The Effect of Blood Donation Frequency and Gender on Physiological Response to Blood Loss

The Effect of Blood Donation Frequency and Gender on Physiological Response to Blood Loss

The effect of blood donation frequency and gender on physiological response to blood loss

Stephanie Melton and Jessica Ochoa

Department of Biological Science

SaddlebackCollege

Mission Viejo, CA92692

The human body has several physiological compensation mechanisms for blood loss. A change in blood pressure is one such mechanism. A blood donor loses approximately ten percent of total blood volume when donating blood. Ten percent is a blood volume significant enough to stimulate compensation mechanisms. This study was conducted to test the hypothesis that there is a significant difference between the pre- and post-donation blood pressures in first-time donors, compared to frequent donors. The objective of the study was to evaluate if donors physiologically adapt to blood loss if blood loss occurred frequently. The study took pre- and post-blood donation blood pressures from thirty frequent donors and thirty first-time donors. Our results indicate that there is not a significant difference in the change in systolic and diastolic blood pressures pre- and post- donation in frequent donors compared to first-time donors. (unpaired t-test, two-tailed, p>0.05) These results suggest that frequent donors do not adapt to blood loss. Also within this study frequent male donors were compared to frequent female donors and first time male donors were compared to first time female donors. The study found that there was no significant difference in the body’s physiological response that correlates to gender.

Introduction

The human body contains, on average, five pints of blood (Velasquez, 1987). Blood is an essential bodily fluid that is comprised of hematocrit, or red blood cells, and plasma. The red blood cells contain the hemoglobin protein that carries oxygen to organs and muscles and aids in the removal of carbon dioxide. Each hemoglobin contains a heme groups, to which iron binds. This iron is the binding site for oxygen (Franchini, 2008). The circulation of blood throughout the body is maintained by heart rate, cardiac output, and blood pressure. Cardiac output and blood pressure are monitored by baroreceptors in the aortic arch and carotid arteries. Baroreceptors detect the amount and the pressure of blood passing through the aorta and carotid arteries during each heart beat (Mancia, 1986). Baroreceptors are also responsible for moderating heart rate in response to changes in blood pressure (Parati, 218).

Whole blood donation involves the removal of 500 mL of blood (hematocrit and plasma) from the donor. This volume corresponds to a reduction of approximately 10 percent of total blood volume (Velasquez, 1987). With the loss of hematocrit, approximately 225-250 mg of heme is removed (Salonen, 446). Consequently, the concentration of oxygen in the body is reduced (Meyers, 1997). The loss of oxygen, if severe enough, will decrease tissue perfusion, which will eventually lead to cellular hypoxia, organ damage, and death (Peng, 2005).

When a subject loses blood (hemorrhage), the body initiates several neurohumoral compensation feedback mechanisms. Some mechanisms are immediate; others are slow-acting, long-term mechanisms (Haberthur, 2003). The volume of blood lost directly corresponds to the severity of the compensation. During a minor amount of blood loss, physiological compensation is not noticeable. However, when blood loss is around 10 percent, such as with blood donation, several compensatory mechanisms occur in the body.

The immediate mechanisms are initiated by the baroreceptors. When the baroreceptors in the aortic arch and carotid arteries detect a reduced blood volume, signals are sent from the sympathetic nervous system causing heart rate to increase, arteriole beds in muscle and skin to constrict, and veins to constrict (McGuill, 1989). The combination of these three responses is effective in the maintenance of arterial pressure, venous return to the heart, and cardiac output (McGuill, 1989). This ensures organs and tissues remain adequately perfused. With a blood loss volume greater than 10 percent, a subject would suffer significant decrease in blood pressure and cardiac output, as well as tachycardia, and further arteriolar constriction (McGuill, 1989).

The long term mechanisms function to replace the lost blood volume. These responses include the secretion of antidiruetic hormone and the activation of renin-angiotensin aldosterone hormone system (McGuill, 1989). These hormones function in the kidneys to reduce the amount of fluid lost in urine through the re-absorption of fluids. This re-absorption of fluid increases blood pressure by increasing the volume of fluid in the body (McGuill, 1989).

Another long-term response is the release of erythropoietin by the kidneys to stimulate the production of new red blood cells (Salonen, 1998). Approximately eight weeks recovery time is required between blood donations. This recovery time allows the blood volume that was removed to be replenished by the production of new red blood cells.

Several studies have been conducted to evaluate the effect of acute blood loss on blood pressure and mean arterial pressure (MAP). (What exactly is MAP?)One study found that acute loss of blood resulted in a slight decrease in systolic blood pressure and no change in diastolic blood pressure post blood donation in hypertensive subjects (Velasquez, 1987). A separate study found that hemorrhage resulted in a sympathetic nervous system response (i.e., increase heart rate and blood pressure) (Haberthur, 2003).

This study was conducted to evaluate the effects of blood loss on systolic and diastolic blood pressure, heart rate, and mean arterial pressure. Whole blood donors were the participants. The purpose of the study was to determine if people physiologically adapt to blood loss if the body is subjected to the stress of hemorrhage frequently. Such adaptations would include a lessened increase in heart rate, less arteriolar and venous constriction, and a lessened increase in blood pressure. This study focused on changes in pre- and post-donation systolic and diastolic blood pressures, heart rate, and MAP. The hypothesis being tested is that there is a significant difference between the pre- and post-donation blood pressures, heart rate, and MAP in first-time donors compared to frequent donors.

Materials and Methods

The study subjects consisted of blood donors at various American Red Cross donation centers throughout Orange County, California. The subjects were divided into two groups depending on the frequency of blood donation. Frequent donors were classified as donors who donate blood three or more times a year. First-time donors were donors who had not previously donated blood. The subjects were further divided into two based on sex, male and female. The two data groups consisted of frequent donors and first-time donors. Other variables affecting heart health were not taken into consideration. Since the only factor being evaluated is the change in blood pressure, heart rate, and mean arterial pressure due to blood loss, any extraneous health conditions were not considered to significantly influence the data. The data groups consisted of 30 first time donors and 30 frequent donors. Of these, half were male and half were female. Overall the prediction was there would be a reduced change in the pre- and post-donation for frequent donors compared to first-time donors. Specifically, it was predicted that frequent donors would have a smaller decrease in blood pressure than first time donors. The change in heart rate was predicted to smaller in frequent donors than first time donors. The drop expected in mean arterial pressure was predicted to be less in frequent donors than first time donors.

Data were collected from October 15, 2009 to November 6, 2009. Each donor was asked the frequency of blood donation to categorize the subject in the correct data group. The sex of the donor was also recorded. Using a sphygmomanometer and stethoscope, the subject’s blood pressures were taken auscultatively before and after donating blood. Heart rate was palpated at the wrist before and after donation as well. Mean arterial pressure was calculated from the blood pressures using the equation:MAP=[(2D)+S]/3, where D equals diastolic blood pressure and S equals systolic blood pressure.

Where D equals diastolic blood pressure and S equals systolic blood pressure. (You could probably leave it as you had it, but I think this looks a bit sharper)

The collected data were statistically analyzed using Excel software (Microsoft Corporation, Redmond, Washington) to determine if there was a significant difference in pre- and post- donation systolic and diastolic blood pressures, heart rate, and mean arterial pressures between the first time donors and frequent donors and between males and females. The first statistical test, a paired F-test with variances, was used to determine if there were unequal variances between the data groups. The F-test was followed with a two-tailed, unpaired T-test. The T-test was used to determine if a significant difference exists between the pre- and post-donation systolic and diastolic blood pressures, heart rate, and mean arterial pressure of frequent and first-time blood donors. T-tests will also be performed to determine if there is a significant difference between males and females for all data collected.(Delete space between p and parenthesis) ( p<0.05 will be considered as significant.)

Results

The results of the statistical analysis indicated that there was not a significant difference between blood pressure, heart rate, and MAP of frequent donors and first time donors and between males and females. For frequent donors, the mean change in systolic blood pressure was a drop of 1.7 mmHg (sd=6.2). The mean change in diastolic blood pressure was a drop of 0.8 mmHg (sd=6.6). For first-time donors, the mean change in systolic blood pressure was a drop of 2.3 mmHg (sd=7.8). The mean diastolic blood pressure change was a drop of 3.4 mmHG (sd=10.2). Each group had a sample size of 11 donors. The mean change in heart rate for frequent donors was an increase in 2.6 BPM (sd=10.8). For first time donors, the mean change in heart rate was an increase in 3.4 BPM (sd=8.4). The change in average MAP for frequent donors was a drop of 1.2 mmHG (sd=5.5) and for first time donors was a drop in 3.0 mmHG (sd=7.7).

The average change in male systolic blood pressure for frequent donors was a drop of 1.1 mmHG (sd=4.6). For first time donors, the average drop in systolic blood pressure was 2.5 mmHG (sd=8.2). For frequent female donors, the drop in mean drop in blood pressure was 2.7 mmHG (sd=7.6); first time female donors experienced an average drop of 2.0 mmHG (sd=7.8). Male frequent donors and first time donors experienced a drop in diastolic pressure of 1.1 mmHG (sd=8.2) and 5.3 mmHG (sd=11.4), respectively. Females, experienced a drop of 0.5mmHG (sd=5.0) for frequent donors and 1.4 mmHG (sd=8.3) for first time donors.Males who donated frequently had an average decrease in heart rate of 0.2 BPM (sd=13.2). First time male donors had an increase of 1.5 BPM (sd=6.3). For female donors, those who donated frequently experienced an average increase of 4.9 BPM (sd=7.0). First time donors had an average increase of 5.9 BPM (sd=6.3)Mean arterial pressure dropped for frequent male donors by 1.06 mmHG (sd=6.4). The drop for first time male donors was 4.36 mmHG (sd=9.0). For female frequent donors, the drop in MAP was 1.28 mmHG (sd=4.60). The drop for first time donor was 1.58 mmHG (sd=6.34).

(I know you are doing a F-test, a test in differences of standard deviation, but do you have to report SEM and N=# along with the mean; since you are also doing a T-test)

The results of the F-test indicated that there were unequal variances between frequent and first time donors for all parameters evaluated except the change in diastolic blood pressure for frequent and first time donors, the change in systolic blood pressure in males, and the change in heart rate in male donors, and the change in heart rate for frequent donors between males and females (p<0.05) What was the actual P-value?.

The results of the two-tailed, unpaired T-test indicated that there was not a significant difference between pre-and post donation systolic pressures between frequent and first time donors, (T-test assuming unequal variances, t=0.26, df=40, and p>0.05) (Figure 1). The data also indicated that there was not a significant difference in the pre- and post-donation diastolic pressures (T-test assuming equal variances, t=0.98, df=37, and p>0.05) (Figure 2).(Consistency – In your figures your results are to the hundredth place; while in the results portion they are to the tens place.)

Your Y-axis label is also difficult to read


Figure 1. Mean change in systolic blood pressure versus frequency of donation. The mean change in systolic blood pressure for frequent donors was a drop of 1.73±1.3 mmHG (±SEM), N=11. The mean change in systolic blood pressure for first-time donors was a drop of 2.27±1.7 mmHG (±SEM), N=11. Mean change in systolic blood pressure was not significantly different between frequent and first-time donors (p>0.05, two-tailed, unpaired t-test).

Figure 2. Mean change in diastolic blood pressure versus frequency of donation. The mean change in blood pressure for frequent donors was a drop of 0.82 ±1.4 mmHG (±SEM), N=11. The mean change in blood pressure for first-time donors was a drop of 3.32±2.2 (±SEM), N=11. Mean change in systolic blood pressure was not significantly different for frequent donors and first-time donors (p>0.05, two-tailed, unpaired t-test).

The results of the two-tailed, unpaired T-test for pre- and post-donation heart rate between frequent and first time donors indicated that there was not a significant difference, (T-test assuming unequal variances, t=-0.41, df=40, and p>0.05) (Figure 3).

Figure 3. Mean change in heart rate versus frequency of donation. The mean change in heart rate for frequent donors was an increase of 2.18±2.3 BPM (±SEM), N=11. The mean change in heart rate for first-time donors was an increase of 3.36±1.8 BMP (±SEM), N=11. Mean change in heart rate was not significantly different for frequent donors and first-time donors (p>0.05, two-tailed, unpaired t-test).

The results of the two-tailed, unpaired T-test for pre- and post-donation MAP between frequent and first time donors indicated that there was not a significant difference, (T-test assuming unequal variances, t=-0.89, df=38, and p>0.05) (Figure 4).


Figure 4. Mean change in mean arterial pressure versus frequency of donation. The mean change in MAP for frequent donors was a decrease of 1.18±1.2 mmHG (±SEM), N=11. The mean change in MAP for first-time donors was a decrease of 2.97±1.6 mmHG (±SEM), N=11. Mean change in heart rate was not significantly different for frequent donors and first-time donors (p>0.05, two-tailed, unpaired t-test).

The second set of statistical tests ran were comparing systolic and diastolic blood pressure, heart rate, and MAP for male and females. For frequent male and female donors, there was no significant difference in the systolic (T-test assuming unequal variances, t=0.61, df=17, and p>0.05) (Figure 5) or diastolic blood pressures (T-test assuming unequal variances, t=-0.19, df=17, and p>0.05) (Figure 6). For first time male and female donors, there was also no significant difference in the systolic (T-test assuming unequal variances, t=-0.16, df=20, and p>0.05) (Figure 7) or diastolic blood pressures (T-test assuming unequal variances, t=-0.92, df=18, and p>0.05) (Figure 8).


Figure 5. Mean change in systolic blood pressure versus gender for frequent donors. The mean change in systolic blood pressure for frequent male donors was a decrease of 1.09±1.4 mmHG (±SEM), N=11. The mean change in systolic blood pressure for frequent female donors was a decrease of 2.73±2.3 mmHG (±SEM), N=11. Mean change in systolic blood pressure was not significantly different for frequent donors and first-time donors (p>0.05, two-tailed, unpaired t-test).

Figure 6. Mean change in systolic blood pressure versus gender for first time donors. The mean change in systolic blood pressure for frequent male donors was a decrease of 2.55±2.5mmHG (±SEM), N=11. The mean change in systolic blood pressure for first time female donors was a decrease of 2.00±2.4mmHG (±SEM), N=11. Mean change in systolic blood presssure was not significantly different for frequent donors and first-time donors (p>0.05, two-tailed, unpaired t-test).

The results of the two-tailed, unpaired T-test for pre- and post-donation diastolic blood pressure between frequent male and female donors indicated that there was not a significant difference, (T-test assuming unequal variances, t=-0.19, df=17, and p>0.05) (Figure 7). The results for first time male and female donors also indicated there was not a significant difference (T-test assuming unequal variance, t=-092, df=18, and p>0.05) (Figure 8).