Blood pressure and leg deoxygenation are exaggerated during treadmill walking in patients with peripheral artery disease

Sex differences in the purinergic 2 receptor-mediated blood pressure response to treadmill exercise in rats with simulated peripheral artery disease

We investigated the role played by ATP-sensitive purinergic 2 (P2) receptors in evoking the pressor response to treadmill exercise in male and female rats with and without femoral arteries that were ligated for ∼72 h to induce simulated peripheral artery disease (PAD). We hypothesized that PPADS (P2 receptor antagonist, 10 mg iv) would reduce the pressor response to 4 min of treadmill exercise (15 m·min-1, 1° incline) and steady-state exercise plasma norepinephrine (NE) values in male and female rats, and that the magnitude of effect of PPADS would be greater in rats with simulated PAD ("ligated") than in sham-operated rats. In males, PPADS significantly reduced the difference between steady-state exercise and baseline mean arterial pressure (ΔMAP) response to treadmill exercise in sham (n = 8; pre-PPADS: 12 ± 2, post-PPADS: 1 ± 5 mmHg; P = 0.037) and ligated (n = 4; pre-PPADS: 20 ± 2, post-PPADS: 11 ± 3 mmHg; P = 0.028) rats with a similar magnitude of effect observed between groups (P = 0.720). In females, PPADS had no effect on the ΔMAP response to treadmill exercise in sham (n = 6; pre-PPADS: 9 ± 2, post-PPADS: 7 ± 2 mmHg; P = 0.448) or ligated (n = 6; pre-PPADS: 15 ± 2, post-PPADS: 16 ± 3 mmHg; P = 0.684) rats. When NE values were grouped by sex independent of ligation/sham status, PPADS significantly reduced plasma NE in male (P = 0.016) and female (P = 0.027) rats. The data indicate that P2 receptors contribute to the sympathetic response to exercise in both male and female rats but that the sympathoexcitatory role for P2 receptors translates into an obligatory role in the blood pressure response to exercise in male but not in female rats.NEW & NOTEWORTHY Here, we demonstrate that purinergic 2 (P2) receptors contribute significantly to the blood pressure response to treadmill exercise in male rats both with and without simulated PAD induced by femoral artery ligation. We found no role for P2 receptors in the blood pressure response to treadmill exercise in female rats, thus revealing clear sex differences in P2 receptor-mediated blood pressure control during exercise.

Physiological responses during walking in men and women with intermittent claudication

BACKGROUND

Miyasato et al. show that peak oxygen consumption, walking economy, anaerobic threshold, and cardiovascular responses (heart rate, blood pressure, and rate pressure product) during walking were similar between men and women with peripheral artery disease and intermittent claudication. There were no differences in the physiological responses to walking between men and women with intermittent claudication. Sex per se is not a factor that demands changes in walking prescription for patients with intermittent claudication.

OBJECTIVE

Peak oxygen consumption (VO2peak), anaerobic threshold, walking economy, and cardiovascular responses during walking are used to guide and monitor walking training in patients with peripheral artery disease and intermittent claudication. Women with peripheral artery disease and intermittent claudication present greater impairments than men, and evaluating training markers according to sex for decisions regarding walking prescription in this population is important. This study aimed to compare VO2peak, walking economy, anaerobic threshold, and cardiovascular responses during walking in men and women with peripheral artery disease and intermittent claudication.

METHODS

Forty patients (20 men and 20 women with similar baseline characteristics) underwent a cardiopulmonary treadmill test (3.2km/h and 2% increase in slope every 2 minutes until maximal leg pain). The VO2 and rate-pressure product were assessed. Data from men and women were compared using t-tests.

RESULTS

There were no significant differences between men and women (VO2peak: 15.0±4.8 versus 13.9±2.9mL∙kg-1∙min-1, p=0.38; walking economy: 9.6±2.7 versus 8.4±1.6mL∙kg-1∙min-1, p=0.09; anaerobic threshold: 10.5±3.2 versus 10.5±2.2mL∙kg-1∙min-1, p=0.98; rate pressure product at 1st stage: 13,465± 2,910 versus 14,445±4,379bpm∙mmHg, p=0.41; and rate pressure product at anaerobic threshold:13,673±3,100 versus 16,390±5,870bpm∙mmHg, p=0.08 and rate pressure product at peak exercise: 21,253±6,141 versus 21,923±7,414bpm∙mmHg, p=0.76, respectively).

CONCLUSION

Men and women with peripheral artery disease and similar baseline characteristics presented similar responses to walking, suggesting that decisions regarding walking prescription and monitoring can be made regardless of sex in this specific population.

Neurocirculatory regulation and adaptations to exercise in chronic kidney disease

Chronic kidney disease (CKD) is characterized by pronounced exercise intolerance and exaggerated blood pressure reactivity during exercise. Classic mechanisms of exercise intolerance in CKD have been extensively described previously and include uremic myopathy, chronic inflammation, malnutrition, and anemia. We contend that these classic mechanisms only partially explain the exercise intolerance experienced in CKD and that alterations in cardiovascular and autonomic regulation also play a key contributing role. The purpose of this review is to examine the physiological factors that contribute to neurocirculatory dysregulation during exercise and discuss the adaptations that result from regular exercise training in CKD. Key neurocirculatory mechanisms contributing to exercise intolerance in CKD include augmentation of the exercise pressor reflex, aberrations in neurocirculatory control, and increased neurovascular transduction. In addition, we highlight how some contributing factors may be improved through exercise training, with a specific focus on the sympathetic nervous system. Important areas for future work include understanding how the exercise prescription may best be optimized in CKD and how the beneficial effects of exercise training may extend to the brain.

Bradykinin 2 receptors contribute to the exaggerated exercise pressor reflex in a rat model of simulated peripheral artery disease

We investigated the role played by bradykinin 2 (B2) receptors in the exaggerated exercise pressor reflex in rats with a femoral artery ligated for 72 h to induce simulated peripheral artery disease (PAD). We hypothesized that in decerebrate, unanesthetized rats with a ligated femoral artery, hindlimb arterial injection of HOE-140 (100 ng, B2 receptor antagonist) would reduce the pressor response to 30 s of electrically induced 1 Hz hindlimb skeletal muscle contraction, and 30 s of 1 Hz hindlimb skeletal muscle stretch (a model of mechanoreflex activation isolated from contraction-induced metabolite production). We hypothesized no effect of HOE-140 in sham-operated "freely perfused" rats. In both freely perfused (n = 4) and "ligated" (n = 4) rats, we first confirmed efficacious B2 receptor blockade by demonstrating that HOE-140 injection significantly reduced (P < 0.05) the peak increase in mean arterial pressure (peak ΔMAP) in response to hindlimb arterial injection of bradykinin. In subsequent experiments, we found that HOE-140 reduced the peak ΔMAP response to muscle contraction in ligated (n = 14; control: 23 ± 2; HOE-140: 17 ± 2 mmHg; P = 0.03) but not freely perfused rats (n = 7; control: 17 ± 3; HOE-140: 18 ± 4 mmHg; P = 0.65). Furthermore, HOE-140 had no effect on the peak ΔMAP response to stretch in ligated rats (n = 14; control: 37 ± 4; HOE-140: 32 ± 5 mmHg; P = 0.13) but reduced the integrated area under the blood pressure signal over the final ∼20 s of the maneuver. The data suggest that B2 receptors contribute to the exaggerated exercise pressor reflex in rats with simulated PAD, and that contribution includes a modest role in the chronic sensitization of the mechanically activated channels/afferents that underlie mechanoreflex activation.

Sensory neuron inositol 1,4,5-trisphosphate receptors contribute to chronic mechanoreflex sensitization in rats with simulated peripheral artery disease

The mechanoreflex is exaggerated in patients with peripheral artery disease (PAD) and in a rat model of simulated PAD in which a femoral artery is chronically (∼72 h) ligated. We found recently that, in rats with a ligated femoral artery, blockade of thromboxane A2 (TxA2) receptors on the sensory endings of thin fiber muscle afferents reduced the pressor response to 1 Hz repetitive/dynamic hindlimb skeletal muscle stretch (a model of mechanoreflex activation isolated from contraction-induced metabolite production). Conversely, we found no effect of TxA2 receptor blockade in rats with freely perfused femoral arteries. Here, we extended the isolated mechanoreflex findings in "ligated" rats to experiments evoking dynamic hindlimb skeletal muscle contractions. We also investigated the role played by inositol 1,4,5-trisphosphate (IP3) receptors, receptors associated with intracellular signaling linked to TxA2 receptors, in the exaggerated response to dynamic mechanoreflex and exercise pressor reflex activation in ligated rats. Injection of the TxA2 receptor antagonist daltroban into the arterial supply of the hindlimb reduced the pressor response to 1 Hz dynamic contraction in ligated but not "freely perfused" rats. Moreover, injection of the IP3 receptor antagonist xestospongin C into the arterial supply of the hindlimb reduced the pressor response to 1 Hz dynamic stretch and contraction in ligated but not freely perfused rats. These findings demonstrate that, in rats with a ligated femoral artery, sensory neuron TxA2 receptor and IP3 receptor-mediated signaling contributes to a chronic sensitization of the mechanically activated channels associated with the mechanoreflex and the exercise pressor reflex.

Quantifying tissue perfusion after peripheral endovascular procedures: Novel tissue perfusion endpoints to improve outcomes

Peripheral artery disease (PAD) is a flow-limiting condition caused by narrowing of the peripheral arteries typically due to atherosclerosis. It affects almost 200 million people globally with patients either being asymptomatic or presenting with claudication or critical or acute limb ischemia. PAD-affected patients display increased mortality rates, rendering their management critical. Endovascular interventions have proven crucial in PAD treatment and decreasing mortality and have significantly increased over the past years. However, for the functional assessment of the outcomes of revascularization procedures for the treatment of PAD, the same tests that have been used over the past decades are still being employed. Those only allow an indirect evaluation, while an objective quantification of limb perfusion is not feasible. Standard intraarterial angiography only demonstrates post-intervention vessel patency, hence is unable to accurately estimate actual limb perfusion and is incapable of quantifying treatment outcome. Therefore, there is a significant necessity for real-time objectively measurable procedural outcomes of limb perfusion that will allow vascular experts to intraoperatively quantify and assess outcomes, thus optimizing treatment, obviating misinterpretation, and providing significantly improved clinical results. The purpose of this review is to familiarize readers with the currently available perfusion-assessment methods and to evaluate possible prospects.

Body mass-normalized moderate dose of dietary nitrate intake improves endothelial function and walking capacity in patients with peripheral artery disease

Peripheral artery disease (PAD) is characterized by the accumulation of atherosclerotic plaques in the lower extremity conduit arteries, which impairs blood flow and walking capacity. Dietary nitrate has been used to reduce blood pressure (BP) and improve walking capacity in PAD. However, a standardized dose for PAD has not been determined. Therefore, we sought to determine the effects of a body mass-normalized moderate dose of nitrate (0.11 mmol nitrate/kg) as beetroot juice on serum nitrate/nitrite, vascular function, walking capacity, and tissue oxygen utilization capacity in patients with PAD. A total of 11 patients with PAD received either nitrate supplement or placebo in a randomized crossover design. Total serum nitrate/nitrite, resting BP, brachial and popliteal artery endothelial function (flow-mediated dilation, FMD), arterial stiffness (pulse-wave velocity, PWV), augmentation index (AIx), maximal walking distance and time, claudication onset time, and skeletal muscle oxygen utilization were measured pre- and postnitrate and placebo intake. There were significant group × time interactions (P < 0.05) for serum nitrate/nitrite, FMD, BP, walking distance and time, and skeletal muscle oxygen utilization. The nitrate group showed significantly increased serum nitrate/nitrite (Δ1.32 μM), increased brachial and popliteal FMD (Δ1.3% and Δ1.7%, respectively), reduced peripheral and central systolic BP (Δ-4.7 mmHg and Δ-8.2 mmHg, respectively), increased maximal walking distance (Δ92.7 m) and time (Δ56.3 s), and reduced deoxygenated hemoglobin during walking. There were no changes in PWV, AIx, or claudication (P > 0.05). These results indicate that a body-mass normalized moderate dose of nitrate may be effective and safe for reducing BP, improving endothelial function, and improving walking capacity in patients with PAD.

Effects of supervised exercise therapy on blood pressure and heart rate during exercise, and associations with improved walking performance in peripheral artery disease: Results of a randomized clinical trial

OBJECTIVE

Supervised exercise therapy (SET) improves walking ability in people with peripheral artery disease (PAD). However, the effects of SET on cardiovascular health in PAD remain unclear. Using data from a randomized clinical trial, this post hoc analyses investigated the effects of a 6-month SET intervention, compared with a control group, on changes in blood pressure (BP) and heart rate (HR) during a graded treadmill exercise test in people with PAD.

METHODS

We randomized 210 participants with PAD to either SET (3× weekly) or control (1× weekly health lectures) for 6 months. A graded treadmill exercise test, 6-minute walk test, and Walking Impairment Questionnaire were completed at baseline and the 6-month follow-up. BP and HR were measured at the end of each 2-minute stage of the graded treadmill exercise test. Mixed effects regression models compared the overall mean 6-month change in systolic BP, diastolic BP, pulse pressure (PP), and HR during the first 5 stages of the graded treadmill exercise test between groups.

RESULTS

Of the 210 randomized participants with PAD, 176 (67 ± 9 years; 72 [41%] female, 115 [65%] Black) completed the graded treadmill exercise test at baseline and the 6-month follow-up. Compared with the control group at the 6-month follow-up, SET significantly decreased overall mean systolic BP (-12 mm Hg; P < .001), PP (-9 mm Hg; P < .001), and HR (-7 b/min; P < .01) during a graded treadmill exercise test but not diastolic BP. Among participants randomized to SET, a greater decrease in systolic BP, PP, and HR during a graded treadmill exercise test was significantly associated with a greater improvement in 6-minute walk distance (systolic BP, r = -0.19 [P = .03] and PP, r = -0.23 [P < .01]; and HR, r = -0.21 [P < .01]) and with maximal treadmill walking distance (systolic BP, r = -0.21 [P < .01] and PP, r = -0.17 [P = .03]) at the 6-month follow-up. A greater decrease in the HR during a graded treadmill exercise test was significantly associated with a better WIQ distance score (r = -0.27; P = .03) at the 6-month follow-up.

CONCLUSIONS

In people with PAD, compared with a control group, SET improved cardiovascular health, measured by changes in BP and HR during exercise. The degree of improvement in cardiovascular health correlated with the degree of improvement in walking performance in people with PAD. NCT: 01408901.

The dynamic adjustment of mean arterial pressure during exercise: a potential tool for discerning cardiovascular health status

The regulation of mean arterial pressure (MAP) during exercise has important physiological and clinical implications. Kinetics analysis on numerous physiological variables following the transition from unloaded-to-loaded exercise has revealed important information regarding their control. Surprisingly, the dynamic response of MAP during this transition remains to be quantified. Therefore, ten healthy participants (5/5 M/F, 24 ± 3 yr) completed repeated transitions from unloaded to moderate- and heavy-intensity dynamic single-leg knee-extensor exercise to investigate the on-kinetics of MAP. Following the transition to loaded exercise, MAP increased in a first-order dynamic manner, subsequent to a time delay (moderate: 23 ± 10; heavy: 19 ± 9 s, P > 0.05) at a speed (τ, moderate: 59 ± 30; heavy: 66 ± 19 s, P > 0.05), which did not differ between intensities, but the MAP amplitude was doubled during heavy-intensity exercise (moderate: 12 ± 5; heavy: 24 ± 8 mmHg, P < 0.001). The reproducibility [coefficient of variation (CV)] during heavy intensity for unloaded baseline, amplitude, and mean response time, when assessed as individual transitions, was 7 ± 1%, 18 ± 2%, and 25 ± 4%, respectively. Averaging two transitions improved the CVs to 4 ± 1%, 8 ± 2%, and 13 ± 3%, respectively. Preliminary findings supporting the clinical relevance of evaluating MAP kinetics in middle-aged hypertensive (n = 5) and, age-matched, normotensive (n = 5) participants revealed an exaggerated MAP response in both older groups (P < 0.05), but the MAP response was slowed only for the patients with hypertension (P < 0.05). It is concluded that kinetics modeling of MAP is practical for heavy-intensity knee-extensor exercise and may provide insight into cardiovascular health and the effect of aging.NEW & NOTEWORTHY Kinetics analysis of physiological variables following workload transitions provides important information, but this has not been performed on mean arterial pressure (MAP), despite the clear clinical importance of this variable. This investigation reveals that kinetic modeling of MAP following unloaded-to-loaded knee-extensor exercise is practical and repeatable. Additional preliminary findings in hypertensive and, age-matched, normotensive subjects suggest that MAP kinetics may provide insight into cardiovascular health and the effect of aging.

Acute effects of leg heat therapy on walking performance and cardiovascular and inflammatory responses to exercise in patients with peripheral artery disease

Lower-extremity peripheral artery disease (PAD) is associated with increased risk of cardiovascular events and impaired exercise tolerance. We have previously reported that leg heat therapy (HT) applied using liquid-circulating trousers perfused with warm water increases leg blood flow and reduces blood pressure (BP) and the circulating levels of endothelin-1 (ET-1) in patients with symptomatic PAD. In this sham-controlled, randomized, crossover study, sixteen patients with symptomatic PAD (age 65 ± 5.7 years and ankle-brachial index: 0.69 ± 0.1) underwent a single 90-min session of HT or a sham treatment prior to a symptom-limited, graded cardiopulmonary exercise test on the treadmill. The primary outcome was the peak walking time (PWT) during the exercise test. Secondary outcomes included the claudication onset time (COT), resting and exercise BP, calf muscle oxygenation, pulmonary oxygen uptake (V̇O2 ), and plasma levels of ET-1, interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-α). Systolic, but not diastolic BP, was significantly lower (~7 mmHg, p < .05) during HT when compared to the sham treatment. There was also a trend for lower SBP throughout the exercise and the recovery period following HT (p = .057). While COT did not differ between treatments (p = .77), PWT tended to increase following HT (CON: 911 ± 69 s, HT: 954 ± 77 s, p = .059). Post-exercise plasma levels of ET-1 were also lower in the HT session (CON: 2.0 ± 0.1, HT: 1.7 ± 0.1, p = .02). Calf muscle oxygenation, V̇O2 , COT, IL-6, and TNF-α did not differ between treatments. A single session of leg HT lowers BP and post-exercise circulating levels of ET-1 and may enhance treadmill walking performance in symptomatic PAD patients.

Thromboxane A2 receptors mediate chronic mechanoreflex sensitization in a rat model of simulated peripheral artery disease

The exercise pressor reflex is a feedback autonomic and cardiovascular control mechanism evoked by mechanical and metabolic signals within contracting skeletal muscles. The mechanically sensitive component of the reflex (the mechanoreflex) is exaggerated in patients with peripheral artery disease (PAD) and in a rat model of simulated PAD in which a femoral artery is chronically ligated. Products of cyclooxygenase enzyme activity have been shown to chronically sensitize the mechanoreflex in PAD, but the identity of the muscle afferent receptors that mediate the sensitization is unclear. We hypothesized that injection of the endoperoxide 4 receptor (EP4-R) antagonist L161982 or the thromboxane A₂ receptor (TxA₂-R) antagonist daltroban into the arterial supply of the hindlimb would reduce the pressor response to repetitive, dynamic hindlimb skeletal muscle stretch (a model of isolated mechanoreflex activation) in rats with a femoral artery that was ligated ~72 h before the experiment but not in rats with freely perfused femoral arteries. We found that EP4-R blockade had no effect on the pressor response (peak Δmean arterial pressure) to stretch in freely perfused (n = 6, pre: 14 ± 2, post: 15 ± 2 mmHg, P = 0.97) or ligated (n = 8, pre: 29 ± 4, post: 29 ± 6 mmHg, P = 0.98) rats. In contrast, TxA₂-R blockade had no effect on the pressor response to stretch in freely perfused rats (n = 6, pre: 16 ± 3, post: 17 ± 4 mmHg, P = 0.99) but significantly reduced the response in ligated rats (n = 11, pre: 29 ± 4, post: 17 ± 5 mmHg, P < 0.01). We conclude that TxA₂-Rs contribute to chronic mechanoreflex sensitization in the chronic femoral artery-ligated rat model of simulated PAD.NEW & NOTEWORTHY We demonstrate that thromboxane A₂ receptors, but not endoperoxide 4 receptors, on the sensory endings of thin fiber muscle afferents contribute to the chronic sensitization of the muscle mechanoreflex in rats with a ligated femoral artery (a model of simulated peripheral artery disease). The data may have important implications for our understanding of blood pressure control during exercise in patients with peripheral artery disease.

Association of Blood Pressure Responses to Submaximal Exercise in Midlife With the Incidence of Cardiovascular Outcomes and All-Cause Mortality: The Framingham Heart Study

Background

Few studies examined the associations of midlife blood pressure (BP) responses to submaximal exercise with the risk of cardiovascular outcomes and mortality in later life.

Methods and Results

We evaluated 1993 Framingham Offspring Study participants (mean age, 58 years; 53.2% women) attending examination cycle 7. We related BP responses to submaximal exercise with prevalent subclinical cardiovascular disease (CVD) using multivariable linear regression models. We also related BP responses to submaximal exercise to the incidence of hypertension, CVD, and all‐cause mortality using Cox proportional hazards regression models. Each SD increment of exercise BP was associated with higher log‐transformed left ventricular mass (systolic blood pressure [SBP], β=0.02, P=<0.001; diastolic blood pressure [DBP], β=0.01, P=0.004) and carotid intima‐media thickness (SBP, β=0.08, P=<0.001). Rapid BP recovery (per 1 SD increment) was associated with lower log left ventricular mass (SBP_recovery; β=−0.03, P=<0.001) and carotid intima‐media thickness (SBP_recovery, β=−0.07, P=0.003; DBP_recovery, β=−0.09, P=0.003). Additionally, Each SD increment of exercise BP was associated with a higher risk of incident hypertension (SBP, hazard ratio [HR], 1.40; 95% CI, 1.20–1.62; DBP, HR, 1.24; 95% CI, 1.11–1.40) and CVD (DBP, HR, 1.15; 95% CI, 1.02–1.30). Finally, the multivariable‐adjusted HR for each 1‐SD increment of BP recovery was 0.46 (SBP_recovery, 95% CI, 0.38–0.54) and 0.55 (DBP_recovery, 95% CI, 0.45–0.67) for hypertension; 0.80 (SBP_recovery, 95% CI, 0.69–0.93) for CVD; and 0.76 (SBP_recovery, 95% CI, 0.65–0.88) for all‐cause mortality.

Conclusions

Higher submaximal exercise BP and impaired BP recovery after submaximal exercise in midlife may be markers of subclinical and clinical CVD and mortality in later life.

Patients With Peripheral Arterial Disease With Exaggerated Pressor Response Have Greater Ambulatory Dysfunction Than Patients With Lower Pressor Response

We determined whether patients with peripheral arterial disease (PAD) who have either an exaggerated or a negative pressor response during treadmill walking have shorter peak walking time (PWT) and claudication onset time (COT) than patients with a normal pressor response, independent of comorbid conditions. A total of 249 patients were categorized to 1 of 3 groups based on systolic blood pressure (SBP) responses at 2 minutes of treadmill walking (speed = 2 mph, grade = 0%): group 1 (negative pressor response, SBP < 0 mm Hg), group 2 (normal pressor response, SBP 18 mm Hg), and group 3 (exaggerated pressor response, SBP > 18 mm Hg). After adjusting for comorbid conditions, group 3 (exaggerated) had significantly reduced COT (P = .011) and PWT (P = .002) compared to group 2 (normal), while group 1 (negative) and group 2 (normal) were not different. Patients with symptomatic PAD with an increase in SBP > 18 mm Hg after 2 minutes of treadmill walking experience claudication earlier and thus have greater ambulatory dysfunction, compared to patients with PAD with a normal pressor response, whereas patients with PAD with negative pressor response had a similar walking performance. The implication is that the magnitude of pressor response to only 2 minutes of treadmill walking can partially explain the degree of ambulatory dysfunction in patients with PAD.

Systemic and regional hemodynamic response to activation of the exercise pressor reflex in patients with peripheral artery disease

Patients with peripheral artery disease (PAD) have an accentuated exercise pressor reflex (EPR) during exercise of the affected limb. The underlying hemodynamic changes responsible for this, and its effect on blood flow to the exercising extremity, are unclear. We tested the hypothesis that the exaggerated EPR in PAD is mediated by an increase in total peripheral resistance (TPR), which augments redistribution of blood flow to the exercising limb. Twelve patients with PAD and 12 age- and sex-matched subjects without PAD performed dynamic plantar flexion (PF) using the most symptomatic leg at progressive workloads of 2-12 kg (increased by 1 kg/min until onset of fatigue). We measured heart rate, beat-by-beat blood pressure, femoral blood flow velocity (FBV), and muscle oxygen saturation (SmO2) continuously during the exercise. Femoral blood flow (FBF) was calculated from FBV and baseline femoral artery diameter. Stroke volume (SV), cardiac output (CO), and TPR were derived from the blood pressure tracings. Mean arterial blood pressure and TPR were significantly augmented in PAD compared with control during PF. FBF increased during exercise to an equal extent in both groups. However, SmO2 of the exercising limb remained significantly lower in PAD compared with control. We conclude that the exaggerated pressor response in PAD is mediated by an abnormal TPR response, which augments redistribution of blood flow to the exercising extremity, leading to an equal rise in FBF compared with controls. However, this increase in FBF is not sufficient to normalize the SmO₂ response during exercise in patients with PAD.NEW & NOTEWORTHY In this study, peripheral artery disease (PAD) patients and healthy control subjects performed graded, dynamic plantar flexion exercise. Data from this study suggest that previously reported exaggerated exercise pressor reflex in patients with PAD is driven by greater vasoconstriction in nonexercising vascular territories which also results in a redistribution of blood flow to the exercising extremity. However, this rise in femoral blood flow does not fully correct the oxygen deficit due to changes in other mechanisms that require further investigation.

The exercise pressor reflex and active O2 transport in peripheral arterial disease

It is unclear if the exaggerated exercise pressor reflex observed in peripheral arterial disease (PAD) patients facilitates Oxygen (O2 ) transport during presymptomatic exercise. Accordingly, this study compared O2 transport between PAD patients and healthy controls during graded presymptomatic work. Seven PAD patients and seven healthy controls performed dynamic plantar flexion in the bore of a 3T MRI scanner. Perfusion, T2 * (an index of relative tissue oxygenation), and SvO2 (a measure of venous oxygen saturation) were collected from the medial gastrocnemius (MG) during the final 10 seconds of each stage. Blood pressure was also collected during the final minute of each stage. As expected, the pressor response to presymptomatic work (4 kg) was exaggerated in PAD patients compared to controls (+14 mmHg ± 4 and +7 mmHg ± 2, P ≤ 0.034). When normalized to changes in free water content (S0 ), T2 * was lower at 2 kg in PAD patients compared to controls (-0.91 Δms/ΔAU ± 0.3 and 0.57 Δms/ΔAU ± 0.3, P ≤ 0.008); followed by a greater increase in perfusion at 4 kg in the PAD group (+18.8 mL/min/100g ± 6.2 vs. -0.21 mL/min/100g ± 3.2 in PAD and controls, P ≤ 0.026). Lastly, SvO2 decreased at 4 kg in both groups (-13% ± 4 and -2% ± 4 in PAD and controls, P ≤ 0.049), suggesting an increase in O2 extraction in the PAD group. Based on these findings, O2 transport appears to be augmented during graded presymptomatic work in PAD patients, and this may be partially mediated by an exaggerated pressor response.

Investigation of the mechanisms of cyclooxygenase-mediated mechanoreflex sensitization in a rat model of simulated peripheral artery disease

Mechanical and metabolic stimuli within contracting skeletal muscles reflexly increase sympathetic nervous system activity and blood pressure. That reflex, termed the exercise pressor reflex, is exaggerated in patients with peripheral artery disease (PAD) and in a rat PAD model with a chronically ligated femoral artery. The cyclooxygenase (COX) pathway contributes to the exaggerated pressor response during rhythmic skeletal muscle contractions in patients with PAD, but the specific mechanism(s) of the COX-mediated exaggeration are not known. In decerebrate, unanesthetized rats with a chronically ligated femoral artery ("ligated" rats), we hypothesized that hindlimb arterial injection of the COX inhibitor indomethacin would reduce the pressor response during 1-Hz dynamic hindlimb skeletal muscle stretch; a model of the activation of the mechanical component of the exercise pressor reflex (i.e., the mechanoreflex). In ligated rats (n = 7), indomethacin reduced the pressor response during stretch (control: 30 ± 4; indomethacin: 12 ± 3 mmHg; P < 0.01), whereas there was no effect in rats with "freely perfused" femoral arteries (n = 6, control: 18 ± 5; indomethacin: 17 ± 5 mmHg; P = 0.87). In ligated rats (n = 4), systemic indomethacin injection had no effect on the pressor response during stretch. Femoral artery ligation had no effect on skeletal muscle COX protein expression or activity or concentration of the COX metabolite prostaglandin E₂. Conversely, femoral artery ligation increased expression of the COX metabolite receptors endoperoxide 4 and thromboxane A₂-R in dorsal root ganglia tissue. We conclude that, in ligated rats, the COX pathway sensitizes the peripheral endings of mechanoreflex afferents, which occurs principally as a result of increased expression of COX metabolite receptors.NEW & NOTEWORTHY We demonstrate that the mechanoreflex is sensitized by the cyclooxygenase (COX) pathway within hindlimb skeletal muscles in the rat chronic femoral artery ligation model of simulated peripheral artery disease (PAD). The mechanism of sensitization appears attributable to increased receptors for COX metabolites on sensory neurons and not increased concentration of COX metabolites. Our data may carry important clinical implications for patients with PAD who demonstrate exaggerated increases in blood pressure during exercise compared with healthy counterparts.

A systematic review of diagnostic techniques to determine tissue perfusion in patients with peripheral arterial disease

Introduction: Peripheral arterial disease (PAD) may cause symptoms due to impaired tissue perfusion of the lower extremity. So far, assessment of PAD is mainly performed by determination of stenosis or occlusion in the large arteries and does not focus on microcirculation. Several diagnostic techniques have been recently introduced that may enable tissue perfusion measurements in the lower limb; however, most have not yet been implemented in clinical daily practice. This systematic review provides an overview of these diagnostic techniques and their ability to accurately detect PAD by peripheral tissue perfusion. Areas covered: A literature search was performed for articles that described a diagnostic technique to determine tissue perfusion in patients with known PAD compared with healthy controls. Expert opinion: So far, transcutaneous oxygen measurements are most often used to measure tissue oxygenation in PAD patients, but evidence seems too low to define this technique as a gold standard, and implementing this technique for home monitoring is difficult. New potentially suitable diagnostic tests should be non-invasive, contact-free, and quick. Further research is needed for all of these techniques before broad implementation in clinical use is justified, in hospital, and for home monitoring.

Vascular Inflammation, Calf Muscle Oxygen Saturation, and Blood Glucose are Associated With Exercise Pressor Response in Symptomatic Peripheral Artery Disease

We determined whether calf muscle oxygen saturation (StO2) and vascular biomarkers of inflammation and oxidative stress were associated with an exercise pressor response during treadmill walking in 179 patients with symptomatic peripheral artery disease (PAD). The exercise pressor response was measured as the change in blood pressure from rest to the end of the first 2-minute treadmill stage (2 mph, 0% grade). There was a wide range in the change in systolic blood pressure (−46 to 50 mm Hg) and in diastolic blood pressure (−23 to 38 mm Hg), with mean increases of 4.3 and 1.4 mm Hg, respectively. In multiple regression analyses, significant predictors of systolic pressure included glucose ( P < .001) and insulin ( P = .039). Significant predictors of diastolic pressure included cultured endothelial cell apoptosis ( P = .019), the percentage drop in exercise calf muscle (StO2; P = .023), high-sensitivity C-reactive protein ( P = .032), and glucose ( P = .033). Higher levels in pro-inflammatory vascular biomarkers, impaired calf muscle StO2 during exercise, and elevated blood glucose were independently associated with greater exercise pressor response in patients with symptomatic PAD. The clinical implication is that exercise and nutritional interventions designed to improve inflammation, microcirculation, and glucose metabolism may also lower blood pressure during exercise in patients with symptomatic PAD.

Greater Exercise Pressor Response Is Associated With Impaired Claudication Outcomes in Symptomatic Peripheral Artery Disease

We determined whether a greater exercise pressor response during a constant-load treadmill test was associated with lower peak walking time (PWT) and claudication onset time (COT) measured during a graded maximal treadmill test in 304 patients with symptomatic peripheral artery disease (PAD). The exercise pressor response was assessed by measuring heart rate and blood pressure (BP) at rest and during a constant-load treadmill test (speed = 2 mph, grade = 0%). After only 2 minutes of walking, mean heart rate increased by 26 beats/min from rest and mean systolic BP increased by 16 mm Hg. In adjusted analyses, increases in systolic BP (P = .021), heart rate (P = .002), mean arterial pressure (P = .034), and rate-pressure product (P < .001) from rest to 2 minutes of constant-load exercise were negatively associated with COT. Similarly, increases in heart rate (P = .012) and rate-pressure product (P = .018) from rest to 2 minutes of constant-load exercise were negatively associated with PWT. A greater exercise pressor response observed after only 2 minutes of walking at no incline was independently associated with impaired claudication outcomes in patients with symptomatic PAD. The implication is that the exercise pressor response is an important and easily obtained clinical measurement that partially explains differences in PWT and COT.

Oxygen availability and skeletal muscle oxidative capacity in patients with peripheral artery disease: implications from in vivo and in vitro assessments

Evidence suggests that the peak skeletal muscle mitochondrial ATP synthesis rate ( V_max) in patients with peripheral artery disease (PAD) may be attenuated due to disease-related impairments in O₂ supply. However, in vitro assessments suggest intrinsic deficits in mitochondrial respiration despite ample O₂ availability. To address this conundrum, Doppler ultrasound, near-infrared spectroscopy, phosphorus magnetic resonance spectroscopy, and high-resolution respirometry were combined to assess convective O₂ delivery, tissue oxygenation, V_max, and skeletal muscle mitochondrial capacity (complex I + II, state 3 respiration), respectively, in the gastrocnemius muscle of 10 patients with early stage PAD and 11 physical activity-matched healthy control (HC) subjects. All participants were studied in free-flow control conditions (FF) and with reactive hyperemia (RH) induced by a period of brief ischemia during the last 30 s of submaximal plantar flexion exercise. Patients with PAD repeated the FF and RH trials under hyperoxic conditions (FF + 100% O₂ and RH + 100% O₂). Compared with HC subjects, patients with PAD exhibited attenuated O₂ delivery at the same absolute work rate and attenuated tissue reoxygenation and V_max after relative intensity-matched exercise. Compared with the FF condition, only RH + 100% O₂ significantly increased convective O₂ delivery (~44%), tissue reoxygenation (~54%), and V_max (~60%) in patients with PAD ( P < 0.05), such that V_max was now not different from HC subjects. Furthermore, there was no evidence of an intrinsic mitochondrial deficit in PAD, as assessed in vitro with adequate O₂. Thus, in combination, this comprehensive in vivo and in vitro investigation implicates O₂ supply as the predominant factor limiting mitochondrial oxidative capacity in early stage PAD. NEW & NOTEWORTHY Currently, there is little accord as to the role of O₂ availability and mitochondrial function in the skeletal muscle dysfunction associated with peripheral artery disease. This is the first study to comprehensively use both in vivo and in vitro approaches to document that the skeletal muscle dysfunction associated with early stage peripheral artery disease is predominantly a consequence of limited O₂ supply and not the impact of an intrinsic mitochondrial defect in this pathology.