Ian B. Stewart

The human spleen during physiological stress

AbstractMany mammals have the ability to autotransfuse a large quantity of red blood cells from the spleen into the active circulation during times of stress. This enhancement of the oxygen transport system has benefited the athletic mammal, that is, the thoroughbred horse, fox and greyhound in an improved aerobic performance. The role of the spleen in sequestering 50% of the total red cell volume in seals and horses, during times of inactivity, dramatically reduces the viscosity of the blood and therefore the work of the heart. In comparison, the human spleen contains only a small percentage of red blood cells, and has been primarily thought of as a lymphoid organ. Many mammals have the ability to autotransfuse a large quantity of red blood cells from the spleen into the active circulation during times of stress. This enhancement of the oxygen transport system has benefited the athletic mammal, that is, the thoroughbred horse, fox and greyhound in an improved aerobic performance. The role of the spleen in sequestering 50% of the total red cell volume in seals and horses, during times of inactivity, dramatically reduces the viscosity of the blood and therefore the work of the heart. In comparison, the human spleen contains only a small percentage of red blood cells, and has been primarily thought of as a lymphoid organ.The aim of this review is to emphasise the similarities between the human spleen and that of several athletic mammalian species during acute physiological stress. In the athletic mammalian model the expulsion of blood from the spleen is facilitated via the sympathetic nervous system resulting in contraction of smooth muscle within the splenic capsule. In comparison, the lack of smooth muscle contained within the human splenic capsule has meant that active contraction of the spleen has historically been viewed as unlikely, although evidence of contractile proteins within the red pulp have suggested otherwise.Exercise results in haemoconcentration, which has been attributed solely to a reduction in plasma volume. Indirect calculation of plasma volume changes utilise haemoglobin and haematocrit and assume that the circulating red cell volume remains constant. However, several studies have suggested that the human spleen could account for 30% of the increase in haematocrit. This would result in a substantial overestimation of the reduction in plasma volume, indicating that the expulsion of red blood cells from the spleen must not be overlooked when utilising these equations.

Effect of training on the response of plasma vascular endothelial growth factor to exercise in patients with peripheral arterial disease

Expansion of the capillary network, or angiogenesis, occurs following endurance training. This process, which is reliant on the presence of VEGF (vascular endothelial growth factor), is an adaptation to a chronic mismatch between oxygen demand and supply. Patients with IC (intermittent claudication) experience pain during exercise associated with an inadequate oxygen delivery to the muscles. Therefore the aims of the present study were to examine the plasma VEGF response to acute exercise, and to establish whether exercise training alters this response in patients with IC. In Part A, blood was collected from patients with IC (n=18) before and after (+20 and +60 min post-exercise) a maximal walking test to determine the plasma VEGF response to acute exercise. VEGF was present in the plasma of patients (45.11+/-29.96 pg/ml) and was unchanged in response to acute exercise. Part B was a training study to determine whether exercise training altered the VEGF response to acute exercise. Patients were randomly assigned to a treatment group (TMT; n=7) that completed 6 weeks of high-intensity treadmill training, or to a control group (CON; n=6). All patients completed a maximal walking test before and after the intervention, with blood samples drawn as for Part A. Training had no effect on plasma VEGF at rest or in response to acute exercise, despite a significant increase in maximal walking time in the TMT group (915+/-533 to 1206+/-500 s; P=0.009) following the intervention. The absence of a change in plasma VEGF may reflect altered VEGF binding at the endothelium, although this cannot be confirmed by the present data.

Acute formoterol administration has no ergogenic effect in nonasthmatic athletes.

PURPOSE To determine the effect of formoterol (formoterol fumarate dihydrate) on the aerobic and anaerobic capacities of highly trained athletes. METHODS 10 male athletes (age = 26.2 +/- 0.9, VO(2max) = 65.6 +/- 2.4 mL x kg(-1) x min(-1)) with minimal bronchial reactivity to aerosols (i.e., negative methacholine challenge test) completed three identical exercise sessions differing only by the medication administered. Formoterol (F) a long-acting beta(2)-agonist, presently not approved for international competition by the I.O.C. Medical committee, was compared with salbutamol (S), an accepted bronchodilator, and a placebo (P). Formoterol (12 microg), salbutamol (400 microg), or placebo was administered by a Turbuhaler, 10 min before exercise testing in a double-blind, randomized, three-way crossover design. Testing sessions included a Wingate anaerobic test followed 15 min later by an incremental cycle ergometer test to exhaustion. RESULTS There were no significant differences between the groups in VO(2max) (F = 66.5 +/- 2.7; S = 67.8 +/- 2.5; P = 67.5 +/- 2.1 mL x kg(-1) x min(-1)) or Wingate peak power (F = 885 +/- 40; S = 877 +/- 40; P = 885 +/- 44 W) values. During the maximal aerobic test, no differences were observed in maximum minute ventilation, respiratory exchange ratio, heart rate, or work between the three experimental conditions. Also, there were no differences in the Wingate anaerobic test variables, total work, or fatigue index. CONCLUSION Formoterol, administered in one aerosolized therapeutic dose, does not have an ergogenic effect in elite athletes without asthma.

Spontaneous pacing during overground hill running.

PURPOSE To investigate speed regulation during overground running on undulating terrain. METHODS After an initial laboratory session to calculate physiological thresholds, eight experienced runners completed a spontaneously paced time trial over three laps of an outdoor course involving uphill, downhill, and level sections. A portable gas analyzer, global positioning system receiver, and activity monitor were used to collect physiological, speed, and stride frequency data. RESULTS Participants ran 23% slower on uphills and 13.8% faster on downhills compared with level sections. Speeds on level sections were significantly different for 78.4 +/- 7.0 s following an uphill and 23.6 +/- 2.2 s following a downhill. Speed changes were primarily regulated by stride length, which was 20.5% shorter uphill and 16.2% longer downhill, whereas stride frequency was relatively stable. Oxygen consumption averaged 100.4% of runners individual ventilatory thresholds on uphills, 78.9% on downhills, and 89.3% on level sections. Approximately 89% of group-level speed was predicted using a modified gradient factor. Individuals adopted distinct pacing strategies, both across laps and as a function of gradient. CONCLUSIONS Speed was best predicted using a weighted factor to account for prior and current gradients. Oxygen consumption (VO2) limited runners speeds only on uphill sections and was maintained in line with individual ventilatory thresholds. Running speed showed larger individual variation on downhill sections, whereas speed on the level was systematically influenced by the preceding gradient. Runners who varied their pace more as a function of gradient showed a more consistent level of oxygen consumption. These results suggest that optimizing time on the level sections after hills offers the greatest potential to minimize overall time when running over undulating terrain.

The asthmatic athlete, inhaled beta agonists, and performance.

IntroductionThe large increase in the number of athletes who apply to use inhaled beta agonists (IBAs) at the Olympic Games is a concern to the medical community. This review will examine the use of IBAs in the asthmatic athlete, the variability that exists between countries and sport, and outline a plan to justify the use of these medications. Data SourcesMuch of this article is a result of an International Olympic Committee (IOC) Medical Commission-sponsored meeting that took place in May 2001. Records of the use of IBAs at previous Olympics were reviewed. MEDLINE Searches (PubMed interface) were performed using key words to locate published work relating to asthma, elite athletes, performance, treatment, and ergogenic aids. Main ResultsSince 1984 there have been significant increases in the use of IBAs at the Olympic Games as well as marked geographical differences in the percentage of athletes requesting the use of IBAs. There are large differences in the incidence of IBA use between sports with a trend towards increased use in endurance sports. There are no ergogenic effects of any IOC-approved IBA given in a therapeutic dose. ConclusionsIn many cases, the prescription of IBAs to this population has been made on empirical grounds. Beginning with the 2002 Winter Games, athletes will be required to submit to the IOC Medical Commission clinical and laboratory evidence that justifies the use of this medication. The eucapnic voluntary hyperpnea test will be used to assess individuals who have not satisfied an independent medical panel of the need to use an IBA.

A home‐based progressive resistance exercise programme for patients with venous leg ulcers: a feasibility study

This study aimed to assess the feasibility of a home‐based exercise programme and examine the effects on the healing rates of venous leg ulcers. A 12‐week randomised controlled trial was conducted investigating the effects of an exercise intervention compared to a usual care group. Participants in both groups (n = 13) had active venous ulceration and were treated in a metropolitan hospital outpatients clinic in Australia. Data were collected on recruitment from medical records, clinical assessment and questionnaires. Follow‐up data on progress in healing and treatments were collected fortnightly for 12 weeks. Calf muscle pump function data were collected at baseline and 12 weeks from recruitment. Range of ankle motion data were collected at baseline, 6 and 12 weeks from recruitment. This pilot study indicated that the intervention was feasible. Clinical significance was observed in the intervention group with a 32% greater decrease in ulcer size (P = 0·34) than the usual care group, and a 10% (P = 0·74) improvement in the number of participants healed in the intervention group compared to the usual care group. Significant differences between groups over time were observed in calf muscle pump function parameters [ejection fraction (P = 0·05), residual volume fraction (P = 0·04)] and range of ankle motion (P = 0·01). This pilot study is one of the first to examine and measure clinical healing rates for participants involved in a home‐based progressive resistance exercise programme. Further research is warranted with a larger multi‐site study.

Experimental hypoxia in human eyes : Implications for ischaemic disease

OBJECTIVE This study investigated neuroretinal activity under normoxic and hypoxic conditions with the multifocal electroretinogram (mfERG). METHODS We used two mfERG paradigms, the fast flicker and slow flash stimulation modes, to measure neuroretinal activity in five healthy participants who breathed room air and a reduced oxygen mixture (14% oxygen, balance nitrogen). We analysed concentric ring N1P1 and P1N2 response density amplitudes, the P1 implicit times as well as the local scalar product (SP) response densities. RESULTS During hypoxia there was a significant reduction of the scalar product response density for the fast flicker (p<0.001) and for the slow flash mfERG (p<0.001). The N1P1 and P1N2 response densities were lower especially for the central three rings; although these reductions were not significant between the two oxygen conditions, they indicated an overall distortion of the mfERG waveform. CONCLUSIONS It is demonstrated that a post-receptoral, primarily ON and OFF bipolar cell deficit is evident in the central retina of healthy young people during short term hypoxia. SIGNIFICANCE Our findings suggest that persons with pre-existing ischaemic eye disease may be at risk when exposed to hypoxic conditions.

A comparison between conductive and infrared devices for measuring mean skin temperature at rest, during exercise in the heat, and recovery

Purpose Skin temperature assessment has historically been undertaken with conductive devices affixed to the skin. With the development of technology, infrared devices are increasingly utilised in the measurement of skin temperature. Therefore, our purpose was to evaluate the agreement between four skin temperature devices at rest, during exercise in the heat, and recovery. Methods Mean skin temperature (T-sk) was assessed in thirty healthy males during 30 min rest (24.0 ± 1.2°C, 56 ± 8%), 30 min cycle in the heat (38.0 ± 0.5°C, 41 ± 2%), and 45 min recovery (24.0 ± 1.3°C, 56 ± 9%). T-sk was assessed at four sites using two conductive devices (thermistors, iButtons) and two infrared devices (infrared thermometer, infrared camera). Results Bland–Altman plots demonstrated mean bias ± limits of agreement between the thermistors and iButtons as follows (rest, exercise, recovery): -0.01 ± 0.04, 0.26 ± 0.85, -0.37 ± 0.98°C; thermistors and infrared thermometer: 0.34 ± 0.44, -0.44 ± 1.23, -1.04 ± 1.75°C; thermistors and infrared camera (rest, recovery): 0.83 ± 0.77, 1.88 ± 1.87°C. Pairwise comparisons of T-sk found significant differences (p < 0.05) between thermistors and both infrared devices during resting conditions, and significant differences between the thermistors and all other devices tested during exercise in the heat and recovery. Conclusions These results indicate poor agreement between conductive and infrared devices at rest, during exercise in the heat, and subsequent recovery. Infrared devices may not be suitable for monitoring T-sk in the presence of, or following, metabolic and environmental induced heat stress.

Physiological Tolerance Times while Wearing Explosive Ordnance Disposal Protective Clothing in Simulated Environmental Extremes

Explosive ordnance disposal (EOD) technicians are required to wear protective clothing to protect themselves from the threat of overpressure, fragmentation, impact and heat. The engineering requirements to minimise these threats results in an extremely heavy and cumbersome clothing ensemble that increases the internal heat generation of the wearer, while the clothing’s thermal properties reduce heat dissipation. This study aimed to evaluate the heat strain encountered wearing EOD protective clothing in simulated environmental extremes across a range of differing work intensities. Eight healthy males [age 25±6 years (mean ± sd), height 180±7 cm, body mass 79±9 kg, V˙O2max 57±6 ml.kg−1.min−1] undertook nine trials while wearing an EOD9 suit (weighing 33.4 kg). The trials involved walking on a treadmill at 2.5, 4 and 5.5 km⋅h−1 at each of the following environmental conditions, 21, 30 and 37°C wet bulb globe temperature (WBGT) in a randomised controlled crossover design. The trials were ceased if the participants’ core temperature reached 39°C, if heart rate exceeded 90% of maximum, if walking time reached 60 minutes or due to fatigue/nausea. Tolerance times ranged from 10–60 minutes and were significantly reduced in the higher walking speeds and environmental conditions. In a total of 15 trials (21%) participants completed 60 minutes of walking; however, this was predominantly at the slower walking speeds in the 21°C WBGT environment. Of the remaining 57 trials, 50 were ceased, due to attainment of 90% maximal heart rate. These near maximal heart rates resulted in moderate-high levels of physiological strain in all trials, despite core temperature only reaching 39°C in one of the 72 trials.

Randomised controlled trial of an automated, interactive telephone intervention to improve type 2 diabetes self-management (Telephone-Linked Care Diabetes Project): study protocol

BackgroundAn estimated 285 million people worldwide have diabetes and its prevalence is predicted to increase to 439 million by 2030. For the year 2010, it is estimated that 3.96 million excess deaths in the age group 20-79 years are attributable to diabetes around the world. Self-management is recognised as an integral part of diabetes care. This paper describes the protocol of a randomised controlled trial of an automated interactive telephone system aiming to improve the uptake and maintenance of essential diabetes self-management behaviours.Methods/DesignA total of 340 individuals with type 2 diabetes will be randomised, either to the routine care arm, or to the intervention arm in which participants receive the Telephone-Linked Care (TLC) Diabetes program in addition to their routine care. The intervention requires the participants to telephone the TLC Diabetes phone system weekly for 6 months. They receive the study handbook and a glucose meter linked to a data uploading device. The TLC system consists of a computer with software designed to provide monitoring, tailored feedback and education on key aspects of diabetes self-management, based on answers voiced or entered during the current or previous conversations. Data collection is conducted at baseline (Time 1), 6-month follow-up (Time 2), and 12-month follow-up (Time 3). The primary outcomes are glycaemic control (HbA1c) and quality of life (Short Form-36 Health Survey version 2). Secondary outcomes include anthropometric measures, blood pressure, blood lipid profile, psychosocial measures as well as measures of diet, physical activity, blood glucose monitoring, foot care and medication taking. Information on utilisation of healthcare services including hospital admissions, medication use and costs is collected. An economic evaluation is also planned.DiscussionOutcomes will provide evidence concerning the efficacy of a telephone-linked care intervention for self-management of diabetes. Furthermore, the study will provide insight into the potential for more widespread uptake of automated telehealth interventions, globally.Trial Registration NumberACTRN12607000594426