Precautions When Estimating Blood Pressure
There are certain precautions which must be strictly observed when deductions are drawn from the manometer readings. The psychic factor must be reckoned with. Any emotion may cause marked variations in the pressure. Excitement and anger are especial sources of error. Even the slight excitement arising from taking the first blood pressure on a nervous patient especially is apt to give false values. Usually the readings must be taken many times at the first sitting and the first few may have to be set aside. Worry is a potent factor in raising the pressure. A walk to the physician's office, especially if rapid, has its effect.
The position of the patient when the blood pressure is taken is important. Usually in the office the pressure is taken when the patient sits in a chair. He should assume a relaxed, comfortable attitude. The readings should be made at the same time of day and at the same interval between meals. The pressure in both arms should be measured and comparisons should be made only between readings on the same arm. These precautions may seem useless and even somewhat trivial, and the conditions difficult to control. But unless they are carefully observed the readings will be false, no comparisons can be drawn between the readings on different days, and the instrument will most probably be blamed. I have known this to happen so often that I can not emphasize too strongly the importance of controlling all the essential conditions which go to make accurate work.
The Value of Blood Pressure
In the past few years there has been a veritable avalanche of blood pressure instrument salesmen who have covered the country, sold instruments, and have made many startling claims for the instrument. They have emphasized its value out of proportion to what the instrument can do even in the hands of one familiar will all the defects. Consequently it is not necessary to emphasize the value of blood pressure. It seems best to utter a few words of caution in regard to its interpretation.
The value lies not in the occasional estimation compared with some other one reading, but in the frequent estimation and in the visualization of the blood pressure picture. For the great majority of diseases the blood pressure has no particular value except to show that the circulation is not materially disturbed. The limits of normal are rather wide, so that consideration of the patient's age, sex, build, etc., will give us some idea of a base line, so to speak, for any one person. Wide departures from relatively normal figures are important, but are not diagnostic or, rather, pathognomonic. I can not help but feel that the diastolic pressure is the most important part of the blood pressure picture. Persistent high diastolic pressure means increased work for the heart, which, if acting for a long time against the high peripheral resistance, must eventually hypertrophy. The arteries become thickened, lose their wonderful elasticity, fibrous tissue is deposited in their walls, and the vicious circle is established which leads to pathologic hypertension.
Blood pressure readings must be intimately mixed with brains in order to be of any great value in diagnosis or prognosis.