Measurement Of Submaximal Respiratory Indexes Of Aerobic Fitness In Parkinson’s Disease

Individualized exercise prescription in Parkinson’s (PD) typically relies on maximal cardiorespiratory testing. Yet, maximal effort may be challenging in patients and ventilatory thresholds-based prescription is preferable for training stimulus standardization across individuals. Impaired chemosensitivity to hypoxia has been described even in early-stage PD. While the cause remains elusive, reduced response to hypoxia may affect our ability to measure submaximal, respiration-based indexes of cardiorespiratory fitness. PURPOSE: to compare values of gas exchange threshold (GET), respiratory compensation point (RCP), oxygen uptake efficiency slope (OUES) in early-stage PD vs controls (C). METHODS: 34 volunteers (68 ± 7 yrs, 25.4 ± 4.0 BMI), 17 with PD (1.8 ± 0.6 H&Y) and 17 age-matched C (35% females in both groups) performed an incremental cycling test to exhaustion. PD were tested in on- medication state. Cardiorespiratory variables were measured breath by breath with a metabolic cart. Maximal values, GET, RCP and OUES were compared between groups by unpaired t-test. The relationship between OUES and VO2max was tested with Pearson correlation. RESULTS: While the maximal heart rate (HRmax) reached upon exhaustion was lower in (mostly β-blocked) PD vs C (81.8 ± 12.3 vs 95.5 ± 9.6 % of estimated HRmax, p < .001), a comparable and elevated respiratory quotient corroborated maximal effort in both populations (1.11 ± 0.07 vs 1.15 ± 0.09, p = .09). Similar values of maximal ventilation (67.2 ± 22.7 vs 70.9 ± 13.8 l·min-1, p = .60) and VO2max (24.8 ± 6.2 vs 25.2 ± 5.6 ml·Kg-1·min-1, p = .80) were reached upon exhaustion by PD and C, respectively. Thresholds were identified in 100% of PD and C participants: comparable values of GET (14.7 ± 3.5 vs 15.1 ± 3.3 ml·Kg-1·min-1, p = .80) and RCP (21.3 ± 5.1 vs 20.3 ± 4.7 ml·Kg-1·min-1, p = .50) were detected in the two groups. OUES was similar in both groups (2.25 ± 0.61 vs 2.12 ± 0.53, p = .52) and moderately correlated with VO2max (r2 = 0.44, p < .001). CONCLUSIONS: Respiration-based indexes of cardiorespiratory fitness such a GET, RCP and OUES can be effectively measured in early-stage PD and C alike. Submaximal, sensitive to training and optimal for exercise intensity tailoring, these indexes offer a valuable tool for testing, monitoring and exercise prescription for symptoms management in PD. Provincia Autonoma di Bolzano-Ufficio Innovazione e Tecnologia