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

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

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

Cerebrospinal fluid opening pressure: The effect of body mass index and body composition

Objectives: Idiopathic intracranial hypertension (IIH) is strongly related to obesity. The relationship between intracranial pressure, body mass index (BMI), percentage body fat and distribution of body fat in non-IIH patients remains less clear. The aim of this study was to examine the relationship between intracranial pressure and body type in non-IIH patients. Patients and Methods: Lumbar puncture manometry was used to measure cerebrospinal fluid opening pressure (CSFOP). BMI, in addition to neck, waist and hip circumferences were Journal Pre-proof calculated. Air displacement plethysmography (BODPOD) was used to assess body composition. Results: Data was collected from 100 subjects. 11 subjects with conditions known to cause raised intracranial pressure were excluded from analysis. According to Pearson correlation factors displaying a significant relationship with CSFOP included: BMI (R = 0.635, p<0.0001); waist circumference (R = 0.498, p<0.0001), hip circumference (R = 0.513, p<0.0001) and percentage body fat (R = 0.435, p<0.001). Multivariate analysis indicated that BMI was the only independent factor which predicted CSFOP. Sub-analysis according to gender indicated that BMI was predictive in females and percentage body fat was predictive in males. We did not identify any differences in BMI, percentage body fat or distribution of body fat in 7 IIH patients and 7 weight-matched non-IIH patients. Conclusion: BMI and %body fat both positively correlated with CSFOP, but BMI was more predictive in women and %body fat was more predictive in men. We did not find a relationship between distribution of body fat and CSFOP

The effect of an acute bout of resistance exercise on carotid artery strain and strain rate

Arterial wall mechanics likely play an integral role in arterial responses to acute physiological stress. Therefore, this study aimed to determine the impact of low and moderate intensity double-leg press exercise on common carotid artery (CCA) wall mechanics using 2D vascular strain imaging. Short-axis CCA ultrasound images were collected in 15 healthy men (age: 21 ± 3 years; stature: 176.5 ± 6.2 cm; body mass; 80.6 ± 15.3 kg) before, during, and immediately after short-duration isometric double-leg press exercise at 30% and 60% of participants’ one-repetition maximum (1RM: 317 ± 72 kg). Images were analyzed for peak circumferential strain (PCS), peak systolic and diastolic strain rate (S-SR and D-SR) and arterial diameter. Heart rate (HR), systolic and diastolic blood pressure (SBP and DBP) were simultaneously assessed and arterial stiffness indices were calculated post hoc. A two-way repeated measures ANOVA revealed that during isometric contraction, PCS and S-SR decreased significantly (P < 0.01) before increasing significantly above resting levels post-exercise (P < 0.05 and P < 0.01 respectively). Conversely, D-SR was unaltered throughout the protocol (P = 0.25). No significant differences were observed between the 30% and 60% 1RM trials. Multiple regression analysis highlighted that HR, BP and arterial diameter did not fully explain the total variance in PCS, S-SR and D-SR. Acute double-leg press exercise is therefore associated with similar transient changes in CCA wall mechanics at low and moderate intensities. CCA wall mechanics likely provide additional insight into localized intrinsic vascular wall properties beyond current measures of arterial stiffness

Carotid artery wall mechanics in young males with high cardiorespiratory fitness

The influence of cardiorespiratory fitness (CRF) on arterial stiffness in young adults remains equivocal. Beyond conventional measures of arterial stiffness, 2D strain imaging of the common carotid artery (CCA) provides novel information related to the intrinsic properties of the arterial wall. Therefore, this study aimed to assess the effect of CRF on both conventional indices of CCA stiffness and 2D strain parameters, at rest and following a bout of aerobic exercise in young healthy males. Short‐axis ultrasound images of the CCA were recorded in 34 healthy men [22 years (95%CI, 19–22)] before, and immediately after 5‐minutes of aerobic exercise (40% VO2max). Images were analysed for arterial diameter, peak circumferential strain (PCS), and peak systolic and diastolic strain rates (S‐SR, D‐SR). Heart rate (HR), systolic and diastolic blood pressure (SBP, DBP) were simultaneously assessed and Petersons' elastic modulus (Ep) and Beta stiffness (β1) were calculated. Participants were separated post hoc into moderate and high fitness groups [VO2max: 48.9 ml.kg‐1 min‐1 (95%CI, 44.7–53.2) vs. 65.6 ml.kg‐1 min‐1 (95%CI, 63.1–68.1); P 0.13) but were elevated in the moderate‐fitness group post‐exercise (P 0.05). High‐fit individuals exhibit elevated CCA PCS and S‐SR, which may reflect training‐induced adaptations that help to buffer the rise in pulse‐pressure and stroke volume during exercise