24-h blood pressure recordings in type I diabetic patients

Ambulatory blood pressure (AMBP) is of particular interest in diabetes because of the close association between elevated BP and diabetic nephropathy and the attenuated night drop in some diabetic subgroups: (1) Normoalbuminuric patients: If standardized for type of day (work or day off), coefficient of variation (CV) for 24 h AMBP is 2%–3% and 5%–6% for night/day ratio. The male-female difference in AMBP seen in healthy subjects is reduced in diabetes. Smoking did not significantly affect AMBP. AMBP is increased in patents with high normal urinary albumin excretion (UAE). Night/day ratio of AMBP and night heart rate is higher in long than short term diabetic patients. This difference in night/day ratio is not significant if the slightly higher UAE in long-term patients is accounted for. (2) Microalbuminuric patients: Diastolic night/day ratio is increased compared with healthy controls, with the value for normoalbuminuric patients in between. A large overlap between groups is evident. Thus the prognostic value of a single abnormal night/day ratio is doubtful. If divided into dippers and nondippers, no difference in extracellular- or plasma volume is found, but nondippers have a lower plasma aldosterone and arginine vasopressin level, possibly to counteract volume expansion. (3) Patients with overt nephropathy: A marked increased in AMBP and a clear reduction of the nocturnal blood pressure fall is seen. In conclusion, AMBP (but not night/day ratio) is highly reproducible. The association between elevated AMBP, elevated night/day ratio, and pathological UAE is detectable even in normoalbuminuric patients. The prognostic importance of abnormal circadian variation of BP is unsettled.     

Intra-arterial pressure alterations during tail-cuff blood pressure measurements in normotensive and hypertensive rats

The heating and restraint inherent to tail-cuff measurement of systolic blood pressure (SBP) in rats may alter SBP and introduce a 'biological' error in its estimation by this technique. This problem was examined in unanesthetized normotensive and hypertensive rats fitted with an arterial catheter. All SBP values recorded in unrestrained rats during a 2 h period were averaged by computer and compared with intra-arterial SBP measurements observed while the rat was being subjected to the tail-cuff procedure. With the latter procedure, SBP was 16 +/- 2 mmHg lower in normotensive rats (P less than 0.001) and 7 +/- 3 mmHg higher in hypertensive rats (P less than 0.05) than when the rats were unrestrained. The effects of heat and restraint, both separately and in combination, on SBP were evaluated during four additional 30-min monitoring periods. In both groups of rats, restraint failed to alter SBP and heat lowered it slightly. The two stimuli, combined, lowered SBP in normotensive rats, but raised it by 12 +/- 2 mmHg in hypertensive rats (P less than 0.01). Thus, tail-cuff SBP measurements represent under- and overestimates in normotensive and hypertensive rats, respectively, since the two groups respond to the procedure in opposite manners.     

Effects of insufficient sleep on blood pressure in hypertensive patients: A 24-h study

The influence of acute sleep deprivation during the first part of the night on 24-h blood pressure monitoring (ABPM) was studied in 36 never-treated mild to moderate hypertensive patients. According to a crossover design, they were randomized to have either sleep deprivation or a full night’s sleep 1 week apart, during which they were monitored with ABPM. Urine samples for analysis of nocturnal urinary excretion of norepinephrine were collected. During the sleep-deprivation day, both mean 24-h blood pressure and mean 24-h heart rate were higher in comparison with those recorded during the routine workday, the difference being more pronounced during the nighttime (P < .01). Urinary excretion of norepinephrine showed a significant increase at night during sleep deprivation (P < .05). Blood pressure and heart rate significantly increased in the morning after a sleep-insufficient night (P < .05). These data suggest that lack of sleep in hypertensive patients may increase sympathetic nervous activity during the night and the following morning, leading to increased blood pressure and heart rate. This situation might represent an increased risk for both target organ damage and acute cardiovascular diseases.     

Effects of daily walking on office,home and 24-h blood pressure in hypertensive patients

Abstract

Aerobic exercise has been recommended in the management of hypertension. However, few studies have examined the effect of walking on ambulatory blood pressure (BP), and no studies have employed home BP monitoring. We investigated the effects of daily walking on office, home, and 24-h ambulatory BP in hypertensive patients. Sixty-five treated or untreated patients with essential hypertension (39 women and 26 men, 60?±?9 years) were examined in a randomized cross-over design. The patients were asked to take a daily walk of 30–60?min to achieve 10?000 steps/d for 4 weeks, and to maintain usual activities for another 4 weeks. The number of steps taken and home BP were recorded everyday. Measurement of office and ambulatory BP, and sampling of blood and urine were performed at the end of each period. The average number of steps were 5349?±?2267/d and 10?049?±?3403/d in the control and walking period, respectively. Body weight and urinary sodium excretion did not change. Office, home, and 24-h BP in the walking period were lower compared to the control period by 2.6?±?9.4/1.3?±?4.9?mmHg (p?<?0.05), 1.6?±?6.8/1.5?±?3.7?mmHg (p?<?0.01), and 2.4?±?7.6/1.8?±?5.3?mmHg (p?<?0.01), respectively. Average 24-h heart rate and serum triglyceride also decreased significantly. The changes in 24-h BP with walking significantly correlated with the average 24-h BP in the control period. In conclusion, daily walking lowered office, home, and 24-h BP, and improved 24-h heart rate and lipid metabolism in hypertensive patients. However, the small changes in BP may limit the value of walking as a non-pharmacologic therapy for hypertension.     

The importance of 24-h blood pressure control

The primary goal of antihypertensive therapy is to restore blood pressure to normal levels and to prevent the complications associated with hypertension. In order to maximize these goals by improving patient compliance, clinical researchers have focused on developing antihypertensive agents that can be given once daily. These agents provide many advantages over multiple-dose daily therapies, but it should not be assumed that they are all equivalent in providing adequate blood pressure control over the full 24-h dosing interval. Ambulatory blood pressure monitoring has uncovered important differences in commonly used once-daily therapies and has provided additional insights into the cardiovascular risks associated with high blood pressure loads and blood pressure variability. In addition to ambulatory blood pressure monitoring data, the calculated trough:peak ratio provides useful information on an agent's ability to provide smooth and consistent blood pressure control. Using such assessments, it has been found that agents with a trough:peak ratio > or = 0.50 are better able to control blood pressure over the full 24h while maintaining natural circadian patterns. Ambulatory blood pressure monitoring studies assessing a recently introduced class of antihypertensive drugs, the angiotensin receptor blockers, have demonstrated 24-h efficacy with once-daily dosing, particularly with the newer agents.     

Reproducibility of the circadian blood pressure pattern in 24-h versus 48-h recordings: the Spanish Ambulatory Blood Pressure Monitoring Registry

OBJECTIVES: To assess the reproducibility of the circadian blood pressure (BP) pattern over a 48-h period by comparing the first 24 h of ambulatory blood pressure monitoring (ABPM) with the following 24 h and with the mean over 48 h. PATIENTS AND METHODS: Patients undergoing 48-h ABPM within the National ABPM Registry of the Spanish Society of Hypertension, based on 800 Spacelabs 90207 monitors distributed throughout Spain in hypertension units and primary healthcare centres, were included. Between June 2004 and September 2005, 611 valid 48-h ABPM recordings were obtained, 235 corresponded to patients without antihypertensive treatment. RESULTS: The percentages of patients classified as non-dipper for the first 24 h, the second 24 h and the 48-h average were 47, 50 and 48%, respectively. When the first and second 24-h periods were compared, 147 (24%) subjects switched from dipper (D) to non-dipper (ND) or vice-versa. When the first 24-h period was compared to the 48-h average, 66 (11%) subjects switched patterns. The proportions were similar separately for systolic blood pressure (SBP) and diastolic blood pressure (DBP) and between treated and untreated patients. In subjects with poor ABPM reproducibility, night-to-day ratios were of an intermediate value between those of subjects always classified as D or ND. CONCLUSION: Categorization of D or ND based on a single 24-h ABPM is moderately reproducible, since one out of every five patients change profile over the following 24 h. Nevertheless, the use of 48-h ABPM in clinical practice should be assessed according to cost-effectiveness criteria. Night-to-day ratios may be helpful in identifying patients with a stable profile.     

Factors determining the 24-h blood pressure profile in normotensive patients with type 1 and type 2 diabetes

Some controversy still exists about factors involved in the abnormal circadian pattern of blood pressure (BP) in diabetes, while prognostic value of non-dipping condition is being increasingly recognised. This study was aimed at evaluating the relative influence of autonomic neuropathy (AN) and albumin excretion on 24-h BP profile in type 1 and type 2 diabetes. We measured AN cardiovascular tests, 24-h ambulatory BP, and urinary albumin excretion rate (UAE) in 47 type 1 and 34 type 2 normotensive non-proteinuric diabetic patients. In type 1 diabetic patients day-night differences (Delta) in systolic and diastolic BP were lower in those with AN than in those without (3 +/- 9 vs 10 +/- 6%, P < 0.01, and 8 +/- 9 vs 16 +/- 6%, P < 0.001), and in univariate regression analysis they were inversely related to both autonomic score, index of degree of AN (r = -0.61, P < 0.001 and r = -0.65, P < 0.001), and to 24-h UAE (r = -0.39, P < 0.01 and r = -0.46, P < 0.001). In type 1 diabetic patients AN was also associated with lower nocturnal decrease in UAE (patients with AN vs without AN: -37 +/- 214 vs 49 +/- 37%, P < 0.05), and with a stronger relationship between simultaneous 24-h UAE and 24-h BP (for systolic BP patients with AN vs without AN: r = 0.62, P < 0.01 vs r = 0.28, NS). In type 2 diabetic patients Delta systolic BP was reduced in patients with AN compared to those without (4 +/- 7 vs 10 +/- 4%, P < 0.01), and it was related only to autonomic score (r = -0.42, P < 0.01). Using a stepwise regression analysis, in type 1 diabetic patients autonomic score was the variable of primary importance for Delta BP, while in type 2 diabetic patients it was the unique determinant not only of Delta systolic BP but also of 24-h systolic BP. In conclusion, AN is the pivotal factor of blunted nocturnal fall in BP in both type 1 and type 2 diabetic patients. In type 1 diabetic patients AN is associated with attenuated circadian pattern of albuminuria and with a steeper relationship between albuminuria and BP, in type 2 diabetic patients AN is the only factor related to elevated 24-h BP levels. Longitudinal studies are needed to establish the potential role of autonomic dysfunction as a progression promoter for nephropathy and hypertension in type 1 and type 2 diabetes respectively.     

Effect of a mineral salt diet on 24-h blood pressure monitoring in elderly hypertensive patients

The influence of a mineral salt on 24-h ambulatory blood pressure (BP) monitoring was studied in 20 elderly hypertensive subjects residing in an old peoples home. Ordinary table and cooking salt was substituted with a special Na-reduced, K-, Mg-, and l-lysine HCl-enriched mineral salt (Pansalt(R)) for 6 months. Antihypertensive therapy was uninterrupted. An ambulatory BP monitor (Suntech Accutracker) measured BP every 20 min during the day and every 30 min at night, before and 6 months after starting the diet. Nine patients (45%) decreased both systolic and diastolic BP significantly: systolic BP fell from 154.92 +/- 33.67 mm Hg to 143. 45 +/- 53.1 mm Hg (P < or = 0.01) during the daytime from 6 am to midnight; and from 139.80 +/- 32.84 mm Hg to 137.87 +/- 31.17 mm Hg (P < or = 0.01) from midnight to 6 am. Diastolic BP fell from 85.34 +/- 24.85 mm Hg to 70.29 +/- 18.31 mm Hg (P < or = 0.01) during the daytime from 6 am to midnight; and from 77.1 +/- 22.92 mm Hg to 67.76 +/- 15. 63 mm Hg (P < or = 0.01) at night. Blood pressure in the other 11 subjects showed no improvement. Heart rate also fell in the subjects, from 69.44 +/- 21.62 beats per minute (bpm) to 66.94 +/- 11.51 bpm (< or = 0.01) during the day, and from 61.28 +/- 12.82 bpm to 60.43 +/- 10.33 bpm (P < or = 0.01) during the night. It is concluded that decreased intake of Na and increased intake of both K and Mg can be useful in controlling high BP.     

Correlations and otherwise between blood pressure, cardiac mass and resistance vessel characteristics in hypertensive, normotensive and hypertensive/normotensive hybrid rats

We have measured heart weight and properties of 150-200 microns mesenteric resistance vessels from spontaneously hypertensive (SHR), Wistar-Kyoto (WKY), two-kidney, one clip Goldblatt renal hypertensive (RHR) and outbred Wistar rats, as well as in SHR/WKY F2-hybrid rats. All rats were 14-weeks-old. In the SHRs, WKYs, RHRs and Wistars the mean blood pressures (measured intra-arterially) were, respectively: 136, 111, 164 and 100 mmHg. In the SHR/WKYs the systolic blood pressures (measured regularly over a two-week period by the tail cuff method) were normally distributed between the values obtained from control SHRs and WKYs. Relative heart weight and resistance vessel media thickness/lumen diameter ratio correlated (P less than 0.001) with blood pressure between SHRs, WKYs, RHRs and Wistars; however, no significant correlation was seen in SHR/WKYs. By contrast, the calcium sensitivity of the resistance vessel noradrenaline response did correlate (P less than 0.01) with blood pressure in the SHR/WKYs, but did not correlate between the pure strains (calcium sensitivity of the SHR and Wistar vessels was similar, but higher than that of the WKY vessels; induction of renal hypertension did not affect calcium sensitivity). The results suggest that although the cardiac enlargement and increased resistance vessel media/lumen ratio of 14-week SHRs may be advantageous for these animals, these structural abnormalities may not be primary causes of the hypertension. Furthermore, the results indicate that it is the WKYs which are abnormal in having a low calcium sensitivity of their resistance vessels, but suggest also that this reduced sensitivity may be associated with mechanisms which help to keep the WKYs normotensive.     

Effects of rilmenidine on 24-h rhythmicity of blood pressure and spontaneous baroreflex sensitivity in essential hypertensive subjects

OBJECTIVE: To study the effects of the centrally acting imidazoline-like compound rilmenidine on the circadian and short-term cardiovascular rhythms derived from continuous blood pressure (BP) recordings in patients with mild essential hypertension. METHODS: This was a single-center, open study. Recordings were obtained from eight subjects, using a Portapres during two 24-h hospitalizations: the first after the inclusion visit and the second 4 weeks after starting rilmenidine treatment (1 or 2 mg/day). For circadian analysis of cardiovascular variables, 10 min were selected every hour to obtain 24 periods per subject for each session. Spontaneous baroreflex sensitivity (BRS) was estimated using the sequence technique and the cross-spectral analysis between systolic BP and interbeat intervals. RESULTS: Rilmenidine significantly reduced the overall systolic and diastolic BP and heart rate (P < 0.001). The effects of rilmenidine on BP and heart rhythm were marked during the daytime. Rilmenidine reduced the low-frequency (LF) component of systolic BP variability throughout the 24 h. The highest values of spontaneous BRS were observed at night. Rilmenidine increased the BRS obtained by the slope of the sequence method throughout the 24-h period (P < 0.001). The LF gain was significantly increased with rilmenidine during the day and the night. CONCLUSIONS: Rilmenidine may differentially affect the baroreflex-dependent (phasic or reflex) and the baroreflex-independent (tonic) autonomic outflow. The 24-h approach reinforced this concept, since indexes of BRS were increased throughout the 24-h period while BP was reduced during the daytime.     

Limited reproducibility of 24-h ambulatory blood pressure monitoring

Abstract

Results of 24-h ambulatory blood pressure monitoring (ABPM) including average blood pressure, variability, and nocturnal dipping are considered the gold standard for diagnosis and the best predictor of the future end organ damage in chronic hypertension. Here we report on the reproducibility of ABPM results for these three measures over a period of months. A total of 35 hypertensive patients (43% female, mean age 64 years), underwent two separate ABPM recordings within 14 weeks, with unchanged medical treatment and lifestyle in the interim. The day and night average blood pressure, dipping status of systolic pressure, and the standard deviation of systolic and diastolic blood pressure as a measure of variability were compared between the two recordings. Individual values for average systolic and diastolic pressures showed only a modest correlation between the two measurements (r?=?0.56, r?=?0.81, p?<?0.01). Standard deviations of 24-h pressure were also positively but weakly correlated (r?=?0.4, p?<?0.001). The occurrence of dipping was reproducible in 71% of the patients. Average blood pressure, pressure variability, and dipping as assessed by ABPM are only moderately reproducible. Clinical decision-making based on single ABPM datasets should be made with caution, and repetition of ABPM seems justified in some cases.     

Effects of high-calorie diet on blood pressure and sodium retention in spontaneously hypertensive rats and normotensive Wistar-Kyoto rats

Previous reports from our laboratory have documented that spontaneously hypertensive rats (SHR) have insulin resistance and that insulin resistance is enhanced by high-caloric diet (HCD) feeding. The aim of this study was to elucidate the effect of HCD on blood pressure and sodium retention in both SHR and normotensive Wistar-Kyoto rats (WKY). SHR and WKY were divided into two groups. One group of rats was fed normal diet (ND). The other rats were fed HCD. After the 8-week feeding period, insulin suppression tests were performed. The animals were individually housed in metabolic cages for the last 2 days of the experiment. Food consumption was recorded for 24 h, and a 24-h urine was collected to calculate the sodium excretory ratio. In both strains, body weight was significantly increased by HCD feeding. Blood pressure was significantly elevated in SHR by HCD feeding, whereas that of WKY was not affected by HCD feeding. In both strains, steady-state plasma glucose (SSPG) during the insulin suppression test was higher in the HCD group than in the ND group. SSPG was consistently higher in SHR than in WKY treated with HCD. Urinary sodium excretion ratio was significantly decreased in SHR by HCD, and plasma potassium concentrations were significantly lower in SHR with HCD than in SHR with ND, whereas those of WKY were not affected by HCD feeding. SHR are more sensitive to the induction of insulin resistance than WKY, resulting in sodium retention and elevation of blood pressure.     

24 h rhythm of blood pressure and forearm peripheral resistance in normotensive and hypertensive subjects confined to bed

OBJECTIVES: To define whether a diurnal rhythm of peripheral resistance exists in normotensive and hypertensive subjects, has any relationship with that of blood pressure and differs in dipper and non-dipper hypertensives. DESIGN AND METHODS: Forty-three subjects (13 normotensives and 30 mild-to-moderate essential hypertensives) confined for 24 h to bed were included. Blood pressure was recorded for 22 h at 15 min intervals, plethysmographic forearm flow was simultaneously measured and forearm resistance calculated. The analysis was performed for the whole 22 h period and for three 4 h truncated periods, two of certain wakefulness and one of certain sleep. RESULTS: A circadian rhythm of forearm resistance was shown in the normotensives, paralleling that of blood pressure. All the normotensives were dippers, with a nocturnal blood pressure dip (systolic/diastolic) of -4.5/-6.0%. In the hypertensives, the day/night blood pressure trends were not homogeneous: 21 showed higher blood pressure values during waking time, with a trend quite similar to that of the normotensives, whereas the other nine were non-dippers. Resistance was lower during sleep than during waking both in the normotensives and in the dipper hypertensives, whereas in the non-dippers it was higher during sleep. CONCLUSIONS: A sleep/waking rhythm of peripheral resistance with the highest values during daytime and the lowest during night-time does exist in normotensive as well as in the majority of hypertensive subjects resting continuously in bed, and therefore is largely independent of physical activity. Only in a minority of hypertensive patients are higher values of peripheral resistance present during sleep.     

24-h blood pressure monitoring in normal tension glaucoma: night-time blood pressure variability

Systemic arterial hypotension, hypertension and altered ocular blood flow are known risk factors in glaucoma. In this study, 24-h ambulatory blood pressure monitoring was performed in patients with normal tension glaucoma (NTG) and controls to evaluate blood pressure variability. In all, 51 patients with NTG and 28 age-matched controls were included in this prospective study. A 24-h ambulatory blood pressure monitoring (SpaceLabs Medical Inc., Redmond, USA) was performed and systolic, diastolic and mean arterial blood pressures were measured every 30 min during daytime (0800-2000) and night time (0000-0600). To evaluate blood pressure variability a variability index was defined as the s.d. of blood pressure measurements. Night-time blood pressure depression ('dip') was calculated (in percent of the daytime blood pressures). Patients with NTG exhibited higher night-time diastolic (P = 0.01) and mean arterial blood pressure values (P = 0.02) compared to controls, whereas systolic blood pressure data were not significantly different. The variability indices of night-time systolic, diastolic and mean arterial blood pressure measurements were significantly increased in patients with NTG compared to controls (P < 0.05). The night-time blood pressure depression of systolic (P = 0.47), diastolic (P = 0.11) and mean arterial blood pressures (P = 0.28) was not significantly different between patients with NTG and controls. In conclusion, patients with NTG showed increased variability of night-time blood pressure measurements compared to controls. Increased fluctuation of blood pressure may lead to ocular perfusion pressure fluctuation and may cause ischaemic episodes at the optic nerve head.     

Aldosterone excess and resistance to 24-h blood pressure control

BACKGROUND: Aldosterone excess has been reported to be a common cause of resistant hypertension. To what degree this represents true treatment resistance is unknown. OBJECTIVE: The present study aimed to compare the 24-h ambulatory blood pressure monitoring (ABPM) levels in resistant hypertensive patients with or without hyperaldosteronism. METHODS: Two hundred and fifty-one patients with resistant hypertension were prospectively evaluated with an early-morning plasma renin activity (PRA), 24-h urinary aldosterone and sodium, and 24-h ABPM. Daytime, night-time, and 24-h blood pressure (BP) and nocturnal BP decline were determined. Hyperaldosteronism (H-Aldo) was defined as suppressed PRA (<1.0 ng/ml per h or <1.0 mug/l per h) and elevated 24-h urinary aldosterone excretion (>/= 12 mug/24-h or >/= 33.2 nmol/day) during ingestion of the patient's routine diet. RESULTS: In all patients, the mean office BP was 160.0 +/- 25.2/89.4 +/- 15.3 mmHg on an average of 4.2 medications. There was no difference in mean office BP between H-Aldo and normal aldosterone status (N-Aldo) patients. Daytime, night-time, and 24-h systolic and diastolic BP were significantly higher in H-Aldo compared to N-Aldo males. Daytime, night-time, and 24-h systolic BP were significantly higher in H-Aldo compared to N-Aldo females. Multivariate analysis indicated a significant interaction between age and aldosterone status such that the effects of aldosterone on ambulatory BP levels were more pronounced with increasing age. CONCLUSIONS: In spite of similar office BP, ABPM levels were higher in resistant hypertensive patients with H-Aldo. These results suggest that high aldosterone levels impart increased cardiovascular risk not reflected by office BP measurements.     

24-h ambulatory blood pressure and retinopathy in normoalbuminuric IDDM patients

Summary The role of blood pressure elevation in the incidence and progression of diabetic retinopathy is not clearly established and results have been conflicting. Blood pressure and urinary albumin excretion (UAE) are closely related. In order to evaluate the independent relationship between retinopathy and blood pressure elevation, precise information on UAE is essential, as confounding by renal disease (incipient or overt), cannot otherwise be excluded.The aim of the present study was to evaluate the association between diabetic retinopathy and 24-h ambulatory blood pressure (AMBP) in a group of well-characterized normoalbuminuric IDDM patients. In 65 normoalbuminuric (UAE < 20 μg/min) IDDM patients we performed 24-h AMBP (Spacelabs 90 207) with readings at 20-min intervals. Fundus photographs were graded independently by two experienced ophthalmologists. UAE was measured by RIA and expressed as geometric mean of three overnight collections made within 1 week. HbA_{1 c} was determined by HPLC. Tobacco use and level of physical activity were assessed by questionnaire. Fifteen patients had no detectable retinal changes [grade 1], 35 had grade 2 retinopathy; and 15 had more advanced retinopathy [grade 3–6]. Diastolic night blood pressure was significantly higher in patients with diabetic retinopathy compared to patients without retinopathy (68 ± 8 mmHg [grade 3–6] and 65 ± 6 mmHg [grade 2], compared to 61 ± 4 mmHg [grade 1], p = 0.02). Diurnal blood pressure variation was significantly blunted in the patients with retinopathy as indicated by a higher night/day ratio of diastolic blood pressure (84.6 % ± 4 [grade 3–6], and 81.2 % ± 6 [grade 2] compared to 79.1 % ± 4 [grade 1], p = 0.01). Heart rate tended to be higher in patients in group 2 and 3–6 compared to patients without retinopathy with p values of 0.07 and 0.11 for day-time and 24 h values, respectively. Mean HbA_{1 c} increased significantly with increasing levels of retinopathy (p < 0.01). Patients were similar regarding sex, age, tobacco use, and level of physical activity. Notably, UAE was almost identical in the three groups (5.0 × /÷1.7 [grade 1], 3.9 × /÷1.8 [grade 2], and 5.1 × /÷1.6 μg/min [grade 3–6]). In conclusion, night blood pressure is higher and circadian blood pressure variation blunted in patients with retinopathy compared to patients without retinopathy despite strict normoalbuminuria and similar UAE levels in the groups compared. Our data suggest that the association between blood pressure and diabetic retinopathy is present also when coexisting renal disease is excluded. Disturbed diurnal variation of blood pressure is a pathophysiological feature related to the development of both retinopathy and nephropathy in IDDM patients. [Diabetologia (1998) 41: 105–110] Received: 27 May 1997 and in revised form: 5 September 1997     

Comparison of 1-hour and 24-hour blood pressure recordings in central or peripheral baroreceptor-denervated rats

We compared the mean arterial pressure and heart rate activity of conscious, unrestrained rats during 1-hour and 24-hour continuous recording sessions, 3 to 4 weeks after either sinoartic denervation, placement of electrolytic lesions in the nucleus tractus solitarii, or sham operations. Sinoaortic denervation and nucleus tractus solitarii lesions both eliminated the reflex bradycardia to a phenylephrine-induced pressor response. No difference was found in the average level and lability of the mean arterial pressure between 1-hour and 24-hour recordings for any group. No elevation in the average mean arterial pressure of rats with nucleus tractus solitarii lesions was observed, although a mild hypertension was noted in half the sinoarotic-denervated rats, while the other half were normotensive. Group differences were not found for heart rate or heart rate variability; however, 24-hour recordings yielded significantly higher values than 1-hour recordings for all groups. Both medullary lesions and sinoaortic denervation significantly increased the lability of the mean arterial pressure, but the magnitude of the increase was significantly greater in the rats with lesions. The lability of the mean arterial pressure in sinoaortic-denervated rats depended largely on movement-related depressor responses that produced a negative skew in the frequency distribution of their mean arterial pressure. Rats with nucleus tractus solitarii lesions exhibited both pressor and depressor responses that resulted in pressure distributions that had a slight positive skew similar to that displayed by control rats. It is concluded that short-term continuous recordings of mean arterial pressure and heart rate accurately estimate the altered cardiovascular activity of baroreceptor-denervated rats. The differences in the cardiovascular responses of central and peripheral baroreceptor-denervated rats are believed to be due to the more extensive destruction by nucleus tractus solitarii lesions of central neurons and pathways involved in cardiovascular regulation.