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Query: UMLS:C0020538 (hypertension)
 170,190 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The classical theory of spontaneous pulsation of the retinal veins is that during systole intraocular pressure exceeds venous pressure, causing the veins to collapse. We show that this theory is internally inconsistent and not in accord with experimental data. It is inconsistent in assuming both (a) that oscillations of intraocular pressure (IOP) occur because the veins cannot immediately discharge the systolic arterial inflow and (b) that retinal venous pressure (RVP) can fluctuate independently of IOP during the cardiac cycle. It is not in accord with experimental data, which shows that RVP always exceeds IOP and that fluctuations in the latter are instantly transmitted to the former. We present an alternative theory that does not have these problems. We assume the following. (1) Inflow to the retinal venous tree from the capillaries is constant, the pulsatile arterial flow having been completely damped by the arterioles and capillaries. (2) Outflow from the central retinal vein (CRV) varies during the cardiac cycle because oscillations of IOP, transmitted to the intraocular CRV, are of greater amplitude than oscillations in cerebrospinal fluid pressure, transmitted to the extraocular CRV. By showing that the radial blood flow distending the veins obeys a diffusion equation and by employing an "equivalent cylinder" analysis of the branched venous tree to simplify the boundary conditions, we demonstrate that, with the above assumptions and the additional assumption of low amplitude of radial flow, the CRV will pulsate, and the pulsations will remain confined to a small segment near the exit point. The proposed theory can explain disappearance of pulsation with intracranial hypertension, intensification of pulsation in glaucoma, and variability in the linear extent and amplitude of pulsation among normal individuals. The theory may also be applied to other venous pulsations, such as the respiratory pulsation of the terminal portions of large veins entering the thorax or the cardiac cycle pulsation of the superior vena cava.
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PMID:Spontaneous pulsation of the retinal veins. 982 53

A noninvasive method to obtain pressure-lumen area (P-A) measurements of the human brachial artery is introduced. The data obtained from this method are analyzed using a mathematical model of the relationship between vessel pressure and lumen area including vessel collapse and hypertension. An occlusive arm cuff is applied to the brachial artery of ten normal subjects. The cuff compliance is determined continuously by means of a known external volume calibration pump. This permits the computation of the P-A curve of the brachial artery under the cuff. A model is applied to analyze the P-A relation of each subject. The results show that the lumen area varies considerably between subjects. The in vivo resting P-A curve of the brachial artery possesses features similar to that of in vitro measurements. A primary difference is that the buckling pressure is higher in vivo, presumably due to axial tension, as opposed to in vitro where it is near zero or negative. It is found that hypertension causes a shift in the P-A curve towards larger lumen areas. Also, the compliance-pressure curve is shown to shift towards higher transmural pressures. Increased lumen area provides an adaptive mechanism by which compliance can be maintained constant in the face of elevated blood pressure, in spite of diminished distensibility.
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PMID:Noninvasive measurement of the human brachial artery pressure-area relation in collapse and hypertension. 984 35

Studies of Asian Pacific American populations are often flawed because while the population is quite heterogeneous, researchers usually collapse them into a single category, making it impossible to assess the health status or needs of individual Asian Pacific American ethnic groups. Using a probability sample of Guam residents, the analysis reported here addresses the problem by documenting the health status and characteristics of Chamorro and Filipino hypertensives. In contrast to predictions from the literature, Chamorros have a higher prevalence of hypertension than Filipinos. Additional results show that hypertensive Chamorro men and women are from lower socioeconomic status levels than their Filipino counterparts, while hypertensive men and women of both ethnic groups appear equally likely to be overweight and to suffer diabetes. Male hypertensives are at greater risk for psychological distress than normotensives, and have a greater chance of heart failure. Compared to Filipinos, hypertensive Chamorros are more likely to evaluate their overall physical health as poor.
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PMID:The health status and characteristics of hypertensives in Guam. 1005 Jan 85

Obstructive sleep apnoea is a frequently occurring disease that can have important consequences including disabling hypersomnolence and sleepiness as well as cardiovascular diseases like hypertension. Treatment modalities are, however, limited. The efficacy of nasal continuous positive airway pressure (CPAP) stands out, but not all patients can tolerate this treatment or be compliant with it. Efficacious alternative therapies are still remarkably few in number. It is demonstrated and concluded that only patients with mild forms of the disease can currently be considered for non-CPAP treatments. Patients with predominantly breathing pattern abnormalities can be cured with medical therapy. Those with predominantly upper airway collapse and with mildly elevated critical closing pressure can be treated with surgical procedures such as uvulopalatopharyngoplasty (UPPP). The exact indications for electrical stimulation of the hypoglossal nerve are still to be determined, although preliminary results seem to be promising for well-selected patients.
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PMID:Non-CPAP treatment of obstructive sleep apnoea. 1006 34

Flow-dependent vasodilation has been recognized to play an important role in the perfusion of the myocardium and the occurrence of myocardial ischaemia. In the past few years, the role of the endothelium in the regulation of coronary artery dimensions has gained a lot of attraction. Changes in coronary artery size are caused through the contraction and relaxation of the smooth musculature within the vessel wall. Vasoactive substances released from the endothelium play a crucial role in the regulation of vessel size and coronary vasomotor tone. During physiologic exercise, normal coronary arteries dilate, whereas stenotic arteries constrict. This abnormal behaviour of the stenotic artery has been associated with the occurrence of myocardial ischaemia, and has been thought to be either due to: endothelial dysfunction with reduced release or production of the endothelial derived relaxant factor (EDRF); an increased sympathetic stimulation during exercise; enhanced platelet aggregation with release of thromboxane A2 and serotonin; and/or a passive collapse of the disease-free vessel segment within the stenosis when blood-flow velocity increases during exercise. Thus, a diseased coronary endothelium may have a dramatic effect on the function of the coronary arteries, and may cause or contribute to the occurrence of myocardial ischaemia under high-demand situations, e.g. physical exercise or mental stress. Changes in flow-dependent vasodilation have been described in various disease states, e.g. hypercholesterolaemia, hypertension, diabetes mellitus, but also in valvular heart disease, heart failure and transplantation. Most of these alterations are due to functional changes of the endothelium, but vascular remodelling of the coronary arteries with thickening of the intima and an enlargement of the artery may affect these functional changes importantly.
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PMID:Flow-dependent vasodilation in the coronary circulation: alterations in diseased states. 1009 79

A specialist pediatric renal nursing service provides a link between hospital and home. Such support aims to reduce hospitalization and disruption to schooling and family routine. A 3-year prospective study monitored the progress and documented the nursing support to and contacts with 13 children (5 of whom were under 5 years of age) who commenced continuous cycling peritoneal dialysis (CCPD). Mean duration of CCPD was 14 months. Home and clinic contacts included telephone calls (65% of contacts), home, school, nursery, respite care, and community visits. Nine families received respite care from a home-care pediatric renal nurse, with children under 5 years receiving 68% of such visits. A total of 388 inpatient days were recorded. These included admission for catheter and dialysis training (125 days). hypertension (83 days), dialysis-related admissions (66 days), peritonitis (43 days), vomiting (31 days), and surgical procedures and infections (40 days). Nine peritonitis episodes occurred in 8 children (incidence 1 per 20 patient-months), and one death (cardiovascular collapse) occurred on CCPD. Seven children received a transplant, with the median waiting time for transplant being 7 months (range: 3-14 months). This study documents the spectrum of nursing support we have evolved to support children on CCPD and their families in the hope of reducing morbidity and hospitalization.
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PMID:Nursing contacts and outcomes in a pediatric CCPD program. 1064 41

A 41-year old primigravida underwent caesarean section because of foetal distress following prostin induction of labour. Intraoperative coagulopathy, haemorrhage and hypotension necessitated a hysterectomy. Subsequently, she developed respiratory and renal failure, requiring mechanical ventilation and haemodialysis. She made a full recovery. The likely diagnosis was amniotic fluid embolism (AFE), a rare complication of pregnancy with a variable presentation, ranging from cardiac arrest and death through to mild degrees of organ system dysfunction with or without coagulopathy. The differential diagnosis includes pre-eclamptic toxaemia/pregnancy-induced hypertension, anaphylaxis and pulmonary embolism. There is no diagnostic test for AFE; the finding of foetal elements in the maternal circulation is non-specific. Historically, AFE was thought to induce cardiovascular collapse by mechanical obstruction of the pulmonary circulation. It is now thought that a combination of left ventricular dysfunction and acute lung injury occur, with activation of several of the clotting factors. An immunological basis for these effects is postulated. There is no specific therapy and treatment is supportive. The mortality of the condition remains high.
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PMID:Amniotic fluid embolism: a case report and review. 1069 74

A 48-year-old man with a history of hypertension and diabetes mellitus was hospitalized with sudden onset of severe chest pain. He was in cardiogenic shock with a systolic pressure of 60 mm Hg. His electrocardiogram (ECG) showed ST-segment elevation in the precordial leads suggestive of acute anteroseptal myocardial infarction. The ST-segment returned to baseline after the systolic blood pressure rose to 100 mm Hg with the administration of sympathomimetic agents. Aortography and transesophageal echocardiography demonstrated type A aortic dissection and aortic regurgitation. Aortography and short-axis transesophageal echocardiography showed during diastole almost complete collapse of the true lumen of the ascending aorta caused by the intimal flap. The patient underwent surgical repair of the aortic dissection and implantation of Palmaz stents in the carotid arteries. Decreased blood pressure and the presence of aortic regurgitation accelerated the collapse of the true lumen during diastole in the ascending aorta, resulting in functional obstruction of the left main coronary artery, which may have been related to ST-segment changes in this case.
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PMID:A case of aortic dissection with transient ST-segment elevation due to functional left main coronary artery obstruction. 1071 27

The sleep apnoea/hypopnoea syndrome (SAHS) is characterized by repeated upper airway narrowing or collapse during sleep. The obstruction is caused by the soft palate and/or base of tongue collapsing against the pharyngeal walls because of decreased muscle tone. These episodes are accompanied by hypoxaemia, surges in blood pressure, brief arousal from sleep and pronounced snoring. Individuals with occult disease are at heightened risk of motorway accidents because of excessive sleepiness, sustained hypertension, myocardial infarction, and stroke. The signs and symptoms of SAHS may be recognisable in the dental practice. Common findings in the medical history include daytime sleepiness, snoring, hypertension, and type 2 diabetes mellitus. Common clinical findings include male gender, obesity, increased neck circumference, excessive fat deposition in the palate, tongue (macroglossia) and pharynx, a long soft palate, a small recessive mandible and maxilla, and calcified carotid artery atheromas on panoramic and lateral cephalometric radiographs. Dentists who recognise these signs and symptoms have an opportunity to diagnose patients with occult SAHS. After confirmation of the diagnosis by a physician, dentists can participate in the management of the disorder by fabricating mandibular advancement appliances that enlarge the retroglossal space by anterior displacement of the tongue and performing corrective upper airway surgery that prevents recurrent airway obstruction.
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PMID:Dentistry's role in the diagnosis and co-management of patients with sleep apnoea/hypopnoea syndrome. 1097 58

Measurement of arterial compliance is of interest in evaluating patients with atherosclerosis and other diseases which affect the vessels. Arterial compliance is the relation between changes in transmural pressure and volume of an arterial segment, where a high compliance signifies large changes in volume per change in transmural pressure. The relation between changes in transmural pressure and volume is far from linear as compliance increases progressively with decreases in blood pressure. A change in compliance could indicate static changes in arterial wall composition, i.e. the relation between elastic and collagen fibres and accumulation of disease related deposits or dynamic changes caused by alterations in muscular tone. The most used method reflecting arterial compliance is the measurement of pulse wave velocity. However, the pulse wave velocity method measures compliance at ambient transmural pressures and is affected both by the actual blood pressure and the rate of pressure change. Another commonly used method employs the echo-tracking technique to measure the arterial diameter simultaneously with continuous blood pressure monitoring. By this method it is possible to calculate arterial compliance for continuous pressure values between the diastole and the systole. The volume-oscillometry method is based on the fact that the artery can be made to collapse at the end of the diastole by an occlusive cuff while it remains open in a pressure dependent manner during the rest of the cardiac cycle. Changes in the arterial volume is transmitted to the cuff, where it induces a measurable change in pressure, and hence the volume of the artery can be calculated at different values of transmural pressures. Using this method on normal subjects has shown that the arterial compliance decreases with increasing age and that females have lower compliance than males primarily due to a smaller diameter of their arteries. It has also been shown that patients with essential (diastolic) hypertension have compliances which are higher or equal to those of normal subjects, and that patients with systolic hypertension have lower arterial compliances than normal subjects. The former finding is in contrast with pulse wave velocity measurements, where diastolic hypertension was associated with low arterial compliance.
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PMID:Measurement of arterial compliance in vivo. 1097 6


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