x1 is related to medical treatment/science/practice, or is medicinal, or is medical, or is related to healthcare, or is related to the practice/occupation of medicine or being a medical practitioner (doctor, nurse, midwife, pharmacist, technician, etc.; also: psychologists, psychiatrists, physical therapists, physicians, veterinarians, hospital administrators, vel sim.), or pertains to hospitals or caregiving, concerning general class of subjects/patients x2 or ailment/body-part x3 or form of treatment/care x4.
No implication that the subject is human. For veterinarian, x2 is non-human animals in general or some subset thereof. Dentistry, orthodontics, optometry, epidemiology, etc. all are included. Plant or agricultural science related to taking care of ailing plants or preventing their ailments is included (x2 is plants (and possibly fungi)). All reproductive or fertility sciences or services, excepting sex work or similar, are included; obstetrics and reproductive health are included; family planning, abortion services, and contraception science or services are included. Palliative, hospice, and euthanization care are included. Mental health and wellness care, in the form of therapy or similar, is included. This list is not exhaustive.