The transient thermal clearance method for regional blood flow measurement--the influence of tissue heat conduction

Circadian periodicity of cerebral blood flow revealed by laser-Doppler flowmetry in awake rats: relation to blood pressure and activity

Cardiovascular parameters such as arterial blood pressure (ABP) and heart rate display pronounced circadian variation. The present study was performed to detect whether there is a circadian periodicity in the regulation of cerebral perfusion. Normotensive Sprague-Dawley rats (SDR, approximately 15 wk old) and hypertensive (mREN2)27 transgenic rats (TGR, approximately 12 wk old) were instrumented in the abdominal aorta with a blood pressure sensor coupled to a telemetry system for continuous recording of ABP, heart rate, and locomotor activity. After 5-12 days, a laser-Doppler flow (LDF) probe was attached to the skull by means of a guiding device to measure changes in brain cortical blood flow (CBF). After the animals recovered from anesthesia, measurements were taken for 3-4 days. The time series were analyzed with respect to the midline estimating statistic of rhythm (i.e., mean value of a periodic event after fit to a cosine function), amplitude, and acrophase (i.e., phase angle that corresponds to the peak of a given period) of the 24-h period. The LDF signal displayed a significant circadian rhythm, with the peak occurring at around midnight in SDR and TGR, despite inverse periodicity of ABP in TGR. This finding suggests independence of LDF periodicity from ABP regulation. Furthermore, the acrophase of the LDF was consistently found before the acrophase of the activity. From the present data, it is concluded that there is a circadian periodicity in the regulation of cerebral perfusion that is independent of circadian changes in ABP and probably is also independent of locomotor activity. The presence of a circadian periodicity in CBF may have implications for the occurrence of diurnal alterations in cerebrovascular events in humans.

Faster procedure for deriving regional blood flow by the noninvasive transient thermal clearance method

The noninvasive transient clearance method provides absolute quantitative measurement of skin blood flow. It is based on thermally insulating the skin under investigation and measuring the time constant of the resultant exponential skin temperature increase. Conventional assessment of the time constant, by measuring the temperature increase until final equilibrium skin temperature is achieved, has the disadvantage of long time of measurement. A procedure shortening the measurement time is presented. The time constant of the exponential temperature increase is calculated without obtaining the final equilibrium temperature. The method can be used for calculating the time constant of an exponential change of any variable, even though the asymptotic value of that variable is not known.

The relationship between systolic blood pressure and microvascular resistance in non-diabetic and diabetic subjects

Skin blood flow and microvascular resistance were measured in the feet of hypertensive and normotensive subjects by the non-invasive transient thermal clearance method. Skin blood flow decreased and microvascular resistance increased as a function of systolic brachial blood pressure for the non-diabetic subjects who were not treated by vasoactive medication. The relationship between blood flow and systolic blood pressure for diabetic patients and for patients who were treated by enalapril was poor. The average resistance for non-diabetic patients treated by enalapril was lower than that of untreated non-diabetic subjects. For diabetic patients no significant difference in resistance between enalapril treated and untreated patients was found. The results demonstrate that for non-diabetic patients the role of microvascular resistance in hypertension is significant while it is less important in diabetic patients.

Detection of breast cancer by measuring areolar blood flow--a pilot study

Regional blood flow in the areola was measured by using the non-invasive transient thermal clearance method in normal breasts and in breasts involved with cancer. Areolar blood flow (ABF) in normal breasts was almost constant for women in the age range 20-60y, but decreased at higher ages. ABF in breasts involved with cancer was higher than that in the contralateral breast, and higher than the average normal ABF in the corresponding age group. The effect was more prominent in the left breast. The transient thermal clearance method provides a potential non-invasive means for detection of breast cancer.