Biomedical subjects

Jennifer H Walsh

Publications and source records attributed to Jennifer H Walsh.

7 recordsLinked to original sources

PubMed2005

Quantitative upper airway imaging with anatomic optical coherence tomography.

BACKGROUND: Measurements of upper airway size and shape are important in investigating the pathophysiology of obstructive sleep apnea (OSA) and in devising, applying, and determining the effectiveness of treatment modalities. We describe an endoscopic optical technique (anatomic optical coherence tomography, aOCT) that provides quantitative real-time imaging of the internal anatomy of the human upper airway. METHODS: Validation studies were performed by comparing aOCT- and computed tomography (CT)-derived measurements of cross-sectional area (CSA) in (1) conduits in a wax phantom and (2) the velo-, oro-, and hypopharynx during wakefulness in five volunteers. aOCT scanning was performed during sleep in one subject with OSA. RESULTS: aOCT generated images of pharyngeal shape and measurements of CSA and internal dimensions that were comparable to radiographic CT images. The mean difference between aOCT- and CT-derived measurements of CSA in (1) the wax phantom was 2.1 mm(2) with limits of agreement (2 SD) from -13.2 to 17.4 mm(2) and intraclass correlation coefficient of 0.99 (p < 0.001) and (2) the pharyngeal airway was 14.1 mm(2) with limits of agreement from -43.7 to 57.8 mm(2) and intraclass correlation coefficient of 0.89 (p < 0.001). aOCT generated quantitative images of changes in upper airway size and shape before, during, and after an apneic event in an individual with OSA. CONCLUSIONS: aOCT generates quantitative, real-time measurements of upper airway size and shape with minimal invasiveness, allowing study over lengthy periods during both sleep and wakefulness. These features should make it useful for study of upper airway behavior to investigate OSA pathophysiology and aid clinical management.

Adult↗

PubMed2004

Comparison of forearm blood flow responses to incremental handgrip and cycle ergometer exercise: relative contribution of nitric oxide.

The contribution of endothelium-derived nitric oxide (NO) to exercise hyperaemia remains controversial. Disparate findings may, in part, be explained by different shear stress stimuli as a result of different types of exercise. We have directly compared forearm blood flow (FBF) responses to incremental handgrip and cycle ergometer exercise in 14 subjects (age +/-s.e.m.) using a novel software system which calculates conduit artery blood flow continuously across the cardiac cycle by synchronising automated edge-detection and wall tracking of high resolution B-mode arterial ultrasound images and Doppler waveform envelope analysis. Monomethyl arginine (L-NMMA) was infused during repeat bouts of each incremental exercise test to assess the contribution of NO to hyperaemic responses. During handgrip, mean FBF increased with workload (P < 0.01) whereas FBF decreased at lower cycle workloads (P < 0.05), before increasing at 120 W (P < 0.001). Differences in these patterns of mean FBF response to different exercise modalities were due to the influence of retrograde diastolic flow during cycling, which had a relatively larger impact on mean flows at lower workloads. Retrograde diastolic flow was negligible during handgrip. Although mean FBF was lower in response to cycling than handgrip exercise, the impact of L-NMMA was significant during the cycle modality only (P < 0.05), possibly reflecting the importance of an oscillatory antegrade/retrograde flow pattern on shear stress-mediated release of NO from the endothelium. In conclusion, different types of exercise present different haemodynamic stimuli to the endothelium, which may result in differential effects of shear stress on the vasculature.

Enzyme Inhibitors↗

PubMed2004

Comparison of resistance and conduit vessel nitric oxide-mediated vascular function in vivo: effects of exercise training.

Exercise training improves vascular function in subjects with cardiovascular disease and risk factors, but there is mounting evidence these vascular adaptations may be vessel bed specific. We have therefore examined the hypothesis that exercise-induced improvements in conduit vessel function are related to changes in resistance vessel function. Endothelium-dependent and -independent conduit vessel function were assessed by using wall-tracking of high-resolution brachial artery ultrasound images of the response to flow-mediated dilation (FMD) and nitroglycerine [glyceryl trinitrate (GTN)] administration. Resistance vessel endothelium-dependent and -independent function were assessed using intrabrachial administration of acetylcholine (ACh) and nitroprusside (SNP). Randomized crossover studies of 8-wk exercise training were undertaken in untreated hypercholesterolemic (n = 10), treated hypercholesterolemic (n = 10), coronary artery disease (n = 8), and Type 2 diabetic subjects (n = 15). Exercise training significantly enhanced responses to ACh (P < 0.05) and FMD (P < 0.0001). There were no significant changes in either SNP or GTN responses. The correlation between ACh and FMD responses at entry was not significant (r = 0.186; P = 0.231), and training-induced changes in the ACh did not correlate with those in FMD (r = -0.022; P = 0.890). Similarly, no correlation was evident between the SNP and GTN responses at entry (r = -0.010; P = 0.951) or between changes in these variables with training (r = -0.211; P = 0.191). We conclude that, although short-term exercise training improves endothelium-dependent nitric oxide-mediated vascular function in both conduit and resistance vessels, the magnitude of these improvements are unrelated.

Acetylcholine↗

PubMed2004

Vasomotor responses to hypoxia in type 2 diabetes.

Type 2 diabetes is associated with vascular dysfunction, accelerated atherosclerotic morbidity, and mortality. Abnormal vasomotor responses to chemoreflex activation may contribute to the acceleration of atherosclerotic diabetes complications, but these responses have not previously been investigated. We measured forearm mean blood flow (MBF) and mean vascular conductance (MVC) responses to isocapnic hypoxia in seven healthy and eight type 2 diabetic subjects during local intra-arterial saline infusion and alpha-adrenergic blockade (phentolamine). The effects of hypoxia on saline and phentolamine responses significantly differed between groups; relative to normoxia, the %DeltaMVC with hypoxia during saline was -3.3 +/- 11.2% in control and 24.8 +/- 13.3% in diabetic subjects, whereas phentolamine increased hypoxic %DeltaMVC to similar levels (39.4 +/- 9.7% in control subjects and 48.0 +/- 11.8% in diabetic subjects, P < 0.05, two-way ANOVA). Absolute normoxic MBF responses during saline infusion were 91.9 +/- 21.1 and 77.9 +/- 15.3 in control and diabetic subjects, respectively, and phentolamine increased normoxic MBF to similar levels (165.2 +/- 40.1 ml/min in control subjects and 175.9 +/- 32.0 ml/min in diabetic subjects; both P < 0.05). These data indicate that diabetic and control subjects exhibit similar responses to hypoxia in the presence of alpha-adrenergic blockade despite evidence of exaggerated alpha-mediated vasoconstriction at rest.

Adrenergic alpha-Antagonists↗

PubMed2003

Exercise-induced improvement in endothelial dysfunction is not mediated by changes in CV risk factors: pooled analysis of diverse patient populations.

We have pooled data from a series of our exercise training studies undertaken in groups with a broad range of vascular (dys) function to the examine the hypothesis that exercise-induced improvements in the conduit and/or resistance vessel function are related to improvements in risk factors for cardiovascular (CV) disease. Endothelium-dependent and -independent conduit vessel function were assessed by using wall tracking of high-resolution ultrasound images of the brachial artery response to flow-mediated dilation (FMD) and glyceryl trinitrate. Resistance vessel function was assessed using intrabrachial administration of acetylcholine (ACh), sodium nitroprusside, and NG-monomethyl-l-arginine. Randomized cross-over studies of 8-wk exercise training were undertaken in untreated hypercholesterolemic (n = 11), treated hypercholesterolemic (n = 11), coronary artery disease (n = 10), chronic heart failure (n = 12), Type 2 diabetic (n = 15), and healthy control subjects (n = 16). Exercise training did not significantly alter plasma lipids, blood pressure, blood glucose, waist-to-hip ratio, or body mass index values, despite significant improvement in both FMD and ACh responses. There were no correlations between changes in any risk factor variables and indexes of either resistance or conduit vessel function. We conclude that, in these subjects with antecedent vascular dysfunction, the beneficial effects of relatively short-term exercise training on vascular function are not solely mediated by the effects of exercise on CV risk factors.

Acetylcholine↗

PubMed2003

Effects of exercise training on conduit and resistance vessel function in treated and untreated hypercholesterolaemic subjects.

AIMS: Despite the importance of both lipid metabolism and physical activity to cardiovascular health, few studies have examined the effect of exercise training on vascular function in hypercholesterolaemic humans. METHODS AND RESULTS: A randomized, cross-over design investigated the effect of 8 weeks of combined aerobic and resistance exercise training on conduit and resistance vessel function in 11 untreated subjects with hypercholesterolaemia and 11 subjects taking lipid-lowering medication. High-resolution vascular ultrasonography following forearm ischaemia and glyceryl trinitrate administration determined conduit vessel endothelium-dependent and independent function. Strain-gauge plethysmography, with intra-aerial infusions of acetylcholine, sodium nitroprusside and N(G)-monomethyl-L-arginine, determined resistance vessel function. Flow-mediated dilation and the forearm blood flow response to acetylcholine improved significantly following training in the treated subgroup (both P<0.05) but not the untreated, although the blood flow response to N(G)-monomethyl-L-arginine was augmented following training in the untreated subjects (P<0.05), indicating greater basal nitric oxide bioactivity. Training did not alter responsiveness to glyceryl trinitrate or sodium nitroprusside. CONCLUSIONS: Combined aerobic and resistance training improves endothelium-dependent conduit and resistance vessel function in hypercholesterolaemic subjects taking lipid-lowering medications and basal nitric oxide bioactivity in untreated hypercholesterolaemic subjects. Exercise training may provide additional cardiovascular benefits for hypercholesterolaemic patients including those taking lipid-lowering medication.

Cholesterol↗

PubMed2003

Exercise training improves conduit vessel function in patients with coronary artery disease.

It is well established that endothelial dysfunction is present in coronary artery disease (CAD), although few studies have determined the effect of training on peripheral conduit vessel function in patients with CAD. A randomized, crossover design determined the effect of 8 wk of predominantly lower limb, combined aerobic and resistance training, in 10 patients with treated CAD. Endothelium-dependent dilation of the brachial artery was determined, by using high-resolution vascular ultrasonography, from flow-mediated vasodilation (FMD) after ischemia. Endothelium-independent vasodilation was measured after administration of glyceryl trinitrate (GTN). Baseline function was compared with that of 10 control subjects. Compared with matched healthy control subjects, FMD and GTN responses were significantly impaired in the untrained CAD patients [3.0 +/- 0.8 (SE) vs. 5.8 +/- 0.8% and 14.5 +/- 1.9 vs. 20.4 +/- 1.5%, respectively; both P < 0.05]. Training significantly improved FMD in the CAD patients (from 3.0 +/- 0.8 to 5.7 +/- 1.1%; P < 0.05) but not responsiveness to GTN (14.5 +/- 1.9 vs. 12.1 +/- 1.4%; P = not significant). Exercise training improves endothelium-dependent conduit vessel dilation in subjects with CAD, and the effect, evident in the brachial artery, appears to be generalized rather than limited to vessels of exercising muscle beds. These results provide evidence for the benefit of exercise training, as an adjunct to routine therapy, in patients with a history of CAD.

Brachial Artery↗