PubMed · 9514475
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K Isaaz. 1998-03-01. Pulsed Doppler tissue imaging.. https://pubmed.ncbi.nlm.nih.gov/9514475/
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A previously developed Krogh-type theoretical model was used to estimate capillary density in human skeletal muscle based on published measurements of oxygen consumption, arterial partial pressure of oxygen, and blood flow during maximal exercise. The model assumes that oxygen consumption in maximal exercise is limited by the ability of capillaries to deliver oxygen to tissue and is therefore strongly dependent on capillary density, defined as the number of capillaries per unit cross-sectional area of muscle. Based on an analysis of oxygen transport processes occurring at the microvascular level, the model allows estimation of the minimum number of straight, evenly spaced capillaries required to achieve a given oxygen consumption rate. Estimated capillary density values were determined from measurements of maximal oxygen consumption during knee extensor exercise and during whole body cycling, and they range from 459 to 1,468 capillaries/mm2. Measured capillary densities, obtained with either histochemical staining techniques or electron microscopy on quadriceps muscle biopsies from healthy subjects, are generally lower, ranging from 123 to 515 capillaries/mm2. This discrepancy is partly accounted for by the fact that capillary density decreases with muscle contraction and muscle biopsy samples typically are strongly contracted. The results imply that estimates of maximal oxygen transport rates based on capillary density values obtained from biopsy samples do not fully reflect the oxygen transport capacity of the capillaries in skeletal muscle.
This study used transthoracic echocardiography, including pulsed-wave Doppler, to register coronary flow parameters in 55 healthy neonates. Intraobserver variability was tested in 20 neonates. A Doppler tracing of sufficient quality for analysis was obtained in the left anterior descending coronary artery (LAD) in 53 of 55 studies (96.4% feasibility) and in the right coronary artery (RCA) in 11 of 55 studies (20.0% feasibility). Estimation of intraobserver variability showed coefficients of variation of 7.5-8.0% for diastolic LAD Doppler flow parameters and volume flow but 17.5% for systolic peak flow velocity. Doppler flow parameters were significantly higher in the LAD than in the RCA. Correlation was found between LAD Doppler flow parameters and age, left ventricular (LV) mass, mitral peak early wave velocity as a measure of diastolic LV function, and the aortic velocity time integral/minute as a measure of systolic LV function. This study shows that diastolic LAD Doppler flow parameters and flow volume can be obtained in neonates by transthoracic echocardiography with acceptable reproducibility. In healthy neonates, left coronary flow parameters are linearly related to age, LV mass, and LV systolic and diastolic function. RCA flow parameters in neonates are lower than in the LAD.
BACKGROUND: The distal splenorenal anastomosis (Warren's operation) has been indicated for the treatment of high digestive bleeding caused by esophagic varices because it would ideally reduce the venous pressure in the cardiotuberositary territory without changing the mesenteric-portal venous flow. However, the changes it produce in the splenic territory have not been fully understood. AIM: To appraise the late morphologic and hemodynamic changes in the splenic territory produced by the distal splenorenal anastomosis in patients with portal hypertension due to mansoni's hepatosplenic schistosomiasis complicated by esophagic bleeding. METHOD: Ultrasonography-Doppler study of the splenic region of 52 patients with portal hypertension due to mansoni's schistosomiasis and previous bleeding by esophagic varices. They were divided in two groups: 40 non operated upon and 12 with a distal splenorerenal anastomosis. The following parameters and indices were compared between the two groups: a) morphometric parameters (splenic artery and vein's diameter, splenic diameters (longitudinal, transversal and antero-posterior); b) velocimetric parameters of the splenic vessels (systolic peak velocity in the splenic artery, mean flow velocity in the splenic vein; c) biometric index of the spleen (longitudinal x transversal); volumetric index of the spleen (longitudinal x transversal x antero-posterior x 0,523); hemodynamic indices of the splenic artery's impedance: pulsatility and resistivity. RESULTS: The patients with distal splenorenal anastomosis showed: a) reduction in splenic indices: volumetric (non operated 903,83 +/- 452, 77 cm / distal splenorenal anastomosis 482,32 +/- 208,02 cm (46,64%)) and biometric (non operated 138,14 +/- 51,89 cm /distal splenorenal anastomosis 94,83 +/- 39,83 cm (33,35%)); b) no change: splenic artery's diameter (non operated 0,57 +/- 0,16 cm/distal splenorenal anastomosis 0,57 +/- 0,23 cm); velocity in the splenic artery non operated 107 +/- 42,02 cm/seg/distal splenorenal anastomosis 89,81 +/- 41,20 cm/seg), resistivity (non operated 0,58 +/- 0,008/distal splenorenal anastomosis 0,56 +/- 0,06) and pulsatility (non operated 0,91 +/- 0,19/distal splenorenal anastomosis 0,86 +/- 0,15, splenic vein (non operated 1,10 +/- 0,30 cm/distal splenorenal anastomosis 1,19 +/- 0,29 cm); c) increase: mean flow velocity in the splenic vein (non operated 20,54 +/- 8,45 cm/seg/distal splenorenal anastomosis 27,83 +/- 9,29 cm/seg). CONCLUSIONS: The comparison of the ultrasonography Doppler results of the two groups of patient (non operated and distal splenorenal anastomosis) showed that in patients with distal splenorenal anastomosis there was a decrease of the volume of spleen; increase in the mean flow velocity in the splenic vein; no changes in the morphologic and hemodinamyc parameters of the splenic artery neither in its velocimetric indices.