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Anesthesiology:
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Baroreflex Activity in Hypertensive Patients

Prys-Roberts, Cedric D.M., Ph.D., F.R.C.A.

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To the Editor:
—I read with great interest the study by Parlow et al.1 concerning baroreflex activity in hypertensive patients and the apparently beneficial effect of clonidine in reversing the impaired heart rate control found in these patients.
The authors state in their introduction “By contrast, cardiac baroreflex sensitivity has not previously been studied . … in surgical patients with concomitant hypertension.” This statement comes in the same paragraph as a reference to my first article on studies of anesthesia in relation to hypertension. 2 On page 132 of our article, Table 5 summarizes assessments of baroreflex activity in three groups of patients: 7 normotensive patients, 7 untreated hypertensive patients, and 12 treated hypertensive patients, all studied awake before administration of anesthesia and during stable anesthesia before surgery. Our values for baroreflex slope in the awake treated hypertensive patients (4.1 ms/mmHg, SD 3.0) were very similar to those presented by Parlow et al., and the decreased values during anesthesia in our patients (0.9 ms/mmHg, SD 1.8) were also very similar to the values in Parlow et al. ’s placebo group. For various reasons, we were only able to achieve satisfactory baroreflex slopes for six of the patients in the postoperative period and therefore did not include those data in our report. Those six patients had baroreflex slopes that were not significantly different from their preoperative values.
In rereading our report after reading that by Parlow et al., I was struck by a fact that I had not previously given much thought to but that may be very relevant in light of Parlow et al. ’s findings. Seven of our 12 treated hypertensive patients were receiving methyldopa (500–1,500 mg total daily dose) either alone or in combination with bethanidine. Methyldopa is metabolized to α-methylnoradrenaline, now known to be a weak(ish) α2-adrenoceptor agonist. Could it be that the relative postoperative cardiovascular stability that we described for our treated hypertensive (as opposed to the untreated hypertensive) patients was the result of residual effects of the methyldopa that they had received up to and including the morning of surgery?
Cedric Prys-Roberts D.M., Ph.D., F.R.C.A.
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References

1. Parlow JL, Bégou G, Sagnard P, Cottet-Emard JM, Levron JC, Annat G, Bonnet F, Ghignone M, Hughson R, Viale J-P, Quintin L: Cardiac baroreflex during the postoperative period in patients with hypertension: Effect of clonidine. A NESTHESIOLOGY 1999; 90:681–92

2. Prys-Roberts C, Meloche R, Foëx P: Studies of anaesthesia in relation to hypertension: I. Cardiovascular responses of treated and untreated patients. Br J Anaesth 1971; 43:122–37

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