HN = Hypertensiver Notfall, could be "acute hypertension" as described below. "Hypertensive emergeny" is another possibility, it depends on your context (which leads me to believe it's the first one).

The objective of emergency treatment is prevention of hypertensionrelated adverse events (e.g., stroke, cardiac failure, encephalopathy). This usually requires only a modest reduction in BP. Attempts to rapidly achieve normal BP are contraindicated. In patients with chronic hypertension, a rapid lowering BP to “normal” can decrease needed perfusion to the heart and brain resulting in ischemia. For this reason, in individuals with longstanding hypertension or hypertension of unknown duration, an initial BP reduction (10-20%) followed by gradual normalization of BP is recommended. In acute hypertension, the therapy should be directed towards bringing the BP to normal values.

as the heading is:
"Neurologischer Befund" (neurological findings)
"Kein Meningi[s]mus" (no meningeal syndrome)
"NAP frei"
(NAP-Nervenaustrittspunkte? - nerve exits, nerve points)

"HN o. B." must have something to do with a nerve/the nerves;
could be e.g. "Hirnnerv(en)" (cranial or cerebral nerve(s)) or "Hörnerv" (auditory / cochlear / acoustic / hearing nerve)

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Note added at 2002-03-25 02:47:07 (GMT)
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\"o.B. \" is of course \"ohne Befund\" meaning \'no abnormality discovered\', \'no appreciable disease\' (NAD) or just \'negative\'