Capps and Mathews1 have made a careful study of the subject of venous pressure and have correlated the available experimental and clinical data in substantiation of the value of further studies in venous pressure.

Mall in 1892 demonstrated that the portal vein is controlled by constrictor fibers from the splanchnic nerves, and considerable proof has been offered by Roy and Sherrington to show that the systemic veins also are supplied by vasomotor nerves. Other valuable contributions to our knowledge of venous pressure have been made by Frey, von Basch," Bayliss and Starling, and Sewall."

6

On the clinical side, investigations are meager as yet. Calvert called attention to the value of a rising venous pressure as a danger signal in pleural effusions. Hooker and Eyster' carried out a series of observations on venous pressure changes in various diseases of the heart without conclusive results.

That the veins, like the arteries, have the power to maintain their blood-pressure within wide limits was emphasized by Moritz and Tabora 10 who found that it was necessary to withdraw over 500 c.c. of blood by venesection in a human being, before any appreciable fall in the venous pressure occurred.

1 J. A. Capps and S. A. Mathews, Jour. A. M. A., Aug. 9, 1913, vol. lxi, No. 6, p. 388.

2 Arch. f. Physiol., 1892, p. 409.

Jour. Physiol., 1890, xi, 85.

• Deutsch. Arch. f. klin. Med., 1902, Ixxiii, 511.

Wien. med. Presse, 1904, xx, 962.

Jour. Physiol., 1894, xvi, 159.

Henry Sewall, Jour. A. M. A., Oct. 20, 1906, p. 1279.

Bull. Johns Hopkins Hos., February, 1908.

Bull. Johns Hopkins Hos., 1908, p. 274.

10 Verhandl. d. Ver. d. inn. Med. Berlin, 1909, p. 379.

Yandell Henderson1 has advanced the plausible hypothesis that the function of the venopressor (constricting) mechanism is essential to maintain an optimum feeding pressure to the heart. This theory is further substantiated by the newer researches of Hooker2 on venous bloodpressure in man. He finds that normal venous pressure is independent of the ordinary changes in peripheral arterial resistance and that the capacity of the veins may vary without affecting the internal pressure.

Factors Influencing Venous Pressure.-Effect of Posture on Venous Pressure.-Change of posture from the erect to the horizontal causes a fall in venous pressure, while change of posture from the horizontal to the erect causes a rise in venous pressure. In the extensive researches of Barach and Marks3 these changes uniformly occurred. The position of the part in relation to the heart is an important, if not the most important factor determining venous pressure in the normal person. Although we find that the veins of the feet do not exhibit the degree of pressure as compared with the arm, that would be expected if calculated on the basis of position (von Recklinghausen).

Exercise either local or general causes a slight rise (to about twice the normal pressure); the same may result from sudden change in external temperature. Actual arterial pressure does not affect the venous pressure nearly as much as does general cardiac decompensation and failure of the right heart. The smaller capillaries are probably more dependent for their changes, upon venous pressure than upon arterial pressure.

1 Henderson and Barringer, Am. Jour. Physiol., 1913, xxxi, 352.

1 Amer. Jour. Physiol., 1914, xxxii.

Arch. Int. Med., May 15, 1913, No. 5.

Respiratory Variation.-There is a respiratory variation occurring in the external jugular amounting to from 3 to 4 cm. of water.

Defective cardiac action, particularly that of the right heart results in venous stasis which is accompanied by a rise in venous pressure.

Myocardial degeneration is accompanied by a marked rise in venous pressure which may exceed 25 cm. of water at the cardiac level.

Intravenous Injection.-This procedure causes a temporary increase in venous pressure which, in proportion, affects venous more than it does arterial pressure.

External Compression.-Anything which generally compresses the veins in any unit of the body, as an extremity or the abdomen, will increase venous pressure. This fact is important in connection with the care of chronic cardiac decompensation and this knowledge may be employed to prevent syncope after tapping.

Diurnal Rhythm.-According to Hooker1 the venous pressure in man exhibits a diurnal rhythm, rising throughout the day from 10 to 20 cm. of water and falling again during the night. Thus his average figures are by day 15 cm. of water, at night during sleep 7 to 8.

Relation of Pulse Pressure to Venous Pressure.―The tendency for both pulse pressure and venous pressure is to increase simultaneously in cardiac cases, irrespective of the lesion.

The Normal Venous Pressure.-As may be expected from the preceding and from the marked influences of gravity, posture and other ever-present factors, there are as yet no

1 Am. Jour. Physiol., 1913, xxxii, 356.

very narrow limits which may be considered as determining normal venous pressures. That the figures given below are clinically satisfactory is shown by the work of Hooker and Eyster1 who studed venous pressure in the facial vein and the external jugular in dogs taking simultaneous observations by the direct method of placing a canula in the facial vein and studying the external jugular by the indirect method and by comparison, obtained variations rarely exceeding one (1) cm. of water.

Clinical Importance of Venous Pressure. From our present knowledge of the physiology of the circulation and of its pathologic change in cardiac decompensation, there is little doubt that the venous pressure plays an important part in the proper filling of the heart chambers and that a normal venous pressure at the level of the heart is essential to a normal cardiac output. This is shown to be true at least in part by the fact that pulse pressure and venous pressure vary simultaneously in health (see above), also by the evident over-distention of the veins in cardiac decompensation from whatever cause, and the marked, and sometimes spectacular, relief afforded by appropriate and timely

1 Loc. cit.

venesection. These facts all indicate that venous pressure, when high, is at least one factor which interferes with the normal action of the auricle, rendering it, for the time, powerless to functionate properly until relieved by a vigorous reduction in venous pressure. In this connection, Bishop has pointed out that in determining the seriousness of arterial hypotension, the chief factor is the approximation of venous and arterial pressure, and that a low pressure need not necessarily be serious, per se, unless the venous pressure is abnormally high, and further that it is this altered relation between the normal venous and arterial pressures that determines the seriousness of general venous congestion.

Concerning pulmonary venous pressure, we have no method of clinical value by which the degree and changes in pulmonary venous pressure may be determined. Clinical phenomena, particularly the wetness or dryness of the lungs in cardiac cases will determine this.

Effects of Drugs on Venous Tension.-A carefully planned and rigidly checked series of experiments by Capps and Mathews1 are worthy of consideration as they comprise almost our sole accurate data. They employed the method of Moritz and Tabora (see page 146). The summary of their results is as follows:

Digitalis Group.-Digitalis 130 to 120 gr., digipuratum 1 c.c., strophanthin 120 to 60 gr., all used intravenously. No effect on venous pressure.

Epinephrin.-1.2 to 10 min. 1-1000 sol. diluted in 20 c.c. salt solution. Small doses no effect, large doses rise in venous pressure from 10 to 80 mm. H2O.

1 Loc. cit.