Pflügers Archiv : European journal of physiology
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Guyton's theory on venous return, implying a linear relationship between blood flow and central venous pressure, was tested in an intact circulation after thoracotomy and airtight chest closure. In eleven Yorkshire pigs (approx. 10 kg) we measured flow in the pulmonary artery and aorta and pressure in the central veins and aorta during pentobarbital anesthesia and mechanical ventilation. To change central venous pressure different lung volumes were randomly applied at intervals of 5 min in a series of inspiratory hold procedures of 7.2 s. ⋯ After a delay of 2-4 heart beats also a decrease in left ventricular output and aortic pressure occurred. Subsequently, the lower venous return during inspiratory hold was mainly sustained by the lower aortic pressure, but nevertheless fulfilled the linear relationship mentioned above. For analysis of flow and pressure changes in the systemic circulation during changes of central venous pressure a tube of constant flow resistance was used as a conceptual mode.(ABSTRACT TRUNCATED AT 250 WORDS)
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The arterial (a), mixed venous (v), and arterial-mixed venous differences (A-V) of hydrogen ion concentration ([H+]), PCO2, HCO-3 and base excess (BE) were measured during 3 h in control (C), water-depleted (WD) and water- and salt-depleted (WSD) dogs. In WD animals the difference in hydrogen ion concentration between venous and arterial blood increased because the [H+] increased more in venous than in arterial blood. In WSD animals (A-V) [H+] remained unchanged since both [H+]a and [H+]v increases were parallel. [H+] variations seem to represent the changes in fixed-acid concentration of blood. ⋯ It therefore might be that PvCO2 increase is a direct consequence of hemodynamic impairment. In WD and WSD, BE decreased progressively in both arterial and mixed venous samples. BEa values were lower than BEv values after the experiment began. (A-V) BE decreased in an exponential manner in both experimental groups; this change could be ascribed to the increased level of deoxygenated hemoglobin in mixed venous blood, thus giving rise to a decrease in fixed acid concentration.
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With a newly developed quadrupole mass spectrometer several blood gas partial pressures are recorded simultaneously and continuously. In the mass filter the separation of the ions to be detected takes place in a hyperbolic electric field with variable direct and alternating voltages with a constant frequency of 2.4 MHz. For blood gas analysis a fully relaxed experimental animal was artifically ventilated and provided with arterial and venous catheters. ⋯ The distance from the measuring tip to the mass spectrometer was 150 cm. Experiments with blood, in vivo equilibrated with gas mixtures, showed good reproducibility; the mean error of the helium partial pressure, for example, was less than 4%. During respiration using a gas mixture with 40% argon, the time constant t63% was found to be 55 s for the whole experimental arrangement including the experimental animal.
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In three awake dogs in a hypobaric chamber at 140 m and at 3550 m, resting ventilation, pulmonary gas exchanges, respiratory gases and pH of the arterial blood, acid-base status in the cerebrospinal fluid (csf), and ventilatory responses to transient O2-inhalation were studied before (intact) and after chronic bilateral carotid body denervation (cbd). 1. The hypoxic chemoreflex drive of ventilation was reduced by about half in cbd dogs. 2. At low altitude, sino-carotid body denervation resulted in hypoventilation and respiratory acidosis in the arterial blood and csf. 3. ⋯ Neither in intact nor in cbd dogs, the ventilatory changes at altitude were related to the changes in csf pH. It is concluded that the rate of ventilatory acclimatization to altitude is dependent upon the strength of the arterial chemoreceptor drive. Integrity of this chemoreflex drive of breathing is essential in determining the eupneic level of ventilation and normal acid-base status of the blood and csf at low altitude and at high altitude.
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In order to clarify the genesis of the human pressure and flow pulse contours of the distal leg arteries, in particular the posterior tibial artery, pulse recordings were performed with transcutaneous techniques under normal conditions and in the state of strong vasodilatation (reactive hyperaemia) in the distal parts of the lower legs. From the experimental results it is concluded that the contour of the incident pressure wave arriving in the leg arteries is very similar to the pressure pulse contour of the abdominal aorta, while the resulting contour in the leg arteries is determined by this incident wave and superimposed reflected waves. The latter arise from positive reflection in the periphery of the lower legs. ⋯ By considering this wave travel, the genesis of the characteristic contours of the pressure and flow pulses of the lower leg arteries is explained in a satisfactory way. This is demonstrated by a simplified graphical pulse construction as well as by the calculation of pulse contours on the basis of a theoretical tube model of the arterial system with the aid of a digital computer. The results of these calculations are discussed with respect to the findings of previous investigators who used analog and digital models of the arterial system.