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Keywords:

  • antral contractions;
  • gastric accommodation;
  • hunger;
  • migrating motor complex;
  • ultrasonography

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Conclusion
  8. Grants
  9. References

Abstract  Strain rate imaging (SRI) is a non-invasive ultrasound (US) modality that enables the study of mechanical deformation (strain) with high spatial and temporal resolution. A total of 244 contractions in seven healthy volunteers were studied by SRI on two separate days to characterize radial strain of antral contractions in the fasting and fed states and to assess the influence of intravenous erythromycin. Gastric accommodation and emptying were assessed by 2D ultrasonography. The perception of hunger was registered by the participants. The strain increased from early to late phase II and phase III activity by (median) 18%, 58% and 82%, respectively, < 0.05. Erythromycin infusion in phase I induced contractions with median strain of 35%, but did not increase postprandial strain. Both fasting and postprandially, lumen-occlusive contractions with erythromycin were more frequent than in naturally occurring contractions, 69%vs 48%, P = 0.036 and 40%vs 5%, < 0.001 respectively. All subjects had rumbling in their abdomens when intraluminal air was detected sonographically (85% of all phase III contractions) and that rumbling was perceived by the participant as maximal awareness of hunger. SRI enabled detailed strain measurement of individual antral contractions. Erythromycin initiated fasting antral contractions and increased the number of lumen-occlusive contractions.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Conclusion
  8. Grants
  9. References

The gastrointestinal tract is a tube that deforms due to muscle activity and movement of luminal contents. Its function depends on mechanoreceptors located in the gastrointestinal wall. Although traditionally considered to be tension-sensitive,1,2 there is increasing evidence that mechanoreceptors respond to tissue deformation.3–7 Tissue deformation, measured as stretch ratio or strain, has been studied by B-Mode ultrasonography,8 elastography9 and magnetic resonance imaging (MRI).10 Ultrasound strain rate imaging (SRI) is a modality that utilizes the recording of tissue velocity imaging (TVI) to obtain strain and strain rate.11 SRI measures the strain rate as the gradient of the velocity component of two points along the US beam.11 The method was originally developed to assess myocardial contractility12 but later has been used to evaluate strain in the gastric antrum.8 The accuracy of the SRI for low velocity deformation as encountered in the gastrointestinal tract has been validated in a slowly moving rubber phantom13 and later in an in vitro porcine antrum.14

The aim of this study was to characterize radial strain of the proper muscle layer of the antral wall during different phases of the migrating motor complex (MMC), during lumen-occlusive vs non-lumen-occlusive contractions, postprandially, and after erythromycin; and to evaluate the relationship between antral strains with gastric emptying and proximal gastric accommodation. Secondary aims were to study the relationship between phase III activity, visible luminal air and the sensation of hunger.

Materials and methods

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Conclusion
  8. Grants
  9. References

Subjects

Seven healthy volunteers (four males) were included and completed this study (age, 27.1 ± 2.9 years; weight, 65.1 ± 7.3 kg; height, 1.75 ± 0.1 m; BMI, 21.2 ± 1.3 kg m−2). The subjects included staff and medical students at Haukeland University Hospital, Bergen, Norway. The subjects did not have any known disease and no symptoms of gastrointestinal disease or those associated with functional dyspepsia according to the Rome II criteria.15 Except for the use of contraceptive pills in two females, no subjects used medication. Nor did they have any known drug allergies. All subjects gave written informed consent. The protocol was approved by the regional ethics committee and procedures were carried out according to the revised Helsinki declaration.

The study protocol

The subjects were studied between 8:00 am and 12:00 pm after an overnight fast of minimum 8 h. The protocol consisted of two examination days at least 1 week apart. The study was conducted in a randomized single-blinded fashion with the subjects unaware of the nature of the intravenous infusion. The same operator conducted all the scanning procedures. During both study days, the contractions of at least one MMC cycle from phase I to the next phase I were acquired. The MMC phases were identified ultrasonographically. The period without antral contractions (motor quiescence) was considered as phase I of the MMC. Contractions in the last 10 min before the next ‘motor quiescence’ were considered as phase III. Contractions between these two phases were considered as phase II, which was divided into periods of equal lengths ‘early phase II’ and ‘late phase II’. Placebo (0.9% normal saline), 5 mL min−1 or Erythromycin 5 mL min−1 (5 mg mL−1) was administered intravenously 10 min after the termination of phase III. The infusion lasted for 20 min, followed by 5 min of preparation before the subjects ingested the liquid meal. The fasting area of the proximal stomach and antral cross-sectional area (CSA) were acquired about 5 min before the ingestion of the meal. The areas of the proximal stomach and antral CSAs were acquired at 1, 10, 20 and 40 min after finishing the ingestion of the soup. Postprandial contractions between the CSA measurements were measured.

Ultrasonography and strain rate imaging

A digital US scanner (SystemFive; GE Vingmed Ultrasound A/S, Horten, Norway) with custom SRI acquisition software was used to obtain tissue and strain rate images. A handheld linear probe was used for the acquisition of SRI cineloops for all experiments, utilizing a tissue frequency of 6.7 MHz and a Doppler frequency of 5.7 MHz. The frame rate was 16–18 frames per second. A strain length of 1.9 mm was used.14 The strain rate and strain along the beam were displayed by colour coding of a window superimposed on the B-mode images (Fig. 1). The pulse repetition frequency (PRF) was set to 0.25 kHz to reduce the scaling error introduced by the relatively low strain.13

image

Figure 1.  An antral contraction with strain curve: A–D represent subsequent sequences of an antral contraction in a 329 frames cineloop as seen in the software programme for strain rate imaging (SRI) analysis. In frame 1 (A), the anterior antral wall is blue, indicating thickening of the anterior antral wall. In frame 107 (B) the wall (W) becomes yellow (thinner), indicating relaxation of the antrum. The strain curve (E) becomes negative (double arrow). Frame 207 (C) shows a contraction with thickening of the wall (blue colour coding on the wall). Frame 329 (D) shows the last relaxation (yellow colour coding on the wall). E shows the strain curve (yellow lines) with the black double arrow pointing to the corresponding frame in A–D. Time (s) is represented in the x-axis and strain values (%) in the y-axis. The red double arrow at the peak represents duration of the peak. The spikes (S) represent pulsation from the aorta. White line measures strain outside area of interest.

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The subjects were seated comfortably on a chair, leaning slightly backwards. The area of interest was identified approximately 2 cm proximal to the pylorus, with the right liver lobe cranially and the superior mesenteric artery and aorta posteriorly. The antrum was continuously monitored by US. When a contraction, identified as an instant decrease of the antral luminal CSA or change in circularity, was detected, a cineloop including the whole contraction was saved. The process of saving a contraction took about 15–20 s, depending on the length of the cineloop. At the end of US scanning, all the cineloops were transferred to a work station for further analysis.

The US scanning for accommodation and gastric emptying

The same scanner with a curvilinear US transducer (3.5 MHz) was used for the assessment of the area of the proximal stomach using a method previously described.16 With the curvilinear US probe held vertically in the epigastrium, the proximal stomach was identified between the liver and the left kidney. Gastric emptying was measured by using a previously validated US-based method.17,18 The antral CSA was repeatedly measured at 1, 10, 20 and 40 min postprandially. In a sagital plane at about 2 cm proximal to the pylorus and including the right liver lobe anteriorly, the antral CSA was identified using the linear US transducer described above.

The test meal

Five-hundred millilitres of commercial meat soup (Toro clear meat soup; Rieber & Søn A/S, Bergen, Norway) containing 1.8 g protein, 0.9 g fat, and 1.1 g carbohydrate (20 kcal) (all soluble in water) was ingested during a period of 4 min. The soup was boiled and then cooled to 37 °C to reduce the amount of air bubbles after ingestion. The pH of the soup varied between 5.4 and 5.7, and the osmolarity was 350 mOsm kg−1 H2O.16,19

Symptom score and perception of hunger

Subjective abdominal symptoms (pain, nausea, fullness, satiety and total discomfort) were assessed by a visual analogue scale consisting of a 100-mm-long line with zero indicating no perception and 100 mm indicating maximum of perception.20,21 The subjects also registered any symptom that was associated with maximal awareness of hunger. Furthermore, they were specifically asked upon every ultrasonographically detected contraction whether they experienced any sensation at that time. To minimize a possible bias, they were also asked about sensation when no contractions were detected.

Strain rate imaging strain analysis

The US cineloops were analysed with dedicated software (TVI version 6.1; GE Vingmed Ultrasound). SRI was averaged across the US beams in the muscularis propria of the anterior antral wall.14 The muscularis propria was identified as the layer between the interface echo just below the serosa anteriorly and the interface echo between muscularis propria and submucosa posteriorly,22 (W in Fig. 1A–D). The following parameters were calculated: peak strain (%) (maximum strain value measured from the lowest to the highest point in the strain curve), time to peak (TTP: the time from the start of the contraction at the lowest point in the SRI curve to peak strain), time to baseline (TTB: time from the peak to baseline) and total duration of the contraction (TCT = TTP + TTB) (Fig. 1E). The average strain velocity was calculated as peak strain/TTP (% s−1). Average relaxation velocity during deceleration was calculated as peak strain/TTB (% s−1). The duration of the peak strain was calculated as the time from 5% of peak strain measured before the peak to 5% of peak strain measured after the peak (Fig. 1E). To explore the effect of the strength of contraction on the different parameters, contractions were categorized into three groups according to strength: low-strain contractions (LSC = strain <50%), medium-strain contractions (MSC = strain 50–99%) and high-strain contractions (HSC > 100%).

Lumen occlusion

Antral CSA was measured at maximal contraction assessed visually as the minimum CSA. The tracing was made along the inner boundary of the muscularis propria. Contractions with CSA <1.0 cm2 were considered as lumen occlusive. This 1.0-cm2 cut-off was chosen on the basis of the manometry catheters which are 0.4–0.6 mm in diameter and the thickness of the mucosa is 2–3 mm, corresponding to an area of approximately 1.0 cm2.

Configuration of the strain curve

A contraction curve was considered as typical when there was only one peak. A non-typical contraction curve, on the other hand, was a curve with more than one peak or with a contraction on top of another contraction (Fig. 2).

image

Figure 2.  Configuration of strain curves: examples of different configurations of strain curves (yellow lines). (A) represents the typical curve characterized by a single peak. (B) represents atypical curves where more than one peak occurs. White line measures strain outside area of interest.

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Accommodation and gastric emptying

After transferring the US images to the workstation, software (EchoPac3D; GE Vingmed) was used to calculate the area of the proximal stomach using the method described by Gilja.16,23 The inner surface of the proximal stomach was traced and the antral CSA was measured by tracing the inner limit of the muscularis propria.

Statistical analysis

The results are given as median, minimum and maximum values for non-parametric data. Comparison of these parameters between the groups was performed using Friedman’s test for repeated measurements and Dunn’s test for post hoc analysis. For the area of the proximal stomach and antral CSA, two-way analysis of variance (anova) was used to compare their mean values in the different postprandial periods, with placebo and erythromycin and the results were reported as mean ± SEM. Chi-squared test was used to analyse the difference in distribution in the MMC and postprandially with and without erythromycin for the strength of contraction, lumen occlusion, and for the configuration of the strain curve. Linear correlation coefficient, mean difference and limits of agreement (SD) according to Bland and Altman24 were calculated to analyse the association and agreement between the two readings (n = 18 contractions) for the assessment of inter- and intra-observer variation. < 0.05 was chosen as level of statistical significance.

Results

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Conclusion
  8. Grants
  9. References

Analysis of 244 contractions was carried out. Fourteen erythromycin contractions were excluded because the area of interest moved outside the US field during the contractions. Table 1 displays the distribution of contractions during the fasting phases and in the postprandial period. One subject had phase III activity when the scanning started. In this subject, the following phase I activity lasted for 29 min before the first contraction of the next phase II activity appeared. In the other subjects in whom the scanning started during phase I activity, phase I lasted for 55.3 ± 36.6 min. The mean duration of phase II activity for all subjects was 33.7 ± 9.7 min. The whole postprandial period was analysed as one continuous period, because no difference was found in the characteristics of strain and time aspects between the postprandial periods 1–10, 10–20 and 20–40 min.

Table 1.   Strain values in different phases of the migrating motor complex and postprandial periods
 No. contractions Strain (%) LSC No. (%) MSC No. (%) HSC No. (%)Lumen-occlusive contractions No. (%)
  1. Strain given as median (minimum–maximum). The distribution of the low-strain contraction (LSC), medium-strain contractions (MSC) and high-strain contractions (HSC) are shown. Ery, erythromycin.

Early phase I2718 (4–66)24 (89)3 (11)0 (0)7 (25.9)
Late phase II3558 (12–181)13 (37)13 (37)9 (26)16 (48.6)
Phase III3982 (9–262)13 (33)10 (26)16 (41)25 (64.1)
Postprandial5837 (6–159)40 (69)10 (17)8 (14)3 (5.2)
Ery (fasting)3235 (6–523)22 (69)5 (17)5 (14)22 (68.8)
Ery (postprandial)5328 (6–726)36 (68)12 (23)3 (9)24 (45.3)
Total24438 (4–726)148 (61)53 (22)43 (18)98 (40.2)

Symptom score and perception of hunger

In the fasting state on both study days, all subjects reported ‘zero’ (no sensation) for all five symptoms. ‘zero’ was also reported for pain, nausea and discomfort in the whole postprandial period. For fullness and satiation the areas under the curve for erythromycin was larger than for placebo, but not statistically significant. All the subjects experienced rumbling in their stomachs during phase III and during erythromycin contractions. This rumbling was perceived as maximal awareness of hunger. Intraluminal air was more frequently detected by US in phase III (33/39 or 85%) and with erythromycin (24/32 or 75%) than in early (8/26 or 30%) and late phase II (16/35 or 46%), P < 0.001. Each time the subject indicated that there was rumbling, intra-gastric air was detected by US (100% of 33 contractions with intraluminal detected air in phase III). A significant positive correlation was found between the detection of intraluminal air and phase III (r = 0.460, P < 0.001).

Characteristics of strain and time aspects

In the fasting state, anterior radial strain increased gradually from early to late phase II (< 0.001) and reached a peak during phase III activity (< 0.001) (Table 1, Fig. 3). Postprandial strain values did not differ from that in the different phases of MMC. SRI enables detailed analysis of different time aspects such as TTP, TTB and TCT (Table 2). Strain and relaxation velocities are also presented in Table 2. Strain velocity showed variation in the different phases, fasting and postprandially, with or without erythromycin (Fig. 4). Anterior radial strain of contractions after the administration of erythromycin during phase I did not differ from that of spontaneous fasting contractions (Fig. 3). However, some erythromycin contractions had considerably high strain values (Table 1). Postprandial anterior radial strain with erythromycin was lower compared with late phase II (< 0.05) and phase III (< 0.01) activity, but did not differ from postprandial strain with placebo (Fig. 3). The strain velocity was lower in the postprandial period with erythromycin than in late phase II and phase III. TTB was shorter in the postprandial period with erythromycin than in late phase II and phase III (< 0.01).

image

Figure 3.  Fasting and postprandial antral strain: the plots show the median, interquartile range, outliers and extreme cases of individual variables of strain values %, both fasting and postprandial, with and without erythromycin. The significance level between the phases is shown. bsl00077, without erythromycin; □, with erythromycin; Ery, erythromycin.

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Table 2.   Time aspects in different phases of the migrating motor complex and postprandial periods
 TTP (s)TTB (s)TCT (s)Strain velocity (% s−1)Relaxation velocity (% s−1)
  1. Time to peak (TTP), time to baseline (TTB), total contraction time (TCT), average strain velocity (strain velocity = peak strain/TTP) and average relaxation velocity (relaxation velocity = peak strain/TTB) in fasting and postprandial, with and without erythromycin. All values are given as median (minimum–maximum). Ery, erythromycin.

Early phase II3.1 (0.8–8.0)3.1 (0.6–8.4)7.1 (2.2–16.0)5.9 (1.5–40.5)7.3 (0.8–109.3)
Late phase II4.7 (1.6–8.9)5.5 (2.1–11.2)10.9 (5.0–14.9)14.3 (3.2–47.6)9.2 (3.9–49.5)
Phase III4.9 (2.0–10.2)5.5 (1.9–13.7)10.7 (4.4–21.0)16.6 (2.3–83.9)14.3 (2.0–54.8)
Postprandial4.5 (1.0–12.4)4.1 (0.4–12.3)10.0 (2.6–23.0)7.3 (1.7–29.2)9.5 (2.2–80.2)
Ery (fasting)4.4 (1.2–9.0)4.3 (1.9–12.0)10.3 (3.7–16.9)7.7 (2.8–350.1)7.6 (2.2–94.5)
Ery (postprandial)4.3 (1.7–15.2)4.6 (1.2–12.5)9.3 (3.1–27.4)6.7 (1.4–47.8)6.1 (1.7–182.6)
image

Figure 4.  Fasting and postprandial strain velocity: The plots show the median, interquartile range, outliers and extreme cases of individual variables of average strain velocity (strain %/TTP), both fasting and postprandial, with and without erythromycin. The significance level between the phases is shown. bsl00077, without erythromycin; □, with erythromycin; Ery, erythromycin.

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Configuration of the strain curve

Two-hundred and seven contractions (84.8%) had typical strain curve. In the fasting state, the frequency of atypical contractions was 11% without erythromycin and 25% with erythromycin (< 0.05). No significant difference was found in the postprandial state (10%vs 23%, = 0.079).

Characteristics of lumen-occlusive contractions

Lumen-occlusive contractions had higher strain values and strain velocity, as well as longer TTP (Fig. 5). Erythromycin induced more frequent lumen-occlusive contractions, both fasting (68.6%vs 48.5%, < 0.05) and postprandially (45.3%vs 5.2%, < 0.001). Females had more frequent lumen-occlusive contractions than those of males: 47/92 (51%) vs 51/152 (37%), < 0.01. The frequency of lumen-occlusive contractions gradually increased from early phase II to phase III activity (= 0.01) (Table 1). Of the weak-strain contractions, 21%, 54% and 69% were lumen occlusive in early phase II, late phase II and phase III respectively (< 0.01).

image

Figure 5.  Lumen-occlusive contraction: different aspects of lumen occlusive and non-lumen-occlusive contractions. Panels A, B and C show median strain values (%), strain velocity and time to baseline respectively.

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Gastric accommodation and emptying

Erythromycin reduced the total postprandial area of the proximal stomach (< 0.001) (Fig. 6A). The area of the proximal stomach returned to the fasting level at 20 min postprandial with erythromycin (mean: 12.5 ± 0.7 vs 7.2 ± 0.05 cm2, > 0.05), but not with placebo (16.9 ± 0.7 vs 7.3 ± 0.3 cm2, < 0.001), but it did at 40 min (mean: 10.2 ± 0.9 vs 7.3 ± 0.3 cm2, > 0.05). No difference in antral CSA with erythromycin and placebo was found. Nevertheless, antral CSA at 10 min postprandial was smaller with erythromycin than with placebo (mean: 5.2 ± 0.8 vs 7.2 ± 0.6 cm2, P < 0.05) (Fig. 6B).

image

Figure 6.  Postprandial proximal and antral areas: A: the area of the proximal stomach (cm2) fasting and at 1, 10, 20 and 40 min after the ingestion of 500 mL of a liquid test meal. Data are shown as mean ± SEM. P-values indicate the comparison between erythromycin and placebo at the same postprandial time. B: the antral cross-sectional area (CSA) in the same postprandial periods. P-values indicate the comparison between mean of placebo and erythromycin CSA. Data are shown as mean ± SEM.

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The inter- and intra-observer variation

The intra-observer variation of strain estimation was good (r = 0.991, < 0.001), with mean difference and limits of agreement: −4.8 ± 23.0%. The inter-observer variation was acceptable (r = 0.920, < 0.001), with mean difference and limits of agreement: 8.7 ± 65.1%.

Discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Conclusion
  8. Grants
  9. References

This study shows that radial strain in the anterior antral wall during contractions gradually increased from the beginning of phase II to reach a maximum in phase III, before quiescence appeared in phase I, confirming previous findings using manometry.25–27 In addition, we found that LSC occur both in phase II and phase III of the MMC as well as postprandially. In previous manometric studies, pressure waves below certain limits were considered as artefacts and hence, excluded from analysis.28 However, in another manometric study, small contractions creating microwaves were shown to exist in phase I and II of the MMC cycle.26 Manometry also detects contractions not necessarily taking place at the position of the pressure port,29 implying that low-strain contractions, often non-lumen occlusive, may have an additive effect on the global intra-gastric pressure, influencing the detected amplitude of the pressure waves.30 In this study, postprandial contractions did not differ from fasting phase II contractions in terms of strength, TTP, TTB and total duration (Fig. 3). Manometric studies have shown that postprandial contractions are weaker than fasting contractions.31,32 In this study, we found that fewer contractions are lumen occlusive after a meal than in fasting state (5.2%vs 48.5%). SRI is particularly valuable in the evaluation of such contractions, as they are unlikely to be detected by manometry.

There are several visualization modalities that have been used for the assessment of antral motor activity. Scintigraphy has been shown to be more sensitive than manometry in the detection of antral contractions, especially proximally, where these contractions are usually non-lumen occlusive.33 However, scintigraphy is associated with exposure to radiation and cannot be performed repeatedly. No published studies that compare MRI and scintigraphy with US are available. The advantage of MRI is its ability to assess the motor activity of both the proximal stomach and the antrum simultaneously.34 However, the temporal and spatial resolution of MRI has been considered insufficient for the detection of transient or small wall movements.34 An important limitation is the need for intraluminal contrast (meal) that often resides in the proximal stomach, since most MRI scanner operate on subjects in the supine position.35

Intravenous administration of erythromycin in phase I led to the induction of phase II like contractions. Other observations indicated that erythromycin induces phase III-like contractions.36 This can be explained by the finding that erythromycin induced more frequent lumen-occlusive contractions that are likely to be detected manometrically. SRI, however, showed that many of these contractions are of low- and medium strain. Erythromycin elicits more atypical contractions and it is possible that these contractions could be a form of premature contractions.

Generally, lumen-occlusive contractions had higher strain values than those of non-lumen-occlusive contractions (Fig. 5). However, some of these contractions had low strain values. Lumen-occlusive contractions with low pressure amplitudes as detected by manometry have been reported.29 In this study, we found that the frequency of weak contractions that induce lumen occlusion increases towards phase III.

SRI facilitates the study of individual antral contractions with spatial and temporal resolution not readily obtainable by other methods. Conventional US has been shown to be the most sensitive method for detecting antral contractions.29,31,37 Many antral contractions are non-lumen occlusive, while manometry which is considered as the gold standard for measurement of contractility, usually detects only lumen-occlusive contractions.29 Nevertheless, the SRI method has the same shortcomings as ultrasonography in general: adipose tissue and air within the lumen impair image quality. However, in our study, none had to be excluded for these reasons. The inter- and intra-observer were acceptable. The main drawback of SRI in studying gut motility is the inability to evaluate the progress of contractions along the gastrointestinal tract. Furthermore, only radial strain was measured in this study, while circumferential and longitudinal strain may be important in the clinical setting.

Erythromycin reduced the area of the proximal stomach, indicating impaired accommodation (Fig. 6A). Our finding confirms previous results showing that erythromycin inhibited accommodation to a meal.38 We also found that the antral CSA was significantly smaller at 10 min postprandially with erythromycin, as compared with placebo, indicating more rapid gastric emptying (Fig. 6B). This study showed no difference in the characterization of postprandial antral contractions after the ingestion of a liquid meal with erythromycin and placebo (Fig. 3 and Tables 1 and 2). However, the increased gastric emptying could partly be attributed to the increased frequency of lumen-occlusive contractions. These lumen-occlusive contractions had higher strain values, longer duration and higher strain velocities than those of non-lumen-occlusive contractions. The pulsatile emptying pattern of liquid meals was found to be associated with long-lasting, non-lumen occlusive proximal gastric contractions that become lumen-occlusive towards the antrum and pylorus.30 Strain velocity or the rate by which the proper muscle layer contracts radially, has not been reported before. Strain levels within the gastric wall and strain velocity are likely to influence the intraluminal flow dynamics and subsequently gastric emptying. Another factor that may contribute to the observed rapid gastric emptying is the reduced relaxation of the proximal stomach with erythromycin (Fig. 6). Previous studies have demonstrated that the proximal stomach is the main determinant of gastric emptying of liquid meals.39,40

We found that hunger sensations were strongly linked to phase III contractions. These hunger pangs were sensed as rumbling in the epigastrium and coincided with the presence of air in the antral lumen. Without referring to the MMC, which was not discovered at that time, Cannon and Washburn41 found an association between hunger pangs and gastric contractions. As the contractions in their experiment preceded the sensation, they suggested that the hunger sensation resulted from these contractions. This apparent difference in the temporal association between the contractions and the hunger pangs may be explained by the fact that Cannon and Washburn studied the contractions of the proximal stomach, while we observed antral contractions. Phase III contractions seem to move air within the gastric lumen, possibly from the proximal stomach to the antrum. This movement of air is sensed as rumbling and hunger pangs.

Conclusion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Conclusion
  8. Grants
  9. References

SRI is a non-invasive method that enables quantification of individual antral contractions with great details in terms of strain, duration and characteristics of phasic variations. SRI non-invasively identified the well-established pattern of the MMC. Erythromycin reduced gastric accommodation, increased gastric emptying and induced more frequent lumen-occlusive contractions. The sensation of hunger was associated with the presence of intraluminal air in phase III that was perceived as rumbling. SRI could be useful for studying motility disorders of the stomach.

Grants

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Conclusion
  8. Grants
  9. References

Aymen B. Ahmed was supported by a scholarship from the University of Bergen. The study was also supported by grants from the Innovest Strategic Research Programme, Haukeland University Hospital.

References

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Conclusion
  8. Grants
  9. References
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  • 3
    Barlow JD, Gregersen H, Thompson DG. Identification of the biomechanical factors associated with the perception of distension in the human esophagus. Am J Physiol Gastrointest Liver Physiol 2002; 282: G6839.
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    Drewes AM, Pedersen J, Liu W, Arendt-Nielsen L, Gregersen H. Controlled mechanical distension of the human oesophagus: sensory and biomechanical findings. Scand J Gastroenterol 2003; 38: 2735.
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    Gregersen H, Drewes AM, Gilja OH. Tension receptors: theoretical construct or fact? Gastroenterology 2005; 128: 8034.
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    Petersen P, Gao C, Arendt-Nielsen L, Gregersen H, Drewes AM. Pain intensity and biomechanical responses during ramp-controlled distension of the human rectum. Dig Dis Sci 2003; 48: 13106.
  • 8
    Gilja OH, Heimdal A, Hausken T et al. Strain during gastric contractions can be measured using Doppler ultrasonography. Ultrasound Med Biol 2002; 28: 145765.
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