Optical and other methods for the assessment of arterial and venous insufficiency

There are a number of different techniques used to diagnose vascular insufficiency ranging from expensive hospital based equipment to less expensive devices used in primary care centres. Currently, some of these devices are unsuitable for use on patients with diabetes or DVI and have poor sensitivity for detecting moderate PAD patients. Additionally, some of the tests, particularly for DVI, require tourniquets or the patient to perform postural changes which some may find difficult. This may extend testing time. The study investigated 2 groups of patients, one with PAD and the other with DVI. The arterial group consisted of 46 controls and 57 patients. PPG probes were placed on the index finger and great toe. The venous group consisted of 24 controls and 25 patients and PPG probes were placed behind the knee and 10 cm above the medial malleolus. Duplex ultrasound was used as the gold standard to assess the arteries and veins in the lower limbs. The aim was to investigate whether signals acquired from patients at rest using Photoplethysmography (PPG) could be used as a screening tool. Pulse wave transit time (PWTT) and shape analysis techniques were used on the pulses from the patients with PAD, while time base and spectral analysis techniques were used on the waveforms of patients with DVI. PWTT and shape analysis techniques achieved sensitivities and specificities of 82% and 84% respectively. Accuracy dropped to 70% for detecting patients with moderate PAD. Spectral analysis techniques gave the best results for detecting patients with DVI achieving sensitivities and specificities of 69% and 80% respectively. In conclusion, reducing the signal acquisition time on patients with PAD did not significantly reduce the sensitivity and specificity. Without any patient movement it was difficult to separate patients with DVI from healthy normals.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Optical and other methods for the assessment of arterial and venous insufficiency

There are a number of different techniques used to diagnose vascular insufficiency ranging from expensive hospital based equipment to less expensive devices used in primary care centres. Currently, some of these devices are unsuitable for use on patients with diabetes or DVI and have poor sensitivity for detecting moderate PAD patients. Additionally, some of the tests, particularly for DVI, require tourniquets or the patient to perform postural changes which some may find difficult. This may extend testing time. The study investigated 2 groups of patients, one with PAD and the other with DVI. The arterial group consisted of 46 controls and 57 patients. PPG probes were placed on the index finger and great toe. The venous group consisted of 24 controls and 25 patients and PPG probes were placed behind the knee and 10 cm above the medial malleolus. Duplex ultrasound was used as the gold standard to assess the arteries and veins in the lower limbs. The aim was to investigate whether signals acquired from patients at rest using Photoplethysmography (PPG) could be used as a screening tool. Pulse wave transit time (PWTT) and shape analysis techniques were used on the pulses from the patients with PAD, while time base and spectral analysis techniques were used on the waveforms of patients with DVI. PWTT and shape analysis techniques achieved sensitivities and specificities of 82% and 84% respectively. Accuracy dropped to 70% for detecting patients with moderate PAD. Spectral analysis techniques gave the best results for detecting patients with DVI achieving sensitivities and specificities of 69% and 80% respectively. In conclusion, reducing the signal acquisition time on patients with PAD did not significantly reduce the sensitivity and specificity. Without any patient movement it was difficult to separate patients with DVI from healthy normals

The Effects of Transcutaneous Electrical Neurostimulation on Analgesia and Peripheral Perfusion

Peripheral arterial occlusive disease (PAOD) affects 8 to 12 million Americans over the age of 50. As the disease progresses, arterial occlusions arising from atherosclerotic lesions inhibit normal metabolic vasodilation in the peripheries, resulting in limb ischemia and claudication. Pharmacological and surgical treatments currently used to treat both the hemodynamic and pain symptoms associated with PAOD can involve adverse and potentially life-threatening side effects. Thus, there is a need for additional innovative therapies for PAOD. Neurostimulation has a known analgesic effect on both acute and chronic pain. Although the exact mechanisms remain under investigation, local vascular tone may be modulated by neurostimulation in addition to pain modulation. The Gate Control Theory proposes that electrical activation of mechanoreceptive afferent somatosensory nerves, specifically Aβ fibers, inhibits pain signaling to the brain by activating an inhibitory interneuron in the dorsal horn of the spinal cord which dampens signaling from afferent, C type peripheral nociceptor nerves. Interestingly, Aβ fiber activation may also inhibit norepinephrine release from sympathetic nerve terminals on efferent neurons by activating α-2 adrenergic receptors along the same dermatome, resulting in localized vasodilation in both limbs. Ultimately, electrical stimulation may decrease mean blood pressure and increase local blood flow. The focus of this study was to optimize protocols and perform a small scale clinical study to investigate hemodynamic and analgesic responses to neurostimulation during acute ischemia. We hypothesized that ganglial transcutaneous electrical neurostimulation (TENS) and interferential current (IFC) treatments would decrease pain perception and vascular resistance in the periphery in young, healthy subjects. We further hypothesized that IFC may have a greater hyperemic and analgesic effect on acute ischemia than TENS as its current waveform may be more efficient at overcoming skin impedance. Interestingly, we found trends suggesting that TENS and IFC may increase vascular resistance (VR) and have no noticeable analgesic effect, though TENS may have a slightly lower increase in VR associated with an increase in pain. Further work characterizing the hemodynamic effects of different stimulus waveforms is needed to inform future research into possible neuromodulation therapies for ischemic disease

Objective assessment of microcirculatory response in venous disease to therapy

Venous stasis is associated with leucocyte & endothelial activation as well as local growth factor response in chronic venous distasease (CVD). There is no good data on the response of this increased activation to treatment. The theme of this thesis was to show changes in leucocyte/endothelial activation as well as microcirculatory stasis in response to medical, surgical and compression therapy. Thus these may act as objective measures of response to treatment. Vascular endothelial growth factor (VEGF) is being investigated extensively in various arterial scenarios I demonstrated high plasma levels of among patients with CVD for the first time. Levels in patients were about 60% higher (82pg Vs 52 pg in controls). This may represent an (reparative!) angiogenic response existing along with the leucocyte inflammatory response. I used a model of medical treatment (60 days oral flavonoid therapy) and demonstrated significant change in plasma VEGF (50% reduction i.e. 98 pg to 57 pg/dl), ICAM (32%), VCAM (29%) & lactoferrin (36%) levels in patients. Thus I showed that endothelial cell activation (ECA) as well as VEGF might be used as an objective surrogate marker in CVD. I propose that amelioration of endothelial activation may be a mechanism of action for these compounds. I studied the response of these parameters to surgical treatment of varicose veins in 20 patients. I showed that there is an increased plasma lactoferrin at 4 weeks that goes below starting base line levels at 6 months (865 Vs 870 Vs 519). VEGF levels continued to increase (65 Vs 83 Vs 134 pg/dl) in these patients and this may represent vascular remodelling. Although not all of them are easily explainable, the microcirculatory parameters were shown to have a definable response to therapy. I used a new apparatus (Laser capillary anemometer) to assess the response of the velocity of blood in the microvasculature of patients with venous, arterial or mixed disease. I demonstrated that compression increases velocity of blood in the sub-papillary plexus & lower levels of compression (20 mm Hg) are more effective in increasing velocity in patients with mixed disease. This may explain the basis for using compression therapy in these patients. Thus I have shown that various parameters of microcirculation may be used to assess the response to therapy in CVD. Future uses of these findings may include design of new and novel therapeutic approaches and to prognosticate for the development of skin changes and ulceration of the leg in CVD

Inactivity and exercise in peripheral arterial disease: effect on vascular health and functional capacity

Background: Peripheral arterial disease (PAD) is a form of cardiovascular disease characterized by atherosclerotic occlusion of blood flow to peripheral tissue. Intermittent claudication, a symptom of PAD, can severely impair functional capacity and daily physical activity. Exercise is an established treatment for PAD and improvement in endothelial function is proposed as a mechanism through which exercise improves PAD symptoms. Study 1: This study determined total daily sedentary time and the duration of sedentary bouts in 22 men and women, 69.0 ± 8.4 yr, with PAD and examined the relation between these behaviours and disease severity, functional capacity, CV risk factors, endothelial function, and quality of life (QOL). Participants spent 68% of the waking day sedentary and 36% of this time was accumulated in sedentary bouts >60 min. Excessive sedentary time was related to PAD severity and QOL. Prolonged sedentary bouts were related to PAD severity and CV risk factors. Study 2: This study compared the effect of acute intermittent walking to the onset of claudication (OC) and to maximal claudication (MC) on endothelial function and inflammatory markers in 10 men and women, 70.4 ± 7.9 yr, with PAD. Acute intermittent exercise to both OC and MC had no effect on endothelial function or inflammatory markers. Study 3: The effect of a 12-week community-based exercise programme on endothelial function, disease severity, functional capacity, daily activity and sedentary behaviour, and QOL was evaluated in 11 men and women, 67.6 ± 9.2 yr, with PAD. There was a significant improvement in endothelial function, functional capacity, daily activity and sedentary behaviour, and QOL. Conclusion: Reducing and breaking up sedentary time may have positive health implications in PAD. Intermittent exercise to MC may be a more effective and time efficient exercise prescription than submaximal exercise. Community-based exercise is an effective treatment option for PAD