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Air plethysmographic evaluation of calf muscle pump function according to age
(Portuguese PDF version)

Carlos Alberto Engelhorn¹, Cristina Veronese Beffa², Galvane Bochi³, Renata Corrêa Pullig⁴, Fernando Silveira Picheth⁵, Sérgio Salles Cunha⁶

1. Professor of Angiology, Pontifícia Universidade Católica do Paraná.
2. Vascular Surgeon.
3. Resident Doctor, General Surgery, Hospital Santa Casa de Curitiba.
4. Specialist in Angiology and Vascular Surgery, Brazilian Society of Angiology and Vascular Surgery.
5. Head of the Vascular Surgery Division, Hospital Santa Casa de Curitiba.
6. PhD, Clinical Research Director, Jobst Vascular Center, Toledo, Ohio, EUA.

Correspondence:
Dr. Carlos Alberto Engelhorn
Rua Deputado Heitor Alencar Furtado, 1720/901
CEP 81200-110 - Curitiba - PR
Tel.: +55 (41) 279.1241 Fax: +55 (41) 362.0133
E-mail: engelhor@bsi.com.br

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ABSTRACT

Objective: We believe that the aging of the human body might be associated with the progressive impairment of the muscle pump function, which may cause chronic venous insufficiency. The aim of this study is to evaluate, by way of air plethysmography, the calf muscle pump function in healthy people with no clinical signs of severe chronic venous insufficiency, divided into specific age groups.

Methods: Thirty lower limbs of 22 people with chronic venous insufficiency were evaluated; the limbs were classified as CEAP class I or II, and were split into two groups of 15 limbs: group A, people under 40 years of age and group B, those over 40 years. A hemodynamic evaluation of all patients was performed with air plethysmography. A statistical analysis of plethysmographic parameters, which allowed for the differentiation of calf muscle pump function between the two groups, was performed.

Results: Of all plethysmographic parameters analyzed in groups A and B, ejection fraction - EF (P = 0.05) and the venous filling index - VFI (P = 0.048) were the ones that best discriminated the groups studied, showing statistically significant differences.

Conclusion: Ejection fraction and the venous filling index are the most reliable parameters to assess muscle pump function.

Key-words: muscles, plethysmography, venous insufficiency.
Palavras-chave: músculos, pletismografia, insuficiência venosa.

J Vasc Br 2003;2(1):13-16

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INTRODUCTION

The function of the venous system of the lower extremities is to take deoxygenated blood from muscles and cutaneous tissues in these extremities up to the heart. The system also works as a local blood reservoir. The calf veins, together with the surrounding tissues, form a functional unit known as peripheral heart, which actively drains venous blood during physical exercise.^1-3

The muscle pump (peripheral heart) in healthy individuals ejects blood in such an effective way as to reduce intravascular venous pressure to values close to zero. It may also raise this pressure to values above 200 mmHg. To make this muscle pump work properly the following are necessary: good draining pervious veins with competent valves, eutonic and eutrophic musculature, neural integrity and free joints. Failures in any of these elements may reduce effectiveness of the peripheral heart and predispose the leg to chronic venous insufficiency (CVI).²

It is believed that muscle pump function deteriorates with age. This may be further explained by a higher incidence of deep venous thrombosis (DVT) in individuals over forty years of age, due to a decrease of venous compliance and the presence of valve lesions. Other factors such as poor physical conditioning and muscular atrophy are also involved.^4,5

The objective of this study was to use air plethysmography (APG) to evaluate the calf muscle pump function in patients with no clinical signs of severe chronic venous insufficiency, distributed into specific age groups.

MATERIAL AND METHODS

Population

Venous hemodynamic evaluation was performed in 30 lower limbs of 22 female patients aged between 18 and 63 years. These patients were rated as having lesions of CVI levels I or II according to clinical features included in the CEAP classification system established by the Society of Vascular Surgery.⁶ In other words, we included patients with telangiectasia, reticular veins and/or varicose veins without edema. Exclusion criteria were: CVI classes III to VI; previous history of DVT and surgery of varicose veins; collagenosis; chronic arterial insufficiency; orthopedic disorders such as knock-knee (genu valgum), bowleg (genu varum), decrease of mobility, ankle ankylosis; lack of cooperation and pregnancy.

Lower limbs to be studied were divided into two groups of 15 each, according to age. Group A was formed by patients under forty years of age while group B included patients above that age. The mean ages for groups A and B were respectively 28 and 50 years. Parameters assessed through APG were: venous volume (VV), residual volume fraction (RVF), venous filling index (VFI) and ejection fraction (EF).
All tests took place from January to August 2000 in the Noninvasive Vascular Laboratory of the Hospital de Caridade da Santa Casa, Curitiba, Pontifícia Universidade Católica do Paraná (PUC/PR).

Methods

Venous hemodynamic evaluation was performed on all patients using air plethysmography (Narcosul equipment), according to the technique defined by Christopoulos et al.⁷

In this technique, examination starts with the patient in the supine position with the lower limb to be studied elevated at an angle of 45 . Five minutes are awaited for venous emptying of the limb. A pneumatic cuff is coupled to a computerized sensor and positioned around the leg, from the knee to near the malleolar line and then filled with air up to 6 mmHg for calibration of the equipment. This is done by the injection of 50 ml of air. After the equipment is calibrated, the patient is asked to stand, keeping the limb under study at rest. This step allows filling the veins through their points of reflux and through the arterial influx up to a maximum value that corresponds to the venous volume (VV). It is known that the parameter defined as 90% of the venous filling time (VFT90) corresponds to the average venous filling index (VFI) up to 90% of the VV. VFI is defined as 90%VV/VFT90.

With the limb filled with blood, the patient performs a dorsiflexion movement of the ankle. The volume of blood ejected (EV) by the calf is then registered. The ejection fraction (EF) is calculated as EF = EV/VVx100%. Afterwards, with the limb filled with blood, a series of ten consecutive movements is performed in order to calculate the residual volume (RV) and the residual volume fraction (RVF) of blood. RV is measured during exercise and in relation to the zero final volume. RVF is calculated as RV/VVx100%. The patient then returns to the supine position with the leg elevated and at rest (Figure 1).

Figure 1 - Diagram showing the examination technique and how to obtain the plethysmographic parameters.

The plethysmographic parameters used to compare the groups in this study were: VV, RVF, VFI, EF, and VFT90.

Statistical analysis

The average results of VV, RVF, VFI, EF, and VFT90 obtained from groups A and B through APG were compared using Student's t test.

RESULTS

Out of 30 extremities with CVI, 10 were of level I and 20 of level II. In group A (15 lower limbs), six limbs were of level I and nine of level II. In group B (15 lower limbs), four were of level I and 11 of level II.

From all APG parameters analyzed in groups A and B, EF and VFI were those that best discriminated the groups. There were significant differences (P = 0.05) and (P = 0.048), respectively, in terms of muscle pump function in patients above and under 40 years of age (Figure 2).

Figure 2 - Comparison of the plethysmographic parameters among patients younger (A) and older (B) than 40 years old.

Results from APG in normal individuals and with altered muscle pump function are shown in Figures 3 and 4.

Figure 3 - Example of an air plethysmography performed in a patient younger than 40 years old who presented normal function of the calf muscle pump. Note (arrow) the normal VFI.

Figure 4 -Plethysmographic assessment of a patient older than 40 years old showing alterations (arrows) in EF and VFI.

DISCUSSION

Unlike the peripheral arterial system that works under the influence of high transmural pressures, the venous system is more affected by external pressures, forming a functional unit with the surrounding tissues.³

Evident changes in the venous wall and in muscle pump function are vital factors for the pathophysiology of venous disease.³ Gibbs et al. suggest that the soleus veins become dilated and tortuous with age.⁴ In addition, some studies have shown that dorsoplantar flexion decreases with age and is approximately 15% lower in the eighth decade of life as against the third decade.^8,9

A higher incidence of DVT has been reported in patients above 40 years of age in the postoperative period when compared with younger patients. The loss of elasticity of soleus veins over the years, the decrease of muscular mass in the venous pump and the important association with other diseases such as neoplasia, heart diseases and obstructive lung disease can explain the high predisposition of elderly individuals to thromboembolic events.¹⁰

Several studies were carried out to elucidate the mechanisms involved in the high incidence of DVT after the fourth decade of life. Their results, however, were inconclusive in regard to platelet number and adhesiveness, blood clotting mechanism and decrease in fibrinolytic activity among patients from different ages.⁴

Ambulatory venous pressure is considered to be a golden standard when evaluating hemodynamics in patients with CVI. However, due to its invasiveness, its role in following up these patients is controversial.⁴ In addition, Bays et al. demonstrated that RVF values obtained through APG present good correlation with ambulatory venous pressure.¹¹

Schina et al. studied healthy volunteers of different ages and evidenced that VV and EF were significantly lower in elderly patients, while RVF was significantly increased. The increase of RVF in elderly patients may be attributed to muscle pump fatigue or reduced effectiveness, associated or not with venous reflux.⁴

Labropoulos et al. studied CVI patients younger than 60 years old, with no previous history of deep venous thrombosis, and whose disease lasted less than 10 years. Significant differences were not found in EF of these patients considering the several levels of CVI.⁵ On the other hand, according to Bermudez,² EF and RVF are the plethysmographic variables that best quantify the muscle pump function.² Differently from EF, which does not rely on reflux, RVF depends on both reflux and ejection capacity of the muscle pump.¹²
Sugimoto et al. reported a case of a male patient with leg ulcer unresponsive to rigorous conservative treatment, in which phlebography presented absence of deep venous obstruction and venous reflux, but APG revealed severe failure of the calf muscle pump as the cause of venous stasis.¹³ In this same study, EF was considered to be the best plethysmographic parameter for evaluation of muscle pump function.

In the present study, EF and VFI were the parameters that best assessed muscle pump function. Residual volume values were higher in patients above 40 years of age (group B), but this difference was not statistically significant. However, the presence of reflux in level II patients (majority of group B), even when asymptomatic, might have contributed to the statistical significance of VFI as a discriminating parameter of the deterioration of calf muscle pump function.

Despite some limitations, such as sample size, occasional presence of reflux in level II patients and the nonuse of imaging exams to rule out deep venous thrombosis, the authors concluded that there was some evidence of changes in calf muscle pump function and that these changes are related to age. Also, they concluded that EF and the VFI could be used routinely as the trustworthiest parameters to evaluate patients with signs of nonsevere CVI.

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