone produced only partial generalization, while 2-Me-5-HT and cisapride did not produce generalization. The results indicate that INDO administration may exert discriminative control over saccharin preference mediated mainly by 5-HT(1B/2C) receptors, but with an important contribution of 5-HT(1A) receptors.

5-Methoxytryptamine↗
PubMed2001

Effect of sequential intermittent pneumatic compression on both leg lymphedema volume and on lymph transport as semi-quantitatively evaluated by lymphoscintigraphy.

Sequential Intermittent Pneumatic Compression (SIPC) is an accepted method for treatment of peripheral lymphedema. This prospective study evaluated the effect in 11 patients of a single session of SIPC on both lymphedema volume of the leg and isotope lymphography (99Tc dextran) before SIPC (control) and 48 hours later after a 3 hour session of SIPC. Qualitative analysis of the 2 lymphoscintigrams (LS) was done by image interpretation by 3 physicians on a blind study protocol. The LS protocol attributed an index score based on the following variables: appearance, density and number of lymphatics, dermal backflow and collateral lymphatics in leg and thigh, visualization and intensity of popliteal and inguinal lymph nodes. Volume of the leg edema was evaluated by measuring limb circumference before and after SIPC at 6 designated sites. Whereas there was a significant reduction of circumference in the leg after SIPC (p<0.05), there was no significant difference in the index scores of the LS before and after treatment. This acute or single session SIPC suggests that compression increased transport of lymph fluid (i.e., water) without comparable transport of macromolecules (i.e., protein). Alternatively, SIPC reduced lymphedema by decreasing blood capillary filtration (lymph formation) rather than by accelerating lymph return thereby restoring the balance in lymph kinetics responsible for edema in the first place.

Adult↗
PubMed2000

Continued experience with physical examination alone for evaluation and management of penetrating zone 2 neck injuries: results of 145 cases.

PURPOSE: Our preliminary experience with physical examination alone in the evaluation of penetrating zone 2 neck injuries for vascular trauma was previously reported in 28 patients over a 2-year period (1991-1993). The purpose of the current study was to examine the results of this approach in a much larger group of patients over an 8-year period. METHODS: The medical records for all patients admitted to our level I trauma center (all of them entered into our prospective protocol) between December 1991 and April 1999 with penetrating zone 2 neck trauma were reviewed for their initial presentation and any documented vascular injury. RESULTS: A total of 145 patients made up the study group; in 30 of these patients, the penetrating trajectory also traversed zone 1 or 3. Thirty-one patients (21%) had hard signs of vascular injury (active bleeding, expanding hematoma, bruit/thrill, pulse deficit, central neurologic deficit) and were taken immediately to the operating room; 28 (90%) of these 30 patients had either major arterial or venous injuries requiring operative repair (the false-positive rate for physical examination thus being 10%). Of the 114 patients with no hard signs, 23 underwent arteriography because of proximity of the injury to the vertebral arteries or because the trajectory included another zone. Of these 23 arteriograms, three showed abnormalities, but only one required operative repair. This case had no complications relating to the initial delay. The remaining 91 patients with no hard signs were observed without imaging or surgery for a minimum of 23 hours, and none had any evidence of vascular injury during hospitalization or during the initial 2-week follow-up period (1/114; false-negative rate for physical examination, 0.9%). CONCLUSIONS: This series confirms the earlier report indicating that patients with zone 2 penetrating neck wounds can be safely and accurately evaluated by physical examination alone to confirm or exclude vascular injury. The missed-injury rate is 0.7% (1/145) with this approach, which is comparable to arteriography in accuracy but less costly and noninvasive. Long-term follow-up is needed to confirm this management option.

Adult↗
PubMed2000

Assessment of insecticide resistance in five insect pests attacking field and vegetable crops in Nicaragua.

Field populations of Hypothenemus hampei (Ferrari), Plutella xylostella (L.), Spodoptera exigua (Hübner), Helicoverpa zea (Boddie) and Bemisia tabaci (Gennadius) were tested for resistance to several insecticides commonly used in Nicariagua. Assays were conducted to estimate the LD50s or LC50s and the corresponding resistance ratios. A diagnostic concentration was used to discriminate between susceptible and resistant strains of H. hampei. The tests with >6,000 H. hampei adults collected from six different sites indicate the absence of resistance to endosulfan. Resistance to cypermethrin, deltamethrin, chlorfluazuron, thiocyclam, and methamidophos was documented in six field populations of P. xylostella. High levels of resistance to cypermethrin and deltamethrin, but moderate levels of resistance to chlorpyriphos and methomyl, were also documented in two field populations of S. exigua. Moderate levels of resistance to cypermethrin, deltamethrin and chlorpyriphos were also documented in three field populations of H. zea. Moderate to high levels of resistance to bifenthrin, methamidophos and endosulfan were documented in four field populations of B. tabaci. The presence of significant correlations between LD50s or LC50s suggests the occurrence of cross-resistance or simultaneous selection for resistance by different insecticides with different modes of action. Our data could not differentiate between these two possibilities. Because insecticides will continue being used in Nicaragua, a resistance management program is urgently needed. The implementation of integrated pest management tactics must be accompanied by specific regulations for pesticide registration. In the future, pesticide registration regulations in Nicaragua should include periodic resistance monitoring. The mechanisms to cover the costs of resistance monitoring and resistance management should also be established.

Animals↗
PubMed1998

[Improvement in the treatment of acute myocardial infarct by the establishment of a thrombolysis unit in a cardiology servic].

INTRODUCTION AND OBJECTIVES: Lack of available beds in the coronary care unit, makes time to thrombolysis still too long. Although fibrinolytic therapy is administered in the emergency department in most hospitals, mean in-hospital delay continues to be long. Our purpose was to improve the treatment of these patients and to evaluate if this delay could be shortened by creating a thrombolysis unit for the treatment of patients with acute myocardial infarction. METHODS: A thrombolysis unit in the cardiology department was set up to treat patients with acute myocardial infarction who couldn't be admitted directly in the coronary care unit because of lack of available beds. Time to treatment in both groups of patients were compared. RESULTS: Two hundred twenty-five patients with acute myocardial infarction and ST-segment elevation were included: 86 (38%) of them were admitted to the thrombolysis unit and the other 139 (62%) to the coronary care unit. There were no differences in baseline characteristics or in the pre-hospital delay between both groups. Time from hospital admission to thrombolysis was 59 minutes in patients treated in the thrombolysis unit versus 70 minutes in those treated in the coronary care unit (p < 0.001), and time from the admission to both units to fibrinolytic therapy was of 20 minutes versus 30 minutes respectively (p < 0.0001). There were no differences between both groups in the incidence of complications. CONCLUSIONS: In-hospital delay in thrombolysis remains too long. Implementation of a thrombolysis unit in the cardiology department shortens this delay and offers the possibility to treat patients with acute myocardial infarction at least as well as in the coronary care unit, without dependence on the availability of free beds in this unit.

Coronary Care Units↗
PubMed1998

Maxillary protraction: treatment and posttreatment effects.

This study evaluated the treatment response and posttreatment follow-up of children with Class III malocclusions treated with palatal expansion and reverse-pull face mask to the maxilla. The sample included 22 white children, 9 boys and 13 girls. Treatment began at a mean age of 9.8 years (range 5.6 to 13.3 years) and lasted 0.7 years (range 0.3 to 1.3 years). With a protraction force of 600 to 800 gm, the patients were treated until a 2 mm positive overjet had been attained. Radiographs were taken before treatment (T1), immediately after face mask treatment (T2), and 1.4 years after treatment (T3). An age and sex matched sample of untreated white schoolchildren served as normal controls. The results showed that the anterior maxilla was protracted forward 1.6 mm per year more than normal. The posterior maxilla dropped inferiorly more than the anterior maxilla. The mandible was rotated downward and backward, while the lower incisors were uprighted. The effects on the mandible were attributed to a significant chincup effect exerted by the face mask. After treatment, the maxilla relapsed relatively backward in the anterior and upward in the posterior, negating some of the treatment results. The mandible resumed a normal growth direction, and the lower incisors flared more than normal.

Adolescent↗
PubMed1997

Cocaine administration enhances platelet reactivity to subendothelial components: studies in a pig model.

Myocardial infarction in cocaine abusers may be related to a direct platelet-activating effect. We analysed this possibility in an experimental model. Studies were carried out in eight normal, anaesthetized pigs with a weight of 30.7 +/- 3.7 kg. Blood samples were withdrawn before and 20 min after i.v. administration of cocaine (10 mg kg-1; at 1 mg kg-1 every 2 min). Modifications in platelet responses to arachidonic acid (AA; 1.4 mmol L-1), ADP (1-4 microM), synthetic thromboxane endoperoxide analogue (U46619; 1 microM), collagen (2.5-5 micrograms mL-1), adrenaline (10 microM) and ristocetin (0.8-1 mg mL-1) were tested by conventional aggregometry. Changes in the capacity of platelets to form aggregates on damaged subendothelium were assessed by means of an ex vivo perfusion system in which blood was circulated for 10 min at 800 s-1, a shear rate similar to that found in normal coronary arteries. The interaction of platelets with perfused denuded arterial segments was morphometrically quantified and expressed as a percentage of damaged vessel surface covered by platelets (%CS). Cocaine administration did not influence platelet aggregation patterns in pigs. However, there was a significant increase in the interaction of pig platelets with subendothelial structures after cocaine infusion (%CS = 40 +/- 17% vs. 27 +/- 16% baseline; mean +/- SD; P < 0.01). Cocaine administration in this animal model increases the reactivity of platelets exposed to subendothelium. These results support the concept that the administration of cocaine to pigs has a prothrombotic effect by facilitating the interaction of platelets with damaged arteries.

Animals↗
PubMed1997

[The effects of a cardiac rehabilitation program on 2 populations of coronary patients: acute myocardial infarct and coronary bypass surgery].

UNLABELLED: Cardiac rehabilitation programmes (CRP) have proven beneficial in coronary heart disease. The purpose of this study was to evaluate the effects of our CRP on two coronary heart disease populations: after acute myocardial infarction (AMI-CRP) and after coronary artery bypass surgery (CABG-CRP). Results were compared to control groups (AMI-C and CABG-C). POPULATION: Group AMI-CRP: n = 43 patients, mean age = 48.7 +/- 9.8 years; Group AMI-C: n = 20 patients, mean age = 59.2 +/- 11.5 years; Group CABG-CRP: n = 54 patients, mean age = 54.9 +/- 9.7 years; Group CABG-C: n = 20 patients, mean age = 56.5 +/- 9.9 years. All patients are male and there were no significant differences in ventricular function and coronary disease severity. Parameters were evaluated in the AMI groups at discharge, 3 and 12 months after acute episode; in the CABG groups 3 and 12 months after surgery. RESULTS: Both CRP groups improved their exercise capacity (significantly improved the peak values of METs and double product). A favorable lipid profile change (total cholesterol and HDL) was induced in the CABG-CRP group and more significant in the AMI-CRP group. No significant differences were observed in obesity indexes (body weight and BMI > or = 27.8 Kg/m2). A increase in nonsmokers was important in all groups. Professional reintegration was 91.7% in the AMI-CRP group and 84.4% in the CABG-CRP group. The CRP groups showed a better knowledge of the disease, and a beneficial change in relation to themselves and the world that resulted in a decrease in depression and anxiety. CONCLUSIONS: Participation in our cardiac rehabilitation program, either after AMI or after CABG, improves cardio-respiratory fitness, favorably influences blood lipid profiles, and improves self-reliance and quality of life.

Adult↗
PubMed1996

Serological response to Helicobacter pylori in gastric and non-gastric cancer.

1. We aimed to evaluate the seroprevalence of Helicobacter pylori (H. pylori) in gastric cancer, non-gastric cancer and outpatients by ELISA and iso-electric focusing, and to compare histology and serology for H. pylori in gastric cancer and outpatients. 2. In 124 patients with gastric cancer, 78 patients with non-gastric cancer and 110 outpatients, H. pylori seroprevalence was assessed by ELISA and isoelectric focusing. Gastric cancer and outpatients underwent endoscopy with biopsies. 3. Seroprevalence by ELISA was significantly higher in gastric cancer compared with non-gastric cancer (84% versus 56%, P < 0.001) but not with outpatients (84% versus 74%). Iso-electric focusing detection of H. pylori was comparable to ELISA: 85, 51 and 75% in gastric cancer, non-gastric cancer and outpatients respectively. Oligoclonal iso-electric focusing was significantly more frequent in gastric cancer compared with non-gastric cancer and outpatients: 69% versus 45 and 46% respectively, P < 0.01. The reliability of H. pylori detection by antral biopsy was significantly lower in gastric cancer compared with outpatients: 36% versus 74% (P < 0.001). In gastric cancer, ELISA and iso-electric focusing were significantly more reliable than histology in H. pylori detection (84 and 85% versus 36% respectively) (P < 0.001). 4. Serological immune response to H. pylori in gastric cancer, non-gastric cancer and outpatients seems different both quantitatively and qualitatively; serology was more reliable than histology in detection of H. pylori in gastric cancer.

Adult↗
PubMed1996

[Basic concepts on the assessment of arterial baroreceptor sensitivity with non invasive methods. Estimate of the spontaneous gain of the arterial baroreceptor].

Arterial baroreceptors are sensitive to variation in both blood and pulse pressure. When there is an increase in those pressures, the baroreceptors increase the rhythm in which electric impulses are discharged. The impulses are transmitted by the receptors to the nervous centres of the brainstem. Once processed, these signals turn into sympathetic and vagal impulses. The vagal efferents control heart rate and the sympathetic efferents control heart rate, myocardial contractility and peripheral resistance. If there is an increase in blood pressure, then there will be a reflex decrease in the sympathetic activity and an increase in the parasympathetic one. The cardiac cronotropic response to blood pressure variation is very fast-with a delay of one or two beats. The amplitude of the response is a sigmoidal function. The greatest inclination of the response curve, that is to say, the area of greatest variation of the RR interval per unit of pressure, characterises the gain of the baroreceptors. The traditional method for obtaining the gain of the baroreceptor is a pharmacological one. Generally, the patient is given phenilephrine intravenously, in bolus and then the correlation between heart rate and the increase in intra-arterial blood pressure (reflex bradycardia) is calculated. Lately, it has been used the calculation of the spontaneous gain of the baroreceptor starting from a study carried out on the normal fluctuations in blood pressure and in the pulse interval both in time and frequency domain. The first case deals with the calculation of the gain of the function of transfer between the variations both in blood pressure and the RR intervals in the LF and the HF bands. The second case deals with the analysis of the occurrence of sequences of three beats with successive increases or decreases in blood pressure and in the RR interval. The gain is obtained from the linear regression of all the sequences. The application of these techniques to the recordings of blood pressure obtained by non-invasive methods (Finapress) makes possible that this procedure be followed under real conditions since it requires no previous stimulation of the cardiovascular system, which would probably interfere with the mechanisms to be evaluated, and requires no equipment in the condition which is normally required by experimental methodology.

Blood Pressure↗