Validity and reliability of cardiorespiratory measurements recorded by the LifeShirt during exercise tests

The LifeShirt is a novel ambulatory monitoring system that records cardio respiratory measurements outside the laboratory. Validity and reliability of cardiorespiratory measurements recorded by the LifeShirt were assessed and two methods of calibrating the LifeShirt were compared. Participants performed an incremental treadmill test and a constant work rate test (65% peak oxygen uptake) on four occasions (>48 In apart) and wore the LifeShirt, COSMED system and Polar Sport Tester simultaneously. The LifeShirt was calibrated using two methods: comparison to a spirometer; and 800 ml fixed-volume bag. Ventilation, respiratory rate, expiratory time and heart rate recorded by the LifeShirt were compared to measurements recorded by laboratory equipment. Sixteen adults participated (6M: 10F); mean (SD) age 23.1 (2.9) years. Agreement between the LifeShirt and laboratory equipment was acceptable. Agreement for ventilation was improved by calibrating the LifeShirt using a spirometer. Reliability was similar for the LifeShirt and the laboratory equipment. This study suggests that the LifeShirt provides a valid and reliable method of ambulatory monitoring. (C) 2009 Elsevier B.V. All rights reserved.

Sedentary aging increases resting and exercise-induced intramuscular free radical formation

Mitochondrial free radical formation has been implicated as a potential mechanism underlying degenerative senescence, although human data are lacking. Therefore, the present study was designed to examine if resting and exercise-induced intramuscular free radical-mediated lipid peroxidation is indeed increased across the spectrum of sedentary aging. Biopsies were obtained from the vastus lateralis in six young (26 ± 6 yr) and six aged (71 ± 6 yr) sedentary males at rest and after maximal knee extensor exercise. Aged tissue exhibited greater (P < 0.05 vs. the young group) electron paramagnetic resonance signal intensity of the mitochondrial ubisemiquinone radical both at rest (+138 ± 62%) and during exercise (+143 ± 40%), and this was further complemented by a greater increase in a-phenyl-tert-butylnitrone adducts identified as a combination of lipid-derived alkoxyl-alkyl radicals (+295 ± 96% and +298 ± 120%). Lipid hydroperoxides were also elevated at rest (0.190 ± 0.169 vs. 0.148 ± 0.071 nmol/mg total protein) and during exercise (0.567 ± 0.259 vs. 0.320 ± 0.263 nmol/mg total protein) despite a more marked depletion of ascorbate and uptake of a/ß-carotene, retinol, and lycopene (P < 0.05 vs. the young group). The impact of senescence was especially apparent when oxidative stress biomarkers were expressed relative to the age-related decline in mitochondrial volume density and absolute power output at maximal exercise. In conclusion, these findings confirm that intramuscular free radical-mediated lipid peroxidation is elevated at rest and during acute exercise in aged humans.

Reliability of blood pressure determination with the Finapres with altered physiological states or pharmacodynamic conditions

The blood pressure waveform is modified on distal propagation by phenomena such as dispersion, reflection and the state of the arterial compliance. The consequent effects are amplification and narrowing of the wave, with an increased systolic, reduced diastolic and essentially unaltered mean blood pressure. The Finapres measures the peripheral pressure using the volume clamp principle; it has not been validated under altered physiological conditions and during pharmacodynamic interventions. We studied simultaneous Finapres and brachial blood pressures (using a conventional oscillometric sphygmomanometer—Vitalmap) in ten normal volunteers at rest, and during dynamic exercise and a cold pressor test. The effects of pharmacodynamic intervention were examined following beta-adrenoceptor blockade with propranolol (160 mg) or beta-adrenoceptor modulation with the beta-adrenoceptor partial agonist celiprolol (400 mg). The Finapres systolic pressure was significantly higher than the brachial value during all three test states. The difference between the systolic pressures measured by the two devices was shown to increase significantly during the cold pressor test, but not during dynamic (supine bicycle) exercise. The Finapres diastolic pressure was significantly higher than the Vitalmap value during exercise and the cold pressor test. The differences between the two methods increased significantly over time. Beta-adrenergic blockade with propranolol or modulation with celiprolol had no significant interaction with the pressure differences between the Finapres and Vitalmap techniques. The results would support the view that the Finapres can provide blood pressure information which is robust under most circumstances. Although this pharmacodynamic intervention did not alter the relationship between the peripheral and central blood pressure, it is important to note that this dynamic relationship is sensitive to circulatory loading conditions and wave transmission characteristics; it is possible that the Finapres could be less reliable in clinical settings where potent vasoactive agents were being administered.

Jettisoning Ballast or Fuel? Caudal Autotomy and Locomotory Energetics of the Cape Dwarf Gecko Lygodactylus capensis (Gekkonidae)

Many lizard species will shed their tail as a defensive response (e.g., to escape a putative predator or aggressive conspecific). This caudal autotomy incurs a number of costs as a result of loss of the tail itself, loss of resources (i.e., stored in the tail or due to the cost of regeneration), and altered behavior. Few studies have examined the metabolic costs of caudal autotomy. A previous study demonstrated that geckos can move faster after tail loss as a result of reduced weight or friction with the substrate; however, there are no data for the effects of caudal autotomy on locomotory energetics. We examined the effect of tail loss on locomotory costs in the Cape dwarf gecko Lygodactylus capensis (similar to 0.9 g) using a novel method for collecting data on small lizards, a method previously used for arthropods. We measured CO2 production during 5-10 min of exhaustive exercise (in response to stimulus) and during a 45-min recovery period. During exercise, we measured speed (for each meter moved) as well as total distance traveled. Contrary to our expectations, tailless geckos overall expended less effort in escape running, moving both slower and for a shorter distance, compared with when they were intact. Tailless geckos also exhibited lower excess CO2 production (CO2 production in excess of normal resting metabolic rate) during exercising. This may be due to reduced metabolically active tissue (tails represent 8.7% of their initial body mass). An alternative suggestion is that a change in energy substrate use may take place after tail loss. This is an intriguing finding that warrants future biochemical investigation before we can predict the relative costs of tail loss that lizards might experience under natural conditions.

Systemic oxidative-nitrosative-inflammatory stress during acute exercise in hypoxia; implications for microvascular oxygenation and aerobic capacity

New Findings

What is the central question of this study?Exercise performance is limited during hypoxia by a critical reduction in cerebral and skeletal tissue oxygenation. To what extent an elevation in systemic free radical accumulation contributes to microvascular deoxygenation and the corresponding reduction in maximal aerobic capacity remains unknown.What is the main finding and its importance?We show that altered free radical metabolism is not a limiting factor for exercise performance in hypoxia, providing important insight into the fundamental mechanisms involved in the control of vascular oxygen transport.

Exercise performance in hypoxia may be limited by a critical reduction in cerebral and skeletal tissue oxygenation, although the underlying mechanisms remain unclear. We examined whether increased systemic free radical accumulation during hypoxia would be associated with elevated microvascular deoxygenation and reduced maximal aerobic capacity (). Eleven healthy men were randomly assigned single-blind to an incremental semi-recumbent cycling test to determine  in both normoxia (21% O_{2) and hypoxia (12% O2) separated by a week. Continuous-wave near-infrared spectroscopy was employed to monitor concentration changes in oxy- and deoxyhaemoglobin in the left vastus lateralis muscle and frontal cerebral cortex. Antecubital venous blood samples were obtained at rest and at  to determine oxidative (ascorbate radical by electron paramagnetic resonance spectroscopy), nitrosative (nitric oxide metabolites by ozone-based chemiluminescence and 3-nitrotyrosine by enzyme-linked immunosorbent assay) and inflammatory stress biomarkers (soluble intercellular/vascular cell adhesion 1 molecules by enzyme-linked immunosorbent assay). Hypoxia was associated with increased cerebral and muscle tissue deoxygenation and lower  (P < 0.05 versus normoxia). Despite an exercise-induced increase in oxidative–nitrosative–inflammatory stress, hypoxia per se did not have an additive effect (P > 0.05 versus normoxia). Consequently, we failed to observe correlations between any metabolic, haemodynamic and cardiorespiratory parameters (P > 0.05). Collectively, these findings suggest that altered free radical metabolism cannot explain the elevated microvascular deoxygenation and corresponding lower  in hypoxia. Further research is required to determine whether free radicals when present in excess do indeed contribute to the premature termination of exercise in hypoxia.}

The Utility of Cardiopulmonary Exercise Testing in Difficult Asthma

Background: Unexplained persistent breathlessness in patients with difficult asthma despite multiple treatments is a common clinical problem. Cardiopulmonary exercise testing (CPX) may help identify the mechanism causing these symptoms, allowing appropriate management.

Methods: This was a retrospective analysis of patients attending a specialist-provided service for difficult asthma who proceeded to CPX as part of our evaluation protocol. Patient demographics, lung function, and use of health care and rescue medication were compared with those in patients with refractory asthma. Medication use 6 months following CPX was compared with treatment during CPX.

Results: Of 302 sequential referrals, 39 patients underwent CPX. A single explanatory feature was identified in 30 patients and two features in nine patients: hyperventilation (n = 14), exercise-induced bronchoconstriction (n = 8), submaximal test (n = 8), normal test (n = 8), ventilatory limitation (n = 7), deconditioning (n = 2), cardiac ischemia (n = 1). Compared with patients with refractory asthma, patients without “pulmonary limitation” on CPX were prescribed similar doses of inhaled corticosteroid (ICS) (median, 1,300 µg [interquartile range (IQR), 800-2,000 µg] vs 1,800 µg [IQR, 1,000-2,000 µg]) and rescue oral steroid courses in the previous year (median, 5 [1-6] vs 5 [1-6]). In this group 6 months post-CPX, ICS doses were reduced (median, 1,300 µg [IQR, 800-2,000 µg] to 800 µg [IQR, 400-1,000 µg]; P < .001) and additional medication treatment was withdrawn (n = 7). Patients with pulmonary limitation had unchanged ICS doses post CPX and additional therapies were introduced.

Conclusions: In difficult asthma, CPX can confirm that persistent exertional breathlessness is due to asthma but can also identify other contributing factors. Patients with nonpulmonary limitation are prescribed inappropriately high doses of steroid therapy, and CPX can identify the primary mechanism of breathlessness, facilitating steroid reduction.

Exercise rehabilitation following intensive care unit discharge for recovery from critical illness

Background: Skeletal muscle wasting and weakness are significant complications of critical illness, associated with the degree of illness severity and periods of reduced mobility during mechanical ventilation. They contribute to the profound physical and functional deficits observed in survivors. These impairments may persist for many years following discharge from the intensive care unit (ICU) and may markedly influence health-related quality of life. Rehabilitation is a key strategy in the recovery of patients following critical illness. Exercise based interventions are aimed at targeting this muscle wasting and weakness. Physical rehabilitation delivered during ICU admission has been systematically evaluated and shown to be beneficial. However its effectiveness when initiated after ICU discharge has yet to be established. Objectives: To assess the effectiveness of exercise rehabilitation programmes, initiated after ICU discharge, on functional exercise capacity and health-related quality of life in adult ICU survivors who have been mechanically ventilated for more than 24 hours. Search methods:We searched the following databases: the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library), OvidSP MEDLINE, Ovid SP EMBASE, and CINAHL via EBSCO host to 15th May 2014. We used a specific search strategy for each database. This included synonyms for ICU and critical illness, exercise training and rehabilitation. We searched the reference lists of included studies and contacted primary authors to obtain further information regarding potentially eligible studies. We also searched major clinical trials registries (Clinical Trials and Current Controlled Trials) and the personal libraries of the review authors. We applied no language or publication restriction. We reran the search in February 2015. We will deal with any studies of interest when we update the review.  Selection criteria:We included randomized controlled trials (RCTs), quasi-RCTs, and controlled clinical trials (CCTs) that compared an exercise interventioninitiated after ICU discharge to any other intervention or a control or ‘usual care’ programme in adult (≥18years) survivors ofcritical illness. Data collection and analysis:We used standard methodological procedures expected by The Cochrane Collaboration. Main results:We included six trials (483 adult ICU participants). Exercise-based interventions were delivered on the ward in two studies; both onthe ward and in the community in one study; and in the community in three studies. The duration of the intervention varied according to the length of stay in hospital following ICU discharge (up to a fixed duration of 12 weeks).Risk of bias was variable for all domains across all trials. High risk of bias was evident in all studies for performance bias, although blinding of participants and personnel in therapeutic rehabilitation trials can be pragmatically challenging. Low risk of bias was at least 50% for all other domains across all trials, although high risk of bias was present in one study for random sequence generation (selection bias), incomplete outcome data (attrition bias) and other sources. Risk of bias was unclear for remaining studies across the domains.All six studies measured effect on the primary outcome of functional exercise capacity, although there was wide variability in natureof intervention, outcome measures and associated metrics, and data reporting. Overall quality of the evidence was very low. Only two studies using the same outcome measure for functional exercise capacity, had the potential for pooling of data and assessment of heterogeneity. On statistical advice, this was considered inappropriate to perform this analysis and study findings were therefore qualitatively described. Individually, three studies reported positive results in favour of the intervention. A small benefit (versus. control)was evident in anaerobic threshold in one study (mean difference, MD (95% confidence interval, CI), 1.8 mlO2/kg/min (0.4 to 3.2),P value = 0.02), although this effect was short-term, and in a second study, both incremental (MD 4.7 (95% CI 1.69 to 7.75) Watts, P value = 0.003) and endurance (MD 4.12 (95% CI 0.68 to 7.56) minutes, P value = 0.021) exercise testing demonstrated improvement.Finally self-reported physical function increased significantly following a rehabilitation manual (P value = 0.006). Remaining studies found no effect of the intervention.Similar variability in with regard findings for the primary outcome of health-related quality of life were also evident. Only two studies evaluated this outcome. Following statistical advice, these data again were considered inappropriate for pooling to determine overall effect and assessment of heterogeneity. Qualitative description of findings was therefore undertaken. Individually, neither study reported differences between intervention and control groups for health-related quality of life as a result of the intervention. Overall quality of the evidence was very low.Mortality was reported by all studies, ranging from 0% to 18.8%. Only one non-mortality adverse event was reported across all patients in all studies (a minor musculoskeletal injury). Withdrawals, reported in four studies, ranged from 0% to 26.5% in control groups,and 8.2% to 27.6% in intervention groups. Loss to follow-up, reported in all studies, ranged from 0% to 14% in control groups, and 0% to 12.5% in intervention groups. Authors’ conclusions:We are unable, at this time, to determine an overall effect on functional exercise capacity, or health-related quality of life, of an exercise based intervention initiated after ICU discharge in survivors of critical illness. Meta-analysis of findings was not appropriate. This was due to insufficient study number and data. Individual study findings were inconsistent. Some studies reported a beneficial effect of the intervention on functional exercise capacity, and others not. No effect was reported on health-related quality of life. Methodological rigour was lacking across a number of domains influencing quality of the evidence. There was also wide variability in the characteristics of interventions, outcome measures and associated metrics, and data reporting.If further trials are identified, we may be able to determine the effect of exercise-based interventions following ICU discharge, on functional exercise capacity and health-related quality of life in survivors of critical illness.

Exercise rehabilitation following intensive care unit discharge for recovery from critical illness: Executive summary of a Cochrane Collaboration systematic review

Skeletal muscle wasting and weakness are major complications of critical illness and underlie the profound physical and functional impairments experienced by survivors after discharge from the intensive care unit (ICU). Exercise-based rehabilitation has been shown to be beneficial when delivered during ICU admission. This review aimed to determine the effectiveness of exercise rehabilitation initiated after ICU discharge on primary outcomes of functional exercise capacity and health-related quality of life. We sought randomized controlled trials, quasi-randomized controlled trials, and controlled clinical trials comparing an exercise intervention commenced after ICU discharge vs. any other intervention or a control or ‘usual care’ programme in adult survivors of critical illness. Cochrane Central Register of Controlled Trials, Medical Literature Analysis and Retrieval System Online (MEDLINE), Excerpta Medica Database, and Cumulative Index to Nursing and Allied Health Literature databases were searched up to February 2015. Dual, independent screening of results, data extraction, and quality appraisal were performed. We included six trials involving 483 patients. Overall quality of evidence for both outcomes was very low. All studies evaluated functional exercise capacity, with three reporting positive effects in favour of the intervention. Only two studies evaluated health-related quality of life and neither reported differences between intervention and control groups. Meta-analyses of data were precluded due to variation in study design, types of interventions, and selection and reporting of outcome measurements. We were unable to determine an overall effect on functional exercise capacity or health-related quality of life of interventions initiated after ICU discharge for survivors of critical illness. Findings from ongoing studies are awaited. Future studies need to address methodological aspects of study design and conduct to enhance rigour, quality, and synthesis.