One of the earliest sub-clinical stages associated with atherosclerosis is endothelial dysfunction (ED), which has been shown to predict future cardiovascular events. Chronic exercise is thought to improve endothelium-dependent vasodilation; however, few studies have evaluated the effects of acute exercise on vascular function (VF). Moreover, studies evaluating ED following an exercise training program lack a standardized time frame in which to measure VF. Although most studies require subjects to abstain from exercise for 24 hours prior to any VF measure, no study to date has assessed VF longer than 24 hours after the cessation of exercise. Additionally, no studies have compared VF responses in obese and non-obese individuals following acute exercise. Purpose: Therefore, the purpose of this study was to evaluate VF, as determined by the assessment of forearm blood flow (FBF) and vascular reactivity (VR) before and up to 48 hours after a single bout of maximal exercise in obese and non-obese males. Methods: Twelve obese (37.0 ± 1.1 kg/m2) and twelve non-obese (21.9 ± 0.3 kg/m2) males volunteered to participate. FBF was assessed before and during reactive hyperemia (RH). FBF measures were obtained prior to (PRE-E), immediately after (POST-E), and at 1 (POST-1), 2 (POST-2), 24 (POST-24), and 48 (POST-48) hours after exercise. Total excess flow, calculated as the difference between baseline FBF and FBF during RH, was used as an indicator of VR. Blood samples were also obtained at each time point to evaluate the response of interleukin-6 (IL-6) and tumor necrosis factor alpha (TNF-α), which are potential modifiers of VF. Results: Baseline FBF and FBF during RH were significantly (P < 0.05) increased in both groups POST-E before returning to baseline values by POST-1. VR was enhanced in both groups POST-E, although the magnitude of change was greater in non-obese males. VR was significantly (P < 0.05) increased in non-obese males POST-E and was not significantly (P < 0.05) reduced until POST-48. Concentrations of IL-6 and TNF-α were unchanged in response to exercise in non-obese and obese males. Conclusions: An acute bout of maximal exercise significantly increased forearm endothelium-dependent vasodilation in non-obese and obese males. Additionally, an increased reactive vasodilation was observed only in non-obese males following exercise. These results also suggest that in non-obese males, measurements used to verify improvements in VF following exercise training should be employed after a minimum of 48 hours following physical activity.

A number of investigators have examined psychological stress-induced endothelial dysfunction, however, the underlying mechanisms for these responses have not been clearly elucidated. The purpose of this study was to compare the effects of mental challenge on forearm blood flow, total antioxidant capacity (a measure of oxidative stress), the release of norepinephrine (NE; stress induced neurotransmitter), and pro-inflammatory cytokine responses [both lipopolysaccharide (LPS)-stimulated TNF-α and IL-6 cytokine and mRNA] in lean and obese individuals. Twelve subjects who had a BMI above 30 kg/m2 and were above 30% body fat were categorized as obese and twelve subjects with a BMI below 25 kg/m2 and were below 25% body fat were categorized as lean subjects. Blood samples were drawn and forearm blood flow was assessed prior to and following subjects’ participation in a mental challenge protocol consisting of a computer-based Stroop Color-Word task and mental arithmetic task, for a total of 20 minutes. The mental challenge elicited an elevation in HR and NE in both the lean and obese groups. Furthermore, both lean and obese groups demonstrated an increase in FBF following the mental challenge, whereas no changes in total antioxidant capacity were observed. In addition, the lean group exhibited an increase in LPS-stimulated TNF-α cytokine production from baseline to following the mental challenge, whereas the obese group demonstrated a decrease in LPS-stimulated TNF-α cytokines. This corresponded with a decrease in LPS-stimulated TNF-α mRNA expression in the obese group, although the obese subjects maintained higher levels of both measurements (LPS-stimulated TNF-α cytokine and mRNA expression) compared with the lean group. Furthermore, in the LPS-stimulated IL-6 cytokine response, the obese group demonstrated a greater increase than the lean group following the mental challenge, even though both groups showed an increase in LPS-stimulated IL-6 mRNA expression. These findings suggest that the magnitude and direction of LPS-stimulated TNF-α cytokine response and mRNA expression and LPS-stimulated IL-6 cytokine response to acute stress may be dependent upon the effects of the additional percentage of body fat seen in obese individuals.

Despite over a century of inquiry, the mechanisms that achieve the close matching of oxygen supply to demand during exercise remain elusive. It has been proposed that in addition to its role as the primary oxygen carrier, the red blood cell (RBC) functions as a roving oxygen sensor, linking the oxygen demand at the muscle with oxygen delivery via the circulation (Ellsworth et al. 1995). It is hypothesised that the RBC would release adenosine triphosphate (ATP) in proportion to the number of unoccupied binding sites on the haemoglobin molecule as it traverses regions of high oxygen demand such as the microcirculation of active skeletal muscle. ATP would then stimulate the release of vasodilatory substances from the endothelium which would diffuse to neighbouring vascular smooth muscle resulting in vasodilation and an increase in blood flow in accordance with the oxygen demand set by the muscle. The first step in establishing a role for this mechanism during exercise in humans is to determine whether ATP increases in the venous blood draining an active muscle bed. Based on the handful of published studies, there is an increase in ATP concentration in the femoral vein during knee extensor exercise. However the response has not been studied in other vascular beds in humans. As such, the main aim of this thesis was to measure the ATP response to dynamic handgrip exercise. Secondary aims were to determine whether the response was modified by hypoxia, and to provide information about the timing of the changes in ATP concentration during a bout of handgrip exercise. These questions were addressed in Studies 3 and 4. Because blood flow is central to this hypothesis, a substantial portion of this thesis was also associated with the measurement of forearm blood flow (FBF) using venous occlusion strain gauge plethysmography (VOSGP), and this was conducted in Studies 1 and 2. VOSGP is based on the assumption that with venous outflow prevented, any increase in limb volume is proportional to the rate of arterial inflow. The rate of arterial inflow is determined as the slope of the change in limb volume over time. The slope must be calculated over the initial linear portion of this relationship, when arterial inflow is unaffected by the inevitable rise in venous pressure associated with venous occlusion. VOSGP was initially used to measure blood flow at rest and in response to pharmacological interventions which produced only modest increases in arterial inflow (Joyner et al. 2001). However, measurement of the high rates of arterial inflow that occur with exercise may challenge the limits of this technique. Tschakovsky et al. (1995) reported a marked reduction in arterial inflow over the first four cardiac cycles during venous occlusion following static handgrip exercise that elevated blood flow to 22-24 mL/min/100mL. Only during the first cardiac cycle was arterial inflow unaffected by cuff inflation. As such, the window for measuring high rates of arterial inflow may be very brief. Therefore Study 1 aimed to determine whether blood flow could be measured using VOSGP across the range of arterial inflows that occur with dynamic handgrip exercise. Participants (n = 7) completed four, five-minute bouts of dynamic handgrip exercise at 15, 30, 45, and 60% of maximum voluntary contraction (MVC). FBF was measured using VOSGP at rest, and following five minutes of dynamic handgrip exercise. The slope of the change in limb volume was measured over the first one, two, three, and four consecutive cardiac cycles following the onset of occlusion. FBF was 2.5 ± 0.5 at rest, and 16.5 ± 4.9, 24.9 ± 9.4, 44.1 ± 22.0, and 57.8 ± 14.9 mL/min/100mL following five minutes of exercise at 15, 30, 45, and 60% MVC, respectively. At rest, arterial inflow decreased across the four cardiac cycles (P = 0.017 for the main effect), however post-hoc pairwise comparisons revealed no significant differences between any of the cardiac cycles. In contrast, the inclusion of two, three, or four cardiac cycles at 30 and 60% MVC, and three or four cardiac cycles at 15 and 45% MVC resulted in reductions in calculated arterial inflow compared with using the first cardiac cycle alone (P > 0.05). The inclusion of just two cardiac cycles resulted in a 9-26% reduction in calculated arterial inflow depending on the workload. This reduction was even more pronounced when three (19-40%) or four (26-50%) cardiac cycles were included. In conclusion, resting FBF can be calculated over at least four cardiac cycles during venous occlusion at rest. However, exercising FBF should be calculated from the first cardiac cycle only following dynamic handgrip exercise across the range of intensities used in this study. This extends the findings of Tschakovsky et al. (1995) who demonstrated this effect following handgrip exercise at a single intensity. Study 2 was designed to establish the FBF response to dynamic handgrip exercise, whether the workloads produced different blood flow responses, and to establish the within- and between-day reproducibility of FBF measured using VOSGP. In Part A (within-day reproducibility), participants (n = 7) completed three trials of dynamic handgrip exercise at four intensities (15, 30, 45, and 60% MVC), with each exercise trial separated by 10 minutes of rest. In Part B (between-day reproducibility) participants (n = 7) completed three trials of dynamic handgrip exercise at 15, 30, and 45% MVC on three separate days within a two week period. FBF was measured at rest, and each minute of exercise during brief (5-7 second) pauses in contractions. FBF response. FBF increased from rest at all workloads (P > 0.05), and then plateaued between Minutes 1 to 5 at the 15 and 30% MVC workloads and between Minutes 2 and 5 at the 45% workload (P > 0.05 for each minute compared to Minute 5). Too few participants completed the 60% workload to permit any statistical analysis. FBF reached values of 13.0 ± 2.0, 26.8 ± 8.4, 44.8 ± 14.9, and 52.9 ± 5.1 mL/min/100mL in the final minute of exercise at the 15, 30, 45, and 60% MVC workloads. FBF was different between the 15, 30, and 45% workloads by Minute 3 (P > 0.05). Reproducibility. The within-day test-retest reliability of exercising FBF was poor to moderate (ICC = 0.375-0.624) with individual coefficients of variation (CVs) ranging from 6-25%, 9-23%, and 9-31% for the 15, 30, and 45% MVC workloads, respectively. The between-day test-retest reliability for resting FBF was moderate (ICC = 0.644, P > 0.05; individual CVs between 1 and 31%). Between-day test-retest reliability for exercising FBF was poor to moderate (ICC = 0.381-0.614), with individual CVs ranging from 14-24%, 8-23%, and 6-18% for the 15, 30, and 45% workloads, respectively. It was concluded from this study that VOSGP provides adequately reproducible measurements to detect changes in FBF of the magnitude seen between workloads in this study. However, the variability in the measurement precludes its use when smaller differences are of interest. Based on the previous findings reporting an increase in ATP concentration during dynamic knee extensor exercise in the leg (Gonzalez-Alonso et al. 2002; Yegutkin et al. 2007), Study 3 was designed to determine whether ATP concentration increased in the venous effluent during dynamic handgrip exercise in the forearm. Since the deoxygenation of haemoglobin is a primary stimulus for ATP release from red blood cells, a further aim was to determine whether this response was augmented by systemic hypoxia. Participants (n = 6) completed four, five-minute bouts of dynamic handgrip exercise at 30, 45, 65, and 85% MVC under normoxia (inspired oxygen fraction = 0.21) and hypoxia (inspired oxygen fraction = 0.12). Blood samples for the determination of ATP concentration were drawn at rest and 180 seconds after the onset of exercise at each workload from a catheter inserted into a forearm vein. Venous plasma ATP concentration at rest was 0.28 ± 0.11 μM/L and remained unchanged during exercise at workloads up to 85% MVC (P > 0.05). Systemic hypoxia, sufficient to reduce arterial oxygen saturation to 83 ± 2%, also failed to alter the plasma ATP concentration (P = 0.148). The lack of a change in ATP concentration was unexpected but there are several possible explanations. It is possible, although unlikely, that ATP was not released in the forearm microcirculation. The previous demonstration that ATP increased in response to static handgrip exercise (Forrester and Lind 1969) would suggest that this was probably not the case. When considered in the context of the findings from Study 4, the most plausible explanation is that a less than optimal blood sampling site may have hindered the measurement of a change in ATP. The blood flow response at the onset of dynamic exercise in the forearm is at least biphasic; Phase 1 describes the immediate, large increase in blood flow within 2 seconds of the onset of exercise and is believed to be governed by mechanical factors whereas Phase 2 has a latency of ~20 seconds and describes a further, slower increase until blood flow reaches steady state (Saunders et al. 2005b). The temporal characteristics of Phase 2, along with the fact that blood flow during this phase is closely related to the metabolic rate of the muscle, suggest regulation by metabolic factors. Currently there is scant evidence detailing the time course of vasodilator release, although it is important to demonstrate that the release of a vasodilatory substance precedes the blood flow response it is proposed to influence (Delp 1999). ATP is released from red blood cells in proportion to the offloading of oxygen and a reduction in the oxygen content of venous blood draining a muscle bed occurs within 10 seconds of the onset of exercise. Thus the release of ATP should follow soon thereafter. As such, Study 4 was designed to determine whether ATP increased in the venous effluent of the forearm following 30 and 180 seconds of dynamic handgrip exercise at 45% MVC; and whether this increase corresponded with a decrease in venous oxygen content. Participants (n = 10) completed two bouts of dynamic handgrip exercise at 45% MVC; the first was one minute in duration, and the second was four minutes in duration. Venous blood samples for the determination of ATP and venous oxygen content were drawn at rest and during exercise from a catheter inserted in a retrograde manner into the median cubital vein. Arterialised samples for the estimation of arterial blood gases and ATP concentration were obtained from the non-exercising hand. ATP concentration in arterialised blood from the non-exercising arm was 0.79 ± 0.30 μM/L at rest and remained unchanged at both time points during exercise (P > 0.05). ATP concentration in the venous blood of the exercising arm increased from 0.60 ± 0.17 μM/L at rest to 1.04 ± 0.33 μM/L 30 seconds after the onset of exercise (P > 0.05), and remained at this higher level after 180 seconds (0.92 ± 0.26 μM/L, P > 0.05 versus rest). This corresponded with a decrease in venous oxygen content from 103 ± 23 mL/L at rest to 68 ± 16 mL/L 30 seconds after the onset of exercise (P > 0.05) and 76 ± 15 mL/L (P > 0.05 versus rest) 180 seconds into exercise. Furthermore, at 180 seconds of exercise, ATP concentration was moderately and inversely related to venous oxygen content (r = -0.651, p > 0.05). In conclusion, this study provides the first evidence that ATP concentration is increased in the blood draining the exercising forearm muscles in response to dynamic handgrip exercise. The finding that ATP concentration was increased just 30 seconds after the onset of exercise is also novel, and particularly interesting in the context of the recently reported dynamic response characteristics of the forearm blood flow response. In conclusion, the work contained within this thesis provides several important findings. The first study has provided evidence that measuring high rates of arterial inflow using VOSGP is possible, but that the window for making these measurements is small, probably as brief as a single cardiac cycle. The second study demonstrated that while the reproducibility of forearm blood flow measurements using VOSGP is poor, it is adequate to detect the large changes that occurred between workloads. However, VOSGP cannot be used to detect more modest differences. Common to both Study 3 and 4 was the measurement of ATP at rest, and 180 seconds after the onset of dynamic handgrip exercise at 45% MVC. The primary difference was the position of the catheter which was inserted in an antegrade manner in Study 3, and in a retrograde manner in Study 4. Since ATP was unchanged in Study 3 but increased under similar conditions in Study 4, it is likely that ATP was also released during exercise in Study 3, but that a less than optimal blood sampling site precluded its measurement. This illustrates the necessity to sample blood from as close as possible to the probable site of ATP release, the muscle microcirculation. The most important and novel findings from this body of work come from Study 4. This is the first study to demonstrate an increase in ATP concentration in the forearm in response to dynamic handgrip exercise. However, the most novel finding was that ATP concentration was elevated just 30 seconds after the onset of exercise. Such an early increase has not previously been reported during dynamic exercise in any vascular bed. This is an important finding since establishing the time course for the release of vasodilatory substances is critical to our understanding of the mechanisms that regulate blood flow during exercise.

Thesis (Ph. D.)--Virginia Commonwealth University, 2009. / Prepared for: Dept. of Health and Human Performance. Title from resource description page. Includes bibliographical references.

O objetivo deste estudo foi comparar a resposta do vascular durante o teste de estresse mental em adultos sedentários (SED) e fisicamente ativos (FA) com apneia obstrutiva do sono (AOS). Os pacientes não tratados com AOS e sem outras comorbidades foram classificados em SED e FA de acordo com o Questionário Internacional de atividade física. A pressão sanguínea, a freqüência cardíaca, o fluxo sanguíneo do antebraço (FSA) (pletismografia) e a condutância vascular do antebraço (CVA = FSA/pressão sanguínea x 100) foram medidas continuamente em repouso (4 min), seguidas de 3 min do teste Stroop Color Word Test (SCWT) também conhecido como teste de estresse mental. Quarenta pacientes com AOS (homens = 24, idade = 50 ± 1 anos, índice de massa corporal = 29 ± 0,5 Kg/m2, índice de apneia hipopnéia = 39 ± 4 eventos/h) divididos em SED (n = 21) e FA (n = 19) apresentaram diferença significativa na quantidade de tempo gasto em atividade física (17 ± 9 vs. 245 ± 33 minutos/semana, respectivamente). Os grupos foram semelhantes em relação ao sexo, idade, índice de massa corporal, frequência cardíaca do nível educacional e pressão arterial média em repouso, bem como percepção de estresse no final do SCWT. Em contraste, FSA basal (1,7 ± 0,08 mL/min/100mL vs 2,5 ± 0,19 mL/min/100mL) e CVA (1,7 ± 0,07 vs 2,5 ± 0,2) foram significativamente menores no grupo SED quando comaprados a FA, respectivamente (p <0,05). A resposta de frequência cardíaca e pressão arterial ao SCWT foram semelhantes e aumentou em ambos os grupos. O FSA (3,5 ± 0,2 mL/min/100mL vs 2,4 ± 0,14 mL/min/100mL) e a CVA (3,5 ± 0,2 vs 2,3 ± 0,1) durante SCWT foi significativamente menor no grupo SED quando comparados ao grupo FA (P <0,05). Houve uma correlação significativa entre a atividade física no tempo de lazer e FSA (r = 0,57; P <0,05) e CVA (r = 0,48; P <0,05). Conclui-se, que, a resposta vascular nos pacientes com AOS é influenciada pelo nível de atividade física de lazer. O alto nível de atividade física pode proteger a disfunção cardiovascular em repouso e na condição de estresse mental em pacientes com AOS moderado a severo / The objective of this study was to compare a vascular response during the mental stress test in sedentary (SED) and physically active (PA) patients with obstructive sleep apnea (OSA). Patients not treated with OSA and without other comorbidities were classified in SED and PA according to the International Questionnaire of Physical Action. Blood pressure, heart rate, forearm blood flow (plethysmography) and forearm vascular conductance (FVC = FBF / blood pressure x 100) were measured continuously at rest (4 min), followed by 3 min of the test Stroop Color Word Test (SCWT) also known as mental stress test. Forty patients with OSA (men = 24, age = 50 ± 1 years, body mass index = 29 ± 0.5 kg / m2, apnea hypopnea index = 39 ± 4 events / h) divided in SED (n = 19) and PA (n = 19) presented a significant difference in the amount of time spent in physical activity (17 ± 9 vs. 245 ± 33 minutes / week, respectively). The groups are similar in relation to gender, age, body mass index, heart rate at educational level, and mean resting blood pressure, as well as perceived stress at the end of SCWT. In contrast, baseline FBF (1.7 ± 0.08 mL/min/100mL vs 2.5 ± 0.19 mL/min/100mL) and FVC (1.7 ± 0.07 U vs 2.5 ± 0.2 U) were significantly lower without SED group when compared to PA, respectively (p <0.05). The heart rate and blood pressure response to SCWT were similar and increased in both groups. The FBF (3.5 ± 0.2 mL/min/100mL vs 2.4 ± 0.14 mL/min/100mL) and the FVC (3.5 ± 0.2 U vs 2.3 ± 0.1 U) during SCWT was much lower in the SED group when compared to the group PA (P <0.05). There was a significant correlation between physical activity without leisure time and FBF (r = 0.57, P <0.05) and FVC (r = 0.48, P <0.05). In conclusion, the vascular response in OSA patients is influenced by the level of leisure physical activity. The high level of physical activity may protect a cardiovascular dysfunction at rest and mental stress condition in patients with moderate to severe OSA

O objetivo deste estudo foi comparar a resposta do vascular durante o teste de estresse mental em adultos sedentários (SED) e fisicamente ativos (FA) com apneia obstrutiva do sono (AOS). Os pacientes não tratados com AOS e sem outras comorbidades foram classificados em SED e FA de acordo com o Questionário Internacional de atividade física. A pressão sanguínea, a freqüência cardíaca, o fluxo sanguíneo do antebraço (FSA) (pletismografia) e a condutância vascular do antebraço (CVA = FSA/pressão sanguínea x 100) foram medidas continuamente em repouso (4 min), seguidas de 3 min do teste Stroop Color Word Test (SCWT) também conhecido como teste de estresse mental. Quarenta pacientes com AOS (homens = 24, idade = 50 ± 1 anos, índice de massa corporal = 29 ± 0,5 Kg/m2, índice de apneia hipopnéia = 39 ± 4 eventos/h) divididos em SED (n = 21) e FA (n = 19) apresentaram diferença significativa na quantidade de tempo gasto em atividade física (17 ± 9 vs. 245 ± 33 minutos/semana, respectivamente). Os grupos foram semelhantes em relação ao sexo, idade, índice de massa corporal, frequência cardíaca do nível educacional e pressão arterial média em repouso, bem como percepção de estresse no final do SCWT. Em contraste, FSA basal (1,7 ± 0,08 mL/min/100mL vs 2,5 ± 0,19 mL/min/100mL) e CVA (1,7 ± 0,07 vs 2,5 ± 0,2) foram significativamente menores no grupo SED quando comaprados a FA, respectivamente (p <0,05). A resposta de frequência cardíaca e pressão arterial ao SCWT foram semelhantes e aumentou em ambos os grupos. O FSA (3,5 ± 0,2 mL/min/100mL vs 2,4 ± 0,14 mL/min/100mL) e a CVA (3,5 ± 0,2 vs 2,3 ± 0,1) durante SCWT foi significativamente menor no grupo SED quando comparados ao grupo FA (P <0,05). Houve uma correlação significativa entre a atividade física no tempo de lazer e FSA (r = 0,57; P <0,05) e CVA (r = 0,48; P <0,05). Conclui-se, que, a resposta vascular nos pacientes com AOS é influenciada pelo nível de atividade física de lazer. O alto nível de atividade física pode proteger a disfunção cardiovascular em repouso e na condição de estresse mental em pacientes com AOS moderado a severo / The objective of this study was to compare a vascular response during the mental stress test in sedentary (SED) and physically active (PA) patients with obstructive sleep apnea (OSA). Patients not treated with OSA and without other comorbidities were classified in SED and PA according to the International Questionnaire of Physical Action. Blood pressure, heart rate, forearm blood flow (plethysmography) and forearm vascular conductance (FVC = FBF / blood pressure x 100) were measured continuously at rest (4 min), followed by 3 min of the test Stroop Color Word Test (SCWT) also known as mental stress test. Forty patients with OSA (men = 24, age = 50 ± 1 years, body mass index = 29 ± 0.5 kg / m2, apnea hypopnea index = 39 ± 4 events / h) divided in SED (n = 19) and PA (n = 19) presented a significant difference in the amount of time spent in physical activity (17 ± 9 vs. 245 ± 33 minutes / week, respectively). The groups are similar in relation to gender, age, body mass index, heart rate at educational level, and mean resting blood pressure, as well as perceived stress at the end of SCWT. In contrast, baseline FBF (1.7 ± 0.08 mL/min/100mL vs 2.5 ± 0.19 mL/min/100mL) and FVC (1.7 ± 0.07 U vs 2.5 ± 0.2 U) were significantly lower without SED group when compared to PA, respectively (p <0.05). The heart rate and blood pressure response to SCWT were similar and increased in both groups. The FBF (3.5 ± 0.2 mL/min/100mL vs 2.4 ± 0.14 mL/min/100mL) and the FVC (3.5 ± 0.2 U vs 2.3 ± 0.1 U) during SCWT was much lower in the SED group when compared to the group PA (P <0.05). There was a significant correlation between physical activity without leisure time and FBF (r = 0.57, P <0.05) and FVC (r = 0.48, P <0.05). In conclusion, the vascular response in OSA patients is influenced by the level of leisure physical activity. The high level of physical activity may protect a cardiovascular dysfunction at rest and mental stress condition in patients with moderate to severe OSA