Noninvasive determination of local wavespeed and distensibility of the femoral artery by comb-excited Fourier velocity-encoded magnetic resonance imaging: measurements on athletic and nonathletic human subjects

Is individual day-to-day variation of arterial stiffness associated with variation of maximal aerobic performance?

Background

Maximal aerobic capacity, e.g. maximal oxygen uptake (V̇O₂max), is not constant, and it has a time-dependent variation based on the condition of individual. On the other hand, arterial properties play an important role in determining aerobic performance, and lower arterial stiffness is associated with higher cardiorespiratory fitness levels. This study examined whether individual variations in maximal aerobic performance are associated with arterial stiffness.

Methods

Twenty-four (mean age, 19.8 ± 0.2 y) and 10 (mean age, 21.2 ± 0.2 y) recreationally active young men and women participated in Experiment 1 (Ex1) and in Experiment 2 (Ex2), respectively. Aerobic performance was assessed using a graded power test (Ex1) or a 1500-m time trial (Ex2). Simultaneously, brachial-ankle pulse wave velocity (baPWV) was measured as an index of arterial stiffness in both Ex1 and Ex2 before the exercise trials. In both experiments, subjects returned for measurement of baPWV and V̇O₂max or 1500-m time trial at 1 month after first measurements.

Results

No significant differences in mean baPWV, V̇O₂max or 1500-m run time were seen between first and second visits. Mean baPWV was significantly lower on days when participants showed higher V̇O₂max or better 1500-m run time (P = 0.001 each) than on days when participants showed lower V̇O₂max or worse 1500-m run time. In addition, a significant relationship was seen between individual changes in baPWV from first to second visits and changes in V̇O₂max (P=0.0001) or 1500-m run time (P=0.04).

Conclusion

These findings suggest that individual day-to-day variations in maximal aerobic performance are associated with variations in arterial stiffness.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13102-021-00231-1.

The role of oxygen transport in atherosclerosis and vascular disease

Atherosclerosis and vascular disease of larger arteries are often associated with hypoxia within the layers of the vascular wall. In this review, we begin with a brief overview of the molecular changes in vascular cells associated with hypoxia and then emphasize the transport mechanisms that bring oxygen to cells within the vascular wall. We focus on fluid mechanical factors that control oxygen transport from lumenal blood flow to the intima and inner media layers of the artery, and solid mechanical factors that influence oxygen transport to the adventitia and outer media via the wall's microvascular system-the vasa vasorum (VV). Many cardiovascular risk factors are associated with VV compression that reduces VV perfusion and oxygenation. Dysfunctional VV neovascularization in response to hypoxia contributes to plaque inflammation and growth. Disturbed blood flow in vascular bifurcations and curvatures leads to reduced oxygen transport from blood to the inner layers of the wall and contributes to the development of atherosclerotic plaques in these regions. Recent studies have shown that hypoxia-inducible factor-1α (HIF-1α), a critical transcription factor associated with hypoxia, is also activated in disturbed flow by a mechanism that is independent of hypoxia. A final section of the review emphasizes hypoxia in vascular stenting that is used to enlarge vessels occluded by plaques. Stenting can compress the VV leading to hypoxia and associated intimal hyperplasia. To enhance oxygen transport during stenting, new stent designs with helical centrelines have been developed to increase blood phase oxygen transport rates and reduce intimal hyperplasia. Further study of the mechanisms controlling hypoxia in the artery wall may contribute to the development of therapeutic strategies for vascular diseases.

Evaluating the progressive cardiovascular health benefits of short-term high-intensity interval training

PURPOSE

High-intensity training is recognised as a time-efficient way of improving aerobic fitness. However, there is a lack of consensus regarding the temporal nature of adaptation response and which peripheral and cardiac changes occur using the same exercise stimulus and protocol. Therefore, this study aimed to evaluate the progression of vascular and cardiac changes over a 6-week training period.

METHODS

Twelve healthy males (age 21 ± 2 years; 42.5 ± 8.3 ml min^-1 kg^-1) participated in a high-intensity training programme consisting of 1-min sprints, interspersed with 2 min active recovery, 3 days/week for 6 weeks on a cycle ergometer. Cardiac, vascular, blood lipids and VO_2max measurements were taken at 0, 3 and 6 weeks and compared against a participant-matched control group (age 21 ± 2 years; 37.7 ± 8.3 ml min^-1 kg^-1).

RESULTS

There was a significant improvement in VO_2max (42.5 ± 8.3-47.4 ± 8.5 ml min^-1 kg^-1; p = 0.009) in the training group and a significant decrease in systolic blood pressure (8%) from 0 to 6 weeks (p = 0.025). There was a small yet significant decrease in ejection fraction and increased end-systolic volume in both groups over time (p = 0.01) with no significant interaction effect (p > 0.05). A between-group difference in peak velocity of early diastolic mitral annular motion was also observed (p = 0.01). No improvements were seen in blood lipid profiles, central arterial stiffness and cardiometabolic risk score.

CONCLUSIONS

Six weeks of high-intensity training increases aerobic fitness and is enough to stimulate initial reductions in peripheral pressure, but not sufficient to elicit structural and functional cardiac changes, reduce arterial stiffness or lower CV risk.

Usefulness of arterial compliance in the thigh in predicting exercise capacity in individuals without coronary heart disease

This study examined the relation between arterial compliance of the lower extremities and aerobic capacity in patients with a broad spectrum of cardiovascular risk but without overt coronary heart disease (CHD). Local arterial compliance was noninvasively measured in the thigh and calf in 104 men and 99 women using air plethysmography. Subjects also underwent maximal exercise treadmill testing as a measure of aerobic capacity. In univariate analysis, age (r = -0.49, p <0.001), systolic blood pressure at rest (r = -0.27, p <0.001), pulse pressure (r = -0.39, p <0.001), total cholesterol (r = -0.25, p <0.001), triglycerides (r = -0.025, p <0.001), non-high-density lipoprotein cholesterol (r = -0.23, p <0.001), high-sensitivity C-reactive protein (r = -0.21, p = 0.002), and low-density lipoprotein cholesterol (r = -0.15, p = 0.03) all demonstrated a significant inverse association with treadmill time. Thigh and calf compliance demonstrated a significant positive association with treadmill time (r = 0.48, p <0.001; r = 0.46, p <0.001). In multivariate analysis, thigh compliance (p = 0.003), age (p <0.001), gender (p = 0.005), and triglycerides (p = 0.017) were independent predictors of treadmill time. In conclusion, thigh compliance measured with a simple-to-use, fully automated device independently predicts aerobic fitness in patients with a wide range of cardiovascular risk but without CHD.

Local and regional wave speed in the aorta: effects of arterial occlusion

Arterial wave speed is widely used to determine arterial distensibility and has been utilised as a surrogate marker for vascular disease. A comparison between the results of the traditional foot-to-foot method for measuring wave speed to those of the pressure-velocity loop (PU-loop) method is one of the primary objectives of this paper. We also investigate the regional wave speed along the aorta, and the effect of arterial occlusion on the PU-loop measured in the ascending aorta. In 11 anaesthetised dogs, a total occlusion lasting 3 min was produced at four sites: upper thoracic, diaphragm, abdominal and left iliac artery. Pressure and flow in the ascending aorta and pressure proximal to the occlusion site were measured, and data were collected before, during the occlusion and after the occlusion had been removed. In control conditions, the wave speeds determined by the PU-loop in the aortic root were systematically lower than those measured by the foot-to-foot method. During thoracic and diaphragm occlusions, mean aortic pressure and wave speed increased significantly but returned to control values after each occlusion had been removed. The PU-loop is an objective and easy to use method for determining wave speed and can be advantageous for use in short arterial segments when local measurements of pressure and velocity are available.

Large artery stiffness: implications for exercise capacity and cardiovascular risk

1. Large artery stiffness, or its inverse, compliance, determines pulse pressure, which, in turn, influences myocardial work capacity and coronary perfusion, both of which impact on exercise capacity and cardiovascular risk. 2. In support of a role for arterial properties in exercise performance, aerobically trained athletes (aged 30-59 years) have lower arterial stiffness than their sedentary counterparts. Furthermore, in healthy older subjects (aged 57-80 years), time to exhaustion on treadmill testing correlated positively with arterial compliance. 3. Arterial stiffness is more closely linked to exercise capacity and myocardial risk in patients with coronary disease where, independently of degree of coronary disease, those with stiffer proximal arteries have a lower exercise-induced ischaemic threshold. 4. Moderate aerobic training elevates resting arterial compliance by approximately 30%, independently of mean pressure reduction, in young healthy individuals but not in isolated systolic hypertensive patients. Rat training studies support a role for exercise training in structural remodelling of the large arteries. 5. High-resistance strength training is associated with stiffer large arteries and higher pulse pressure than matched controls. 6. Large artery stiffness is an important modulator of the myocardial blood supply and demand equation, with significant ramifications for athletic performance and ischaemic threshold in coronary disease patients. Moderate aerobic training, but not high-resistance strength training, reduces large artery stiffness in young individuals whereas older subjects with established isolated systolic hypertension are resistant to such adaptation.

Assessment of arterial blood flow characteristics in normal and atherosclerotic vessels with the fast Fourier flow method

The purpose of this study was to scrutinize the ability of magnetic resonance imaging (MRI)-performed measurements to compare arterial flow patterns in patients with peripheral arterial occlusive disease (PAOD), healthy volunteers (HV) and endurance athletes (EA). MRI blood flow data were partially repeated with Doppler ultrasound (DUS) with a view to a methodical comparison. Additionally, pulse wave velocity was assessed with the MUFF technique. For this purpose, MRI-performed flow measurements were performed in the common femoral artery in 21 patients with PAOD, in 34 HV and in 12 EA. The analysis included maximum flow velocities (MFV), velocity/time profile (VTP), pulse wave velocity (Vpulse), and vessel diameter (VD). In addition, MFV and VD were observed by DUS in most individuals. The results revealed a significant change regarding arterial blood flow characteristics in patients compared with HV and EA, with respect to the span between the peak positive and negative blood flow velocity in the femoral artery. The pulse wave velocity in patients was markedly elevated compared with healthy individuals. Furthermore, a complete, characteristic change in the VTP could be observed in patients. The methodical comparison between DUS and MRI showed a good correlation. Multi-slice Fourier flow data have indicated markedly increased pulse wave velocity in PAOD patients. Changes in the arterial blood flow can be clearly observed with MRI. In the future, this might offer a noninvasive possibility not only for the evaluation of the stage of the disease, but also for the detection of early, pre-clinical stages of atherosclerosis.

The effects of voluntary running on cardiac mass and aortic compliance in Wistar-Kyoto and spontaneously hypertensive rats

OBJECTIVE

To investigate the effects of voluntary running exercise from 4-20 weeks of age on aortic compliance in Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR).

DESIGN

For each species we made comparisons between rats housed with an exercise wheel locked (10 rats) and unlocked (10 rats).

METHODS

Rats were killed using CO2 asphyxia and the aorta and heart of each rat were rapidly removed. The heart was dissected and weighed. A 4 mm descending proximal aortic ring was mounted on wires in an organ bath for determination of static compliance from the slope of the diameter-pressure relationship derived using Laplace's equation.

RESULTS

During the final 2 weeks of training WKY rats ran an average of 7.9 +/- 1.0 km/24 h compared with 1.0 +/- 0.2 km/24 h for SHR. Body weights of WKY rats and SHR and of animals housed with locked and unlocked exercise wheels did not differ. The septum, left ventricle and total heart weights and left ventricular:body weight ratios of sedentary SHR were greater than those of sedentary WKY rats. Trained WKY rats had significantly higher atrial, left and right ventricular and total heart weights and left ventricular:body weight ratios than did untrained WKY rats. Aortic compliance was higher in trained than it was in sedentary WKY rats (12.3 +/- 0.4 versus 14.2 +/- 0.5 microm/mmHg, P < 0.05). There was no difference between heart weights and aortic compliances of SHR housed with exercise wheels locked and unlocked.

CONCLUSION

Exercise-trained WKY rats had greater intrinsic aortic compliance when it was measured statically in vitro, which supports results of previous human work revealing a blood-pressure-independent component in the elevation of arterial compliance with training. The lower physical activity of the SHR strain used in this study could contribute to their higher blood pressures and lack of change in aortic compliance with exercise training.