Lung Function and Pulmonary Hyperreactivity



Lung Function and Bronchial Hyperreactivity

Nicole Beydon MD1

1Assistance Publique-Hôpitaux de Paris ; Lung Function Test – physiology department, Armand Trousseau Hospital, 26 Avenue du Docteur Arnold Netter 75571 Paris Cedex 12. France.

Tel : 01 44 73 63 32

Fax: 01 44 73 63 36

E-mail: nicole.beydon@trsb.aphp.fr

Introduction

Bronchial hyperreactivity (BHR) is commonly measured in children, and thanks to technological advances BHR is now feasible in infants and young children. Asthma is usually defined as a combination of respiratory symptoms often related to allergy, in children with a bronchial disease that encompasses: obstruction, BHR, and inflammation. However, recent findings on airways smooth muscle properties and bronchial structure (anatomical and remodeling) slightly complicate the scheme. Eventually allergy, inflammation, smooth muscle and structure are involved differently in each individual and are responsible for the occurrence and, sometimes, the persistence of the disease (1,2,3). This holistic view of asthma disease in children should help us to interpret new data on the natural course of BHR from infancy to adulthood, and to determine the best way to use BHR measurements in our daily practice.

BHR assessment is performed during bronchial challenge (BC) from which the result must not only be “positive or negative test”, but also include the lung function testing (LFTing) techniques used and the changes measured in the LF indices. Moreover, the decision-making should include the awareness that the use of BC result in an individual is a translation of a knowledge that comes from epidemiological studies conducted in groups of patients

Technological aspects

Type of bronchial challenges

Pharmacological tests are divided into direct tests (methacholine, histamine, carbachol) that primarily stimulate bronchial smooth muscle, and indirect tests (hypertonic saline, Adenosine Mono-Phosphate (AMP), mannitol) of which the response relies on a local cellular reaction. Physical tests (exercise, eucapnic hyperventilation of dry and/or cold air) are also considered as indirect tests, however they do not allow a graded assessment of BHR. Pharmacological tests are more often used because they require minimal cooperation from the child and, therefore, can be implemented in all age groups. Exercise tests are commonly used in children with respiratory complain on exertion.

Age of the patient

The LFT techniques used in paediatric population have to be adapted to the child’s age and maturity, which leads to consider cooperative and non cooperative children. The former are explored as adults, whereas the latter are tested using specific techniques. As a result, young children who require a BC should be referred to a Lab that routinely use techniques adapted to the young children and handled by a trained staff.

Children of more than 6 years of age are thought to be able to perform LFT like adults do. But in practice, and particularly for long duration test like BC, before 8 to 10 years of age some children can show a large variability in spirometry results (4) or sometimes completely lose interest as the test proceeds, providing no final result. It is the technician’s ability to detect children with short concentration span that warrants the reliability of the test. Indeed, a sub-maximal forced expiration maneuver in the course of a BC must not be interpreted as bronchoconstriction. In that case, additional techniques usually used in children younger than 6 years have to be used (see below). However, in school age children and adolescents, spirometry is the recommended technique to measure BHR, with the same cutoffs than the ones used in adults (5). The cutoff for a positive response to direct pharmacological tests is a 20% baseline decrease in Forced Expiratory Volume in 1 s (FEV1), and a positive response to indirect tests a 15% baseline decrease in FEV1.

The preschool children are known as the difficult ones, because they have to be tested awake but might be reluctant to participate in the test if not correctly supervised. Once again, trained staff and a welcoming lab (decorating colors, posters, games, adapted furniture…) are mandatory to gain the child’s confidence and collaboration. The techniques used to assess BHR in this age group are direct measurements of bronchial obstruction (resistance measurement, wheezing detection) or measurements of induced ventilation-perfusion mismatch (transcutaneous partial pressure of oxygen (TcPO2), percutaneous oxygen saturation (SpO2))(6,7,8). The cutoff for a positive bronchial response is a 20% or a 5% baseline decrease in TcPO2 or in SpO2, respectively, or a SpO2 ................
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