Biomedical subjects
Publications and source records attributed to J Timbal.
The consequences of gynecological disorders and pregnancy are reviewed, as well as the impact of the stresses of aerospace on female and feto-maternal physiology. Current regulations leave the physician a high degree of discretion. Most of the restrictions on employment which do exist are not due to gynecological reasons.
In order to test the reality of a circadian evolution of systolic time intervals, an experiment was conducted on six subjects resting in a supine position for 24 h. Heart rate (HR), systole (S), diastole (D), presystole (PS), isovolumetric contraction time (IVCT), normal and corrected ventricular pre-ejection and ejection time (LPEP, LPEPc, LVET, LVETc) were computed by electric rheoplethysmography every 3 h in supine and sitting positions. Evidence of the existence of a circadian rhythm was clear in supine subjects; especially LPEP and LVET acrophases were, respectively, 4.03 +/- 2.36 h and 4.31 +/- 1.15 h. In sitting subjects, a circadian rhythm was evidenced for IVCT, LVETc and LPEP/LVET, and on the difference of resting-sitting for PS, IVCT and LPEP, suggesting a decrease in orthostatic tolerance at the end of the night. However, values for characteristics of circadian rhythms (mean, amplitude, phase) strongly depend upon experimental conditions (position, activity, diet). A phase difference between systolic times and HR was also observed. This phenomenon was due to an advance in phase of D relative to S. Finally, all these results show that it is always necessary to take circadian factors into consideration during cardiovascular studies, especially for the preparation of protocols and the interpretation of results.
An experiment was conducted to validate the use of electrical impedance plethysmography for measuring systolic time intervals. This method is of interest in aerospace medicine since it is a noninvasive technique and very easy to use without causing discomfort to the subject. The equipment, with electrodes placed in front of the heart, gave both the first derivative of the electrical impedance variation and the E.C.G. The tracings were compared to simultaneous recordings of either the carotid pulse or blood pressures obtained by right and left catheterization. The results did not permit us to determine the right side systolic times. However, demarcated points of the plethysmogram permitted us to determine accurately the beginning of left mechanical systole and aortic opening and closure. Consequently, this method can determine the left ejection time (LPEP), the left isovolumetric contraction time (LIVCT), and the ventricular ejection time (LVET) with good accuracy.
This paper describes a statistical technique which permits study of, for example, complex biological rhythms with a known fundamental period. This technique uses the principles of variance analysis. The main calculation phases are: the regression calculation on a periodic time function; the study (by variance analysis) of the validity of the mathematical model; the study of the parallelism between subjects; and, finally, the study of the significance of each harmonic component. The calculation is completed by determining confidence intervals: those of the harmonic function parameters, followed by those of the function extremes.
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Subjects exposed to tolerable thermal constraints of equal intensity at rest and during exercise start sweating at lower mean body temperatures during exercise and the sweating rate increases faster during exercise than at rest.
The steady-state convective heat transfer coefficient in water has been determined by partitional calorimetry for 17 nude subjects. Four water velocities were investigated: 0, 0.05, 0.10, and 0.25 m-s-1; and the water temperature ranged from 33.7 to 18 degrees C. In still water, hc varied from 43 W-m-2-degrees C-1 in thermoneutral conditions and a shivering rate less than 90 W-m-2 to 54 W-m-2-degrees C-1 in cold water with a shiver rate greater than 110 W-m-2. The equation, hc=0.09 (Gr-Pr)0.275, give a good approximation of this coefficient. In stirred water and for the same limits of shivering, hc can be expressed as a power function of the velocity: hc = 272.9 v0.5 and hc = 497.1 v0.65, respectively. These equations show that the flow is laminar in thermoneutral conditions and intermediate between laminar and turbulent in cold water. A study of the influence of skinfold on the magnitude of hc shows that higher values of this coefficient were obtained for thin subjects than for fat ones, concomitant with more intense shivering. The utilization of a theoretical physical model for computations of hc gave excessively high values because such methods do not embody the body shape factor and reduction of water flow adjacent to the skin.
Metabolic rate (M), mean skin temperature (Tsk) and rectal temperature (Tre) were studied during 2 h exposure to cold in the air (Ta = 15-25 degrees C) and in water (TH2O = 24-32 degrees C). From the results, it was possible to draw tentative equations of the metabolic response in transient and steady state as functions of body temperatures: Mair = 41,3-57.77 dTsk/dt-5.01 (Tskt-Tsk0) and Mwater = Mair + 984.15-23.79 Tre. These equations show an important difference between the two groups of experiments: in water, both Tsk and Tre are required, whereas Tsk suffices in air. This leads to discuss the usage of mean weighted skin temperature and rectal temperature to describe peripheral and central input respectively, specially on man in cold air, in the range of these experiments.
A mathematical model has been developed to anticipate the physiological responses and the thermal state of a naked human under exposure to cold, taking into account his morphological characteristics (skinfold, size, weight) and the environmental conditions (air or water temperature and velocity, barometric pressure and hygrometry). The skinfold conditions the body's thermal conductance and the metabolism depends both on rectal (Tre) and mean skin (Tsk) temperatures. After being tested, this model was used to study the evolution of Tre. It shows the influence of the skinfold which accounts for most of the inter-individual differences. It also permits discussion of survival possibilities during immersion and completes data provided by previously established curves.
Sweat rates and body temperatures of human subjects were measured at 0200, 1000, and 1800 h during a heat exposure of 90 min. The latent period of sweating was not significantly altered in the evening but significantly shortened during the night. Mean body temperature corresponding to the onset of sweating was nearer to the basal body temperature during the night, while during the day the difference between these two temperatures became larger. This phenomenon seems related to the circadian cycle of vasomotor adjustment, since during the night body conductance was higher than during the day and corresponded to a state of a vasodilatation similar to that observed at the onset of sweating. During the day, this situation was reversed. During steady state, the following changes were observed: sweating rate, night less than morning less than evening; skin temperatures, night less than morning less than evening; and rectal temperature increase, morning less than evening less than night. It is hypothesized that these changes are due to either different metabolic rates or an imbalance between heat gains and losses which preserve the circadian rhythm of the body temperature, even under thermal loads.
From a practical viewpoint, thermal sweating during exercise can be described by an exponential equation. The errors from this mathematical model are of few importance. Nevertheless, metrologic and physiological factors can complicate theoretically the model.
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