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Biomedical subjects

R S Rees

Publications and source records attributed to R S Rees.

At least 19 recordsLinked to original sources
PubMed1992

An improved method of in vivo wound disruption and measurement.

Biomechanical studies of wound strength are important because of new investigations in growth factors, cytokines, and fetal wounds. We compared two traditional methods of wound disruption measurement with a novel computerized model designed for in vivo experiments. An Instron tensiometer (INSTS) and an air insufflated positive pressure device (AIPPD) were compared with a vacuum-controlled wound chamber device (VCWCD). The VCWCD produced vacuum at the wound site and wound disruption was monitored with two video camera/recorders. Rats were marked with a template guide for a 2.5 cm, full-thickness, abdominal incisional wound. Rats were divided into three groups and studied at 2, 7, or 14 days after wounding. The recorded images were computer digitalized to generate wound strength curves from a three-dimensional model. A comparison of the wound disruption curves demonstrated that the VCWCD was comparable to the INST or AIPPD in normal wound healing (P greater than .40). The VCWCD provided data with less standard error at 2 days after wounding (P less than 05). In separate series of experiments, VCWCD was tested in the early phases of healing and was found to be sensitive to change at intervals of 48 hr after wounding (P less than .005). The INST or AIPPD methods could not perform this task because of an unacceptable level of random error after tissue manipulation. The VCWCD system was considered superior for evaluating early wound healing because it was an in vivo method which required minimal wound manipulation.

Animals↗
PubMed1992

Angioedema associated with lisinopril.

Angioedema has been reported to occur in association with all angiotensin-converting enzyme inhibitors used in the United States. We reviewed nine cases of angioedema associated with lisinopril use seen in the emergency department at our hospital among 1,970 patients that had been prescribed lisinopril from March 1989 to May 1990. Cases were considered as probably (six cases) or possibly (three cases) drug related, depending on the temporal relationship of the initiation of therapy and the onset of angioedema. All of the cases had edema of the lips, buccal mucosa, and or face. None presented with laryngeal edema or stridor. The angioedema resolved within 1 to 2 days with diphenhydramine treatment and discontinuation of lisinopril. Our data suggest that the incidence of angioedema associated with lisinopril is greater than that associated with captopril or enalapril.

Adult↗
PubMed1991

Valve and great vessel stenosis: assessment with MR jet velocity mapping.

For measurement of poststenotic jet velocities with magnetic resonance (MR) imaging, the authors reduced the echo time (TE) of the field even-echo rephasing (FEER) velocity mapping sequence from 14.0 to 3.6 msec, so minimizing the problem of MR signal loss from turbulent fluid. In vitro use of rotating disk and stenotic flow phantoms confirmed that the 3.6-msec TE sequence enables accurate measurement of jet velocities of up to 6.0 m/sec (r = .996). Peak jet velocity measurements were made with MR imaging in 36 patients with stenosis of native heart valves (n = 9), conduits (n = 19), or Fontan connections (n = 2) or with aortic coarctation (n = 6). Peak velocity measurements made with MR imaging agreed well with measurements made with Doppler ultrasound (US), which were available in 18 cases (standard deviation = 0.2 m/sec). Velocity mapping with fast-echo MR imaging is likely to have considerable importance as a noninvasive means of locating and evaluating stenoses, particularly at sites inaccessible to US, but care must be taken to prevent errors caused by malalignment, signal loss, phase wrap, or partial-volume effects.

Adult↗
PubMed1990

Serum amyloid P component: its role in platelet activation stimulated by sphingomyelinase D purified from the venom of the brown recluse spider (Loxosceles reclusa).

Serum amyloid P component or serum amyloid protein is a ubiquitous, highly conserved glycoprotein whose function is unknown. Although the related pentraxin, C-reactive protein, is an acute phase reactant in man, there is no direct evidence that human serum amyloid protein is involved in an inflammatory response. Here we show that serum amyloid protein is required by sphingomyelinase D, the principal necrotic agent of the venom of Loxosceles reclusa, for the in vitro-activation of human platelets. Furthermore, this platelet activation is dependent upon the presence of only serum amyloid protein; no other plasma components are necessary. Secretion of [3H]-serotonin and aggregation of platelets are nearly maximal following incubation of the platelets with purified sphingomyelinase D (0.3 micrograms/ml) and 5 micrograms/ml pure serum amyloid protein in the presence of calcium. Since the platelets are no longer activated when this 10% physiologic amount of serum amyloid protein is omitted, serum amyloid protein is likely to have a role in the necrosis caused by brown recluse spider venom.

Animals↗
PubMed1990

Magnetic resonance velocity mapping.

Magnetic resonance velocity mapping is achieved by encoding velocity at each point in a tomographic imaging plane in the phase of the magnetic resonance signal. Although this can be achieved with almost any imaging sequence, cine gradient echo sequences are particularly suitable because of the high signal from blood and the ability to repeat the sequence rapidly to form a cine image. The technique has been shown to be accurate by in vitro and in vivo validation, with flow measurements in the great vessels having an accuracy of approximately 6%. A potential problem arises from loss of signal from turbulent blood flow, but this can be overcome with the use of even echo rephasing and echo times below 5 ms. Using such sequences, velocities of up to 6 m s-1 have been measured clinically and pressure gradients across valves as great as 16 kPa (120 mmHg) can be computed. Clinical application has centred on the measurement of flow in the pulmonary circulation and in shunts and conduits in patients with congenital heart disease. Other applications include the measurement of valvular regurgitation and stenosis, and flow in coronary artery bypass grafts. Flow in native coronary arteries has been measured but the technique requires further development before such measurements can be considered reliable. Real time imaging using echo planar velocity mapping has been achieved and it is hoped that this will make coronary artery flow measurements more robust.

Blood Flow Velocity↗
PubMed1989

Pulmonary artery distensibility and blood flow patterns: a magnetic resonance study of normal subjects and of patients with pulmonary arterial hypertension.

Pulmonary artery distensibility was studied with spin-echo magnetic resonance imaging in 20 normal subjects of variable age and in four patients with pulmonary arterial hypertension. The distensibility was found to be significantly lower (8%) in patients with pulmonary arterial hypertension than it was in normal subjects (23%). No age-related difference occurred. Magnetic resonance velocity mapping of the pulmonary artery blood flow was performed in 26 normal subjects--11 had mapping in the mid pulmonary artery, 15 had mapping in the distal pulmonary artery, and mapping in the four patients with pulmonary arterial hypertension was in the mid pulmonary artery. The pulmonary artery flow volume was compared with aortic flow and left ventricular stroke volume and a very good correlation was found. A retrograde flow of 2% occurred in the normal subjects serving to close the pulmonic valve. Antegrade plug flow occurred in most normal subjects but varied among individuals. There were also other variations in the flow pattern among normal individuals. All patients with pulmonary arterial hypertension had a markedly irregular ante- and retrograde flow and a large retrograde flow (average 26%). Magnetic resonance imaging offers a noninvasive way to evaluate pulmonary arterial hypertension as well as to quantitate pulmonary and aortic flows in, for example, left-to-right shunts.

Adult↗
PubMed1989

Quantitation of antegrade and retrograde blood flow in the human aorta by magnetic resonance velocity mapping.

Magnetic resonance velocity mapping was used in 24 normal subjects to study two-dimensional velocity profiles in the proximal and mid-ascending aorta, and to quantify both forward and reverse flow. The aortic flow measurements were validated by comparison with left ventricular stroke volume in all subjects and by comparison with pulmonary flow measurements in 12. Agreement was good with standard errors of the estimate of 7.8 and 7.1 ml, and correlation coefficients of 0.93 and 0.95, respectively. Systolic velocity maps were similar in the proximal aorta and the mid-ascending aorta, with maximum early systolic flow along the left posterior wall. Toward the end of systole and throughout diastole, a channel of reverse flow developed in the same region in the mid-ascending aorta, but in the proximal aorta it split to enter the sinuses of Valsalva, predominantly the left and the right coronary sinuses. Mean percentage ratio of retrograde-to-antegrade flow was 6.3%, with the majority of retrograde flow occurring in early diastole. The findings suggest that the retrograde flow is related to coronary artery flow and it is possible that aortic disease, which is known to influence aortic flow patterns, may also influence coronary flow.

Adolescent↗
PubMed1989

Chemical shift magnetic resonance imaging of human atheroma.

Fifteen necropsy specimens of human descending aorta and from eight patients with atheromatous vascular disease were studied by magnetic resonance imaging at 0.5 T. Images were acquired in coronal and transverse planes to localised protruding lesions and then chemical shift imaging was performed by techniques described by Dixon and by Hinks. These techniques produce images in which signal strength is proportional to lipid content. The signal was expressed as a percentage of that from extravascular fat. The total lipid content and its distribution within the plaques were noted. After imaging, the postmortem specimens were examined histologically and the lipid content of the plaque was assessed on a semiquantitative scale. The distribution of lipid within the plaque and between intima and media was also noted. The findings of chemical shift imaging agreed well with histological examination both for total lipid content and for distribution within each plaque. Chemical shift imaging also provided an assessment of the lipid content of the plaques measured in living patients, but validation was more difficult. The usefulness of the technique in routine clinical practice remains to be established.

Aorta, Abdominal↗
PubMed1989

Regional aortic compliance studied by magnetic resonance imaging: the effects of age, training, and coronary artery disease.

Arterial compliance was measured in 70 healthy volunteers, 13 athletes, and 17 patients with coronary artery disease. Magnetic resonance images were acquired at end diastole and end systole through the ascending aorta, the aortic arch, and the descending thoracic aorta. Regional compliance was derived from the change in luminal area in a slice of known thickness and from the pulse pressure. Total arterial compliance was also measured from the left ventricular stroke volume and the pulse pressure. In the volunteers, mean (SD) regional compliance (microliters/mm Hg) was greatest in the ascending aorta (37 (18], lower in the arch (31 (15], and lowest in the descending aorta (18 (8], and it decreased with age. Compliance in the athletes was significantly higher than in their age matched controls (41 (16) versus 22 (11) microliters/mm Hg). In the patients with coronary artery disease it was significantly lower (12 (4) v 18 (10] than in age matched controls. Total arterial compliance also fell with age in those with coronary artery disease although there was more variation. The results suggest a possible role for compliance in the assessment of cardiovascular fitness and the detection of coronary artery disease.

Adult↗
PubMed1988

Plasma components are required for platelet activation by the toxin of Loxosceles reclusa.

We have used a partially purified toxin from the venom of the brown recluse spider, Loxosceles reclusa, to study its effects on human platelets isolated from plasma proteins. This toxin, which produced skin necrosis in rabbits, contained sphingomyelinase D activity. The toxin induced platelet aggregation and secretion of [3H]serotonin in human plasma but not in buffer or in human neonate plasma. Ca2+ was required for the interaction of toxin, platelets, and plasma factor(s). The addition of C-reactive protein restored aggregation and serotonin release of platelets incubated in human neonate plasma. The ADP-degrading enzyme, apyrase, and the non-steroidal, anti-inflammatory drug, indomethacin, inhibited platelet aggregation, suggesting that ADP secreted from platelet storage granules and indomethacin-sensitive pathway(s) are involve in the toxin-induced human platelet activation (aggregation and serotonin release). Generation of platelet activating factor (PAF) from the platelet by brown recluse toxin is not likely since the PAF receptor antagonist, BN 52021, did not inhibit platelet aggregation induced by the brown recluse toxin.

Adenosine Diphosphate↗
PubMed1988

Brown recluse spider bites of the upper extremity.

Brown recluse spider bites may cause painful, necrotic, slow-healing wounds. When these bites involve the hand and upper extremity, they can also create severe functional deficits and long-term disability. We reviewed an 11-year experience with brown recluse bites to the hand and upper extremity. Data from patients (n = 31) indicated a 20% incidence of functional complications (n = 6) unless conservative wound management, dapsone, and antibiotics were used. Delayed surgical excision was preferable until wounds were free from active inflammation. Painful, recurrent wound breakdown and hand dysfunction were more common with early surgical excision. These complications were successfully treated with steroids, sympathetic blockade, and early aggressive physical therapy.

Adolescent↗
PubMed1988

Left ventricular volume measured rapidly by oblique magnetic resonance imaging.

Magnetic resonance measurements of left ventricular volume and ejection fraction based on measurements of area and length in a single oblique plane containing the long axis of the ventricle were compared with measurements made by summing the areas of the chamber in multiple contiguous slices. The multislice technique is known to be accurate, but the single slice technique is much quicker; it takes only nine minutes of acquisition time for both volume and ejection fraction. In 25 normal subjects there was good agreement between the two methods of measuring volume with a mean (SD) difference between measurements of 2.0 (6.6) ml. In 20 patients with previous infarction it was less good with a mean (SD) difference of 4.5 (18.1) ml. The mean (SD) difference of ejection fraction measurements was -0.019 (0.038) in the normal subjects and -0.059 (0.106) in the patients, and the discrepancy between the two techniques was greatest in the patients with a pronounced abnormality of wall motion and low ejection fraction. In a further 25 normal subjects, the agreement between single plane volume measurements in the vertical and horizontal long axis planes was good, indicating that either plane is suitable for rapid measurement. Single plane measurements of left ventricular volume and ejection fraction can be made with the accuracies stated, which are sufficient for routine clinical use except in patients with a pronounced abnormality of wall motion. In combination with measurements of regional wall thickness and motion, previously described, the technique offers a rapid non-invasive assessment of both global and regional left ventricular function.

Adult↗
PubMed1988

Magnetic resonance velocity mapping in aortic dissection.

We describe three patients with chronic aortic dissection in whom both spin-echo magnetic resonance imaging (MRI) and cine field-echo imaging were performed. The field even-echo rephasing (FEER) sequence showed the intimal flaps much more clearly than the spin-echo sequence and provided a distinction between thrombus and static blood. Velocity mapping allowed flow measurements in the true and false lumens. The management of the three patients was based upon the information provided by MRI. It is suggested that MRI may avoid invasive investigation and be the method of choice in haemodynamically stable patients with aortic dissection provided that the FEER sequence is used.

Aged↗
PubMed1987

Analysis of vesicle fluid following the sting of the lionfish Pterois volitans.

Fluid aspirated from blisters following a lionfish (Pterois volitans) sting was analyzed utilizing combined capillary column gas chromatography and negative ion chemical ionization mass spectrometry. Analysis for prostaglandin F2 alpha demonstrated 16.91 ng/ml, for prostaglandin E2 0.143 ng/ml, for 6-keto-prostaglandin F1 alpha less than 0.1 ng/ml (nondetectable) and for thromboxane B2 1.65 ng/ml. Platelet aggregation studies showed that blister fluid caused aggregation of isolated platelets only, which was inhibited by heat treatment or by the presence of normal donor plasma.

Adult↗
PubMed1987

Magnetic resonance velocity mapping: clinical application of a new technique.

Magnetic resonance velocity mapping is a new technique which provides a display of velocity within the cardiovascular system at any point of the cardiac cycle. A short field echo sequence with even echo rephasing is used to obtain a signal from rapidly moving blood and a cine display is provided by rapid repetition of the sequence. The amplitude image shows the anatomy, with blood giving a high signal and areas of turbulent flow no signal. The phase image is a map of velocities at each point in the image plane. Thirteen cases are described in which the technique either provided a diagnosis or helped in functional assessment. Flow through atrial and ventricular septal defects was seen, although turbulent flow distal to the ventricular shunts led to some loss of quantitative information. In three patients with valve disease jets of abnormal flow were seen because of signal loss and it is suggested that the size of the area of turbulence may be used to quantify the severity of regurgitation. Velocities were measured in four coronary artery bypass grafts in two patients, and low velocity was seen in a graft with distal disease that supplied the infarcted territory. Velocity was reduced distal to an aortic coarctation and it was increased at the site of narrowing caused by thrombosis in a deep vein. The speed and direction of flow in the central vessels in a patient with complex congenital heart disease helped to establish the anatomy. The technique provides useful information in a wide range of disorders of the cardiovascular system, and in some cases may avoid the need for invasive investigation.

Adolescent↗
PubMed1987

Blood flow patterns in the human aorta studied by magnetic resonance.

Magnetic resonance velocity mapping by the field even echo rephasing sequence was used to provide two dimensional velocity profiles in the ascending and the descending aorta. Flow patterns were studied in ten healthy volunteers by a display method that gave clear details of the profiles. Velocity profiles in the ascending aorta were skewed in systole with an axis of skew roughly symmetrical about the plane of the aortic arch. During diastole flow was reversed along the posterior left wall of the ascending aorta while it continued forwards at the anterior right wall. In the descending aorta plug flow occurred but with minimal skew. Flow along the right wall was reversed during diastole. Turbulent flow did not occur in the ascending or descending aorta of any healthy subject. Magnetic resonance velocity mapping is a very powerful tool for the study of cardiovascular physiology. Its non-invasiveness, its quantitative two-dimensional data, its accuracy, and its high spatial resolution make it suitable for clinical use.

Aorta↗