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ARTICLES: Ronald I. Herning, Warren E. Better, Kimberly Tate, and Jean L. Cadet Cerebrovascular perfusion in marijuana users during a month of monitored abstinence Neurology 2005; 64: 488-493 [Abstract] [Full text] [PDF]

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Cerebrovascular perfusion in marijuana users during a month of monitored abstinence

Joseph W McSherry   (16 April 2005)

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Ronald I. Herning, PhD   (16 April 2005)

Cerebrovascular perfusion in marijuana users during a month of monitored abstinence 16 April 2005
Joseph W McSherry, Fletcher Allen Health Care Inc 111 Colchester Avenue, Burlington, VT 05401 Send Correspondence to journal: Re: Cerebrovascular perfusion in marijuana users during a month of monitored abstinence joe.mcsherry{at}vtmednet.org Joseph W McSherry	A striking feature of this article is the lack of a dose effect on the devastating effects of cannabis use. The light users (3.5 joints per week) have Perfusion Indices (PI) similar to the heavy users (70 joints per week), both significantly higher than controls. Perhaps this is because, like tobacco users, the smokers seek a dose of drug. The heavy users, younger and starting earlier, may be less economically successful and smoke stems while the light, older users may be able to purchase flowers that are 20 times as potent. Inconsistent observation and technique should also be considered. In addition, the PIs of the users fall above the reported PIs of complicated diabetics. Yet the controls in this study also have PIs in the range of the complicated diabetics, higher than uncomplicated diabetics and the controls for the earlier study. [1] Perhaps the lower diastolic pressure of the users vs controls (70 vs 79) is contributory. The conclusion that the differences observed reflect higher resistance in the parenchyma is unclear. With mean flow rates at least as high in users as controls, this contrasts with the findings in hypertensive patients who have reduced flow velocity after years of hypertension. [2] Reduced flow with increased resistance at a constant pressure makes sense. Increased flow at reduced pressure (users) does not suggest increased peripheral resistance. An earlier article involving some of these subjects [3] showed increased executive function with increasing use among above average IQ persons. This study confirms other observations that early use is a risk factor for heavy use. Uncertainty about dosage levels among smokers helps us understand why there are so few approved studies for smoked cannabis as medicine. References 1. Lee KY, Sohn YH, Baik JS, Kim GW, Kim S-J. Arterial pulsatility as an index of cerebral microangiopathy in diabetes. Stroke 2000;31:1111- 1115. 2. Cho S, Kim GW, Shhn YH. Blood flow velocity changes in the middle cerebral artery as an index of chronicity of hypertension. J Neurol Sci 1997;50:77-80. 3. Bolla KI, Brown K, Eldreth D, Tate K, Cadet JL. Dose-related neurocognitive effects of marijuana use. Neurology 2002;116:173-185.
Reply to McSherry 16 April 2005
Ronald I. Herning, PhD, Molecular Neuropsychiatry Branch, National Institute on Drug Abuse PO Box 5180, Baltimore, MD 21224 Send Correspondence to journal: Re: Reply to McSherry RHERNING{at}intra.nida.nih.gov Ronald I. Herning, PhD	We thank Dr. McSherry for his interest in our article. His suggestion that self-titration of the smoked dose of marijuana might account for the lack of dose effect on the first test session is interesting. It may explain the lack of a difference in the blood flow velocity measures at the recording session early in abstinence. Both marijuana users [4] and tobacco smokers [5] were reported to be able to control their dose by changing their smoking behavior. In retrospect, the determination quantitative levels of THC in urine would have been a more scientific way to group subjects in this study. The same technologist tested all subjects in this study. Thus, technique can be ruled out as a possible factor. We also argue that blood pressure differences were not likely responsible for the PI differences. While diastolic pressure was decreased in the marijuana users compared to the control subjects, diastolic velocity did not differ between the control and marijuana groups. Our conclusion of higher resistance in the parenchyma is based on the PI data and not directly on velocity data as Dr. McSherry suggests. Lam and Newell [6] have stated “In the absence of stenosis or vasospasm, the pulsatility of the flow velocity pattern reflects distal cerebrovascular resistance... Neither index (PI or RI) provides meaningful information regarding the cause of the change, however; for example, an increase in PI can be due cerebrovasoconstriction or to high intracranial pressure.” Diastolic (mean increase of about 14 mm Hg) and systolic (mean increase of about 27 mm Hg) blood pressure were significantly increased in the hypertensive patients compared to controls. [2] In our study, only diastolic pressure was decreased in the marijuana users by 9 mm Hg compared to the control subjects. Perhaps the increase in PI in the hypertensive patients might be related to an increase in intracranial pressure and the increase in PI in the marijuana users might be due to a distal increase in cerebrovascular resistance. Further research is needed. References 4. Herning RI, Hooker WD, Jones RT Tetrahydrocannabinol content and differences in marijuana smoking behavior. Psychopharmacology, 1986; 90:160-162. 5. Herning RI, Jones RT, Benowitz N, Mines AH How a cigarette is smoked determines nicotine blood levels. Clinical Pharmacology and Therapeutics, 1983; 33:84-90. 6. Lam AM, Newell DW, Intraoperative use of transcranial Doppler ultrasonograpy. Neurosurgey Clinics of North America 1996; 7:709-722.