Modelling emboli with floating fir cones.
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Brain Ischemia↗
Biomedical subjects
Stephen E Greenwald
Publications and source records attributed to Stephen E Greenwald.
Twin-twin transfusion syndrome: the influence of intrauterine laser photocoagulation on arterial distensibility in childhood.
BACKGROUND: In twin-twin transfusion syndrome (TTTS), the donor and recipient fetus are exposed to differing volume loads and show discordant intertwin vascular compliance in childhood despite identical genotype. We hypothesized that discordance is prevented by intrauterine endoscopic laser ablation of placental anastomoses, which abolishes intertwin transfusion. We tested this by examining pulse wave velocity (PWV) in brachial arteries of twin survivors of TTTS treated with and without laser therapy. METHODS AND RESULTS: One hundred children (50 twin pairs, 27 with TTTS) were studied. Group 1 comprised 14 monochorionic (MC) twin pairs with TTTS treated symptomatically; group 2 comprised 13 MC twin pairs with TTTS treated by laser. The control groups comprised 12 MC twin pairs without TTTS (group 3) and 11 dichorionic twin pairs (group 4). Fetal cardiovascular data, predictive factors for, and duration of TTTS and cord blood were collected prospectively. We measured blood pressure and PWV photoplethysmographically at a median corrected postnatal age of 11 months (range, 1 week to 66 months). Both TTTS groups showed marked intertwin PWV discordance, unlike MCDA control subjects. The PWV discordance seen in laser treated twin pairs resembled that of dichorionic control subjects (heavier individual with higher PWV), whereas group 1 showed the opposite (negative) intertwin discordance (ANOVA F (1,45)=4.5, P=0.04). No significant differences in blood pressure or intrauterine growth were observed between TTTS groups. CONCLUSIONS: Vascular programming is evident in monozygotic twins with intertwin transfusion and is altered but not abolished by intrauterine therapy to resemble that seen in dichorionic twins.
Arteries↗
Validation of a device to measure arterial pulse wave velocity by a photoplethysmographic method.
We aimed to validate a new method for measuring arterial pulsewave transit time and pulsewave velocity (a measure of arterial elasticity), based on the principle of photoplethysmography (PPG), and to compare transcutaneous values with those obtained by intra-arterial measurements. Three validation experiments are described. (a) PPG pulse wave delay times (defined as the time interval between the ECG R wave and the foot of the arterial pulse wave measured at the wrist or ankle) were compared to values obtained simultaneously from an established methodology (Doppler ultrasound). (b) Aortic pulsewave delay times in 17 subjects obtained non-invasively by the PPG method were compared with those obtained from the intra-arterial pressure wave. (c) Repeatability measurements of PWV on the same subjects were carried out over two timescales (minutes and hours) in the arm, the leg and the trunk. The Doppler and PPG delay times correlated well, as did intra-arterial and transcutaneous values. Repeatability at short timescales was good (coefficients of variation (CV) < 6% for all measurement sites) and, at the longer timescale, was satisfactory (CVs in the aorta, the arm and leg were 6.3, 13.1 and 16.0, respectively). The PWV values agreed well with others in the literature. We conclude that the PPG technique provides a complement to existing methods for the non-invasive measurement of arterial compliance. Its simplicity and ease of use make it suitable for large-scale epidemiological studies.
Ankle↗
Prolonged calcium transients and myocardial remodelling in early experimental uraemia.
BACKGROUND: Cardiovascular disease is the most common cause of premature death in patients with end-stage renal disease, possibly due to a specific 'uraemic cardiomyopathy'. This study was designed to investigate the cardiac changes induced by a moderate impairment of renal function in a model of uraemia. METHODS: Male Wistar rats (n=11) were rendered uraemic by 5/6 nephrectomy or sham operated (n=11). After 4 weeks, cardiac dimensions were measured from fixed tissue sections using a digital image analysis technique. In parallel groups of animals, cardiac myocytes were isolated and studied for evidence of functional changes attributable to uraemia. After steady-state field stimulation at 0.5 Hz, intracellular Ca(2+) handling (using Fura-2) was investigated. Up to 20 consecutive transients were averaged as the extracellular Ca(2+) was increased. RESULTS: The 5/6 nephrectomy group had a 75% reduction in glomerular filtration rate, and a 2- to 3-fold increase in serum urea and creatinine compared with sham-operated control animals (P<0.0001). However, the blood pressure was found to be similar in each group. Histology of the intact hearts (five pairs) showed a significant increase in tissue cross-sectional area (14%; P<0.04), cross-sectional area of the left ventricle (22%; P<0.04), and a significant increase in left ventricular wall thickness (15%; P<0.03). In the single cardiac cell study, under basal conditions (1-2 mM extra-cellular Ca(2+)) no significant differences in intracellular Ca(2+) were observed, but in high extracellular Ca(2+) the uraemic cells were slower to return to diastolic intracellular Ca(2+) levels (P<0.05). CONCLUSIONS: The data provide evidence of altered myocardial structure and function in early experimental uraemia. The changes described are consistent with concentric hypertrophy of the left ventricle, which occurs in the absence of hypertension.
Animals↗