Delivering effective Defence Engagement (Health): lessons from Operation TRENTON (South Sudan).

This paper describes the Defence Engagement (Health) (DE(H)) component of the medical mission within the UK deployment to South Sudan under Op TRENTON, the UK troop contribution to the United Nations Mission in South Sudan (UNMISS). The DE(H) activities provided advice and mentoring to the Vietnamese military medical services to support the predeployment preparation and training of their medical contingent that would undertake a relief in place of the UK personnel providing a Level 2 hospital in Bentiu, South Sudan. The paper describes these UK DE(H) activities at the strategic, operational and tactical levels to show the integration across these levels from January 2017 until the handover of command in South Sudan on 26 October 2018. The UK worked alongside personnel from the US and Australian military medical services to deliver a Field Training Exercise and other capability-building events for personnel from the Vietnamese 175 Military Hospital. The paper shows how a DE(H) programme can have strategic effects by bringing another nation into a United Nations mission, increasing UK diplomatic activity with a partner country, and by ensuring continuity of medical cover to a key UNMISS location after the withdrawal of the UK medical contingent. This paper forms part of a special issue of BMJ Military Health dedicated to DE(H).

Using network analysis to detect associations between suspected painful health conditions and behaviour in dogs.

Pain associated with chronic health conditions in non-human animals is an important animal welfare issue. To identify animals in pain and develop an understanding of the mechanisms by which pain affects behaviour, it is therefore important to establish the direct behavioural effects of painful health conditions. We reanalyse data from a cross-sectional survey that considered the presence or absence of a painful condition in dogs and quantified their affective predispositions using the Positive and Negative Activation Scale (PANAS). By applying ideas from network theory, we conceptualise pain as a stressor that exerts direct effects on a network of interacting behavioural variables, and subsequently estimated a network model of conditional dependence relations. Painful health conditions were positively conditionally associated with age (posterior mean partial correlation, ρ = 0.34; standard deviation [SD]=0.05), and negatively conditionally associated with the item 'your dog is full of energy' (ρ = -0.14; SD=0.06). In turn, the energy item was conditionally associated with other PANAS items which were marginally associated with pain, such as items representing ease of excitability and persistence in play. This suggests these marginal effects might be indirectly mediated via the energy item. Further, utilising the posterior predictive distribution we estimated that the median conditional probability (95% credible interval) of a painful health condition given an answer of 'strongly agree' on the energy item was 0.08 (0.05, 0.11), which increased to 0.32 (0.09, 0.58), given a response of 'strongly disagree'. This provides a potentially clinically useful interpretation of the conditional dependencies detected in the network.

Effect of exercise, heat stress and dehydration on myocardial performance.

BACKGROUND: Myocardial dysfunction is a well-documented outcome of extended periods of high cardiac output. Whether similar effects occur during firefighting, an occupation characterized by repeated periods of work compounded by dehydration and heat stress, is uncertain. AIMS: To investigate the independent and combined effects of moderate heat stress and dehydration on indicators of myocardial performance following intermittent, submaximal treadmill exercise while wearing personal protective equipment (PPE). METHODS: Twelve aerobically fit young men (age 21.5±2.6 years; maximal oxygen uptake [VO2max] 60.3±4.4ml kg(-1) min(-1)) performed intermittent treadmill walking exercise consisting of three 20min bouts at an intensity of ~40% VO2max separated by two periods of rest in four different conditions in random order: (i) no heat stress-euhydrated, (ii) heat stress-euhydrated (heat stress created by wearing PPE, (iii) no heat stress-dehydrated and (iv) heat stress-dehydrated. We measured core temperature by a telemetric gastrointestinal pill. We determined cardiac variables by standard echocardiographic techniques immediately before and ~30min after exercise. RESULTS: We recorded no significant changes in markers of systolic (ejection fraction, shortening fraction, tissue Doppler-S) or diastolic (mitral peak E velocity, tissue Doppler-E' and E/E') function following exercise in any of the four conditions. CONCLUSIONS: In this model of exercise designed to mimic the work, heat stress and dehydration associated with firefighting activities, we observed no negative effects on myocardial inotropic or lusitropic function.

Regional and global left ventricular function following a simulated 5 km race in sports-trained adolescents.

The effects of a short, high-intensity bout of exercise on cardiac systolic and diastolic function are not well understood in adolescent athletes. Consequently, the aims of the study were to evaluate global left ventricular (LV) systolic and diastolic function, as well as segmental wall motion responses (cardiac strain), prior to as well as 45 and 225 min following a simulated 5 km cross-country race. Twenty trained, adolescent males (age: 15.2 ± 0.7 years) volunteered for exercise testing. LV fractional shortening and the ratio of early (E) and late (A) peak flow velocities reflected global systolic and diastolic function, respectively. Peak longitudinal mitral annular septal tissue velocities were also determined during systole and diastole. Longitudinal strain (ε) and strain rates were determined across the LV. LV fractional shortening was significantly (P < 0.05) higher at 225 min post-race (37.6 ± 5.8%) compared to pre-race (34.5 ± 4.7%) and 45 min post-race (34.9 ± 5.4 %). This difference was abolished after adjusting for post-race heart rates. There was a significant (P < 0.05) decrease in the E:A ratio at both 45 min (2.04 ± 0.57) and 225 min post-race (2.20 ± 0.66) compared to the pre-race value (2.80 ± 0.68). When these data were adjusted for post-race heart rates, these pre-post-race differences in E:A ratio were abolished. There were no significant alterations in either tissue Doppler velocities or longitudinal ε. The evidence suggests that a 5 km race does not lead to any significant post-exercise attenuation in global or regional LV systolic and diastolic function in trained adolescents.

Right ventricular myocardial responses to progressive exercise in young adult males.

Recent attention has been focused on possible unique features of the right ventricular response to exercise. This study investigated a) the responses of right ventricular cardiac dynamics and myocardial function to a standard bout of progressive cycle exercise in healthy young males, and b) the effect of level of aerobic fitness on these responses. 14 athletically-trained males (20.4±1.5 years) and 11 normally-active males (21.1±1.3 years) underwent a progressive upright cycle test to exhaustion with measurement of gas exchange variables and assessment of right ventricular stroke volume, systolic and diastolic myocardial velocities, and tricuspid inflow velocities by standard Doppler echocardiographic techniques at rest, submaximal and peak exercise. Stroke volume rose initially by approximately 27% in each group, followed by stable values to exhaustion. Values of maximal stroke index and maximal oxygen uptake were significantly greater in the trained group than the normally-active males (62±10 ml m(-2), 54.3±4.0 ml kg(-1) min(-1); 49±7 ml m(-2), 40.3±5.6 ml kg(-1) min(-1), respectively). No significant differences were observed in increases in systolic or diastolic myocardial velocities, peak pulmonary outflow velocity, systolic ejection rate, or tricuspid inflow velocity between the 2 groups. The magnitude of change of these variables was similar to those previously described for left ventricular responses to similar exercise. This study revealed no unique features of right ventricular functional responses to an acute exercise challenge in young males.

Influence of sex on ventricular remodeling in collegiate athletes.

AIM: Previous reports indicate that the "athlete's heart" is more prominent in males than females, but the mechanisms responsible for this sex difference have not been elucidated. This study examined male-female differences in cardiac mass and volume in highly trained athletes and normally active individuals to assess the relative contributions of pre-existing sex differences and sports training to cardiac findings. METHODS: Echocardiographic and electrocardiographic findings were compared between 20 male and 21 female collegiate athletes and 22 male and 29 female normally-active subjects. RESULTS: Cardiac mass (per kg lean body mass) was significantly greater in the male compared to female athletes (3.62±0.55 and 3.31±0.56 g.kg-1, respectively). A similar magnitude of difference in average relative cardiac mass was observed between the normally active males and females, and cardiac mass was greater in athletic versus nonathletic groups by +14.9% in the males and +13.3% in the females. Relative left ventricular volume was greater in the male athletes (47.5±6.3 ml•BSA-1.5) compared to male nonathletes (42.9±6.1 ml•BSA-1.5); no such difference was observed in the females. CONCLUSION: These findings suggest that sex differences in both the untrained state and magnitude of training response contribute to male-female differences in the "athlete's heart"

Structural hemispheric asymmetries in the human precentral gyrus hand representation.

The superior region of the precentral gyrus (preCG) is known to be actively involved with hand function and has been proposed as a possible neural correlate of handedness. To test this hypothesis, we used a combined voxel-based morphometric (VBM) asymmetry analysis of structural MRI, along with diffusion MRI (dMRI) tractography to investigate laterality indices of corticomotor white matter (WM) pathways, based on measures of fractional anisotropy (FA). The relationship between measures of motor performance and FA laterality indices was also investigated. In a cohort of 14 right-handed healthy participants, the VBM asymmetry analysis revealed an area within the preCG associated with hand representation. The tractography analysis revealed that this region possessed a number of major WM intrahemispheric connections to the brain stem, thalamus, cerebellum, postcentral, caudal middle and superior frontal, and superior and inferior parietal corticomotor regions. Within the corticospinal tracts, we found FA was significantly higher in the left hemisphere compared with the right. Furthermore, significant correlations were found between FA asymmetry measures projecting from this region, namely corticospinal tracts and those connecting the postcentral gyri, with grip strength and finger-tapping performance, respectively. A number of the motor pathways projecting from this region also exhibited leftward asymmetry of FA distributions. The findings from this study highlight the role of the left motor cortex in skilled motor performance and provide a framework for the study of the relationship between handedness and preCG hand representation in larger normative populations.

Skin microvascular reactivity in trained adolescents.

Whilst endothelial dysfunction is associated with a sedentary lifestyle, enhanced endothelial function has been documented in the skin of trained individuals. The purpose of this study was to investigate whether highly trained adolescent males possess enhanced skin microvascular endothelial function compared to their untrained peers. Seventeen highly and predominantly soccer trained boys (V(O)(2)(peak): 55 +/- 6 mL kg(-1) min(-1)) and nine age- and maturation-matched untrained controls (V(O)(2)(peak): 43 +/- 5 mL kg(-1) min(-1)) aged 13-15 years had skin microvascular endothelial function assessed using laser Doppler flowmetry. Baseline and maximal thermally stimulated skin blood flow (SkBF) responses were higher in forearms of trained subjects compared to untrained participants [baseline SkBF: 11 +/- 4 vs. 9 +/- 3 perfusion units (PU), p < 0.05; SkBF(max): 282 +/- 120 vs. 204 +/- 68 PU, p < 0.05]. Similarly, cutaneous vascular conductance (CVC) during local heating was superior in the forearm skin of trained versus untrained individuals (CVC(max): 3 +/- 1 vs. 2 +/- 1 PU mmHg(-1), p < 0.05). Peak hyperaemia following arterial occlusion and area under the reactive hyperaemia curve were also greater in forearm skin of the trained group (peak hyperaemia: 51 +/- 21 vs. 35 +/- 15 PU, p < 0.05; area under curve: 1596 +/- 739 vs. 962 +/- 796 PUs, p < 0.05). These results suggest that chronic exercise training in adolescents is associated with enhanced microvascular endothelial vasodilation in non-glabrous skin.

Aerobic cost in elite female adolescent swimmers.

Maximal performance in swimming depends on metabolic power and the economy of swimming. Thus, the energy cost of swimming (economy= VO(2)/V, C(s)) and maximal aerobic power (VO(2max)) in elite young female swimmers (n=10, age: 15.3+/-1.5 years) and their relationships to race times (50-1,000 m) and national ranking were examined. VO(2) increased exponentially with velocity (V), (VO(2)=5.95+(-10.58 V)+5.84 V(2)) to a maximal VO(2) of 2.71+/-0.50 L x min(-1) (46.7+/-8.2 mL x kg(-1) x min(-1)) at a free swimming velocity of 1.37+/-0.07 m x s(-1). C(s) was constant up to 1.2 m x s(-1) (21.5 mL x m(-1)), however was significantly higher at 1.36 m x s(-1) (27.3 mL x m(-1)). Peak [La] was 5.34+/-2.26 mM. C(s) expressed as a percentage of Cs at maximal swimming velocity was significantly correlated with race times and ranking across a number of distances. The data for these elite females demonstrate that the energy cost of swimming is a good predictor of performance across a range of distances. However, as swimming performance is determined by a combination of factors, these findings warrant further examination.

Cardiovascular responses to static exercise: a re-appraisal.

Traditional findings of circulatory responses to a bout of static exercise include an abrupt rise in systolic and diastolic blood pressure, small increases in cardiac output with no rise in stroke volume, and unaltered systemic vascular resistance. These characteristics are not, however, consistent with current concepts of circulatory adjustments to high intramuscular pressure and inability of the heart to generate increases in cardiac output by heart rate alone. When circulatory responses to static exercise are in considered on a per-beat basis, at times of circulatory flow, these conflicts are resolved, as systemic vascular resistance is observed to rise, and augmentation of cardiac output can be accounted for by improvements in myocardial contractility.

Determinants of endurance exercise capacity in the heat in prepubertal boys.

The goal of this study was to identify factors which limit exercise endurance in hot ambient conditions in prepubertal boys. Eight healthy non-acclimatized, highly physically active prepubertal boys performed steady load cycling at approximately 65 % peak VO (2) to exhaustion in both cool (19.6 +/- 0.6 degrees C, 66.4 +/- 11.0 % relative humidity) and hot (31.0 +/- 0.3 degrees C, 56.9 +/- 2.0 % relative humidity) environmental conditions. Cardiac output, oxygen uptake, rectal temperature (T (re)), rating of perceived exertion (RPE), blood pressure, and calculated arterial venous oxygen difference were obtained serially in each testing session, and percent dehydration was calculated from body weight loss. Endurance time was significantly shorter in the hot condition (29.30 +/- 6.19 minutes versus 41.38 +/- 6.30 minutes in the cool room). No significant differences in circulatory markers or hydration status were observed either during testing or between cycling thermal conditions. Rate of rise of T (re) was greater during exercise in the heat, but no significant difference in T (re) between conditions was observed at exhaustion. Mean values of RPE were consistently greater during exercise in the heat, but these differences did not reach statistical significance. These findings support the concept that rises in core temperature and/or brain perception (RPE) rather than circulatory insufficiency may be the critical factors defining limits to exercise in the heat.

Exercise tolerance in a hot and humid climate in heat-acclimatized girls and women.

This study compared physiological responses associated with exercise tolerance in girls (G) and women (W) of similar fitness and heat acclimatization level during exercise in a hot and humid outdoor environment (33.4 degrees C and 55.1 % RH; WBGT = 29.9 +/- 0.2 degrees C). Nine pre-menarcheal G (age = 11.3 yr) and nine W (age = 26.8 yr), matched for aerobic capacity and heat acclimatization level, performed a cycling session at 60 % VO2max until fatigue. A sports drink was provided periodically to prevent dehydration. Tolerance time was not different between the groups (G = 56.9 +/- 6.3, W = 76.5 +/- 9.9 min, p > 0.05). During exercise, sweat rate (G = 9.1 +/- 1.1, W = 12.0 +/- 1.1 ml.m(-2).min(-1)), the increase in rectal temperature [T(re)] (G = 0.9 +/- 0.1, W = 1.1 +/- 0.1 degrees C), and heat storage (G = 10.6 +/- 5.3, W = 20.5 +/- 4.5 W.m(-2)) did not differ between the groups. At fatigue, T(re) (G = 38.2 +/- 0.1, W = 38.4 +/- 0.1 degrees C), heart rate (G = 167.3 +/- 7.3, W = 171 +/- 3.3 beats.min(-1)), stroke index (G = 48.3 +/- 1.5, W = 52.4 +/- 1.8 ml.m(-2)), and forearm skin blood flow (G = 9.5 +/- 1.3, W = 11.7 +/- 1.5 ml.100 ml(- 1).min(-1)) did not differ between the groups. Similar to women, the main reasons reported by girls to stop exercising in the heat were localized leg fatigue and gluteus muscle discomfort. We conclude that heat-acclimatized girls exhibit an adequate cardiovascular and thermoregulatory adjustment while exercising in a hot and humid outdoor environment when hypohydration is prevented.

Cardiac responses to progressive upright exercise in adult male cyclists.

AIM: Previous investigations have indicated that maximal stroke volume is the primary factor which differentiates physiological aerobic fitness (VO2max) in endurance athletes from nonathletes. Understanding the pattern of stroke volume response to progressive exercise may provide insights into the mechanisms which are responsible for this difference. METHODS: Doppler echocardiography was used to estimate stroke volume changes with maximal upright cycle exercise in 8 highly trained adult cyclists (mean age 30.5+/-1.6 years) and 16 age-matched nontrained males. Ventricular dimensions were measured during exercise using 2-dimensional echocardiography (parastemal long axis view). Findings were compared to a group of untrained adult male subjects. RESULTS: Mean maximal oxygen uptake was 73.7+/-7.0 and 47.4+/-7.5 ml x kg(-1) x min(-1) in the 2 groups, respectively. Stroke volume rose in both the cyclists and nontrained subjects at the onset of exercise but then plateaued without significant change to exhaustion. Values for stroke index were significantly greater at rest and all levels of exercise in the cyclists (maximal 85+/-13 versus 61+/-13 ml x m(-2)). Two dimensional echocardiograms during exercise in the cyclists revealed a small initial rise in left ventricular end-diastolic dimension and then a small decline, while systolic dimension decreased progressively, resulting in a rise in shortening fraction. CONCLUSION: These findings are consistent with the concept that determinants of stroke volume at rest are most influential in defining differences in maximal stroke volume between athletes and nonathletes.

Determinants of diastolic cardiac filling during exercise.

AIM: To examine relative contributions of factors responsible for cardiac diastolic filling during exercise by investigating changes in systemic venous return (as indicated by alterations in cardiac output) after abrupt cessation of skeletal muscle pump function. METHODS: Two cycle exercise studies differing in subject population (men, boys), intensity (submaximal, maximal), and technique for assessing cardiac output (thoracic bioimpedance, Doppler echocardiography). Study 1 involved 12 healthy boys (mean age 12.0+/-1.3 years) and study 2 was composed of 9 young adult men (mean age 27.0+/-3.7 years). RESULTS: Decline in cardiac output averaged 15.8% within the first 15 sec of passive recovery in study 1, while a decrease of 10.9% was observed at 20 sec of passive recovery in study 2. Active pedaling recovery in study 2 slowed the decrease in cardiac output. CONCLUSION: Factors other than the skeletal muscle pump, particularly forward cardiac flow, are capable of maintaining high levels of systemic venous return during early passive recovery. However, this model is unlikely to reflect hemodynamics during exercise, since skeletal muscle contractions impede arterial inflow but augment systemic venous return by increasing the arterial-venous pressure gradient.

Circulatory responses to progressive exercise: insights from positional differences.

The influence of body position on cardiac responses to progressive exercise was examined in 13 healthy circumpubertal boys. The subjects (mean age 12.5 +/- 1.4 y) performed a progressive cycle test with an identical protocol in the sitting and supine positions. Stroke volume and left ventricular dimensions were assessed with Doppler and two-dimensional echocardiography, respectively. During supine exercise, no changes were seen in stroke volume or left ventricular preload (end-diastolic dimension) with increasing exercise intensity. At rest, mean values for stroke volume and cardiac output were 16.4 % and 27.1 % lower, respectively, with subjects upright compared to supine. With upright exercise these variables rose to become insignificantly different than supine values. Stroke volume while cycling upright rose by 29 % by the second workload but remained stable at higher work intensities. The initial increase in stroke volume observed only when cycling upright presumably reflects mobilization of dependent blood in the lower extremities. The mechanisms governing cardiac responses to exercise when supine and upright are otherwise identical.

Myocardial performance during maximal exercise in adolescents with anorexia nervosa.

AIM: To examine cardiac responses and indicators of myocardial function during maximal exercise in adolescent girls with anorexia nervosa. METHODS: Eight girls (mean age 16.3+/-2.7 years) who satisfied criteria for the diagnosis of anorexia nervosa underwent maximal cycle testing. Cardiac stroke volume and peak aortic velocity and mean acceleration of flow (markers of myocardial contractility) were assessed using Doppler echocardiography and compared to healthy control subjects. Gas exchange variables were measured using open circuit spirometry techniques. RESULTS: Resting and maximal heart rates were less in the patients, and maximal oxygen uptake was significantly lower than controls. Maximal stroke index was greater in the patients than controls, with a normal pattern of response to progressive exercise. Peak aortic velocity and mean acceleration of flow were similar in the two groups when adjusted for heart rate. CONCLUSION: Findings of low heart rate and aerobic fitness previously described in patients with anorexia nervosa were confirmed. However, there was no evidence of abnormal myocardial performance during maximal exercise testing.

The circulatory response to exercise: role of the peripheral pump.

The circulation of blood during upright exercise involves a two-pump system, a central cardiac pump and a peripheral pump responsible for systemic venous return. Axiomatically, the function of the two pumps must be equal, and certain evidence suggests that the peripheral pump may "drive" the circulation during exercise. Despite its potential importance to circulatory reserve and aerobic fitness, little is known regarding the determinants of the peripheral pump. Pumping function of skeletal muscle and the suction effect of the left ventricle presumably are principal factors in defining systemic venous return. This review, which focuses on data in humans, examines current information regarding the peripheral pump and its potential role as a critical determinant of maximal cardiac output, maximal oxygen uptake, and endurance fitness.

Hemodynamic responses to increasing cycle cadence in 11-year old boys: role of the skeletal muscle pump.

Previous studies in adults have indicated a rise in the metabolic cost of increasing cycling cadence at constant work rates. This study examined the metabolic and cardiovascular responses to pedaling rates of 41, 63, and 83 rpm at both zero-load and 50-watts load in 12 prepubertal boys. Increasing cadence from 41 to 83 rpm produced a 52.9% and 23.1% rise in gross energy expenditure in the two work conditions, respectively, despite the constant external work rate. This augmented energy expenditure was accounted for entirely by internal work, as no changes in work metabolic cost (difference between loaded and unloaded cycling) were observed as cadence increased. The rise in energy expenditure with higher pedaling rate during the zero load and 50 watt conditions was accompanied by increases in both heart rate and stroke volume. Arterial venous oxygen difference did not change with increased cadence but was significantly higher with loaded cycling, suggesting that skeletal muscle pump effectiveness is negatively influenced by increased load but not by increased pedaling rate.

Dynamics of left ventricular diastolic filling during exercise: a Doppler echocardiographic study of boys 10 to 14 years old.

STUDY OBJECTIVE: Factors influencing diastolic filling of the left ventricle may serve as critical determinants of both maximal cardiac output and oxygen uptake. This study was conducted to assess diastolic filling dynamics of the left ventricle during progressive upright cycle exercise in children. METHODS: Twelve boys aged 10 to 14 years underwent cycle testing with determination of transmitral flow velocities and pressure gradients as well as cardiac stroke volume using Doppler echocardiography. RESULTS: Estimated diastolic filling period shortened from 0.479 +/- 0.043 s at rest to 0.138 +/- 0.015 s at peak exercise. The peak and mean transmitral pressure gradient rose fourfold from rest to peak exercise. Mitral flow volume per beat rose by only 40% and remained stable beyond mild-to-moderate intensity work. CONCLUSIONS: Increases in transmitral pressure gradient with exercise may serve principally to augment velocity of ventricular filling with the progressively shortening diastolic time period.

Organized sports for children and preadolescents.

Participation in organized sports provides an opportunity for young people to increase their physical activity and develop physical and social skills. However, when the demands and expectations of organized sports exceed the maturation and readiness of the participant, the positive aspects of participation can be negated. The nature of parental or adult involvement can also influence the degree to which participation in organized sports is a positive experience for preadolescents. This updates a previous policy statement on athletics for preadolescents and incorporates guidelines for sports participation for preschool children. Recommendations are offered on how pediatricians can help determine a child's readiness to participate, how risks can be minimized, and how child-oriented goals can be maximized.