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  • 1
    Electronic Resource
    Electronic Resource
    Systolic coronary flow reduction in the canine heart in situ: Effects of left ventricular pressure and elastance (1996)
    Springer
    Basic research in cardiology 91 (1996), S. 468-478 
    Details
    ISSN: 1435-1803
    Keywords: LV pressure ; LV elastance ; end-systolic pressure-volume relation ; dobutamine ; systolic coronary flow
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract In the externally perfused coronary bed of the isolated heart, LV elastance (Elv) rather than LV pressure (Plv) appears to be the major factor responsible for systolic coronary flow reduction, although effects of both have been demonstrated. However, normal perfusion in the presence of intact autoregulation in the heart in situ may modify these effects. To investigate the systolic coronary flow (Qsyst) responses to changes in end-systolic Elv and in systolic Plv in the intact coronary bed, we studied 7 anesthetized dogs. Dogs were vagotomized, paced and instrumented with Doppler flow probes. Elv, obtained from micromanometer- and conductance-catheters, was changed by dobutamine infusion (10μg/kg/min) and characterized by its slope (Ees) and volume position at 15 kPa (V15). Plv was changed stepwise by volume loading. Correction for metabolism induced changes in Qmean was made. Thus, we found that dobutamine increased Ees by 44% (p〈0.0001), decreased V15 by 43% (p〈0.0001), and reduced corrected Qsyst significantly (p〈0.001) from 22.8 to 13.8 ml/min, while Plv (9.5–19.5 kPa) did not affect corrected Qsyst (p〉0.5). We conclude that systolic coronary flow reduction is related to both elastance parameters, Ees and V15, and not to Plv in the normally perfused canine heart in situ.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00788728
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  • 2
    Electronic Resource
    Electronic Resource
    The effect of variations in airflow pattern on gas exchange. A theoretical study
    Amsterdam : Elsevier
    Respiration Physiology 25 (1975), S. 217-234 
    Details
    ISSN: 0034-5687
    Keywords: Airflow pattern ; Alveolar-capillary gas exchange ; Breathing pattern ; Homogeneous lung
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Medicine
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0034-5687(75)90098-5
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  • 3
    Electronic Resource
    Electronic Resource
    Cerebral blood flow velocity pattern in healthy and asphyxiated newborns: a controlled study (1987)
    Springer
    European journal of pediatrics 146 (1987), S. 461-467 
    Details
    ISSN: 1432-1076
    Keywords: Perinatal asphyxia ; Cerebral blood flow velocity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract In a controlled study serial determinations of cerebral blood flow velocity using Doppler ultrasound and repeated real-time ultrasonographic- or computerized axial tomographic studies of the brain were performed in 17 (nearly) full-term newborns who experienced perinatal asphyxia and in 17 healthy matched controls during the first week of life. A higher cerebral blood flow velocity was found during the first 4 days of life, indicating a lower cerebrovascular resistance in the asphyxiated infants compared to the control infants. These haemodynamic changes coincided with cerebral oedema and neurological abnormalities. It is speculated that the changes in the cerebral circulation in asphyxiated infants are at least partly caused by cerebral oedema-induced increase of intracranial pressure due to severe perinatal asphyxia. Serial Doppler ultrasound investigations of the brain may be a useful non-invasive method for early detection and follow-up of the consequences of severe perinatal asphyxia.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00441595
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  • 4
    Electronic Resource
    Electronic Resource
    The effect of sarcoplasmic reticulum blockade on the force/frequency relationship and systolic contraction patterns in the newborn pig heart (1997)
    Springer
    Pflügers Archiv 435 (1997), S. 130-136 
    Details
    ISSN: 1432-2013
    Keywords: Key words Contractility ; Left ventricle ; End-systolic pressure-volume relationship ; Conductance catheter ; Neonate ; Experimental ; Sarcoplasmic reticulum ; Ryanodine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  We investigated the relationship between heart rate and contractility in seven anaesthetized young piglets by measuring contractility at different atrial pacing rates. To study the origin of this relationship we repeated the measurements after blocking the sarcoplasmic reticulum calcium release channel with ryanodine. We assessed contractility using indices derived from instantaneous left ventricular pressure and volume measured by micromanometric and conductance catheters during rapid inferior vena cava occlusion, thus generating the end-systolic pressure-volume relationship, which was characterized by its slope E es, and the maximum rate of change of ventricular pressure (dP/dt max)/end-diastolic volume relationship, also charaterized by its slope. All animals showed an increase in contractility with increasing heart rate (intact force/frequency relationship) which was abolished after ryanodine. The most striking effect of ryanodine on baseline haemodynamics was the dramatic decrease of dP/dt max to about 50% of its original value, while peak developed pressure and E es did not change. We conclude that the young piglet, despite its immaturity, has a functional sarcoplasmic reticulum, illustrated by an intact force/frequency relationship. In addition, blockade of the sarcoplasmic reticulum in vivo has profoundly different effects during early and late systole, indicating that indices of contractility derived during different parts of the cardiac cycle represent different aspects of systole.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004240050492
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  • 5
    Electronic Resource
    Electronic Resource
    Effect of coronary occlusion and reperfusion on local electrical resistivity of myocardium in dogs (1993)
    Springer
    Basic research in cardiology 88 (1993), S. 167-178 
    Details
    ISSN: 1435-1803
    Keywords: Myocardial electrical resistivity ; electrical anisotropy ; LAD occlusion ; reperfusion ; four electrode technique
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The effect of coronary occlusion and reperfusion on myocardial electrical resistivity was studied in nine anesthetized open-chest dogs. Anisotropic resistivity was measured on the anterior free wall of the left ventricle (LV) before (control) and during transient occlusion of the left anterior descending (LAD) coronary artery, and during reperfusion. To measure local resistivity longitudinal (RL) and transverse (RT) to epicardial muscle fiber direction, a sensor was developed based on the four electrode (FE) technique with an electrode distance of 1 mm. Previous calculations showed that measurements with this system were confined to a 2-mm-thick epicardial layer. Control values for RL and RT were 243±32Ω·cm and 358±45Δ·cm (mean±SD, n=9) respectively. During a 2-min LAD occlusion, RL increased gradually by 12.4% (p〈0.05) and RT by 7.8% (p〈0.05) above the preceding control values. During a 5-min reperfusion period resistivities returned towards control values, but tended to remain elevated. RL showed a slight initial further increase during the first min of reperfusion and remained significantly above control values during 3 min of reperfusion. RT returned to values not significantly different from control after about 1 min of reperfusion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00798265
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  • 6
    Electronic Resource
    Electronic Resource
    Dependence of anisotropic myocardial electrical resistivity on cardiac phase and excitation frequency (1994)
    Springer
    Basic research in cardiology 89 (1994), S. 411-426 
    Details
    ISSN: 1435-1803
    Keywords: Myocardial electrical anisotropy ; cardiac phase-excitation frequency ; epicardial sensor ; myocardial blood volume
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Knowledge of myocardial electrical resistivity is of interest because passive electrical properties govern the electrotonic spread of current through the myocardium and influence the shape and velocity of the excitation wave. In addition, measurements of myocardial resistivity may provide information about tissue structure and components. The aim of the present study was to determine the excitation frequency dependence and the changes during the cardiac cycle of anisotropic myocardial electrical resistivity. Longitudinal and transverse myocardial resistivity were measured using an epicardial sensor in four open-chest dogs with excitation frequencies in the range of 5–60 kHz. Mean longitudinal resistivity gradually decreased from 313±49 Ω·cm at 5 kHz to 212±32 Ω·cm at 60 kHz, transverse resistivity decreased from 487±49 to 378±53 Ω·cm. To analyze the phasic changes, we compared mean resistivity (averaged over the full cardiac cycle) with resistivity during four cardiac phases: pre-ejection, ejection, early diastole and late diastole. Longitudinal resistivity was significantly higher during the ejection phase (+9.6±4.1 Ω·cm) and lower during late diastole (−6.9±2.9 Ω·cm). Transverse resistivity was significantly higher during late diastole (+4.0±2.3 Ω·m). The values during the other cardiac phases were not significantly different from mean resistivity. The phasic changes in longitudinal and transverse resistivity during the cardiac cycle were independent of the excitation frequency. We speculate that these changes are related to geometrical changes, especially to changes in myocardial blood volume.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00788279
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  • 7
    Electronic Resource
    Electronic Resource
    Pretreatment with allopurinol in cardiac hypoxic-ischemic reperfusion injury in newborn lambs exerts its beneficial effect through afterload reduction (1999)
    Springer
    Basic research in cardiology 94 (1999), S. 23-30 
    Details
    ISSN: 1435-1803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The aim of this study was to determine whether allopurinol (ALLO) reduces reperfusion injury inflicted upon the heart resulting from excess production of free oxygen radicals after hypoxia and ischemia (HI) in newborn animals. We, therefore, produced severe HI in 13 newborn lambs by low O2-ventilation and blood volume reduction. One hour before HI seven lambs received ALLO (20 mg/kg i.v.), six received a placebo (CONT). Cardiac function and hemodynamic parameters were assessed by sequential measurement of left ventricular (LV) contractility through the end-systolic pressure-volume relation (ESPVR) using the conductance catheter method. Stroke volume (SV), cardiac output (CO), and aortic pressure (Pao) were measured and ejection fraction and total peripheral resistance (TPR) were calculated before HI, upon resuscitation (UR), and at 60 and 120 min post-HI. To estimate the effect of ALLO on redox status and anti-oxidative capacity, we measured concentrations of uric acid, sulfhydryl (SH), malondialdehyde (MDA), ascorbic acid (AA), and dehydroxylated ascorbic acid (DHAA) in plasma obtained from the coronary sinus and calculated the AA/DHAA ratio. Compared to CONT lambs, TPR in ALLO treated lambs decreased significantly, accompanied by a rise in CO and SV. ALLO did not affect myocardial contractility, because the ESPVR showed no significant differences between groups. AA/DHAA and SH showed a significant decrease in ALLO animals vs pre-HI, but not in CONT animals. Uric acid was significantly decreased in ALLO as compared to pre-HI and CONT animals. MDA was significantly increased in CONT animals at 15 min post-HI as compared to pre-HI, whereas in ALLO animals MDA showed a significant increase at 120 min post-HI vs CONT. We conclude that pretreatment with ALLO has a beneficial effect on the pump function by afterload reduction but not by changes in contractility. Furthermore, ALLO inhibited uric acid formation with a consequent decrease in anti-oxidative capacity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003950050123
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