Article, Pulmonology

Single-breath counting: a pilot study of a novel technique for measuring pulmonary function in children

Original Contribution

Single-breath counting: a pilot study of a novel technique for measuring pulmonary function in children?,??

Syed Sameer Ali MD a,?, Charles OConnell MD b, Lawrence Kass MD a, Gavin Graff MD c

aDepartment of Emergency Medicine, Penn State Hershey Medical Center, Hershey, PA 17033, USA

bPenn State University College of Medicine, Penn State Hershey Medical Center, Hershey, PA 17033, USA

cDepartment of Pediatrics, Penn State Hershey Medical Center, Hershey, PA 17033, USA

Received 8 June 2009; revised 9 July 2009; accepted 10 July 2009

Abstract

Introduction: Although peak expiratory flow rate is the conventional way to measure asthma severity in adults, its use is problematic in children because it is effort dependent. Forced expiratory volume in 1 second (FEV1) and the ratio of FEV1 to forced vital capacity (FEV1/FVC) are more accurate, but generally not available in the emergency department (ED). A better test is needed. Single-breath counting (SBC) is the measurement of how far an individual can count in a normal speaking voice after a maximal effort inhalation. The count is in cadence to a metronome set at 2 beats per second. Previous work has suggested that SBC correlates with standard measures of pulmonary function in adults. However, it has never been tested in children.

Objectives: The aims of this study are to determine if SBC can be easily performed by children and to assess the correlation between SBC and standard measures of pulmonary function in a pediatric population.

Methods: This was a prospective observational study of a convenience sample of children presenting to the pulmonary clinic for scheduled pulmonary function testing (PFT). Peak expiratory flow rate, FEV1, FVC, forced expiratory flow 25% to 75%, and FEV1/FVC were measured and recorded. After PFT, subjects were asked to perform SBC. Three attempts were allowed, and the average was recorded. Correlation was determined by the Pearson coefficient.

Results: Sixty-seven children (ages 5-18 years, 64% male) were enrolled. All were able to understand and complete the testing. Indications for PFT includED asthma and/or allergies (n = 44), cystic fibrosis (n = 9), and other chronic diseases (n = 14). The correlations (r) of SBC to peak expiratory flow rate, FEV1, FVC, forced expiratory flow 25% to 75%, and FEV1/FVC were 0.55, 0.66, 0.71, 0.44, and

-0.29, respectively (P b .05 for all results).

Conclusion: Single-breath counting is easy to perform in children, seems to correlate well with standard measures of pulmonary function, and shows promise for measuring asthma severity in children. Further

? Presented at the Annual Meeting of the Society for Academic Emergency Medicine, Washington, DC: May 29-June 1, 2008.

?? Syed Sameer Ali, MD, Principal Investigator, was responsible for conceiving the study idea, study design, data analysis, and authoring the manuscript; Charles O’Connell, was involved in data collection and analysis; Lawrence Kass, MD, was involved in conceiving the study idea, design, data analysis, and editing the manuscript; and Gavin Graff, MD, was involved in study design and data analysis.

* Corresponding author. Department of Emergency Medicine, Penn State Hershey Medical Center-H043, P.O. Box 850, 500 University Drive, Hershey, PA

17033, USA. Tel.: +1 717 531 8955; fax: +1 717 531 4587.

E-mail address: [email protected] (S.S. Ali).

0735-6757/$ – see front matter (C) 2011 doi:10.1016/j.ajem.2009.07.006

34 S.S. Ali et al.

work to define the range of reference SBC values (as a function of age and/or body size) and an evaluation of the utility of SBC in an ED population of acute asthmatics is indicated.

(C) 2011

1. Introduction

Asthma is the most common chronic disease in children in the United States, with approximately 5.5 million children affected [1]. The National Asthma Education and Prevention Program was initiated by the United States Department of Health and Human Services in 1989 with the ultimate goal of decreasing asthma-related morbidity and mortality and educating health professionals and patients. It provides guidelines for objective assessment of exacerbation severity in children at home as well as in the physician’s office. It recommends the routine use of standardized pulmonary function testing (PFT) in children, but many physicians find it difficult to comply with this standard, especially in the emergency department (ED) [2].

Standard measures of pulmonary function such as forced expiratory volume in 1 second (FEV1) and peak expiratory flow rate (PEF) are objective, have high sensitivity, and have excellent positive predictive values. However, they have limited utility in children. A more useful method of assessing pulmonary function in asthmatic children is required.

Single-breath counting (SBC) is the measurement of how far an individual can count in a normal speaking voice after a maximal effort inhalation. The count is in cadence to a metronome set at 2 beats per second. In adults, it seems to correlate with standard measures of pulmonary function

forced expiratory flow 25% to 75% (FEF25%-75%) and FEV1/ FVC ratio were measured and recorded as per protocol. After obtaining verbal consent from the study participants, SBC was demonstrated by the investigator using a standard digital metronome (DM-50; Seiko, Tokyo, Japan) with both visual and audible cues. The metronome was set at 2 beats per second, and counting was started with the number “1.” Participants were then asked to perform SBC. No test runs were permitted. Three attempts were allowed and documen- ted. The average was calculated and recorded.

2.1. Statistical analysis

Correlation was determined by the Pearson product correlation coefficient (r). Statistical analysis was performed using SAS Statistical Software (Cary, NC). The study protocol was approved by the institutional review board. Significance was set at P b .05.

3. Results

A total of 67 children were enrolled, with ages ranging from 5 to 18 years. The median age was 12 years, and 64% were male. Indications for PFT included asthma and/or allergies (66%), cystic fibrosis (13%), and other chronic

diseases (21%). Single-breath counting showed fair correla-

[3,4]. However, it has never been tested in children. Because

of its simplicity, it has the potential to facilitate greater

tion with PEF (r = 0.53) and with FEF

25%-75%

(r = 0.44)

cooperation from children and therefore be more reliable. The objectives of this pilot study were to determine if SBC can be easily performed by children and to assess the correlation between SBC and standard measures of pulmon- ary function in a pediatric population.

2. Methods

This was a prospective observational study conducted during a period of 3 consecutive months of a convenience sample of children ages 5 to 18 years presenting to the pediatric pulmonary clinic for scheduled PFT. All children presenting for PFT were evaluated. However, children who were unable to count or were unable to understand or cooperate with the process were excluded. Basic demo- graphics (age, sex, height, and weight), indications for PFT, and any comorbidities were recorded. Pulmonary function testing was performed by a certified pulmonary function technician using a Viasys Encore Spirometer (Dublin, Ohio), according to the American Thoracic Society guidelines [5]. Peak expiratory flow rate, FEV1, forced vital capacity ,

(Figs. 1 and 2). There was good correlation between SBC and FEV1 (r = 0.66) as well as with FVC (r = 0.71) (Figs. 3 and 4). Single-breath counting showed a weak negative correlation (r = -0.29) with the FEV1/FVC ratio (Fig. 5). All results were significant at the 95% Confidence level.

Fig. 1 SBC versus PEF (r = 0.53).

Single breath counting in children 35

Fig. 2 SBC versus FEF25%-75% (r = 0.44). Fig. 4 SBC versus FVC (r = 0.71).

All enrolled subjects were able to understand the instructions and complete the study without difficulty. No subjects were excluded due to lack of cooperation or difficulty in performing SBC. Total time spent on instruc- tions was only 30 seconds per patient. There were no dropouts or observed complications.

Discussion

Some of the most valuable PFTs for assessment of asthma severity, response to treatment, and making Disposition decisions are FEV1 and PEF. FEV1 and PEF both reflect changes in the degree of airway obstruction. FEV1 is the most reproducible airway function parameter and is the superior test for estimating small airway obstruction [6]. However, FEV1 can only be obtained using a spirometer. PEF in general provides a simple, quantitative, and usually reproducible measure of the existence and severity of airflow obstruction and is easily obtainable in most EDs using peak flow meters. The biggest drawback, however, is that the

Fig. 3 SBC versus FEV1 (r = 0.66).

measurement of PEF is dependent on effort and skill; patients need instructions, demonstrations, and frequent reviews of technique [2]. It reflects and measures only the rate of flow from the large airways and is affected by the few hundred milliliters of expired air starting from full inflation of the lungs, the strength of the thoracic and abdominal muscles, and the degree of muscular effort generated by the patient [7].

This has led many asthma experts to challenge the advisability of home PEF monitoring for children with asthma [8,9]. It has been shown by Nemr et al [10] that reproducibility is an issue with PEF. In fact, they have shown that the PEF underestimates the degree of airway obstruction because the patient with air trapping may be able to generate a quick burst of air at the beginning of a forced exhalation, sufficient to give a normal PEF reading, leading to false reassurance and potentially Catastrophic outcomes [10,11]. Saetta et al [11] have reported PEF values in asymptomatic children documented to have persistent airway obstruction by FEV1 and FEF25%-75%.

Fig. 5 SBC versus FEV1/FVC (r = -0.29).

36 S.S. Ali et al.

However, despite its shortcomings, PEF is still the most easily available and commonly used objective measure of asthma severity.

Our results show fair correlation between PEF and SBC (r = 0.53), quite similar to the correlation (r = 0.68) obtained by Ushkow et al [4] in adults. FEV1 reflects both obstructive disease (when decreased out of proportion to the FVC) and restrictive disease (when reduced proportio- nately to the FVC). Our results show good correlation between SBC and FEV1 (r = 0.66). The same correlation was obtained by Bartfield et al [3] and Ushkow et al in adults [4]. This suggests that SBC may be sensitive to both obstructive and restrictive disease.

Forced vital capacity is the maximal volume of air that can be forcefully expired after full inhalation. It is reduced in restrictive disease or severe airflow obstruction (air trapping or “pseudorestriction”). We have found a strong correlation between SBC and FVC (r = 0.71). FEF25%-75% is the average flow over the middle half of FVC. It is a more sensitive measure of small airways narrowing than FEV1. Our results show fair correlation between SBC and FEF25%-75% (r = 0.44), again suggesting that both obstructive and restrictive diseases can affect SBC.

We found a relatively weak negative correlation between SBC and the FEV1/FVC ratio (r = -0.29). This ratio has been shown to be the most accurate measure of obstructive disease [12]. FEV1 decreased out of proportion to FVC correlates with obstructive disease. Proportional decrease in the 2 measures suggests restrictive disease. The significance of our observation of a negative correlation with the ratio is unclear but raises interesting questions. It may reflect increased sensitivity of SBC to restrictive disease over obstructive disease, but further investigation is necessary.

Limitations

Because this was a pilot study designed to evaluate the ease of performing SBC in children and assess the correlation of SBC with standard measures of pulmonary function, it was performed on a convenience sample of a selected population. Therefore, our results cannot be extrapolated to other settings. Our sample size was too small to perform subgroup analysis. We did not compare instructions for performing SBC with instructions for performing peak flow. A set of reference SBC values (as a function of age and/or body size) does not exist. This will be important in determining the clinical significance of a measurement in a particular patient. We are presently working on creating such a table of reference values, including detailed age group analysis.

Conclusions

Single-breath counting is very easy to perform in children, seems to correlate well with standard measures of pulmonary function, and shows promise for measuring asthma severity in children. It may reflect both restrictive and obstructive diseases and might be useful to demonstrate improvement with acute asthma treatment. Further work to define the range of reference SBC values (as a function of age and/or body size) and an evaluation of the utility of SBC in an ED population of acute asthmatics is underway.

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