HOME       SELECTED ARTICLES  . . .     FEEDBACK     SEARCH

Archives of Surgery, Vol. 92, pp 44-46, January 1966

W. G. FEGAN, M.Ch., F.R.C.S.I.     J. C. MILLIKEN, M.D., F.R.C.S.E., F.R.C.S.I.

D. E. FITZGERALD, M.Sc., L.R.C.P.& S.I.

DUBLIN, IRELAND

This paper is based on data obtained by direct recording of the pressures in the major intra- abdominal veins during respiration with the subject horizontal and erect. This investigation was carried out in an effort to determine whether or not normal respiration produces alterations of intra-abdominal venous pressure which are sufficient to contribute to central flow while the subject is erect.

With the patient under local anaesthetic, catheters of PE200 polyethylene were introduced into the iliac veins or inferior vena cava via the long or short saphenous vein. In a few instances difficulty was experienced in negotiating the saphenofemoral junction and a Seldinger guide was used. During the introduction of the catheters and at various times between recordings, the catheters were flushed with a slow infusion of heparinized saline. The exact levels at which recordings were made were established by injecting 60% sodium diatrizoate (Urografin) through the catheter in each case. The pressures were recorded with a Sanborn pressure transducer connected to a strain gauge amplifier, and the figures obtained in the erect position were corrected for the hydrostatic pressure of the column of saline present between the catheter tip and the transducer.

Ten recordings were made with the patients standing and horizontal. The levels at which the pressures were obtained ranged from the external iliac vein to the inferior vena cava. The detailed data are in Tables 1 and 2.

SCAN TABLES

The pressure recorded at the end of expiration was taken as representing the basic value at any particular level. This was, on an average, 7.5 mm Hg with the subject horizontal and 26.0 mm Hg when erect. Variation of the individual values obtained in the horizontal position was small (range 3 to 10 mm Hg) and was independent of the site of the catheter tip. With the patient in the erect position the basic pressure varied directly with the level of the catheter tip and was found to be 7 mm Hg in the inferior vena cava (one reading), 22 mm Hg in the common iliac vein (three readings), and 31 mm Hg in the external iliac vein (six readings).

Inspiration produced a rise in pressure in all cases. The average values of this rise in the horizontal and erect positions were 6.3 and 8.7 mm Hg, respectively. It is noteworthy that in all but two instances the increase in pressure produced with the subject standing exceeded that produced in the horizontal position although the basic pressure was considerably higher.

Previous investigations of the mechanism by which blood is returned from the lower limb in the erect human have been largely directed to the calf, or soleal, portion of the peripheral venous pump, since it is in this area that the clinical features of venous insufficiency are most frequently seen. The principle of action of the soleal portion has been described in some detail^{1, 2} and has been confirmed by simultaneous measurements of the pressures in the superficial and deep veins.^{3, 4}

So far, comparatively little attention has been focused on the muscular compartments in the foot and the thigh, which form separate but functionally complementary components of the whole peripheral pump system. That each compartment is capable of returning the blood in it, at least to the level of the next compartment above is evident from the fact that venous stasis is not a common feature in amputation stumps. However, the uppermost valves in the return pathway are found in the common femoral or iliac veins,⁵ and the relative importance of the various factors concerned in the return of blood to the heart from the large intra-abdominal veins above the level of those valves has not been determined. Apart from the studies of Pentecost et al⁶ there is little information with regard to the venous return from this region when the subject is erect.

Confusion still exists with regard to the effect of respiration on venous return. Brecher and Mixter⁷ have shown that the reduced intrathoracic pressure associated with inspiration has a definite aspirating effect on the blood in the intrathoracic veins. Eckstein et al⁸ noted an increased flow in the inferior vena cava on diaphragmatic contraction in open-chest dogs. Using a double-lumen catheter in humans, Walker and Pickard⁹ have demonstrated a negative pressure in the inferior vena cava immediately above the diaphragm, with a positive pressure below it, and noted that both of these pressures were augmented on deep respiration. They found that inspiration raised the subdiaphragmatic vena caval pressure by 6 mm Hg in the horizontal position, a figure which closely corresponds to the values obtained in the present investigation.

Consideration of the comparatively minor nature of the contractions of the lower limb muscles which occur in association with the maintenance of balance when the subject is at rest in the upright position suggests that such contractions alone are insufficient to produce the pressure required to overcome the hydrostatic effect of the whole column of blood extending from the heart to the feet.

The rhythmic compression of the deep veins which occurs during exercise is reduced to a minimum. Furthermore, since it has been shown⁹ that the arterial wave pattern disappears almost immediately below the diaphragm, vis a fronte is clearly not a significant factor below this level.

The data presented here show conclusively that respiration is associated with rhythmic and substantial elevations of pressure in the intra-abdominal veins, and that the value of the inspiratory increment is greater when the subject is erect. These findings confirm the action of an abdominal component of the peripheral venous pump, which is responsible, in a manner similar to that of the other components, for the return of blood from the area served by it.

Recordings were made of the intra-abdominal venous pressures and of the effect of respiration on these pressures in humans in the horizontal and erect positions. Inspiration was found to have produced a significant increase in pressure in all cases.

This increase was enhanced on assumption of the erect position, even though a marked increase in the hydrostatic pressure occurred, especially in the iliac veins. These observations clearly demonstrate the existence of an abdominal component of the peripheral venous pump and support the conclusion that the efficiency of its action is greater when the subject is erect.

Furthermore, since the abdominal component is the only part of the peripheral venous pump which continues to act rhythmically while the subject is recumbent it may be that this is a factor in the relatively greater frequency with which thrombosis occurs in the more peripheral deep veins in bedridden patients.

1. Cockett, f. b. - Diagnosis and Surgery of High Pressure Venous Leaks in the Leg, Brit.. Med. J. 2: 1399, 1956.
2. Dodd, H. and Cockett, F. B. - Pathology and Surgery of the Veins of the Lower Limbs, London: E & S. Livingstone, 1956.
3. Hojensgard, I. C. and Sturup, H. - Varicose Veins, Acta Chir. Scand. 49: 133, 1949.
4. Fegan, W. G., FitzGerald, D. E. and Milliken, J. C. - The results of Simultaneous Pressure Recordings from the Superficial and Deep Veins of the Leg, Irish J. Med. Sci. 6: 363, 1964.
5. Ludbrook, J. and Beale, G. - Femoral Venous Valves in Relation to Varicose Veins, Lancet 1: 79, 1962.
6. Pentecost, B. L., Irving, D. W. and Shillingford, J. P. - The Effects of Posture on the Blood Flow in the Inferior Vena Cava, Clin. Sci. 24: 149, 1963.
7. Brecher, G. A.. and Mixter, G., Jr. - Effect of Respiratory Movements on Superior Cava Flow Under Normal and Abnormal Conditions, Amer. J. Physiol. 172: 457, 1953.
8. Eckstein, R. W., Wiggers, C. J. and Graham, G. R. - Phasic Changes in Inferior Cava Flow of Intravascular Origin, Amer. J. Physiol. 148: 740, 1947.
9. Walker, W. F. and Pickard, C. - Respiration and the Inferior Vena Cava, Bull. Int. Soc. Chir. 3: 257, 1962.

HOME       SELECTED ARTICLES  . . .     FEEDBACK     SEARCH