At my doctor’s office, the nurse takes my blood pressure. “Hmmm,” she muses, pumping up the cuff again.”It’s a little high. You’re probably nervous.” It’s called white-coat hypertension, the tendency to get anxious in medical settings, causing a transient rise in blood pressure. Test it again at home with one of those handy automatic sphygmomanometers from the drug store, and you’re back in the normal range. (Now try to say sphygmomanometer three times fast.)
Blood pressure is determined by the amount of blood the heart pumps in conjunction with the arterial resistance. The narrower the arteries, the greater the resistance. Greater resistance causes higher blood pressure. High blood pressure, a.k.a. hypertension, is classified as primary or secondary. Primary has no identifiable cause; it just happens and it is the most common kind in adult humans. Secondary hypertension is a sequela of some other illness, such as kidney disease. This is the most common form in cats and dogs.
What? Hold the phone! Did I just say that Laurel, the Labrador, and Hardy, the house cat, get high blood pressure? That’s right. In fact one study showed more than 90 percent of dogs and 60 percent of cats with chronic kidney failure had secondary hypertension. Other predisposing conditions may include adrenal gland disease, feline hyperthyroidism, and diabetes. So when you take Laurel and Hardy to the veterinarian for their annual visits, why don’t we automatically pull out a stethoscope and cuff like the one at your physician’s and check their blood pressure?
Let’s start with learning how sphygmomanometers work in people. When the nurse inflates that cuff, it occludes blood flow in an artery near the surface of your arm. The nurse listens with a stethoscope, while gradually deflating the cuff. When the pressure in the artery exceeds the pressure in the cuff, blood starts to flow again, making a turbulent sound audible through the stethoscope. That number is the systolic pressure, i.e., the pressure of the blood flow when the heart is contracting. As the cuff continues to deflate, the turbulence eventually disappears. That is the diastolic pressure, i.e., the pressure between heart beats.
The problem for veterinarians is that the plumbing works a little differently in Laurel and Hardy than in people. You simply can’t hear the sound of their arterial blood flow with a stethoscope. So we had to find other methods to measure our patients’ pressure. The only way to accurately check diastolic pressure on cats and dogs is to surgically place a probe in an artery — not something you want to do routinely. So we settle for measuring only systolic pressure. We still use a cuff but then add one of two hi-tech methods of “hearing” that arterial blood flow.
A Doppler uses ultrasonic waves to detect the flow and make it audible. An oscillometric device uses changes in pulsatile pressure oscillation to sense the changes in flow. This fancy equipment causes another major difference between a physician’s sphygmomanometer and mine. Cost. A standard human set-up, complete with stethoscope, cuff, and gauge can be purchased for under $75, while veterinary monitors range from $1,000 to $3,000.
Taking our measurements is a bit trickier when working with animals. We need a wide variety of cuffs to fit a wide variety of pets, from dainty cats to hefty mastiffs. Then we have to get Laurel to lie down, and Hardy to hold still. Readings are most accurate when the limb in question is level with the heart, and without any excessive movement. For you or me, the nurse simply holds our arm while we chitchat cooperatively from our chair. For Laurel and Hardy that means convincing them to lie flat on their side, motionless on the exam table.
Sure. Hardy is already panicked because you chased him around the bedroom for 10 minutes before stuffing him into his carrier and driving him, howling all the way, to my office. Laurel is completely beside himself because that yappy Yorkie kept barking at him in the waiting room and then the technician took his temperature — rectally. And now he’s going to lie flat, quiet, and relaxed, while we check blood pressure? I think not.
When we know ahead of time that we want to check for hypertension, we try to keep Laurel and Hardy as calm as possible beforehand, then take three to five readings, as the animal acclimates to the procedure — or at least, that’s what we hope. “Normal” is a difficult thing to assess, with all the variables and vagaries of veterinary practice but, in general a systolic of 110-160 mm Hg is acceptable. If we get consistently higher readings, we have to decide if this is the veterinary version of white-coat syndrome or real, persistent hypertension that warrants treatment.
To do this, it is recommended we repeat the procedure a week later, and maybe again a week after that, always with minimal stress. Ideally that means a home visit. If I can sidle up to Hardy while he’s asleep on your bed, get that cuff around his leg, and take a reading before he has time to get agitated, then we will have more confidence that the measurement accurately reflects his day-to-day blood pressure. If it’s high at home, then we can prescribe the same types of medications used in human medicine to get that systolic number down to a safer level.
Back at my doctor’s, I sigh and once again promise myself to exercise more and eat less. The truth is I’m probably more relaxed at Dr. Nieder’s office than at my own, and my blood pressure tends to run borderline high even at home. Hypertension in people has been called “the silent killer” because there are often no visible symptoms until the sudden onset of serious consequences, such as heart attack or stroke. If Laurel the Lab and Hardy the house cat have predisposing conditions, they, too, may be at risk. Check with your veterinarian about whether your pet should be evaluated for hypertension. It’s no laughing matter.