تقيس الممرضة ضغط الدم؛ يفحص الطبيب المريض الذي يتنفس بعمق.

Because the subject is الممرضة = the nurse, and ممرضة is feminine.

In the present/imperfect tense:

• تَفْعَلُ-type forms can mark she does
• يَفْعَلُ-type forms can mark he does

So:

• تقيس = she measures
• يقيس = he measures

The second verb is يفحص because الطبيب = the doctor is masculine.

This is a very common MSA word order: verb + subject + object.

So:

• تقيس الممرضة ضغط الدم = literally Measures the nurse the blood pressure
• يفحص الطبيب المريض = literally Examines the doctor the patient

In natural English, of course, we say The nurse measures... and The doctor examines...

You can also say:

• الممرضة تقيس ضغط الدم
• الطبيب يفحص المريض

That subject-first order is also correct. The verb-first order often sounds a bit more formal or more narrative in MSA.

Because ضغط الدم is an iḍāfa construction, often called a genitive/possessive construction.

It literally means:

• ضغط = pressure
• الدم = the blood

Together: pressure of the blood = blood pressure

In an iḍāfa:

• the first noun usually does not take الـ
• the second noun can make the whole phrase definite

So:

• ضغط دم = blood pressure / a blood pressure reading
• ضغط الدم = the blood pressure

This is one of the most common noun patterns in Arabic.

الذي is a relative pronoun. Here it means who, that, or who is depending on how you translate it.

So:

• المريض الذي يتنفس بعمق = the patient who is breathing deeply

A key point: in Arabic, when the noun is definite, you normally use a relative pronoun like الذي.

Compare:

• المريض الذي يتنفس بعمق = the patient who is breathing deeply
• مريضٌ يتنفس بعمق = a patient who is breathing deeply

In the second example, with an indefinite noun, Arabic often does not use الذي.

It describes المريض = the patient.

So the structure is:

• يفحص الطبيب
• المريض
• الذي يتنفس بعمق

That means:

• The doctor examines the patient who is breathing deeply.

The most natural reading is that the relative clause attaches to the nearest suitable noun, which is المريض.

Because it has to match المريض.

المريض is:

• masculine
• singular
• definite

So the matching relative pronoun is:

• الذي = masculine singular

If the noun were feminine singular, you would use:

• التي

For example:

• المريضة التي تتنفس بعمق = the female patient who is breathing deeply

Literally, بعمق means with depth:

• بـ = with / by
• عمق = depth

But in normal English, it means deeply.

So:

• يتنفس بعمق = he breathes deeply / he is breathing deeply

Arabic often uses a preposition + noun where English uses an adverb.

Other similar patterns:

• بسرعة = quickly
• ببطء = slowly
• باهتمام = attentively

They can mean either, depending on context.

The Arabic imperfect tense often covers:

• simple present: measures, examines, breathes
• present progressive: is measuring, is examining, is breathing
• habitual actions: usually measures, etc.

So in context, this sentence could naturally be understood as:

• The nurse measures the blood pressure; the doctor examines the patient who is breathing deeply. or
• The nurse is measuring the blood pressure; the doctor is examining the patient who is breathing deeply.

English forces you to choose more explicitly than Arabic does.

Most everyday Arabic writing leaves out short vowels and case endings.

So you see:

• تقيس الممرضة ضغط الدم؛ يفحص الطبيب المريض الذي يتنفس بعمق

But in fully vocalized formal Arabic, it would be something like:

• تَقيسُ الممرضةُ ضغطَ الدمِ؛ يَفحَصُ الطبيبُ المريضَ الذي يتنفّسُ بعمقٍ

Those endings show:

• الممرضةُ = subject
• ضغطَ = object in the iḍāfa
• الدمِ = genitive after iḍāfa
• الطبيبُ = subject
• المريضَ = object

In normal unvowelled text, readers understand the roles from:

• word order
• grammar patterns
• meaning

Because several nouns here are definite:

• الممرضة = the nurse
• الدم = the blood
• الطبيب = the doctor
• المريض = the patient
• الذي = the relative pronoun who/that

Arabic uses الـ very often to mark definiteness, much more visibly than English does.

Also, in ضغط الدم, the whole phrase is definite because the second noun is definite:

• ضغط الدم = the blood pressure

It works much like the English semicolon: it links two closely related clauses.

Here it separates:

1. تقيس الممرضة ضغط الدم
2. يفحص الطبيب المريض الذي يتنفس بعمق

So the meaning is roughly:

• The nurse measures the blood pressure; the doctor examines the patient who is breathing deeply.

Arabic punctuation uses ؛ as the semicolon symbol.

This is about sun letters and moon letters.

In:

• الطبيب, the ط is a sun letter, so the ل of الـ is not pronounced separately. It sounds like aṭ-ṭabīb.
• الدم, the د is also a sun letter, so it sounds like ad-dam.

But in:

• الممرضة, the م is a moon letter, so the ل is pronounced: al-mumarriḍa.

This only affects pronunciation, not spelling. The article is still written الـ in all these words.