Biomedical subjects
Publications and source records attributed to N Boon.
Endogenous catecholamines in excess are known to cause dilated cardiomyopathy. A patient presented with dilated cardiomyopathy after many years of overusing an adrenaline inhaler. Pathological features and a considerable improvement in myocardial function after withdrawal implicated the exogenous catecholamine excess in the pathogenesis of the cardiomyopathy.
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When captopril was first introduced for the management of hypertension, its short plasma half-life led to its use as a thrice daily regimen. However, further experience suggests that the biological action is more prolonged than the plasma half-life might suggest. This study examined the effect of varying the frequency of administration (once, twice and three times daily) of a fixed daily dosage of 75 mg captopril on ambulatory BP in a double-blind cross-over study in 15 patients with mild to moderate hypertension. Each patient had six ambulatory BP recordings with placebo alternating with active phase. The three regimens (75 mg daily, 37.5 mg twice daily and 25 mg three times daily) reduced the daily mean BP equally and significantly compared with placebo. Three patients with very high pretreatment plasma renin values showed some loss of BP control immediately prior to the first dose in the morning in the 75 mg single dose phase (i.e. 24 hours post dose); but group analysis showed no difference in mean BP at this time point with the three treatment regimens. We conclude that in spite of its short plasma half-life, captopril can effectively control BP over the whole day with a once daily regimen.
Blood pressure variability throughout the day has been found to be inversely related to baroreflex sensitivity, as is the response to injected phenylephrine, mental stress and sleep. It is concluded that variability in blood pressure results in some degree from defective buffering of blood pressure by the baroreceptors.
In order to study blood pressure variability we have measured blood pressure, heart rate, plasma noradrenaline and adrenaline concentration and plasma renin activity during sleep and during the waking process in 20 subjects with borderline hypertension. The responses to a number of standardized tests were also measured. These were reading, mental arithmetic, change in posture, physical exercise and the response to intravenously injected phenylephrine and noradrenaline. The sensitivity of the baroreflex for heart rate control was also determined from the relationship between heart period (R-R interval) and change in systolic pressure after the injection of phenylephrine. Blood pressure was also recorded continuously for 24 hours. From the lowest levels achieved during sleep, blood pressure rose as the subjects regained consciousness but was not restored to its baseline value until mental activity was also restored by reading. Blood pressure rose further with mental arithmetic. These changes were accompanied by a greater proportional rise in plasma adrenaline than in plasma noradrenaline concentrations. Plasma renin activity changed little. The pressor responses to phenylephrine and noradrenaline were inversely related to baroreceptor sensitivity. The fall in blood pressure with sleep and the rise with mental arithmetic was also inversely related to the sensitivity of the reflex. Systolic pressure recorded throughout the day was inversely related to the R-R interval in each subject. The slope of this relationship and range of R-R interval was greatest in the subjects with the most sensitive baroreflexes.
Blood pressure variability has been studied from 24-h direct arterial pressure recordings in 109 subjects (36 normals and 73 hypertensives). Baroreflex sensitivity was also measured. From the 24-h record a linear relationship was found between systolic pressure and heart period. The slope was related to baroreflex sensitivity (r = 0.66, P less than 0.001). Those with shallow slopes had a high systolic pressure level and greater variability, thus efficient control of heart rate limits blood pressure variability.
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The MELD score has now been implemented in the United States for liver allocation, but it has not been validated in Europe. Its association with posttransplant outcome is unclear. Optimal cutoff values of MELD and Child-Pugh scores to predict death on the liver waiting list were defined in a series of 137 cirrhotic patients listed for liver transplantation. Six-month actuarial survival while on the waiting list was 90% with a Child-Pugh <11 and MELD <17, whereas it decreased progressively to 40% at 6 months after listing for those having a Child-Pugh and MELD score >10 and >16. Analysis of a series of 112 patients (85 chronic liver disease and 27 hepatocellular carcinoma) revealed no change in MELD value at the time of transplantation compared to the score at the time of listing (mean +/- SD: 15.5 +/- 7.7 vs 15 +/- 5.8) with a mean waiting time of 118 days. Using either the optimal cutoff for MELD score (<17 or >16) or seven different strata (3 to 7, 8 to 10, 11 to 13, 14 to 16, 17 to 19, 20 to 22, 23 to 39), whether measured at listing or just before liver transplantation, there was no significant difference (chi(2) 4.97, P = .58) in survival: 82.7% and 63% at 6 and 60 months, overall. Our data confirm that the MELD score with only three parameters is as good as the Child-Pugh score to predict mortality on the Eurotransplant waiting list. The optimal cutoff to assess higher priority for the bad category is >16. There was no negative impact on short- or long-term prognosis of the bad categories of MELD.
We have measured baroreflex sensitivity and blood pressure in 13 subjects during sleep and three stages of progressive mental arousal after waking. Baroreflex sensitivity was measured by correlating the increase in pulse interval with the increase in systolic pressure produced by an intravenous injection of 80 micrograms of phenylephrine. Blood pressure was measured directly from the brachial artery. During sleep, blood pressure fell and baroreflex sensitivity increased; with increasing mental arousal, blood pressure rose and baroreflex sensitivity decreased. These results suggest that baroreflex activity may be involved in the medium-term regulation of blood pressure during the day and night in addition to its recognized role in buffering acute changes in blood pressure.