Distribution of Extracellular Fluid in Legs with Venous Edema and Lymphedema

Abstract

Background:

This study aimed to determine the specific fluid distribution pattern in legs with lymphedema (LE) in comparison to normal legs and legs with venous edema (VE) using bioelectrical impedance analysis (BIA).

Methods and Results:

BIA was performed in 47 patients with lymphedema (LE; 63 legs), 33 patients with venous edema (VE; 60 legs), and 33 normal subjects (N; 66 legs). The ratio of intracellular fluid (ICF) resistance (R_i) to extracellular fluid (ECF) resistance (R_e) of a whole leg normalized to the right arm (R_i/R_{e leg}), a surrogate parameter for ECF/ICF, and the R_i/R_e of the thigh and calf without normalization (R_i/R_{e thigh}, R_i/R_{e calf}, respectively) were obtained. Increases in R_i/R_{e leg} (N 2.5 ± 0.7, VE 3.9 ± 3.7, LE 3.7 ± 1.5), R_i/R_{e thigh} (N 1.8 ± 0.5, VE 3.2 ± 3.8, LE 3.8 ± 1.9), and R_i/R_{e calf} (N 2.6 ± 0.6, VE 4.6 ± 1.7, LE 4.4 ± 2.2) were confirmed in VE and LE compared to normal subjects. However, the ratios of R_i/R_{e calf} to R_i/R_{e thigh} in normal subjects and those with untreated VE/LE were all ∼1.5 (N 1.5 ± 0.3, VE 1.5 ± 0.7, LE 1.6 ± 0.7).

Conclusions:

Fluid content was increased in legs with VE and LE compared to normal subjects, while the mode of gravitational fluid distribution was similar among all legs. Thus, no specific finding for LE was confirmed.

Introduction

Bioelectrical impedance analysis (BIA) has been used for the assessment of arm lymphedema (LE) since the early 1990s^1,2 and currently is also used for leg LE.^3–5 The magnitude of the electrical impedance is inversely proportional to the volume of fluid in the tissue.⁶ Accordingly, the ratio of extracellular fluid (ECF) to intracellular fluid (ICF) volumes can be expressed as the inverse ratio of each resistance, that is, R_i (the impedance of ICF) and R_e (the impedance of ECF). The increase in this R_i/R_e has been considered as a sensitive diagnostic criterion for early LE,⁷ because the changes predominantly or solely occur in ECF volume in the early stage of LE development. However, as LE progresses further, the fluid increases in protein content with cellular infiltration, eventually developing tissue fibrosis and fat deposition. As a result, the overall limb volume may continue to increase, but fluid content decreases proportionately.⁶ Furthermore, LE is often complicated by other types of edema caused by venous insufficiency, cardiac/renal failure, hypoalbuminemia, side effects of medications, and so on. Therefore, increased fluid content alone is not a sufficient explanation for LE.

Generally, the symptoms in legs with venous edema (VE) are evident in the lower part of the leg, but swelling of the thigh can be evident, particularly in secondary LE. In contrast, we previously reported that subcutaneous echo-free space observed with ultrasonography, which indicated local fluid accumulation in subcutaneous tissue, was similarly distributed according to gravity both in legs with VE and LE.⁸ Thus, it is unclear whether there is a specific fluid distribution pattern for LE when compared to legs with other types of edema or normal legs. The current study attempted to answer this question.

Patients and Methods

This study was approved by the Institutional Review Board of Yamaguchi University Hospital (Ube, Yamaguchi, Japan). All participants gave informed consent before enrollment. The subjects included in the current study were 33 patients with VE and 47 patients with leg LE who attended our clinic between April 2015 and September 2015. Thirty-three healthy volunteers were also assessed. The diagnoses were made by patient histories, physical examinations, blood tests, chest radiograms, and electrocardiograms, to exclude edemagenic conditions due to systemic diseases. A duplex venous ultrasound was performed to find any reflux in the deep veins, saphenous veins, accessory saphenous veins, and perforators. Subcutaneous tissue ultrasonography^8,9 was also performed to find changes in echogenicity that possibly correlated with inflammatory change and echo-free space that indicated accumulation of free fluid. Absence of any abnormal findings in the above examinations was confirmed in normal subjects. In this study, edema found in the legs with primary venous insufficiency, post-thrombotic syndrome, and functional venous insufficiency (FVI) were all regarded as VE. FVI was defined as below:

• No reflux or occlusion in the deep veins, saphenous veins, accessory saphenous veins, or perforators on duplex venous ultrasound

• Confirmed severe gait disturbance and/or prolonged sitting due to joint problems, general weakness, obesity, and so on

• No other edemagenic conditions, for example, cardiac/hepatic/renal failure

In the current study, LE complicated by apparent venous disorders was excluded. The clinical severity of LE was judged according to the Consensus Document of the International Society of Lymphology¹⁰ as follows:

Stage 0: A latent or subclinical condition in which limb swelling is not yet evident.

Stage I: An early accumulation of fluid that subsides with limb elevation.

Stage II: Tissue swelling that is not reduced by limb elevation alone. Pitting manifests in earlier stage II, but the limb may or may not pit in later stage II as excess fat and fibrosis supervene.

Stage III: Lymphostatic elephantiasis in which pitting can be absent and trophic skin changes such as acanthosis, further deposition of fat and fibrosis, and watery overgrowths have developed.

An asymptomatic contralateral leg with unilateral LE might be regarded as Stage 0 LE because the leg could have reduced lymph transport due to intrapelvic lymph node dissection in secondary LE or possible congenital abnormality in primary LE. However, they were excluded from the analysis because these legs had no edema. Participant characteristics are summarized in Table 1.

Table 1.

Subject Characteristics

	Normal (N = 33)	Venous edema (N = 33)	Lymphedema (N = 47)	p
Age, years; median (range)	35 (23–79)	74 (46–86)^a	70 (31–88)^a	<0.0001
Height, cm; median (range)	160 (143–180)	151 (143–169)	155 (140–176)	<0.0001
Weight, kg; median (range)	58 (45–105)	57 (43–98)	55 (40–88)^a,b	<0.01
BMI, kg/m²; median (range)	23 (19–34)	25 (19–41)	22 (15–31)^b	<0.001
Sex (male:female)	12:21	5:28	9:39	N.S.
Dominant side (right:left)	31:2	30:3	43:5	N.S.
Edema laterality (unilateral:bilateral)		6:27	31:16	<0.0001
Legs	(N = 66)	(N = 60)	(N = 63)
Diagnosis		PVI 18	Primary lymphedema 4
		PTS 3	Secondary lymphedema 44
		FVI 39	Stage I 3
			Stage II 54
			Stage III 6
Edema side (dominant:nondominant)		29:31	31:32	N.S.
Treatment (untreated:treated)		39:21	14:49	<0.0001

p < 0.05 versus normal.

0.05 versus venous edema.

BMI, body mass index; FVI, functional venous insufficiency; PTS, post-thrombotic syndrome; PVI, primary venous insufficiency.

A bioimpedance spectrometer (U-400; Impedimed Ltd, Brisbane, Australia) was used for BIA. All assessments were performed between 11 a.m. and 3 p.m. Assessment within 1 hour after a meal and/or exercise was avoided. Participants were set supine in a room maintained at 25°C, and the skin was degreased using alcohol swabs before the attachment of electrodes. Specially designed electrodes that could be used both for current drive and voltage sensing were attached on the dorsal wrists and the anterior surface of the leg at three levels (ankle, upper edge of the patella, groin) for three protocols as below:

Protocol 1: This was performed in patients with unilateral leg edema and normal subjects only. The impedance in a leg with edema (or the right leg in normal subjects) normalized to the contralateral normal leg (or the left leg in normal subjects) was obtained.

Protocol 2: This was performed in all participants. The impedance in each leg normalized to the right arm was obtained.

Protocol 3: This was performed in all participants. The impedances in the thigh and calf without normalization were separately obtained.

Protocol 1 and 2 were performed using the standard equipotential electrode arrangement. Detailed electrode positions in Protocol 3 are demonstrated in Figure 1.

FIG. 1.

Electrode positions in Protocol 3. The electrode position at the ankle was the same with that used in the standard equipotential electrode arrangement. At the knee level, the middle of the electrode was placed at the level of upper edge of patella, but it was attached slightly medial to the patella. At the groin level, the electrode was placed just below the crease of the front aspect of the groin. However, in the subjects with small stature, this was sometimes needed to be shifted proximally to keep interelectrode distance >20 cm.

Statistical analyses

The results are expressed as mean ± standard deviation or count, unless otherwise indicated. Simple linear regression analysis was used to study the correlation between R_i/R_e obtained by different methods and to test the correlation between R_i/R_e and the sum of R_i/R_e for the thigh and calf. To test for differences in subject characteristics and differences in R_i/R_e, R_i, and R_e in legs with various conditions, the Kruskal–Wallis test was used. The Mann–Whitney U-test was used for multiple comparisons. Statistical analyses were performed using JMP 11.0 (SAS Institute, Cary, NC). A p-value <0.05 was considered significant.

Results

The currently used BIA device was originally designed to calculate R_i and R_e of a leg normalized to the contralateral leg, which is essentially applicable only to unilateral edema. To obtain R_i and R_e of both legs, we tried to use the right arm for normalization and to verify whether the method is valid. R_i/R_e of a leg normalized to the contralateral leg (R_i/R_{e leg (cont)}) and that normalized to the right arm (R_i/R_{e leg (rarm)}) were compared in patients with unilateral leg edema (tested leg = diseased leg, n = 37) and in normal subjects (tested leg = right leg, n = 33). A good linear correlation between R_i/R_{e leg (cont)} and R_i/R_{e leg (rarm)} was obtained both in patients with unilateral leg edema (R² = 0.97, p < 0.0001) and in normal subjects (R² = 0.84, p < 0.0001) (Fig. 2). The regression lines obtained from these legs were very similar. Accordingly, it seemed reasonable to compare edematous legs and normal legs directly using R_i/R_{e leg (rarm)} instead of R_i/R_{e (cont)}. Among the current study groups, no significant differences were observed in terms of sex and limb dominance, while significant differences were observed in terms of age, physique, edema laterality, and treatment status, which might affect the results according to a report by Ward et al.³ However, we decided to use R_i/R_{e leg (rarm)} as a guide for fluid volume status regardless of these factors, because these were directly and/or indirectly related to the nature of the diseases.

FIG. 2.

Correlation between R_i/R_e of a leg normalized to the contralateral leg (R_i/R_{e leg (cont)}) and that normalized to the right arm (R_i/R_{e leg (rarm)}) in patients with unilateral leg edema and normal subjects.

Next, we measured the extracellular and intracellular impedances of thigh (R_{e thigh}, R_{i thigh}) and calf (R_{e calf}, R_{i calf}), respectively, and correlated them with those of the whole leg (R_{e leg}, R_{i leg}). Theoretically, R_{e leg} and R_{i leg} each should be equal to the sum of R_{e thigh} and R_{e calf}, and R_{i thigh} and R_{i calf}, respectively. This was roughly true both in the thigh (R² = 0.74, p < 0.0001) and calf (R² = 0.35, p < 0.0001), although a certain range of deviation was observed (Fig. 3). Therefore, it seemed acceptable to divide the whole leg impedance into the impedances of thigh and calf for analysis.

FIG. 3.

(A) Correlation between the extracellular impedances of a whole leg (R_{e leg}) and the sum of the extracellular impedances of thigh (R_{e thigh}) and calf (R_{e calf}). (B) Correlation between the intracellular impedances of a whole leg (R_{i leg}) and the sum of the intracellular impedances of thigh (R_{i thigh}) and calf (R_{i calf}).

BIA in legs with VE, LE, and normal legs

The results showed that R_i/R_{e leg}, a surrogate parameter for ECF/ICF of a whole leg, was increased both in VE and LE compared to that in N (N 2.5 ± 0.7, VE 3.9 ± 3.7, LE 3.7 ± 1.5), and this was true regardless of treatment status (Fig. 4A left). Since R_{i leg} was similar among these legs (Fig. 4A right), this increase in R_i/R_{e leg} was considered to be caused by a decrease in R_{e leg} (Fig. 4A middle). When the thigh and calf were separately evaluated, the same phenomenon was confirmed in the calf. Namely, R_i/R_{e calf} was increased in legs with edema (N 2.6 ± 0.6, VE 4.6 ± 1.7, LE 4.4 ± 2.2); this was true regardless of treatment status (Fig. 4B left), due to a decrease in R_{e calf} (Fig. 4B middle), while R_{i calf} in these legs was similar (Fig. 4B right). In the thigh, an increase in R_i/R_{e thigh} was again confirmed in legs with edema (N 1.8 ± 0.5, VE 3.2 ± 3.8, LE 3.8 ± 1.9). However, this was slightly affected by treatment status (Fig. 4C left). R_{e thigh} was decreased in treated VE, and a further decrease was observed in treated/untreated LE (Fig. 4C middle). In contrast to the calf, R_{i thigh} was increased both in VE and LE compared to N (Fig. 4C right). The ratios of R_i/R_{e calf} to R_i/R_{e thigh} (C/T ratio) were compared and were almost the same in N and untreated VE/LE. A significant decrease in C/T ratio was observed between treated and untreated LE, but this was not the case in VE (Fig. 4D).

FIG. 4.

(A) R_i/R_{e leg}, R_{e leg}, and R_{i leg} in normal legs, legs with venous edema, and lymphedema. (B) R_i/R_{e calf}, R_{e calf}, and R_{i calf} in normal legs, legs with venous edema, and lymphedema. (C) R_i/R_{e thigh}, R_{e thigh}, and R_{i thigh} in normal legs, legs with venous edema, and lymphedema. (D) Ratios of R_i/R_{e calf} to R_i/R_{e thigh} in normal legs, legs with venous edema, and lymphedema. R_i/R_{e rarm}, R_{e rarm}, R_{i rarm}, R_i/R_{e calf}, R_{e calf}, R_{i calf}, R_i/R_{e thigh}, R_{e thigh}, and R_{i thigh}: as in Figures 1 and 2. N: normal legs, Vu: legs with untreated venous edema, Vt: legs with treated venous edema, Lu: legs with untreated lymphedema, Lt: legs with treated lymphedema. *:p < 0.05 versus normal legs. ^†: p < 0.05 between treated and untreated legs.

Discussion

The increase in R_i/R_e in the whole leg, thigh, and calf could be demonstrated in VE and LE. Moreover, it was found that C/T ratio was similarly about 1.5 in N and untreated VE/LE. This indicated that distribution of fluid in a leg according to gravity was constant regardless of fluid status in the leg. Accordingly, we could not find any particular feature in LE in terms of fluid distribution pattern.

In the current study, C/T ratio was decreased by treatment in LE, but not in VE. We previously reported that a greater decrease of fluid in the calf, which was confirmed as decreased subcutaneous echo-free space, was found compared to that in the thigh in treated LE.⁹ This might be related to hosiery design, with relatively insufficient interface pressure at the thigh that could cause “the toothpaste in the toothpaste tube” phenomenon, in which fluid was squeezed by a higher compression below to a lower compression area above. In contrast, this decrease in C/T ratio was not observed in VE. One possible explanation is the nature of the disease and its treatment. With compression therapy, most VE is resolved; thus, diligent patients did not appear in the clinic because they could manage the symptoms by themselves. Since LE caused persistent leg swelling, the more diligent the patient, the more regularly he/she appeared. Therefore, it was speculated that less compliant patients and/or nonresponders had VE, while more diligent patients had LE.

Interestingly, R_i was similarly increased in the thigh with VE and LE. It is known that fluid with a relatively high protein content accumulates in LE¹⁰ and that chronic inflammation is ongoing in legs with LE and VE.¹¹ These might have changed the electrolyte concentration and/or capacitive resistance of the cell membrane, resulting in a change in the coefficient of resistivity.^12,13 Further investigation will be needed to clarify this issue.

Limitations

Since our clinic manages a limited number of patients with leg edema, we could only assess a small numbers of legs, particularly those with untreated LE. However, as LE treatment is gaining popularity, many patients had already started some form of compression therapy before they visited our clinic. A study, including a larger number of patients, will be needed to draw definite conclusions.

Conclusion

BIA demonstrated that fluid content was increased both in legs with VE and LE, compared to N, while the mode of gravitational fluid distribution was similar among all legs. Thus, no specific finding for LE was confirmed using BIA in the present study.

Footnotes

Author Disclosure Statement

No competing financial interests exist.

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