Hypothesis-Driven Research (20+ years of burn-related research) Craig Crandall PhD Thermal and Vascular Physiology Laboratory Institute for Exercise and Environmental Medicine; University of Texas Southwestern Medical Center Dallas
Brown Recluse
11/28/95
12/6/95
12/11/95
Epidermis HEALTHY SKIN Dermis Subcutaneous Tissue Muscle THIRD DEGREE BURN SPLIT-THICKNESS SKIN GRAFT
Curiosity How do humans “thermoregulate”?
Question: What are the implications of such an injury and subsequent grafting on skin blood flow and sweating? Identify a hypothesis and design an experiment to test that hypothesis.
ECG 30 Graft Skin Blood Flow (au) 28 26 24 22 20 18 16 14 Control Skin Blood Flow (au) 16 15 14 13 12 11 10 9 8 15 seconds
Laser doppler scanner-grafted skin 1.75 P < 0.05 Graft Photo Image Graft 1.50 ∆ CVC (au/mm Hg) 1.25 HEAT STRESS 1.00 NORMOTHERMIA 0.75 0.50 0.25 Flux Image 0.00 Control Graft 0 500 1000
Increases in cutaneous vascular conductance during whole-body heating at control and grafted sites across differing durations post- graft surgery. 1.50 Control P<0.01 Graft 1.25 ∆ CVC (au/mm Hg) 1.00 0.75 0.50 0.25 0.00 5-9 Months 26-38 Months 50-86 Months
2.0 ∆ SR from Baseline (mg/cm 2 /min) 1.8 P < 0.05 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 Control Graft
Increase in sweat rate (SR) to whole-body heating 2.5 Control P<0.01 Graft 2.0 ∆ SR (mg/cm 2 /min) 1.5 1.0 0.5 0.0 2-3 Years 4-8 Years 5-9 Months 26-38 Months 50-86 Months J Burn Care Res 2009
Question: Where are the deficits resulting in impaired increases in skin blood flow and sweating in grafted skin? Identify a hypothesis and design an experiment to test that hypothesis.
Dose response curves to exogenous acetylcholine (ACh) in normal and grafted skin 1.8 ∆ CVC from Baseline (au/mmHg) Control 1.6 Graft 1.4 1.2 1.0 0.8 0.6 0.4 0.2 EC 50 :P=0.003 0.0 1x10 -7 1x10 -6 1x10 -5 1x10 -4 1x10 -3 1x10 -2 1x10 -1 [ACh] J Burn Care Res 2007
Dose response curves to exogenous sodium nitroprusside (SNP) in normal and grafted skin 1.8 ∆ CVC from Baseline (au/mmHg) Control 1.6 Graft 1.4 1.2 1.0 0.8 0.6 0.4 0.2 EC 50 :P=0.33 0.0 5x10 -8 5x10 -7 5x10 -6 5x10 -5 5x10 -4 5x10 -3 5x10 -2 [SNP] J Burn Care Res 2007
Increases in sweat rate (SR) to exogenous acetylecholine (ACh) from normal and grafted skin 1.4 ∆ SR from Baseline (mg/cm 2 /min) Control 1.2 Graft 1.0 0.8 0.6 0.4 0.2 0.0 -0.2 1x10 -7 1x10 -6 1x10 -5 1x10 -4 1x10 -3 1x10 -2 1x10 -1 [ACh] J Burn Care Res 2007
“We had a new recruit die here last week due to a heat- induced arrhythmia. His core temp was 106 ° F (~41 ° C). He died standing in the chow line- and had done very minimal exertion that day (2 mi walk several hours earlier). The guy had burn injuries at age 11- he had skin grafts covering 30% of his trunk- to include one axilla. Our Army medical fitness regulations make no mention of skin grafting/burns as a disqualifier and we are seeking additional knowledge to see if we need to change the regulation. Since so many of our soldiers have recently acquired burn injuries and are subjected to tremendous thermal stress we think that this is a very important question.”
So what’s next? Identify a hypothesis and design an experiment to test that hypothesis.
Groups • 17-40% BSA grafted; BSA grafted: 30±7%. 40±13 years. • >40% BSA grafted; BSA grafted: 54±11%. 34±11 years • Non-grafted controls. 32±10 years
Skin grafts impair temperature regulation. (40 °C and 30% RH) Ganio, Schlader, Pearson, Lucas, Gagnon, Rivas, Kowalske, Crandall, 2015
Question: Can impaired thermoregulatory responses be modified? Identify a hypothesis and design an experiment to test that hypothesis.
Pre-heat Heat acclimation: 90 min of exercise (@ Post-heat acclimation 45% VO 2 max) in 40°C, 30% RH for 7 acclimation evaluation consecutive days evaluation Day 1 Day 2 Day 3 Day 4 Day 5 Day 6 Day 7
2 way ANOVA Group: P<0.001 Acclimation: P<0.001 Interaction: P=0.073 2.5 Pre-Acclimation Post-Acclimation Temperature (Deg C) 2.0 Increase in Internal 1.5 1.0 0.5 0.0 Control 17-40% >40% Subject Groups
Pre-Heat Acclimation Post-Heat Acclimation
Schlader et al. J Appl Phyisol 2015
Donor Sites Question: What questions come to mind regarding donor sites? Identify a hypothesis and design an experiment to test that hypothesis.
Donor Sites 400 Uninjured 1.5 Donor Cutaneous Blood Flow (PU) 300 P=0.26 Local Sweat Rate (mg/cm^2/min) 1.0 200 P=0.78 0.5 100 0 0.0 Pre-Exercise Post-Exercise Uninjured Donor
Serendipitous Findings Maximal Aerobic Capacity
J Burn Care Res 2015 ACSM age and sex normative scale: ~75% of burn survivors had a VO 2max in the lowest 20 th percentile. American Heart Association Normative Scale: 88% of burn survivors had a VO 2max below the age-adjusted normative values 80% of burn survivors had a VO 2max in the lowest quartile of the Aspenes database (4631 subjects)
Question: Why are burned individuals generally unfit (consider the variables that influence aerobic capacity)? Identify a hypothesis and design an experiment to test that hypothesis.
Cardiovascular Deconditioning 4000 Actual age-related decrease in VO 2max in uninjured individuals 3000 VO 2max (ml/min) 2000 1000 20 30 40 50 60 70 Age (years)
1 day hospitalization per 1% BSA burned
Cardiovascular Deconditioning 4000 Actual age-related decrease in VO 2max in uninjured individuals 3000 VO 2max (ml/min) 2000 1000 20 30 40 50 60 70 Age (years)
Cardiovascular Deconditioning 4000 Actual age-related decrease in VO 2max in uninjured individuals 3000 VO 2max (ml/min) 2000 1000 20 30 40 50 60 70 Age (years)
10+ years post-injury
Question: Are these “adverse” responses modifiable? Identify a hypothesis and design an experiment to test that hypothesis.
Pre- and post-6 months exercise training Assessments Steady state followed by maximal oxygen uptake evaluation (X 2) Assessments of vascular function (FMD, nitro, PWV) Quality of life surveys Functional capacity assessments Cardiac structure/function (MRI and/or echo) Body composition (DEXA) Muscle biopsy (citrate synthase & cytochrome C oxidase activity) Blood volume assessment Pulmonary function testing
6 month Endurance Exercise Training Pre-exercise training Group: P= 0.008 Post-exercise training Pre/Post: P<0.001 Group x Pre/Post: 0.51
GM068865-12; ~$3.5 million W81XWH-15-1-0647; ~$2.0 million
US Army Standards of Medical Fitness, AR 40-501 2-28-(1) Prior burn injury (to include donor sites) involving a total body surface area of 2-28-(2) Prior burn injury involving less than 40 percent total body surface area, which results in a loss or degradation of thermoregulatory function does not meet the standard Where’s the data to support these guidelines?
Psycho-social
2.0 R=0.59; P<0.01 70 kg; 175 cm; 1.8 m 2 ; 33% graft = 1.2 m 2 for heat dissipation. 1.6 Delta Tcore (°C) 1.2 0.8 0.4 108 kg; 195 cm; 2.4 m 2 BSA … so he has ~1.6 m 2 BSA ungrafted skin available to dissipate heat 0.0 10 20 30 40 50 60 70 80 Body Surface Area Grafted (%)
2.0 R=0.71; P<0.01 1.6 Delta Tcore (°C) 1.2 0.8 0.4 0.0 0.4 0.8 1.2 1.6 2.0 Body Surface Area Available for Heat Dissipation (m 2 )
2.0 Control subjects 1.6 Delta Tcore (°C) 1.2 0.8 0.4 0.0 0.4 0.8 1.2 1.6 2.0 Body Surface Area Available for Heat Dissipation (m 2 )
‡ different from pre-HA (main effect; P=0.05)
* * *
24 °C (75 °F), 20% humidity 39 °C (102 °F), 20% humidity 2.5 2.5 Elevation in Core Temperature (°C) Elevation in Core Temperature (°C) 2.0 0% burn injury 2.0 0% burn injury 20% burn injury 20% burn injury * 40% burn injury 40% burn injury 60% burn injury 60% burn injury * 1.5 1.5 * * 1.0 1.0 0.5 0.5 * P<0.01 from 0% burn 0.0 0.0 0 10 20 30 40 50 60 0 10 20 30 40 50 60 Time of Exercise (min) Time of Exercise (min)
Individuals with significant skin grafts are generally more sedentary. Distribution of maximal oxygen uptake in 34 skin graft patients 20 76% in the lowest Number of Subjects in Each Category two categories 15 10 5 0 10 20 30 40 50 60 70 80 90 Percentile Ranking for Maximal Oxygen Uptake Percentile rankings for age and sex adjusted maximum oxygen uptake Ganio, Pearson, Schlader, Brothers, Lucas, Rivas, Kowalske, Crandall, 2014
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