Thermoregulatory Response Of The Human Body Physical Education Essay

Introduction

The human body relies upon the maintenance of a stable internal environment at reasonably consistent thermal conditions, ranging from 36-37Ëš Celsius, (Rhoades et al, 2003). Deviations from this narrow range can cause catastrophic and even debilitating conditions. This is important such as when the body is under cold stress. Thermoregulation is dependent on the integration of signals from peripheral thermoreceptors, conveying information about skin temperature; and central thermoreceptors which monitor core temperature. Both peripheral and central thermoreceptor afferents go to the posterior hypothalamus (Longstaff, 2005), where temperatures detected outside the thermoneutral range is initiated with appropriate physiological responses to return core body temperature to normal.

Key physiological mechanisms in response to the decrease in environmental temperature is to reroute blood flow from the periphery to the core organs that is, peripheral vasoconstriction to conserve body heat, shivering which increases muscular activity, tone and metabolic rate, and piloerection which is able to contribute to heat conservation.

The autonomic nervous system (ANS) is divided into two categories: the sympathetic nervous system, stimulating various effector organs, heart rate and force, and blood flow to the skin as well as to the skeletal muscles and brain, whereas the parasympathetic nervous system is primarily involved in conserving the body’s resources and maintaining organ functions during periods of physical inactivity such as slowing down heart rate and stimulating digestion (Brown et al, 2006).

Temperature regulation can function to control the sympathetic activity to cutaneous vessels and subsequently peripheral blood flow. Thus cutaneous vessels are influenced by reflexes involved in both arterial pressure regulation and temperature regulation (Mohrman & Heller, 2006), such as, an increase in baroreceptors firing rate results in a decrease in sympathetic output and simultaneous increase in parasympathetic output.

Potential applications for this study may be applied to modern-day research in both the science and medical fields with regards to frostbite, hypothermia and trench foot. By gaining an insight to the underlying mechanisms involved, this may also be relevant to the development of drugs and prevention methods in reducing potential side effects to the human body with regards to conditions and illnesses brought on by hypothermia.

The idea of this study is to investigate the contribution of thermoreceptor activity in maintaining homeostasis not only during cold stress but also, overall temperature control mechanisms activated by the body, but also the main thermoreceptor activity the body gives precedence to in response to a conflicting thermal stimulus to the periphery while under cold stress. This will be achieved by observing the alterations of each parameter of oral and core temperatures as well as heart rate, blood pressure, skin temperatures, patella reflex, metabolic rate and respiratory rate from set point values each taken before the cooling period and relevant parameters during the extra testing.

Method

Subjects Studies were conducted upon 19 healthy subjects of which 10 were male and 9 female (age: 19.47 +/- 0.22 yr; height: 169.81 +/- 2.36 cm; weight: 68.31 +/- 3.00 kg). Subjects where selected voluntarily, were not taking medication(s) and where informed prior to experimentation about the objectives of the study and procedures involved. The experiments were conducted within the same day with participation from all subjects.

Protocol design and practice of measurements Consumption of food 30 minutes prior to testing was prohibited and bladders to be emptied immediately before experimentation. Subjects wearing shorts and a t-shirt were seated in a relaxed, sitting position on a chair for 40 minutes at room temperature of 22°C where the appropriate physiological data was recorded at 10 minute intervals – the control period. Within each 10 minute interval the core temperature, oral temperature and respiration rate were recorded once, blood pressure and patella reflex recorded twice; and heart rate and all skin temperatures were recorded three times. Upon completion of the control period that is, after 40 minutes, baseline values were established for each parameter. At time points 10, 20, 30 and 40 minutes, the following parameters were measured:

Core Temperature: To measure core temperature, a soft-thermistor was used, this entailed the ear to be cleaned before the subject slowly placed the thermistor into the auditory canal. A small amount of cotton wool was used to plug the canal which prevented both air from entering and the thermistor from falling out before it was heavily taped down. The core temperature is monitored for the length of the entire experiment (80 minutes) and measurements recorded once for every 10 minute interval during the cooling period.

Oral Temperature: A clinical thermometer was used to measure the oral temperature. The thermometer was placed beneath the tongue and held in this position for 2 minutes while lips were closed. Temperature was recorded once within each 10 minute interval of the control period.

Skin Temperature: Using the “Ezi Scan” thermometer, skin temperature for the forehead, forearm and finger were measured. This was held without making contact, as close as possible to the target area, with all three skin temperature measurements recorded three times during each 10 minute interval.

Blood Pressure: An automatic blood pressure machine was used to record blood pressure. Systolic and diastolic blood pressure measurements were recorded twice for every 10 minute interval simultaneously. The machine was able to automatically record blood pressure as it had an electronic sensor that detected blood flow. Once the individual had placed the monitoring cuff around their arm, the cuff was inflated to a pressure greater than the systolic pressure. The monitor continued to measure pressure as the cuff deflated until it was lower than the diastolic pressure. The device then gave a digital readout of the systolic and diastolic pressures.

Heart Rate: To measure heart rate a heart rate monitor consisting of a transmitting belt and a receiving watch were utilised. Water was placed on the transmitting electrodes and attached on the chest. Measurements were taken three times for every 10 minute interval of the control period.

Patella Reflex: A patella reflex hammer was used to obtain patellar reflexes from the subject. The approximate angle of knee extension is recorded with a protractor twice during the 10 minute interval.

Respiration rate and Metabolic rate: Respiratory rate was calculated using the formula: f(number breaths)/3 minutes. This required the use of the Douglas bag method which collected the total volume of expired air over a three minute period while E and FEO2 were determined from the data collected from the gas analyser and gas meter.

Metabolic rate was determined from oxygen consumption under the assumption that expired volume is equal to inspired volume and that 20.1KJ of energy was produced with one litre of oxygen consumption. Oxygen consumption rate was determined using: O2 (l/min) = E (pulmonary ventilation per minute) x (0.2093- FEO2).

Lastly, metabolic rate was determined by: O2 (l/min) x 20.1(Kj/l) x 60/ Body surface area (m2), where the body surface area (m2): 0.00718 x (weight in kg^0.425) x (height in cm^0.725)

During the 40 minute cooling period immediately following the control period, the lower limbs of the subject, just over the knees were placed in cold water (10-12°C) and a large fan was placed to blow air over the back for the course of the cooling period. The data obtained for each parameter was recorded at 10 minute intervals at timepoints 10, 20, 30 and 40 minutes as per the method used in control period.

Extra Test The control period for the extra test commenced immediately after the completion of the cooling period during which relevant parameter values were recorded and baseline data was established, while the subjects’ legs were still immersed in water and the fan still blowing cold air. The initial set of control measurements, the core and oral temperatures, skin temperatures, blood pressure and heart rate were measured once as soon as the control for the extra test started. Upon obtaining baseline values, the extra test was conducted with the subject’s hand placed in a bucket of warm water while the fan was still on and the lower limbs still immersed in the cold water bath. This occurred for a five minute period and measurements of the parameter were taken at 30 second intervals. Core temperature and the three skin temperatures as well as heart rate were taken at every 30 second interval, whereas oral temperature was taken at every minute mark; 1, 2, 3, 4 and 5. However, blood pressure was measured at 1, 3 and 5 minutes. Extra test and cooling was stopped after the final measurements had been taken.

Statistical analysis

A paired t-test was used to compare two data sets, each control value with the previous control value and evaluate whether they were significantly different. Each control value was compared to the previous control value which would ensure that the subjects were in a relaxed, constant state. The different parameter for the cooling values were then compared with the final control time point, t=-10 minutes for each respective parameter. All intervals of the extra test were compared against the control for each extra test parameter. Differences were considered statistically significant if the p-value was less than 0.05.

Other statistical analyses were also included in the graphical representation. Error bars in both vertical directions which were used on the graphs to indicate the error in a reported measurement which provides a general idea of variability. The standard deviation was also calculated where it is used to measure the variability of a data set, but more importantly, the measure of confidence in statistical inferences whereas the standard error of mean represented the accuracy of the mean. The two are linked: SEM = SD/(square root of sample size).

Results

Figure 1 shows that core temperature declined significantly (pFigure 2 indicates the changes in skin temperature of the forehead, forearm and finger during a control period and cooling period. During the cooling period, all body temperatures decreased. Significant values to coincide with the decrease during the cooling period from t=-10min of the control period were obtained (pFigure 3 illustrates the changes in systolic and diastolic blood pressures as well as mean arterial pressure, during a 40min control period in which each control timepoint was compared with the pervious and 40min cooling period where values obtained were compared with t=-10min of the control period. It can be deduced that all blood pressures initially increased before reaching a relatively steady state during the cooling experiment. Significant values (pFigure 4 indicates that heart rate declined throughout the control and cooling periods with significant values suggesting this decline as compared with previous control timepoints at t=-10min of the control period respectively (pFigure 5 shows the changes in the angles obtained with the patella reflex. However, no significant values were obtained in either the control or cooling periods when compared with the previous control time or t=-10min of the control period respectively (pFigure 6 indicates the differences in respiratory rate during a control and cooling period. Although the rate remained constant, significant values (pFigure 7 shows the differences in litres of expired ventilation of the data set. However, no significant values were obtained in either the control or cooling periods, therefore parameter did not alter significantly upon comparisons with previous control or final 40min mark of control value respectively, (pFigure 8 illustrates the changes in the volume (litres) of oxygen consumption throughout the entire experiment, the control and cooling periods. However, no significant values were obtained in either period (pFigure 9 shows the differences in metabolic rate (kJ/m2/hr) during the control and cooling periods. However, no significant values were obtained throughout the experiment upon comparisons with previous control or final 40min mark of control value respectively; therefore parameter did not alter significantly (pFigure 10 indicates the changes in core and oral temperature during the extra testing period. Although significant values were obtained for core temperature, t=210sec p=0.0041, t=240sec p=0.0119, t=270sec p=0.0349, t=300sec p=0.0207, (36.16±0.17, 36.16±0.16, 36.17±0.16 and 36.16±0.16 – ËšC respectively); it remained constant whilst the subject’s hand was placed in warm water, and continuous cooling of lower limbs occurred simultaneously when compared to extra test control time, (p

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