Temperature monitor Dry gas volume meter
Adhesive Tape Thermometer
Nose clip Oxygen analyser
Mouthpiece Carbon Dioxide analyser
Inspiratory and expiratory valve Barometer
Wide bore tubing Stop clock
Scales
Method
The subject was weighed before the experiment started
One subject was needed for this experiment, who was wearing shorts and training shoes. The subject was weighed before the experiment started. The skin temperature probes were attached with adhesive tape to the subject’s body, one placed on the right of the sternum, one on the fingertip, and the other on the belly of the gastrocnemius muscle of the calf. The aural thermistor was then placed in the ear and covered up with cotton wool. One member of the group supervised the subject at all times whilst the other members of the group recorded on physiological measurement each.
The subject sat down in a chair in ambient temperature for 30 minutes and every 5 minutes their temperatures were recorded. Also, every 10 minutes their oxygen consumption was measured using the Douglas Bag technique. This method was performed by connecting the mouthpiece to the tubing, then the other end of the tubing to the expiratory side of the valve box, which was connected to the empty Douglas Bag.The valve was opened and the stop clock was started and the subject expirated into the Douglas Bag for a 5 minute period. A nose clip was placed on the subject’s nose so that all expirated air was collected in the Douglas Bag. After the 5 minute period the valve was closed and the clock was stopped. The Douglas Bag was then taken to the dry gas volume meter which also has the oxygen analyser connected to it and was connected to the apparatus. The bag was then gently squeezed to expel its contents. The volume was then read off and the oxygen carbon dioxide meter value was noted. The temperature was also recorded.
After 30 minutes, the subject was again weighed and then placed in a hot temperature controlled room at 40 C with a relative humidity of 20%. Attached to the same equipment, the subject then cycled at 1.25kp for 30 minutes and the Douglas Bag method only had a duration of 3 minutes every 10 minutes. After 30 minutes the subject was quickly taken out of the hot room and was weighed. Exercise was then immediately resumed for another 30 minutes at the same rate and the temperatures and the expiration volumes were also measured. After the last 30 minute period the subject was removed from the hot room and weighed.
Results
See attached Excel spreadsheet:
Following the observations seen in the spreadsheet the following calculations were made to create a more accurate set of results:
M(metabolic rate) = VO2 x 21.2 x 1000
60 x S.A(m2)
21.2 = The energy that 1 litre of oxygen provides (kJ)
1000 = Converts kJ into J.
60 = Converts J per min to J per second.
S.A = Surface Area of body (m2) Measured using the surface area nomogram
W(mechanical energy) = Load(kp) x revs per min x 0.978
S.A (m2)
H = (T skin – T air)
(Rd) x S.A
T skin = Mean skin surface temperature
T air = Air temperature
Rd = Thermal resistance of clothing (0.07 in light clothing)
S.A = Surface area of body (m2)
E(evaporative heat loss) = Weight loss (g) x 2.4 x 1000
60 x tomes between weighings (mins) x S.A
1000 = Convert kJ into J
60 = Convert J per min into J per second
2.4 = on the assumption that 1g of water evaporated is the equivalent of 1kJ of heat energy lost
Discussion
There was an anomalous result discovered in the analysis of the experiment. There seemed to be a huge drop in heat balance after the resting stage of the experiment. We soon discovered that the subject was wearing a T-shirt in the first weighing process but when the subject was weighed for a second time, just before they were placed into the temperature controlled room, they had removed the T-shirt.
As seen in the ‘heat balance components’ graph, in the first thirty minutes of the experiment where the subject sat stationary in a chair, there was no heat loss and no heat gain therefore a heat balance. This is because the heat that is produced through respiration in the body is lost through mechanisms such as radiation where 60% of heat is lost via radiation as infrared electromagnetic waves from all objects at temperatures above absolute zero. Evaporation also occurs where sweat that is produced by the body is converted into vapour. There is also a small percentage of heat lost through convection and conduction. These mechanisms are stimulated due to the activation of the warmth receptors (Organs of Ruffini) which are situated in the dermis of the skin increase their firing frequency to the central thermoreceptors in the pre-optic region of the hypothalamus.
During the exercise phase of the experiment it was seen in the graphs that as exercise began, the heat production and heat loss increased. The heat production increases due to the increased rate of respiration, but the body has its own mechanisms to bring that temperature back down to normal. There is a regulation in cutaneous blood flow via the tone of the sympathetic nerve impulses. With increased heat there is a decrease in sympathetic nervous tone which causes vasodilation and increased blood flow to the skin which inevitably increases heat loss through radiation. During this process the venous return is superficial and the counter-current exchange is low due to the increased blood flow through the vascular beds. It is because of these mechanisms that the core temperature only varied by 1oC throughout the experiment. It is also due to the increased cutaneous blood flow that the mean skin temperature varied by around 5oC.Once environmental temperature exceeds body core temperature, the only effective method of heat loss is via the evaporation of sweat from the surface of the skin.This is done via the eccrine glands in which every person has two to three million of. These glands are coiled regions in the dermis which secrete sweat on stimulation via cholinergenic sympathetic nerves or the circulation of adrenaline or noradrenaline.
Due to the anomalous result that was identified, the heat balance curve that has been plotted has a sharp decrease at the beginning of exercise. From analysis of all the other values that were recorded it is seen that there should not be a large decrease in heat balance but there should be a gradual decline in heat balance which gives a smooth curve on the graph.
The values of heat loss and heat loss via evaporation show that all heat loss at rest is via other mechanisms rather than sweating but during exercise the main avenue for heat loss is through evaporation because the values for E are greater than that for H in the exercise stage of the experiment. As seen in ‘Heat Balance Components’ the body was in heat balance in only the rest stage of the experiment. The heat production was equal to heat loss.
To improve the accuracy of the experiment the subject should not be removed from the temperature controlled room to get weighed. There should be scales in the room. The temperature could also be recorded at more frequent intervals so that a more accurate curve can be plotted.
