By Country Doctor

Edna Lavoie has had horrendous blood pressure readings for several decades, but she has never had a stroke or heart attack. Her eye doctor swears her retinae are healthy. Whenever she takes a pill that even begins to normalize her blood pressure, she complains of severe dizziness.

Dwayne Lieber’s home blood pressure cuff never reads anywhere close to our manual office sphygmomanometers, even though it is a good brand that usually seems quite accurate for our other patients who own the same model.

Donald Dickinson and Jane Green seem to be a pair of Jekyll and Hyde characters as far as their blood pressures are concerned; every other visit they seem to have a normal blood pressure in the 125/80 range and the rest of the time their systolic pressures are between 180 and 200.

Blood pressure measurements are routinely done every time a patient visits the doctor and hypertension is one of the most common diagnoses in primary care. A patient’s blood pressure is sometimes done with an automatic cuff, sometimes by the nurse or medical assistant and sometimes by the doctor. It is actually a complicated matter, fraught with problems and potential pitfalls.

The earliest form of experimental blood pressure recordings involved placing a catheter in an animal’s artery and measuring the height of a pillar of blood in a vertical hose or tube. Pressure recordings in shorter intra-arterial catheters are still done sometimes today.

The Russian military physician Nikolai Korotkoff described in 1905 the sounds you hear over an artery that is compressed by a blood pressure cuff, with slowly decreasing pressure. The first Korotkoff sound closely matches the intra-arterial systolic blood pressure, and the disappearance of Korotkoff’s sounds, roughly speaking, marks the diastolic or “resting” intra-arterial pressure.

Sir William Osler described in 1892, long before Korotkoff pioneered blood pressure measurements, how older patients with stiff, sclerotic arteries may seem to have higher blood pressures than they actually have. “Osler’s maneuver” is when an artery is compressed until no pulsations can be felt and the examiner can still feel the walls of the artery beyond the point of compression.

Edna Lavoie’s apparently uncontrolled hypertension came into question when I checked her radial blood pressure by holding my finger on her pulse at her wrist while slowly releasing my sphygmomanometer. Her radial blood pressure was consistently 130 to 135. Her arteries are still palpable when the cuff is pumped higher, although there is no palpable pulse – a positive Osler’s sign, and proof that she just has stiff arteries and pseudohypertension. In her case the “echo” in her stiff arteries sounds like the first Korotkoff sound.

Dwayne Lieber’s digital blood pressure cuff, like all others, doesn’t listen for Korotkoff’s sounds. Instead, it records the oscillations, or vibrations, of blood pumping through arteries that are partly compressed by a blood pressure cuff. Exactly where the cutoffs are for what is recorded as systolic and diastolic pressure can vary between machines, and these settings are not publicly shared. For this reason, digital cuff sometimes don’t give the same readings as manual cuffs.

Donald Dickinson and Jane Green have two different problems with the same resulting variability in their blood pressure measurements.

Don has atrial fibrillation. His irregular heart rhythm causes some of his beats to be full volume beats, like a full tank toilet flush, while other beats occur before the left ventricle of the heart has filled completely with blood. Just like a premature toilet flush, this causes a less effective fluid surge, and a lower blood pressure for that particular heart beat. An examiner who lets the blood pressure cuff deflate too quickly might miss some of the louder, higher pressure beats at the upper end off cuff inflation.

Jane is squeamish about having the blood pressure cuff pumped up hard, and some nurses don’t like to make her uncomfortable. Her typical blood pressure has been 180/80, but when you listen to her Korotkoff’s sounds, you can hear each beat from 180 down to 155 or so, then there is silence all the way down to 125, when the beat picks up and then stops at 80, her diastolic pressure. This “silent gap” explains why some examiners record her higher, true blood pressure, and others only record 120-125, because they only pump up the blood pressure cuff to 150 or so in order not to cause her pain.

Even a healthy person with a regular heartbeat, examined by the most expert clinician, can have wildly varying blood pressure. Stress, pain, recent salt intake, and normal physical activity can cause a person’s blood pressure to go up. Some people’s blood pressure goes up every time they enter a doctor’s office. Several careful measurements in different settings are sometimes needed to determine who has high blood pressure and who doesn’t.

I know one hypertension specialist, a nephrologist, who never trusts blood pressure readings done by anyone else. He has an old mercury sphygmomanometer he has used during his entire career. He knows his science and his equipment, and he has perfected his technique over many years. We should all treat blood pressure measurements that seriously.

Country Doctor is a Swedish-born family physician in a small town in rural Maine. This post originally appeared on Country Doctor’s blog, A Country Doctor Writes.