Lower-Limb Arterial Stiffness: Assessment, Novel Physiological Insight and Clinical Potential

There is an urgent need to identify novel cardiovascular biomarkers which can improve cardiovascular disease (CVD) risk prediction and permit timely-efficacious treatment; necessary to combat the unabated rise in global CVD. Arterial stiffness, representing the ability of an artery to accommodate changes in blood pressure by corresponding changes in dimension, has emerged as an important biomarker of CVD risk. Central (aortic) arterial stiffness, assessed using carotid-femoral pulse wave velocity (cfPWV), is the reference standard, improving the prediction of cardiovascular events beyond conventional risk factors. Whilst cfPWV is a powerful discriminator of CVD risk, its dependence on blood pressure limits its clinical utility. In contrast to cfPWV, the clinical value of lower-limb arterial stiffness has received little attention and its role in CVD risk is not well understood; its measurement may well improve CVD risk prediction by providing unique CVD risk information. The purpose of this thesis is to identify the clinical utility of lower-limb arterial stiffness, assessed using femoral-ankle PWV (faPWV). Using experimental and epidemiological research approaches, this thesis demonstrated that faPWV can be assessed simply with accuracy and precision and provides additional CVD risk information beyond conventional risk factors and existing lower-limb arterial health measures. The assessment of faPWV also permits determination of the aortic-femoral arterial stiffness gradient (af-SG), a novel biomarker of promising clinical utility. This thesis demonstrated that the af-SG has stronger associations with CVD than cfPWV alone, can be determined with acceptable precision, and is blood pressure independent. These findings indicate that the assessment of lower-limb arterial stiffness could be of clinical utility and may permit better identification of CVD risk

Strength and forearm volume differences in boulderers and sport climbers

Summary – Twenty-eight participants were divided into three groups: control (n=10), sport climbers (n=9) and boulderers (n=9) to investigate the determinants of grip strength between climbing disciplines. Forearm volume (FAV) was measured using water displacement method. Maximal volitional contraction (MVC) was assessed using an open crimp grip on a climbing specific fingerboard apparatus. There were no significant differences in FAV between disciplines. However, there was a significant main effect for MVC and MVC/FAV across all groups. Boulderers had higher MVC than sport (MD=7.5 CI=1.8-13.2) and controls (MD=17.7 CI= 11.9-23.6) and sport climbers was higher than controls (MD= 10.2 CI = 4.5-15.9. The findings suggest that the greater MVC seen in boulderers and sport climbers may be a result of neural adaptations, not muscular hypertrophy

Editorial: Non-Invasive Measures of Cardiovascular Function and Health: Special Considerations for Assessing Lifestyle Behaviours

In recent decades it has become clear that lifestyle behaviors such as diet (1), risky alcohol consumption (2), cigarette smoking (Wang et al.), sedentary behavior (3), and physical inactivity (4) are all factors contributing to cardiovascular disease (CVD) incidence and mortality. And, as cardiovascular diseases remain the largest cause of death in the Western world, gaining further knowledge of cardiovascular dysfunction in response to these lifestyle behaviors is of paramount importance. This Research Topic which includes 14 research papers (Figure 1), has helped further our knowledge in three important areas of lifestyle behaviors and cardiovascular physiology: First, it has highlighted the importance several modifiable, behavioral risk factors associated with CVD (El-Battrawy et al.;Wang et al.; Zuo et al.), second, it has expanded our understanding of a number of biomarkers and risk scores which are related to CVD (Bo et al.; Cang et al.; Hsu et al.; Tsai et al.; Ying et al.), third it helped us to better understand and interpret markers of arterial stiffness (Elliot et al.; Lane-Cordova and Bouknight; Stone et al.) and lastly, it has allowed us to provide guidance on how to assess cardiovascular function in response to a common and biologically novel lifestyle behavior, prolonged sitting (Stoner et al.). Collectively this new information is an important step forwards in improving our understanding of CVD, and allows us to work toward the development of public health policy aimed at reducing the CVD burden

Systolic and Diastolic Left Ventricular Mechanics during and after Resistance Exercise

PURPOSE: To improve the current understanding of the impact of resistance exercise on the heart, by examining the acute responses of left ventricular (LV) strain, twist and untwisting rate ('LV mechanics'). METHODS: LV echocardiographic images were recorded in systole and diastole before, during and immediately after (7-12 s) double leg press exercise at two intensities (30% and 60% of maximum strength, 1-repetition-maximum, 1RM). Speckle tracking analysis generated LV strain, twist and untwisting rate data. Additionally, beat-by-beat blood pressure was recorded and systemic vascular resistance (SVR) and LV wall stress were calculated. RESULTS: Responses in both exercise trials were statistically similar (P > 0.05). During effort, stroke volume decreased while SVR and LV wall stress increased (P 0.05). Immediately following exercise, systolic LV mechanics returned to baseline levels (P < 0.05) but LV untwisting rate increased significantly (P < 0.05). CONCLUSIONS: A single, acute bout of double leg-press resistance exercise transiently reduces systolic LV mechanics, but increases diastolic mechanics following exercise, suggesting that resistance exercise has a differential impact on systolic and diastolic heart muscle function. The findings may explain why acute resistance exercise has been associated with reduced stroke volume but chronic exercise training may result in increased LV volumes

Differences in oxygenation kinetics between the dominant and non-dominant flexor digitorum profundus in rock climbers

Purpose. This study examined differences in oxygenation kinetics in the non-dominant and dominant flexor digitorum profundus (FDP) of rock climbers. Methods. Participants consisted of 28 sport climbers with a range of on-sight abilities (6a+ to 8a French Sport). Using near infrared spectroscopy, oxygenation kinetics of the FDP was assessed by calculating the time to half recovery (t½ recovery) of the tissue saturation index (TSI) following 3-5 min of ischemia. Results. A 2-way mixed model ANOVA found a non-significant interaction (p =0.112) for TSI x sex. However, there was a significant the main effect (p =0.027) handedness (dominant vs. non-dominant FDP). The dominant forearm recovered 13.6% quicker (t½ recovery mean difference = 1.12 sec, 95% CI 0.13 to 2.10 sec) compared to the non-dominant FDP. This was not affected by 6-month on-sight climbing ability or sex (p =0.839, p =0.683). Conclusions. Significant intra-individual differences in oxygenation kinetics of the FDP were found. Improvements in oxygenation kinetics within the FDP are likely due to the abilities of the muscle to deliver, perfuse and consume oxygen. These enhancements may be due to structural adaptations in the microvasculature such as an increase in capillary density and an enhanced improvement in capillary filtration

The validity and reliability of continuous-wave near -infrared spectroscopy for the assessment of leg blood volume during an orthostatic challenge.

Near-infrared spectroscopy (NIRS) can potentially be used to assess the cardiovascular autonomic system by monitoring orthostatic challenge-induced shifts in lower limb blood volume. However, in order to be of clinical utility the test must be valid, reliable, and relatively simple to conduct. Purpose: To induce lower limb blood volume shifts using a 10min 70o head-up tilt, and: (1) in the soleus, determine the validity of an inexpensive continuous wave (cw)-NIRS device by comparing to a criterion frequency-domain (fd-) NIRS device, (2) determine the between-day reliability of soleus assessments obtained from cw-NIRS and fd-NIRS; and, (3) compare the between-day reliability for fd-NIRS assessments obtained at the soleus (standard) and gastrocnemius (simpler alternative). Methods: Fifteen non-smoking healthy adults were tested on 3 different mornings, under standardized conditions, separated by a maximum of 7 days. Total haemoglobin concentration (tHb) was continuously monitored bi-laterally in the medial soleus using cw-NIRS and fd-NIRS. For site comparison, tHb was measured in the medial gastrocnemius using fd-NIRS. Results: (1) The area under the curve (AUC) for cw-NIRS and fd-NIRS assessments at the soleus were not significantly different (p =.619). (2) The criterion (0.75) intra-class correlation coefficient (ICC) was exceeded for both cw-NIRS and fd-NIRS. (3) The criterion ICC was exceeded for both soleus and gastrocnemius assessments. Conclusion: Continuous-wave NIRS can be used to monitor orthostatic stress-induced shifts in lower leg blood volume with acceptable validity and reliability. This orthostatic test may present a relatively simple and inexpensive approach for assessing the cardiovascular autonomic nervous system