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Biomedical subjects

Robert Carter

Publications and source records attributed to Robert Carter.

At least 19 recordsLinked to original sources
PubMed2006

Economic evaluation of Australian stroke services: a prospective, multicenter study comparing dedicated stroke units with other care modalities.

BACKGROUND AND PURPOSE: Level I evidence from randomized controlled trials demonstrates that the model of hospital care influences stroke outcomes; however, the economic evaluation of such is limited. An economic appraisal of 3 acute stroke care models was facilitated through the Stroke Care Outcomes: Providing Effective Services (SCOPES) study in Melbourne, Australia. The aim was to describe resource use up to 28 weeks poststroke for each model and examine the cost-effectiveness of stroke care units (SCUs). METHODS: A prospective, multicenter, cohort study design was used. Costs and outcomes of stroke patients receiving 100% treatment in 1 of 3 inpatient care models (SCUs, mobile service, conventional care) were compared. Health-sector resource use up to 28 weeks was measured in 1999. Outcomes were thorough adherence to a suite of important clinical processes and the number of severe inpatient complications. RESULTS: The sample comprised 395 participants (mean age 73 [SD 14], 77% first-ever strokes, males 53%). When compared with conventional care (n=84), costs for mobile service (n=209) were significantly higher (P=0.024), but borderline for SCU (n=102, P=0.08; 12,251 Australian dollars; 15,903 Australian dollars; 15,383 Australian dollars respectively). This was primarily explained by the greater use of specialist medical services. The incremental cost-effectiveness of SCUs over conventional care was 9867 Australian dollars per patient achieving thorough adherence to clinical processes and 16,372 Australian dollars per patient with severe complications avoided, based on costs to 28 weeks. CONCLUSIONS: Although acute SCU costs are generally higher, they are more cost-effective than either mobile service or conventional care.

Aged↗
PubMed2006

Hypohydration and prior heat stress exacerbates decreases in cerebral blood flow velocity during standing.

Hypohydration is associated with orthostatic intolerance; however, little is known about cerebrovascular mechanisms responsible. This study examined whether hypohydration reduces cerebral blood flow velocity (CBFV) in response to an orthostatic challenge. Eight subjects completed four orthostatic challenges (temperate conditions) twice before (Pre-EU and Pre-Hyp) and following recovery from passive heat stress ( approximately 3 h at 45 degrees C, 50% relative humidity, 1 m/s air speed) with (Post-EU) or without (Post-Hyp) fluid replacement of sweat losses (-3% body mass loss). Measurements included CBFV, mean arterial pressure (MAP), heart rate (HR), end-tidal CO(2), and core and skin temperatures. Test sessions included being seated (20 min) followed by standing (60 s) then resitting (60 s) with metronomic breathing (15 breaths/min). CBFV and MAP responses to standing were similar during Pre-EU and Pre-Hyp. Standing Post-Hyp exacerbated the magnitude (-28.0 +/- 1.4% of baseline) and duration (9.0 +/- 1.6 s) of CBFV reductions and increased cerebrovascular resistance (CVR) compared with Post-EU (-20.0 +/- 2.1% and 6.6 +/- 0.9 s). Standing Post-EU also resulted in a reduction in CBFV, and a smaller decrease in CVR compared with Pre-EU. MAP decreases were similar for Post-EU (-18 +/- 4 mmHg) and Post-Hyp (-21 +/- 5 mmHg) from seated to standing. These data demonstrate that despite similar MAP decreases, hypohydration, and prior heat stress (despite apparent recovery) produce greater CBFV reduction when standing. These observations suggest that hypohydration and prior heat stress are associated with greater reductions in CBFV with greater CVR, which likely contribute to orthostatic intolerance.

Adult↗
PubMed2006

No effect of moderate hypohydration or hyperthermia on anaerobic exercise performance.

PURPOSE: This study examined the effects of hypohydration and moderate hyperthermia (core temperature elevation) on anaerobic exercise performance in a temperate environment. METHODS: Eight active males completed two passive heat exposure trials (180 min, 45 degrees C, 50% rh) with (EUH) and without (HYP) fluid replacement. A single 15-s Wingate anaerobic test (WAnT) was used to assess anaerobic performance (peak power, mean power, and fatigue index) before (-180 min) and again at three time points after passive heat exposure to include immediately (0 min), 30 min, and 60 min after in a temperate environment (22 degrees C). Rectal temperature (Tc) was measured throughout the experiment. RESULTS: HYP reduced body mass (2.7+/-0.7%) (P<0.05) but had no effect on any WAnT performance measure. Passive heat exposure elicited moderate hyperthermia in both trials (EUH: 0.6 degrees C; HYP: 1.0 degrees C) and returned to baseline within 30-60 min following similar decay curves. HYP Tc remained higher (0.4 degrees C) than EUH throughout testing (P<0.05), but moderate hyperthermia itself produced no independent effect on anaerobic exercise performance in either trial. CONCLUSIONS: This study demonstrates that neither moderate HYP nor the moderate hyperthermia accompanying HYP by passive heat exposure affect anaerobic exercise performance in a temperate environment.

Adult↗
PubMed2006

Thermoregulatory control following dynamic exercise.

Post-exercise thermoregulatory control in humans has received limited attention. In the post-exercise period skin blood flow and sweating return to pre-exercise levels despite a persistent elevation in esophageal temperature, suggesting an alteration in thermoregulatory control. The esophageal temperature response post-exercise appears to be correlated to the marked cardiovascular changes that occur after dynamic exercise. Recent work has shown that non-thermoregulatory factors associated with hemodynamic changes and hydration status post-exercise may influence the regulation of core temperature during exercise recovery. This review will characterize the thermal response and describe our current understanding of the physiological influences on thermoregulatory control during recovery from dynamic exercise.

Body Temperature Regulation↗
PubMed2005

Hypohydration impairs endurance exercise performance in temperate but not cold air.

This study compared the effects of hypohydration (HYP) on endurance exercise performance in temperate and cold air environments. On four occasions, six men and two women (age = 24 +/- 6 yr, height = 170 +/- 6 cm, weight = 72.9 +/- 11.1 kg, peak O2 consumption = 48 +/- 9 ml.kg(-1).min(-1)) were exposed to 3 h of passive heat stress (45 degrees C) in the early morning with [euhydration (EUH)] or without (HYP; 3% body mass) fluid replacement. Later in the day, subjects sat in a cold (2 degrees C) or temperate (20 degrees C) environment with minimal clothing for 1 h before performing 30 min of cycle ergometry at 50% peak O2 consumption followed immediately by a 30-min performance time trial. Rectal and mean skin temperatures, heart rate, and ratings of perceived exertion measurements were made at regular intervals. Performance was assessed by the total amount of work (kJ) completed in the 30-min time trial. Skin temperature was significantly lower in the cold compared with the temperate trial, but there was no independent effect of hydration. Rectal temperature in both HYP trials was higher than EUH after 60 min of exercise, but the difference was only significant within the temperate trials (P < 0.05). Heart rate was significantly higher at 30 min within the temperate trial (HYP > EUH) and at 60 min within the cold trial (HYP > EUH) (P < 0.05). Ratings of perceived exertion increased over time with no differences among trials. Total work performed during the 30-min time trial was not influenced by environment but was less (P < 0.05) for HYP than EUH in the temperate trials. The corresponding change in performance (EUH-HYP) was greater for temperate (-8%) than for cold (-3%) (P < 0.05). These data demonstrate that 1) HYP impairs endurance exercise performance in temperate but not cold air but 2) cold stress per se does not.

Adult↗
PubMed2005

Human water needs.

Healthy humans regulate daily water balance remarkably well across their lifespan despite changes in biological development and exposure to stressors on hydration status. Acute or chronic body water deficits result when intakes are reduced or losses increase, but day-to-day hydration is generally well maintained so long as food and fluid are readily available. Total water intake includes drinking water, water in beverages, and water in food. Daily water needs determined from fluid balance, water turnover, or consumption studies provide similar values for a given set of conditions. A daily water intake of 3.7 L for adult men and 2.7 L for adult women meets the needs of the vast majority of persons. However, strenuous physical exercise and heat stress can greatly increase daily water needs, and the individual variability between athletes can be substantial.

Body Water↗
PubMed2005

Epidemiology of hospitalizations and deaths from heat illness in soldiers.

PURPOSE: Serious heat illness has received considerable recent attention due to catastrophic heat waves in the United States and Europe, the deaths of high-profile athletes, and military deployments. METHODS: This study documents heat illness hospitalizations and deaths for the U.S. Army from 1980 through 2002. Hospitalization data were obtained from the Total Army Injury Health Outcomes Database (TAIHOD) coded according to the International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM). North Atlantic Treaty Organization Standardization Agreement codes were searched for heat injuries in an effort to detect cases that were not found during the ICD-9-CM search. RESULTS: Five-thousand two-hundred forty-six soldiers were hospitalized, and 37 died due to heat illness. Our results indicate: 1) approximately 60% reduction in hospitalization rates (fewer heat exhaustion cases) over the 22-yr period; 2) fivefold increase in heat stroke hospitalization rates (1.8 per 100,000 in 1980 to 14.5 per 100,000 in 2001); 3) heat stroke cases were associated with dehydration (17%), rhabdomyolysis (25%), and acute renal failure (13%); 4) lower hospitalizations rates among African and Hispanic Americans compared with Caucasians (incidence density ratio, 0.76 [95% confidence interval, 0.71-0.82]; 5) greater rates of hospitalizations and heat strokes among recruits from northern than southern states (incidence density ratio, 1.69 [95% confidence interval, 1.42-1.90]; and 6) greater rates of hospitalizations and heat strokes among women than men (incidence density ratio, 1.18 [95% confidence interval, 1.09-1.27]). CONCLUSIONS: Exertional heat illness continues to be a military problem during training and operations. Whereas the hospitalization rate of heat illness is declining, heat stroke has markedly increased.

Adolescent↗
PubMed2005

Running performance differences between men and women:an update.

More than a decade ago it was reported in the journal Nature that the slope of improvement in the men's and women's running records, extrapolated from mean running velocity plotted against historical time, would eventually result in a performance intersection of the sexes across a variety of running distances. The first of these intersections was to occur for 42 000 m before the 21st century. Most of the error in this prediction is probably explained by the linear mathematical treatment and extrapolation of limited performance data, since including world record-setting running performances for women before and after 1985 results in a non-linear data fit. The reality of early, disproportionate improvements in women's running that gave the appearance of an impending convergence with men is best explained by an historical social sports bias. Women's times have now reached a plateau similar to that observed for men at comparative performance milestones in the marathon. Sex differences at distances from 100 to 10 000 m show similar trends. The remaining sex gaps in performance appear biological in origin. Success in distance running and sprinting is determined largely by aerobic capacity and muscular strength, respectively. Because men possess a larger aerobic capacity and greater muscular strength, the gap in running performances between men and women is unlikely to narrow naturally.

Adult↗
PubMed2004

Trial application of a Model of Resource Utilization, Costs, and Outcomes for Stroke (MORUCOS) to assist priority setting in stroke.

BACKGROUND AND PURPOSE: Cost-effectiveness data for stroke interventions are limited, and comparisons between studies are confounded by methodological inconsistencies. The aim of this study was to trial the use of the intervention module of the economic model, a Model of Resource Utilization, Costs, and Outcomes for Stroke (MORUCOS) to facilitate evaluation and ranking of the options. METHODS: The approach involves using an economic model together with added secondary considerations. A consistent approach was taken using standard economic evaluation methods. Data from the North East Melbourne Stroke Incidence Study (NEMESIS) were used to model "current practice" (base case), against which 2 interventions were compared. A 2-stage process was used to measure benefit: health gains (expressed in disability-adjusted life years [DALYs]) and filter analysis. Incremental cost-effectiveness ratios (ICERs) were calculated, and probabilistic uncertainty analysis was undertaken. RESULTS: Aspirin, a low-cost intervention applicable to a large number of stroke patients (9153 first-ever cases), resulted in modest health benefits (946 DALYs saved) and a mean ICER (based on incidence costs) of US 1421 dollars per DALY saved. Although the health gains from recombinant tissue-type plasminogen activator (rtPA) were less (155 DALYs saved), these results were impressive given the small number of persons (256) eligible for treatment. rtPA dominates current practice because it is more effective and cost-saving. CONCLUSIONS: If used to assess interventions across the stroke care continuum, MORUCOS offers enormous capacity to support decision-making in the prioritising of stroke services.

Acute Disease↗
PubMed2004

The tetraspanin CD81 is necessary for partitioning of coligated CD19/CD21-B cell antigen receptor complexes into signaling-active lipid rafts.

Tetraspanins have been hypothesized to facilitate the organization of functional multimolecular membrane complexes. In B cells the tetraspanin CD81 is a component of the CD19/CD21 complex. When coligated to the B cell Ag receptor (BCR), the CD19/CD21 complex significantly enhances BCR signaling in part by prolonging the association of the BCR with signaling-active lipid rafts. In this study CD81 is shown to associate with lipid rafts upon coligation of the BCR and the CD19/CD21 complex. Using B cells from CD81-deficient mice we demonstrate that in the absence of CD81, coligated BCR and CD19/CD21 complexes fail to partition into lipid rafts and enhance BCR signaling from rafts. Furthermore, a chimeric CD19 protein that associates only weakly if at all with CD81 fails to promote the association of coligated BCR with lipid rafts. The requirement for CD81 to promote lipid raft association may define a novel mechanism by which tetraspanins function as molecular facilitators of signaling receptors.

Adjuvants, Immunologic↗
PubMed2004

Daily body mass variability and stability in active men undergoing exercise-heat stress.

The purpose of this study was to quantify the variability and stability of 1st morning body mass (BM) fluctuations during daily exercise in the heat while following traditional fluid intake guidance. Data from 65 men were examined retrospectively. BM fluctuations were monitored over 4 to 15 consecutive days. Group daily variation in BM was 0.51+/-0.20 kg. Group coefficient of variation was 0.66+/-0.24%, normally distributed, and not related to either absolute BM (r = 0.04) or number of measurements (r = 0.34). Three days resulted in a similar variability estimate compared to 6 or 9 d, although precision was improved with 9 d. In conclusion, 3 consecutive BM measurements provide an accurate assessment of daily BM variability, which is less than 1% for active men when replacing 100% of sweat losses during exercise. The data also suggest that daily BM is a sufficiently stable physiological parameter for potential daily fluid balance monitoring.

Adolescent↗
PubMed2004

Branched-chain amino acid supplementation and human performance when hypohydrated in the heat.

The serotonin system may contribute to reduced human performance when hypohydrated in the heat. This study determined whether branched-chain amino acid (BCAA) supplementation could sustain exercise and cognitive performance in the heat (40 degrees C dry bulb, 20% relative humidity) when hypohydrated by 4% of body mass. Seven heat-acclimated men completed two experimental trials, each consisting of one preparation and one test day. On day 1, a low-carbohydrate diet was eaten and subjects performed exhaustive cycling (morning) and treadmill exercise in the heat (afternoon) to lower muscle glycogen and achieve the desired hypohydration level. On day 2, subjects consumed an isocaloric BCAA and carbohydrate (BC) or carbohydrate-only drink during exercise. Experimental trials included 60 min of cycle ergometry (50% peak oxygen uptake) followed by a 30-min time trial in the heat. A cognitive test battery was completed before and after exercise, and blood samples were taken. BC produced a 2.5-fold increase (P < 0.05) in plasma BCAA and lowered (P < 0.05) the ratios of total tryptophan to BCAA and large neutral amino acid. Blood prolactin, glucose, lactate, and osmolality were not different between trials but increased over time. Cardiovascular and thermoregulatory data were also similar between trials. BC did not alter time-trial performance, cognitive performance, mood, perceived exertion, or perceived thermal comfort. We conclude that BCAA does not alter exercise or cognitive performance in the heat when subjects are hypohydrated.

Adult↗
PubMed2004

The cost of seasonal respiratory illnesses in Australian children: the dominance of patient and family costs and implications for vaccine use.

Respiratory viral infections are one of the next group of diseases likely to be targeted for prevention in childhood by the use of vaccines. To begin collecting necessary epidemiology and cost information about the illnesses caused by these viruses, we conducted a prospective cohort study in 118 Melbourne children between 12 and 71 months of age during winter and spring 2001. We were interested in calculating an average cost per episode of community-managed acute respiratory disease, in identifying the key cost drivers of such illness, and to identify the proportion of costs borne by the patient and family. There were 202 community-managed influenza-like illnesses identified between July and December 2001, generating 89 general practitioner visits, and 42 antibiotic prescriptions. The average cost of community-managed episodes (without hospitalisation) was dollar 241 (95% CI dollar 191 to dollar 291), with the key cost drivers being carer time away from usual activities caring for the ill child (70% of costs), use of non-prescription medications (5.4%), and general practice visits (5.0%). The patient and family met 87 per cent of total costs. The lowest average cost occurred in households from the highest income bracket. Acute respiratory illness managed in the community is common, with the responsibility for meeting the cost of episodes predominantly borne by the patient and family in the form of lost productivity. These findings have implications for preventive strategies in children, such as the individual use of, or implementation of public programs using, currently available vaccines against influenza and vaccines under development against other viral respiratory pathogens.

Age Distribution↗
PubMed2003

Active recovery attenuates the fall in sweat rate but not cutaneous vascular conductance after supine exercise.

The purpose of this study was to identify whether baroreceptor unloading was responsible for less efficient heat loss responses (i.e., skin blood flow and sweat rate) previously reported during inactive compared with active recovery after upright cycle exercise (Carter R III, Wilson TE, Watenpaugh DE, Smith ML, and Crandall CG. J Appl Physiol 93: 1918-1929, 2002). Eight healthy adults performed two 15-min bouts of supine cycle exercise followed by inactive or active (no-load pedaling) supine recovery. Core temperature (T(core)), mean skin temperature (T(sk)), heart rate, mean arterial blood pressure (MAP), thoracic impedance, central venous pressure (n = 4), cutaneous vascular conductance (CVC; laser-Doppler flux/MAP expressed as percentage of maximal vasodilation), and sweat rate were measured throughout exercise and during 5 min of recovery. Exercise bouts were similar in power output, heart rate, T(core), and T(sk). Baroreceptor loading and thermal status were similar during trials because MAP (90 +/- 4, 88 +/- 4 mmHg), thoracic impedance (29 +/- 1, 28 +/- 2 Omega), central venous pressure (5 +/- 1, 4 +/- 1 mmHg), T(core) (37.5 +/- 0.1, 37.5 +/- 0.1 degrees C), and T(sk) (34.1 +/- 0.3, 34.2 +/- 0.2 degrees C) were not significantly different at 3 min of recovery between active and inactive recoveries, respectively; all P > 0.05. At 3 min of recovery, chest CVC was not significantly different between active (25 +/- 6% of maximum) and inactive (28 +/- 6% of maximum; P > 0.05) recovery. In contrast, at this time point, chest sweat rate was higher during active (0.45 +/- 0.16 mg.cm(-2).min(-1)) compared with inactive (0.34 +/- 0.19 mg.cm(-2).min(-1); P < 0.05) recovery. After exercise CVC and sweat rate are differentially controlled, with CVC being primarily influenced by baroreceptor loading status while sweat rate is influenced by other factors.

Adult↗
PubMed2003

Lifetime cost of stroke subtypes in Australia: findings from the North East Melbourne Stroke Incidence Study (NEMESIS).

BACKGROUND AND PURPOSE: Little is known about any variations in resource use and costs of care between stroke subtypes, especially nonhospital costs. The purpose of this study was to describe the patterns of resource use and to estimate the first-year and lifetime costs for stroke subtypes. METHODS: A cost-of-illness model was used to estimate the total first-year costs and lifetime costs of stroke subtypes for all strokes (subarachnoid hemorrhages excluded) that occurred in Australia during 1997. For each subtype, average cost per case during the first year and the present value of average cost per case over a lifetime were calculated. Resource use data obtained in the North East Melbourne Stroke Incidence Study (NEMESIS) were used. RESULTS: The present value of total lifetime costs for all strokes was Aus 1.3 billion dollars (US 985 million dollars). Total lifetime costs were greatest for ischemic stroke (72%; Aus 936.8 million dollars; US 709.7 million dollars), followed by intracerebral hemorrhage (26%; Aus 334.5 million dollars; US 253.4 million dollars) and unclassified stroke (2%; Aus 30 million dollars; US 22.7 million dollars). The average cost per case during the first year was greatest for total anterior circulation infarction (Aus 28 266 dollars). Over a lifetime, the present value of average costs was greatest for intracerebral hemorrhage (Aus 73 542 dollars), followed by total anterior circulation infarction (Aus 53 020 dollars), partial anterior circulation infarction (Aus 50 692 dollars), posterior circulation infarction (Aus 37 270 dollars), lacunar infarction (Aus 34 470 dollars), and unclassified stroke (Aus 12 031 dollars). CONCLUSIONS: First-year and lifetime costs vary considerably between stroke subtypes. Variation in average length of total hospital stay is the main explanation for differences in first-year costs.

Acute Disease↗
PubMed2003

Fluid balance and endurance exercise performance.

Dehydration alters cardiovascular, thermoregulatory, central nervous system, and metabolic functions. One or more of these alterations will degrade endurance exercise performance when dehydration exceeds 2% of body weight. These performance decrements are accentuated by heat stress. To minimize the adverse consequences of body water deficits on endurance exercise performance, it is recommended that fluid intake be sufficient to minimize dehydration to less than 2% of body weight loss. This can usually be achieved with fluid intakes of under 1 L x h(-1).

Body Water↗