An Expert System on Detection, Evaluation and Treatment of Hypertension - Artificial Intelligence and Symbolic Computation - page 255

Table 1. Classification of BP

Category SBP mmHg DBP mmHg

Normal < 120 and < 80

Prehypertension 120-139 or 80-89

Hypertension, Stage 1 140-159 or 90-99

Hypertension, Stage 2 ≥ 160 or ≥ 100

Table 2. Refined classification of BP

Category SBP mmHg DBP mmHg

Normal < 120 and < 80

Prehypertension 120-139 or 80-89

Hypertension, Stage 1 140-159 or 90-99

Hypertension, Stage 2a 160-179 or 100-109

≥ 180 ≥ 110

Hypertension, Stage 2b or

Table 3. Table 1, once corrected

Category SBP mmHg DBP mmHg

Normal < 120 and < 80

120-139 and < 90

Prehypertension or

< 140 and 80-89

140-159 and < 100

Hypertension, Stage 1 or

< 160

and 90-99

Hypertension, Stage 2 ≥ 160 or ≥ 100

It seems clear that the four regions that Table 1 pretends to define are those
in Figure 2.
But only the “Normal” and “Stage 2 Hypertension” regions are correctly
defined. For instance, if the pseudo-classification of Table 1 was followed strictly,
the diagnosis for a patient with SBP = 130 mmHg ∧ DBP = 100 mmHg would
be a double “Prehypertension” and “Stage 2 Hypertension”! The reason is that
the regions “Prehypertension” and “Stage 1 Hypertension” defined by those
tables don't have the shape shown in Figure 2. For instance, the Prehypertension
region really defined by Table 1 is shown in Figure 3. Therefore, the regions are
not disjoint, so Table 1 doesn't provide a real classification. Admitting that the
intention of those who wrote Table 1 was to describe the regions in Figure 3, a
correct description would appear in Table 3.
The same problem arises in Table 2. It is similarly corrected (Table 4). Curi-
ously, these inaccuracies were found when implementing the corresponding IF...
THEN... rules, so there has been a certain feedback from the implementation.