Normal Blood Pressure Criteria

Blood pressure is measured in millimeters of mercury (mm Hg) and has two key numbers:

• Systolic Blood Pressure (SBP): The pressure when the heart beats and pumps blood.
• Diastolic Blood Pressure (DBP): The pressure when the heart rests between beats.

Defining Normal Blood Pressure

According to major health organizations, normal blood pressure is generally defined as:

• Systolic pressure less than 120 mm Hg ($SBP < 120 \\text{ mm Hg}$)
• Diastolic pressure less than 80 mm Hg ($DBP < 80 \\text{ mm Hg}$)

This combination is crucial for cardiovascular health. Both conditions must be met.

Evaluating the Options

Let's examine the given options based on the standard definition:

• Option 1: $SBP < 120 \\text{ mm Hg}$ and $DBP < 80 \\text{ mm Hg}$ - This matches the standard definition of normal blood pressure.
• Option 2: $SBP < 120 \\text{ mm Hg}$ and $DBP < 90 \\text{ mm Hg}$ - While the SBP is normal, a DBP < 90 mm Hg falls into the elevated or stage 1 hypertension category, not strictly normal.
• Option 3: $SBP < 80 \\text{ mm Hg}$ and $DBP < 120 \\text{ mm Hg}$ - This reverses the typical values and is incorrect. An SBP < 80 mm Hg is hypotensive.
• Option 4: $SBP < 130 \\text{ mm Hg}$ and $DBP < 80 \\text{ mm Hg}$ - An SBP between 120-129 mm Hg is considered 'elevated' blood pressure, not normal.

Therefore, the only option that strictly defines normal blood pressure is having both systolic and diastolic values below the specified thresholds.