Subcutaneous Interstitial Fluid Research Articles

Subcutaneous interstitial fluid colloid osmotic pressure in dehydrated rats.

We collected interstitial fluid for measurement of colloid osmotic pressure (COPi) of normally hydrated and dehydrated rats with two methods: (1) saline-soaked nylon-wicks implanted in vivo for 1 h; and (2) the crossover method, i.e. titration with wicks pre-loaded with serial dilutions of rat plasma implanted post mortem for 15-20 min. All wicks were implanted in subcutis on the back. Dehydration was induced by injection of 40 mg furosemide followed by 24 h water deprivation. The saline-soaked wick method gave an average control COPi of 10.8 mmHg, 2-3 mmHg lower than the corresponding pressure obtained with the crossover method. This discrepancy between the methods increased to 10-11 mmHg in dehydrated animals, indicating that the saline-soaked wick method underestimates COPi even more during dehydration than during control conditions. The mean COPi of 22.8 mmHg (SD = 3.7, n = 9) obtained in dehydrated rats using the crossover method corresponds well with what is to be expected from the reduction in interstitial fluid volume. The present study suggests that the frequently used implantation period for saline-soaked wicks of 60 min should be prolonged to 90-120 min. It further shows that the rise in COPi is about 3 times more important than the fall in interstitial fluid hydrostatic pressure in restricting mobilization of interstitial fluid during dehydration.

Transcapillary forces of the subcutaneous tissue in patients with coronary artery disease: a comparison between pulsatile and nonpulsatile flow during extracorporeal circulation

The aim of this study was to evaluate subcutaneous transcapillary fluid balance during pulsatile and nonpulsatile extracorporeal circulation (ECC). Changes in the transcapillary fluid balance were studied by measuring subcutaneous interstitial fluid pressure (Pif) using the 'wick in needle' (WIN) method, as well as measuring subcutaneous interstitial fluid colloid osmotic pressure (COPif), using either the wick technique or the blister suction technique. The measurements were performed on the chest wall at the heart level. Simultaneous recordings of plasma colloid osmotic pressure (COPpl) were carried out. Nineteen male patients undergoing aortocoronary bypass grafting were subjected to nonpulsatile flow (group I, n = 11) or pulsatile flow (group II, n = 8) during ECC. Preoperatively there was no difference in the Starling forces between the two groups. During ECC the COP gradient (COPpl-COP if) was reversed to the same extent in the two groups. At three hours and six hours following ECC, COPif in the pulsatile group (12.1 mmHg and 11.4mmHg respectively) was significantly higher than in the nonpulsatile group (10.8mmHg and 10.3mmHg respectively). When weaning from ECC as well as three hours and six hours following ECC, Pif in the pulsatile group was significantly lower than in the nonpulsatile group. Conclusion: in the early postoperative period there is less dilution of the subcutaneous interstitial tissue following application of pulsatile flow during ECC compared to nonpulsatile flow.

Transcapillary colloid osmotic gradient and body fluid volumes in renal failure

The aim was to study the transcapillary fluid balance in dialysis patients during and after ultrafiltration. Plasma and subcutaneous interstitial fluid (wick technique) colloid osmotic pressure, plasma volume (I125-albumin space) and extracellular fluid volume (radiosulfate space) were measured in nine patients on maintenance hemodialysis before (pre-dialysis state) and after (dry-weight state) ultrafiltration. In the pre-dialysis state, interstitial colloid osmotic pressure was reduced compared to normal controls (12.7 +/- 3.5 versus 15.8 +/- 2.7 mmHg, mean values +/- SD) and transcapillary colloid osmotic gradient increased (15.3 +/- 3.0 versus 12.8 +/- 2.7 mmHg). Ultrafiltration resulted in a parallel decrease of plasma volume and interstitial fluid volume of 19 to 20%, and an increase in mean interstitial colloid osmotic pressure of 3.4 mmHg and in mean transcapillary colloid osmotic gradient of 1.9 mmHg. The mean ultrafiltration rate was 21.9 +/- 1.9 ml/min and the plasma refilling rate was 16.5 +/- 2.7 ml/min. It is concluded that the changes in plasma and interstitial fluid colloid osmotic pressure tend to preserve plasma volume and limit the interdialytic increase in interstitial fluid volume.

Colloid osmotic pressures, plasma volume and interstitial fluid volume in patients with heart failure.

In 13 patients with heart failure colloid osmotic pressure in plasma (IIp) and in subcutaneous interstitial fluid from thorax (IIi) (wick technique), plasma volume (PV) and interstitial fluid volume (IFV) were measured and correlated to haemodynamic parameters (cardiac index (CI) and right atrial pressure (RAP]. In seven patients with anasarca measurements of IIp, IIi, PV and IFV were repeated after fluid withdrawal (mean 7786 ml) by ultrafiltration. In the patients, IIi was reduced compared with normal subjects (11.5 +/- 3.4 versus 15.8 +/- 2.7 mmHg, p less than 0.01 (mean +/- SD] and transcapillary colloid osmotic gradient (IIp - IIi) increased (14.6 +/- 2.3 versus 12.8 +/- 2.7 mmHg, p less than 0.05). The IFV in the patients was increased to 137% of values in normal subjects (p less than 0.01) and the ratio PV/IFV significantly reduced. Correlations were found between IIi and CI (r = 0.69, p less than 0.01) and IIi and RAP (r = 0.78, p less than 0.01). Ultrafiltration led to a parallel decrease in PV and IFV and increase in IIp. The results indicate that reduced IIi is an important factor limiting peripheral oedema in heart failure and the reduction is more pronounced in severe heart failure. The reduction of IIi is due to both dilution of interstitial proteins and to reduction of interstitial protein mass by lymphatic wash-out.

Interstitial fluid volume, plasma volume and transcapillary colloid osmotic gradient in patients with hepatic cirrhosis and fluid retention.

Colloid osmotic pressure in plasma (IIp) and in subcutaneous interstitial fluid (IIi) (wick technique), plasma volume (PV) and interstitial fluid volume (IFV) were measured in 12 patients with hepatic cirrhosis and fluid retention. The value of IIp (mean +/- SD) was 21.4 +/- 4.2 mmHg (28.6 +/- 3.4 mmHg in normal subjects (p less than 0.01)), mean IIi was 8.6 +/- 2.2 mmHg (15.8 +/- 2.7 mmHg in normal subjects (p less than 0.01)) and mean transcapillary colloid osmotic gradient (IIp-IIi) was 12.7 +/- 3.8 mmHg compared to 12.8 +/- 2.7 mmHg in normal subjects (p greater than 0.1). Mean PV was increased by 21% compared to normal values (p less than 0.01) and IFV increased by 43% (p less than 0.01). The study demonstrates that reduction in IIp in hepatic cirrhosis is accompanied by a decrease of IIi in subcutaneous tissue resulting in unchanged transcapillary colloid osmotic gradient. The reduction in IIi can partly be explained by simple dilution and partly by a decrease in interstitial protein mass. The wash-down of interstitial proteins in non-splanchnic tissues reduces the tendency to oedema and hypovolaemia.

Protein concentration of lymph and interstitial fluid in the rat tail.

Lymph was collected from tail lymphatics of anesthetized rats, subcutaneous interstitial fluid was obtained by implanting nylon wicks, and tendon interstitial fluid was obtained by centrifugation of pieces of tendon. Spontaneous lymph flow rates averaged 70 nl X min-1 X g skin-1. Protein concentrations and colloid osmotic pressures of sampled fluids differed significantly. Tail lymph had the highest protein concentration relative to plasma [lymph-to-plasma ratio 0.71 +/- 0.03 (SE) n = 10], followed by wick fluid (0.62 +/- 0.02, n = 9), with tendon fluid lowest (0.50 +/- 0.03, n = 10). Albumin and immunoglobulin G (IgG) concentrations in samples of tail skin and tendon were assayed by rocket immunoelectrophoresis. Comparison of their distribution volumes at lymph or tendon fluid concentrations, respectively, with interstitial fluid volumes measured as 2-h 51Cr-ethylenediaminetetraacetic acid space minus 5-min 125I-albumin space indicated that 50-60% of the interstitial volume in these tissues is not available for distribution of albumin or IgG. Low lymph flow and high interstitial protein content of rat tail indicate a slow turnover of interstitial protein. This suggests that interstitial washout of protein plays a role in limiting edema only after a sustained or chronic increase in fluid filtration.

Interstitial fluid volume, plasma volume and colloid osmotic pressure in patients with nephrotic syndrome

Colloid osmotic pressure in plasma (IIp) and in subcutaneous interstitial fluid (IIi) (wick technique), plasma volume (PV) and interstitial fluid volume (IFV) were measured in nephrotic patients (n = 11) and in healthy controls. Six of the patients were treated with ultrafiltration and the parameters were measured before and after withdrawal of mean 7460 ml (total ultrafiltrate in two sessions). In the nephrotic patients mean IIp was 11.6 mmHg and IIi was 3.9 mmHg compared to 28.6 mmHg and 15.8 mmHg, respectively, in healthy controls. PV was in the normal-to-high range and IFV was increased to 150% of the valued in controls. No statistically significant change in PV, IIp or IIi was found after ultrafiltration, and IFV was reduced by 20%. The results indicate that reduction in IIi is an important oedema-preventing factor and that the reduction in interstitial protein mass is more than proportional compared to the degree of hypoproteinaemia. Ultrafiltration in the rate and magnitude we have used, leads to reduction in IFV, but small changes in PV, IIp or IIi.

Transcapillary forces in patients with lower limb ischemia

Starling pressures (interstitial fluid pressure, plasma and interstitial fluid colloid osmotic pressures) were measured in subcutaneous tissue at the ankle in 20 healthy controls and 27 patients with lower limb atherosclerosis. Subcutaneous interstitial fluid pressure (Pif) of the leg was also measured in seven patients with arterial emboli of the lower limb. Interstitial fluid was collected by implantation of nylon wicks and Pif was measured by the 'wick-in-needle', technique. The calculated reabsorption pressure (equal to capillary pressure if no net filtration occurs) was 18.3 mmHg in the group with atherosclerosis, which was higher than in controls (15.8 mmHg, P less than 0.05). Colloid osmotic pressure of interstitial fluid (COPif) was significantly lower in patients with atherosclerosis than in controls (5.9 v. 9.2 mmHg). This finding in itself could make those patients more susceptible to edema formation postoperatively. On the other hand, there was no correlation between COPif and ankle systolic blood pressure within the group of patients. There was a slight, but statistically significant positive correlation between ankle systolic blood pressure and Pif in patients with lower limb atherosclerosis although mean Pif was not different from controls (-1.0 v. -0.8 mmHg). In patients with arterial emboli, however, Pif was lower (mean -4.5 mmHg).

Pressure-volume recordings of human subcutaneous tissue: A study in patients with edema following arterial reconstruction for lower limb atherosclerosis

The interstitial fluid pressure-volume relationship was studied in patients who developed leg edema following arterial reconstruction for femoropopliteal atherosclerosis. The increase in subcutaneous tissue volume of the operated limbs was estimated by surface measurements and computed tomography. The subcutaneous interstitial fluid pressure ( P if) of the legs was recorded by the wick-in-needle technique and averaged −0.7 mm Hg in healthy controls. Postoperatively, P if was −0.8 mm Hg in patients who did not develop local edema compared to +2.2 mm Hg in patients with postoperative edema. if increased with increasing subcutaneous tissue volume in patients with moderate edema (0–100% subcutaneous tissue volume increase), but insignificant further increase in P if was observed with additional edema (100 to 600%). A maximal P if of +5 mm Hg was observed in edematous legs indicating a high compliance of the subcutaneous tissue in patients with postreconstructive leg edema.

Colloid osmotic pressure of human subcutaneous interstitial fluid sampled by nylon wicks: Evaluation of the method

Interstitial fluid was collected from human subcutaneous tissue by implantation of multifilamentous nylon wicks on the side of thorax. The skin was anaesthetized by a small injection of lidocaine. Direct measurement of colloid osmotic pressure in a control group of 20 healthy volunteers gave a mean of 15.8 (SD 2.3) mmHg in wick fluid and 26.9 (SD 4.1) mmHg in serum samples. Standard deviation of the method for wick fluid samples was 1.2 mmHg. Significant blood contamination occurred in less than 20% of the wicks. Fluid content in wicks varied within narrow limits independent of its colloid osmotic pressure. The dynamics of wick fluid protein uptake was studied by uptake of 131I albumin from plasma, and by measurement of colloid osmotic pressure after 30, 60, 120 and 180 min of implantation. The results showed an initial rapid uptake from plasma of a major part of the wick fluid proteins within 30 min. After 120 min wick fluid colloid osmotic pressure reached the same level whether the wicks were 'primed' with serum proteins or not. Altogether these observations support the view that wick fluid reflects interstitial tissue fluid with respect to colloid osmotic pressure when the wicks are implanted for 60 min.

Colloid osmotic pressure of human subcutaneous interstitial fluid sampled by nylon wicks: Evaluation of the method

Colloid osmotic pressure of human subcutaneous interstitial fluid sampled by nylon wicks: Evaluation of the method

Subcutaneous interstitial fluid pressure during external loading.

Interstitial fluid pressure (IFP) distribution generated as a result of externally applied pressure (EAP) may play an important role in the etiology of decubitus ulcers. In the forelimbs of 10 thiopental sodium-anesthetized Yorkshire pigs, weighing 16-20 kg, we placed wick catheters 2-5 mm below the skin. After equilibration, we applied a pediatric cuff and added EAP. With zero EAP, the IFP was -3.9 +/- 1.4 (SD) mmHg. In each case of EAP, IFP as measured with the wick catheter increased and reached a plateau within 10-15 min. In normal tissues, IFP reached approximately 65-75% of EAP. When we created an edematous condition by preinfusing with excess saline, IFP was found to reach 100% of EAP. The total normal stress in the tissue, generated as a result of external cuff pressure, can be considered as a sum of interstitial fluid pressure and extranormal stress. Integrity of the fibrous network and pore fraction may be important in transmitting pressure to the fluid.

Interstitial fluid pressure in rats measured with a modified wick technique

Subcutaneous interstitial fluid pressure ( P i) was measured in anesthetized rats with the “wick-in-needle” technique: A thin hypodermic needle was provided with a 2- to 4-mm-long sidehole and filled with multifilamentous nylon thread. A polyethylene tube, connecting the needle to a pressure transducer, could be compressed by a screw clamp, displacing a volume of about 0.2 μl. Compression caused a marked rise in pressure, but return to control level was obtained within 1 to 5 min. Decompression caused opposite pressure changes, confirming satisfactory fluid communication between needle and tissue fluid. Control P i (measured with saline-filled needle) ranged from −2.5 to +1.0 mm Hg, with mean values of −0.65 mm Hg (SD 0.82, n = 44) on the back and −1.2 mm Hg (SD 0.8, n = 11) on the hindlimb. Similar values were obtained with the needle filled with serum or 1% hyaluronic acid. Severe reduction of femoral arterial pressure reduced hindlimb P i gradually to −3 to −4 mm Hg in the course of 1 to 2 hr. P i was also reduced after 3–7 days of dehydration (−2 to −6 mm Hg) and rose rapidly with rehydration. Edema and a rise of hindlimb P i to positive values were observed when femoral venous pressure was increased from the control level of 3 to 12 mm Hg or more for a period of 24 hr.

Water filtration of the forearm in short- and long-term diabetes mellitus.

Blood flow and capillary filtration coefficient (CFC) were measured by strain-gauge plethysmography on the upper and lower third of the forearm in 9 normal subjects and 29 well regulated patients with diabetes mellitus of varying duration (less than 10 years, 10 to 20 years, and more than 20 years). There was no difference in blood flow in the four groups, but CFC was significantly increased in long-term diabetes (duration above 20 years) when measured at the distal part of the forearm near the wrist. Calculations showed that this was probably due to the relatively high contribution of connective tissue in this part of the forearm. Increased water filtration in connective tissue in long-term diabetics is in accordance with earlier findings of a lowered subcutaneous interstitial fluid albumin concentration in long-term diabetics, this being explained by an increase in net water outflux from the microcirculation.

Effect of Increased Venous Pressure on the Hydrostatic and Colloid Osmotic Pressure in Subcutaneous Interstitial Fluid in Rats: Edema-Preventing Mechanisms

The purpose of the present experiments was to study the effect of a rise in local venous pressure (Pv) on interstitial fluid hydrostatic (Pi) and colloid osmotic pressure (COPi) in rats. The Pv of the hind limb was increased by ligating the iliac veins and the inferior caval vein. Interstitial fluid for protein and COP determination was sampled from subcutaneous tissue of the hind limbs by a wick technique, and the Pi was measured by a modified Scholander technique. When the Pv was increased from 3 to 12 mm Hg, the COPi fell from 9 to 4 mm Hg. The Pi averaged -1 mm Hg under control conditions and was unchanged when the Pv was elevated to 12 mm Hg. No edema was detected. Higher rises in venous pressures resulted in further but less pronounced falls in interstitial fluid COP. Edema developed and the Pi increased to +1 to 2 mm Hg. The results show that the fall in COPi is an important edema-preventing factor during increased venous pressure, whereas a rise in Pi only seems to oppose further increase of an already existing edema.

Effect of increased venous pressure on the hydrostatic and colloid osmotic pressure in subcutaneous interstitial fluid in rats: edema-preventing mechanisms.

The purpose of the present experiments was to study the effect of a rise in local venous pressure pressure (Pv) on interstitial fluid hydrostatic (Pi) and colloid osmotic pressure (COPi) in rats. The Pv of the hind limb was increased by ligating the iliac veins and the inferior caval vein. Interstitial fluid for protein and COP determination was sampled from subcutaneous tissue of the hind limbs by a wick technique, and the Pi was measured by a modified Scholander technique. When the Pv was increased from 3 to 12 mm Hg, the COPi fell from 9 to 4 mm Hg. The Pi averaged -1 mm Hg under control conditions and was unchanged when the Pv was elevated to 12 mm Hg. No edema was detected. Higher rises in venous pressures resulted in further but less pronounced falls in interstitial fluid COP. Edema developed and the Pi increased to +1 to 2mm Hg. The results show that the fall in COPi is an important edema-preventing factor during increased venous pressure, whereas a rise in Pi only seems to oppose further increase of an already existing edema.

Transport of large molecules from plasma to interstitial fluid and lymph in dogs.

Transport of large molecules from plasma to interstitial fluid and lymph in dogs.