Thermal Clearance Research Articles

Theoretical feasibility of vasodilator-enhanced local tumor heating

Normal arterioles, in contrast to the abnormal microvasculature of many solid tumors, provide a target for selective drug action which can enhance local heat treatment of the tumors. Measurements of tissue blood flow with radioactive microspheres and estimates of changes in blood flow with thermal clearance methods revealed that vasodilator drugs either decreased or did not alter blood flow in hamster melanoma, rat hepatoma and canine transmissible venereal tumor while increasing perfusion in adjacent normal tissues 2 to 4-fold. Solutions of the bio-heat transfer equation, which take into account such selective effects of vasodilators on blood flow in normal tissues, clearly demonstrate improved selective heating for spheroidal tumors over 2 cm in diameter. In the presence of vasodilator drug effect, steady-state center tumor temperatures of 45–50°C can be achieved by increased power input, while surrounding normal tissues remain below 42°C.

A critique of the use of a thermal clearance probe for the measurement of skin blood flow

A critique of the use of a thermal clearance probe for the measurement of skin blood flow

Is there an active mechanism limiting the influence of the sympathetic system on the cerebral vascular bed? Evidence for vasomotor escape from sympathetic stimulation in the rabbit

The influence of the cervical sympathetic chain on cerebral circulation in the rabbit was studied by means of 3 complementary techniques. Two dynamic techniques involving chronically implanted probes were used: blood flow in the caudate nucleus (CN) was measured by thermal clearance; tissue PO 2 and PCO 2 in the same structure were measured by mass spectrometry. Other variables measured continuously and simultaneously included arterial blood pressure (BP), PaO 2 and PaCO 2. The third technique was a tissue sampling method based on the Fick principle and using 14C 1 ethanol as tracer. Blood flow in 7 regions was measured at stable BP, PaO 2 and PaCO 2. Stimulation of the sympathetic chain at 15 Hz induced mean maximal decreases in CN blood flow of 23.9% (thermal clearance) and 24.4% (ethanol technique). Mean decrease of PO 2 in the CN at 15 Hz was 16.6%. Significant falls in blood flow were observed with the ethanol technique in all 7 structures measured. During prolonged stimulation (> 1 min) CN blood flow and PO 2 were found to escape towards the baseline level, which was sometimes even exceeded during the stimulation (blood flow). Stimulation frequency had only a very moderate influence on the rate of escape, and no evidence of a metabolic mechanism was found, although injection of barbiturate decreased the escape. These results are discussed with respect to the conflicting evidence on the effects of sympathetic stimulation in the brain, and to possible mechanisms for the escape phenomenon.

Measurement of blood flow, tissue PO2 and tissue PCO2 continuously and simultaneously in the same structure of the brain

Continuous measurements of blood flow and partial pressures of physiological gases have been made simultaneously in the same structure of the brain. This was made possible by the development of 2 techniques (a) blood flow measurement by a thermal clearance technique using a single probe heated sequentially (b) tissue gas partial pressure measurement by means of mass spectrometric analysis of minute amounts of gas drawn out of the tissue via an implanted cannula. Probe responses were linear functions of the 2 variables measured, and observed variations could therefore be expressed as a percentage of meanbase line level. As the probes were implanted chronically, these measurements could be repeated over several days in unanaesthetised animals.

A Transcutaneous Po2Electrode Incorporating a Thermal Clearance Local Blood Flow Sensor

Several possible methods for estimating and recording skin blood flow by thermal clearance are presented. The method chosen for trial with an O2 electrode was to thermoregulate an annular anode which covered the cathode, surrounding it like a heat shell, and to measure the cooling of the cathode by blood flow, by implanting a thermistor near the surface of the cathode. This device is far less affected by ambient temperature than is simple measurement of heating power in an uninsulated tcPO2 electrode.

Estimation of the nutrient skin blood flow using a segmented thermal clearance probe

Summary A segmented thermal clearance probe modified from similar heated thermocouple devices adapted for non-invasive application, is described. This instrument responds rapidly to changes in the nutrient skin bloodflow in the papillary dermis to a depth of 1·5 mm. It differentiates nutrient from total skin bloodflow. The dimensions of its components can be modified in order to assess bloodflow changes at different depths depending on different experimental or clinical requirements.

Techniques for continuous measurement of local cerebral blood flow, PaO 2 , PaCO 2 and blood pressure in the non-anesthetized animal.

Techniques have been developed for the study of cerebral blood flow (CBF) in non-anesthetized, non-curarized animals. Continuous recording of one or several local CBF in subcortical structures can be made, simultaneously with continous recordings of cerebral temperature,PaO2,PaCO2, arterial pressure and the E.Co.G. The CBF measurements, obtained by a thermal clearance method, are semi-quantitative.PaO2 andPaCO2 are measured quantitatively directly in the aorta by mass spectrography. Conventional techniques are used for the arterial pressure and the E.Co.G. recordings. The main advantage of the techniques described is the possibility of undertaking repeated long-duration recordings of the principal cerebro-vascular variables on animals not affected by operation stress or by drugs capable of modifying the regulation of CBF.

Determination of regional cerebral cortical blood flow using a heat clearance technique

A heat clearance method is described for measuring regional cerebral cortical blood flow, involving the injection of a small amount of cool saline into the cerebral circulation. Blood flow is estimated from the slope of the subsequent thermal clearance curve, temperature being measured by a small thermistor probe situated under the dura in contact with cerebral cortical tissue. The method is compared with the well established technique involving 85Kr an a correlation coefficient of 0.89 is obtained. The heat clearance technique, however, has the added advantages that the cost of tracer and monitoring equipment is small and that probes may be chronically implanted.

Regional cerebral blood flow measurement in the presence of raised intracranial pressure: A comparison between thermal and krypton-85 beta clearance

Two methods of measuring regional cerebral blood flow in the presence of raised intracranial pressure have been assessed against the krypton-85 beta washout technique. The first method was to count the beta emanations of krypton-85 through intact but devascularized dura; this gave excellent correlation with simultaneous measurements made by the same technique but with the dura open ( r = + 0.951; P < 0.001) with a very small scatter of results (2 Sy = 0.14 ml./gm./minute). The second method measured thermal clearance rate after the intracarotid injection of cool saline. This also gave a good correlation with the krypton-85 beta method ( r = + 0.889; P < 0.001) but the scatter of results was much wider (2 Sy = 0.48 ml./gm./minute). A further disadvantage of the thermal clearance technique was the difficulty in obtaining steady states during measurement of blood flow.

Homeostatic mechanisms in the hypothalamus

1. The homeostatic readjustments associated with neuronal activity were studied through an analysis of local blood flow, temperature and electrical activity (EEG) in the hypothalamus of unrestrained cats with permanently implanted probes. 2. Three characteristic types of correlations among the three parameters were distinguished during the arousal response. Type 1 consisted of an increase in blood flow and temperature coinciding with EEG arousal. Type 2 occurred with prolonged, very mild reticular stimulation. During maintained EEG activation, the temperature and blood flow increased but only after a long latency. Type 3 was characterized by an immediate, transient increase in blood flow. 3. Small volumes of hypothalamic tissue were gently heated without stimulation by passing a train of square waves. This temperature rise represents physical heat production. When the hypothalamus was heated with stimulation, the hypothalamic temperature rose in two distinct steps. The first step was similar to the temperature rise due to physical heat production, the second step, representing metabolic heat production. The second temperature step was markedly depressed by small doses of pentobarbital; however, no significant changes in the first temperature step were observed. 4. It is concluded that metabolic heat production rather than thermal clearance probably determines the physiological temperature rise and the sudden-decrease type of blood flow response represents a sympathetic cerebrovascular reaction, and the occurrence of the immediate (first type) or of the delayed (second type) of response pattern depends on the rapidity of accumulation of vasodilator substances and on the rate of metabolic heat production.

Evaluation of local tissue blood flow by continuous direct measurement of thermal conductivity.

ArticleEvaluation of local tissue blood flow by continuous direct measurement of thermal conductivity.L Levy, H Graichen, J A Stolwijk, and M CalabresiL Levy, H Graichen, J A Stolwijk, and M CalabresiPublished Online:01 May 1967https://doi.org/10.1152/jappl.1967.22.5.1026MoreSectionsPDF (766 KB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInEmailWeChat Previous Back to Top Next Download PDF FiguresReferencesRelatedInformationCited ByNoninvasive, in vivo determination of uterine fibroid thermal conductivity in MRI-guided high intensity focused ultrasound therapy27 August 2014 | Journal of Magnetic Resonance Imaging, Vol. 41, No. 6Flow Measurement13 April 2011Changes in skin thermal clearance during anaesthesiaAnaesthesia, Vol. 41, No. 4Skin blood flow changes in anaesthetized humans: comparison between skin thermal clearance and finger pulse amplitude measurementEuropean Journal of Applied Physiology and Occupational Physiology, Vol. 54, No. 6Combined Intracranial Pressure and Multilevel Continuous Local Cerebral Blood Flow Monitoring: Local Perfusion FluctuationsProposed methods for the measurement of regional renal blood flow using heat transfer analysisAnnals of Biomedical Engineering, Vol. 13, No. 3-4Cortical blood flow: thermal diffusion vs isotope clearance.Stroke, Vol. 12, No. 4The effect of alpha-adrenergic innervation on caudate blood flowAnnals of Neurology, Vol. 7, No. 2NONINVASIVE MEASUREMENT OF NET OXYGEN TRANSPORT: A FEASIBILITY STUDYCerebral blood flow regulation. II. Vasodilator mechanisms.Stroke, Vol. 8, No. 2Cerebral blood flow regulation: vascular resistance adjustments in the circle of Willis.Stroke, Vol. 7, No. 2 More from this issue > Volume 22Issue 5May 1967Pages 1026-9 https://doi.org/10.1152/jappl.1967.22.5.1026PubMed6025742History Published online 1 May 1967 Published in print 1 May 1967 Metrics