Measurements of gallbladder motor function by ultrasonography: towards standardization

Digestive and Liver Disease 35 (Suppl. 3) (2003) S56–S61 www.elsevier.com / locate / dld

Measurements of gallbladder motor function by ultrasonography: towards standardization P. Portincasa a , *, A. Moschetta a , A. Colecchia b , D. Festi c , G. Palasciano a a

Section of Internal Medicine, Department of Internal Medicine and Public Medicine, University Medical School of Bari, Piazza G. Cesare, 70124 Bari, Italy b Department of Internal Medicine and Gastroenterology, University of Bologna, Bologna, Italy c Department of Medicine and Aging, University ‘ G. d’ Annunzio’, Chieti, Italy

Abstract As real-time ultrasonography is a cheap, noninvasive, relatively easy, validated and reproducible technique, it can be repeated over time to document time-related changes of gallbladder motor function. Ultimately, functional ultrasonography estimates gallbladder shape and volume in fasting state and in response to a test meal (liquid or mixed solid–liquid, provided there is sufficient fat content) or exogenous stimulus (e.g., i.v. cholecystokinin or ceruletide). Although functional ultrasonography of the gallbladder has been mainly used for research purposes in specific referral centres, its simplicity makes such a technique appealing in the clinical setting to assess gallbladder motor function in both health and disease. Indications include the study of healthy subjects and of patients during pathophysiologically relevant conditions; in particular when subjects are at risk for gallbladder stasis and gallstone disease or during gallstone disease when a decision concerning medical dissolution therapy is required.  2003 Editrice Gastroenterologica Italiana S.r.l. Published by Elsevier Ltd. All rights reserved. Keywords: Cholecystokinin; Gallstones; Motility; Test meal; Ultrasound

1. Introduction The gallbladder is a pear-shaped bag containing bile; due to its position below the right lobe of the liver and its liquid content, it can be easily visualized by ultrasonography. The study of gallbladder morphology must provide information on shape (i.e., regular, irregular), volume (i.e., normal, decreased, increased), wall (i.e., normal, thickened, cholesterolosis, adenomyomas), and content (i.e., non-echoic, sludge, stones, neoplasms). The major functions of the gallbladder are the emptying of concentrated bile in response to nutrients, filling of hepatic bile during the interprandial period and mixing of its contents [1]. All these functions depend on contraction– relaxation of the gallbladder’s smooth muscle and the neuro-endocrine coordination between the gallbladder, cystic duct, sphincter of Oddi and the intestine. Cholecystokinin is the main hormone involved in postprandial gallbladder contraction. There is also considerable *Corresponding author. Tel.: 139-080-547-8227; fax: 139-080-5478232. E-mail address: [email protected] (P. Portincasa).

gallbladder contraction in the fasting state, associated with phase III of the gastrointestinal migrating motor complex and release of the intestinal hormone motilin [2]. Previous techniques have employed duodenal intubation [3], oral cholecystography [4], and radionuclide scanning [5] to study gallbladder motorfunction [6,7]. However, major pitfalls for such techniques are invasiveness, indirect information on gallbladder function and morphology, and use of radiations. The development of real-time ultrasonography has greatly improved the study of gallbladder motor function, even with simple, inexpensive routine equipment [8]. The present section will focus on some aspects of functional ultrasonograpy for the study of gallbladder motility.

2. Equipment Standard ultrasound equipment with linear or convex 3.5 or 5.0 MHz probes and ‘built-in’ software facilities (automatic measurements of distances, areas and volumes), are generally sufficient for the study of gallbladder motor-

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Table 1 Indices of gallbladder motor function to be considered at functional ultrasonography Index

Explanation

Unit

Essential •Fasting volume •Post-stimulus volumes •Residual volume

Maximum volume after 8–12 h fasting Volumes estimated during the observation time Smallest volume observed during the observation time

•Ejection volume(s) •Ejection fraction

Expelled volume observed during the observation time Greatest volume expelled during the observation time

•Half-emptying time (T 50 )

Time to 50% decrease of fasting volume

(ml) (ml) (ml)* (% fasting volume)** (ml) (ml)* (% fasting volume)** (min)

Additional •Total emptying time •Integrated gallbladder contraction

Time to reach maximal emptying Area under ejection curve (trapezoidal rule)[

•Emptying rate •Refilling rate •Handling of hepatic bile

Slope of linear part of emptying curve Slope of linear part of refilling curve Flux of bile through the gallbladder

(min) (ml3120 min 21 ) (% fasting volume3120 min 21 ) (2ml3min 21 ) (ml3min 21 ) (ml)

* and ** are reciprocal values (only one of each is given); [ according to Ref. [56].

function. For clinical and research purposes, a printer and / or a VHS recorder may allow the storage of images for later analysis.

3. Stimuli The gallbladder is studied in the fasting state and in response to a stimulus inducing smooth muscle contraction. As a result, real-time ultrasonography can easily pick up time-related changes of gallbladder volume. However, time-dependent changes of gallbladder volume are a function of the stimulus being used (see below). Exogenous stimuli include i.v. administration of physiologically relevant hormones such as the cholecystokinin-

octapeptide (CCK8) or the CCK-analogue cerulein (Takus  , Pharmacia-Upjohn) which is given intravenously at a dose of 0.3 mg / kg body weight. Whereas both standardization and reproducibility are better since ‘luminal’ processes are lacking (e.g., gastric emptying, duodenal digestion, etc.), important pitfalls are potential side effects (e.g., abdominal cramps, nausea, etc.) and unavailability of the substances, which remain still experimental. However, the use of i.v. cholecystokinetic drugs is of interest during biliary drainage to identify cholesterol monohydrate crystals (e.g., patients referred for episodes of acute pancreatitis) or to study biochemical composition of bile (e.g., before and after litholitic therapies in patients with gallstones) [9,10]. Another exogenous stimulus—i.v. administration of amino acids—induces effective gallbladder

Fig. 1. Example of a study protocol of gallbladder motility by functional ultrasonography.

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emptying; rapid infusion of a 125-ml amino acid mixture over 5 min (2.1 g per min) gives a 64% reduction in gallbladder volume within 30 min, whereas a 50-ml infusion over 5 min gives only a 22% reduction [11]. Endogenous stimuli include a standard test meal which contains appropriate amounts of fat (i.e., at least 10–12 g) [12] to achieve sufficient release of endogenous CCK and subsequent gallbladder contraction. For this, either mixed (i.e., solid–liquid) [12–14] or liquid test meals [12] can be used. Liquid test meals commercially available (e.g., Ensure plus  , Abbot; Nutridrink  , Nutricia) include 200– 250 ml liquid solutions of about 300 Kcal and about 40% carbohydrates, 40% fat and 20% protein, with about 400 mOsm / l. Another well studied endogenous stimulus is cholestyramine, an anionic exchange resin which binds intraluminal bile salts; given at low doses (8 g orally), effective gallbladder contraction is achieved during fasting. The most likely explanation we could provide is the interruption of the negative feedback operating between intestinal bile salts and motilin (also CCK?) release [15– 17]. The most important feature of a good stimulus should be its ability to discriminate between ‘normal’ and ‘abnormal’ gallbladder contraction [13,18–20].

gallbladders; in a small number of healthy subjects the formula gave results comparable to those obtained with to the sum-of-cylinders method [21].

5. Construction of volume–time emptying curves After calculation, gallbladder volumes are plotted vs. time at fixed time-points to draw emptying–refilling curves in the fasting state or after the stimulus being used. Table 1 summarizes the most relevant ultrasonographic indices of gallbladder motor function encountered in the literature [8,12,13,19–24]. Depending on the main aim of the study of gallbladder motility (e.g., clinical or research purposes), several indices can be provided.

6. Protocol The study of gallbladder motor function should provide

4. Measurement of gallbladder volume Longitudinal, transverse, and oblique scans at the right hypocondrium in the supine or sitting position are used to measure the length and, by rotating the probe by 908, the width and depth of the gallbladder. For estimation of gallbladder volume, the following two formulas are generally employed:

• Sum-of-cylinders method [8]: the gallbladder volume is equal to the sum of cylinders of equal heights perpendicular to the length of the organ: volume5 0.7853h3(S ni 50 d i 2 )3E 2 (where 0.7855constant value derived from p / 4; h5height of each cylinder, n5number of cylinders, d i 5diameter of the ith cylinder; E5correction factor applied for displacement of the sagittal scan from the central axis of the gallbladder5[(depth1width) / 2d max ] where width and depth are derived from transverse scan; d max 5 maximal diameter of cylinder). Although this method is generally considered the ‘gold standard’ for calculating the gallbladder volume, it is tedious and time consuming, unless a computer program is used. Thus, its use should be restricted to the study of more dysmorphic, asymmetrical gallbladders. • Ellipsoid method [21]: volume5length3depth3 width30.523 (where 0.5235p / 6, depth5antero-posterior diameter, width5latero-lateral diameter). Volume is in ml (cm 3 ) when diameters are taken in cm. The formula can be reliably applied to regularly shaped

Fig. 2. Time-related changes of gallbladder volume after ingestion of a standard liquid test meal (Nutridrink  , Nutricia, The Netherlands). Data obtained from a control group of healthy subjects in Southern Italy (N5103; mean6S.E.) [33]. (A) Volume–time emptying curve where volume is in ml; (B) volume–time emptying curve where volume is in % fasting volume. Broken lines show the normal cut-off values for ejection fraction and half-emptying time.

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Table 2 Indices of gallbladder motor function in healthy subjects, stratified according to sex (from Ref. [33]) N

Fasting volume (ml)

Residual volume (%)

Half-emptying time (min)

Males Cut-off

51 M12SD

22.860.8 #40

26.661.4 #50

21.160.8 #35

Females Cut-off

52 M12SD

19.760.8 #31

24.561.2 #50

21.560.9 #35

data on time-related changes of volume during fasting (during interdigestive motor cycle) [2] and time-related changes of postprandial volume [8]. Depending on the length of the observation time and the type of stimulus employed (containing more or less nutrients), the profile of the volume–time curve can [13,20]—or cannot [25]— show a refilling part, thus affecting the estimation of the ‘true’ residual volume. This situation needs to be taken into account in particular with mixed highly-caloric test meals. A more dynamic interpretation of gallbladder motility is that short-lasting episodes of emptying–refilling continuously occur within major (slow) episodes of gallbladder emptying and refilling [23,26,27]. A practical consideration is that the study of this activity requires frequent ultrasonographic measurements (i.e., every 1–2 min) and time-consuming mathematical formulas [24]; this cannot be easily done on a routine basis, unless the calculation of an additional index (amount of bile handled by the gallbladder) is needed (Table 1). A more concise approach is to measure fasting gallbladder volume (two consecutive measurements 10 min apart) and postprandial volumes at 30 and 45 min to document the smallest residual volume of the gallbladder [13,28]. These few measurements provide a general estimate of postprandial gallbladder emptying. However, more accurate pathophysiological studies require frequent and prolonged measurements of the gallbladder volume (e.g., every 10– 15 min, up to 120–180 min postprandially). Altogether, these measurements document the speed of gallbladder emptying and the refilling phase which usually reaches 80% of fasting volume within 180 min postprandially. Fig. 1 provides an example of a study protocol [12,13,17,29– 32].

7. Definition of normal values This is an essential step and should be routinely provided by each centre. Data should be given according to the stimulus employed for inducing gallbladder emptying. As an example, Fig. 2 depicts the time-related changes of gallbladder volume in normal subjects in the fasting and postprandial state. As stimulus, 200 ml liquid test meal (Nutridrink  , Nutricia, The Netherlands) was used with 13 g fat. The definition of a database with gallbladder motility measurements in health and disease was the aim of a

recent large ultrasonographic study from our group [33]. Data for healthy subjects stratified by sex are given in Table 2.

8. Clinical relevance For many years the study of gallbladder motor function by ultrasonography has been employed to evaluate pathophysiological aspects of gallbladder function, mainly in patients with gallstone disease. It is now clear that gallbladder motility is impaired in a subgroup of gallstone patients [6,13,14,19,20,34]. Gallbladder stasis plays a key role in the pathogenesis of cholesterol gallstones [35,36] and in conditions associated with gallstone formation: vagotomy, pregnancy, use of estroprogestins, total parenteral nutrition, diabetes, obesity, rapid weight loss during very-low caloric diets, acromegaly and use of octreotide [31,32,37,38]. The study of gallbladder motility by ‘functional’ ultrasonography improves the selection of those gallstone patients eligible for oral litholysis. A good gallbladder ‘response’ (i.e., .50% ejection fraction [39] or ,6 ml residual volume [25]) suggests the patency of the cystic duct and a higher chance of clearance of fragments and gallstones. Abnormal gallbladder emptying has been shown in a subgroup of patients with acalcolous biliary pain [40]. The ultrasonographic technique can be used to study of the effect of prokinetic drugs on gallbladder Table 3 Characteristics of the ultrasonographic study of gallbladder motility Pitfalls —Inadequate visualization of the gallbladder (obesity, chronic cholecystitis, large gallbladders or biliary obstruction) —Operator-dependent —Need for trained operator —Frequent measurements —Sometime difficult calculations Advantages —Prolonged measurements (fasting, poststimulus) —Noninvasive —Risk-free —Optimal compliance —Accurate and reproducible —Unexpensive —Simultaneous studies possible (e.g., gallbladder morphology, stomach, liver, pancreas, etc.)

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motility [41,42–51]. This may also be the case in a series of patients at increased risk for gallstone formation, such as those with gallbladder sludge [51–54] and obese patients [32]. The effect of other drug potentially affecting gallbladder motility can also be assessed by ultrasonography [38,55].

9. Pitfalls and advantages These should be systematically evaluated and a list is reported in Table 3.

10. Conclusions Of the various methods available for measurement of gallbladder motorfunction, functional ultrasonography provides a series of essential information. As an easily available technique, it can result in a major impact on daily practice. The methodology is acceptable in the workup of both healthy subjects and subsets of patients in which abnormal gallbladder motility needs evaluation. However, it is essential to apply standardized procedures and to provide reference data to facilitate the comparison of results.

Conflict of interest statement None declared.

List of abbreviations CCK, Cholecystokinin; CCK8, Cholecystokinin-octapeptide.

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