Section 4: Cardiovascular Diseases

4.4 Abnormal Blood Pressure

4.4a. Hypertension

Hypertension is defined as systolic blood pressure of 140 mm Hg or greater, diastolic blood pressure of 90 mm Hg or greater, or taking antihypertensive medication (National Institutes of Health [NIH], 1997). Blood pressure classification criteria for individuals 18 years of age and older who are not taking antihypertensive medication and who do not have an acute illness have been provided by the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure (NIH, 1997). Those criteria are outlined in Table 8.

Table 8  Blood Pressure Classification Criteria for Individuals 18 years of Age and Older*

(Reproduced, with permission, from The National Institutes of Health, Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure November, 1997)

      * Not taking antihypertensive drugs and not acutely ill. When systolic (SBP) and diastolic blood pressures (DBP) fall into different categories, the higher category should be selected to classify the individual’s blood pressure status. For example, 160/92 mm Hg should be classified as stage 2 hypertension, and 174/120 mm Hg should be classified as stage 3 hypertension. Isolated systolic hyper-tension is defined as SBP of 140 mm Hg or greater and DBP below 90 mm Hg and staged appropriately (e.g., 170/82 mm Hg is defined as stage 2 isolated systolic hypertension). In addition to classifying stages of hypertension on the basis of average blood pressure levels, clinicians should specify presence or absence of target organ disease and additional risk factors. This specificity is important for risk classification and treatment.
      † Optimal blood pressure with respect to cardiovascular risk is below 120/80 mm Hg. However, unusually low readings should be evaluated for clinical significance.
      ‡ Based on the average of two or more readings taken at each of two or more visits after an initial screening.

According to the American Heart Association (2000), one in four American adults have high blood pressure. Of those with high blood pressure, 14.8 percent are not on therapy (special diet or drugs), 26.2 percent are on inadequate therapy, and 27.4 percent are on adequate therapy. Individuals with lower educational and income levels that are obese and are physically inactive have diabetes, who smoke, and/or have a family history of hyper-tension are at higher risk of developing hypertension. Also at increased risk are non-Hispanic blacks and Mexican Americans. Risk for hypertension also increases with age (Cressman and Gifford, 1990). Complications of hypertension include increased risk for stroke, coronary artery disease, myocardial infarctions, and kidney disease.

Hypertension and Driving Literature Review

As with many chronic medical conditions, there is a paucity of literature on the relationship between hypertension and motor vehicle crashes. For individuals with hypertension who experience complications from the disease, their risk for motor vehicle crashes would be related to the presence and/or severity of the disease (e.g., cerebrovascular accidents [CVA’s], myocardial infarcts). The reader is directed to those sections of the review that are applicable (e.g., Cardiovascular, Cerebrovascular, Renal Diseases). In one study, Schmidt, Frerick, Kraft, Schenk, and Löw-Kröger (1992) examined cognitive and on-road performance of 20 hypertensive individuals pre-treatment (Mean systolic BP = 149 ± 15.8 mm Hg; diastolic BP = 101.4 ± 6.6), following antihypertensive medication (Mean systolic BP = 132.5 ± 13 mm Hg; diastolic BP = 91.7 ± 8.2), and 15 normotensive controls (Mean systolic BP = 127.7 ± 20.8 mm Hg; diastolic BP = 84.3 ± 8.3). Prior to treatment, there were significant differences between the hypertensives and controls on tests of attention and concentration. Untreated hypertensives made fewer correct responses and had an error rate double that of controls. Following treatment (with moxonidine), however, the hypertensive patients performed at a level comparable to the controls. Unfortunately, measures from the road test included only assessments such as lane positioning, maintenance of speed, and maintaining a safe distance.

There is a growing body of literature documenting the relationship between hypertension and cognitive impairment (see Waldstein, 1995 for an excellent review). As noted by Waldstein, hypertensive individuals of all ages generally show a consistent pattern of impairments on tests of learning and memory, attention and mental flexibility, and abstract reasoning. Less consistent results have been reported on tests of visuospatial, vasoconstriction, psychomotor, and perceptual functioning (cf. Waldstein, 1995).

Hypertension is one of the primary risk factors for vascular dementia, the second leading cause of dementia in the elderly person (Marshall, 1993). Multiple infarct and ischemic white matter lesions are suggested causes of vascular dementia, both of which have been associated with hypertension (Strandgaard and Paulson, 1994). It is interesting to note that results from a 15-year longitudinal study in Goteborg, Sweden revealed that higher systolic blood pressure at age 70, and higher diastolic blood pressure at ages 70 and 75 predicted the presence of a dementia at age 79-85 (Skoog, Lernfelt, Palmertz, et al., 1996).

In summary, there is a large body of literature documenting the relationship between hypertension and impaired cognitive performance. Although there are no data available linking the presence of high blood pressure to an increased risk of motor vehicle crashes, it seems prudent, based on the available literature between hypertension and cognitive impairment, for licensing agencies to be alerted to the role that hypertension may play in motor vehicle crashes.

Consideration also must be given to the effects of antihypertensive medication on cognitive performance. For example, Larson, Kruskull, Buchner, and Reifler (1987) investigated the effects of medication on cognitive performance. Results of their investigation led the authors to conclude that antihypertensive agents are major culprits of cognitive deficits.