Separating permeability and haemodynamic components of microvascular transport
1
Track 19. Biotransport 7004 Tu, 14:30-14:45 (P23) HANS Head and Neck Support for racing - performance update R. Hubbard 1, H. Gramling 2. 1Michigan State University, East Lansing, Michigan, USA, 2FIA Institute, Stuttgart, Germany Introduction: HANS ® head and neck support for racing is a yoke and collar structure and is held to the upper chest by double shoulder belts. In a crash, tethers from collar to helmet straighten as shoulder belts are loaded to restrain the head with the torso. Crash sled testing by Mercedes Benz (MB) [1] shows HANS substantially reduces head motions and neck loads. Recently, SFI Foundation initiated certification for head and neck restraints [2] that requires more severe crash sled testing. Here, results from these more severe tests are compared to previous results. Methods: SFI crash sled testing is described in their specification [2] with 70 G peak sled acceleration and 70 kph velocity change. MB tests [1] were run at 37 G and 55 kph. Neck loads are most significant for racing injury with an injury threshold of 4000 N. Results and Discussion: In SFI tests with sled acceleration of 70 G, peak chest accelerations and neck tensions were respectively 91 G and 5122N without HANS, and 82G and 1410N with HANS. At MB with 37G sled acceleration, chest accelerations and neck tensions were respectively 63G and 4730N without HANS, and 59G and 1120N with HANS. In both SFI and MB testing, HANS substantially reduced neck loads and the risk of injury. The differences in dummy chest accelerations and neck tensions were not proportional the sled acceleration. This is probably due to seat back angle, which in SFI testing was 20 degrees (like NASCAR and DTM) and 45 degrees at MB (like FIA F1). With more reclined seats, the upper torso moves farther forward before restraint by shoulder belts leading to greater dynamic overshoot as found by Melvin [3]. References [1] Gramling H., Hubbard R. Sensitivity analysis of the HANS head and neck support. 2000; SAE paper 2000-01-3541. [2] SFI Foundation Specification 38.1. 2004. [3] Melvin J., et al. Race car restraint system frontal crash performance testing. 1994; SAE paper 942482. 7627 Tu, 14:45-15:00 (P23) Heat stress in motorsports racing C. Meistelman 1, G. Savourey 2, Y. Besnard 2. 1Dept of Anaesthesia, H6pital de Brabois, La Tronche, France, 2Centre de recherche du service de sant6 des arm6es, La Tronche, France The need to wear fire resistant clothing in conjunction with the high temper- atures found in closed cars during racing (60°C.) have led to the question of human tolerance. Methods: First we used PREDICTOL, a PC program, to determine the thermo- physiological duration limited exposures (DLE) in predetermined environments, taking into account the water vapour permeability index (im) and the thermal resistance (Rct) of various protective garments. In the second part of the study five trained male volunteers, wearing four different racing suits, performed a physical. The temperature of the hot climatic chamber was 60°C. and the relative humidity (RH) was set to 60%. Results: The results of the simulations in hot environment (40°C.; RH: 60%) demonstrate that when using conventional racing suits the DLE to reach a cen- tral body temperature of 38°C. (ISO 7933) was 46 min. It decreased to 21 min when the ambient temperature was set to 45°C. When wearing conventional racing suits central core temperature reached 38°C in approximately 15 to 20 min. When using a new generation racing suit (permeability index increased by 24%), tolerance to physical exercise was improved and the increase in central core temperature was delayed. The use of an air force full face helmet, rather than a conventional helmet, improved the tolerance and slowed down the increase in body temperature. Water vapour pressure, measured on the skin, reached a plateau of approximately 8 kPa with a conventional garment whereas it ranged from 6.5 to 7 kPa with the new generation. In conclusion, the risk of heat stress in motor sports highlights the need for new protective racing suits. It is obvious that the control of micro-environment can be efficient in the future. 19.1. Microvascular Transport $373 Track 19 Biotransport 19.1. Microvascular Transport 4443 Tu, 11:00-11:30 (P20) Separating permeability and haemodynamic components of microvascular transport C.C. Michel. Biomedical Sciences, Imperial College, London, UK Although it has been known for half a century that solute transport between the blood and the tissues is influenced by changes in vascular perfusion as well as changes in permeability, increased vascular permeability is most frequently as- sessed from estimates of the net flux or clearance of labelled macromolecules from plasma to tissues. In addition to being dependent on the permeability coefficients, which are related to the structure of the endothelial barrier, blood-tissue transport of macromolecules (vascular leakage) is influenced by the distribution of microvascular perfusion, which determines the exchange area of endothelium and the magnitude of flow, which influences the mean pressure within the exchange vessels. In the first part of this lecture, I shall analyse blood tissue clearance of macromolecules in situations where both permeability and haemodynamic conditions change using data from studies in single microvessels where changes in permeability coefficients have been measured and data from studies where microvascular blood flow and vascular leakage have been estimated in same the preparation. In this analysis, it is assumed that the haemodynamic and permeability factors are independent. In the second part, I will review evidence that permeability to small hydrophilic solutes itself may be influenced by microvascular flow and consider whether such an effect of flow on permeability might influence vascular leakage of macromolecules. 4123 Tu, 11:30-11:45 (P20) Integration of microvascular transport within a network: Considerations of vessel architecture, sex, and conditioning V.H. Huxley. Dept. Medical Pharmacology & Physiology and National Center for Gender Physiology, University of Missouri School of Medicine, Columbia, MO, USA As techniques have been developed to make quantitative measures of solute and volume flux to assess exchange in vessels of known anatomical location within microvascular networks it has become accepted that basal transport coefficients may vary with tissue function and thus by organ. What is less well deliberated, and the subject of this presentation, are the influences of vessel types (e.g. arterioles, capillaries, and venules), sex, age, and the physical condition (e.g. exercise trained EX vs. sedentary SED) on basal transport parameters and, of immediate impact on the understanding of the dynamic regulation of exchange at the organ level, the responses of these parameters to vasoactive compounds. The outcome of considering the "variables" is the discerning that volume and solute homeostasis can be achieved by multiple routes. A further consequence is that representation of transport parameters as single values masks the contributions of components central to the ability to design replacement organs or treat diseases resulting from failure to match substrate and fluid delivery with demand. Supported by NIH HL078816 & HL075186, NASA-MU partnership for Under- standing Sex differences in Physiology 5241 Tu, 11:45-12:00 (P20) The revised Starling Principle and steady state reabsorption from interstitium to blood F.E. Curry 1, R.H. Adamson 1, J. Ly 1, X. Zhang 2, S. Weinbaum 2. 1Department of Physiology and Membrane Biology, University of California at Davis, CA, USA, 2Departments of Biomedical and Mechanical Engineering, City College, CUNY, NY, USA The revised Starling Principle for fluid exchange states that the effective osmotic pressure difference across the walls of microvessels is across the endothelial glycocalyx (~p-~g), rather than between plasma and tissue (in- terstitium) (~p-~t). ~g is determined by fluxes of water and solute across the glycocalyx and other endothelial pathways, and by gradients of protein concentration in the inter-endothelial cleft and interstitium. During filtration, ~g is lower than ~t because diffusion of protein from the interstitium into the space beneath the glycocalyx is reduced by the convective flow of the low protein ultrafiltrate channeled through infrequent breaks in the junction strand (J Physiol 557: 889, 2004). During reabsorption, this convective flow is reversed, and interstitial protein is expected to accumulate beneath the
Transcript of Separating permeability and haemodynamic components of microvascular transport
Track 19. B io t ranspor t
7004 Tu, 14:30-14:45 (P23) HANS Head and Neck Suppor t for racing - per formance update
R. Hubbard 1 , H. Gramling 2. 1Michigan State University, East Lansing, Michigan, USA, 2 FIA Institute, Stuttgart, Germany
Introduct ion: HANS ® head and neck support for racing is a yoke and collar structure and is held to the upper chest by double shoulder belts. In a crash, tethers from collar to helmet straighten as shoulder belts are loaded to restrain the head with the torso. Crash sled testing by Mercedes Benz (MB) [1] shows HANS substantially reduces head motions and neck loads. Recently, SFI Foundation initiated certification for head and neck restraints [2] that requires more severe crash sled testing. Here, results from these more severe tests are compared to previous results. Methods: SFI crash sled testing is described in their specification [2] with 70 G peak sled acceleration and 70 kph velocity change. MB tests [1] were run at 37 G and 55 kph. Neck loads are most significant for racing injury with an injury threshold of 4000 N. Results and Discussion: In SFI tests with sled acceleration of 70 G, peak chest accelerations and neck tensions were respectively 91 G and 5122N without HANS, and 82G and 1410N with HANS. At MB with 37G sled acceleration, chest accelerations and neck tensions were respectively 63G and 4730N without HANS, and 59G and 1120N with HANS. In both SFI and MB testing, HANS substantially reduced neck loads and the risk of injury. The differences in dummy chest accelerations and neck tensions were not proportional the sled acceleration. This is probably due to seat back angle, which in SFI testing was 20 degrees (like NASCAR and DTM) and 45 degrees at MB (like FIA F1). With more reclined seats, the upper torso moves farther forward before restraint by shoulder belts leading to greater dynamic overshoot as found by Melvin [3].
References [1] Gramling H., Hubbard R. Sensitivity analysis of the HANS head and neck
support. 2000; SAE paper 2000-01-3541. [2] SFI Foundation Specification 38.1. 2004. [3] Melvin J., et al. Race car restraint system frontal crash performance testing.
1994; SAE paper 942482.
7627 Tu, 14:45-15:00 (P23) Heat stress in motorsports racing
C. Meistelman 1 , G. Savourey 2, Y. Besnard 2. 1Dept of Anaesthesia, H6pital de Brabois, La Tronche, France, 2Centre de recherche du service de sant6 des arm6es, La Tronche, France
The need to wear fire resistant clothing in conjunction with the high temper- atures found in closed cars during racing (60°C.) have led to the question of human tolerance. Methods: First we used PREDICTOL, a PC program, to determine the thermo- physiological duration limited exposures (DLE) in predetermined environments, taking into account the water vapour permeability index (im) and the thermal resistance (Rct) of various protective garments. In the second part of the study five trained male volunteers, wearing four different racing suits, performed a physical. The temperature of the hot climatic chamber was 60°C. and the relative humidity (RH) was set to 60%. Results: The results of the simulations in hot environment (40°C.; RH: 60%) demonstrate that when using conventional racing suits the DLE to reach a cen- tral body temperature of 38°C. (ISO 7933) was 46 min. It decreased to 21 min when the ambient temperature was set to 45°C. When wearing conventional racing suits central core temperature reached 38°C in approximately 15 to 20 min. When using a new generation racing suit (permeability index increased by 24%), tolerance to physical exercise was improved and the increase in central core temperature was delayed. The use of an air force full face helmet, rather than a conventional helmet, improved the tolerance and slowed down the increase in body temperature. Water vapour pressure, measured on the skin, reached a plateau of approximately 8 kPa with a conventional garment whereas it ranged from 6.5 to 7 kPa with the new generation. In conclusion, the risk of heat stress in motor sports highlights the need for new protective racing suits. It is obvious that the control of micro-environment can be efficient in the future.
19.1. Microvascular Transport $373
Track 19
Biotransport
19.1. Microvascular Transport 4443 Tu, 11:00-11:30 (P20) Separat ing permeabi l i ty and haemodynamic components o f microvascular transport C.C. Michel. Biomedical Sciences, Imperial College, London, UK
Although it has been known for half a century that solute transport between the blood and the tissues is influenced by changes in vascular perfusion as well as changes in permeability, increased vascular permeability is most frequently as- sessed from estimates of the net flux or clearance of labelled macromolecules from plasma to tissues. In addition to being dependent on the permeability coefficients, which are related to the structure of the endothelial barrier, blood-tissue transport of macromolecules (vascular leakage) is influenced by the distribution of microvascular perfusion, which determines the exchange area of endothelium and the magnitude of flow, which influences the mean pressure within the exchange vessels. In the first part of this lecture, I shall analyse blood tissue clearance of macromolecules in situations where both permeability and haemodynamic conditions change using data from studies in single microvessels where changes in permeability coefficients have been measured and data from studies where microvascular blood flow and vascular leakage have been estimated in same the preparation. In this analysis, it is assumed that the haemodynamic and permeability factors are independent. In the second part, I will review evidence that permeability to small hydrophilic solutes itself may be influenced by microvascular flow and consider whether such an effect of flow on permeability might influence vascular leakage of macromolecules.
4123 Tu, 11:30-11:45 (P20) Integrat ion o f microvascular transport within a network: Considerat ions o f vessel architecture, sex, and condi t ioning V.H. Huxley. Dept. Medical Pharmacology & Physiology and National Center for Gender Physiology, University of Missouri School of Medicine, Columbia, MO, USA
As techniques have been developed to make quantitative measures of solute and volume flux to assess exchange in vessels of known anatomical location within microvascular networks it has become accepted that basal transport coefficients may vary with tissue function and thus by organ. What is less well deliberated, and the subject of this presentation, are the influences of vessel types (e.g. arterioles, capillaries, and venules), sex, age, and the physical condition (e.g. exercise trained EX vs. sedentary SED) on basal transport parameters and, of immediate impact on the understanding of the dynamic regulation of exchange at the organ level, the responses of these parameters to vasoactive compounds. The outcome of considering the "variables" is the discerning that volume and solute homeostasis can be achieved by multiple routes. A further consequence is that representation of transport parameters as single values masks the contributions of components central to the ability to design replacement organs or treat diseases resulting from failure to match substrate and fluid delivery with demand. Supported by NIH HL078816 & HL075186, NASA-MU partnership for Under- standing Sex differences in Physiology
5241 Tu, 11:45-12:00 (P20) The revised Starl ing Principle and steady state reabsorpt ion f rom interst i t ium to b lood F.E. Curry 1 , R.H. Adamson 1 , J. Ly 1 , X. Zhang 2, S. Weinbaum 2. 1Department of Physiology and Membrane Biology, University of California at Davis, CA, USA, 2Departments of Biomedical and Mechanical Engineering, City College, CUNY, NY, USA
The revised Starling Principle for fluid exchange states that the effective osmotic pressure difference across the walls of microvessels is across the endothelial glycocalyx (~p-~g), rather than between plasma and tissue (in- terstitium) (~p-~t). ~g is determined by fluxes of water and solute across the glycocalyx and other endothelial pathways, and by gradients of protein concentration in the inter-endothelial cleft and interstitium. During filtration, ~g is lower than ~ t because diffusion of protein from the interstitium into the space beneath the glycocalyx is reduced by the convective flow of the low protein ultrafiltrate channeled through infrequent breaks in the junction strand (J Physiol 557: 889, 2004). During reabsorption, this convective flow is reversed, and interstitial protein is expected to accumulate beneath the
