Thermal Diffusion Probe Research Articles

Variation in canopy conductance of Cunninghamia lanceolata forest and its response to environmental factors after an extreme rainfall event

AbstractCanopy conductance (gc) is a crucial parameter in simulating evapotranspiration and modulating water exchange, but its variation mechanism has regional uncertainties and complex environmental co‐controls. In addition, the effect of extreme rainfall on gc cannot be ignored under the changing climate. Here, we investigated the variation and environmental controls on gc and the effect of extreme rainfall events in a Cunninghamia lanceolata forest across the subtropical area of Southern China. In July 2020, an extreme rainstorm hit the source area of the Xin'an River, with the cumulative rainfall on July 7 and 8 reaching 216.6 mm. The thermal diffusion probe method was used to measure the density of sap flow, and the environmental factors such as air temperature (Ta), net solar radiation (Rn) and soil water content (SWC) were monitored during the growing seasons of 2020 and 2021. Ultimately, gc obtained by the Penman‐Monteith equation was adopted since the result from the Köstner equation was overestimated. gc showed a unimodal curve on the diurnal scale, and this characteristic was more obvious after the extreme rainfall. Daily gc appeared a fluctuating pattern with a maximum in summer. gc was simultaneously affected by Ta, Rn, water vapour pressure difference (VPD), SWC, among which Ta was the most significant driving factor at both the diurnal and daily timescales. The regulation of Ta, VPD and SWC on gc had obvious thresholds, and the most definite response mode was VPD (2020: 1.25 kPa; 2021: 0.95 kPa). SWC and Ta were the dominant factors after the rainfall period, and the promotion effect of VPD on post‐rainy days turned to inhibition effect on typical sunny days. These findings will further reveal the water exchange mechanism between atmosphere and vegetation and impacts of environmental factors in subtropical coniferous forests, especially after the extreme rainfall events.

Characteristics of Changes in Sap Flow-Based Transpiration of Poplars, Locust Trees, and Willows and Their Response to Environmental Impact Factors

The sap flow and transpiration of three typical tree species (poplar, locust tree, and willow) in Ningxia are crucial for sustaining the ecosystem in the Ningxia Yellow River Irrigation area. However, there is a lack of clarity regarding the variations in sap flow and transpiration of these trees and their corresponding responses to environmental factors. From February to December 2021, this study selected 30 samples representing the three typical trees in the irrigation area and monitored their tree sapwood sap flow continuously and dynamically using the Thermal Diffusion Probe method. This study yielded several key findings: (1) Variations exist in sap flow density and transpiration among the three typical trees, with willows exhibiting higher sap flow density and transpiration than poplars and locust trees. (2) Tree transpiration showed a highly significant positive correlation with net radiation, temperature, and vapor pressure deficit, along with a highly significant negative correlation with relative humidity. (3) Soil moisture content undergoes changes under precipitation and artificial drip irrigation, but its correlation with tree transpiration is limited. (4) The primary environmental factors influencing poplars, locust trees, and willows are temperature, soil moisture content at a depth of 30 cm, and soil moisture content at a depth of 60 cm.

Sap Flow Velocity in Fraxinus pennsylvanica in Response to Water Stress and Microclimatic Variables.

In arid and semiarid regions with water shortage, forestry development is limited by water availability. Understanding how tree sap flow responds to water stress and microclimatic variables is essential for the management of trees and the understanding of the eco-physiological properties of trees in arid areas. In the city of Tianjin in northern China, we measured the sap flow of Fraxinus pennsylvanica, a widely distributed urban greening tree species in semiarid regions of China. We measured the sap flow in four F. pennsylvanica trees over 6 months (April–September 2021), using a thermal diffusion probe method, and simultaneously monitored microclimatic variables and soil moisture. Results indicated that high nighttime sap flow velocity might be produced under the water stress condition. In addition, the nighttime sap flow velocity under the water stress condition was more susceptible to the combined effects of meteorological factors at night. The daytime sap flow velocity exerted a highly significant positive effect on the nighttime sap flow velocity during the whole research period, and the model fit was higher in the early growing season than that in the late growing season (early growing season: R2 = 0.51, P < 0.01; late growing season: R2 = 0.36, P < 0.01). Vapor pressure deficit had a positive effect on daytime sap flow. However, net vapor pressure deficit restrained daytime sap flow velocity when the intercorrelation between the microclimatic variables was removed. Our study highlights that drought areas perhaps have higher nighttime sap flow and that more emphasis should be placed on nighttime sap flow and the response of nighttime sap flow to microclimatic variables. In addition, the influence of other microclimatic variables on vapor pressure deficit needs to be considered when analyzing the relationship between daytime sap flow and vapor pressure deficit. An increase in net VPD can suppress the daytime sap flow.

Low sap flow of Picea crassifolia and its influencing factors in Qilian Mountains, China

As an important part of ecological hydrology, transpiration is the basis for analyzing forest water cycle and healthy growth, and important for forest protection and scientific management. We used thermal diffusion probes (TDP) to continuously monitor sap flow of Picea crassifolia in the Qilian Mountains from 2017 to 2018 to explore water consumption of P. crassifolia, and analyze the main controlling factors for the growth and transpiration of spruce. The results showed that the instantaneous change of P. crassifolia sap flow showed a single-peak curve in sunny days, a multi-peak or double-peak curve in cloudy days, and basically no obvious regularity in rainy days. The sap flow density of Qinghai spruce was consistent with the dynamics of solar radiation. The sap flow started earlier and ended later on sunny days, and lasted for 12 to 14 hours. Due to the high altitude (2700 m), low air temperature, and low vapor pressure difference (VPD) in this area, the overall sap flow density was low, with an average of (0.86±0.49) kg·d-1. On the hourly scale, the instantaneous rate of sap flow was significantly affected by solar radiation and VPD. On the daily scale, soil temperature and soil moisture content of the 0-40 cm layer were significantly related to sap flow density. The spruce sap flow density decreased with the decreases of solar radiation, air temperature, and VPD. In the high-altitude forest area of Qilian Mountains, lower soil and air temperature as well as lower VPD and solar radiation were the causes of low sap flow in Picea crassifolia in this area.

Effects of environment and canopy structure on stem sap flow in a Larix principis-rupprechtii plantation.

Accurately quantifying the impacts of environmental factors and canopy structure on stem sap flow is of great significance for deeply understanding water use strategies of trees in changing environment. The stem sap flow of Larix principis-rupprechtii plantation was observed using thermal diffusion probes from June to September of 2019 in the Xiangshuihe small watershed of Liupan Mountains, with the meteorological conditions, root-zone soil water content and canopy structure being simultaneously recorded. We first analyzed the relationships of sap flow rate (Jc) to potential evapotranspiration (PET), relative extract water (REW) and canopy leaf area index (LAI), and then quantified their relative contribution to Jc. The results showed that the response of Jc to PET, LAI, and REW conformed to binomial, linearly increase and saturated exponential function, respectively. The Jc model coupling multiple factors was established as a continuous multiplication of the response functions of Jc to PET, REW and LAI, which had good simulation precision. PET was the main factor leading to the difference of Jc in different weather conditions. The average contribution rate of PET had obvious difference in sunny (with a contribution rate of 40.3%), cloudy (4.3%), and rainy days (-26.3%). PET and LAI were the leading factors affecting the Jc variation among months. The ranges of the contribution rates of PET and LAI were from -23.1% to 16.8% and from -12.3% to 11.0%, respectively. The Jc model coupling the multi-factor effect developed in this study could be used to predict Jc, and quantify the impacts of each leading factor, which had the potential to be an effective tool to analyze the water use of trees in the changing environment.

Responses of transpiration to variation in evaporative demands and soil water in a larch plantation at the south side of Liupan Mountains, China

Quantifying the response of tree transpiration (T) to the variation of soil water supply capability and atmospheric evaporative demand is beneficial for a better prediction of water use and hydrological cycles in forests and deepen the understanding of the relationship between forest and water. Larix principis-rupprechtii in the Xiangshuihe watershed at the south side of Liupan Mountains was used as the research object. We simultaneously monitored sap flow density by thermal diffusion probe and the environmental factors. The response of the T to the soil volumetric water content (VWC) and potential evapotranspiration (PET) was analyzed. The results showed the response curve of T to VWC was quite similar under any different PET levels. With increasing VWC, T increased rapidly and then slowly, and began to be stable when VWC reached a threshold. This process could be well fitted by the saturated exponential function. However, the VWC threshold was different, and its value increased with rising PET. The relationship of daily T to PET was a quadra-tic equation, and PET also had a threshold effect. A stand transpiration model considering the effect of soil water supply capacity and atmospheric evaporative potential was founded which coupled the response relationship of T to PET and VWC in the rapid growth season. This model could well estimate the diurnal variation of transpiration, and provide guidance for the management of plantation water control.

Applicability of thermal dissipation probe in the determination of trunk flow of Platycladus orientalis under cyclic heating mode

To evaluate the adaptability of the cyclic heating mode in the thermal diffusion probe method (TDP) in the measurement of trunk sap flow and the accuracy of the measurement of tree transpiration water consumption, we selected Platycladus orientalis as the research object and set three different heating modes: 60 min/0 min (continuous heating mode), 30 min/30 min (cyclic heating mode with 30 min heating and 30 min cooling), 10 min/50 min (cyclic heating mode with 10 min heating and 50 min cooling). Based on the measured value of the whole tree container wei-ghing method, the temperature gradient characteristics of different heating modes were analyzed using the measurement technology of thermal diffusive trunk sap flow. The Granier's corrected formulas of cyclic heating modes were constructed, with its error being analyzed by validity verification. The results showed that sap flow rate calculated by the cyclic heating mode was consistent with the diurnal variation of the transpiration rate measured by the whole tree weighing method. The temperature of cyclic heating mode could quickly rise, fall and performed stably. The sap flow calculated by Granier's original formula was 61.3% lower than that by weighing method. The corrected Granier formula in the mode of 10 min/50 min and 30 min/30 min were Fd=0.0177K0.9457 (R2=0.88) and Fd=0.0378K1.3146(R2=0.85), respectively. The difference of sap flow rate in P. orientalis by the new formula was smaller than that measured by the whole tree weighing method, and the error of transpiration rate calculated by the 10 min/50 min correction formula was the smallest, 5.9% lower than that calculated by the weighing method, and thus could express the real flow rate. The 10 min/50 min cyclic heating mode could be used to reduce the effect of natural temperature difference, cut down power consumption, and accurately reflect the actual sap flow rate of P. orientalis.

Adaptability of Granier empirical formula in sap flow measurement of Populus tomentosa based on whole tree weighing method

We evaluated the adaptability of Granier's empirical formula in the measurement of trunk sap flow in Populus tomentosa. The thermal diffusion probe method (TDP) was used to mea-sure sap flow rate, and the whole tree weighing was simultaneously measured for each tree. We compared results from the Granier empirical formula with that from the whole tree weighing to find out whether Granier formula had any error in measuring the trunk sap flow of P. tomentosa. The transpiration rate by the whole tree weighing method and the temperature difference coefficient K by the thermal diffusion method were fitted with power exponential regression to establish a corrected Granier formula. Compared with the transpiration rate measured by the whole tree weighing method, sap flow rate calculated by the Granier empirical formula was underestimated by 67.7%. Therefore, a calibrated Granier correction formula of P. tomentosa was established: Fd=0.0135K0.6952(R2=0.77). The calculated result from this calibrated formula was only 3.4% lower than the transpiration rate estimated with the whole tree weighing method, which showed good consistency. Thus, the calculation of the P. tomentosa sap flow rate should be corrected when using the Granier empirical formula.

模拟穿透雨减少对锐齿栎(Quercus aliena var. acuteserrata)树干液流密度的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 模拟穿透雨减少对锐齿栎(Quercus aliena var. acuteserrata)树干液流密度的影响 DOI: 10.5846/stxb201903060423 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国际竹藤中心基本科研业务费专项基金项目（1632018002，1632018004，1632017016）；国家重点研发计划（2018YFC0507301） Effects of manipulated throughfall reduction on sap flux density of Quercus aliena var. acuteserrata Author: Affiliation: Fund Project: International Bamboo and Rattan Center"s special funds for basic research and operation fees;National Key R&D Program 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:降水格局变化是全球气候变化的重要特征之一，未来气候变化下，较为频繁和严峻的干旱将威胁地球中纬度部分地区的森林，但森林植被如何响应季节性干旱胁迫及其机制尚不清楚。北亚热带-暖温带过渡区分布着以锐齿栎（Quercus aliena var. acuteserrata）为优势树种的落叶阔叶林，研究其水分蒸腾代谢过程对干旱的响应是评估气候变化对过渡区天然落叶阔叶林生态系统水碳影响的关键科学问题。在典型的锐齿栎天然林中通过开展模拟穿透雨减少大型野外实验，采用Granier热扩散式探针技术监测锐齿栎树干液流密度的动态变化，研究了不同径级锐齿栎树干液流密度对模拟干旱的响应规律。结果表明：（1）穿透雨减少对树干液流密度的影响呈现季节变异。在7月份，林内穿透雨减少显著降低了锐齿栎的树干液流密度，但生长季后期的10月份林内穿透雨减少反而使锐齿栎树干液流密度显著升高。（2）不同径级的锐齿栎树干液流密度在生长季内对干旱有不同的响应，特别是小径级的树干液流密度与其他径级有较多的不同。小径级的锐齿栎树干液流密度在5、7月份表现为减雨样地显著小于对照样地，在9、10月份则表现为减雨样地显著大于对照样地。中径级的锐齿栎树干液流密度在5、10月份表现为减雨样地显著大于对照样地，在7月份则表现为减雨样地极显著小于对照样地。大径级的锐齿栎树干液流密度在6、7月份表现为减雨样地显著小于对照样地，在10月份则表现为减雨样地显著大于对照样地。 Abstract:The change in precipitation pattern is one of the characteristics of global climate change. Some regions at mid-latitude might experience more frequent and severe drought. However, it is unclear how the precipitation change will affect the forest vegetation in those regions. Amongst, Quercus aliena var. acuteserrata is the dominant canopy tree species of deciduous broad-leaved forests in the warm temperate zone of middle China. Understanding the evapotranspiration responses of Q. aliena to drought induced by climate change is crucial to elucidate carbon-water coupling process. In order to explore the warm-temperate deciduous broad-leaved forest response to precipitation change, a manipulated throughfall reduction experiment was conducted in Baotianman National Nature Reserve since 2013. The Granier thermal diffusion probe (TDP) was used to measure the dynamic change of sap flux density of Q. aliena. The results showed that the throughfall reduction had significant effects on the sap flux density (Js) during the growing season. Firstly, the throughfall reduction significantly reduced the sap flux density of Q. aliena in July. However, in the late growing season (October), the throughfall reduction increased the sap flux density of Q. aliena significantly. Therefore, the sap flux density of Q. aliena differently responded to the throughfall reduction among months during the growing season. Secondly, the sap flux density of Q. aliena of different tree sizes showed different responses to drought during the growing season, especially the small trees (diameter at breast height, DBH≤21 cm) was different from that of medium (21 cm 参考文献 相似文献 引证文献

Canopy pruning as a strategy for saving water in a dry land jujube plantation in a loess hilly region of China

AimsSoil drying has occurred widely in artificial plantations in the semiarid loess region because the water consumption exceeds the rainfall. Jujube (Ziziphus jujube Mill. CV. Lizao) plantations have been planted to improve the economic income since 2000. In order to prevent soil drying and sustain artificial plantation development, we examined the relationships between the canopy size, water consumption, and water use efficiency in a dry land jujube plantation. MethodsSeven treatments were tested comprising native jujube with no pruning and dwarfing jujube under different pruning levels ranging from 1 to 6. Jujube is a popular dwarfing canopy type in this region with a tree height of 2.2 m and this comprised level 1. Jujube received increased intensities of pruning as well as decreases in tree height and canopy size for levels 2–4. Jujube received severe pruning to a tree height of only 1.1 m at level 5, and the canopy was removed with only 30–40 cm of the trunk left for level 6. Soil water was detected using CNC100 neutron tubes. A thermal diffusion probe was used to monitor the sap flow in jujube trees throughout the whole growth period. ResultsDuring our study period, 2014 was a wet year with rainfall of 460.4 mm and 2015 was a dry year with rainfall of only 380.8 mm. Transpiration and water consumption by jujube decreased significantly whereas the soil water content increased as the pruning intensity increased in these two years. Compared with 15-year-old native jujube, the annual soil water consumption by 15-year-old dwarfing jujube (pruned at level 1) was 6.54 mm less and the soil water consumption depth moved upward by 2.2 m. The soil water recovered faster for jujube at level 6 and the soil water restoration depth reached 4.6 m after 3 years, with an annual restoration depth of 153.3 cm. Compared with level 1 jujube, at level 5, the height was halved, the transpiration was about 22.1%, and the water use efficiency was significantly improved by 1.1 times, thereby demonstrating that the water consumption could be regulated by the canopy size. Level 2 jujube had the highest water use efficiency with the optimal pruning level in the local region. ConclusionsWe found that pruning could effectively decrease water consumption, relieve deep soil drying, and improve the water use efficiency in jujube. The pruning level should be determined based on the water consumption rate and average rainfall to obtain high yields.

Brain Multimodality Monitoring: A New Tool in Neurocritical Care of Comatose Patients.

Neurocritical care patients are at risk of developing secondary brain injury from inflammation, ischemia, and edema that follows the primary insult. Recognizing clinical deterioration due to secondary injury is frequently challenging in comatose patients. Multimodality monitoring (MMM) encompasses various tools to monitor cerebral metabolism, perfusion, and oxygenation aimed at detecting these changes to help modify therapies before irreversible injury sets in. These tools include intracranial pressure (ICP) monitors, transcranial Doppler (TCD), Hemedex™ (thermal diffusion probe used to measure regional cerebral blood flow), microdialysis catheter (used to measure cerebral metabolism), Licox™ (probe used to measure regional brain tissue oxygen tension), and continuous electroencephalography. Although further research is needed to demonstrate their impact on improving clinical outcomes, their contribution to illuminate the black box of the brain in comatose patients is indisputable. In this review, we further elaborate on commonly used MMM parameters, tools used to measure them, and the indications for monitoring per current consensus guidelines.

Evaluation of a New Brain Tissue Probe for Cerebral Blood Flow Monitoring in an Experimental Pig Model.

Bedside monitoring of cerebral blood flow (CBF) may provide new insights into the pathophysiology of brain injury, allow early detection of secondary ischemia, and help guide therapy. To evaluate a new brain tissue probe for serial CBF monitoring using near-infrared spectroscopy and indocyanine green dye dilution (NeMo Probe) compared with the existing thermal diffusion probe (QFlow 500 Probe). In 7 pigs, the NeMo Probe and QFlow 500 Probe were inserted into the subcortical white matter. Parallel measurements were recorded during (1) baseline, (2) hypotension, (3) hypertension, and (4) hyperventilation. Thereafter, protocol points 1 through 4 were repeated once. The Spearman correlation (rs), Bland-Altman plot, concordance rate, and coefficient of variation were used for statistical analysis. There was poor agreement between 56 pairs of absolute CBF values (rs = 0.52, P < .001). The mean bias was 10.7 mL·100 g·min with limits of agreement of -33.0 to 54.3 mL·100 g·min. The analysis of 49 pairs of changes in CBF showed a good correlation (rs = 0.83, P < .001), and the concordance rate was 93.3%. The coefficient of variation from repeated measurements under comparable physiological conditions was 51.6% for the QFlow 500 Probe and 12.9% for the NeMo Probe. Absolute CBF values obtained with the NeMo Probe and QFlow 500 Probe cannot be interpreted as equivalent. However, the NeMo Probe provides acceptable trending ability and reproducibility from repeated measurements, whereas the reproducibility of the QFlow 500 Probe was poor. Future clinical studies are warranted to evaluate the NeMo Probe in the setting of acute brain injury. CBF, cerebral blood flowCBV, cerebral blood volumeICG, indocyanine greenICP, intracranial pressureMAP, mean arterial pressuremttICG, mean transit time of indocyanine greenNIRS, near-infrared spectroscopy.

Measurement and Modeling of Tissue Thermal Conductivity With Variable Water Content and Compression

The effects of water content and compression level on tissue thermal conductivity were studied. These effects are important in electrosurgery, as tissue is subjected to both compression and thermal heating. Ex vivo canine spleen tissue was used in this study. A thermal diffusion probe technique was employed to measure the tissue thermal conductivity in three different conditions. First, the tissue thermal conductivity with different water content levels was measured. The measured thermal conductivity decreased as the percentage of water within the tissue decreased. Second, the tissue thermal conductivity under compression, up to 77%, was measured and it showed a 9% reduction as the load was applied. Third, desiccated tissue was compressed, and the thermal conductivity was measured. The compression effect on thermal conductivity was less prominent in the desiccated tissue because less water was squeezed out due to compression. A three-phase Maxwell–Eucken model was developed to predict the tissue thermal conductivity for varying water content and compression levels. The model used the ratio of air, tissue fiber, and water to predict the thermal conductivity and showed a good agreement with the experimental data.

Determining Evapotranspiration of a Chinese Willow Stand with Three-Needle Heat-Pulse Probes

Quantifying evapotranspiration (ET) and partitioning it into its individual components, evaporation (E) and transpiration (T), is essential to understanding eco-hydrological systems and guiding agricultural production practices. Our study tested the possibility of using heat-pulse probes (HPP) to determine E, T, and ET. Values of E and T were determined using the sensible heat balance theory and heat ratio method (HRM), respectively. Field experiments were conducted in a small stand of 10 Salix matsudana trees growing in a sandy soil on the Loess Plateau, China. An arrangement of five three-needle HPP sets determined E throughout the 3- to 33-mm soil layer. Sap flux density (vₛ) was determined by three HPP-sets inserted in the sapwood of three sample trees at breast height; up-scaling was used to determine T at the stand level. Summing E and T gave the stand ET. The HPP E, vₛ, and ET values were compared with those obtained from microlysimeters (MLS), thermal diffusion probes (TDP), and the water budget method, respectively. Daily HPP E had a moderate, but significant (R² = 0.47; P < 0.001) linear relationship with MLS E. Total HPP E was 13.4% lower than MLS E. Hourly HPP vₛ had a highly significant linear relationship (R² = 0.87; P < 0.001) to TDP vₛ but was consistently underestimated by 49%. Adjusting the original wound-size correction factor removed this bias. Summing the HPP E (67.3 mm) and T (89.0 mm) gave the ET (156.3 mm), which was 21.0 mm higher than the water budget ET estimate. We concluded that using HPP to estimate ET, E, and T was a promising approach, suitable for providing long-term, continuous, in situ, and high time-resolution estimations, even though certain issues still need to be resolved.

Is local hypoperfusion the reason for transient neurological deficits after STA-MCA bypass for moyamoya disease?

Hyperperfusion is believed to be the cause of transient neurological events (TNEs) in patients with moyamoya disease (MMD) who have undergone an extracranial-to-intracranial (EC-IC) bypass between the superficial temporal artery (STA) and the middle cerebral artery (MCA). The objective of this study was to evaluate this possibility by analyzing cerebral blood flow (CBF) data obtained with thermal diffusion probes used at the authors' center. The authors examined postoperative cerebral perfusion in 31 patients with MMD who underwent a direct EC-IC STA-MCA bypass. A Hemedex Q500 flow probe was placed in the frontal lobe adjacent to the bypass and connected to a Bowman cerebral perfusion monitor, and CBF data were statistically analyzed using JMP 8.0.2 software. Seven patients experienced a TNE after surgery in the left hemisphere (that is, after left-sided surgery), manifesting as dysphasia approximately 24 hours postoperatively and which had improved by 48 hours. No TNEs were observed after right-sided surgeries. Operative and postoperative CBFs in the left side with the TNE were compared with those in the left side with no TNE and on the right side. A detailed analysis of 64,980 minute-by-minute flow observations showed that the initial postbypass CBF was higher on the left side where the TNEs occurred. This CBF increase was followed by a widely fluctuating pattern and a statistically significant and sharp drop in perfusion (p < 0.001, mean difference of CBF between groups, paired t-test) associated with a TNE not observed in the other 2 groups. On the basis of the authors' initial observations, an early-onset altered pattern of CBF was identified. These findings suggest local hypoperfusion as the cause of the TNEs. This hypoperfusion may originate from competing blood flows resulting from impaired cerebral autoregulation and a fluctuating flow in cerebral microcirculation.

Inverse neurovascular coupling to cortical spreading depolarizations in severe brain trauma.

Cortical spreading depolarization causes a breakdown of electrochemical gradients following acute brain injury, and also elicits dynamic changes in regional cerebral blood flow that range from physiological neurovascular coupling (hyperaemia) to pathological inverse coupling (hypoperfusion). In this study, we determined whether pathological inverse neurovascular coupling occurred as a mechanism of secondary brain injury in 24 patients who underwent craniotomy for severe traumatic brain injury. After surgery, spreading depolarizations were monitored with subdural electrode strips and regional cerebral blood flow was measured with a parenchymal thermal diffusion probe. The status of cerebrovascular autoregulation was monitored as a correlation between blood pressure and regional cerebral blood flow. A total of 876 spreading depolarizations were recorded in 17 of 24 patients, but blood flow measurements were obtained for only 196 events because of technical limitations. Transient haemodynamic responses were observed in time-locked association with 82 of 196 (42%) spreading depolarizations in five patients. Spreading depolarizations induced only hyperaemic responses (794% increase) in one patient with intact cerebrovascular autoregulation; and only inverse responses (-24% decrease) in another patient with impaired autoregulation. In contrast, three patients exhibited dynamic changes in neurovascular coupling to depolarizations throughout the course of recordings. Severity of the pathological inverse response progressively increased (-14%, -29%, -79% decrease, P < 0.05) during progressive worsening of cerebrovascular autoregulation in one patient (Pearson coefficient 0.04, 0.14, 0.28, P < 0.05). A second patient showed transformation from physiological hyperaemic coupling (44% increase) to pathological inverse coupling (-30% decrease) (P < 0.05) coinciding with loss of autoregulation (Pearson coefficient 0.19 → 0.32, P < 0.05). The third patient exhibited a similar transformation in brain tissue oxygenation, a surrogate of blood flow, from physiologic hyperoxic responses (20% increase) to pathological hypoxic responses (-14% decrease, P < 0.05). Pathological inverse coupling was only observed with electrodes placed in or adjacent to evolving lesions. Overall, 31% of the pathological inverse responses occurred during ischaemia (<18 ml/100 g/min) thus exacerbating perfusion deficits. Average perfusion was significantly higher in patients with good 6-month outcomes (46.8 ± 6.5 ml/100 g/min) than those with poor outcomes (32.2 ± 3.7 ml/100 g/min, P < 0.05). These results establish inverse neurovascular coupling to spreading depolarization as a novel mechanism of secondary brain injury and suggest that cortical spreading depolarization, the neurovascular response, cerebrovascular autoregulation, and ischaemia are critical processes to monitor and target therapeutically in the management of acute brain injury.

Abstracts fromThe 32nd AnnualNational Neurotrauma SymposiumJune 29–July 2, 2014San Francisco, California

Abstracts fromThe 32^nd AnnualNational Neurotrauma SymposiumJune 29–July 2, 2014San Francisco, California

Abstract W P370: Is Local Hypoperfusion the Basis of Transient Neurological Deficits After STA-MCA Bypass in Moyamoya Disease?

Object: Hyperperfusion is believed to be the cause of transient neurological deficits in patients who have undergone an STA-MCA bypass for Moyamoya disease (MMD). We evaluated this on the basis of cerebral blood flow data from thermal diffusion probes used at our center. Methods: We studied postoperative cerebral perfusion in 31 patients with MMD who underwent a direct STA-MCA bypass. A Hemedex Q500 flow probe (Hemedex, Inc, Cambridge, MA) with a Bowman cerebral perfusion monitor was placed in the frontal lobe adjacent to the bypass, and flow data was analysed using JMP 8.0.2 (SAS Inc., Cary, NC). Seven patients experienced a transient neurological event (TNE) after the left-sided operation, manifesting as dysphasia around 24 hours postoperative and improving by 48 hours. The patterns of median cerebral blood flows with respect to time were plotted for the 3 groups (left side with TNE, the left side with no TNE and the right side) with smoothing by the moving average method. Observations were divided into time blocks (1 = 0-8 hours, 2 = 8-16 hours, 3 = 16-24 hours, 4 = 24-32 hours, 5 = &gt; 32 hours). Differences in median blood flow between various time blocks and between groups were also analysed to evaluate any significant differences. These were correlated with the clinical picture. Results: An average of 20 hours (IQR 10-32 hours) of postoperative flow data was available for each patient. A detailed analysis of 64980 minute-by-minute flow observations shows that the initial post-bypass flow was higher on the left side where TNEs occurred, followed by a widely fluctuating pattern and a sharp drop in the perfusion corresponding with a deficit (p &lt; 0.001, mean difference of flow, t-test) when compared to the other groups where deficits were not observed. Conclusion: Based on our observations we demonstrate a pattern of blood flow that suggests local hypoperfusion as the cause of the deficit on the backdrop of impaired autoregulation and a fluctuating blood flow, contrary to the traditional view that attributes these to hyperperfusion.

Response of blood flow to hyperthermia in human prostate tumors: Opportunities for enhanced radiation effect and drug delivery.

189 Background: Tissue perfusion may be a significant factor affecting outcome of prostate cancer treatment. Hyperthermia has been shown to have beneficial anti-cancer effects when combined with other anti-neoplastic modalities including radiation, chemotherapy, and immunotherapy. For instance, hyperthermia may increase prostate perfusion resulting in radiosensitization through increased oxygenation and chemotherapy through enhanced drug delivery. We previously reported significant benefit to the addition of hyperthermia to radiation on a phase II trial for men with locally advanced prostate cancer. To better understand tissue perfusion in patients with prostate cancer and response to hyperthermia, we measured perfusion levels in patients on this trial before and after hyperthermia. Methods: Prostate perfusion was measured before and immediately after heating in a total of 21 hyperthermia treatments in 14 patients with prostate cancer. A trans-rectal ultrasound device with a water cooled jacket was used to heat the prostate. Prostate tissue temperatures were measured using three multisensory thermocouple probes. Perfusion was measured with the TDP-200 Thermal Diffusion Probe, a thermistor-based device which quantifies perfusion with a modified wash-out technique. Results: In 19 treatments in which perfusion was measured before heating, average and standard deviation was 18.3 ± 10.6 ml/100g-min and in 17 treatments in which perfusion was measured after heating, it was 30.7 ± 20.8 ml/100g-min. This represents a statistically significant increase of 68% (p = 0.018). Perfusion increased 12 of 15 treatments in which measurements were obtained before and after hyperthermia. Notably, prostate tissue that was most ischemic prior to heating experienced the largest heat-induced perfusion increase. Conclusions: Prostate perfusion increased significantly with a majority of hyperthermia treatments. Enhanced prostate oxygenation may have been a contributing factor to the benefit noted with hyperthermia in this phase II trial. The use of hyperthermia to augment prostate perfusion to enhance radiation, chemotherapy, and immunotherapy warrants further investigation.

Abstract TP421: Cerebral Blood Flow Dynamics and Head-of-Bed Changes in the Setting of Subarachnoid Hemorrhage

Background: Head-of-bed (HOB) elevation is usually restricted in patients with aneurysmal subarachnoid hemorrhage (SAH). This practice is believed to prevent cerebral hypoperfusion. Objective: The goal of this study is to correlate HOB changes (0 o and 90 o ) with cerebral blood flow using Trans-cranial Doppler (TCD) and thermal diffusion probe in SAH patients. Methods: Thirteen patients with SAH were prospectively enrolled in the study. Eight patients underwent placement of a thermal diffusion probe for regional CBF measurement in the same setting when placing a ventriculostomy. CBF values were measured by TCD alone (13 subjects) or concurrently with thermal diffusion probe (8 subjects) with the patients in a flat (0 o ) and upright sitting position (90 o ) at day 3, 7, and 10. Results: The average increase in blood flow velocity when changing HOB from 0 o to 90 o was 7.8% on day 3, 0.1% on day 7, and 13.1% on day 10. The middle cerebral artery had the least changes in velocity compared to the anterior cerebral and the posterior cerebral arteries. The average regional CBF measurement was 22.7 +/- 10.3 ml/100g/min in the supine position and 23.6 +/- 9.1 mg/100g/min in the sitting position. The changes were not statistically significant. No change in clinical exam was appreciated. None of the patients developed clinical cerebral vasospasm. Conclusion: Changing HOB position in the setting of SAH did not significantly affect either cerebral blood flow velocity or regional blood flow. This data suggests that early mobilization should be considered given the detrimental effects of prolonged bed rest.