How to feel the pulse and what to feel in it : practical hints for beginners / by William Ewart.

Date:
1892
Catalogue details

Licence: Public Domain Mark

Credit: How to feel the pulse and what to feel in it : practical hints for beginners / by William Ewart. Source: Wellcome Collection.

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

    59/136 (page 39)
    The Mean Arterial Pressure.—The Pulse-curves and the Respiratory Undulations of Blood-pressure. Assuming for a moment that the resistance is steady, the recurring systoles of the heart will cause rhythmic variations of the pressure. These arc termed the “pulse- curves.” Inasmuch as the rise and the fall which they occasion are small, these oscillations do not greatly affect the main level of pressure; and we are able to speak of ’ the mean arterial pressure as being steady. The same is true of the rather larger oscillations due to respiration, known as “ respiratory undulations.” As soon, however, as the pcriphercd resistance is altered, whether in plus or in minus, the mean pressure suffers alteration also; and the circulation as a whole requires re-adjustment. This is brought about in various ways, but chiefly by a modification of the strength of the ventricular systole, and of its frequency. Amount of the Intra-arterial and Intra-ventricular Pressures. Measured by the height to which the blood in the artery can lift a column of mercury placed in com- munication with it, the blood-pressure in the Brachial Artery {of man) is 120 mm. In the warm-blooded animals the blood-pressure varies (according to the size of each) between 90 mm. and upwards of 200 mm. The blood-pressure within the human aorta has been estimated at 68 oz., or 4 lb. 4 oz. (in the horse it is 11 lb. 9 oz.). In the human pulmonary artery, if we were to adopt as correct the generally received statement that the right ventricular wall is one-third thinner than the left, it would be about one-third less. But according to Michael Foster (book i. chap. iv.