Patient monitoring during and after open heart surgery by an improved deep body thermometer

Development of a new method for the noninvasive measurement of deep body temperature without a heater

The conventional zero-heat-flow thermometer, which measures the deep body temperature from the skin surface, is widely used at present. However, this thermometer requires considerable electricity to power the electric heater that compensates for heat loss from the probe; thus, AC power is indispensable for its use. Therefore, this conventional thermometer is inconvenient for unconstrained monitoring. We have developed a new dual-heat-flux method that can measure the deep body temperature from the skin surface without a heater. Our method is convenient for unconstrained and long-term measurement because the instrument is driven by a battery and its design promotes energy conservation. Its probe consists of dual-heat-flow channels with different thermal resistances, and each heat-flow-channel has a pair of IC sensors attached on its top and bottom. The average deep body temperature measurements taken using both the dual-heat-flux and then the zero-heat-flow thermometers from the foreheads of 17 healthy subjects were 37.08 degrees C and 37.02 degrees C, respectively. In addition, the correlation coefficient between the values obtained by the 2 methods was 0.970 (p<0.001). These results show that our method can be used for monitoring the deep body temperature as accurately as the conventional method, and it overcomes the disadvantage of the necessity of AC power supply.

A non invasive wearable sensor for the measurement of brain temperature

As the thermoregulation centres are deep in the brain, the cerebral temperature is one of the most important markers of fever, circadian rhythms physical and mental activities. However due to a lack of accessibility, the brain temperature is not easily measured. The axillary, buccal, tympanic and rectal temperatures do not reflect exactly the cerebral temperature. Nevertheless the rectal temperature is used as probably the most reliable indicator of the core body temperature. The brain temperature can be measured using NMR spectroscopy, microwave radiometry, near infrared spectroscopy, ultra-sound thermometry. However none of those methods are amenable to long term ambulatory use outside of the laboratory or of the hospital during normal daily activities, sport, etc. The brain core temperature "BCT" sensor, developed by the Biomedical Microsensors dpt of LPM at INSA-Lyon is a flexible active sensor using "zero-heat-flow" principle. The sensor has been used for experimental measurement: brain temperature during mental activity, and in hospital for the study of circadian rhythms. The results are in agreement with the measurement by the rectal probe. There are 2 versions of this sensor: a non ambulatory for the use in hospitals, and an ambulatory version using teletransmission. We are working for improving the autonomy of the ambulatory version up to several days. This wearable biomedical sensor (WBS) can be used for circadian assessment for chronobiology studies and in medical therapies.

Non-contact determination of vital sign alterations in hypovolaemic states induced by massive haemorrhage: an experimental attempt to monitor the condition of injured persons behind barriers or under disaster rubble

To assess a non-contact method to determine the physical alteration of human subjects confined behind a barrier or under disaster rubble, an experimental, non-contact monitoring system was tested on rabbits in a hypovolaemic state. New Zealand male rabbits behind a barrier were subjected to hypovolaemic shock induced by the withdrawal of arterial blood (2ml per 100g body weight). The hypovolaemic state was determined by linear discriminant analysis using non-contact-derived variables: heart rate X1 and respiratory rate X2. Sixteen rabbits were equally divided between the hypovolaemic and control groups. To obtain the heart and respiratory rates simultaneously, the fast Fourier transform (FFT) was performed on the 1215MHz microwave radar analogue output. The linear discriminant function calculated by non-contact-derived variables was negative in the eight hypovolaemic rabbits and positive in the eight controls, so that the linear discriminant function could distinguish the hypovolaemic group from the control group. The Mahalanobis D-square (an index for classification accuracy) was 5908; the classification error rate corresponding to this value was small and negligible. The hypovolaemic rabbits developed metabolic acidosis (HCO3- 18.6+/-11.1 mmol l(-1) and pH 7.15+/-0.18 in arterial blood). The systolic blood pressure of the hypovolaemic group and the control was 56+/-4 and 83+/-6 mmHg, respectively (p < 0.01). The proposed method appears promising for applications to monitor the condition of human subjects behind barriers or under disaster rubble.

A new method to detect systemic inflammatory response syndrome by continuous monitoring system: an experimental study in rats

A continuous monitoring system was designed for detection of systemic inflammatory response syndrome (SIRS) using spectrum analyser and local temperature mapping system with deep body thermometer. This method demonstrated significant increases of heart and respiratory rates and deep body temperature from normal levels within 120 minutes after lipopolysaccharide administration in rats. Our monitoring system appears promising for clinical detection of SIRS in the early stages to prevent multiple organ failure.

A Novel Method to Prevent Secondary Exposure of Medical and Rescue Personnel to Toxic Materials Under Biochemical Hazard Conditions Using Microwave Radar and Infrared Thermography

In order to prevent secondary exposure of medical personnel to toxic materials under biochemical hazard conditions, we performed a noncontact determination of exposure to toxic conditions via 1215-MHz microwave radar and thermography. A toxic condition was induced by intravenous administration of lipopolysaccharide (LPS) in rabbits. The exposure to LPS was determined by linear discriminant analysis using non-contact derived variables.

Comparison of distal oesophageal temperature with "deep" and tracheal temperatures

PURPOSE

To compare distal oesophageal (reference) temperature with "deep-sternal," "deep-forehead," and tracheal temperatures, establishing the accuracy and precision of each.

METHODS

We studied 20 patients undergoing general anaesthesia for gynaecological surgery. Their lungs were mechanically ventilated with a circle system, at a fresh-gas flow rate of 6 L.min-1 Respiratory gases were not warmed or humidified. Tracheal temperatures were recorded from a Trachelon tube inserted approximately 21 cm. Deep-body temperatures were measured at the sternum and forehead using a Coretemp thermometer. The principle of the method is to null thermal flux through a cutaneous disk, thus obliterating thermal gradients between the sides of the disk, skin surface, and subcutaneous tissues. Distal oesophageal temperatures were measured from thermocouples incorporated into oesophageal stethoscopes. Tracheal and deep-tissue temperatures were compared with oesophageal temperature using regression and Bland and Altman analyses.

RESULTS

Tracheal, sternal, and forehead temperatures correlated similarly with distal oesophageal temperature, correlation coefficients (r2) being 0.7 in each case. The offset (oesophageal temperature minus study site) was considerably larger for tracheal temperature (0.7 degree C) than for the other sites (0.2 degree C). However, the precision was only 0.3 degree C at each site.

CONCLUSION

Our data suggest that tracheal temperatures may not be an adequate substitute for conventional core-temperature monitoring sites. In contrast, the accuracy and precision of deep-tissue temperature monitoring at the sternum and forehead was sufficient for clinical use.

Evaluation of the peripheral circulatory status of the neonate during homeothermal adjustment by plethysmo-time-interval

The plethysmo-time-interval (PTI) is the time interval between the beginning of the QRS complex on an ECG and the upstroke of the pulse wave on a plethysmogram, as measured by pulse oximetry. In the present study, we investigated homeothermal acclimatization to the extra-uterine environment in human neonates using the Coretemp thermometer and a pulse oximeter. Temperature was measured at three sites: the central deep temperature (CDT) on the upper sternum, the peripheral deep temperature (PDT) on the flat part of the left sole of the foot and the surface temperature (ST) at the side of the abdomen. After delivery, CDT and ST were higher than PDT. The difference between CDT and PDT was large at first, but gradually decreased. PDT, initially in the range of 32.4 +/- 0.28 degrees C, reached a stable value (34.4 +/- 0.41 degrees C) at 2.5 h after delivery. PTI was prolonged in parallel with PDT. The difference between CDT and PDT probably reflected the contraction of skin vessels, particularly the arterioles, which occurs as a body defense mechanism against heat loss. As PTI was prolonged in parallel with PDT, we demonstrated objectively that this catch-up phenomenon of PDT after delivery was affected by the increase in skin blood flow as a result of dilatation of peripheral arterioles. It was concluded that PTI can be used to evaluate the peripheral circulatory status of the neonate, even during homeothermal adjustment after birth, by applying a new principle of pulse oximetry that is widely used in neonatal intensive care units.

The application of intrascrotal deep body temperature measurement for the noninvasive diagnosis of varicoceles

The authors used intrascrotal deep body (intratesticular) temperature measurement in an attempt to make the diagnosis of varicoceles more objective. Two hundred five male patients complaining of infertility were classified into three groups: group A consisted of 84 patients with varicocele; group B of 66 patients without varicocele; and group C of 55 patients after varicocelectomy. The bilateral intrascrotal temperatures were recorded in the supine position and then monitored continuously in the standing position. The maximum temperatures in both positions were compared between each group. The mean temperature of the varicocele group was higher than that of the other two groups in the standing position. The authors studied the difference in temperature (delta T) due to postural change from supine to standing. The mean delta T of the left testis was +0.78 degrees C in the varicocele group, whereas it was approximately -0.5 degrees C in the other two groups. The authors conclude that deep body temperature provides a practical index of the intrascrotal temperature and is useful as one of the objective, clinical criteria for the diagnosis of varicocele.