Journal of Human Hypertension (2007) 21, 341–342 & 2007 Nature Publishing Group All rights reserved 0950-9240/07 $30.00 www.nature.com/jhh
COMMENTARY
Blood pressure lowering effects of non-surgical procedures for vascular decompression: good news to be taken with caution G Grassi1,2 1
Clinica Medica, Dipartimento di Medicina Clinica, Prevenzione e Biotecnologie Sanitarie, Universita` Milano-Bicocca, Ospedale San Gerardo, Monza (Milan), Italy and 2Istituto Auxologico Italiano, Milan, and Centro Interuniversitario di Fisiologia Clinica e Ipertensione, Milan, Italy Journal of Human Hypertension (2007) 21, 341–342. doi:10.1038/sj.jhh.1002134; published online 25 January 2007
The notion that the central nervous system participates at the development, maintenance and progression of the essential hypertensive state dates back to almost a century ago and throughout the years it has received a consistent number of experimental and clinical supports. These include the evidence that central neural factors participate at the short- and long-term blood pressure control and that abnormalities in neurogenic modulation of the cardiovascular function characterize the early as well as the more established forms of the essential hypertensive state.1 A further support to the so-called ‘neurogenic hypothesis’ of hypertension comes from the evidence of a close link between some hypertensive states and neurovascular compression of the rostral ventrolateral medulla, that is, an area of the central nervous system with an important efferent pathway of the sympathetic nervous system.2–5 This association is strengthened by the evidence that in different experimental animal models electrical, chemical or mechanical stimulation of the ventricular medulla triggers a transient pressor response.6–7 It is also strengthened by the finding that in subgroups of patients with severe and/or resistant hypertension microsurgical decompression at the level of the rostral ventrolateral medulla substantially improves blood pressure control, leading to a long-term blood pressure normalization in a not negligible number of patients.3,8–10 The favourable haemodynamic outcome of the surgical intervention is likely to be triggered by a sympathetic deactivation, as several indirect and/or direct markers of adrenergic neural drive, such as plasma and urinary noradrenaline, Correspondence: Professor G Grassi, Clinica Medica, Ospedale San Gerardo dei Tintori, Via Pergolesi 33, 20052 Monza, (Milan) Italy. E-mail:
[email protected] Published online 25 January 2007
low-frequency/high-frequency spectral power ratio as well as efferent postganglionic sympathetic nerve firing rate, have all shown a consistent and rather homogeneous reduction of adrenergic cardiovascular drive following surgical decompression.10–11 In the present issue of the Journal of Human Hypertension, Bakris et al.12 add a new piece of information to the above-mentioned findings, by providing evidence on the favourable blood pressure lowering effects of chiropractic procedures capable to correct misalignment of the Atlas vertebra and thus to induce medullary vascular decompression. According to a double-blind, placebo-controlled study design, hypertensive patients with documented evidence of vertebral misalignment were randomized either to a chiropractic vertebral realignment procedure or to a sham intervention. The primary efficacy end point of the study was represented by the effects of the approach on sphygmomanometric systolic and diastolic blood pressure values, which were reduced at the end of the 8-week follow-up period by about 14 and 8 mm Hg, respectively (placebo-corrected values).12 The intriguing findings provided by Bakris et al. in this pilot study arise a number of questions that hopefully will be matter of future investigations. First, how are satisfactorily documented in the present study are the blood pressure lowering effects of the chiropractic procedure? Second, do the consistent short-term blood pressure lowering effects of the intervention persist over the long-term period? Third, does the lack of any effect of the intervention on heart rate really rule out any participation of sympathetic neural mechanisms at the blood pressure reduction? Fourth, is the procedure associated with additional favourable cardiovascular effects, such as end organ damage regression? Finally, do the results of the present study imply that a misalignment of the Atlas vertebra represents a risk factor for development of
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hypertension and that the chiropractic procedure stands as a new antihypertensive therapeutic approach? A study limitation is represented by the fact that the assessment of the blood pressure lowering effects of the intervention was based on clinical blood pressure measurements, which in a trial testing the effectiveness of a hypertensive intervention is known to encompass various limitations.13 An important one is the lack of information on the ability of the approach to lower blood pressure in daily-life conditions, that is, during the 24-h period. A further ‘intrinsic weakness’ of the study refers to the lack of information on the blood pressure lowering effects of the chiropractic intervention in the long-term period (months and years), as it has been carried out for the evaluation of the antihypertensive effects of surgical microvascular decompression.10 As far as heart rate as marker of adrenergic function is concerned, the lack of any change of this variable following the intervention does not necessarily imply that the chiropractic procedure has no sympatholytic effects. This is because heart rate is a poor and insensitive marker of sympathetic function, poorly correlating with more robust humoral or neurophysiological indices of adrenergic cardiovascular drive, such as plasma noradrenaline or muscle sympathetic nerve firing rate.14–15 Other relationships to adrenergic function, such as age, heredity, concomitant drug therapies and so on, will also need to be considered in any study.16–18 In conclusion, the study by Bakris et al. provides new interesting information on the favourable blood pressure lowering effects of microvascular decompression caused by chiropractic procedure. Before recommending this therapeutic strategy in the current clinical practice, however, it seems reasonable to wait for the results of large-scale clinical trials aimed at defining the long-term effects of the intention on clinic and ambulatory blood pressure as well as on some surrogate end points, such as cardiac and vascular target organ damage.
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