Measuring haemodynamic variables using different techniques and examining the effects of diving reflex, isometric muscle contraction and psychological stress on these variables.
Haemodynamics is the study of factors that determine the movement of blood (Widmaier et al, 2011). The main haemodynamic factors are heart rate and blood pressure. Heart rate is defined as the number of times the heart contracts per minute. Normal resting heart rate in adults ranges between 60 – 100 beats per minute. Monitoring heart rate regularly is important to diagnose medical conditions such as high heart rate (tachycardia) and low heart rate (bradycardia). Heart rate monitors are also used during exercise to heighten efficiency of and individual’s training (Pocock and Richards, 2004).
Blood pressure is the pressure that the blood exerts against the blood vessel walls, especially the walls of the arteries. Two types of blood pressure are recorded; systolic blood pressure – when pressure is high during ventricular systole – and diastolic blood pressure – when pressure is low during ventricular relaxation. Monitoring blood pressure is important because it allow changes to be detected. The common condition of high blood pressure is often asymptomatic, making it difficult to be realised until complications occur (Walerstein, 2010). Diving reflex is a reflex of mammals, reptiles, and birds that causes the body to respond in a number of different ways when the trigeminal facial nerves are stimulated or when the body undergoes apnea. These nerves are stimulated when the face comes in contact with cool water (below 21C). The colder the water, the quicker the physiological changes occur. The physiological changes that occur are bradycardia (slowing down of heart rate) and peripheral vasoconstriction (narrowing of blood vessels). Peripheral vasoconstriction occurs to reduce blood flow to limbs and increase blood flow to organs that require the most oxygen.
A decrease in blood flow increases pressure (Rennie, 2012) Isometric contraction is a phase of normal muscle contraction in which the muscle does not produce any movement externally but internal muscle tension increases. (Marieb and Hoehn, 2004). Isometric contraction causes heart rate to quickly increase initially and depending on the duration and intensity of the exercise heart rate can increase again gradually. Both systolic and diastolic blood pressures also increase. Stress is defined as the changes the body undergoes as it reacts to a stressor. Psychological stress refers to stress that affects the mind such as trauma. A stressor is an agent which causes the body to deviate from its normal homeostatic state. Stress reducing responses that occur include increased adrenaline and noradrenaline production. This increases heart rate and blood pressure (Torpy et al, 2007). The aims of this experiment were to measure heart rate/blood pressure using different methods and to determine the effects of different stressors on haemodynamic variables. Method
The methods were carried out as described in the laboratory schedule (Coventry University, 2012) Results
Blood pressure was measured using two different techniques; a sphygmomanometer and an automatic BP monitor. The results from the sphygmomanometer showed a mean systolic blood pressure (SBP) of 90mmHg and a standard deviation value of 3.74mmHg. Diastolic blood pressure (DBP) had a mean value of 63.4mmHg and a standard deviation value of 4.22mmHg. Mean arterial pressure (MAP) which is calculated below, had a mean value of 72.2mmHg and a standard deviation value of 3.77mmHg. This is shown below in (Fig 1.).
Figure 1. Blood pressure results produced by a sphygmomanometer
The results from the automatic BP monitor showed a mean SBP of 99.8mmHg and a standard deviation value of 6.9mmHg. DBP was recorded with a mean value of 66mmHg and a standard deviation value of 2.24mmHg. MAP had a mean value of 77.2mmHg and standard deviation of 1.33mmHg (Fig 2.). Figure 2. Blood pressure results produced by an automatic BP monitor.
Heart rate was measured by using a stethoscope and also by palpitation. Using the stethoscope the mean heart rate calculated was 80bpm. The standard deviation value was 5.52bpm. The mean heart rate measured using palpitation was 79.4bpm and the standard deviation value was 12.48bpm (Fig 3). Table 2. Heart rate results for group members using a stethoscope and palpitation Heart Rate (bpm)
Heart rate was measured using a stethoscope and blood pressure was measured using a sphygmomanometer. There was a rest interval between each experiment. The mean rest HR, SBP and DBP were 73bpm, 120mmHg and 76mmHg respectively. After two minutes of isometric contraction, HR and SBP increased to 80bpm and 129mmHg respectively and DBP decreased to 74mmHg. After 2 minutes of trigeminal stimulation, HR and DBP increased to 75bpm and 78 mmHg respectively and SBP decreased to 115mmHg. After the arithmetic test, HR, SBP and DBP increased to 75bpm, 130mmHg and 82mmHg respectively. After 2 minutes of isometric contraction and trigeminal stimulation, HR and SBP had increased to 77bpm and 128mmHg and DBP remained the same at 76mmHg.
Blood pressure values varied dependent upon the method used due to the accuracy of each method. The standard deviation values calculated for SBP, DBP and MAP by the sphygmomanometer were 3.74, 4.22 and 3.77mmHg respectively. These low standard deviation values showed that the results recorded by the sphygmomanometer were close to the mean value obtained. The standard deviation values calculated for SBP, DBP and MAP by the automatic BP monitor were 6.9, 2.24 and 2.33mmHg respectively. These standard deviation values were generally low, with the exception of SBP. This showed the accuracy of this method. It can now be concluded that the automatic BP monitor is more reliable than the sphygmomanometer when measuring blood pressure due to the low standard deviation values obtained. Using the sphygmomanometer this could be due to observer bias and using the automatic BP monitor this could be due to improper placing of the cuff or the subject not being in resting position.
There are advantages and disadvantages associated with both methods of measuring blood pressure.A sphygmomanometer uses the ausculatory method, in which korotkoff sounds are detected. The advantages of this method are, it is relatively easy to use and to understand, it is cost effective and it is also transportable. Its disadvantages are, it contains the toxic substance mercury which is hazardous to humans, and the results obtained can be biased depending on the observer therefore it is difficult to obtain precise results. The automatic BP monitor uses the oscillometric method in which oscillations from the blood vessel wall are measured as the cuff gradually deflates. The advantages associated with this technique are, it is mercury free and there is no observer bias. The disadvantages are it is not suitable for all patients specifically those with a weak pulse and irregular heart rate, it is difficult to calibrate and also the algorithms for calculating SBP and DBP differ with each device (MDA, 2000).
Heart rate values differed depending on the method used due to the reliability of each method. The stethoscope was used to amplify apical pulse, which was taken on the chest cavity. Palpitation was used to measure the radial pulse which was taken on the wrist. The radial pulse is most commonly taken but the apical pulse is taken in the presence of a faint radial pulse and when an individual has an irregular heart rate. Standard deviation values were also considered when determining reliability. The results recorded differed from the mean by +/- 5.52bpm when using the stethoscope. While using palpitation the results recorded differed from the mean by +/- 12.48bpm.The standard deviation for the stethoscope method was considerably lower than that of the palpitation method, showing its accuracy. It could then be inferred that using a stethoscope was more reliable than using palpitation when measuring heart rate (Bunker Rosdahl and Kowalski, 2008)
Heart rate and blood pressure values were measured after each stressor had been applied in order to determine the effect of each stressor on the hemodynamic variables. During isometric contraction, electrochemical events take place in the muscle. The excitable muscle fibres are stimulated by motor neurons whose axon branches transmit action potential to the muscle fibres. The action potential then continues to spread, ultimately causing muscle contraction. This muscle contraction then increases blood pressure, resistance and heart rate. (Gladwell and Coote, 2002). The results obtained after isometric contraction showed that HR increased, SBP increased and DBP decreased. These results with the exception of DBP were expected. When the trigeminal nerve was stimulated during the diving reflex stressor, bradycardia occurred due to an increased parasympathetic stimulus sent to the cardiac pacemaker. Vasoconstriction took place as a result of increased activity of the sympathetic nerves supplying the limbs.
This caused an increase in blood pressure. The results obtained after TG stimulation were not as expected as HR increased, SBP increased and DBP decreased. The results of this experiment could be enhanced pairing stimulating the trigeminal nerve using ice packs and also breathing restriction (Hiebert and Burch, 2003). Psychological stress causes a decrease in the parasympathetic control of the heart and also sympathetic control of the heart is completely stopped. This allows heart rate to increase and therefore blood pressure also increases. The results from this experiment were as expected, HR increased and both SBP and DBP increased. Through this series of experiments it can be concluded that the most reliable methods for measuring BP and HR are using an automatic BP monitor and a stethoscope respectively. Stressors such as diving reflex, isometric contraction and psychological can also greatly impact haemodynamic variables.
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