moiram@tektronix.UUCP (10/05/84)
Does anybody know how the blood pressure apparatus (like the ones at the doctor's office) works? The nurse took my blood pressure twice this morning and got 160/110. I've been watching my blood pressure for several years and it normally is about 124/90. I protested that something wasn't right (after several months of emotional stress, I've finally been able to kick back and take it easy for the last six weeks). She decided to try a "larger" cuff and got 114/86. While, this is somewhat lower than I would expect, it IS in the ballpark, and it might be explained by a less stressful lifestyle and more exercise. How does the cuff size influence the reading, and what are the parameters for choosing the cuff size? Moira Mallison tektronix!moiram
ron@brl-tgr.ARPA (Ron Natalie <ron>) (10/08/84)
If you use a cuff that is too small you can get a erroneously high reading. The active part of the cuff is called the bladder. If you have one handy flip it over and look at the inside. You can usually see or feel the rubber bladder that inflates. If you have a large arm, that area may be too small. Our ambulance carries several of the standard size cuff, a pediatric one (a regular cuff won't work at all on really small arms because the bladder wrapps all the way around and tries to flatten itself out) and a leg cuff. The leg cuff, while designed to be used on legs when the arm is not usable, is also the obese arm cuff. Other things that can give erroneous blood pressure are: 1. Cuff placement on the arm: The cuff should be placed so that the bottom is 1" above elbow. 2. Wrong markings on the cuff: The center of the bladder should be placed over the brachial artery. The little label on the cuffs are extremely unreliable. Always check cuffs that you are not familiar with (even ones that are the same model are often labeled differently). Locate the bladder and fold the cuff so that the ends of the bladder are even and this is the center line. 3. Incorrect procedure: When deflating the cuff, there may be a single surge at an erroneously high pressure. One beat is not the systolic pressure. Only when two beats have occured, are you assured that you have found the systolic pressure 4. Not waiting You must wait after attempting to take blood pressure before making another attempt. There may be more, but those are what comes to mind. Ron Natalie Cowenton Volunteer Fire Department
burge@logico.UUCP (John Burge) (10/09/84)
While there may be some physical explanation of the effect of cuff pressure
on MM's blood pressure "readings", does anyone know more about what
blood pressure _is_ than the definition of what it takes to cut off and
restore circulation? Are my arteries "springier" (say) -- more responsive,
maybe even healthier -- if I'm 120/100 than if I'm 120/90? What are the
limits -- how long would I have lasted at 60/40 (lying down)? Doesn't it
depend on a balance between the pressure of the "pump" and the elasticity of
the walls of the "pipes"? Don't they communicate and coordinate in other
ways than pressure (hormones, ANS, electrolytes,...)? Do I have to jog, or
will ERG do it? And how sensitively do that cuff and that dial indicate
(resistance to) failure modes in such a system? (Modulo, perchance, the
attendant's coefficient of sycophanticity.)
--
--John Burge {the.world}!trwrb!logico!burge [818] 887-4950
LOGICON, Operating Systems Division, 6300 Variel #H, Woodland Hills, Ca 9136707077090@sdcc6.UUCP (07077090) (10/10/84)
As you imply, blood pressure is a complex
phenomenon. In the most basic terms, it
is determined by cardiac output and vascular
impedance which has both resistive and
capacitance components. The pulse pressure
(systolic-diastolic) increases with increased
stroke volume and decreased vessel compliance
(capacitance) while mean arterial pressure
depends on cardiac output and vascular resistance.
BP of 120/100 (vs 120/90) implies a higher resistance
(or higher output) and more work for the heart.
As far as we know, there is no lower limit for the
beneficial effects of low blood pressure, until
low pressure itself becomes symptomatic (e.g. with
lightheadedness or fainting). There is a complex
feedback system as you suggest, involving hormones
etc, which is one reason BP is hard to control.
For example, one cause of high BP could be thought of
as the body (kidneys?) "thinking" there is low
intravascular blood volume, and thus "conserving"
as much water in the circulation as possible.
Mikc Blyth
..sdcc3!sdcc6!07077090
UCSD Medical Schoolron@brl-tgr.ARPA (Ron Natalie <ron>) (10/10/84)
Springier? It's not the elasticity of the artery that determines how much pressure it takes to cut off the circulation, it is the pressure of the flow that makes the difference. Systole (indicated by the higher numbers) is an index of how hard the heart is making it's stroke, diastole is the rest (actually, filling) period. The primary reason blood pressure goes up is becuase for some reason the heart is pumping harder to get the same volume of blood through. As your demand for blood contents (oxygen, notably) goes up, the heart has to pump more blood. A more dramatic change happens to the person with the healty heart (not a more serious, just more dramatic) goes into shock. His heart will raise the pressure to keep the volume up until a point is reached and a collapse occurs, while less healthy people will just go into a gradual loosing battle. The rule of thumb is "for an adult male up to age 40, at rest, add his age to 100 for the systolic blood pressure, for females add to 90). Serious low blood pressure indicates shock (loss of volume), high blood pressure indicates the heart is working harder than usual to pump the blood. High blood pressure usually is considered bad because it indicates other problems like arteriosclerosis or it may cause a higher risk of hemmorage due to increased pressure. I don't think anyone claims that blood pressure alone is the problem, but having high blood pressure is a sign for a need for further investigation. Actually, all my experience with blood pressure is emergency medicine based. We use blood pressure as a baseline and watch for changes. We don't condider problems unless the blood pressure is really high (>180) or really low (<80) or it changes drastically. Other indicators like the systolic and diastolic numbers growing closer together idicate a decrease in heart efficiency sometimes due to blood in the pericardium. -Ron w