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To understand better the functioning of a sphygmomanometer, we made some blood pressure measurements in couples, therefore individuating some possible causes of experimental errors.
The table reports the experimental values measured expressed in mmHg over atmosferic pressure.
| Subject 1 - systolic | Subject 2 - diastolic | Subject 1 - systolic | Subject 2 - diastolic |
|---|---|---|---|
| 120 | 70 | 138 | 66 |
| 120 | 68 | 130 | 60 |
| 118 | 70 | 128 | 62 |
| 116 | 70 | 120 | 70 |
| 118 | 66 | 120 | 70 |
The values recorded for the second subject (much more irregular than the first one's) have probably been damaged by experimental errors(see Observations).
The average systolic pressure psys and the average diastolic pressure pdias have been calculated for both subjects. soggetti. The demi-interval was assumed as error.
psys 1 = (118 ± 2) mmHg
εrelative = 1/59 ≈ 0,017
psys 2 = (127 ± 9) mmHg
εrelative = 9/127 ≈ 0,071
pdias 1 = (69 ± 2) mmHg
εrelative = 2/69 ≈ 0,029
pdias 2 = (66 ± 4) mmHg
εrelative = 2/33 ≈ 0,061
To better evaluate the blood pressure from a physical point of view it can be useful to convert the experimental values in other measurement units as the Pascal and the atmosphere.
A simple JavaScript program was used to do the conversions.
| Systolic Pressure | Diastolic Pressure | |
|---|---|---|
| mmHg | 878 ± 2 | 829 ± 2 |
| Pa | 117000 ± 2000 | 110000 ± 3000 |
| atm | 1,16 ± 0,02 | 1,09 ± 0,03 |
| Systolic Pressure | Diastolic Pressure | |
|---|---|---|
| mmHg | 887 ± 9 | 826 ± 4 |
| Pa | 118000 ± 8000 | 110000 ± 7000 |
| atm | 1,17 ± 0,08 | 1,09 ± 0,07 |
The measurements on the second subject have probably been damaged by some experimental errors; the measurer reported he had heard many background sounds during the measurement that he could have mistaken with the real Korotkoff sounds.
The sphygmomanometer needs to be used with some ability to obtain precise measurements; however, these measurements were taken by people who were using this instrument for the first or second time. This could have caused many errors in both measurements.
