dyspnea vs orthopnea

dyspnea and orthopnea both are nouns.

Word	Noun	Adjective	Verb	Adverb
dyspnea	Yes	No	No	No
orthopnea	Yes	No	No	No

As nouns, orthopnea is a hyponym of dyspnea; that is, orthopnea is a word with a more specific, narrower meaning than dyspnea:

dyspnea: difficult or labored respiration
orthopnea: form of dyspnea in which the person can breathe comfortably only when standing or sitting erect; associated with asthma and emphysema and angina pectoris

Other hyponyms of dyspnea include breathlessness, shortness of breath, SOB.

dyspnea (noun)	orthopnea (noun)
difficult or labored respiration	form of dyspnea in which the person can breathe comfortably only when standing or sitting erect; associated with asthma and emphysema and angina pectoris