ORIGINAL ARTICLE Reference values for airway resistance in newborns, infants and preschoolers from a Latin American population LAURA G. GOCHICOA, 1,2 LAURA P. THOMÉ-ORTIZ, 3 MARÍA E. Y. FURUYA, 4 RAQUEL CANTO, 1 MARTHA E. RUIZ-GARCÍA, 1 GUILLERMO ZÚÑIGA-VÁZQUEZ, 3 FILIBERTO MARTÍNEZ-RAMÍREZ 5 AND MARIO H. VARGAS 4 1 Center for Evaluation of the Paediatric Asthma Patient, Centro Médico Santa Teresa, Texcoco, 2 Department of Respiratory Physiology, Instituto Nacional de Enfermedades Respiratorias, 3 Department of Pulmonology, 4 Medical Research Unit in Respiratory Diseases, and 5 Department of Anaesthesiology, Hospital de Pediatría, Centro Médico Nacional Siglo XXI, Instituto Mexicano del Seguro Social, México DF, México ABSTRACT Background and objective: Several studies have determined reference values for airway resistance measured by the interrupter technique (Rint) in paedi- atric populations, but only one has been done on Latin American children, and no studies have been per- formed on Mexican children. Moreover, these previous studies mostly included children aged 3 years and older; therefore, information regarding Rint reference values for newborns and infants is scarce. Methods: Rint measurements were performed on preschool children attending eight kindergartens (Group 1) and also on sedated newborns, infants and preschool children admitted to a tertiary-level paediat- ric hospital due to non-cardiopulmonary disorders (Group 2). Results: In both groups, Rint values were inversely associated with age, weight and height, but the stron- gest association was with height. The linear regression equation for Group 1 (n = 209, height 86–129 cm) was Rint = 2.153 - 0.012 ¥ height (cm) (standard deviation of residuals 0.181 kPa/L/s). The linear regression equa- tion for Group 2 (n = 55, height 52–113 cm) was Rint = 4.575 - 0.035 ¥ height (cm) (standard deviation of residuals 0.567 kPa/L/s). Girls tended to have slightly higher Rint values than boys, a difference that dimin- ished with increasing height. Conclusions: In this study, Rint reference values applicable to Mexican children were determined, and these values are probably also applicable to other pae- diatric populations with similar Spanish-Amerindian ancestries. There was an inverse relationship between Rint and height, with relatively large between-subject variability. Key words: ethnicity, lung function, predicted value, pulmonary function test, Rint technique. INTRODUCTION Measurement of airway resistance by the interrup- ter technique (Rint) is increasingly used because it is non-invasive and relatively easily performed by subjects of any age. 1,2 As with most diagnostic tests, Rint values measured in an individual subject must be compared with reference values derived from a population with the same ethnic background and anthropometric characteristics. Several studies have reported Rint reference values for paediatric populations, 3–10 but to our knowledge, only one study has been done in Latin American children, 10 and none have been performed in Mexican children. Moreover, these studies were mainly focused on children aged 3 years and older; therefore, there is a relative lack of information regarding Rint reference values for new- borns and infants. The aim of the present study was to determine Rint reference values for newborns, infants and preschool children in Mexico. Correspondence: Mario H. Vargas, Unidad de Investigación Médica en Enfermedades Respiratorias, Hospital de Pediatría, Centro Médico Nacional Siglo XXI, IMSS. Av. Cuauhtémoc 330, CP 06720, México DF, México. Email: mhvargasb@ yahoo.com.mx Received 1 August 2011; invited to revise 11 September 2011, 29 November 2011, 3 December 2011; revised 2 November 2011, 2 December 2011, 6 December 2011; accepted 6 December 2011 (Associate Editor: Chi Chiu Leung). SUMMARY AT A GLANCE There are no reference values for airway resistance measured by the interrupter technique (Rint) in Latin American newborns, infants and preschool- ers. In this study of 264 children aged 24 days to 6.6 years, reference values for Rint applicable to Mexican children and those from other Latin American countries were determined. © 2012 The Authors Respirology © 2012 Asian Pacific Society of Respirology Respirology (2012) 17, 667–673 doi: 10.1111/j.1440-1843.2012.02156.x