Oxygen kinetics during 6-minute walk tests in patients with cardiovascular and pulmonary disease.

BACKGROUND: The 6-Minute Walk Test (6MWT) is representative of daily-life activities and reflects the functional capacity of patients. The change of oxygen uptake (VO2) in the initial phase of low-intensity exercise (VO2 kinetics) can be used to assess submaximal exercise performance of patients.The objective of the following study was to analyse VO2 kinetics in patients with different pulmonary and cardiovascular diseases. In addition, we investigated the extent to which VO2 kinetics at the onset of the 6MWT were associated with exercise capacity, morbidity and mortality. METHODS: VO2 kinetics of 204 patients and 16 healthy controls were obtained using mobile telemetric cardiopulmonary monitoring during a 6MWT. A new mean response time (MRT) index (wMRT) was developed to quantify VO2 kinetics by correcting MRT for work rate. The differences in wMRT between disease categories as well as the association between wMRT and patients' exercise capacity and outcome - time to hospitalization/death- were tested. RESULTS: The assessment of a robust wMRT was feasible in 86% (244/284) patients. wMRT was increased in patients compared to healthy controls (p <0.001). wMRT was largest in patients with pulmonary arterial hypertension (PAH). There were significant associations between wMRT and exercise capacity in all patients. High wMRT was found to be associated with a high rate of death and re-hospitalization in patients with CHF (p = 0.024). In patients with pulmonary diseases and pulmonary hypertension wMRT was not associated with outcome (p = 0.952). CONCLUSIONS: Submaximal exercise performance of patients is reduced. O2 kinetics at the onset of exercise are associated with exercise capacity in all patients. wMRT was found to be an important prognostic factor in patients with congestive heart failure (CHF), but not with pulmonary diseases.

Six-minute walk test enhanced by mobile telemetric cardiopulmonary monitoring.

BACKGROUND: The 6-min walk test (6MWT) is frequently used to assess overall cardiopulmonary fitness and to predict outcome, but it yields little diagnostic information. Portable telemetric devices allow performing the 6MWT with real-time cardiopulmonary monitoring. OBJECTIVES: The study was designed to analyze feasibility, safety and clinical usefulness of a mobile cardiopulmonary monitoring (MOB)-enhanced 6MWT. METHODS: From August 2003 to June 2007, 261 consecutive patients with chronic lung and/or heart disease as well as healthy controls underwent MOB-enhanced 6MWTs. A subgroup of 33 individuals had the test done with and without cardiopulmonary monitoring on independent days. RESULTS: No test-related adverse events occurred throughout the study. Whether the 6MWT was done without or with cardiopulmonary monitoring (n = 33) did not significantly influence the walking distance (WD: 528 ± 183 vs. 525 ± 192 m; nonsignificant). Fifty-nine percent (155/261) of the patients fulfilled the maximal test criteria. Distinct disease-specific exercise response patterns as well as treatable co-pathologies were observed. The validity of response patterns was better in case of a maximal test. CONCLUSION: An MOB-enhanced 6MWT is feasible within daily routine and safe in patients with various diseases. It does not negatively affect WD. MOB is a valuable tool to identify factors limiting exercise in patients irrespective of their underlying disease.