Neuro-Cardiovascular Responses to Sympathetic Stimulation in Fighter Pilots

INTRODUCTION: The chronic effects of regular exposure to high acceleration levels (G-force) on the neuro-cardiovascular system are unclear. We compared the mean arterial pressure (MAP) and cardiac autonomic modulation between nonpilots (NP) vs. military fighter (FP) and transport (TP) pilots. Additionally, we correlated the cardiac autonomic indices with the cardiorespiratory fitness and flight experience of FP.METHODS: A total of 21 FP, 8 TP, and 20 NP performed a tilt test (TT), during which beat-to-beat blood pressure and heart rate were recorded.RESULTS: No difference was detected between groups for changes in MAP and heart rate variability indices during the TT. However, the analysis of areas under the curves showed a greater increase in MAP in FP vs. TP and NP. Conversely, there was a greater decrease in indices reflecting vagal modulation in TP vs. FP and NP (rMSSD, pNN50, and SDNN), and a greater increase in heart rate and sympathovagal balance in TP vs. other groups (LF/HF). The maximal oxygen uptake was strongly correlated with the vagal reserve in FP (r = -0.74). Moreover, the total flying hours of FP were positively correlated with resting HFnu (r = 0.47) and inversely correlated with resting LFnu (r = -0.55) and LF/HF (r = -0.46).CONCLUSION: FP had a higher pressor response to TT than TP and NP. Vagal withdrawal and sympathovagal increase induced by TT in FP were similar vs. NP and attenuated vs. TP. Greater cardiorespiratory fitness and accumulated flying hours in FP seemed to favor lower sympathetic and greater vagal modulation at rest.dos Santos Rangel MV, de Sá GB, Farinatti P, Borges JP. Neuro-cardiovascular responses to sympathetic stimulation in fighter pilots. Aerosp Med Hum Perform. 2023; 94(10):761-769.

Body Mass Index but not Physical Activity Level Moderates Lowered Cardiac Baroreflex Sensitivity in People Living with HIV

Reduced cardiac baroreflex sensitivity (cBRS) is an autonomic marker associated with a worse cardiovascular prognosis. Whether cBRS is lowered in people living with HIV (PLHIV) is yet unclear, as well as potential moderator effects of body mass index (BMI) or physical activity (PA) level. The present study aims to compare the spontaneous cBRS in PLHIV vs. HIV-uninfected controls, and to determine among PLHIV the relationship between cBRS vs. body mass index (BMI) and PA level. Total, upward (cBRS+), and downward (cBRS-) cBRS gains were assessed using the sequential method from beat-to-beat blood pressure at rest in 16 PLHIV (46.5±8.4 years) under antiretroviral therapy for at least 6 months, and 16 HIV-uninfected controls (CTL; 42.1±8.0 years). PA level was assessed by the Physical Activity Questionnaire (IPAQ short version) overall score. PLHIV showed lower total cBRS (8.7±3.1 vs. 15.3±7.7 ms.mmHg-1; p < 0.01), cBRS+ (9.2±4.9 vs. 16.0±6.8 ms.mmHg-1; p < 0.01) and cBRS- (9.5±4.9 vs. 15.3±9.3 ms.mmHg-1; p < 0.01) vs. CTL. No between-group difference was found for BMI (PLHIV: 25.2±2.6 vs. CTL: 26.8±3.2 kg.m-2; p > 0.05) or IPAQ score (PLHIV: 2.4±1.0 vs. CTL: 2.0±1.4; p > 0.05). In PLHIV, total cBRS was inversely correlated vs. BMI (r = -0.44; p = 0.04), but not vs. IPAQ score (r = 0.17; p = 0.26). HIV infection may reduce spontaneous cBRS, which seemed to be moderated by higher BMI, but not PA level of PLHIV.

Muscle metaboreflex adaptations to exercise training in health and disease

Abnormalities in the muscle metaboreflex concur to exercise intolerance and greater cardiovascular risk. Exercise training benefits neurocardiovascular function at rest and during exercise, but its role in favoring muscle metaboreflex in health and disease remains controversial. While some authors demonstrated that exercise training enhanced the sensitization of muscle metabolically afferents and improved neurocardiovascular responses to muscle metaboreflex activation, others reported unaltered responses. This narrative review aimed to: (a) highlight the current evidence on the effects of exercise training upon cardiovascular and autonomic responses to muscle metaboreflex activation; (b) analyze the role of training components and indicate potential mechanisms of metaboreflex adaptations; and (c) address key methodological features for future research. Though limited, accumulated evidence suggests that muscle metaboreflex adaptations depend on the individual clinical status, exercise modality, and training duration. In healthy populations, most trials negated the hypothesis of metaboreflex improvement due to chronic exercise, irrespective of the training duration. Favorable changes in patients with impaired metaboreflex, particularly chronic heart failure, mostly resulted from long-term interventions (> 16 weeks) including aerobic exercise of moderate to high intensity, performed in isolation or within multimodal training. Potential mechanisms of metaboreflex improvements include enhanced sensitivity of channels and receptors, greater antioxidant capacity, lower metabolite accumulation, increased functional sympatholysis, and muscle perfusion. Future research should investigate: (1) the dose-response relationship of training components within different exercise modalities to elicit improvements in individuals showing intact or impaired muscle metaboreflex; and (2) potential and specific underlying mechanisms of metaboreflex improvements in individuals with different medical conditions.