Cardiorespiratory fitness during exertion and cardiac autonomic control in individuals with unilateral lower limb amputation

Abstract

Introduction: Amputation of lower limbs can cause changes in the cardiorespiratory system and in cardiac autonomic control. The cardiopulmonary stress test (CPET) and the analysis of heart rate variability (HRV) are, respectively, the gold standard methods for
investigating these outcomes. Little is known about cardiorespiratory fitness at different levels of intensity in amputees, cardiac autonomic control and their relationships. Objective: To investigate cardiorespiratory fitness on exertion, cardiac autonomic
control and the agreement between ventilatory threshold 1 (LV1) and HRV threshold (LiVFC) in individuals with unilateral lower limb amputation. Methods: Sectional study with 6 individuals submitted to a maximum CPET using an incremental protocol in a cycle ergometer for upper limbs. RR intervals were recorded using the electrocardiogram and processed using the KUBIUS software. LiVFC was identified by the three methods proposed from the counting of RR intervals obtained by ECG: Standard deviation (SD1) ≤ 1 ms, SD1≤ 3 ms and Root Mean Square of the Successive Differences (RMSSD) ≤ 1 ms. The following cardiorespiratory variables were
considered: peak oxygen consumption (VO2 peak) relative (ml / kg.min-¹) and absolute (L / min), cardiorespiratory optimum (POC) and LV1. Results: By the methods SD1≤ 1 ms and RMSSD≤ 1 ms, LiVFC was identified in all study participants. Using the SD1≤
3 ms method, it was possible to identify the LiVFC in only 66.7% (N = 04) of the participants. The intraclass correlation coefficients (ICC) between the test power (w) at the time of LV1 and the three indices used to identify the LiVFC were classified as “unacceptable” (<0.40), demonstrating, therefore, an absence of agreement ( between methods. Amputees had lower VO2peak for the same intensity of effort when compared to individuals without amputation, as well as VO2 at submaximal effort intensities, that is, in POC and LV1. However, the group achieved LV1 in percentage values of VO2peak similar to the non-amputated individuals. Conclusion: No agreement was found between LiVFC and LV1 and individuals with MI amputation have less cardiorespiratory fitness at different effort intensities when compared with individuals without amputation.