Twenty-four hour ambulatory blood pressure in the Hypertension Optimal Treatment (HOT) study Giuseppe Mancia a , Stefano Omboni b , Gianfranco Parati a,b , Denis L. Clement c , William E. Haley d , Syed Noor Rahman e and Raol P. L. M. Hoogma f Background and aims The Hypertension Optimal Treatment (HOT) study showed that when antihypertensive treatment reduces diastolic blood pressure well below 90 mmHg, there can be a further reduction of cardiovascular events, particularly myocardial infarction, with no evidence of a J-shaped curve at lower pressures. Of®ce measurement, however, gives no information about blood pressure outside the of®ce. This paper describes a HOT substudy in which patients underwent both of®ce measurement and 24 h ambulatory blood pressure monitoring. Methods The mean age of the substudy population was 62 6 7 years. Substudy patients were treated for a median period of 2 years. All received the dihydropyridine calcium antagonist felodipine, while some also received an ACE- inhibitor, a beta-blocker or a diuretic. Average 24 h, day and night ambulatory blood pressure values were computed at baseline ( n 277) and during treatment ( n 347): 112 patients had been randomized to a target of®ce diastolic blood pressure < 90 mmHg, 117 to < 85 mmHg and 118 to < 80 mmHg. Additional analyses included computation of: (1) trough-to-peak ratio and (2) the smoothness index (the ratio between the average of the 24 hourly blood pressure reductions after treatment and its standard deviation). Results Taking the subgroup as a whole, baseline 24 h average blood pressures (146 6 18/90 6 10 mmHg) were signi®cantly and markedly lower than of®ce blood pressures (170 6 14/105 6 3 mmHg, P < 0.01). Of®ce, 24 h, day and night blood pressures were all signi®cantly reduced by treatment, but there was a smaller fall in ambulatory, than in of®ce pressures. The between group differences in of®ce blood pressure were smaller than those observed in the overall HOT sample. Between-group differences in 24 h blood pressure were even smaller. Trough-to-peak ratios and smoothness indices were lowest in the highest blood pressure target group and highest in the lowest blood pressure target group. Of®ce and ambulatory blood pressures were similar in the groups randomized to placebo ( n 170) or acetylsalicylic acid ( n 177). Conclusion In conclusion, in the HOT study, treatment reduced not only of®ce but also ambulatory blood pressure throughout the 24 h. The reduction was less marked for ambulatory than for of®ce blood pressure. J Hypertens 19:1755±1763 & 2001 Lippincott Williams & Wilkins. Journal of Hypertension 2001, 19:1755±1763 Keywords: ambulatory blood pressure, antihypertensive treatment, calcium- antagonists, of®ce blood pressure, smoothness index, trough-to-peak ratio a Clinica Medica, Dipartimento di Medicina Clinica, Prevenzione e Biotecnologie Sanitarie, Universita Á di Milano-Bicocca, Ospedale San Gerardo, Monza, b IRCCS Ospedale San Luca, Istituto Auxologico Italiano, Milano, Italy, c Department of Cardiovascular Diseases, University Hospital, Gent, Belgium, d Division of Hypertension and Nephrology, The Mayo Clinic, Jacksonville, Florida, e University of Texas Health Science Center at Houston, Houston, USA and f Groene Hart Ziekenhuis, Gouda, The Netherlands. Correspondence and requests for reprints to: Professor Giuseppe Mancia, Clinica Medica and Dipartimento di Medicina Clinica, Prevenzione e Tecnologie Sanitarie, Universita Á di Milano-Bicocca, Milano and Ospedale San Gerardo, Via Donizetti 106, 20052 Monza, (MI), Italy. Tel 39 039 2333357; fax 39 039 322274; e-mail: giuseppe.mancia@unimib.it Received 12 February 2001 Revised 30 April 2001 Accepted 31 May 2001 Introduction The Hypertension Optimal Treatment Study (HOT) [1] showed that when antihypertensive treatment re- duces diastolic blood pressure well below 90 mmHg, there can be a further reduction of cardiovascular events, particularly myocardial infarction, with no evi- dence of a J-curve at lower blood pressures [2]. Of®ce measurements, however, show a limited relationship with blood pressure outside the of®ce [3±6], thus raising the question of whether and to what extent antihypertensive treatment modi®es daily life blood pressure in the HOT patients. This was addressed in a HOT sub-study, in which patients underwent both of®ce measurement and 24 h ambulatory blood pressure monitoring. Methods The ambulatory blood pressure monitoring sub-study was planned at the time of the main protocol and performed in Italy, Belgium, Netherlands, and the USA. To enter the main HOT study, male or female patients aged 50±80 years had to have an of®ce average sitting diastolic blood pressure between 100 and 115 mmHg at three consecutive measurements taken Original article 1755 0263-6352 & 2001 Lippincott Williams & Wilkins