V.O2 Kinetics and clinical factors among patients with peripheral artery disease

The role of the microcirculation and integrative cardiovascular physiology in the pathogenesis of ICU-acquired weakness

Skeletal muscle dysfunction after critical illness, defined as ICU-acquired weakness (ICU-AW), is a complex and multifactorial syndrome that contributes significantly to long-term morbidity and reduced quality of life for ICU survivors and caregivers. Historically, research in this field has focused on pathological changes within the muscle itself, without much consideration for their in vivo physiological environment. Skeletal muscle has the widest range of oxygen metabolism of any organ, and regulation of oxygen supply with tissue demand is a fundamental requirement for locomotion and muscle function. During exercise, this process is exquisitely controlled and coordinated by the cardiovascular, respiratory, and autonomic systems, and also within the skeletal muscle microcirculation and mitochondria as the terminal site of oxygen exchange and utilization. This review highlights the potential contribution of the microcirculation and integrative cardiovascular physiology to the pathogenesis of ICU-AW. An overview of skeletal muscle microvascular structure and function is provided, as well as our understanding of microvascular dysfunction during the acute phase of critical illness; whether microvascular dysfunction persists after ICU discharge is currently not known. Molecular mechanisms that regulate crosstalk between endothelial cells and myocytes are discussed, including the role of the microcirculation in skeletal muscle atrophy, oxidative stress, and satellite cell biology. The concept of integrated control of oxygen delivery and utilization during exercise is introduced, with evidence of physiological dysfunction throughout the oxygen delivery pathway - from mouth to mitochondria - causing reduced exercise capacity in patients with chronic disease (e.g., heart failure, COPD). We suggest that objective and perceived weakness after critical illness represents a physiological failure of oxygen supply-demand matching - both globally throughout the body and locally within skeletal muscle. Lastly, we highlight the value of standardized cardiopulmonary exercise testing protocols for evaluating fitness in ICU survivors, and the application of near-infrared spectroscopy for directly measuring skeletal muscle oxygenation, representing potential advancements in ICU-AW research and rehabilitation.

Abnormal vibration perception threshold alters the gait features in type 2 diabetes mellitus patients

OBJECTIVE

It is generally believed that gait characteristics of diabetic neuropathic patients differ from those of non-diabetic ones. However, it is still unclear how the abnormal foot sensation influences the gait during walking in type 2 diabetes mellitus (T2DM). For the purpose of gaining a better insight into the alterations of detailed gait parameters and figuring out important aspects in the gait indexes by peripheral neuropathy in elder T2DM patients, we compared the gait features in participants with normal glucose tolerance (NGT) controls and diabetic individuals complicated by peripheral neuropathy or not.

SUBJECTS AND METHODS

Gait parameters were observed during the 10-m walk on flat land among different conditions of diabetes in 1,741 participants from three clinical centers. Subjects were divided into four groups: persons with NGT were taken as the control group; patients with T2DM included three subgroups: DM control (no chronic complications), DM-DPN (DM complicated by only peripheral neuropathy), and DM-DPN+LEAD (DM complicated by both neuropathy and artery disease). The clinical characteristics and gait parameters were assessed and compared among these four groups. Analyses of variance were employed to verify possible differences of gait parameters between groups and conditions. Stepwise multivariate regression analysis was performed to reveal possible predictors of gait deficits. Receiver operating characteristic (ROC) curve analysis was employed to find any discriminatory power of diabetic peripheral neuropathy (DPN) for the step time.

RESULTS

In participants burdened with DPN, whether complicated by lower extremity arterial disease (LEAD) or not, step time increased sharply (p < 0.05). Stepwise multivariate regression models showed that independent variables of gait abnormality were sex, age, leg length, vibration perception threshold (VPT), and ankle-brachial index (ABI) (p < 0.01). Meanwhile, VPT was a significant independent predictor of step time, spatiotemporal variability (SD_A), and temporal variability (SD_B) (p < 0.05). ROC curve analysis was explored to find the discriminatory power of DPN for the occurrence of increased step time. The area under the curve (AUC) value was 0.608 (95% CI: 0.562-0.654, p < 0.01), and the cutoff point was 538.41 ms accompanied by a higher VPT. A significant positive association was observed between increased step time and the highest VPT group [odds ratio (OR) = 1.83, 95% CI: 1.32-2.55, p< 0.01]. In female patients, this OR value elevated to 2.16 (95% CI: 1.25-3.73, p< 0.01).

CONCLUSIONS

In addition to sex, age, and leg length, VPT was a distinct factor that associated with altered gait parameters. DPN is associated with increased step time, and the step time increases with worsening VPT in type 2 diabetes.

Vascular permeability of skeletal muscle microvessels in rat arterial ligation model: in vivo analysis using two-photon laser scanning microscopy

Peripheral artery disease (PAD) in the lower limb compromises oxygen supply due to arterial occlusion. Ischemic skeletal muscle is accompanied by capillary structural deformation. Therefore, using novel microscopy techniques, we tested the hypothesis that endothelial cell swelling temporally and quantitatively corresponds to enhanced microvascular permeability. Hindlimb ischemia was created in male Wistar rat's by iliac artery ligation (AL). The tibialis anterior (TA) muscle microcirculation was imaged using intravenously infused rhodamine B isothiocyanate dextran fluorescent dye via two-photon laser scanning microscopy (TPLSM) and dye extravasation at 3 and 7 days post-AL quantified to assess microvascular permeability. The TA microvascular endothelial ultrastructure was analyzed by transmission electron microscopy (TEM). Compared with control (0.40 ± 0.15 μm3 × 106), using TPLSM, the volumetrically determined interstitial leakage of fluorescent dye measured at 3 (3.0 ± 0.40 μm3 × 106) and 7 (2.5 ± 0.8 μm3 × 106) days was increased (both P < 0.05). Capillary wall thickness was also elevated at 3 (0.21 ± 0.06 μm) and 7 (0.21 ± 0.08 μm) days versus control (0.11 ± 0.03 μm, both P < 0.05). Capillary endothelial cell swelling was temporally and quantitatively associated with elevated vascular permeability in the AL model of PAD but these changes occurred in the absence of elevations in protein levels of vascular endothelial growth factor (VEGF) its receptor (VEGFR2 which decreased by AL-7 day) or matrix metalloproteinase. The temporal coherence of endothelial cell swelling and increased vascular permeability supports a common upstream mediator. TPLSM, in combination with TEM, provides a sensitive and spatially discrete technique to assess the mechanistic bases for, and efficacy of, therapeutic countermeasures to the pernicious sequelae of compromised peripheral arterial function.

Identification of new factors associated to walking impairment in patients with vascular-type claudication

OBJECTIVES

Mechanisms of walking limitation in arterial claudication are incompletely elucidated. We aimed to identify new variables associated to walking limitation in patients with claudication.

METHODS

We retrospectively analyzed data of 1120 patients referred for transcutaneous exercise oxygen pressure recordings (TcpO₂). The outcome measurement was the absolute walking time on treadmill (3.2 km/h, 10% slope). We used both: linear regression analysis and a non-linear analysis, combining support vector machines and genetic explanatory in 800 patients with the following resting variables: age, gender, body mass index, the presence of diabetes, minimal ankle to brachial index at rest, usual walking speed over 10 m (usual-pace), number of comorbid conditions, active smoking, resting heart rate, pre-test glycaemia and hemoglobin, beta-blocker use, and exercise-derived variables: minimal value of pulse oximetry, resting chest-TcpO₂, decrease in chest TcpO₂ during exercise, presence of buttock ischemia defined as a decrease from rest of oxygen pressure index ≤15 mmHg. We tested the models over 320 other patients.

RESULTS

Independent variables associated to walking time, by decreasing importance in the models, were: age, ankle to brachial index, usual-pace; resting TcpO₂, body mass index, smoking, buttock ischemia, heart rate and beta-blockers for the linear regression analysis, and were ankle to brachial index, age, body mass index, usual-pace, decrease in chest TcpO₂, smoking, buttock ischemia, glycaemia, heart rate for the non-linear analysis. Testing of models over 320 new patients gave r = 0.509 for linear and 0.575 for non-linear analysis (both p < 0.05).

CONCLUSION

Buttock ischemia, heart rate and usual-pace are new variables associated to walking time.

Oxygen uptake on-kinetics during six-minute walk test predicts short-term outcomes after off-pump coronary artery bypass surgery

PURPOSE

We aimed to investigate the ability of oxygen uptake kinetics to predict short-term outcomes after off-pump coronary artery bypass grafting.

METHODS

Fifty-two patients aged 60.9 ± 7.8 years waiting for off-pump coronary artery bypass surgery were evaluated. The 6-min walk test distance was performed pre-operatively, while simultaneously using a portable cardiopulmonary testing device. The transition of oxygen uptake kinetics from rest to exercise was recorded to calculate oxygen uptake kinetics fitting a monoexponential regression model. Oxygen uptake at steady state, constant time, and mean response time corrected by work rate were analysed. Short-term clinical outcomes were evaluated during the early post-operative of off-pump coronary artery bypass surgery.

RESULTS

Multivariate analysis showed body mass index, surgery time, and mean response time corrected by work rate as independent predictors for short-term outcomes. The optimal mean response time corrected by work rate cut-off to estimate short-term clinical outcomes was 1.51 × 10^-3 min²/ml. Patients with slower mean response time corrected by work rate demonstrated higher rates of hypertension, diabetes, EuroSCOREII, left ventricular dysfunction, and impaired 6-min walk test parameters. The per cent-predicted distance threshold of 66% in the pre-operative was associated with delayed oxygen uptake kinetics.

CONCLUSIONS

Pre-operative oxygen uptake kinetics during 6-min walk test predicts short-term clinical outcomes after off-pump coronary artery bypass surgery. From a clinically applicable perspective, a threshold of 66% of pre-operative predicted 6-min walk test distance indicated slower kinetics, which leads to longer intensive care unit and post-surgery hospital length of stay. Implications for rehabilitation Coronary artery bypass grafting is a treatment aimed to improve expectancy of life and prevent disability due to the disease progression; The use of pre-operative submaximal functional capacity test enabled the identification of patients with high risk of complications, where patients with delayed oxygen uptake kinetics exhibited worse short-term outcomes; Our findings suggest the importance of the rehabilitation in the pre-operative in order to "pre-habilitate" the patients to the surgical procedure; Faster oxygen uptake on-kinetics could be achieved by improving the oxidative capacity of muscles and cardiovascular conditioning through rehabilitation, adding better results following cardiac surgery.

Association between gait characteristics and endothelial oxidative stress and inflammation in patients with symptomatic peripheral artery disease

The aim of the study was to determine whether gait characteristics were associated with endothelial cell inflammation, oxidative stress, and apoptosis and with circulating biomarkers of inflammation and antioxidant capacity in older patients with symptomatic peripheral artery disease (PAD). Gait measurements of 231 symptomatic men and women with PAD were assessed during a 4-m walk test. Patients were further characterized on endothelial effects of circulating factors present in the sera using a cell culture-based bioassay on primary human arterial endothelial cells and on circulating inflammatory and vascular biomarkers. In a multivariate regression model for gait speed, the significant independent variables were age (p < 0.001), intercellular cell adhesion molecule-1 (ICAM-1) (p < 0.001), diabetes (p = 0.003), sex (p = 0.003), and history of cerebrovascular accidents (p = 0.021). In multivariate analyses for gait cadence, the significant independent predictors included high-sensitivity C-reactive protein (HsCRP) (p < 0.001), diabetes (p = 0.001), and hypertension (p = 0.001). In a multivariate regression model for gait stride length, the significant independent variables were HsCRP (p < 0.001), age (p < 0.001), ICAM-1 (p < 0.001), hypertension (p = 0.002), cellular reactive oxygen species production (p = 0.007), and sex (p = 0.008). Higher levels of circulating biomarkers of inflammation and endothelial cell oxidative stress were associated with slower gait speed, slower cadence, and shorter stride length in older symptomatic patients with PAD. Additionally, this profile of impaired gait was more evident in older patients, in women, and in those with diabetes, hypertension, and history of cerebrovascular accidents.