Impact of chronic exercise training on the blood pressure response to orthostatic stimulation

Autonomic and vascular function testing in collegiate athletes following SARS-CoV-2 infection: an exploratory study

Introduction: Recent studies suggest that SARS-CoV-2 infection alters autonomic and vascular function in young, otherwise healthy, adults. However, whether these alterations exist in young competitive athletes remains unknown. This study aimed to assess the effects of COVID-19 on cardiac autonomic control and vascular function in collegiate athletes who tested positive for COVID-19, acknowledging the limitations imposed by the early stages of the pandemic. Methods: Sixteen collegiate athletes from various sports underwent a battery of commonly used autonomic and vascular function tests (23 ± 9, range: 12-44 days post-infection). Additionally, data from 26 healthy control participants were included. Results: In response to the Valsalva maneuver, nine athletes had a reduced early phase II blood pressure response and/or reduced Valsalva ratio. A depressed respiratory sinus arrhythmia amplitude was observed in three athletes. Three athletes became presyncopal during standing and did not complete the 10-min orthostatic challenge. Brachial artery flow-mediated dilation, when allometrically scaled to account for differences in baseline diameter, was not different between athletes and controls (10.0% ± 3.5% vs. 7.1% ± 2.4%, p = 0.058). Additionally, no differences were observed between groups when FMD responses were normalized by shear rate (athletes: 0.055% ± 0.026%/s-1, controls: 0.068% ± 0.049%/s-1, p = 0.40). Discussion: Few atypical and borderline responses to autonomic function tests were observed in athletes following an acute SARS-CoV-2 infection. The most meaningful autonomic abnormality being the failure of three athletes to complete a 10-min orthostatic challenge. These findings suggest that some athletes may develop mild alterations in autonomic function in the weeks after developing COVID-19, while vascular function is not significantly impaired.

Directional sensitivity of the cerebral pressure-flow relationship in young healthy individuals trained in endurance and resistance exercise

NEW FINDINGS

What is the central question of this study? Does habitual exercise modality affect the directionality of the cerebral pressure-flow relationship? What is the main finding and its importance? These data suggest the hysteresis-like pattern of dynamic cerebral autoregulation appears present in long-term sedentary and endurance-trained individuals, but absent in resistance-trained individuals. This is the first study to expand knowledge on the directional sensitivity of the cerebral pressure-flow relationship to trained populations.

ABSTRACT

Evidence suggests the cerebrovasculature may be more efficient at dampening cerebral blood flow (CBF) variations when mean arterial pressure (MAP) transiently increases, compared to when it decreases. Despite divergent MAP and CBF responses to acute endurance and resistance training, the long-term impact of habitual exercise modality on the directionality of dynamic cerebral autoregulation (dCA) is currently unknown. Thirty-six young healthy participants [sedentary (n = 12), endurance-trained (n = 12) and resistance-trained (n = 12)] undertook a 5-min repeated squat-stand protocol at two forced MAP oscillation frequencies (0.05 Hz and 0.10 Hz). Middle cerebral artery mean blood velocity (MCAv) and MAP were continuously monitored. We calculated absolute (ΔMCAv_T /ΔMAP_T ) and relative (%MCAv_T /%MAP_T ) changes in MCAv and MAP with respect to the transition time intervals of both variables to compute a time-adjusted ratio in each MAP direction, averaged over the 5-min repeated squat-stand protocols. At 0.10 Hz repeated squat-stands, ΔMCAv_T /ΔMAP_T and %MCAv_T /%MAP_T were lower when MAP increased compared with when MAP decreased for sedentary (ΔMCAv_T /ΔMAP_T : p = 0.032; %MCAv_T /%MAP_T : p = 0.040) and endurance-trained individuals (ΔMCAv_T /ΔMAP_T : p = 0.012; %MCAv_T /%MAP_T : p = 0.007), but not in the resistance-trained (ΔMCAv_T /ΔMAP_T : p = 0.512; %MCAv_T /%MAP_T : p = 0.666). At 0.05 Hz repeated squat-stands, time-adjusted ratios were similar for all groups (all p>0.605). These findings suggest exercise training modality does influence the directionality of the cerebral pressure-flow relationship and support the presence of a hysteresis-like pattern during 0.10 Hz repeated squat-stands in sedentary and endurance-trained participants, but not in resistance-trained individuals. In future studies, assessment of elite endurance and resistance training habits may further elucidate modality-dependent discrepancies on directional dCA measurements. This article is protected by copyright. All rights reserved.

Cardiovascular regulation: associations between exercise and head-up tilt

It was hypothesized that faster cardiorespiratory kinetics during exercise are associated with higher orthostatic tolerance. Cardiorespiratory kinetics of 14 healthy male subjects (30 ± 4 years, 179 ± 8 cm, 79 ± 8 kg) were tested on a cycle ergometer during exercise with changing work rates of 30 and 80 W. Pulmonary oxygen uptake ( ) was measured breath-by-breath and heart rate (HR), mean arterial blood pressure (MAP), and total peripheral resistance (TPR) were measured beat-to-beat. Muscular oxygen uptake ( ) was estimated from HR and . Kinetic parameters were determined by time-series analysis, using cross-correlation functions (CCF_max(x)) between the parameter and the work rate. Cardiovascular regulations of MAP, HR, and TPR during orthostatic stress were measured beat-to-beat on a tilt seat. Changes between the minima and maxima during the 6° head-down tilt and the 90° head-up tilt positions were calculated for each parameter (Δ_tilt-up). correlated significantly with ΔTPR_tilt-up (r = 0.790, p ≤ 0.001). CCF_max(HR) was significantly correlated with ΔHR_tilt-up (r = -0.705, p = 0.002) and the amplitude in HR from 30 to 80 W (r_SP = -0.574, p = 0.016). The observed correlations between cardiorespiratory regulation in response to exercise and orthostatic stress during rest might allow for a more differential analysis of the underlying mechanisms of orthostatic intolerance in, for example, patient groups.

Impact of mild orthostatic stress on aortic-cerebral hemodynamic transmission: insight from the frequency domain

High cerebral pressure and flow fluctuations could be a risk for future cerebrovascular disease. This study aims to determine whether acute systemic vasoconstriction affects the dynamic pulsatile hemodynamic transmission from the aorta to the brain. We applied a stepwise lower body negative pressure (LBNP) (−10, −20, and −30 mmHg) in 15 young men to induce systemic vasoconstriction. To elucidate the dynamic relationship between the changes in aortic pressure (AoP; estimated from the radial arterial pressure waveforms) and the cerebral blood flow velocity (CBFV) at the middle cerebral artery (via a transcranial Doppler), frequency-domain analysis characterized the beat-to-beat slow oscillation (0.02–0.30 Hz) and the intra-beat rapid change (0.78–9.69 Hz). The systemic vascular resistance gradually and significantly increased throughout the LBNP protocol. In the low-frequency range (LF: 0.07–0.20 Hz) of a slow oscillation, the normalized transfer function gain of the steady-state component (between mean AoP and mean CBFV) remained unchanged, whereas that of the pulsatile component (between pulsatile AoP and pulsatile CBFV) was significantly augmented during −20 and −30 mmHg of LBNP (+28.8% and +32.4% vs. baseline). Furthermore, the relative change in the normalized transfer function gain of the pulsatile component at the LF range correlated with the corresponding change in systemic vascular resistance ( r = 0.41, P = 0.005). Regarding the intra-beat analysis, the normalized transfer function gain from AoP to CBFV was not significantly affected by the LBNP stimulation ( P = 0.77). Our findings suggest that systemic vasoconstriction deteriorates the dampening effect on the pulsatile hemodynamics toward the brain, particularly in slow oscillations (e.g., 0.07–0.20 Hz).

NEW & NOTEWORTHY We characterized the pulsatile hemodynamic transmission from the heart to the brain by frequency-domain analysis. The low-frequency transmission was augmented with a mild LBNP stimulation partly due to the elevated systemic vascular resistance. A systemic vasoconstriction deteriorates the dampening effect on slow oscillations of pulsatile hemodynamics toward the brain.

Oxidative status of the myocardium in response to different intensities of physical training

The intensity of exercise determines the metabolic pathway and the energetic substrate that is spent. Our study sought to identify the effects of different intensities of swimming on myocardial oxidative status and the blood lipid profile. Eighty Wistar rats (male and female) submitted to different intensities of a swimming regimen (low, LS; moderate, MS; or high, HS) for 16 weeks. Samples of blood and myocardium from the left ventricle were collected to determine lipid profiles and oxidative status. Reactive oxygen species (ROS) and antioxidant capacity against peroxyl radicals (ACAP), lipid profiles and lipid peroxidation was analyzed. ROS levels and ACAP were higher in male rats than in female rats overall (p<0.05). However, ACAP in the myocardium was significantly elevated in LS female rats compared to the MS and HS female rats, which had a significantly lower ACAP compared to all other groups. LS and MS training in both sexes and HS training (in females) led to significant decreases in the heart's lipid peroxidation. Amelioration of the lipid profile and reduction in oxidative damage contributed to a physiological state that benefits cardiovascular function in exercised animals. The results show that low and moderate intensity exercise promotes beneficial adaptations.

Influence of single bout of aerobic exercise on aortic pulse pressure

PURPOSE

Regular aerobic exercise has come to the forefront of non-pharmacological treatment for hypertension. In this line, post-exercise hypotension may have a potential tool for efficient blood pressure management. However, less is known about the influence of acute aerobic exercise on aortic pulse pressure (PP), an important property underlying the pathophysiology of cardiovascular disease. We tested the hypotheses that aortic PP would be attenuated with a single aerobic exercise and that its extent would be associated with the delayed return of reflected wave and the leg vasodilatory capacity.

METHODS

In 23 apparent healthy men (22 ± 4 years), hemodynamic variables and aortic pulse wave velocity (PWV) were measured before and 20 and 50 min after a 60-min bout of cycling exercise at moderate intensity (corresponding to 65-75 % heart rate reserve). Aortic pressure was estimated from applanation tonometrically measured radial arterial pressure waveform via general transfer function. Peak calf vascular dilatory capacity was measured with the ischemic exercise-induced hyperemia (via venous occlusion plethysmography).

RESULTS

Finger, brachial, and aortic PP were significantly attenuated following the exercise. At 20 min after the exercise cessation, individual changes in aortic PWV significantly correlated with corresponding changes in aortic PP (r = 0.541, P < 0.05), but this correlation was no longer significant at 50 min after the exercise cessation. Peak calf vascular dilatory capacity was not associated with change in aortic PP.

CONCLUSIONS

We conclude that in young men the aortic PP would be attenuated with the moderate-intensity dynamic exercise partly due to the delayed return of reflection wave from periphery.

Adolescent fatigue, POTS, and recovery: a guide for clinicians

Many teenagers who struggle with chronic fatigue have symptoms suggestive of autonomic dysfunction that may include lightheadedness, headaches, palpitations, nausea, and abdominal pain. Inadequate sleep habits and psychological conditions can contribute to fatigue, as can concurrent medical conditions. One type of autonomic dysfunction, postural orthostatic tachycardia syndrome, is increasingly being identified in adolescents with its constellation of fatigue, orthostatic intolerance, and excessive postural tachycardia (more than 40 beats/min). A family-based approach to care with support from a multidisciplinary team can diagnose, treat, educate, and encourage patients. Full recovery is possible with multi-faceted treatment. The daily treatment plan should consist of increased fluid and salt intake, aerobic exercise, and regular sleep and meal schedules; some medications can be helpful. Psychological support is critical and often includes biobehavioral strategies and cognitive-behavioral therapy to help with symptom management. More intensive recovery plans can be implemented when necessary.

Do we age because we have mitochondria?

The process of aging remains a great riddle. Production of reactive oxygen species (ROS) by mitochondria is an inevitable by-product of respiration, which has led to a hypothesis proposing the oxidative impairment of mitochondrial components (e.g., mtDNA, proteins, lipids) that initiates a vicious cycle of dysfunctional respiratory complexes producing more ROS, which again impairs function. This does not exclude other processes acting in parallel or targets for ROS action in other organelles than mitochondria. Given that aging is defined as the process leading to death, the role of mitochondria-based impairments in those organ systems responsible for human death (e.g., the cardiovascular system, cerebral dysfunction, and cancer) is described within the context of "garbage" accumulation and increasing insulin resistance, type 2 diabetes, and glycation of proteins. Mitochondrial mass, fusion, and fission are important factors in coping with impaired function. Both biogenesis of mitochondria and their degradation are important regulatory mechanisms stimulated by physical exercise and contribute to healthy aging. The hypothesis of mitochondria-related aging should be revised to account for the limitations of the degradative capacity of the lysosomal system. The processes involved in mitochondria-based impairments are very similar across a large range of organisms. Therefore, studies on model organisms from yeast, fungi, nematodes, flies to vertebrates, and from cells to organisms also add considerably to the understanding of human aging.

Effects of physical fitness on relaxed G-tolerance and the exercise pressor response

Fighter pilots are commonly recommended strength training as a means of improving the tolerance to withstand high gravitoinertial (G) loads. Previous studies on the effect of short-term strength-training regimens on G-endurance show equivocal results, with a majority of the studies suggesting improved G-endurance. The mechanisms underlying such improvement are unknown. Presumably, any change in G-tolerance induced by physical training habits should be manifest following long-term training. We also reasoned that during repeated straining maneuvers--as during certain G-endurance protocols--the relaxed G-tolerance and the exercise pressure response may play a significant role in maintaining adequate arterial pressure, and hence that different training modalities might alter G-endurance, by altering the exercise pressor response. Three groups of males were studied, long-term (>6 months) endurance-trained (E; n = 17), strength-trained (S; n = 16) and untrained (U; n = 17) individuals. The pressor response was studied during sustained (40 s) isometric knee extensions at 50 % of the maximal contraction level. Relaxed gradual onset-rate G-tolerance was determined. G-tolerance was similar in the E (4.6 ± 0.5 G), S (4.9 ± 0.8 G) and U (4.6 ± 0.8 G) groups. The mean arterial pressure increase during isometric exercise was higher in the S (36 ± 7 mmHg = mean ± SD) and U (35 ± 16 mmHg) groups than in the E group (28 ± 8 mmHg). The results suggest that relaxed G-tolerance is unaffected by physical training habits, and that the training modality affects the magnitude of the exercise pressor response. However, it seems that the response is blunted by endurance training rather than enhanced by strength training.

Effects of sildenafil on the gastrocnemius and cardiac muscles of rats in a model of prolonged moderate exercise training

Moderate exercise training improves energetic metabolism, tissue perfusion and induces cardiac and skeletal muscle remodeling. Sildenafil, a potent phosphodiesterase-5 inhibitor used to treat erectile dysfunction, reduces infarct size and increases tissue oxygenation in experimental models of cardiovascular disease. We have evaluated the effects of prolonged moderate exercise training and a repeat administration of sildenafil on the rat gastrocnemius and cardiac muscles. Animals were divided into two groups: sedentary and trained. Each group was subdivided into animals treated with vehicle or with two doses of sildenafil (10 or 15 mg/kg/day) during the last week of training. Physical exercise did not induce cardiac hypertrophy, whereas it increased mRNA levels of the PGC-1α, HIF-1α and VEGF genes, which are involved in mitochondrial biogenesis and angiogenesis, and reduced mRNA levels of FoxO3a, MuRF-1 and Atrogin-1. Sildenafil dose-dependently promoted both angiogenesis, as shown by increased capillary density, and muscle atrophy, as shown by muscle fibre size. These effects were more pronounced in trained animals. Our data confirm the beneficial effects of a moderate and prolonged training on cardiovascular and skeletal systems and document the positive and negative effects of sildenafil on these tissues at doses higher than those used in clinical practice. This report may impact on the use of sildenafil as a substance able to influence sports performance.