Antihypertensive Therapy for the Elderly: AnExpert System to Assist Therapeutic Decisions

K. GONDEK, P.P. LAMY, S.M. SPEEDIE, and P.L. JEFFREY

From the University of Maryland at Baltimore, Baltimore, Maryland

GONDEK, K., ET AL.: Antihypertensive therapy for the elderly: an expert system to assist therapeuticdecisions. The prevalence of hypertension among the elderly is high. Recent muJticenter studies haveshown hypertension, especially isolated systolic hypertension, to be a risk factor and treatment to beelective, i/individualized. In addition, the presence of multiple complicating conditions and the need formultiple medications in the elderly increases the required medical knowledge base necessary to appropri-ately determine antihypertensive therapy. To assist the primary provider, an expert system has beendeveloped that provides advice on therapeutic decisions for elderly patients (greater than 65 years old andless than 85 years old). It takes into account such factors as age, sex, lifestyle, site of care, nutritional status,physiologic and pathophysiologic changes, co-existing diseases, multiple drug use, and prior antihyper-tensive drug exposure and response. The system user enters patient̂ characteristics, disease states, risk/actors, relevant laboratory values, and prior drug therapy. The system responds with a set o/recommenda-tions of appropriate therapy individualized for the specific patient. To further assist the process, relativecosts of therapy are also included. The system, consisting of over 200 rules, is currently undergoingvalidation by a panel of cardiologists. It is implemented in IBM's Expert System Environment (ESE) on theIBM 4341. The authors wish to acknowledge the contribution of the ESE software by the IBM Corporation.(PACE, Vol. 11, November Part II 1988)

hypertension, elderly, expert system

IntroductionThe elderly population is increasing as a re-

sult of increased life expectancy and decreasedmortality. The prevalence of hypertension amongthe elderly is high. Approximately 64% of the el-derly may have hypertension. It is estimated thatas few as 50% are treated and of those treated only25% are controlled.* The presence of multiplecomplicating conditions and the need for multiplemedications in the elderly increases the medicalknowledge base necessary to appropriately deter-mine antihypertensive therapy, as well as theneed to access and use that knowledge basequickly and efficiently.

The ElderlyGeneralizing drug therapy is increasingly

difficult due to primary, secondary, and tertiary

Address for reprints: K. Gondek, The University of Marylandat Baltimore, Baltimore, Maryland

aging factors. Exaggerated response to some drugsmay reflect intrinsic changes. Primary visual andauditory problems occur, and secondary homeo-static mechanisms are less efficient. Pharmacoki-netic changes, including altered distribution, me-tabolism, and elimination are the result of physio-logic as well as pathophysiologic changes, whichrequire both monitoring of drug effects and dos-age adjustments. Drug metabolism and excretiondecline, body tissue composition and drug vol-ume of distribution may change, and drug recep-tor sensitivity may be altered.^

The elderly have a higher incidence of ad-verse drug reactions and drug therapy is asso-ciated with a decrease in quality of life standards.^Jachuck et al.* provided insight to the quality oflife of the hypertensive patient. The study ques-tioned the patient, physician, and the patient'sfamily. Physicians thought their patients had bet-tered their quality of life after treatment; the pa-tient sometimes thought they were better andsometimes thought they were worse. The family.

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however, thought the patient was much worse onantihypertensive drug therapy, which includeddiuretics, beta-blockers, and methyldopa. Severalstudies show that impaired well-being is a reasonwhy many hypertensive patients withdraw fromdrug therapy.^"^ Antihypertensive agents cancause adverse drug reactions significant enoughfor the patient to be hospitalized.^ Drug interac-tions and adverse effects are important consider-ations in drug therapy selection due to increaseddrug sensitivity seen in the elderly. As a result,special attention to determining drug dosages aswell as other medications is necessary to decreasethe potential for adverse effects and to optimizetherapeutic outcome. Blood pressure should belowered gradually to allow time for compensatoryresponses to work.

The Physician

Physicians are faced with a growing database, more complex drugs, drug interactions, andadverse drug reactions. In the past 2 years, ap-proximately 2,000 articles have been writtenunder the subject heading "hypertension," whichmakes it difficult to keep current. Newer agentssuch as the angiotension converting enzyme in-hibitors provide alternative therapy. However,many of the newer agents have not been studiedin the elderly.

The Expert System

The expert system is an "artificial intelli-gence" program which uses knowledge and infer-ence procedures to solve problems that are diffi-cult enough to require significant human exper-tise for their solution.^ Expert systems havedemonstrated the ability to process an enormousamount of knowledge in a concise and consistentfashion. It was felt that an expert system programto assist in the antihypertensive therapy decisionwould benefit the patient and the physician byproviding a mechanism to incorporate vastamounts of knowledge into a workable consulta-tion process. The system establishes the data baseby assessing patient-specific information whichincludes laboratory values, concomitant diseases.

concurrent medications, activities of daily living,cognitive function, nutritional status, and priortreatment and control.

The expert system was programmed fromappropriate literature to include geriatrics, cardi-ology, and pharmacology. The system is operatedby physicians, is interactive, and results can beobtained within 2 to 4 minutes. The system mini-mizes the length of time required for consultationby asking only for information necessary to reacha conclusion. In order to achieve its goal, thecomputer asks questions of the user. The questionformat involves multiple choice selections,checklists, and individual numerical or truthvalue (yes/no/unknown) responses. The re-sponse to the questions aids in the interpretationof data entered with the goal being to determinethe appropriate nondrug or drug therapy in theelderly hypertensive. The program content wasvalidated by a board certified cardiologist and hasbeen designed for use by a general practitioner.

The expert system will suggest nondrug ther-apy, the modification of risk factors, such as de-creasing alcohol consumption, decreasing smok-ing, or modifying diet. Other risk factors such asfamily history, end organ damage, and race areobtained to assess the patient's risk for other car-diovascular complications. Drug therapies incor-porated into the program are diuretics, potas-sium-sparing diuretics, angiotensin convertingenzyme inhibitors, beta blockers, calcium chan-nel blockers, vasodilators, and adrenergic inhibi-tors. A combination of nondrug and drug therapymodalities may also be suggested. The antihyper-tensive therapy program will also suggest an al-ternate drug choice, efficacy of the agent, cau-tions, potential drug interactions, potential ad-verse drug reactions, and the relative cost basedon average wholesale prices.

The Expert System,Technical Data

The knowledge base combines facts andheuristics.^ Facts are the body of information thatis widely shared, publicly available, and gener-ally agreed upon by experts in that field. Heuris-tics are an expert's insight or "rules of thumb"used in making a decision. It involves the intu-

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itive or cognitive thoughts that are used to makedecisions. The expert system depends on bothforms of information to make the program ascomplete as possible.

Knowledge is structured in the form of rulesand parameters. Rules are structured into "IF-THEN" statements." For example, "IF family his-tory is positive, THEN risk factor = 1." Parametersare the domain facts or variables, such as age, sex,or race. The expert system has the ability to pro-cess an unspecified or undefined response. A lim-ited number of these responses may be incorpo-rated into the program for a specific drug therapyor nondrug therapy to be suggested. Frequent un-specified responses will result in the inability ofthe program to reach a conclusion.

Inference procedures include both forwardand backward chaining. Forward chaining is"event" driven. It involves an exhaustive use ofthe data base. Backward chaining is "goal"driven; that is, it starts with a specific goal andproceeds until a conclusion can be achieved. Theexpert system uses backward chaining in arrivingat a specific nondrug or drug therapy decision.

Validation

Validation of the expert system to determineaccuracy, completeness, and consistency of theknowledge base was performed.*" A board certi-fied cardiologist reviewed the knowledge baseand recommended some modifications to the pro-gram. "Debugging" the knowledge base was doneby performing 30 test consultations designed byclinical pharmacists. This testing was necessaryto determine which rules were invoked in arriv-ing at conclusions and if they were complete andaccurate.

Conclusions

The antihypertensive therapy program con-sists of 222 rules and 90 parameters. The com-puter suggestions against treatment of 90 elderlypatients in a family practice clinic were assessed.In general, the computer suggestions were moreconsistent than the actual therapy prescribed.Experts agreed with the computer-suggested ther-

apy for 82% of the patients. Nondrug therapy,prescribed as the sole therapy, was suggestedmore frequently than prescribed. The computer-suggested nondrug therapy modalities, secondaryto drug therapy, occurred in almost all patients.

Seventy-five percent of the patients were fe-male, 89% of the patients were black, and ageranged from 65 to 85 with a mean age of 73. Dia-stolic blood pressure while on physician-pre-scribed therapy ranged from 90 to 120 mmHg,with a mean of 98, and systolic blood pressureranged from 120 to 240 mmHg, with a mean of164. The most common missing data elementswere cholesterol, family history, alcohol con-sumption, and smoking, 71%, 42%, 38%, and 31%,respectively. Only 8% of the patients had a solediagnosis of hypertension. The most frequent ofthe concomitant diseases included arthritis, an-gina, and diabetes.

There is a certain inability to generalize forseveral reasons. (1) The validation was performedby a board certified cardiologist. It is necessary tohave a panel of experts in various disciplines re-view the program and suggest changes. (2) Thediffusion and availability of new drugs and druginformation are slow. It was found in the studythat even with literature evidence for the use ofangiotensin converting enzyme inhibitors for pa-tients with congestive heart failure, only one of 90patients received this therapy. (3) A broader pa-tient sample is needed to truly validate the pro-gram. The study population consisted primarily ofelderly black females.

Future Endeavors

The study will be continued in a geriatricclinic. The program will be expanded to includemultiple drug therapy. The need to test the pro-gram in multiple sites is necessary to determinethe validity in the elderly white male population.An expert panel is working to further expand theheuristic portion of the data base.

Summary

In conclusion, it is apparent that efforts totreat the elderly hypertensive are not uniform.

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Patient management may be optimized with theaid of the expert system program which considersthe patient's concurrent medications and con-comitant diseases in reaching its suggestedtherapy.

Acknowledgment: The authors wish to acknowledge theassistance of Michael Fisher, M.D., Veterans AdministrationHospital, Baltimore, Maryland, the IBM corporation, the con-tribution ofthe expert shell, the University of Maryland Medi-cal System, Department of Pharmacy Services, and Depart-ment of Family Practice.

References

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WHO/ISH. 1986 Guidelines for the treatment of 7.mild hypertension. Hypertension 1986; 8:957-961.O'Malley K, et al. Effect of age and sex on humandrug metabolism. Br Med J1971; 3:607.Hurwitz N. Admissions to hospitals due to drugs. 8.Br Med J1969; 1:539.Jachuck SJ, Brierley H, Jachuck S, Willcox PM. 9.The effect of hypotensive drugs on the quality oflife. J R Coll Gen Pract 1982; 32:103-105.Medical Research Council Working Party. MRC 10.trial of treatment of mild hypertension: Principalresults. Br Med J1985; 291:97-104.Helgeland A. The impact on serum lipids of com- 11.hinations of diuretics and B-hlockers alone. J Gar-diovasc Pharmacol 1984; 6(Suppl 3):S474-S476.

WiUiams GH, Groog SH, Levine S, Testa MA, Su-dilovsky A. Impact of antihypertensive therapy onquality of life: Effect of hydrochlorothiazide. J Hy-pertension 1987; 5(Suppl 1):S29-S35.Harvey JJ. Expert systems: Present and future.Gomputers and People 1987; Jan-Feb:12-18.Miller PL. The evaluation of artificial intelligencesystems in medicine. Gomputer Methods and Pro-grams in Biomedicine 1986; 22:5-11.Davis R, Buchanaan B, Shortliffe EH. ProductionRules as a Representation for a Knowledge-BasedGonsultation Program. Artif Intell 1977; 8:15-45.Young FE. Validation of medical software: Presentpolicy of the Food and Drug Administration. AnnIntern Med 1987; 106:628-629.

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