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Vagal Modulation and its Association With Cardiorespiratory Fitness During a Routine Firefighting Shift-work

2017; Lippincott Williams & Wilkins; Volume: 49; Issue: 5S Linguagem: Inglês

10.1249/01.mss.0000518767.33024.66

1530-0315

Luiz Guilherme Grossi Porto, Rosenkranz Maciel Nogueira, Edgard M. K. V. K. Soares, Eugênio C. Nogueira, Carlos Janssen Gomes da Cruz, Guilherme Eckhardt Molina, Keila Elizabeth Fontana, Maria Korre, Denise L. Smith, Stefanos N. Kales, Luiz Fernando Junqueira,

Non-Invasive Vital Sign Monitoring

Firefighting is a hazardous profession with high on-duty cardiovascular mortality, which might be associated with cardiac autonomic dysfunction (CAD) and/or low cardiorespiratory fitness (CRF). PURPOSE: We aimed to evaluate the vagal modulation of the heart in resting supine (SUP) and orthostatic (ORT) postures during a routine 12-hour work period among career firefighters (FF), in association with the CRF. METHODS: We evaluated 30 male military FF, aged 40±3.2 yrs, BMI = 26.3±3.1 kg/m2, CRF = 11.4±1.4 METs, recruited from a Brazilian Fire Department. Vagal modulation was evaluated by means of the short-term time-domain heart rate variability index PNN50%, which is the percentage of successive R-R intervals greater than 50 ms and reflects the beat-to-beat parasympathetic modulation. CRF was estimated by a validated self-reported physical activity questionnaire (Jackson & Blair, MSSE, 1990). PNN50% was measured in a basal condition on an off-duty day (Eva1) and immediately before (Eva2) and after (Eva3) a 12-hour period of work, in resting supine (SUP) and orthostatic (ORT) postures. PNN50% values were compared between the 3 evaluations (Friedman test), two postures (Wilcoxon-test) and by CRF categories (<12 METs vs ≥ 12 METs) after 12 hours of work in ORT (Kruskal Wallis test), at 5% level of significance. RESULTS: Median (min-max) values of PNN50% in SUP and ORT in Eva1-3 are shown on Table. Those with better CRF (n=10) showed higher values of PNN50% in ORT after 12-hours of routine work: 3 (0-60%), as compared to FF with lower CRF: 0 (0 - 8%) (p = 0.047) CONCLUSION: Our data show a physiological decrease on PNN50% to active standing up. We also observed a significant reduction on the vagal modulation in ORT-Eva3 as compared to Eva1. The association between the reduced resting vagal modulation after a 12-hour period of work and low CRF reinforce previous recommendation for implementing physical training among FF as a cardioprotective strategy.(CNPq 480092/2013-3)Table: No title available.