A textbook of human physiology / translated from [the] 6th German edition by W. Stirling.

  • Landois, Leonard
Date:
1888
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Licence: Public Domain Mark

Credit: A textbook of human physiology / translated from [the] 6th German edition by W. Stirling. Source: Wellcome Collection.

Provider: This material has been provided by Royal College of Physicians, London. The original may be consulted at Royal College of Physicians, London.

    178/980 page 126
    muscular fibres of tlie arteries. This experiment shows that it is the vaso-motor centre which is specially acted upon by the venous blood.] [Traube-Hering Curves.—^The following experiment proves that the varying activity of the vaso-motor centre suffices to produce undulations in the blood- pressure tracing. Take a dog, curarise it, expose both vagi and establish artificial respiration ; then estimate the blood-pressure in the carotid. After section of the vagi, the heart will continue to beat more rapidly, but it will be undisturbed by the cardio-inhibitory centre. Thus the central factor in the causation of the blood- pressure remains constant. Suddenly interrupt the respiration, and, as alread}' stated, the blood-pressure will rise steadily and uniformly, owing to the stimulation of the vaso-motor centre by the venous blood. In this case the perix)heral factor, or state of tension of the small arteries throughout the body, is influenced by the condition of the nerve-centre, which controls their action. After a time, the blood- pressure tracing shows a series of bold curves higher than the original tracing. These can only be due to an alteration in the state of the small arteries, brought about by a condition of rhythmical activity of the vaso-motor centre. These curves were described and figured by Traube, and are called the Traube or Traube- Hering curves. As in other conditions, stimulation causes exhaustion, and soon the venous blood paralyses the vaso-motor centre and the small arteries relax, blood flows freely out of the larger arteries, and the blood-pressure rapidly sinks. Variations in the blood-pressure have been observed after a mechanical pump ha.s been substituted for the heart, i.e.^ after all respiratory movements have been set aside, so that the only factor which would account for the phenomena of the Traube- Hering curves is the variation in the peripheral resistance in the small arteries, determined by the condition of the vaso-motor centre.] Variations.—The respiratory undulations of the blood-pressure become more pronounced the greater tlie force of the respirations, which produce greater variations of the intra-thoracic pressure. In man, the diminution of tlie pressure within the trachea is 1 mm. Hg. during tranquil inspixation ; while during forced respiration, when the respiratory passage is closed, it may be 57 mm. Conversely, during ordinary expiration, the pressure is increased within the trachea 2-3 mm. Hg., while during forced expiration, owing to the compression of the abdominal muscles, it may reach 87 mm. Hg. Other Factors.—The increase of the blood-pressure during inspiration, as well as the fall during expiration, must in part depend upon the pressure within the abdomen. As the dia- phragm descends during inspiration, it presses upon the abdominal contents, including the abdominal vessels, whereby the blood-pressure must be increased. The reverse etiect occurs during expiration {Schiixinhurg). [Section of botli jdirenic nerves and opening of the abdominal cavity cause the respiratory undulations almost entirely to disappear. TIk- respiratory undula- tions, therefore, depend in great part upon the changes of the abdominal pressure and the effect of these changes on the amount of blood in the abdominal vessels. When making a blood- pressure experiment, pressure ui)on the abdomen of the animal with the hand causes the blood- pressure to rise rapidly. ] {g) Variations with each Pulse-Beat.—The mean arterial pressure undergoes a variation with each heart-beat or puhe-heat, causing the so-called pulsatory undulations (fig. 107). The mass of blood forced into the arteries with each ventricular systole causes a positive wave and an increase of the pressure corre- sponding with it, which of course corresponds in its development and in its form with the pulse-curve. In the large arteries Volkmann found the increase during the heart-beat to be = i\ (horse) and yV (<iog) of tlif' total pressure. None of the apjjaratus described in § 84 gives an exact representation of the pulse-curve. They all show simply a rise and fall, a simple curve. The sphygmograph alone gives a true expression of the undulations in the blood-pressure which are due to the heart-beat. (A) Arrest of the Heart's Action.—If the heart's action be arrested or interrupted by continued stimulation of the vagus, or by high positive respiratory pressure, the arterial blood-pressure falls enormously, while it rises in the veins as the blood flows into them from the arteries to equilibrate the difference of pressure in the two
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