Note 7 - Stockholders' Equity - Antidilutive Securities (Details) - shares	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Common stock equivalents of convertible promissory notes and accrued interest (in shares)	4,206,312	179,804
Convertible Debt Securities [Member]
Common stock equivalents of convertible promissory notes and accrued interest (in shares)	2,946,525	157,139
Warrant [Member]
Common stock equivalents of convertible promissory notes and accrued interest (in shares)	1,253,387	14,518
Share-Based Payment Arrangement, Option [Member]
Common stock equivalents of convertible promissory notes and accrued interest (in shares)	6,400	8,147