Increased facial temperature as an early warning in Sudden Infant Death Syndrome

Hyperthermia and Heat Stress as Risk Factors for Sudden Infant Death Syndrome: A Narrative Review

BACKGROUND AND OBJECTIVES

Heat stress and hyperthermia are common findings in sudden infant death syndrome (SIDS) victims. It has been suggested that thermal stress can increase the risk of SIDS directly via lethal hyperthermia or indirectly by altering autonomic functions. Major changes in sleep, thermoregulation, cardiovascular function, and the emergence of circadian functions occur at the age at which the risk of SIDS peaks-explaining the greater vulnerability at this stage of development. Here, we review the literature data on (i) heat stress and hyperthermia as direct risk factors for SIDS, and (ii) the indirect effects of thermal loads on vital physiological functions.

RESULTS

Various situations leading to thermal stress (i.e., outdoors temperatures, thermal insulation from clothing and bedding, the prone position, bed-sharing, and head covering) have been analyzed. Hyperthermia mainly results from excessive clothing and bedding insulation with regard to the ambient thermal conditions. The appropriate amount of clothing and bedding thermal insulation for homeothermia requires further research. The prone position and bed-sharing do not have major thermal impacts; the elevated risk of SIDS in these situations cannot be explained solely by thermal factors. Special attention should be given to brain overheating because of the head's major role in body heat losses, heat production, and autonomic functions. Thermal stress can alter cardiovascular and respiratory functions, which in turn can lead to life-threatening events (e.g., bradycardia, apnea with blood desaturation, and glottal closure). Unfortunately, thermal load impairs the responses to these challenges by reducing chemosensitivity, arousability, and autoresuscitation. As a result, thermal load (even when not lethal directly) can interact detrimentally with vital physiological functions.

CONCLUSIONS

With the exception of excessive thermal insulation (which can lead to lethal hyperthermia), the major risk factors for SIDS appears to be associated with impairments of vital physiological functions when the infant is exposed to thermal stress.

Temperature effects on neuronal firing rates and tonic-to-bursting transitions

Temperature fluctuations can affect neurological processes at a variety of levels, with the overall output that higher temperatures in general increase neuronal activity. While variations in firing rates can happen with the neuronal system maintaining its homeostatic firing pattern of tonic firing, or bursting, changes in firing rates can also be associated with transitions between the two patterns of firing. Our computer simulations suggest a possible mechanism directly related to the shortening of the duration of the action potential for higher firing rates with temperature increase. Increased temperatures also shorten the period doubling cascade and chaos transition between tonic and burting regimes.

Automated assessment and tracking of human body thermal variations using unsupervised clustering

The presented approach addresses a review of the overheating that occurs during radiological examinations, such as magnetic resonance imaging, and a series of thermal experiments to determine a thermally suitable fabric material that should be used for radiological gowns. Moreover, an automatic system for detecting and tracking of the thermal fluctuation is presented. It applies hue-saturated-value-based kernelled k-means clustering, which initializes and controls the points that lie on the region-of-interest (ROI) boundary. Afterward, a particle filter tracks the targeted ROI during the video sequence independently of previous locations of overheating spots. The proposed approach was tested during experiments and under conditions very similar to those used during real radiology exams. Six subjects have voluntarily participated in these experiments. To simulate the hot spots occurring during radiology, a controllable heat source was utilized near the subject's body. The results indicate promising accuracy for the proposed approach to track hot spots. Some approximations were used regarding the transmittance of the atmosphere, and emissivity of the fabric could be neglected because of the independence of the proposed approach for these parameters. The approach can track the heating spots continuously and correctly, even for moving subjects, and provides considerable robustness against motion artifact, which occurs during most medical radiology procedures.

Mechanisms Underlying Adaptation of Respiratory Network Activity to Modulatory Stimuli in the Mouse Embryo

Breathing is a rhythmic behavior that requires organized contractions of respiratory effector muscles. This behavior must adapt to constantly changing conditions in order to ensure homeostasis, proper body oxygenation, and CO₂/pH regulation. Respiratory rhythmogenesis is controlled by neural networks located in the brainstem. One area considered to be essential for generating the inspiratory phase of the respiratory rhythm is the preBötzinger complex (preBötC). Rhythmogenesis emerges from this network through the interplay between the activation of intrinsic cellular properties (pacemaker properties) and intercellular synaptic connections. Respiratory activity continuously changes under the impact of numerous modulatory substances depending on organismal needs and environmental conditions. The preBötC network has been shown to become active during the last third of gestation. But only little is known regarding the modulation of inspiratory rhythmicity at embryonic stages and even less on a possible role of pacemaker neurons in this functional flexibility during the prenatal period. By combining electrophysiology and calcium imaging performed on embryonic brainstem slice preparations, we provide evidence showing that embryonic inspiratory pacemaker neurons are already intrinsically sensitive to neuromodulation and external conditions (i.e., temperature) affecting respiratory network activity, suggesting a potential role of pacemaker neurons in mediating rhythm adaptation to modulatory stimuli in the embryo.

Infrared thermal imaging system on a mobile phone

A novel concept towards pervasively available low-cost infrared thermal imaging system lunched on a mobile phone (MTIS) was proposed and demonstrated in this article. Through digestion on the evolutional development of milestone technologies in the area, it can be found that the portable and low-cost design would become the main stream of thermal imager for civilian purposes. As a representative trial towards this important goal, a MTIS consisting of a thermal infrared module (TIM) and mobile phone with embedded exclusive software (IRAPP) was presented. The basic strategy for the TIM construction is illustrated, including sensor adoption and optical specification. The user-oriented software was developed in the Android environment by considering its popularity and expandability. Computational algorithms with non-uniformity correction and scene-change detection are established to optimize the imaging quality and efficiency of TIM. The performance experiments and analysis indicated that the currently available detective distance for the MTIS is about 29 m. Furthermore, some family-targeted utilization enabled by MTIS was also outlined, such as sudden infant death syndrome (SIDS) prevention, etc. This work suggests a ubiquitous way of significantly extending thermal infrared image into rather wide areas especially health care in the coming time.

Hyperthermia Modulates Respiratory Pacemaker Bursting Properties

Most mammals modulate respiratory frequency (RF) to dissipate heat (e.g., panting) and avoid heat stroke during hyperthermic conditions. Respiratory neural network activity recorded in an isolated brain stem-slice preparation of mice exhibits a similar RF modulation in response to hyperthermia; fictive eupneic frequency increases while inspiratory network activity amplitude and duration are significantly reduced. Here, we study the effects of hyperthermia on the activity of synaptically isolated respiratory pacemakers to examine the possibility that these changes may account for the hyperthermic RF modulation of the respiratory network. During heating, modulation of the bursting frequency of synaptically isolated pacemakers paralleled that of population bursting recorded from the intact network, whereas nonpacemaker neurons were unaffected, suggesting that pacemaker bursting may account for the temperature-enhanced RF observed at the network level. Some respiratory neurons that were tonically active at hypothermic conditions exhibited pacemaker properties at approximately the normal body temperature of eutherian mammals (36.81 ± 1.17°C; mean ± SD) and continued to burst at 40°C. At elevated temperatures (40°C), there was an enhancement of the depolarizing drive potential in synaptically isolated pacemakers, while the amplitude of integrated population activity declined. Isolated pacemaker bursting ceased at 41–42°C ( n = 5), which corresponds to temperatures at which hyperthermic-apnea typically occurs in vivo. We conclude that pacemaker properties may play an important role in the hyperthermic frequency modulation and apnea, while network effects may play important roles in generating other aspects of the hyperthermic response, such as the decreased amplitude of ventral respiratory group activity during hyperthermia.

Peripheral chemoreceptor activity in sleeping neonates exposed to warm environments

In neonates, it is often assumed that ventilatory control and heat stress interact. Thus the two factors have been implicated in various pathologies (apnoea, sudden infant death syndrome). However, little is known about the mechanisms of this interaction, and the influence of sleep is still debated. This study aimed at determining the influence of warm exposure on the decrease in ventilation during a hyperoxic test (HT), which is considered to be a measure of peripheral chemoreceptor activity. The test was performed in active (AS) and quiet sleep (QS) in 12 neonates exposed to thermoneutral or warm environments. The HT consisted of 30 s of inspired, 100% O(2). The ventilatory response was assessed in terms of a response time, defined as the time elapsing between HT onset and the first significant change in V(E). Our results show that, in both thermal conditions, the fall in V(E) was higher in AS than in QS. Warm exposure significantly enhanced the ventilatory response in AS (-27.5 +/- 8.7% vs. -38.3 +/- 8.8%, P < 0.01) but not in QS. A thermometabolic drive or inputs from thermoreceptors could be involved in the reinforcement of peripheral chemoreceptor activity in AS in warmer environments, which could contribute to an increasing risk of apnoea in neonates with altered chemoreceptor function. Since hypothalamic structures are involved in thermoregulatory, sleep processes and (probably) in respiratory control, it could well be the principal site where this interaction occurs.

Mesial temporal lobe seizures may activate thermoregulatory mechanisms in humans: an infrared study of facial temperature

Facial temperature T(f), an important link in cerebral thermoregulation and an ignored index of autonomic activity, was studied in three patients with mesial temporal epilepsy. Sets of infrared images were obtained automatically during seizures and also hourly, round-the-clock. For each patient, scan sets were sorted into: (1) ictal; (2) interictal with negligible motion; and (3) interictal with motion. Comparisons of mean, variance, and trend in each scan set among these groups showed considerable variability. However, significant trends in T(f) occurred (P<0.05) in two-thirds of seizures in one patient, three-fourths in another, and two-ninths in the third, consisting of steady decreases in T(f) beginning at peak seizure intensity R(max) and continuing into the postictus. Maximal ictal T(f) was greater than interictal T(f) (P<0.05), but it negatively correlated with R(max) in two subjects. The ictal changes in T(f), which may have a homeostatic role, suggest activation of thermoregulatory mechanisms during mesial temporal seizures.

Response of the respiratory network of mice to hyperthermia

Most mammals modulate respiratory frequency (RF) to dissipate heat (i.e., panting) and avoid heat stroke during hyperthermic conditions. During hyperthermia, the RF of intact mammals increases and then declines or ceases (apnea). It has been proposed that this RF modulation depends on the presence of higher brain structures such as the hypothalamus. However, the direct effects of hyperthermia on the respiratory neural network have not been examined. To address this issue, the respiratory neural network [i.e., ventral respiratory group (VRG)] was isolated in a brain stem preparation taken from the medulla of mice (P0 -P6). Integrated population activity, predominated by inspiratory neurons, was recorded extracellularly from VRG neurons. The bath temperature was then heated from 30 to 40 degrees C, resulting in a biphasic frequency response in VRG activity. Following an initial six- to sevenfold increase and subsequent decline, fictive RF was maintained at a frequency that was higher than baseline frequency; at 40 degrees C, the RF was maintained at about two to four times that at 30 degrees C. The inspiratory burst amplitude and duration were significantly reduced during hyperthermic conditions. An increase in RF and decrease in VRG burst amplitude and duration also occurred when heating from 37 to 40 degrees C. Fictive apnea typically occurred during cooling to the control temperature. Furthermore, changes in hypoglossal motor nucleus activity paralleled those of the VRG, suggesting that temperature modulation of the VRG is likely to have a behaviorally relevant impact on respiration. We conclude that the VRG activity itself is modulated during hyperthermia and the respiratory network is particularly sensitive to temperature changes.