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Original Articles: Gastroenterology

Influence of Esophageal pH Recording on Physical Activity in Children

Michaud, Laurent*; Troadec, Françoise*; Béghin, Laurent*,†; Rifai, Nahida El*; Guimber, Dominique*; Turck, Dominique*; Gottrand, Frédéric*,†

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Journal of Pediatric Gastroenterology and Nutrition: April 2009 - Volume 48 - Issue 4 - p 426-430
doi: 10.1097/MPG.0b013e31817f2827
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Twenty-four-hour pH-metry is considered the gold standard for diagnosis of gastroesophageal reflux (GER) in children (1). In addition to reducing the social-familial and financial constraints associated with hospital procedures, ambulatory esophageal pH recording has the advantage of a smaller impact on a patient's lifestyle and provides a better reflection of occurrences under normal living conditions (meals, sleep, physical activity) (2–4). Recently, the development of a miniaturized device for pH monitoring has made it possible to perform pH-metry in the home environment. Nevertheless, the necessity of carrying this equipment may alter the daily habits of children and therefore reduce their physical activity. The aim of our study was to assess the influence of pH-metry at home on the physical activity of children.


This prospective study included children 3 to 15 years old who were referred for 24-hour pH-metry for suspected GER. Patients with severe chronic disease that could alter physical activity (cystic fibrosis, chronic respiratory failure, motor impairment) and those with mental retardation that could alter the assessment of physical activity were excluded from the study.

Before the procedure, probes (2.8-mm diameter monocrystal antimony multiuse pH electrodes) were calibrated at pH 1.0 and pH 7.0 using appropriate buffers and then introduced transnasally under morning fasting conditions with or without sedation. Sedation was induced in anxious or agitated patients with a mixture of nitrous oxide and oxygen delivered by face mask.

The electrode was connected to an ambulatory recorder pH meter (NL, Orion, Medical Measurement System, BV, Enschede, the Netherlands) weighing 260 g. This was kept in a back bag or carried over the shoulder on the day when pH was monitored. No restriction of physical activity during esophageal pH recording was advised, but swimming and other water activities were contraindicated.

Physical activity was measured with a triaxial accelerometer (type RT3, Stayhealthy, Elkader, IA) that weighed 60 g and measured 12 × 6.5 × 2.2 cm. This device measures acceleration in 3 individual planes and integrates data into 1 value, called vector magnitude (square root of the sum of activity counts in each direction), which is expressed in counts per minute. Data were transferred to Microsoft Excel by use of the Stayhealthy software. The length of time spent in a motorized vehicle was deduced because activity data during these periods could not be differentiated from data arising from the movement of the vehicle.

The physical activity of each child was measured twice: first on the day of pH-metry and later on the same day of the week 7 days before or after the procedure, in random order. All of the children underwent a clinical examination on the day of physical activity assessment to establish that their clinical status was stable and that no intercurrent illness (eg, cold, influenza) could interfere with physical activity. The duration of physical activity measurement was synchronized with the duration of pH-metry and was identical for the 2 periods. We considered that on the day of the pH-metry, the children went to the hospital for probe positioning and that this could induce a bias in comparison with the control period, when the child had no pH-metry. We therefore decided to delete the corresponding period of transportation (the day of the pH-metry) from the recording without pH-metry.

There are no defined published cutoff points for determining levels of activity in children using the RT3 device. To study the influence of esophageal pH recording on the physical activity levels in our population, we first studied 12 healthy children matched for age and sex to the patients. The physical activity of the healthy control children was measured with the R3T accelerometer for 1 hour as follows: the first 20 minutes was designed to record low-level physical activity (watching television, playing video games, reading) with the child in a semisupine or supine position; moderate physical activity (walking) was recorded during the subsequent 20 minutes, and high-level physical activity (running, cycling, other sport activities) was recorded during the last 20 minutes. Accordingly, we defined 3 levels of physical activity as follows: low, 0–200 counts/min, moderate, 201–2000 counts/min, and high, >2001 counts/min.

The physical activity and anthropometric data are expressed as means plus standard deviations and are presented as boxplots. The nonparametric Mann-Whitney test and the paired Wilcoxon test were used to compare variables. The Spearman test was used to test correlations between quantitative variables. P < 0.05 was considered significant. After approval by the ethics committee of our university hospital, informed written consent was obtained from the parents of all patients included in the study.


Thirty-four patients were eligible to enter the study. Data from 12 patients were excluded because of noncompliance with the study protocol (n = 3), technical problems during assessment of physical activity (n = 7), or omission of information regarding the use of motor vehicles (n = 2). Twenty-two patients (18 boys and 4 girls) completed the study (mean age 6.9 ± 2.3 years). Those included in the study did not differ from those who had been excluded with regard to age, weight, or indication for pH-metry assessment. Indications for pH-metry were chronic cough (n = 9), recurrent upper respiratory tract infection (n = 3), asthma (n = 5), laryngitis (n = 1), recurrent vomiting (n = 1), epigastric pain (n = 1), and previous surgical treatment for peptic esophageal stenosis (n = 1).

The mean duration of ambulatory pH-metry was 21 hours, 27 minutes. Of the 22 patients, 12 had GER (defined as a reflux index >5%) during pH-metry. Table 1 summarizes the physical activity values with or without pH-metry. Physical activity was 53% lower on the day of pH-metry than on the day without pH-metry (P < 0.0001). Physical activity decreased in 21 of the 22 patients. In only 1 instance was daily physical activity in the presence of pH-metry identical with that in the absence of pH-metry (Fig. 1). The mean duration of low-level physical activity was significantly higher on the day of pH-metry than on the day without pH-metry: 84% (range 70%–97%) vs 73% (range 57%–85%) (P < 0.0001; Fig. 2).

Intensity of physical activity in 22 patients in the presence or absence of pH-metry
FIG. 1:
Physical activity assessed by triaxial accelerometry in 22 patients in the presence or absence of pH-metry under domestic living conditions.
FIG. 2:
Boxplot showing duration at different levels of physical activity.

The durations of moderate and intense physical activity were significantly lower on the day of pH-metry than on the day without pH-metry. Duration was 16% (range 3%–29%) versus 24% (range 11%–42%; P < 0.005) for moderate activity and 0.2% (range 0%–3.2%) versus 2.2% (range 0%–13.5%; P < 0.0001) for intense activity (Fig. 2).

During ambulatory pH-metry, patients spent 11.3% more time in low-intensity physical activity than on the day without pH-metry, 8.5% less time in moderate-intensity physical activity, and 2% less time in high-intensity physical activity. The pH monitoring was performed during holidays for 7 children and during weekends for 3 children. For all 10 children, the control physical activity measurement (the day without pH-metry) was also performed during holidays or weekends. Only 1 patient attended school during pH-metry and the day of the control physical activity measurement. Ten patients attended school on the day of the control physical activity measurement, whereas on the day of pH-metry, their parents decided to keep them out of school. For 1 patient, no information was available concerning school activity.

There was no significant correlation between reduction in daily physical activity during pH-metry and age (P = 0.4), sex (P = 0.7), or weight (P = 0.9). The reduction in daily physical activity was more pronounced in patients who had a high baseline physical activity (r = 0.8, P < 0.002; Fig. 3). The daily physical activity of children with GER (n = 12) was similar to that of children without GER (237 ± 79 counts per minute vs 280 ± 69 counts per minute, NS).

FIG. 3:
Correlation of physical activity during pH-metry with normal daily physical activity.


Our study showed that 24-hour esophageal pH recording, even when performed under ambulatory conditions in an environment conducive to the maintenance of the habitual lifestyle of children, reduces physical activity substantially (by >50%). The relative amount of low-level physical activity increased during pH-metry, and the relative amount of moderate- and high-level physical activity decreased accordingly. Although some studies suggest that ambulatory esophageal pH recording reduces physical activity (4–8), we were unable to find a study quantifying this effect.

We were surprised that our sample included more boys than girls because this does not reflect the pattern in our clinic or the prevalence of GER in the general population. More girls and their parents refused to participate in the study, and the boys were more enthusiastic about wearing the device in free-living conditions. We do not know whether this underrepresentation of girls biased our results, but we observed no apparent difference in the physical activity patterns or variation between boys and girls.

Accelerometry is a valid, reproducible, and noninvasive diagnostic tool for children. Accelerometry facilitates the objective and prolonged assessment of physical activity (9–17) by recording the time spent at each level of activity. Day-to-day variability in the physical activity level occurs in children and could be a confounding factor in our study. To limit this possible confounder, we studied the children on the same day of the week (excluding weekends) with and without pH monitoring, in a random order, to standardize the methodology as much as possible. The validity of the Tritrac-RD3 activity monitor has been assessed in children in free-living conditions, especially during free-play situations (10). In addition, the intersession reliability coefficient for this device is high during treadmill walking and running (13), suggesting that, in our study, the large difference in physical activity between the days with and without pH-metry reflected actual differences in the physical activity patterns of the children.

There are several possible reasons for the change in physical activity during ambulatory 24-hour pH-metry. First, although electrode insertion is not painful, it can be traumatic for children and can therefore have a psychological impact. Second, parents' fear of accidental dislodgement of the electrode could increase child supervision and lead to a reduction in physical activity. Even though we did not advise any restrictions on physical activity in children undergoing ambulatory pH-metry, we noted that most patients did not attend school on the day of pH-metry. Third, although the electrodes and pH-meter were small, the need to carry the relatively voluminous, heavy material (260 g) could have affected the children's physical activity, especially in running, jumping, and other complex activities.

Triaxial accelerometry has been used in several pediatric populations (14–18); however, to our knowledge, no study has assessed physical activity objectively in children during 24-hour pH-metry. One pediatric study published in 1995 evaluated the impact of ambulatory pH-metry on the family's daily living pattern (4). The study was not designed to examine specifically the changes in physical activity of children undergoing pH monitoring. In this previous study, 36% of parents of children undergoing pH-metry were apprehensive because of the perceived exposure of the child to pain and discomfort, poor acceptance of the equipment in the home environment, and multiple attempts to remove the electrode. Another study showed that pH monitoring changed the activity in 30% of the children, based on the parents' perceptions (6).

Two studies of adults evaluated changes in lifestyle and compared physical activity—assessed only by a questionnaire—in the presence or absence of ambulatory 24-hour pH-metry (7,8). Fass et al (7) reported that pH monitoring was associated with a significant reduction in physical activity and that patients demonstrated a mainly sedentary physical activity pattern. By contrast, Lim et al (8) found that pH-metry had a minimal effect on lifestyle regardless of the presence of GER. Costa et al (19) evaluated the impact of noninvasive ambulatory blood pressure monitoring on physical activity in children. As in our study, physical activity decreased on the day of monitoring, and the authors concluded that this decrease may have reduced blood pressure and therefore led to underestimation of hypertension, a source of bias in the study.

Although not evaluated here, reduction in moderate- and high-level physical activity may influence GER. Several studies in adults have shown that physical activity per se may precipitate reflux or aggravate a preexisting reflux condition (20–24). The mechanisms by which physical activity precipitates reflux include increased intraabdominal pressure (20), reduced frequency of esophageal contractions (21,22), and reduction of salivary secretion and delayed gastric emptying (23,24). Further experimental studies on the effects of physical activity on GER in children are required to assess the clinical consequences of the dramatic reduction in physical activity during pH-metry that we observed.


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Esophageal pH recording; Gastroesophageal reflux; Physical activity

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