target term depends on how you want to structure the sentence.
perhaps use intense coughing, coughing fit/attack/episode

cough reflex is an alternative translation but I don't think that fits this context

This translation makes a certain amount of sense, given that "stöt" by itself typically means "stroke," "impact" or "blow". Also, note below text on assisted coughing, a procedure performed on patients who have trouble taking preliminary deep breaths due to lung ailments:

"A manually assisted cough is the most commonly used assisted coughing method. After taking a deep breath, the patient is asked to cough as forcefully as possible while a simultaneously timed abdominal thrust is performed...."

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Note added at 14 hrs (2011-08-31 17:19:59 GMT)
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Sorry, I meant to say "after". Also, one "hoststöt" would be "a forceful cough". The text would then read, "VA efter flera hoststöt...." = "VA [alveolar ventilation] after several forceful coughs...."

Hoststöt can refer to a single cough, or a coughing episode. In this context, it's likely to be an episode. VA (a test of Alveolar Ventilation) has been carried out following several coughing episodes.

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Note added at 16 hrs (2011-08-31 19:27:10 GMT)
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On reflection, I think vesikulära andningsljud is probably right for VA here, i.e the patient has been asked to cough before listening to lung sound.

So, 'Normal breath sounds after several coughs...'

I don't think there's anything to indicate forcefulness.

From Lindskog, Zetterberg, Medicinsk terminologi: vid hoststöt får utandningsluften en sådan hastighet och turbulens (virvelrörelse) att irriterande gas el. partiklar tillsammans med slemdroppar slungas ut genom munnen

From Taber's Cyclopedic Medical Dictionary: c., effective: Cough in which sputum or any exudate is expectorated. SYN: c., productive

Compare Google descriptions in English and Swedish of the Cough Assist Machine. In Swedish, the machine is "en andningsstödjande apparat som hjälper till med hoststöten". In English, the machine is said to help the patient achieve a productive/effective or stronger cough.

To convey the plural of "flera hoststötar" I would use "productive cough flow" here, although in general it would work to simply use "coughing" instead of "cough(s)" since coughing is a series of coughs.

Any sentence containing "svag hoststöt" obviously has to be considered in its context. A patient producing a "svag hoststöt" may suffer from weak muscles., e.g. In that case, "svag hoststöt" may have to be translated as "poor cough." From link below: For this reason, patients with weak muscles, poor coordination of airway closure and re-opening, or who have airflow obstruction (as in COPD) will have a poor cough and be susceptible to complications including infection in the lower respiratory tract and pneumonia.