Value of the average basal daily walked distance measured using a pedometer to predict maximum oxygen consumption per minute in patients undergoing lung resection

European Journal of Cardio-thoracic Surgery 39 (2011) 756—762 www.elsevier.com/locate/ejcts Value of the average basal daily walked distance measured using a pedometer to predict maximum oxygen consumption per minute in patients undergoing lung resection§,§§ Nuria Maria Novoa a,*, Gonzalo Varela a, Marcelo F. Jiménez a, Jacinto Ramos b Thoracic Surgery Service, Salamanca University Hospital, Salamanca, Spain b Respiratory Unit, Salamanca University Hospital, Salamanca, Spain Received 25 May 2010; received in revised form 29 July 2010; accepted 5 August 2010; Available online 10 December 2010 Abstract Objectives: Maximum oxygen consumption per min (VO2max) is currently considered the most accurate test for the preoperative risk assessment in patients scheduled for pulmonary resection. Due to its high-technology requirements and cost, VO2max is performed less frequently than is desired. The objective of this investigation is to determine if the measurement of the basal daily ambulatory activity of the patients, with a pedometer, can be used to predict VO2max values. Methods: This is a prospective study on 38 patients referred for scheduled lobectomy or pneumonectomy. Daily basal preoperative activity of the patients was measured 3 weeks before surgery by means of an OMROM HJ-72OIT-E2 pedometer. Before surgery, VO2max (dependent variable) was calculated using a Master Screen CPX module of Jaeger-Vyasis-Healthcare. The following independent variables were studied: age, sex, preoperative forced expiratory volume in 1 s percentage (FEV1%) and carbon monoxide diffusing capacity percentage (DLCO%), mean number of steps per day (aerobic and non-aerobic), mean daily time of aerobic activity (in min) and mean daily walked distance (in km). Two linear regression models with bootstrap robust estimation of the standard error of the coefficients were adjusted and the estimated values of VO2max were kept as a new variable for comparison. To avoid collinearity problems, only one of the pedometer records entered the regression model. Results: Data of the series (mean  SD): age 62.8  10.14 years; FEV1% 90.1  21.8; DLCO% 82.8  20.1. After collinearity analysis, mean daily walked distance was chosen as the most representative variable. In the first regression model, ‘Distance’ ( p = 0.000) was highly correlated to the dependent variable (adjusted R2: 0.812). The second model improved the predictive value of the first one adding DLCO% to the model. In this model, DLCO% ( p = 0.000) and ‘Distance’ ( p = 0.002) were correlated to the dependent variable. The adjusted R2 of the second lineal model was 0.935. Conclusion: These preliminary data show that a combination of the measured daily ambulatory activity using a pedometer, especially the mean daily walked distance in km, and the DLCO% of the patient could predict the VO2max value. Larger data series are needed for conclusive results. # 2010 European Association for Cardio-Thoracic Surgery. Published by Elsevier B.V. All rights reserved. Keywords: Pedometer; Major lung resection; Daily ambulatory walked distance; VO2 max; CPET 1. Introduction High-technology cardiopulmonary exercise test (CPET) with calculation of the maximum oxygen consumption per minute (VO2max) is currently considered the most accurate test to predict complications after lung resection in patients with forced expiratory volume in 1 s percentage (FEV1%) or carbon monoxide diffusing capacity percentage (DLCO%) below normal values [1,2]. Thus, VO2max remains the gold standard to § Presented at the 18th European Conference on General Thoracic Surgery, Valladolid, Spain, May 30—June 2, 2010. Winner of the ESTS Brompton Prize. §§ Study supported by a grant of the Spanish Society of Respiratory Pathology (SEPAR) and by a grant of the Consejeria de Salud de Castilla y León (Sacyl). * Corresponding author. Address: Thoracic Surgery Service, Paseo de San Vicente 52—84, 37007 Salamanca, Spain. Tel.: +34 923 291 383; fax: +34 923 291 383. E-mail address: (N.M. Novoa). compare new technologies in risk-estimation analysis. Unfortunately, VO2max is performed less frequently than desired due to its high-technology requirements and costs. Besides, it could be hypothesized that a maximum exercise test performed in the laboratory could not be a perfect surrogate of the actual patient’s fitness necessary for daily living, and more specifically, for the physical activity necessary the following weeks after being discharged after lung resection. Furthermore, for the conditions a test of this type imposes upon the patient, there may be a considerable number of subjects performing sub-optimally. Measuring physical activity in real-life conditions using pedometers, which have been validated as accurate sensors for ambulatory activity measurement [3], could be more objective and, perhaps, equally valid to estimate the exercise capacity before lung resection. Nevertheless, physical activity of daily living has not been studied as a variable predicting the outcome after lung resection. 1010-7940/$ — see front matter # 2010 European Association for Cardio-Thoracic Surgery. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.ejcts.2010.08.025 a N.M. Novoa et al. / European Journal of Cardio-thoracic Surgery 39 (2011) 756—762 The main objective of this investigation is to determine if the measurement of the basal daily activity of the patients with a pedometer correlates with VO2max values measured at the pulmonary function laboratory. As a secondary objective, we investigate if the addition of DLCO% to basal daily activity improves the accuracy of VO2max prediction. 2. Methods 2.1. Population of the study 2.2. Pedometer Daily-living physical preoperative activity was measured using an OMROM Walking Style ProW pedometer. The pedometer allows data acquisition up to 41 days and is capable to differentiate two types of ambulatory activity: the standard and the so-called aerobic mode. After 10 min of continuous walking at a rate of at least 60 steps per min, the aerobic mode is activated and it is deactivated after a 1-min break. At the initial consultation, the patients were instructed on how to use the pedometer and it was adjusted for patients’ weight and stride length. Subjects entering the study were also instructed to wear the pedometer on the belt or waistband from the moment they awoke until they went to bed except while bathing or swimming. The pedometer was firmly attached to their clothes at the waist with the aid of a clip and a secure band. Patients were not encouraged to increase their daily activity but counselling to quit smoking and training on the use of an incentive spirometer was provided. Daily basal activity was measured during the waiting time before surgery. Obtained data were downloaded at admission for surgery. 2.3. CPET and VO2max acquisition A MasterSreen CPX module of Jaeger-Vyasis-Healthcare was used for CPET developing and recording. This module (...truncated)