Quan no puc respirar bé, la metgessa em diu que respiri profundament.

Because Catalan usually drops subject pronouns when the verb already makes the subject clear.

• puc = I can
• So jo is not necessary

You could say Quan jo no puc respirar bé..., but that would usually add emphasis, contrast, or emotional weight.

It can feel like either when or whenever, depending on context.

In this sentence, Quan no puc respirar bé... naturally suggests a repeated or general situation, so in English it may sound like:

• When I can’t breathe well...
• Whenever I can’t breathe well...

Catalan often uses the present tense for this kind of general, repeated situation.

Because bé is an adverb, and it modifies the verb respirar.

• respirar bé = to breathe well

By contrast:

• bo / bona = good as an adjective, used with nouns

So:

• un bon metge = a good doctor
• respirar bé = to breathe well

English also does this distinction: good vs well.

La metgessa means the female doctor.

Catalan often has masculine and feminine forms for professions:

• el metge = the male doctor
• la metgessa = the female doctor

So this sentence specifically refers to a woman doctor.

Because em is an unstressed object pronoun, and in Catalan these pronouns usually go before a conjugated verb.

• em = to me / me
• diu = says / tells

So:

• la metgessa em diu = the doctor tells me

This is very normal Catalan word order. English puts me after the verb, but Catalan places the pronoun before it.

It can mean either, depending on context.

• dir = to say / to tell
• em diu literally = she says to me
• In natural English here, tells me is usually the best translation

So in this sentence, em diu is best understood as tells me.

Because respiri is subjunctive, and Catalan uses the subjunctive here after diu que when the meaning is an instruction, recommendation, or command.

So:

• em diu que respiri profundament = she tells me to breathe deeply
• more literally: she tells me that I should breathe deeply

If the doctor were simply stating a fact, Catalan would normally use the indicative instead:

• em diu que respiro malament = she tells me that I breathe badly

So the subjunctive here shows that this is not just information; it is advice or an instruction.

Yes, the form is ambiguous by itself.

In the present subjunctive, many Catalan verbs have the same form for:

• jo (I)
• ell / ella / vostè (he / she / you formal)

So respiri can mean:

• that I breathe
• that he/she breathe
• that you breathe (formal)

In this sentence, the context makes it clear that it means I:

• la metgessa em diu que respiri...
• The doctor tells me that I should breathe deeply

Here que means that and introduces the subordinate clause.

• em diu que respiri profundament
• literally: she tells me that I should breathe deeply

This is que without an accent.

That matters because:

• que = that
• què = what

So in this sentence, que is a conjunction, not a question word.

Because Catalan often forms adverbs by adding -ment to the feminine form of an adjective.

• profund = deep (masculine)
• profunda = deep (feminine)
• profundament = deeply

This is very similar to English -ly adverbs, although the formation is different.

So:

• respirar profundament = to breathe deeply

The comma separates the introductory time clause from the main clause:

• Quan no puc respirar bé, = introductory clause
• la metgessa em diu que respiri profundament. = main clause

This is natural and standard punctuation in Catalan, just as in English you might write:

• When I can’t breathe well, the doctor tells me to breathe deeply.

It helps the sentence read more clearly.