Cardiovascular Circulation Altering Conditions - Lab Report Example

 Lab Report Introduction Cardiovascular circulation in a human body is maintained by various mechanisms. Heart rate and mean arterial pressure are two important components of our circulation that are regulated in such a way that ensures most efficient blood perfusion to all tissues in the body. There are certain conditions, however, in which demand for blood supply is altered considerably. The aim of this experimental study is to introduce human body to these different conditions and observe how innate regulatory mechanisms respond to the hemodynamic changes. There will be three sets of experiments. In each experiment subjects will be introduced to one variable and then its effect on heart rate and mean arterial pressure will be recorded. Three variables in these experiments are postural changes, exercise and cognitive stressor. Heart rate and mean arterial pressure depends on many factors such as cardiac output, preload, contractility, afterload, venous tone etc. An understanding of these factors and how they are related to each other is crucial to comprehend changes in heart rate and mean arterial pressure during the experiments. In experiment 1 it is expected that both blood pressure and heart rate will decrease reclining and immediately upon standing but will increase steadily over time after that. During exercise, immediately both heart rate and BP should shoot up to meet body requirement but steadily decline with rest. Cognitive stress in experiment 3 is expected to raise both blood pressures as well as heart and in direct proportion to the intensity of induced stress. Procedure Experiment 1: In this experiment the heart rate and mean arterial pressure of the subject was measured in the following postures: 1. Sitting quietly 2. After reclining for 2-3 minutes 3. Immediately after standing from the reclining position (stand in anatomical position) 4. After standing in anatomical position for 3 minutes Experiment 2: For this experiment bench stepping was used as an exercise activity. The height of the bench was about 0.5m for male subjects and 0.4m for female subjects. Heart rate and mean arterial pressure was recorded for subject while sitting quietly at rest. Then he/she was asked to stand quietly for two minute to adjust the body for position change before beginning with the bench stepping exercise. Bench stepping was performed as per following: i. Place the right foot on the step ii. Step up with the left foot and place that foot on the platform (both feet will be on the platform now) iii. Step down with the right foot iv. Bring the left foot down v. Repeat the process again The rate of the bench stepping was set at 2 sec/cycle. The subject performed this exercise for 5 minutes, while maintaining erect posture. The exercise was stopped if subject could not complete it for 5 minutes. After exercise, subject was asked to sit down. Heart rate and blood pressure was recorded immediately upon sitting, 1 min, 2 min, 3 min, 4 min and 5 min after the exercise period. Fitness index for subjects was calculated using the following formula; Index = Duration of exercise (sec) X 100 2 X {sum of the 3 pulse counts in recovery} Experiment 3: For this experiment, a non-invasive blood pressure inducer and pulse plethysmograph were used to record pulse rate and mean arterial blood pressure. Subject was given two sets of 12 words each. He/she was instructed to spell one set of words forward and the other set to spell backward. Following sets of words was used to induce cognitive stress. Set 1: Spell Forward Event, Frame, Flour, Growl, House, Joust, Leach, Learn, Maple, Niche Nectar, Prowl. Set 2: Spell Backward Exert, Frost, Flack, Grant, Heart, Juror, Lucky, Laugh, Mouse, Nickel, Novel, Pearl. As subject was trying to spell these words, maximum, minimum and mean heart rate was recorded during each task individually. Diastolic, systolic and pulse pressures of the subject were also noted. Results 1. Experiment 1: (Postural change) Blood Pressure (mmHg) Pulse Rate (per minute) Sitting quietly (Baseline) 98/62 64 Reclining (after 2-3 minutes) 90/60 58 Immediately upon standing 88/58 78 After standing for 3 minutes 80/62 72 Experiment 2: (Exercise) Fitness Index was calculated for each well conditioned and poorly conditioned subject using the formula as described in the procedure section. Subject 1 (Well Conditioned): Fitness Index = 70.4 Subject 2 (Poorly Conditioned): Fitness Index = 48.7 Following table summarizes the recording for blood pressure and heart rate in both well conditioned and poorly conditioned subject at baseline and different intervals. Baseline Immediately 1 minute 2 minute 3 minute Well conditioned Subject BP: 118/88 mmHg HR: 66 / min BP: 104/80 mmHg HR: 80 / min BP: 112/82 mmHg HR: 74 / min BP: 114/80 mmHg HR: 75 / min BP: 118/72 mmHg HR: 64 / min Poorly conditioned subject BP: 86/60 mmHg HR: 42 / min BP: 102/62 mmHg HR: 120 / min BP: 92/60 mmHg HR: 102 / min BP: 94/64 mmHg HR: 104 / min BP: 90/68 mmHg HR: 102 / min Experiment 3: (Cognitive Stressor) Following table summarizes the results for cognitive stressor experiment. Condition Max HR Min HR Mean HR Systolic BP Diastolic BP Pulse Pressure Baseline 72 / min 57 / min 62 / min 63 mmHg 50 mmHg 56 mmHg Spell forward 74 / min 58 / min 64 / min 87 mmHg 57 mmHg 71 mmHg Spell backward 77 / min 58 / min 64 / min 97 mmHg 66 mmHg 80 mmHg Discussion: There are many factors that can affect heart rate and blood pressure of any healthy individual. But our body has internal regulating capabilities that make sure that these values do not exceed certain limits and should be bought to their normal levels as soon as possible. In this experimental study 3 important factors were analyzed with their respective effect on the heart rate and blood pressure. In the first experiment, subject was asked to adopt different postures, both heart rate and blood pressure was recorded in each positions. The results showed that both blood pressure and heart rate decreased when the subject was in reclined position for 3 minutes. This was expected as the cardiac output increase due to increase in venous return. Secondly, the heart does not have to pump against the gravity; therefore, the flow to the carotid artery is increased. These factors initially elevate blood pressure that stretches the walls of carotid sinus. This in return the decrease the heart rate by inhibiting sympathetic innervations and stimulating parasympathetic innervations to the heart. Systemic vasodilation decrease total peripheral resistance (TPR) and cause decrease in arterial blood pressure. Immediately, upon standing, subject’s blood pressure drops even more, 90/60 to 88/58, as recorded in the result. This can be explained by pooling of blood in the venous system and decrease in the venous tone and venous return to the heart. Cardiac output is decreased leading to instantaneous decrease in blood pressure. The heart rate drops instantaneously but rises again as carotid sinus stop shooting inhibitory signals to the brainstem, sympathetic signals to the heart cause increase in number of beats per minute to compensate for decrease in stroke volume (Marieb & Hoehn, 2010). After 3 minutes have passed it was expected that heart rate and blood pressure would rise. But the results showed a further decrease. Increase in arterial blood pressure was expected because the instantaneous regulators of blood pressure would have caused systemic vasoconstriction, raising the TPR. But the opposite result can be an error in calculation or the timing of measurement could be at fault. In the second experiment, exercise in the form of bench stepping should have elevated both blood pressure and heart rate immediately but then a gradual return to baseline was expected as seen in the poorly conditioned subject. In this subject the heart rate increased from 42 to 120, whereas, blood pressure shot up from 86/60 to 102/62 immediately after the exercise. During exercise, muscle requires more oxygen and their blood flow increases many folds to compensate for this demand. Muscle contraction also increase venous return to the heart leading to increase cardiac output. The increase in heart rate and blood pressure is due to increase sympathetic activity and release of epinephrine in the body. Epinephrine also increases stroke volume by increasing the contractile ability of the heart. (Marieb & Hoehn, 2010). After exercise, slowly the effect of sympathetic outburst fades out returning the heart rate and blood pressure to its baseline values. Blood pressure values for well conditioned subject were not as expected. But the heart rate values elevated immediately and decreased to baseline with progressive minutes. The possible explanation for error in the blood pressure record is the use of inappropriate cuff size. Especially for a well built person like this subject, small cuff size can seriously alter the results. In the third experiment, cognitive stress results completely supported the hypothesis that stress increase heart rate and blood pressure and this increase is proportional to the intensity of induced stress. It is evident from the table that when subject was asked to spell the words forward, the stress caused an increase in the max heart rate, 72 to 74, and pulse pressure, 56 to 71. Other baseline values were also elevated. This increase in max heart rate was even more, 77 beats per minute, when subject stress level was increased upon instructing to spell backward. This can be explained by normal hormonal response mechanism that is initiated in the presence of stress. The release of stress hormones such as epinephrine and nor-epinephrine from adrenal glands cause increase in heart rate and stroke volume by the mechanisms explained earlier. Moreover, these hormones cause vasoconstriction, increasing TPR and arterial blood pressure (Marieb & Hoehn, 2010). Hormone release is also proportional to the intensity of stress to a certain limit, thus, increase in the baseline values is also proportional. This experimental study results supported almost all the hypothesis presented earlier in the introduction. However, some findings were different from hypothetical expectations. The errors could be reduced by increasing the number of subjects and then averaging the results obtained. It should also be ensured that proper instruments are used appropriately with minimum human errors. Reference: Marieb, E. N., & Hoehn, K. (2010). Human anatomy & physiology. San Francisco: Benjamin Cummings. Read More