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THE HAEMODYNAMIC PATTERN IN MILD AND BORDERLINE HYPERTENSION

P. Lund-Johansen, MD

Section of Cardiology, Medical Department, University of Bergen, Bergen, Norway.

In t rod uc t i on : - ___ - -_ - - It is difficult to define precisely mild and borderline

hypertension as well as to establish the starting phase o f primary (or essential) hypertension.

Until the late 1970ties most studies of haemodynamics in tlearlyfl, "mildtt or "borderline" hypertension were done in males aged 20 to 40 years with mean blood pressures (MAP) at the time of the study between 100-110 mmHg. Central haemodynamics was measured invasively.

In the 1980ties several studies have been performed in "hypertensiver1 children and adolescents with considerably lower pressures (the subjects being derived from popula- tion studies or representing offspring from hypertensive parents). Most of these studies have been done non- invasi vely.

The results from a13 these studies might seem to be confusing or even contradictory. The reader should care- fully study the selection criteria (particularly the num- ber of blood pressure recordings), the level of the blood pressure and the experimental set-up.

This short review will focus on some of the most impor- tant results. A more extensive review is found in refe- rence 1 .

Invasive studies in youngma_l_es- with mild or bot-dgt-l-ine h y pe r t P n

R&. Studies from the 1960ties generally agreed that in groups of young males with blood pressure around 140/90

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mmHg or slightly above, cardiac index (CI) was about 15% higher than in normotensive age matched controls. Heart rate (HR) was about 15% higher and stroke index (SI) was normal. Total peripheral resistance index (TPRI) did not differ significantly from controls but was increased when related to the cardiac output. Individual variations were great.

These results supported the concept of a fqhyperkineticft circulatory system being of pathogenetic importance in primary hypertension. The so-called whole body autoregula- tion theory explained why TPRI became increased and CI fell over the following years. The concept was that TPRI increased in order to protect the tissues from "overirri- gation". However, several studies from the mid-1960ties demonstrated an increased oxygen consumption and a normal arteriovenous oxygen difference in these hypertensive subjects and indeed no true luxury perfusion existed. This is generally overlooked - even up in the 1980ties. In my mind the whole body autoregulation theory should not be applied to explain the haemodynamic alterations in primary hypertension.

The cause of the high HR, CI and oxygen consumption in these hypertensive subjects is still unsettled.

Exercise studies. While studies performed during rest only gave no indication of a reduced pump function of the heart in early essential hypertension, observations during steady state exercise in the sitting position on bicycle ergometer gave some surprising results. Even in mildly hypertensive subjects (aged 17 to 29 years) CI during exercise was slightly subnormal. With increasing age the difference between normals and hypertensives became statistically significant. The mechanism was a subnormal ~ - _ I _ - increase in SI in the hypertentensive groups. This was the first indication of a disturbed heart pump function in mild hypertension. The cause was unclear, but many years later, Tarazi and his group demonstrated (by means of the

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gated blood pool isotope technique) that the diastolic filling rate is reduced even in mild hypertension, probably due to reduced compliance (2).

____-__ Borderline hypertension in older age_?:

ages. Messerli et a1 (3) have recently studied 38 normo- tensives and 78 borderline hypertensives, age 15 to 60 years. A high CI was found only in age group 20-29 years (3.39 vs 3.09 l/min/m , respectively). In older age groups CI did not differ between normotensives and border- line hypertensives.

Mild and borderline hypertension also exist in older

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Long-term changes in central haemodynamics in untreated primary hypertension:

We have previously reported central haemodynamics in 34 untreated primary hypertensive subjects aged 17 to 49 years followed over 10 years. In all age groups (17-29, 30-39, 40-49 years) was there an increase in TPRI, a fall in CI and SI - at rest as well as during exercise. In the two youngest age groups a significant increase in dia- stolic arterial pressure (DAP) and in MAP was seen only at 150 W exercise. I n age group 40-49 years the increase in TPRT was very great and there was a significant in- crease in SAP, DAP and MAP at rest as well as during exercise.

Over the next 7 years (from 1975 to 1982) DAP rose to > 100 mmHg in all but seven of the 29 subjects who were below 40 years at the first study, and after 17 years only seven out of 29 subjects are not on antihypertensive treatment.

In eight subjects who had been untreated over 17 years, a third haemodynamic study was performed. The results are seen in figure 1 .

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i w IOOW isow RS 50 W 100 W 150 W

Fig.1. Haemodynamic pattern at rest and during exercise over 17 years. Mean values from 8 males with untreated essential hypertension. First study in 1964-1965, second study after 10 years, third study after 17 years. Note the gradual increase in mean arterial pressure (MAP) and the gradual fall in cardiac index (CI) and in stroke index (SI) together with increase in total peripheral resistance index (TPRI). Stars show statistical significance between study 1 and study 3 . * I: p<O.O5, * * pcO.01, * * * = p<O.OOl.

Follow-up studies from other centers (usually of con- siderably shorter duration and sometimes with differences in methods between the first and the second study) have generally shown similar results.

Thus, based on these long-term haemodynamic observations it might be concluded that in subjects between 20 and 40 years with several blood pressures >

140/90, hypertension seems to persist in the majority - with some increase i.n blood pressure, but this might take more than 15 years. Over the years there is a gradual decrease in CI and SI and an increase in TPRI. These changes confirm what should have been expected on the

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basis of cross-sectional haemodynamic studies.

Adolescents and chGt-e-n with "mild hypgt-tgn-siojl!: In recent years several interesting studies have been

made in teenagers (derived from population studies) generallv representing those above the 90 or 95 percentile with respect to blood pressure.

Hofman et a1 ( 4 ) have reported two such studies, one from Holland, the other from Boston. Tn the first study the llhypertensivell teenage group had a blood pressure of only 132/74 mmHg (controls 120/69 mmHg). Somewhat sur- prisingly the CI (by echocardiography) was lower in the hypertensive group (3.6 versus 4.0 l/min/m N.S.) - the pressure difference being due to increased TPRF?. Similar results were seen in the American study. The authors conclude that a high CI does not appear to be a

common phenomenon in Itearly primary hypertension".

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Several other studies in children and teenagers (also using echocardiograahy) have been performed, but with slightly different results ( 5 ) . In at least two studies CI was slightly higher in the group with the highest blood pressures.

Of particular importance is that left ventricular hypertrophy and increased left ventricular mass have been found in most of these studies. The significance of these minor deviations from normal is not yet known.

Conclusion: Most invasive studies of central haemodynamics in males

20-40 years of age with several blood pressures above 140/90 and MAP between 100 and 110 mmHg, have demonstrated a higher CI than in normotensive control grouas of same age, but since oxygen consumption is also increased, no luxury perfusion exists.

During a 17- year follow-up DAP rose to 100 mmHg or more in most of such subjects. Central haemodvnamics

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changed towards reduction in CI and SI and increase in TPRI. These changes support Folkow’s concept of a gradual restructuring of the high blood pressure compartment in primary hypertension ( 6 ) .

It is, of course, uncertain if these subjects - who certainly were hypertensives - represented the genuine starting phase of essential hypertension when they were studied at the age of 17-29 years. Recent studies in children or teenagers with lower blood pressures - but above the 90 or 95 percentiles - have shown that increased left ventricular wall thickness and increased left ventri- cular mass is seen frequently. Central haemodynamics, however, seem to vary in this group, and a low CI and high TPRI have been reported.

At the present time it seems reasonable to conclude that a variety of haemodynamic patterns might be found in what probably is the starting phase of primary hyperten- sion - increased resistance being the dominating pattern in some subjects, a high CI the dominating abnormality in others. Whether these different patterns represent diffe- rent forms of increased sympathetic activity is not known. However, after 10-17 years increased TPRI is found in the vast ma,jority of subjects with mild or borderline hyper- tension - irrespective of the original pattern.

References (The editors have requested a maximum of 6 re- ferences)

1. Lund-Johansen P: Haemodynamics in early essential hypertension - still an area of controversery. Editorial review. J Hypertension, vol. 1 , No. 2, 1983 (in press).

2. Fouad FM, Tarazi RC, Callagher JH, Macintyre WJ, Cook SA: Abnormal left ventricular relaxation in hyper- tensive patients. Clin Sci 59:411~-414s, 1980.

3. Messerli FH, Frohlich ED, Suraez H, Reisin E, Dreslinski G R , Dunn FG, Cole FE: Borderline hyper- tension: Relationship between age, haemodynamics and

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circulating catecholamines. Circulation 64:760-764, 1981.

4 . Hofman A, Ellison RC, Newburger J, Miettinen 0: Blood pressure and haemodynamics in teenagers. Br Heart J 48:377-380, 1982.

5. Logan AG, Gilbert BW, Haynes RB, Milne BJ, Flanagan PT: Early effect of mild hypertension on the heart. A longitudinal study. Hypertension, Suppl IT, 3:11-187- 11-190, 1981.

6. F o l k o w B: Physiological aspects of primary hyperten- sion. Physiol Rev 62:347-504, 1982.