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Blood pressure and hypertension

Blood Pressure

  • It is the pressure exerted by the circulating blood against any unit area of the blood vessel wall. Stephen Hales (1730) demonstrated the existence of pressure in the blood vessels. Average pressure in the aorta is 98 mm Hg and the mean pressure in veins is 3 mm Hg and this pressure difference (98-3 = 95) moves the through the systemic vessels. This pressure difference between the aorta and veins is the perfusion pressure.

  • BP is highest in aorta (98 mm Hg), moderate in capillaries and lowest in the vena cava (3 mm Hg). This pressure gradient favours the blood flow through the blood vessels.

  • During ventricular systole the arteries show the highest pressure, referred to as systolic pressure. It is due to increased blood volume and distension of the arterial walls. During ventricular diastole, blood continues to flow out of the aorta into small arteries, the volume of blood in the large arteries decreases, the arteries become less distended and blood exert less pressure in the arteries. The minimum pressure reached in the blood vessels before each new ventricular ejection is referred to as diastolic pressure.

Pulse pressure = the difference between systolic and diastolic pressure

  • The pulse pressure increases as the blood flows from aorta to distal arteries and then becomes less and less when the blood moves towards periphery. It disappears in the arterioles and capillaries.

  • Systolic pressure: Indicates the total kinetic energy imparted to the blood by the heart.

  • Diastolic pressure: Reflects the state of peripheral vessels and load on vascular wall.

  • Pulse pressure: Ventricular output and measure the variations of kinetic energy of heart.

  • Mean pressure is the average pressure in a blood vessel over a given period of time. This represents potential energy that draws blood through the systemic circulation.

  • This formula is useful to find out mean pressure in major arteries distal to aorta but not in aorta because the pattern of arterial pressure pulsation change as the pulse moves away from the heart. The pressure pulses are more triangular in large arteries not in aorta.

  • Arterial BP is always expressed in mm Hg whereas capillary and venous pressure can be expressed as mm H2O.

Hypertension

Hypertension is another name for high blood pressure. It can lead to severe health complications and increase the risk of heart disease, stroke, and sometimes death.

Hypertension is more common in older dogs, consistent with the development of underlying disease such as chronic kidney disease, or excessive levels of steroids produced by the adrenal glands in dogs with Cushing’s syndrome. Younger dogs may develop hypertension if they have kidney disease due to infection (such as leptospirosis) or a developmental kidney abnormality.

What are the signs of hypertension?

There are some signs of hypertension that can be observed. These include:

  • Sudden blindness, bleeding inside the globe of the eye, and persistently dilated pupils
  • Detached retinas
  • Nervous system signs like depression, head tilt, seizures, disorientation, wobbly or uncoordinated movements (called “ataxia”), circling, weakness or partial paralysis, or short, rapid, back-and-forth movements of the eyes (called “nystagmus”)
  • Increased drinking and urinating with the progression of chronic kidney disease
  • Blood in the urine (called “hematuria”)
  • Bleeding in the nose and nasal passages (known as “epistaxis” or nosebleed)
  • Heart murmurs or abnormal heart rhythms

What causes hypertension in dogs?

The cause of primary hypertension is unknown. Secondary hypertension accounts for a majority of hypertension in dogs, and can be attributed to kidney disease, adrenal gland disease, diabetes mellitus (less common), pheochromocytoma (adrenal gland tumor and very uncommon), or central nervous system disease (very rare).

How is hypertension typically treated in dogs?

The treatment of dogs with hypertension depends upon the underlying cause, if there is one. If the dog develops a serious complication related to hypertension like acute kidney failure or bleeding into the eye, there may be a need for hospitalization. In general, once any underlying condition is appropriately managed, medication and nutrition are important to normalizing blood pressure.

Medications that are commonly used to manage hypertension in dogs include angiotension converting enzyme (ACE) inhibitors and calcium channel blockers. Additional medications may be required depending upon the response to initial therapy. Therapeutic nutrition is generally accepted as an important part of long-term management.

What kind of monitoring will be required for dog?

The treatment goal for a dog with hypertension is a systolic pressure of 140mmHg or less, and a diastolic pressure of 90mmHg or less. Periodic laboratory testing will be required to monitor for side effects of medication and progression of disease.

Potential complications of hypertension in the dog include:

  • Congestive heart failure
  • Chronic kidney disease
  • Retinal degeneration and subsequent blindness
  • Bleeding into the eye
  • Stroke (cerebral vascular accident)

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