SEARCH

SEARCH BY CITATION

Keywords:

  • bowel preparation;
  • colon;
  • manometry;
  • motility;
  • propagating sequence

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Financial support
  8. References

Background  Colonic manometry is performed using either colonoscopically assisted catheter placement, after bowel preparation, or nasocolonic intubation of the unprepared bowel. There has been little systematic evaluation of the effects of bowel cleansing upon colonic propagating pressure wave sequences.

Methods  Eight healthy volunteers underwent nasocolonic placement of a water-perfused silicone catheter which recorded pressures at 16 recording sites each spaced 7.5 cm apart in the unprepared colon for 24 h. These measures were compared with those obtained in another eight healthy volunteers in whom the catheter was placed to the caecum at colonoscopy in the prepared colon.

Key Results  The colonic motor responses to meals and morning waking, and the normal nocturnal suppression did not differ between the two groups, nor were the overall frequency, regional dependence nor extent of propagating sequences (PS) influenced by bowel preparation. Bowel preparation did result in a significant increase in the frequency of high amplitude PS (22 ± 7 vs 8 ± 4 HAPS/24 h; = 0.003). Additionally, a number of the measures of spatiotemporal organization among consecutive PS (linkage among sequences and predefecatory stereotypical patterning) were significantly altered by bowel preparation.

Conclusions & Inferences  The overall frequency of PSs, the colonic responses to physiological stimuli such a meal and morning waking and nocturnal suppression, are not influenced by prior bowel preparation. However, investigators wishing to study HAPS frequency, or the more complex spatiotemporal relationships among consecutive PSs, should control for bowel preparation when making comparisons among study groups.


Abbreviations
HAPS

high amplitude propagating sequence

PS

propagating sequence

Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Financial support
  8. References

Assessment of pan-colonic (caecum to rectum) motor function is fundamental both to our understanding of the physiology of the large bowel,1 and may be important in helping to elucidate the pathophysiological mechanisms underlying disorders such as constipation.2 Two techniques have been developed for the recording of pan-colonic manometry: retrograde placement of the catheter, via the anus with the aid of a colonoscope;3–5 antegrade placement of a catheter via the nose;2,6 or a combination of both.7 Nasocolonic catheter placement into the unprepared colon is appealing as it achieves recording conditions closer to the true physiological state with stool in situ. However, antegrade placement requires peristaltic propulsion to progress the catheter tip, and, while this technique is feasible in healthy controls and patients with relatively normal transit,2 the technique is not suitable for use in patients with severe colonic dysmotility (e.g. slow transit constipation). Consequently, almost all colonic manometric studies performed in patients with bowel disorders have used retrograde catheter placement and, due to technical limitations, those recordings have usually been limited to sites distal to the hepatic flexure.8–17 If we are to move closer to achieving a meaningful, cost- and time-effective colonic manometric clinical test, and if it is likely that such a test will involve colonoscopic catheter placement, then it is crucial to understand whether prior bowel cleansing influences any of the manometric measures that might represent pathological markers of subtypes of constipation. Clarification of the impact of bowel preparation, if any, on colonic motor activity is also fundamental to permit comparison among studies adopting different manometric techniques.

To date the effect of bowel cleansing upon colonic contractile activity remains unclear. Dinoso et al. reported no apparent change with bowel preparation in the distal colon.18 Conversely, Lémann et al., who recorded motor activity over 60 cm from the ascending colon, demonstrated an increase in frequency of high amplitude propagating contractions (also termed high amplitude propagating sequences, HAPS) in the prepared colon of healthy volunteers.19 This supports previous work from Sarna, who showed an increase in the frequency of giant migrating contractions (canine counterpart to human HAPSs) in the cleansed bowel of strain-gauge instrumented dogs.20 However, no previous study has been able to detail the effect of bowel preparation on true pan-colonic motility. Furthermore, the influence of bowel cleansing on contractile phenomena other than HAPSs, such as antegrade and retrograde propagating sequence (PSs) frequency6 and spatiotemporal organization,21 the colonic meal response,22,23 and stereotypic predefecatory motor patterns24 have never been reported. Our aim in this study, by making pan-colonic manometric recordings with the two established methodologies, was to determine the impact, if any, of prior bowel preparation on the frequency, morphology and spatiotemporal organization of colonic PSs.

Methods

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Financial support
  8. References

Subjects

This study was carried out in two separate locations: (i) the St George Hospital, Sydney, Australia, where nasocolonic intubation and recording of colonic motility in the unprepared bowel was performed in eight healthy controls (two male; mean age: 24 ± 2) and (ii) The Royal London Hospital, London, UK, where colonoscope-assisted placement of the catheter into the prepared bowel was performed in eight subjects (all female; mean age 37 ± 11). Some data from the controls undergoing antegrade placement has been published previously.2,6,21,24

All healthy subjects had a normal bowel habit, defined as between three bowel movements a day and one bowel movement every 3 days, with no symptoms of rectal evacuatory difficulty. None were taking regular medications including laxatives, and none had a history of prior abdominal surgery, other than appendicectomy. All participants had given written, informed consent and the studies were approved of in Australia by the Human Ethics Committees of the South Eastern Area Health Service, Sydney and the University of New South Wales, and in London by the Redbridge & Waltham Forest Local Research Ethics Committee.

Colonic manometric techniques

Nasocolonic placement into the unprepared colon  Placement of nasocolonic catheters has been described in detail previously.6,24 Briefly, a 4.5-m long extruded silicone perfused manometric assembly (Dentsleeve, Wayville, SA, Australia) was employed. The catheter contained 16 recording sites spaced at 7.5 cm intervals from the tip, and was rendered radio-opaque with a barium core; overall diameter was 3.5 mm. A silicone balloon attached to the tip of the catheter could be inflated with water to facilitate transit through the small bowel and colon. Prior to the commencement of recording the location of the catheter tip was confirmed fluoroscopically and in all subjects presented here the catheter tip was at or beyond the sigmoid colon. The position of the catheter was checked again at the end of 24 h recording. Total fluoroscopy time was 30–90 s, and the maximum whole body effective radiation dose equivalent was 0.8–2.4 mSv. Recording commenced at 14:00 hours on day 2, and continued for 24 h, finishing at 14:00 hours on day 3.

Colonoscopic placement into the prepared colon  Placement of catheters using colonoscopy has been described in detail previously.5 Briefly, on the day prior to the catheter insertion, subjects were given a clear fluid diet. Volunteers underwent colon preparation by oral administration of two bisacodyl tablets and 250 mL magnesium citrate. On day 1, after an overnight fast, and under conscious sedation with intravenous fentanyl, midazolam and hyoscine, a catheter of the same configuration as that used for nasocolonic placement was advanced to the caecum under colonoscopic guidance, pulled by a nylon loop held in an endoscopic snare. Once the caecum had been intubated, the nylon loop on the catheter tip was secured to a caecal fold using two haemoclips (Olympus America, Melville, NY, USA).5,25 After recovery from sedation, all subjects were transferred to a private room where they slept overnight. A standard meal was given at 18:00 hours. Recording commenced at 08:00 hours (day 2), approximately 22 h after intubation, to allow for washout of drugs. Recording was continued for 24 h.

Experimental protocol

Subjects ate standard meals at 09:00 hours (breakfast: 300 kcal, 15% protein, 34% fat, 51% carbohydrate) and at 12:00 and 18:00 hours (lunch and dinner: 1000 kcal, 24% protein, 43% fat, 33% carbohydrate). The colonic meal response was derived from the lunchtime meal (day 2, prepared bowel group; day 3, unprepared bowel group). Subjects were instructed to refrain from eating between meals, and were encouraged to consume each meal within 20 min.

During the daytime, subjects were told not to sleep, and either sat semi-erect in bed, or in a chair, where they were allowed to read, watch television, or use a personal computer. If defecation occurred, subjects used a commode, but remained attached to the recording system. The time of this activity was recorded.

Manometry equipment

For both groups of volunteers, each catheter lumen was perfused with distilled water. A low compliance pneumohydraulic perfusion pump drove the perfusate at 0.15 mL min−1 (Dentsleeve). We have previously demonstrated that the rise-rate characteristics afforded by a catheter of this nature is adequate for recording colonic pressure waves.24 At St George Hospital, pressures were measured with 16 external pressure transducers (Abbott Critical Care Systems, North Chicago, IL, USA), with recorded signals being amplified and digitized at 10 Hz by preamplifiers (AqcKnowledge III Software; BIOPAC Systems, Inc. Santa Barbara, CA, USA). In London, this was achieved in the same fashion through a customized modular manometric system (Solar Measurement System, software version 8.7b; Medical Measurement Systems, Enschede, the Netherlands).

Data analysis

To remove the chance of inter-observer variation in the labeling of PSs and HAPSs, the principal author carried out the final analysis of data sets from both control groups. The principal investigator also conducted the first studies in the UK with the London group to ensure that study performance was equivalent to that carried out in Australia.

Definition and identification of propagating sequences  For the purpose of analysis, the colon was divided into 16 regions (region 1 = caecum, region 4 = hepatic flexure, region 8 = splenic flexure, region 12 = proximal sigmoid colon, region 16 = rectum).24 Recording side holes were assigned to the colonic region within which they lay. For the unprepared colon, allocation of recording sites to colonic regions has been described in detail previously.6,24 For the prepared colon, side hole 1 was always in region 1 as it was clipped to the caecum; allocation of the other side holes to colonic regions was performed in the same manner as in the unprepared colon.

Definitions of PSs and HAPSs have also been described in detail previously.6,24 Briefly, a PS was defined as an array of three or more pressure waves recorded in adjacent recording sites in which the conduction velocity between wave onset within that sequence lay between 0.2 and 12 cm s−1. Propagating sequences were further qualified by the terms antegrade or retrograde, depending upon the direction of propagation. A PS was classified as a HAPS, if the amplitude of at least one component propagating pressure wave was >116 mmHg (derived from normal mid-colonic mean amplitude + 2SD recorded in the healthy unprepared colon).6,24 In the first stage of analysis, all PSs and HAPSs were grouped based upon polarity (i.e. antegrade or retrograde). In secondary analysis, HAPS were removed from the data set and dealt with as a separate entity. Those PSs that were not classified as HAPSs were classified as ‘low-amplitude’ PSs.

Colonic response to a 1000-kcal lunch  The 2-h epoch prior to and after the 1000-kcal meal was divided into four 30 min periods. In each of these periods, the HAPS frequency and the retrograde and antegrade PS frequency, velocity, amplitude and extent of propagation were detailed.

Diurnal variation in propagating sequence frequency  The PS frequency per hour in the 8 h epoch between 22:00 and 06:00 hours (nocturnal period) was compared to the frequency per hour between 14:00–22:00 and 06:00–14:00 hours. These epochs were chosen because they matched the epochs used in previous analyses.6

Spatiotemporal organization of antegrade and retrograde propagating sequences  Recently, we have described and validated a technique that examines the relationship among sequential PSs throughout the colon over the 24-h period.21 We have coined the term ‘regional linkage’ to define this relationship. A PS was deemed regionally linked to the PS immediately preceding it if the two PSs originated from different colonic regions but the segments of colon traversed by each PS overlapped. As we have shown previously that retrograde PSs do not display any spatiotemporal organization,21 the regional linkage was only assessed between sequential antegrade PSs.

Spatiotemporal organization of predefecatory PSs  Previously, we defined the predefecatory organization of PSs in healthy volunteers.24 In the 20-min period prior to stool expulsion, three or more PSs were consistently identified. These final three PSs displayed a distal to proximal colonic regional shift in the site of origin leading up to defecation. The association between this stereotypic pattern and episodes of defecation was examined in both groups.

Statistical analysis

A Mann–Whitney U test was used to examine direct comparisons between all PS, low-amplitude PS and HAPS characteristics (frequency, amplitude, velocity, site of origin and extent of propagation) between the prepared and unprepared colon groups. The comparisons between these variables were made for the total colon and for the right colon (ascending and transverse colon) and left colon (descending and sigmoid colon). The same test was used to compare the regional linkage that existed between the two control groups. Comparisons between the basal and postprandial PS characteristic within subjects was performed using a paired t test. Comparisons between the delta values (basal – postprandial) between the prepared and unprepared groups were performed using the Mann–Whitney U test. Chi-squared analysis was used to compare the number of episodes of stool expulsion associated with the stereotypic predefecatory pattern of PSs in each group. Where appropriate the coefficient of variation (CV) is provided to give an indication of variability that exists within certain measured parameters. Data are expressed as mean ± SD, apart from frequency of defecation, which is expressed as median and range. A P value of less than 0.05 was considered statistically significant.

Results

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Financial support
  8. References

All subjects completed the study without complication. Catheter position was maintained in all. In the prepared colon group, resistance encountered to traction during the extubation process confirmed that the catheter remained clipped to the caecal mucosa.

Antegrade propagating sequences

Overall, the mean amplitude of PSs was significantly increased in the prepared colon [70 ± 13 (CV; 19%) vs 46 ± 10 (CV; 22%) mmHg; = 0.004: Table 1, Fig. 1]. The total and regional colonic frequency, velocity and site of origin and extent of propagation of PSs did not differ between the prepared and unprepared bowel (Table 1, Fig. 2). In both groups, PSs originated with a significantly greater frequency in the right than left colon (< 0.001, Table 1, Fig. 2). The extent of propagation of PSs originating in the left colon of both groups was significantly greater than the extent of propagation of PSs originating in the right colon (Table 1; Fig. 1)

Table 1.   Antegrade and retrograde propagating sequence characteristics
 PreparedUnprepared
Right colonLeft colonTotal colonRight colonLeft colonTotal colon
  1. PS, propagating sequence.

  2. For ease of presentation P values between 0.002 and 0.01 are represented as P < 0.01. All other P values are represented as P < 0.001.

  3. *A significant difference (P < 0.01) between the left and right colon within subjects. †A significant difference (P < 0.01) between antegrade and retrograde characteristics within subjects for the same region. ‡A significant difference (P < 0.01) between subject groups for the same region.

Antegrade PS
 Frequency (per 24 h)58 ± 36*38 ± 3092 ± 6040 ± 9*,†21 ± 10†62 ± 7†
 Velocity (cm s−1)1.5 ± 0.51.7 ± 0.41.6 ± 0.41.5 ± 0.31.4 ± 0.41.4 ± 0.3
 Amplitude (mmHg)62 ± 14*,†,‡82 ± 18†,‡70 ± 13†,‡47 ± 18†47 ± 25†46 ± 10†
 Extent of propagation (cm)34 ± 6*,†21 ± 229 ± 5†40 ± 6*,†24 ± 433 ± 5†
Retrograde PS
 Frequency (per 24 h)13 ± 1215 ± 1727 ± 245 ± 512 ± 1117 ± 10
 Velocity (cm s−1)1.4 ± 0.41.4 ± 0.41.4 ± 0.31.5 ± 0.62.5 ± 1.81.9 ± 1.2
 Amplitude (mmHg)29 ± 534 ± 832 ± 626 ± 924 ± 625 ± 6
 Extent of propagation (cm)18 ± 320 ± 319 ± 326 ± 522 ± 622 ± 5
image

Figure 1.  Regional variation in the amplitude of antegrade propagating sequences (PSs), high amplitude propagating sequence (HAPS) and low-amplitude propagating sequences. The histogram shows the amplitude of all propagated pressure waves identified at each colonic region. In the prepared colon, the amplitude of propagating pressure waves is significantly increased (= 0.004). The hatched lines indicated the amplitude of component pressure waves in the HAPSs. The amplitude of the HAPSs is also significantly increased (= 0.001) in the prepared colon. The colored solid lines represent the amplitude of all of the remaining PSs (low-amplitude PSs) once the HAPSs have been removed from the data set. Note there is no difference in the amplitude of low-amplitude PSs between the two groups.

Download figure to PowerPoint

image

Figure 2.  Regional variation in the frequency of initiation and extent of propagation of antegrade propagating sequences (PSs). The histogram at the bottom shows the distribution of antegrade PSs grouped according to the site of origin. The horizontal bars at the top show the mean extent of propagation by sequences originating at the same site. Note that in both groups, PSs originate significantly (< 0.001) more frequently in the proximal than in the distal colon. The extent of propagation of PSs is greater for sequences originating in the proximal colon in both groups. The extent of propagation differs between groups in the caecum only. PSs originating in the caecum of the unprepared colon extent further (= 0.01) than those originating in the same region in the prepared colon. The solid lines are proportional to the propagating sequence frequency (histograms shown at the bottom) and indicates that the ‘density’ of component pressure waves is highest between the splenic flexure and distal descending colon and lowest at the extremities of the colon.

Download figure to PowerPoint

Retrograde propagating sequences

The retrograde PS frequency, velocity, amplitude and site of origin and extent of propagation did not differ between the two groups (Table 1).

High amplitude propagating sequences

In the prepared colon group, there was a significant 2.5-fold overall increase in HAPS frequency [22 ± 7 (CV; 33%) vs 8 ± 4 (CV; 50%) HAPS/24 h; = 0.003, Table 2], and HAPSs overall were also of a significantly greater amplitude [126 ± 20 (CV; 16%) vs 90 ± 17 (CV; 19%) mmHg; = 0.001; Table 2, Fig. 1]. Notably, the extent of propagation of HAPSs originating in the ascending colon was significantly reduced in the prepared bowel (= 0.005; Table 2). In both groups, 44% of HAPSs originated in the ascending colon, and >75% originated proximal to the splenic flexure.

Table 2.   High amplitude propagating sequence characteristics in the prepared and unprepared colon
 PreparedUnprepared
Right colonLeft colonTotal colonRight colonLeft colonTotal colon
  1. HAPS, high amplitude propagating sequence.

  2. For ease of presentation P values between 0.002 and 0.01 are represented as P < 0.01.

  3. *A significant difference (P < 0.01) between the left and right colon within subjects. †A significant difference (P < 0.01) between subject groups for the same region.

HAPS
 Frequency (per 24 h)19 ± 5*,†3 ± 2†22 ± 7†6 ± 42 ± 28 ± 4
 Velocity (cm s−1)1.1 ± 0.2*1.5 ± 0.31.3 ± 0.30.8 ± 0.31.3 ± 0.61.1 ± 0.3
 Amplitude (mmHg)101 ± 20*,153 ± 26†126 ± 20†83 ± 2394 ± 2490 ± 17
Extent of propagation (cm)47 ± 8*†24 ± 338 ± 665 ± 13*28 ± 850 ± 15

Low amplitude propagating sequences

There were no differences with regard to frequency, amplitude, velocity or extent of propagation of ‘low-amplitude’ PSs between the two groups (Fig. 1).

Colonic meal response

In both groups, a 1000-kcal meal induced a significant increase in HAPS frequency compared to the basal period immediately preceding it (prepared: 1 ± 1 vs 4 ± 2; = 0.01; unprepared: 0.3 ± 0.7 vs 2 ± 1; = 0.005). Comparison of the delta values (HAPS basal – HAPS postprandial) showed no difference between the two groups, indicating that the meal response was similar between the groups. The increase in HAPSs was not specific to any particular 30 or 60 min epoch postprandially. The meal had no effect upon low amplitude PS characteristics in either group.

Diurnal variation in propagating sequence frequency

In both groups, there was a twofold decrease in the PS frequency during the nocturnal period (prepared: 5 ± 3 vs 2 ± 2 PS/h, = 0.03; unprepared: 3 ± 1 vs 1 ± 1 PS/h, = 0.01). A comparison of the delta values (day frequency – nocturnal frequency) indicated no significant difference between the groups.

Spatiotemporal organization of antegrade and retrograde propagating sequences

The proportion of antegrade PSs that showed spatiotemporal organization21 was significantly reduced in the prepared colon. Of all antegrade PSs, 82 ± 9% were regional linked in the unprepared bowel, compared to only 57 ± 9% (< 0.001) in the prepared colon.

Defecation and spatiotemporal organization of predefecatory PSs

Defecation frequency was significantly increased in the prepared bowel compared to the unprepared (2.8 ± 0.7 vs 1.2 ± 0.5 bowel motions/24 h; = 0.006). Overall, 21 episodes of defecation, at which mostly watery stool was expelled, were recorded in eight subjects with a prepared bowel (one volunteer was excluded from defecation analysis, as it was unclear from their diary entries if they had opened their bowels or simply urinated), compared to 10 episodes of defecation in the unprepared bowel group. Stool consistency in the unprepared bowel did maintain some form, although was generally described as ‘very soft’. Interestingly, none of the volunteers in the prepared colon group defecated during the first 22 h after placement of the catheter when no water infusion occurred.

Overall, PSs were associated with all but one episode of defecation (in a subject after bowel cleansing), with 60% classified as HAPSs in the prepared bowel group, and 63% in the unprepared bowel group (= NS). In addition, the number of HAPSs or PSs associated with each bowel movement was similar between both groups. However, the stereotypic pattern of PSs prior to stool expulsion was only evident in 5 of the 21 episodes (23%) of defecation in the prepared group, compared to 9 of 10 episodes (90%) in the unprepared group (= 0.001; Fig. 3).

image

Figure 3.  Spatiotemporal maps32 of colonic propagating sequences (PSs) in the 20-min period prior to stool expulsion in three subjects within the prepared and unprepared groups. In every map, each individual ridge represents an antegrade PS. The start of each ridge indicates the site of origin and the time of day the PS occurred. The length of the ridge indicates the extent of propagation. The shading within the ridge indicates the amplitude of the component pressure waves. The hatched arrows link the site of origin of sequential PSs. In the unprepared colon there is a stereotypic distal to proximal shift in the site of origin of the final three PSs prior to stool expulsion. Note that this pattern is not evident in the prepared colon.

Download figure to PowerPoint

Discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Financial support
  8. References

The major findings of this study are that prior bowel preparation can influence the characteristics of some colonic manometric parameters. On the other hand, a number of fundamentally important and reproducible colonic motor responses in which PS feature prominently, as well as overall PS frequency, are not influenced by bowel preparation. Hence, when studying overall PS characteristics (frequency, extent, polarity and velocity), or the augmentation of colonic PSs in response to a meal or to morning waking, or the nocturnal suppression of PSs, investigators could make valid comparisons between data derived from the prepared and unprepared colon and, within limits, comparable data derived from different laboratories. However, a number of parameters that define individual PSs such as HAPS (also called HAPC19) frequency (i.e. amplitude), and the relationships among consecutive PSs such as linkage, and predefecatory stereotypical patterning, are influenced by bowel preparation. If these specific parameters are of primary interest in a particular study, then these specific measures must be compared not only with normative data derived using comparable catheters and experimental conditions, but investigators should also control for the impact of bowel preparation on them.

The vast majority of colonic manometric studies have adopted colonoscopically assisted catheter placement. The necessary prior bowel preparation potentially adds an unphysiological confounder to the acquired manometric data. Our findings confirm previous reports in humans and dogs that bowel cleansing increases the frequency of HAPSs.19,20 The factors that initiate colonic PSs are incompletely understood.4,26 It is likely that the composition, volume, and physical and chemical properties of colonic content all play a role. For example, short chain fatty acids are thought to modulate colonic motility,27 and colonic elongation induced by fecal loading is reported to slow transit by inhibiting propulsive contractile activity.28

Clearly linked to the preparation related increase in HAPSs is our finding that bowel preparation significantly increased the amplitude of these propulsive motor patterns. One possible explanation for this might be that intraluminal content has a ‘damping’ effect upon, and thereby the magnitude of the pressure wave recorded from, the lumen-occluding contraction in that segment of colon. This would be particularly relevant in the left colon, where the more viscous and semi-solid stool is normally present, and where in the prepared bowel we recorded the greatest increase in amplitude. Given the overall increase in pressure wave amplitude following bowel preparation, it is not surprising that the frequency of HAPSs is increased. Indeed our original criterion for HAPSs was a PS with a least one-component pressure wave that exceeded 116 mmHg. This value being the mean + 2SD of the pressure wave amplitude in mid-colon in the unprepared bowel of healthy controls.24 In the present study, there was a greater proportion of pressure waves exceeding that amplitude. If, however, we re-calculate the mean amplitude (+2SD) of propagating pressure wave at the level of the mid-colon in the prepared colon, we attain a value of 170 mmHg. If this were used to define HAPSs in the prepared colon, the frequency of HAPSs would be reduced to 14.6 ± 6.9 HAPS/24 h (data not presented); this value does not differ significantly from HAPS frequency in the unprepared bowel. This fact clearly highlights problems inherent to comparing data recorded by different techniques.

We have shown that bowel preparation does impact the spatiotemporal patterning among consecutive PSs throughout the colon over a 24-h period. We have hypothesized previously that the regional linkage between sequential antegrade PSs assists with continuity of flow.21 The fact that regional linkage was significantly reduced in the prepared colon indicates that colonic content directly influences the organization of pan-colonic PSs. Further evidence for this was apparent in the final 20-min period immediately prior to defecation. Although predefecatory PS and HAPS frequency was equivalent between groups, the distal to proximal regional shift in the site of origin of PSs leading up to defecation24 (the stereotypical predefecatory motor patterns) was mostly absent in the prepared bowel group.

We observed a significant increase in stool frequency in subjects with a prepared colon. The reason for this is not immediately apparent. This increase is unlikely to be explained purely by the volume or temperature of water infused, as these were identical for both groups. However, as episodes of defecation were only observed after commencement of catheter perfusion (i.e. not during the 22-h period immediately following intubation), it maybe that the distribution of the instilled water differs significantly in a full vs empty colon. In the cleansed bowel, fluid may collect more distally resulting in a direct stimulatory effect. It is also feasible that bowel preparation per se may sensitize the colon to water perfusion. However, as the recording commenced approximately 40 h after purgatives were administered, it is unlikely that these physical and chemical agents had any impact upon the recorded data. Similarly, it is extremely unlikely that short-acting drugs used during colonoscopy had any enduring effect. While, conclusions drawn from these data can be reliably attributed to the effect of bowel preparation (with its obligatory intraluminal physical and chemical and potential pharmacological influences) the validity of our conclusions in respect of stool content per se is less certain.

There are obvious potential criticisms with this study. These include the lack of within subject comparison, age, gender, and possibly ethnic and geographic differences, as well as differences in dietary and bowel habits between Australia and the UK. While within subject comparisons, preferably within the one institution, would have been desirable, this was not possible, due to inability to recruit those subjects who had undergone nasocolonic manometry previously and the inability of NSW Health Department to allocated resources to cater for lengthy inpatient physiological studies on healthy humans. Similarly, age- and sex-matched control groups could have made for a stronger study; nevertheless, it is unlikely that these factors could account for the differences noted between groups. To our knowledge there are no published data suggesting such differences, nor have we observed any in nearly 20 years of recording colonic manometry in our own laboratory. Indeed, epidemiological studies have shown that stooling habits do not differ in the healthy elderly,29 and that there are no convincing effects of age alone on colonic transit if the effects of co-morbidity and inactivity are accounted for.30,31 It is also highly unlikely that diet, bowel habits or ethnic differences can account for the differences. Test meals were strictly standardized in both groups. By chance, 80% of the volunteers recruited in Australia were backpackers from England or Europe and were therefore of similar ethnicity. Finally, there is no biological plausibility for any of the above factors affecting the specific PS characteristics noted here. As an increase in HAPS frequency, attributed to bowel preparation has been previously reported in a study using within subject comparisons,19 it would seem unlikely that the same finding in the present study resulted from different patient cohorts and not from the removal of stool from the colon.

In summary, colonic motor responses to commonly assessed physiological stimuli such meals and morning waking are not influenced by bowel preparation. Therefore such responses could be compared in a valid way, among different studies within a laboratory or (within limits) among different laboratories. There are however, a number of quantitative and qualitative parameters that define individual PSs (e.g. HAPS frequency and PS amplitude) and the spatiotemporal organization among consecutive PSs that are influenced by bowel preparation. If these specific parameters are of primary interest in a particular study, then data must be compared with normative data derived using comparable catheters and experimental conditions, including controlling for bowel preparation.

Financial support

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Financial support
  8. References

Dr Phil Dinning was supported by NHMRC Australia. Dr Michal Szczesniak was supported by Gastroenterological Society of Australia Biomedical scholarship.

References

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Financial support
  8. References