Pressure Resistance And Flow In Peripheral Lymphatics

There are considerable variations in the intralymphatic pressures which have been reported, apparently due to differences in methodology. The pressures in the pre-nodal lymphatics depend on the intrinsic contractility of lymphangion and active or passive movements of neighboring muscles (Table 1). Unlike the venous system, hydrostatic pressures are not important in affecting peripheral lymphatic pressures. The pressure in the collecting lymphatics of the leg ranges between 0 and 5 mmHg during the diastolic phase of the lymphangions, whether the leg is erect or supine. During the systolic phase, the mean pressure can reach 50 mmHg and increase to over 100 mmHg if there is any obstruction [10,11].

The resistance to lymph flow in the large lymphatic trunks such as the thoracic duct is low (0.13-0.99 mmHg min/mL in dogs). Resistance in lymph nodes appears to be 50-200 times higher than lymph trunk resistance. Lymph node resistance is reduced by increased inflow pressure and perfusion. Increased pressure in the veins draining a lymph node increases the lymph node resistance to lymph flow.

Table 1 Pressure (mmHg) in Peripheral Lymph Vessels

Resting

During intrinsic

During muscle

Species

Site

pressure

contractions

movement

Man

Leg

0-3

25-50

No direct effect

Foot

8-16

?

?

Dog

Femoral

1-6.5

?

4-33

Guinea pig

Mesenteric

3-15

12-30

Postnodal lymph flow in the human thoracic duct is approximately 1-3 L/ day. The liver contributes 30-50% of this total volume, mainly because the basement membrane of the hepatic capillaries is fenestrated. Intestinal lymph flow is the second greatest contributor to total thoracic duct flow, and this increases with meals. The limbs contribute less than 10% of total lymph flow, their contribution being largely dependent on active and passive movements of the limbs.

There is a marked diurnal variation in lymph output in man [8,9]. During the night, lymph flow is low and the concentrations of protein and enzymes in the lymph are high. Lymph flow can be increased by 83% during muscle contraction seen with ergometer cycling, and by 117% by immersion in a warm-water foot bath [8]. There is an inverse relationship between lymph flow rate and lymph protein concentration. Venous stasis can decrease lymph flow by approximately 50%.

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