Search

Weddell seals undergo lung collapse during dives below 50 m depth. In order to explore the physiological mechanisms contributing to restoring lung volume and gas exchange after surfacing, we studied ventilatory parameters in three Weddell seals between dives from an isolated ice hole on McMurdo Sound, Antarctica. Methods Lung volumes and CO2 elimination were investigated using a pneumotachograph, infrared gas analysis, and nitrogen washout. Thoracic circumference was determined with a strain gauge. Exhaled nitric oxide was measured using chemiluminescence. Results Breathing of Weddell seals was characterized by an apneustic pattern with end-inspiratory pauses with functional residual capacity at the end of inspiration. Respiratory flow rate and tidal volume peaked within the first 3 min after surfacing. Lung volume reductions before and increases after diving were approximately 20% of the lung volume at rest. Thoracic circumference changed by less than 2% during diving. The excess CO2 eliminated after dives correlated closely with the duration of the preceding dive. Nitric oxide was not present in the expired gas. Conclusion Our data suggest that most of the changes in lung volume during diving result from compression and decompression of the gas remaining in the respiratory tract. Cranial shifts of the diaphragm and translocation of blood into the thorax rather than a reduction of thoracic circumference appear to compensate for lung collapse. The time to normalise gas exchange after surfacing was mainly determined by the accumulation of CO2 during the dive. These findings underline the remarkable adaptations of the Weddell seal for restoring lung volume and gas exchange after diving.

The airway occlusion pressure, P0.1, is the negative airway pressure generated during the first 100 msec of an occluded inspiration. P0.1 is a parameter for the neuro-muscular activation of the respiratory system, which is an important determinant for the work of breathing. It has been shown to be a good predictor for successful weaning from mechanical ventilation. Standard P0.1 measurement techniques are based on a total occlusion of the inspiration for more than 100 msec. These measurements are technically complex and therefore not useful for clinical purposes. Furthermore, a significant breath-by-breath variability has been shown for P0.1, which is neglected by any single point measurement technique. Therefore, we have developed a continuous on-line measurement for breath-by-breath determination of P0.1 using the Siemens Servo 900C respirator. In triggered mechanical ventilation the delay time between the onset of the patients inspiration and flow delivery from the respirator is more than 100 msec for this respirator. During that time the inspiration is occluded. Therefore, the trigger effort was proposed to be a good estimate of P0.1. Based on this, we calculated P0.1 as followsc airway pressure (Paw) was registered at the endotracheal tube site of the respiratory tubing, digitized and acquired by a personal computer at 100 Hz. The recorder output of the Servo 900C was connected to the same computer, delivering the electronical signal for the inspiratory valve to open when the inspiratory effort has exceeded the trigger threshold, which needs a minimal delay time of 80 msec. Around 20 msec after this signal flow is delivered from the respirator. The computer runs an algorithm, which recognizes this signal and calculates P0.1 (Servo P0.1) as the slope of the pressure drop during this 100 msec. Paw tracings and the calculated P0.1 values were displayed on the computer screen and stored on disk. This method was validated by comparing it to the standard technique, using a Hans-Rudolph valve for inspiratory occlusion and calculating P0.1 from Paw tracings during the occluded inspiration. For validation we used a mechanical lung model which generated P0.1 values ranging between 1.1-10.3 mbar. For a given adjustment of the lung model two standard measurements (standard P0.1) were made and compared to the Servo P0.1. In a total of 21 measurements the mean Servo P0.1 was 4.9\pm 2.9 mbar; the mean standard P0.1 was 4.3\pm 2.5 mbar. The mean difference between Servo P0.1 and standard P0.1 was 0.6\pm 0.6 mbar (range: -0.3-1.8 mbar). The regression equation for linear regression analysis was: Servo {\rm P}0.1 = 1.15 * {\rm standard\ P}0.1-0.05. This correlation was significant (r=0.99, p

A computerized system is described, combining automatic collection of urine in short intervals (minutes) over long periods (days) and recordings of body temperature, MABP, and heart rate in chronically instrumented conscious dogs. During the studies the dogs are housed in metabolic cages. Indwelling catheters and electrical wires are connected to a specially designed swivel and directed out of the cage to the next room. Infusions, blood sampling, and monitoring can be performed from this room without disturbance to the dogs. Three examples of recordings are given. In one of these examples the sodium excretion patterns on 5 consecutive days under continuous saline infusion in one dog is evaluated. Urine was collected every 20 min. Sodium excretion showed cyclic variations. Fourier analysis exhibited 18-h periods and 4- to 8-h periods. The described system renders, e.g., coherent time series analysis possible for a variety of simultaneously recorded physiological variables and may thus acquire considerable importance for integrative physiology.

In 10 conscious, chronically instrumented beagle dogs we studied the effects of four different dietary sodium intakes (mmol Na/kg body wt/day: 14.5 [excess], 7.5 [high], 2.5 [normal], and 0.5 [low] [plus an additional standardized sodium depletion produced by peritoneal dialysis several days before the experiments]) on cardiac baroreflex sensitivity and renal response to an acute saline load. Full sigmoid barocurves were produced by intravenous injection of phenylephrine (2.5 to 20 micrograms/kg) and nitroglycerine (2.5 to 30 micrograms/kg). The gain of this relationship was significantly decreased by both an excess and low sodium intake (8.0 +/- 1.0 and 8.3 +/- 0.8 beats/min/mm Hg, respectively) when compared with the 2.5 and 7.5 (12.1 +/- 1.4 and 16.0 +/- 1.7 beats/min/mm Hg, respectively) mmol Na/kg/day sodium intake. Water and sodium excretion in response to saline infusion were lower in the 0.5 and 14.5 mmol/kg/day sodium intake groups in spite of the higher atrial natriuretic peptide and lower plasma renin activity and plasma aldosterone levels in the latter. Mean arterial blood pressure, heart rate, and central venous pressure increased during saline loading in all groups; hematocrit and plasma protein concentration decreased similarly in all groups. The results suggest that the rapid renal homeostatic response to an acute salt load in animals kept chronically on normal or moderately increased dietary sodium intake is regulated by baroreflex control of the renal homeostatic response. Excess dietary sodium intake attenuates baroreflex sensitivity and delays sodium and water excretion after acute loading.

Increased activity of the renin-angiotensin system may be involved in sodium and water retention during controlled mechanical ventilation (CMV) with positive end-expiratory pressure (PEEP). We therefore evaluated renal, hemodynamic, and hormonal effects of an acute angiotensin-converting enzyme inhibition (ACEI) during PEEP and extracellular volume expansion in five trained chronically tracheotomized dogs. Three protocols were performed: control, 4 h spontaneous breathing with continuous positive mean airway pressure (Paw) of 4 cmH2O (CPAP 4); CMV 20, CPAP for 1st h, CMV with 20 cmH2O Paw for 2 h (2nd and 3rd h), and 1 h of CPAP (4th h); and CMV20-ACEI, ACEI (Ramipril, 2 mg/kg body wt) followed by the same protocol as in CMV 20. During control, sodium excretion (UNaV) and urine volume (V) increased continuously to 56.2 +/- 2.7 (SE) mumol.min-1.kg body wt-1 and 482 +/- 23 microliters.min-1.kg body wt-1, respectively. UNaV and V increased less during PEEP in CMV 20 and CMV 20-ACEI. However, significantly more sodium and water were retained in CMV 20 than in CMV 20-ACEI (2.3 +/- 0.3 vs. 1.0 +/- 0.3 mmol/kg body wt, and 20 +/- 3 vs. 11 +/- 2 ml/kg body wt) because of a decrease of glomerular filtration rate and fractional UNaV in CMV 20. Heart rate did not change in control, CMV 20, or CMV 20-ACEI. Mean arterial pressure increased during control by 13 mmHg, did not change during CMV 20, and was decreased by 7 mmHg in CMV 20-ACEI.(ABSTRACT TRUNCATED AT 250 WORDS)

18 Kalber (Korpergewicht = 100 ± 20 kg) mit einem kunstlichen Totalherzen werden mit einem Bennett MA-1B Respirator beatmet. Unter den primaren pulmonalen Komplikationen wird der Lungenatelektase eine vorrangige Bedeutung beigemessen. Die statische Thorax-Lungen-„Compliance” nimmt deutlich unter der Perfusion mit der Herz-Lungenmaschine und weniger deutlich unter der des kunstlichen Totalherzens ab. Bei einem Atemzugvolumen von 11 ± 3 x 102 ml und einer Atemfrequenz von 10/min kommen Beatmungsdrucke von 20 bis 30 cm H2O zustande. Dabei werden moglichst niedrige Sauerstoffkonzentrationen in der Inspirationsluft angestrebt. Es wird mit feuchtwarmer Luft positiv-endexspiratorischen Drucken von 6-8 cm H2O und SICH beatmet. Diese Beatmungstechnik gewahrleistet auch in kritischen Versuchsphasen eine normale arterielle Sauerstoffsattigung. Bei vier Versuchstieren war eine Spontanatmung unter Sauerstoffinsufflation uber eine Nasensonde bis maximal 100 Std moglich. In Abhangigkeit von der in- und exspiratorischen Beatmungsphase werden Druckschwankungen im kunstlichen Totalherzen sowie in der Arteria pulmonalis und in der Aorta infolge von Anderungen erstens der Lage des kunstlichen Totalherzens und zweitens der Lungengefaskapazitat analysiert.

Measurements were made with radioactive microspheres of the distribution of renal blood flow in conscious dogs during left atrial distension. Urine volume, sodium excretion, mean arterial blood pressure and heart rate increased during the 60 min period of left atrial distension (increase in left atrial pressure by about 1.0 kPa). Total renal blood flow and cardiac output (electromagnetic flowmeters) did not change. The perfusion rates of four renal zones did not change. Striated muscle blood flow (M. psoas) fell markedly. — Stimulation of left atrial receptors in conscious dogs is followed by an increase in renal and skeletal muscle resistance. The diuresis and natriuresis during left atrial distension is not accompanied by a detectable redistribution of renal cortical blood flow.

Chronically instrumented female beagles were maintained in standardized environmental and dietary conditions allowing careful examination of the mechanisms governing sodium homeostasis. The experimental increase in left atrial pressure (obtained by a reversible mitral stenosis) is accompanied by an increase in sodium excretion (atrial natriuresis, AN). AN served as an experimental manoeuvre from which the mechanisms governing sodium homeostasis could be elucidated. The results allow the following conclusions: (1) The 'signals' arising from distension of the left atrium (e.g. expansion of the extracellular fluid volume) appear not to be a necessary prerequisite for the maintenance of sodium homeostasis. (2) The control mechanisms seem to be very sensitive to changes in total body sodium (TBS). A small reduction in TBS abolishes sodium eliminating processes e.g. saline diuresis, osmotic diuresis, AN. (3) It is probable that a natriuretic factor exists for sodium elimination. In summary, total body sodium appears to be controlled by a series of 'redundant' mechanisms which guarantee an appropriate strategy for the comfort and ultimate survival of the organism. At the moment it is impossible to quantitate the contributions made by the various mechanisms in the control of sodium metabolism.

Es wird uber Narkose— und Operationsverlauf sowie eingehend uber die spezielle Operationstechnik bei Versuchen zum Totalherzersatz an Kalbern berichtet.

Nach einem kurzen Uberblick uber die Entwicklung der Blutpumpen in den letzten 15 Jahren werden die in der Berliner Arbeitsgruppe angewendeten Entwicklungsmethoden beschrieben. Sie betreffen die Schaffung einer fur die Implantation gunstigen Ventrikelform, die Stromung in der Blutpumpe und durch die Ventile, die Herstellung der Ventrikel und schlieslich ihre Testung auf dem Prufstand. In einem weiteren Abschnitt werden geloste Probleme und neue Entwicklungsziele behandelt.

Es wird uber die Technik der postoperativen Versorgung der Versuchstiere nach Totalersatz des Herzens berichtet und auf einige allgemeine Versuchsergebnisse eingegangen. In den Jahren 1972–1973 wurden insgesamt 47 Totalherzimplantationen durchgefuhrt, die langste Uberlebenszeit betrug 126 Std. Anhangsweise wird auf die Leberfunktion und die Sauerstoffschuld der Versuchstiere eingegangen.

Modules of surface-modified porous glass capillaries with a hydraulic conductivity of 0.25-0.70 ml min-1 mmHg-1 m-2 were tested for suitability for clinical haemofiltration by ex vivo dog experiments and by in vitro perfusion. The results show that (1) the construction of reusable haemofilters based on porous glass capillaries is possible; (2) operational data of testmodules are comparable with hollow-fiber high-flux haemofilters based on asymmetric cellulose acetate membranes; and (3) blood-surface interaction of porous glass capillaries is characterized by protein deposition which entails very low protein cutoff.

Die Schwierigkeiten von Messungen im Kreislaufsystem fuhrten zur Entwicklung von Mesmethoden, die sich bei pneumatisch betriebenen kunstlichen Blutpumpen anwenden lassen. Durch Messungen auf der Luftseite der Blutpumpen lassen sich Grosen wie der venose Druck, der venose Ruckstrom und das Herzzeitvolumen bestimmen. Die Theorie und die Mesergebnisse werden dargestellt.

An experimental increase in left atrial pressure (eLAP↗) leads to an increase in sodium excretion (UNa $$\dot V$$ ). This ‘atrial natriuresis’ is probably involved in the adjustment of sodium balance, but the mechanism is not well understood. The present studies were undertaken to examine Twenty-three female beagle dogs were kept under controlled environmental conditions. They had chronically implanted instruments (purse string around the mitral annulus, catheter in the left atrium, carotid loop; 5 dogs were adrenalectomized). PRA waselevated by a chronic low sodium intake (LSI). When eLAP↗ was performed (+1.0 kPa), PRA decreased by about 50% within at least 60 min. PRA was chronicallylowered by a high sodium intake (HSI). Even under HSI conditions a decrease of PRA could be demonstrated if eLAP↗ was performed (by about 50%). However both HSI and LSI dogs showed a marked increase in UNa $$\dot V$$ if eLAP↗ was performed. After the removal of the adrenals a decrease in glomerular filtration rate was observed (40% of the control values), but eLAP↗ led to a similar increase in UNa $$\dot V$$ to that found in intact dogs (Δ mean 110%). These results indicate that stretching of the left atrium leads to a reduction of tubular sodium reabsorption in a twofold manner: 1st by reduction of PRA, possibly followed by a reduction in aldosterone secretion and 2nd by activating an adrenal independent mechanism of unknown origin. This could be a direct influence of angiotensin II on the tubular reabsorption of sodium. These results are compatible with the hypothesis that reflexes out of the low pressure system are important for the adjustment of sodium balance independent of changes in mineralocorticoid activity.

The renal clearance of creatinine was measured following orogastric administration in conscious dogs. Values of creatinine clearance were compared with simultaneously determined values of inulin clearance, when urine volume, glomerular filtration rate and volume status were acutely altered by a variety of experimental manoeuvres. At urine volumes greater than 20 microliters X min-1 X kg-1, creatinine clearance was not significantly different from inulin clearance. At low urine volumes there was some evidence of creatinine reabsorption. It is concluded that the bolus creatinine technique provides reliable estimates of glomerular filtration rate and is particularly applicable to long-term studies in conscious dogs.

Publisher Summary This chapter explores that the maintenance of volume and osmotic concentration of the extracellular fluid is one of the essentials of biological life. Water intake and water excretion determine total body water; sodium intake and sodium excretion determine total body sodium. Extracellular water and sodium content are determinants of volume and osmotic concentration of the extracellular fluid. In the presence of many exogenous disturbances, the constancy of the extracel1ular water and sodium content is kept within a certain range by the action of regulation systems. After a reduction of extracellular sodium and water, renal retention of sodium or water or both, as well as the oral intake has to be stimulated; after an excessive intake, rapid elimination of sodium or water or both is stimulated. The chapter focuses on the adjustment of sodium balance after an oral sodium and water load. All results reported in the chapter stem from conscious dogs, which had been kept under standardized conditions and are instrumented chronically.

Die Einstellung und Aufrechterhaltung der Homoostase der Korperflussigkeiten ist eine wesentliche Voraussetzung des hoher entwickelten Lebens.

The control of sodium balance is very complex. Many different factors act together in the regulation of renal sodium excretion. Some investigators suggest that arterial blood pressure has a direct effect on urinary excretion of sodium and water. They report that whenever arterial pressure increases, urinary excretion of sodium and water also increases. This phenomenon is called pressure diuresis and natriuresis. It has been stated that an increase in arterial pressure of about 30% can increase urinary output as much as three-fold or more. Many studies, especially in the isolated, perfused kidney, support this idea. However, it is not clear how important this mechanism is under physiological conditions.

Renal effects of A II, retention of sodium and water, may be mediated by the stimulation of aldosterone secretion and/or by direct effects of A II on the kidneys. An attempt was made to differentiate between these two possibilities.Conscious, female beagle dogs were used. The dogs were kept under standardized conditions (metabolic cage, daily sodium intake 4.5 mmol X kg-1 bw, chronically implanted arterial and venous catheters, i.v. hormone substitution after adrenalectomy by a portable pump). A II was infused i.v. over a period of 60 min after 60 min control. (Rate: 1, 4, 20 or 200 ng X min-1 X kg-1 bw).Mean arterial blood pressure (MABP) increased with 20 and 200 ng A II X min-1 X kg-1 bw by an average of 34 mm Hg and 65 mm Hg resp. before and after adrenalectomy. Before adrenalectomy: sodium and water excretion decreased always at 4 and 20 ng A II X min-1 X kg-1 bw, whereas a rate of 200 ng A II X min-1 X kg-1 bw had different effects on renal sodium and water excretion. After adrenalectomy: sodium and water excretion decreased at 4 ng A II X min-1 X kg-1 bw. Whereas a rate of 20 and 200 ng. -As no marked alterations of the glomerular filtration rate occurred, sodium retention observed was mainly due to tubular effects of A II. Plasma aldosterone concentration increased at 4, 20 and 200 ng A II X min-1 X kg-1 bw in the intact dogs.(ABSTRACT TRUNCATED AT 250 WORDS)

Conscious, chronically instrumented dogs (n=24; left and right atrial catheter, electromagnetic flow probe around the left renal artery, carotid loop) were used in 97 expts. to study mechanisms mediating postprandial (pp) excretion of sodium and water up to at least 180 min after food intake. The dogs were kept under standardized conditions and maintained on ahigh (14.5 mmol Na/kg b.w./day) or alow (0.5 mmol Na/kg b.w./day) sodium intake diet (HSI, LSI) which was given once daily in the morning. In HSI dogs left atrial pressure (LAP) increased from a fasting control value of 0.2 kPa (2 cm H2O) to 0.7 kPa (7 cm H2O) (120–180 min pp), right atrial pressure from 0.0 kPa (0 cm H2O) to 0.3 kPa (3 cm H2O). 25% of the sodium intake were excreted up to 180 min pp. There was a highly significant positive correlation between pp sodium excretion (U Na V) and pp LAP.U Na V was not related to pp increase in renal blood flow (RBF) and glomerular filtration rate (GFR). Fractional sodium excretion increased from a fasting control value of 0.6% to more than 4% in HSI dogs and from 3.3% to more than 7% in anadrenalectomized HSI dog. DOCA did not diminishU NA V in HSI dogs. In LSI dogs, RBF and GFR increased pp, LAP did not change pp. No substantial increase inU Na V was observed. The close correlation between ppU Na V and pp LAP in HSI dogs supports the hypothesis that intrathoracic vascular receptors are involved in the mediation of volume regulation by stimulation of still unknown natriuretic mechanisms which operate on the tubular level in the presence of high mineralocorticoid activity.

The ability to retain sodium was investigated in six conscious dogs before and after surgical renal denervation. Dietary sodium and water intake were kept constant (2.5 mmol Na X kg-1 bw X day-1 and 91 ml water X kg-1 bw X day-1). Balance experiments were performed from 6 days before to 8 days after having produced a sodium deficit of 6.4 +/- 0.4 (intact dogs) and 5.8 +/- 0.2 (renal denervated dogs) mmol Na X kg-1 bw by means of a peritoneal dialysis (PD). Having the same sodium excretion before PD, intact and renal denervated dogs demonstrated a similar striking decrease of sodium excretion and a similar increase of plasma renin activity after PD until the amount of sodium lost had been replenished (4th day after PD). In intact and renal denervated dogs plasma sodium concentration (PNa) decreased and renal water excretion increased on the first day after PD, indicating a homeostatic response to the fall of PNa. After dietary sodium restriction (from 2.5 to 0.5 mmol Na X kg-1 bw X day-1) a similar striking decrease of renal sodium excretion occurred in intact and renal denervated dogs. It therefore is concluded that in conscious dogs the presence of the renal nerves is not essential in order to maintain body sodium homeostasis after an acute sodium loss or after dietary sodium restriction.

The ultimate goals behind the development of highly sophisticated driving systems for implantable artificial blood pumps are not only to generate a quasi-physiologic ventricle pressure, but also to create physiplogic hemodynamics and physiologic responses to altered circulation conditions1. From the technical point of view this means that the driving unit has to activate the blood pumps to induce physiologic circulation conditions. This main requirement supposes an ideal transmission system between drive and circulation and extensive knowledge of physiology.

In order to quantitate the contribution of the antidiuretic hormone (ADH) to the diuresis of left atrial distension 52 experiments have been performed in 12 conscious, chronically instrumented beagle dogs. Left atrial pressure was increased by a reversible mitral stenosis by about 10 cm H2O (1.0 kPa) for 60 min. Plasma ADH concentration (range between 1.3 and 6.0 pg . ml-1) (radioimmunoassay) decreased in every experiment, the average decrease being about 50%. An i.v. infusion of vasopressin (0.05 mU . min-1 . kg-1) abolished the diuretic effect of left atrial distension or decreased the urine volume below control values; natriuresis was not affected. The magnitude of the vasopressin effect was dependent on the concurrent sodium excretion: when sodium excretion was low during left atrial distension, vasopressin was more effective in reducing the urine volume than when sodium excretion was high. It is concluded that the diuresis of left atrial distension is mediated (a) by a suppression of ADH and (b) by factors controlling sodium excretion, the contribution of these two mechanisms being dependent on the concurrent sodium excretion.

With the 3 applied methods one can investigate and obtain most of the interesting aspects of the flow within blood pumps: an integral picture of the flow, the development and position of stagnation flow, the time course of the velocity in points of special interest, the turbulence, and an integral picture of the mean boundary layer flow. The measurements have shown that the flow in the blood pumps is turbulent, the turbulence can be considered harmless, because its intensity is much weaker than that of a valve; there is a correspondence between the hotfilm method and the dye-washout method, and that there is a correspondence between the dye-washout method and the in vivo clot formation. Pumps, which have been designed according to these measurements, have been implanted in a series of calves. The pumps now have a smooth continuous inner surface and usually show no thrombus formation at all (anticoagulants are used) at the postmortem. Some animals do very well, such as the one in Figure 16 during his daily walk of 500 M on the treadmill. The animal is in its 45th day of survival and remains well to date.

Publisher Summary This chapter discusses the role of receptors located in the left atrium of the heart or the pulmonal vascular bed in the short-term adjustment of sodium balance. The left atrium is a suitable place to measure an extracellular volume deficit. The extracellular volume can only be re-expanded if external sodium is available. Osmocontrol overrides volume control. Elevation of left atrial pressure reduces renin secretion by the kidneys. The renin–angiotensin–aldosterone system has two antinatriuretic components: a faster acting one, namely, AII, and a slower acting one, namely, aldosterone. Atrial natriuresis (AN) can be prevented by acute or chronic reduction of total body sodium. The RAS is more responsible for Na-retention than for Na-elimination, and cardiac denervation prevents AN, but does not disturb the postprandial adjustment of sodium balance.

Conscious, chronically instrumented dogs, maintained on a high sodium intake, were used to investigate whether surgical cardiac denervation impairs the natriuresis associated with left atrial pressure increase produced in three ways: during an increase in left atrial pressure by means of a reversible mitral stenosis (protocol 1); after an i.v. saline load (1.0 ml 0.9% saline min-1 . kg-1 over 60 min) (protocol 2); after an oral saline load (14.5 mmol Na . kg-1 given with the food as isotonic solution) (protocol 3). During a reversible mitral stenosis, in intact dogs, urine volume and sodium excretion increased markedly (from 34--145 microliters . min-1 . kg-1 and from 3--12 mumol . min-1 . kg-1); mean arterial pressure increased by an average of 2 kPa (15 mm Hg) and heart rate by 53 b/min; plasma renin activity fell from 0.37--0.21 ng AI . ml-1 . h-1 . Cardiac denervation eliminated these effects of left atrial distension except for a small increase in heart rate (12 b/min). This indicates that the natriuresis and diuresis during left atrial distension resulted from stimulation of receptors located in the left atrium. In contrast, during protocol 2 and 3, the same amounts of sodium and water were excreted in the cardiac denervated dogs as compared to the intact dogs. A comparable decrease in plasma renin activity also was observed. -- Apparently the presence of the cardiac nerves is not a prerequisite for maintenance of sodium and water homeostasis.

An experimental elevation of left atrial pressure (eLAP) by means of a reversible mitral stenosis is accompanied with an increase in sodium excretion (UNaV) and arterial blood pressure (by about 20 mm Hg, 2.7 kPa), and by a decrease in plasma renin activity. It is well established that an increase in renal perfusion pressure (Pren) can augment UNaV. Therefore the present study was undertaken to examine whether the eLAP-induced natriuresis was caused by the increased Pren. -Four female beagle dogs were kept under controlled environmental conditions. They received a sodium rich diet (14.5 mmol/Na/kg/d). The dogs were chronically instrumented: purse string around the mitral annulus, catheter in the left atrium, carotid loop, pneumatic cuff above the renal arteries, pressure transducer below the renal arteries. Pren was kept constant by means of a digital servofeedback control circuit. The dogs served as their own controls (13 experiments without and 15 experiments with a controlled renal perfusion pressure were performed). After eLAP(+1.0 kPa), UNaV rose from 4.1 +/- 2.6 to 10.3 +/- 3.9 mumol Na/min/kg. If Pren was kept constant, the corresponding values were 4.2 +/- 2.8 and 9.3 +/- 2.9 mumol/min/kg. These data clearly indicate that the atrial natriuresis is not mediated by an augmentation of renal perfusion pressure. Therefore these results support the hypothesis that atrial natriuresis probably is due to en eLAP-induced suppression of the renin-angiotensin-system or other natriuretic mechanisms.

Seitdem vermehrt Tiere den Totalersatz des Herzens durch eine inkorporierte Blutpumpe mehr als 20 Stunden uberleben, ergeben sich zwangslaufig vollig neue Untersuchungsbefunde. Uber die da­bei besonders Interessierenden, namlich die der Hamodynamik, soll im folgenden berichtet werden.

Im Rahmen der Entwicklung eines kunstlichen Herzen ist der Einflus der Ventile auf die Blutstromung von Bedeutung. Da eine isolierte Betrachtung der Ventile nur zu Teilkenntnissen fuhrt, werden die Ventile im Zusammenhang mit den Ventrikeln untersucht. Es wurde ein kunstliches Herz mit BJORK-SHILEY Ventilen in beiden Ventilpositionen mit einem anderen verglichen, das mit tierischen Aortenklappen versehen war. Die teilbiologische Losung (1) soll fur den Tierversuch anwendbar sein.

Fur den Totalherzersatz werden nach mannigfaltigen Entwicklungsstufen im Klinikum Westend der FU Berlin zur Zeit doppelkammerige Blutpumpen vom Diaphragmatyp verwendet, die aus dacron-verstarktem Silastik gefertigt sind und Bjork-Shiley-Ventile in Ein- und Auslasposition besitzen.