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R. Nesher, S. Shulman, G. Nesher, R. Cohen, A. Harris; Diastolic Double Product in Normal Tension Glaucoma – A New Entity to Consider . Invest. Ophthalmol. Vis. Sci. 2006;47(13):4779.
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Evaluate the occurrence of bradycardia–hypotension (decreased double product) during 24–hour monitoring in normotensive patients with normal tension glaucoma (NTG) and episodic symptoms suggestive of low blood pressure.
11 NTG patients, mean age (53+10) with episodic symptoms suggestive of hypotension enrolled in the study. 24–hour monitoring of blood pressure (BP) and heart rate (HR) was performed in each case. Both parameters were automatically measured every 20 minutes during daytime and every hour during nighttime. The diastolic and systolic double product (DDP and SDP) at each reading were calculated by multiplying the HR by the respective BP. DDP<3600 (corresponding to BP of 60mmHg and HR of 60/min, which are the lower limit of normal in the resting state for these parameters) and SDP<5400 (corresponding to BP of 90mmHg and HR 60/min, which are the lower limit of normal for these parameters) were considered abnormally low. DDP<3000 and SDP<4700 were considered moderately abnormal, and DDP<2500 and SDP<4000 (corresponding to HR 50/min and BP of 50 and 80mmHg, respectively) were considered severely abnormal.
DDP was low in all 11 patients in at least one reading, mostly during nighttime. In 8 of them this decrease lasted at least 1 hour. The mean number of abnormally low readings was 8.9+7.3 per patient. Moderately abnormal DDP readings were recorded in 9 of the 11 patients (in 6 of them lasting more than 1 hour), and severely abnormal readings were observed in 6 patients (lasting more than 1 hour in 2 of them). Abnormally low SDP was present in 8 of the 11 patients, lasting more than 1 hour in 5 of them. The mean number of abnormally low SDP readings was 4.7+6.5 per patient. Moderately abnormal SDP readings were recorded in 6 patients (in 3 of them lasting more than 1 hour), and severely abnormal SDP readings were observed in only 3 patients (none lasting more than 1 hour).
A bnormally low DDP was recorded in all patients, lasting more than an hour in most cases. Abnormally decreased DDP, contemplating both the BP and HR, may represent a state of low ocular perfusion in this subgroup of NTG patients. The role and value of DDP recordings should be evaluated in larger–scale controlled studies of NTG patients, combining DDP with ocular blood flow measurements.
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