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| 2. |
- Ganio, Matthew S., et al.
(författare)
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Aerobic Fitness Is Disproportionately Low in Adult Burn Survivors Years After Injury
- 2015
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Ingår i: Journal of Burn Care & Research. - 1559-047X .- 1559-0488. ; 36:4, s. 513-519
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Tidskriftsartikel (refereegranskat)abstract
- A maximal aerobic capacity below the 20th percentile is associated with an increased risk of all-cause mortality (Blair 1995). Adult Adult burn survivors have a lower aerobic capacity compared with nonburned adults when evaluated 38 +/- 23 days postinjury (deLateur 2007). However, it is unknown whether burn survivors with well-healed skin grafts (ie, multiple years postinjury) also have low aerobic capacity. This project tested the hypothesis that aerobic fitness, as measured by maximal aerobic capacity (VO2max), is reduced in well-healed adult burn survivors when compared with normative values from nonburned individuals. Twenty-five burn survivors (36 +/- 12 years old; 13 females) with well-healed split-thickness grafts (median, 16 years postinjury; range, 1-51 years) covering at least 17% of their BSA (mean, 40 +/- 16%; range, 17-75%) performed a graded cycle ergometry exercise to test volitional fatigue. Expired gases and minute ventilation were measured via a metabolic cart for the determination of VO2max. Each subject's VO2max was compared with sex- and age-matched normative values from population data published by the American College of Sports Medicine, the American Heart Association, and recent epidemiological data (Aspenes 2011). Subjects had a VO2max of 29.4 +/- 10.1ml O-2/kg body mass/min (median, 27.5; range, 15.9-53.3). The use of American College of Sports Medicine normative values showed that mean VO2max of the subjects was in the lower 24th percentile (median, 10th percentile). A total of 88% of the subjects had a VO2max below American Heart Association age-adjusted normative values. Similarly, 20 of the 25 subjects had a VO2max in the lower 25% percentile of recent epidemiological data. Relative to nongrafted subjects, 80 to 88% of the evaluated skin-graft subjects had a very low aerobic capacity. On the basis of these findings, adult burn survivors are disproportionally unfit relative to the general U.S. population, and this puts them at an increased risk of all-cause mortality (Blair 1995).
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| 3. |
- Ganio, Matthew S., et al.
(författare)
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Nongrafted Skin Area Best Predicts Exercise Core Temperature Responses in Burned Humans
- 2015
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Ingår i: Medicine & Science in Sports & Exercise. - 0195-9131 .- 1530-0315. ; 47:10, s. 2224-2232
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Tidskriftsartikel (refereegranskat)abstract
- Grafted skin impairs heat dissipation, but it is unknown to what extent this affects body temperature during exercise in the heat.Purpose: We examined core body temperature responses during exercise in the heat in a group of individuals with a large range of grafts covering their body surface area (BSA; 0%-75%).Methods: Forty-three individuals (19 females) were stratified into groups based on BSA grafted: control (0% grafted, n = 9), 17%-40% (n = 19), and >40% (n = 15). Subjects exercised at a fixed rate of metabolic heat production (339 +/- 70 W; 4.3 +/- 0.8 Wkg(-1)) in an environmental chamber set at 40 degrees C, 30% relative humidity for 90 min or until exhaustion (n = 8). Whole-body sweat rate and core temperatures were measured.Results: Whole-body sweat rates were similar between the groups (control: 14.7 +/- 3.4 mLmin(-1), 17%-40%: 12.6 +/- 4.0 mLmin(-1); and >40%: 11.7 +/- 4.4 mLmin(-1); P > 0.05), but the increase in core temperature at the end of exercise in the >40% BSA grafted group (1.6 degrees C +/- 0.5 degrees C) was greater than the 17%-40% (1.2 degrees C +/- 0.3 degrees C) and control (0.9 degrees C +/- 0.2 degrees C) groups (P < 0.05). Absolute BSA of nongrafted skin (expressed in square meters) was the strongest independent predictor of the core temperature increase (r(2) = 0.41). When regrouping all subjects, individuals with the lowest BSA of nongrafted skin (<1.0 m(2)) had greater increases in core temperature (1.6 degrees C +/- 0.5 degrees C) than those with more than 1.5 m(2) nongrafted skin (1.0 degrees C +/- 0.3 degrees C; P < 0.05).Conclusions: These data imply that individuals with grafted skin have greater increases in core temperature when exercising in the heat and that the magnitude of this increase is best explained by the amount of nongrafted skin available for heat dissipation.
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| 4. |
- Lucas, Rebekah A. I., et al.
(författare)
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Age-related changes to cardiac systolic and diastolic function during whole-body passive hyperthermia
- 2015
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Ingår i: Experimental Physiology. - : Wiley. - 0958-0670 .- 1469-445X. ; 100:4, s. 422-434
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Tidskriftsartikel (refereegranskat)abstract
- New Findings What is the central question of this study? The effect of ageing on hyperthermia-induced changes in cardiac function is unknown. What is the main finding and its importance? Using echocardiography, we show that during hyperthermia the systolic and diastolic function can be appropriately augmented to meet cardiac demand in healthy older adults, although overall age-related impairments remain. One exception was late diastolic ventricular filling [i.e. E/A ratio and A/(A+E) ratio], which in the older adults was not further augmented during hyperthermia, unlike their young counterparts. To meet cardiac demand, therefore, healthy older adults appear to depend on an increased left ventricular systolic strain and proportion of their cardiac reserve. The effect of ageing on hyperthermia-induced changes in cardiac function is unknown. This study tested the hypothesis that hyperthermia-induced changes in left ventricular systolic and diastolic function are attenuated in older adults when compared with young adults. Eight older (71 +/- 5years old) and eight young adults (29 +/- 5years old), matched for sex, physical activity and body mass index, underwent whole-body passive hyperthermia. Mean arterial pressure (Finometer Pro), heart rate, forearm vascular conductance (venous occlusion plethysmography) and echocardiographic indices of diastolic and systolic function were measured during a normothermic supine period and again after an increase in internal temperature of approximate to 1.0 degrees C. Hyperthermia decreased mean arterial pressure and left ventricular end-diastolic volumes and increased heart rate to a similar extent in both groups (P>0.05). Ageing did not alter the magnitude of hyperthermia-induced changes in indices of systolic (lateral mitral annular S velocity) or diastolic function (lateral mitral annular E velocity, peak early diastolic filling and isovolumic relaxation time; P>0.05). However, with hyperthermia the global longitudinal systolic strain increased in the older group, but was unchanged in the young group (P=0.03). Also, older adults were unable to augment late diastolic ventricular filling [i.e. E/A ratio and A/(A+E) ratio] during hyperthermia, unlike the young (P<0.05). These findings indicate that older adults depend on a greater systolic contribution (global longitudinal systolic strain) to meet hyperthermic demand and that the atrial contribution to diastolic filling was not further augmented in older adults when compared with young adults.
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| 5. |
- Lucas, Rebekah A. I., et al.
(författare)
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Hypercapnia-induced increases in cerebral blood flow do not improve lower body negative pressure tolerance during hyperthermia
- 2013
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Ingår i: American Journal of Physiology. Regulatory Integrative and Comparative Physiology. - : American Physiological Society. - 0363-6119 .- 1522-1490. ; 305:6, s. R604-R609
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Tidskriftsartikel (refereegranskat)abstract
- Heat-related decreases in cerebral perfusion are partly the result of ventilatory-related reductions in arterial CO2 tension. Cerebral perfusion likely contributes to an individual's tolerance to a challenge like lower body negative pressure (LBNP). Thus increasing cerebral perfusion may prolong LBNP tolerance. This study tested the hypothesis that a hypercapnia-induced increase in cerebral perfusion improves LBNP tolerance in hyperthermic individuals. Eleven individuals (31 +/- 7 yr; 75 +/- 12 kg) underwent passive heat stress (increased intestinal temperature similar to 1.3 degrees C) followed by a progressive LBNP challenge to tolerance on two separate days (randomized). From 30 mmHg LBNP, subjects inhaled either (blinded) a hypercapnic gas mixture (5% CO2, 21% oxygen, balanced nitrogen) or room air (SHAM). LBNP tolerance was quantified via the cumulative stress index (CSI). Mean middle cerebral artery blood velocity (MCAv(mean),) and end-tidal CO2 (PETCO2) were also measured. CO2 inhalation of 5% increased PETCO2 at similar to 40 mmHg LBNP (by 16 +/- 4 mmHg) and at LBNP tolerance (by 18 +/- 5 mmHg) compared with SHAM (P < 0.01). Subsequently, MCAvmean was higher in the 5% CO2 trial during similar to 40 mmHg LBNP (by 21 +/- 12 cm/s, similar to 31%) and at LBNP tolerance (by 18 +/- 10 cm/s, similar to 25%) relative to the SHAM (P < 0.01). However, hypercapnia-induced increases in MCAvmean did not alter LBNP tolerance (5% CO2 CSI: 339 +/- 155 mmHg X min; SHAM CSI: 273 +/- 158 mmHg X min; P = 0.26). These data indicate that inhaling a hypercapnic gas mixture increases cerebral perfusion during LBNP but does not improve LBNP tolerance when hyperthermic.
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| 6. |
- Schlader, Zachary J., et al.
(författare)
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Baroreceptor unloading does not limit forearm sweat rate during severe passive heat stress
- 2015
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Ingår i: Journal of applied physiology. - : American Physiological Society. - 8750-7587 .- 1522-1601. ; 118:4, s. 449-454
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Tidskriftsartikel (refereegranskat)abstract
- This study tested the hypothesis that sweat rate during passive heat stress is limited by baroreceptor unloading associated with heat stress. Two protocols were performed in which healthy subjects underwent passive heat stress that elicited an increase in intestinal temperature of similar to 1.8 degrees C. Upon attaining this level of hyperthermia, in protocol 1 (n = 10, 3 females) a bolus (19 ml/kg) of warm (similar to 38 degrees C) isotonic saline was rapidly (5-10 min) infused intravenously to elevate central venous pressure (CVP), while in protocol 2 (n = 11, 5 females) phenylephrine was infused intravenously (60-120 mu g/min) to return mean arterial pressure (MAP) to normothermic levels. In protocol 1, heat stress reduced CVP from 3.9 +/- 1.9 mmHg (normothermia) to -0.6 +/- 1.4 mmHg (P < 0.001), while saline infusion returned CVP to normothermic levels (5.1 +/- 1.7 mmHg; P > 0.999). Sweat rate was elevated by heat stress (1.21 +/- 0.44 mg.cm(-2).min(-1)) but remained unchanged during rapid saline infusion (1.26 +/- 0.47 mg.cm(-2).min(-1), P = 0.5), whereas cutaneous vascular conductance increased from 77 +/- 10 to 101 +/- 20% of local heating max (P = 0.029). In protocol 2, MAP was reduced with heat stress from 85 +/- 7 mmHg to 76 +/- 8 mmHg (P = 0.048). Although phenylephrine infusion returned MAP to normothermic levels (88 +/- 7 mmHg; P > 0.999), sweat rate remained unchanged during phenylephrine infusion (1.39 +/- 0.22 vs. 1.41 +/- 0.24 mg.cm(-2).min(-1); P > 0.999). These data indicate that both cardiopulmonary and arterial baroreceptor unloading do not limit increases in sweat rate during passive heat stress.
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| 7. |
- Schlader, Zachary J., et al.
(författare)
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Hyperthermia does not alter the increase in cerebral perfusion during cognitive activation
- 2013
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Ingår i: Experimental Physiology. - : Wiley. - 0958-0670 .- 1469-445X. ; 98:11, s. 1597-1607
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Tidskriftsartikel (refereegranskat)abstract
- This study tested the hypothesis that hyperthermia attenuates the increase in cerebral perfusion during cognitive activation. Mean middle cerebral artery blood velocity (MCAV(mean)) served as an index of cerebral perfusion, while the nBack test (a test of working memory) was the cognitive task. Hyperthermia was characterized by elevations (P < 0.001) in skin (by 5.0 +/- 0.8 degrees C) and intestinal temperatures (by 1.3 +/- 0.1 degrees C) and reductions (P < 0.020) in mean arterial pressure (by 11 +/- 10 mmHg), end-tidal CO2 tension (by 3 +/- 6 mmHg) and MCAVmean (by 10 +/- 9 cm s(-1)). Hyperthermia had no influence on nBack test performance (mean difference from normothermia to hyperthermia, -1 +/- 11%; P = 0.276) or, counter to the hypothesis, the increase in MCAV(mean) during nBack testing (mean difference from normothermia to hyperthermia: 0 +/- 16 cm s(-1); P = 0.608). These findings indicate that the capacity to increase cerebral perfusion during cognitive activation is unaffected by hyperthermia.
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