Focused Ultrasound-Enhanced Liquid Biopsy: A Promising Diagnostic Tool for Brain Tumor Patients.

The performance of minimally invasive molecular diagnostic tools in brain tumors, such as liquid biopsy, has so far been limited by the blood-brain barrier (BBB). The BBB hinders the release of brain tumor biomarkers into the bloodstream. The use of focused ultrasound in conjunction with microbubbles has been shown to temporarily open the BBB (FUS-BBBO). This may enhance blood-based tumor biomarker levels. This systematic review provides an overview of the data regarding FUS-BBBO-enhanced liquid biopsy for primary brain tumors. A systematic search was conducted in PubMed and Embase databases with key terms "brain tumors", "liquid biopsy", "FUS" and their synonyms, in accordance with PRISMA statement guidelines. Five preclinical and two clinical studies were included. Preclinical studies utilized mouse, rat and porcine glioma models. Biomarker levels were found to be higher in sonicated groups compared to control groups. Both stable and inertial microbubble cavitation increased biomarker levels, whereas only inertial cavitation induced microhemorrhages. In clinical studies involving 14 patients with high-grade brain tumors, biomarker levels were increased after FUS-BBBO with stable cavitation. In conclusion, FUS-BBBO-enhanced liquid biopsy using stable cavitation shows diagnostic potential for primary brain tumors. Further research is imperative before integrating FUS-BBBO for liquid biopsy enhancement into clinical practice.

Comparison of the clinical performance of a hybrid Alba 4D and the AMC-4 locoregional hyperthermia systems.

OBJECTIVE: The in-house developed 70 MHz AMC-4 locoregional hyperthermia system has been in clinical use since 1984. This device was recently commercialized as the Alba 4D (Medlogix®, Rome, Italy), with a similar geometrical 4-waveguide design. At the time of this study a hybrid Alba 4D was installed at our center, which incorporated elements of the AMC-4. This study aims to compare clinical performance of both devices. METHODS: During one year after clinical acceptance of the hybrid Alba 4D, both devices were used for treatment delivery in patients scheduled for locoregional hyperthermia. Each patient started with the AMC-4, next sessions were allocated to either device. Possible differences between Alba 4D and AMC-4 sessions in power, achieved temperature T0, T10, T50, T90, T100, treatment time and complaints per session, were evaluated using linear mixed models (LMMs) for repeated measures with patient as random effect. RESULTS: From March 2018 to April 2019, eleven patients with cervical, pancreatic, vaginal carcinoma and uterine leiomyosarcoma received 27 locoregional hyperthermia sessions with the Alba 4D and 34 sessions with the AMC-4. Median number of sessions per patient was 5 (range 3-13). Treatment results for both devices were not significantly different: T50 was 40.5 ± 1.0 °C vs. 40.8 ± 0.7 °C, applied power was 500 ± 79 W vs. 526 ± 108 W, for the Alba 4D vs. AMC-4, respectively. CONCLUSION: Results of the first patients treated with the hybrid Alba 4D demonstrated comparable clinical performance of the Alba 4D and AMC-4 locoregional hyperthermia systems, and both devices are expected to yield similar favorable clinical results.

Post-operative re-irradiation with hyperthermia in locoregional breast cancer recurrence: Temperature matters.

PURPOSE: To investigate the impact of hyperthermia thermal dose (TD) on locoregional control (LRC), overall survival (OS) and toxicity in locoregional recurrent breast cancer patients treated with postoperative re-irradiation and hyperthermia. METHODS: In this retrospective study, 112 women with resected locoregional recurrent breast cancer treated in 2010-2017 with postoperative re-irradiation 8frx4Gy (n = 34) or 23frx2Gy (n = 78), combined with 4-5 weekly hyperthermia sessions guided by invasive thermometry, were subdivided into 'low' (n = 56) and 'high' TD (n = 56) groups by the best session with highest median cumulative equivalent minutes at 43 °C (Best CEM43T50) < 7.2 min and ≥7.2 min, respectively. Actuarial LRC, OS and late toxicity incidence were analyzed. Backward multivariable Cox regression and inverse probability weighting (IPW) analysis were performed. RESULTS: TD subgroups showed no significant differences in patient/treatment characteristics. Median follow-up was 43 months (range 1-107 months). High vs. low TD was associated with LRC (p = 0.0013), but not with OS (p = 0.29) or late toxicity (p = 0.58). Three-year LRC was 74.0% vs. 92.3% in the low and high TD group, respectively (p = 0.008). After three years, 25.0% and 0.9% of the patients had late toxicity grade 3 and 4, respectively. Multivariable analysis showed that distant metastasis (HR 17.6; 95%CI 5.2-60.2), lymph node involvement (HR 2.9; 95%CI 1.2-7.2), recurrence site (chest wall vs. breast; HR 4.6; 95%CI 1.8-11.6) and TD (low vs. high; HR 4.1; 95%CI 1.4-11.5) were associated with LRC. TD was associated with LRC in IPW analysis (p = 0.0018). CONCLUSIONS: High thermal dose (best CEM43T50 ≥ 7.2 min) was associated with significantly higher LRC for patients with locoregional recurrent breast cancer treated with postoperative re-irradiation and hyperthermia, without augmenting toxicity.

Clinical Feasibility of a High-Resolution Thermal Monitoring Sheet for Superficial Hyperthermia in Breast Cancer Patients.

Background: Accurate monitoring of skin surface temperatures is necessary to ensure treatment quality during superficial hyperthermia. A high-resolution thermal monitoring sheet (TMS) was developed to monitor the skin surface temperature distribution. The influence of the TMS on applicator performance was investigated, feasibility and ability to reliably monitor the temperature distribution were evaluated in a clinical study. Methods: Phantom experiments were performed to determine the influence of the TMS on power deposition patterns, applicator efficiency, and heat transfer of the water bolus for 434 and 915 MHz applicators. Clinical feasibility was evaluated in 10 women with locoregional recurrent breast cancer. Skin surface temperatures during consecutive treatments were monitored alternatingly with either standard Amsterdam UMC thermometry or TMS. Treatments were compared using (generalized) linear mixed models. Results: The TMS did not significantly affect power deposition patterns and applicator efficiency (1-2%), the reduced heat transfer of the water boluses (51-56%) could be compensated by adjusting the water bolus flow. Skin surface temperatures were monitored reliably, and no alteration of thermal toxicity was observed compared to standard Amsterdam UMC thermometry. Conclusion: Clinical application of the TMS is feasible. Power deposition patterns and applicator efficiency were not affected. Surface temperatures were monitored reliably.

Two high-resolution thermal monitoring sheets for clinical superficial hyperthermia.

PURPOSE: Temperature measurement during superficial hyperthermia is limited by poor spatial resolution. We investigated two sheets to improve temperature monitoring of the skin surface. METHODS AND MATERIALS: Two different sheets were studied with a grid of temperature sensors with one sensor per ~5 cm2. The first was a matrix of multisensor thermocouple probes laced through a silicone sheet. The second sheet had rows of thermistors connected by meandering copper leads mounted on stretchable printed circuit board (SPCB). Accuracy, temperature resolution and two hour stability of both sheets were investigated. Furthermore, we determined the ability to follow body contours, thermal conduction errors and electromagnetic (EM) compatibility to clinically used 434 and 915 MHz hyperthermia applicators. RESULTS: For both sheets the accuracy (≤0.2 °C), temperature resolution (≤0.03 °C) and stability (≤0.01°C hr-1) were adequate for clinical use. Thermal conduction errors ranged from 5.25 - 11.25 mm vs. 2.15 mm for the thermocouple probe and thermistor, respectively. Both sheets could follow body contours, where the ratio air/ water bolus surface was <5%. When aligned perpendicularly to the EM field the meandering copper tracks used on the SPCB did induce self-heating, while the thermocouple probes did not. Self-heating had a linear relationship with the angle of the leads with respect to the EM field direction for both sensors at both frequencies. Self-heating of the thermistor was similar for both frequencies, while it was circa two-fold higher for 915 vs. 434 MHz for the thermocouple. CONCLUSION: The use of SPCB technology for skin surface monitoring was promising. However, suppressing self-heating induced by the horseshoe shaped copper tracks needed for stretchability of the SPCB requires more in-depth investigation. The thermocouple matrix was the most promising for clinical application, meeting 6/7 of the major requirements for skin surface temperature monitoring when positioned perpendicular to the EM field.

Modelling Curved Contact Flexible Microstrip Applicators for Patient-Specific Superficial Hyperthermia Treatment Planning.

This paper describes a method to reconstruct bendable superficial hyperthermia applicators for routine clinical patient-specific treatment planning. The reconstruction uses a CT scan with a flexible silicone dummy applicator positioned on the patient. The curvature was approximated by two second-degree polynomial functions. A realistic treatment series was mimicked using a standard Alderson radiation therapy phantom and a treatment planning model was reconstructed from a CT scan. The variation among treatment curvatures was compared to the modelled curvature. The mathematical approximation of the applicator curvature was validated for this phantom experiment, as well as for clinical treatments. The average maximum variation among the successive mimicked sessions was 3.67 ± 0.69 mm (range 2.98-4.60mm). The maximum deviation between the treatment curvature and the modelled curvature was 4.35 mm. Comparing the treatment and approximated curvature yielded a maximum deviation between 2.98 mm and 4.12 mm. For clinical treatments the maximum deviation of the treatment and approximated curvature varied between 0.48 mm and 1.98 mm. These results allow adequate reconstruction of bendable hyperthermia applicators for treatment planning, which can further improve treatment quality, for example by optimizing the water bolus temperature for patient-specific tumor depths. Predictive parameters for hyperthermia treatment outcome can easily be evaluated and compared for various input parameters.

Temperature and thermal dose during radiotherapy and hyperthermia for recurrent breast cancer are related to clinical outcome and thermal toxicity: a systematic review.

Objective: Hyperthermia therapy (HT), heating tumors to 40-45 °C, is a known radiotherapy (RT) and chemotherapy sensitizer. The additional benefit of HT to RT for recurrent breast cancer has been proven in multiple randomized trials. However, published outcome after RT + HT varies widely. We performed a systematic review to investigate whether there is a relationship between achieved HT dose and clinical outcome and thermal toxicity for patients with recurrent breast cancer treated with RT + HT. Method: Four databases, EMBASE, PubMed, Cochrane library and clinicaltrials.gov, were searched with the terms breast, radiotherapy, hyperthermia therapy and their synonyms. Final search was performed on 3 April 2019. Twenty-two articles were included in the systematic review, reporting on 2330 patients with breast cancer treated with RT + HT. Results: Thirty-two HT parameters were tested for a relationship with clinical outcome. In studies reporting a relationship, the relationship was significant for complete response in 10/15 studies, in 10/13 studies for duration of local control, in 2/2 studies for overall survival and in 7/11 studies for thermal toxicity. Patients who received high thermal dose had on average 34% (range 27%-53%) more complete responses than patients who received low thermal dose. Patients who achieved higher HT parameters had increased odds/probability on improved clinical outcome and on thermal toxicity. Conclusion: Temperature and thermal dose during HT had significant influence on complete response, duration of local control, overall survival and thermal toxicity of patients with recurrent breast cancer treated with RT + HT. Higher temperature and thermal dose improved outcome, while higher maximum temperature increased incidence of thermal toxicity.

Clinical validation of a novel thermophysical bladder model designed to improve the accuracy of hyperthermia treatment planning in the pelvic region.

PURPOSE: Hyperthermia treatment planning for deep locoregional hyperthermia treatment may assist in phase and amplitude steering to optimize the temperature distribution. This study aims to incorporate a physically correct description of bladder properties in treatment planning, notably the presence of convection and absence of perfusion within the bladder lumen, and to assess accuracy and clinical implications for non muscle invasive bladder cancer patients treated with locoregional hyperthermia. METHODS: We implemented a convective thermophysical fluid model based on the Boussinesq approximation to the Navier-Stokes equations using the (finite element) OpenFOAM toolkit. A clinician delineated the bladder on CT scans obtained from 14 bladder cancer patients. We performed (1) conventional treatment planning with a perfused muscle-like solid bladder, (2) with bladder content properties without and (3) with flow dynamics. Finally, we compared temperature distributions predicted by the three models with temperature measurements obtained during treatment. RESULTS: Much higher and more uniform bladder temperatures are predicted with physically accurate fluid modeling compared to previously employed muscle-like models. The differences reflect the homogenizing effect of convection, and the absence of perfusion. Median steady state temperatures simulated with the novel convective model (3) deviated on average -0.6 °C (-12%) from values measured during treatment, compared to -3.7 °C (-71%) and +1.5 °C (+29%) deviation for the muscle-like (1) and static (2) models, respectively. The Grashof number was 3.2 ± 1.5 × 105 (mean ± SD). CONCLUSIONS: Incorporating fluid modeling in hyperthermia treatment planning yields significantly improved predictions of the temperature distribution in the bladder lumen during hyperthermia treatment.

Analysis of clinical data to determine the minimum number of sensors required for adequate skin temperature monitoring of superficial hyperthermia treatments.

PURPOSE: Tumor response and treatment toxicity are related to minimum and maximum tissue temperatures during hyperthermia, respectively. Using a large set of clinical data, we analyzed the number of sensors required to adequately monitor skin temperature during superficial hyperthermia treatment of breast cancer patients. METHODS: Hyperthermia treatments monitored with >60 stationary temperature sensors were selected from a database of patients with recurrent breast cancer treated with re-irradiation (23 × 2 Gy) and hyperthermia using single 434 MHz applicators (effective field size 351-396 cm2). Reduced temperature monitoring schemes involved randomly selected subsets of stationary skin sensors, and another subset simulating continuous thermal mapping of the skin. Temperature differences (ΔT) between subsets and complete sets of sensors were evaluated in terms of overall minimum (Tmin) and maximum (Tmax) temperature, as well as T90 and T10. RESULTS: Eighty patients were included yielding a total of 400 hyperthermia sessions. Median ΔT was <0.01 °C for T90, its 95% confidence interval (95%CI) decreased to ≤0.5 °C when >50 sensors were used. Subsets of <10 sensors result in underestimation of Tmax up to -2.1 °C (ΔT 95%CI), which decreased to -0.5 °C when >50 sensors were used. Thermal profiles (8-21 probes) yielded a median ΔT < 0.01 °C for T90 and Tmax, with a 95%CI of -0.2 °C and 0.4 °C, respectively. The detection rate of Tmax ≥43 °C is ≥85% while using >50 stationary sensors or thermal profiles. CONCLUSIONS: Adequate coverage of the skin temperature distribution during superficial hyperthermia treatment requires the use of >50 stationary sensors per 400 cm2 applicator. Thermal mapping is a valid alternative.

Online Adaptive Hyperthermia Treatment Planning During Locoregional Heating to Suppress Treatment-Limiting Hot Spots.

BACKGROUND: Adequate tumor temperatures during hyperthermia are essential for good clinical response, but excessive heating of normal tissue should be avoided. This makes locoregional heating using phased array systems technically challenging. Online application of hyperthermia treatment planning could help to improve the heating quality. The aim of this study was to evaluate the clinical benefit of online treatment planning during treatment of pelvic tumors heated with the AMC-8 locoregional hyperthermia system. METHODS: For online adaptive hyperthermia treatment planning, a graphical user interface was developed. Electric fields were calculated in a preprocessing step using our in-house-developed finite-difference-based treatment planning system. This allows instant calculation of the temperature distribution for user-selected phase-amplitude settings during treatment and projection onto the patient's computed tomographic scan for online visualization. Online treatment planning was used for 14 treatment sessions in 8 patients to reduce the patients' reports of hot spots while maintaining the same level of tumor heating. The predicted decrease in hot spot temperature should be at least 0.5°C, and the tumor temperature should decrease less than 0.2°C. These predictions were compared with clinical data: patient feedback about the hot spot and temperature measurements in the tumor region. RESULTS: In total, 17 hot spot reports occurred during the 14 sessions, and the alternative settings predicted the hot spot temperature to decrease by at least 0.5°C, which was confirmed by the disappearance of all 17 hot spot reports. At the same time, the average tumor temperature was predicted to change on average -0.01°C (range, -0.19°C to 0.34°C). The measured tumor temperature change was on average only -0.02°C (range, -0.26°C to 0.31°C). In only 2 cases the temperature decrease was slightly larger than 0.2°C, but at most it was 0.26°C. CONCLUSIONS: Online application of hyperthermia treatment planning is reliable and very useful to reduce hot spots without affecting tumor temperatures.

A flexible 70 MHz phase-controlled double waveguide system for hyperthermia treatment of superficial tumours with deep infiltration.

PURPOSE: Superficial tumours with deep infiltration in the upper 15 cm of the trunk cannot be treated adequately with existing hyperthermia systems. The aim of this study was to develop, characterise and evaluate a new flexible two-channel hyperthermia system (AMC-2) for tumours in this region. MATERIALS AND METHODS: The two-channel AMC-2 system has two horizontally revolving and height adjustable 70 MHz waveguides. Three different interchangeable antennas with sizes 20 × 34, 15 × 34 and 8.5 × 34 cm were developed and their electrical properties were determined. The performance of the AMC-2 system was tested by measurements of the electric field distribution in a saline water filled elliptical phantom, using an electric field vector probe. Clinical feasibility was demonstrated by treatment of a melanoma in the axillary region. RESULTS: Phantom measurements showed a good performance for all waveguides. The large reflection of the smallest antenna has to be compensated by increased forward power. Field patterns become asymmetrical when using smaller top antennas, necessitating phase corrections. The clinical application showed that tumours deeper than 4 cm can be heated adequately. A median tumour temperature of 42 °C can be reached up to 12 cm depth with adequate antenna positioning and phase-amplitude steering. CONCLUSIONS: This 70 MHz AMC-2 waveguide system is a useful addition to existing loco-regional hyperthermia equipment as it is capable of heating axillary tumours and other tumours deeper than 4 cm.

Thermal Skin Damage During Reirradiation and Hyperthermia Is Time-Temperature Dependent.

PURPOSE: To investigate the relationship of thermal skin damage (TSD) to time-temperature isoeffect levels for patients with breast cancer recurrence treated with reirradiation plus hyperthermia (reRT + HT), and to investigate whether the treatment history of previous treatments (scar tissue) is a risk factor for TSD. METHODS AND MATERIALS: In this observational study, temperature characteristics of hyperthermia sessions were analyzed in 262 patients with recurrent breast cancer treated in the AMC between 2010 and 2014 with reirradiation and weekly hyperthermia for 1 hour. Skin temperature was measured using a median of 42 (range, 29-82) measurement points per hyperthermia session. RESULTS: Sixty-eight patients (26%) developed 79 sites of TSD, after the first (n=26), second (n=17), third (n=27), and fourth (n=9) hyperthermia session. Seventy percent of TSD occurred on or near scar tissue. Scar tissue reached higher temperatures than other skin tissue (0.4°C, P<.001). A total of 102 measurement points corresponded to actual TSD sites in 35 of 79 sessions in which TSD developed. Thermal skin damage sites had much higher maximum temperatures than non-TSD sites (2.8°C, P<.001). Generalized linear mixed models showed that the probability of TSD is related to temperature and thermal dose values (P<.001) and that scar tissue is more at risk (odds ratio 0.4, P<.001). Limiting the maximum temperature of a measurement point to 43.7°C would mean that the probability of observing TSD was at most 5%. CONCLUSION: Thermal skin damage during reRT + HT for recurrent breast cancer was related to higher local temperatures and time-temperature isoeffect levels. Scar tissue reached higher temperatures than other skin tissue, and TSD occurred at lower temperatures and thermal dose values in scar tissue compared with other skin tissue. Indeed, TSD developed often on and around scar tissue from previous surgical procedures.

Quality assurance guidelines for superficial hyperthermia clinical trials : II. Technical requirements for heating devices.

Quality assurance (QA) guidelines are essential to provide uniform execution of clinical trials with uniform quality hyperthermia treatments. This document outlines the requirements for appropriate QA of all current superficial heating equipment including electromagnetic (radiative and capacitive), ultrasound, and infrared heating techniques. Detailed instructions are provided how to characterize and document the performance of these hyperthermia applicators in order to apply reproducible hyperthermia treatments of uniform high quality. Earlier documents used specific absorption rate (SAR) to define and characterize applicator performance. In these QA guidelines, temperature rise is the leading parameter for characterization of applicator performance. The intention of this approach is that characterization can be achieved with affordable equipment and easy-to-implement procedures. These characteristics are essential to establish for each individual applicator the specific maximum size and depth of tumors that can be heated adequately. The guidelines in this document are supplemented with a second set of guidelines focusing on the clinical application. Both sets of guidelines were developed by the European Society for Hyperthermic Oncology (ESHO) Technical Committee with participation of senior Society of Thermal Medicine (STM) members and members of the Atzelsberg Circle.

Quality assurance guidelines for superficial hyperthermia clinical trials: I. Clinical requirements.

Quality assurance guidelines are essential to provide uniform execution of clinical trials and treatment in the application of hyperthermia. This document provides definitions for a good hyperthermia treatment and identifies the clinical conditions where a certain hyperthermia system can or cannot adequately heat the tumour volume. It also provides brief description of the characteristics and performance of the current electromagnetic (radiative and capacitive), ultrasound and infra-red heating techniques. This information helps to select the appropriate heating technique for the specific tumour location and size, and appropriate settings of the water bolus and thermometry. Finally, requirements of staff training and documentation are provided. The guidelines in this document focus on the clinical application and are complemented with a second, more technical quality assurance document providing instructions and procedure to determine essential parameters that describe heating properties of the applicator for superficial hyperthermia. Both sets of guidelines were developed by the ESHO Technical Committee with participation of senior STM members and members of the Atzelsberg Circle.

Thermal dosimetry for bladder hyperthermia treatment. An overview.

The urinary bladder is a fluid-filled organ. This makes, on the one hand, the internal surface of the bladder wall relatively easy to heat and ensures in most cases a relatively homogeneous temperature distribution; on the other hand the variable volume, organ motion, and moving fluid cause artefacts for most non-invasive thermometry methods, and require additional efforts in planning accurate thermal treatment of bladder cancer. We give an overview of the thermometry methods currently used and investigated for hyperthermia treatments of bladder cancer, and discuss their advantages and disadvantages within the context of the specific disease (muscle-invasive or non-muscle-invasive bladder cancer) and the heating technique used. The role of treatment simulation to determine the thermal dose delivered is also discussed. Generally speaking, invasive measurement methods are more accurate than non-invasive methods, but provide more limited spatial information; therefore, a combination of both is desirable, preferably supplemented by simulations. Current efforts at research and clinical centres continue to improve non-invasive thermometry methods and the reliability of treatment planning and control software. Due to the challenges in measuring temperature across the non-stationary bladder wall and surrounding tissues, more research is needed to increase our knowledge about the penetration depth and typical heating pattern of the various hyperthermia devices, in order to further improve treatments. The ability to better determine the delivered thermal dose will enable clinicians to investigate the optimal treatment parameters, and consequentially, to give better controlled, thus even more reliable and effective, thermal treatments.

Impaired myocardial function does not explain reduced left ventricular filling and stroke volume at rest or during exercise at high altitude.

Impaired myocardial systolic contraction and diastolic relaxation have been suggested as possible mechanisms contributing to the decreased stroke volume (SV) observed at high altitude (HA). To determine whether intrinsic myocardial performance is a limiting factor in the generation of SV at HA, we assessed left ventricular (LV) systolic and diastolic mechanics and volumes in 10 healthy participants (aged 32 ± 7; mean ± SD) at rest and during exercise at sea level (SL; 344 m) and after 10 days at 5,050 m. In contrast to SL, LV end-diastolic volume was ∼19% lower at rest (P = 0.004) and did not increase during exercise despite a greater untwisting velocity. Furthermore, resting SV was lower at HA (∼17%; 60 ± 10 vs. 70 ± 8 ml) despite higher LV twist (43%), apical rotation (115%), and circumferential strain (17%). With exercise at HA, the increase in SV was limited (12 vs. 22 ml at SL), and LV apical rotation failed to augment. For the first time, we have demonstrated that EDV does not increase upon exercise at high altitude despite enhanced in vivo diastolic relaxation. The increase in LV mechanics at rest may represent a mechanism by which SV is defended in the presence of a reduced EDV. However, likely because of the higher LV mechanics at rest, no further increase was observed up to 50% peak power. Consequently, although hypoxia does not suppress systolic function per se, the capacity to increase SV through greater deformation during submaximal exercise at HA is restricted.

Hypoxia, not pulmonary vascular pressure, induces blood flow through intrapulmonary arteriovenous anastomoses.

KEY POINTS: Blood flow through intrapulmonary arteriovenous anastomoses (IPAVA) is increased by acute hypoxia during rest by unknown mechanisms. Oral administration of acetazolamide blunts the pulmonary vascular pressure response to acute hypoxia, thus permitting the observation of IPAVA blood flow with minimal pulmonary pressure change. Hypoxic pulmonary vasoconstriction was attenuated in humans following acetazolamide administration and partially restored with bicarbonate infusion, indicating that the effects of acetazolamide on hypoxic pulmonary vasoconstriction may involve an interaction between arterial pH and PCO2. We observed that IPAVA blood flow during hypoxia was similar before and after acetazolamide administration, even after acid-base status correction, indicating that pulmonary pressure, pH and PCO2 are unlikely regulators of IPAVA blood flow. ABSTRACT: Blood flow through intrapulmonary arteriovenous anastomoses (IPAVA) is increased with exposure to acute hypoxia and has been associated with pulmonary artery systolic pressure (PASP). We aimed to determine the direct relationship between blood flow through IPAVA and PASP in 10 participants with no detectable intracardiac shunt by comparing: (1) isocapnic hypoxia (control); (2) isocapnic hypoxia with oral administration of acetazolamide (AZ; 250 mg, three times a day for 48 h) to prevent increases in PASP; and (3) isocapnic hypoxia with AZ and 8.4% NaHCO3 infusion (AZ + HCO3 (-) ) to control for AZ-induced acidosis. Isocapnic hypoxia (20 min) was maintained by end-tidal forcing, blood flow through IPAVA was determined by agitated saline contrast echocardiography and PASP was estimated by Doppler ultrasound. Arterial blood samples were collected at rest before each isocapnic-hypoxia condition to determine pH, [HCO3(-)] and Pa,CO2. AZ decreased pH (-0.08 ± 0.01), [HCO3(-)] (-7.1 ± 0.7 mmol l(-1)) and Pa,CO2 (-4.5 ± 1.4 mmHg; P < 0.01), while intravenous NaHCO3 restored arterial blood gas parameters to control levels. Although PASP increased from baseline in all three hypoxic conditions (P < 0.05), a main effect of condition expressed an 11 ± 2% reduction in PASP from control (P < 0.001) following AZ administration while intravenous NaHCO3 partially restored the PASP response to isocapnic hypoxia. Blood flow through IPAVA increased during exposure to isocapnic hypoxia (P < 0.01) and was unrelated to PASP, cardiac output and pulmonary vascular resistance for all conditions. In conclusion, isocapnic hypoxia induces blood flow through IPAVA independent of changes in PASP and the influence of AZ on the PASP response to isocapnic hypoxia is dependent upon the H(+) concentration or Pa,CO2.

Dynamic weight loading in older people with hip fracture.

OBJECTIVE: Hip fractures have a high morbidity and mortality in elderly patients. Improving mobility outcomes is crucial in order to decrease the burden of this injury. The objective of this study was to investigate dynamic weight loading in older people with hip fractures using a new device. DESIGN: In an observational study, low-energy hip fracture patients were monitored one day per week with the FeetB@ck system during their admission. Pain, gait and balance scores were noted. Outcome measures of the FeetB@ck system are steps, walking bouts and loading rate. RESULTS: A total of 21 patients with hip fracture were included in the study (mean age 80.3 years (standard deviation 8.3 years)). The number of steps, walking bouts and loading rate had a positive linear relationship with rehabilitation (i.e. gait and balance scores) (p < 0.05). These parameters also differed significantly between patients with short (less than 8 weeks, n = 7), intermediate (between 8 and 12 weeks, n = 8) and long (longer than 12 weeks, n = 6) of rehabilitation (p < 0.01). CONCLUSION: The loading rate is a sensitive weight loading parameter for analysis of dynamic weight loading during rehabilitation in elderly hip fracture patients. This parameter correlates with clinical improvement and can differentiate between fast and slow rehabilitation.

Resting pulmonary haemodynamics and shunting: a comparison of sea-level inhabitants to high altitude Sherpas.

The incidence of blood flow through intracardiac shunt and intrapulmonary arteriovenous anastomoses (IPAVA) may differ between Sherpas permanently residing at high altitude (HA) and sea-level (SL) inhabitants as a result of evolutionary pressure to improve gas exchange and/or resting pulmonary haemodynamics. To test this hypothesis we compared sea-level inhabitants at SL (SL-SL; n = 17), during acute isocapnic hypoxia (SL-HX; n = 7) and following 3 weeks at 5050 m (SL-HA; n = 8 non-PFO subjects) to Sherpas at 5050 m (n = 14). SpO2, heart rate, pulmonary artery systolic pressure (PASP) and cardiac index (Qi) were measured during 5 min of room air breathing at SL and HA, during 20 min of isocapnic hypoxia (SL-HX; PETO2 = 47 mmHg) and during 5 min of hyperoxia (FIO2 = 1.0; Sherpas only). Intracardiac shunt and IPAVA blood flow was evaluated by agitated saline contrast echocardiography. Although PASP was similar between groups at HA (Sherpas: 30.0 ± 6.0 mmHg; SL-HA: 32.7 ± 4.2 mmHg; P = 0.27), it was greater than SL-SL (19.4 ± 2.1 mmHg; P < 0.001). The proportion of subjects with intracardiac shunt was similar between groups (SL-SL: 41%; Sherpas: 50%). In the remaining subjects, IPAVA blood flow was found in 100% of subjects during acute isocapnic hypoxia at SL, but in only 4 of 7 Sherpas and 1 of 8 SL-HA subjects at rest. In conclusion, differences in resting pulmonary vascular regulation, intracardiac shunt and IPAVA blood flow do not appear to account for any adaptation to HA in Sherpas. Despite elevated pulmonary pressures and profound hypoxaemia, IPAVA blood flow in all subjects at HA was lower than expected compared to acute normobaric hypoxia.

Cerebral pressure-flow relationship in lowlanders and natives at high altitude.

We investigated if dynamic cerebral pressure-flow relationships in lowlanders are altered at high altitude (HA), differ in HA natives and after return to sea level (SL). Lowlanders were tested at SL (n=16), arrival to 5,050 m, after 2-week acclimatization (with and without end-tidal PO2 normalization), and upon SL return. High-altitude natives (n=16) were tested at 5,050 m. Testing sessions involved resting spontaneous and driven (squat-stand maneuvers at very low (VLF, 0.05 Hz) and low (LF, 0.10 Hz) frequencies) measures to maximize blood pressure (BP) variability and improve assessment of the pressure-flow relationship using transfer function analysis (TFA). Blood flow velocity was assessed in the middle (MCAv) and posterior (PCAv) cerebral arteries. Spontaneous VLF and LF phases were reduced and coherence was elevated with acclimatization to HA (P<0.05), indicating impaired pressure-flow coupling. However, when BP was driven, both the frequency- and time-domain metrics were unaltered and comparable with HA natives. Acute mountain sickness was unrelated to TFA metrics. In conclusion, the driven cerebral pressure-flow relationship (in both frequency and time domains) is unaltered at 5,050 m in lowlanders and HA natives. Our findings indicate that spontaneous changes in TFA metrics do not necessarily reflect physiologically important alterations in the capacity of the brain to regulate BP.