Methods for assessing blood pressure values in humans

Influence of Meals and Glycemic Changes on QT Interval Dynamics

Thorough QT/QTc studies have become an integral part of early drug development programs, with major clinical and regulatory implications. This analysis expands on existing pharmacodynamic models of QT interval analysis by incorporating the influence of glycemic changes on the QT interval in a semimechanistic manner. A total of 21 healthy subjects enrolled in an open-label phase 1 pilot study and provided continuous electrocardiogram monitoring and plasma glucose and insulin concentrations associated with a 24-hour baseline assessment. The data revealed a transient decrease in QTc, with peak suppression occurring approximately 3 hours after the meal. A semimechanistic modeling approach was applied to evaluate temporal delays between meals and subsequent changes that might influence QT measurements. The food effect was incorporated into a model of heart rate dynamics, and additional delayed effects of the meal on QT were incorporated using a glucose-dependent hypothetical transit compartment. The final model helps to provide a foundation for the future design and analysis of QT studies that may be confounded by meals. This study has significant implications for QT study assessment following a meal or when a cohort is receiving a medication that influences postprandial glucose concentrations.

Sources of inaccuracy in the measurement of adult patients' resting blood pressure in clinical settings: a systematic review

BACKGROUND

To interpret blood pressure (BP) data appropriately, healthcare providers need to be knowledgeable of the factors that can potentially impact the accuracy of BP measurement and contribute to variability between measurements.

METHODS

A systematic review of studies quantifying BP measurement inaccuracy. Medline and CINAHL databases were searched for empirical articles and systematic reviews published up to June 2015. Empirical articles were included if they reported a study that was relevant to the measurement of adult patients' resting BP at the upper arm in a clinical setting (e.g. ward or office); identified a specific source of inaccuracy; and quantified its effect. Reference lists and reviews were searched for additional articles.

RESULTS

A total of 328 empirical studies were included. They investigated 29 potential sources of inaccuracy, categorized as relating to the patient, device, procedure or observer. Significant directional effects were found for 27; however, for some, the effects were inconsistent in direction. Compared with true resting BP, significant effects of individual sources ranged from -23.6 to +33 mmHg SBP and -14 to +23 mmHg DBP.

CONCLUSION

A single BP value outside the expected range should be interpreted with caution and not taken as a definitive indicator of clinical deterioration. Where a measurement is abnormally high or low, further measurements should be taken and averaged. Wherever possible, BP values should be recorded graphically within ranges. This may reduce the impact of sources of inaccuracy and reduce the scope for misinterpretations based on small, likely erroneous or misleading, changes.

[Instrumentation for blood pressure measurements: historical aspects, concepts and sources of error]

According to the International Council of Nurses the measurement of blood pressure is the procedure most performed by nurses in all the world. The aim of this study is to analyse the polemical aspects of instruments used in blood pressure measurement. Considering the analyses of the literature and the American Heart Association Recommendations, the main source of errors when measuring blood pressure are discussed.

Influence of confounding factors on designs for dose-effect relationship estimates

Three types of designs can be used to estimate the drug dose-effect relationship during phase II clinical trials: parallel-dose designs (parallel); cross-over designs (X), and dose-escalation designs ([symbol: see text]). Despite the use of non-linear mixed effect models, the potential influence of confounding factors on [symbol: see text] designs has not been previously fully elucidated; we undertook simulations to investigate this for all three experimental designs. We found that: (i) monotonic spontaneous evolution of the effect (EV) did not affect the maximum effect estimation (Emax) and the dose giving 50 per cent of this (ED50); (ii) EV similar to a regression to the mean gave rise to biases for [symbol: see text] designs; (iii) the introduction of a pharmacodynamic carry-over generates important biases and imprecision for [symbol: see text] designs, even when the carry-over is adjusted for; (iv) the introduction of non-responders resulted in bias and imprecision for both Emax and ED50 in all three designs.

Comparison of finger and intra-arterial blood pressure monitoring at rest and during laboratory testing

The accuracy of blood pressure values obtained by continuous noninvasive finger blood pressure recording via the FINAPRES device was evaluated by comparison with simultaneous intraarterial monitoring both at rest and during performance of tests known to induce fast and often marked changes in blood pressure. The comparison was performed in 24 normotensive or essential hypertensive subjects. The average discrepancy between finger and intra-arterial blood pressure recorded over a 30-minute rest period was 6.5 +/- 2.6 mm Hg and 5.4 +/- 2.9 mm Hg for systolic and diastolic blood pressure, respectively; a close between-method correspondence was also demonstrated by linear regression analysis. The beat-to-beat changes in finger systolic and diastolic blood pressure were on average similar to those measured intra-arterially during tests that induced a pressor or depressor response (hand-grip, cold pressor test, diving test, Valsalva maneuver, intravenous injections of phenylephrine and trinitroglycerine) as well as during tests that caused vasomotor changes without major variations in blood pressure (application of lower body negative pressure, passive leg raising). The average between-method discrepancy in the evaluation of blood pressure changes was never greater than 4.3 and 2.0 mm Hg for systolic and diastolic blood pressure, respectively; the corresponding standard deviations ranged between 4.6 and 1.6 mm Hg. Beat-to-beat computer analysis of blood pressure variability over the 30-minute rest period provided standard deviations almost identical when calculated by separate consideration of intra-arterial and finger blood pressure tracings (3.7 and 3.8 mm Hg, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

[The indirect measurement of arterial pressure: a review]

This study deals with the indirect arterial blood pressure measurement, particularly the American Heart Association recommendations for sphygmomanometry References are made regarding the ratio arm circumference/cuff width and the errors caused by inadequate cuff size. Several variables involved in the procedure of arterial blood pressure measurement are discussed.

Arterial baroreflexes and blood pressure and heart rate variabilities in humans

The factors responsible for 24-hour blood pressure and heart rate variabilities have never been clarified; however, studies performed in unanesthetized animals have shown an increase in blood pressure variability after sinoaortic denervation, and a negative relationship has been reported occasionally between blood pressure variability and baroreflex control of heart rate in humans. We have systematically investigated this issue in 82 ambulant hypertensive subjects using 24-hour intraarterial blood pressure recording (Oxford method) in which blood pressure and heart rate variabilities were measured by calculating the standard deviations of the values obtained throughout the 24 hours or during separate daytime and nighttime periods. Baroreflex sensitivity was assessed by the bradycardic or tachycardic responses to intravenous injections of phenylephrine or nitroglycerin and by the blood pressure response to changes in carotid transmural pressure obtained with a neck chamber. The sensitivity of the baroreceptor-heart rate reflex as assessed by the vasoactive drug technique showed a negative relationship with 24-hour blood pressure variability as well as with daytime and nighttime blood pressure variabilities measured separately (r = -0.28 to -0.50, p less than 0.05). These variabilities also correlated negatively with the sensitivity of the baroreceptor-blood pressure reflex as assessed by the neck chamber technique. By contrast, baroreflex sensitivity showed a positive correlation with heart rate variabilities (r = 0.32 to 0.47, p less than 0.05). The relationship between baroreflex sensitivity and blood pressure and heart rate variabilities was confirmed when the data were analyzed by multiple regression to adjust for blood pressure and age differences among the 82 subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Lack of alerting reactions to intermittent cuff inflations during noninvasive blood pressure monitoring

Intermittent noninvasive blood pressure monitoring is becoming increasingly popular because of the belief that a daytime blood pressure profile can provide a better clinical evaluation of hypertension than that provided by casual blood pressure measurements. This approach has potential limitations, however, one of which is that the cuff inflations permitting blood pressure to be repeatedly measured may induce an alerting reaction and a pressor response in the patients and lead to an overestimation of their daytime blood pressure. Blood pressure in 22 subjects was invasively recorded for 24 hours by the Oxford method. During the day of the recording blood pressure was also measured by a noninvasive device (Vita-Stat 901), which had its cuff applied to the opposite arm from which the intra-arterial signal was derived. For 2 hours the device provided automatic cuff inflations at 10-minutes intervals. For another 2 hours it was programmed to provide cuff inflations only following patients' commands, also at 10-minute intervals. Analysis of the intra-arterial blood pressure trace during the periods preceding and following the automatically or semiautomatically induced cuff inflations showed that these procedures caused no increment in systolic and diastolic blood pressure. This finding applied not only to the mean data but also to each individual measurement considered separately, including the initial one. Our results indicate that automatic and semiautomatic blood pressure monitorings do not induce an alarm reaction and a blood pressure rise and thus do not overestimate daytime blood pressure values.

What is the role of ambulatory blood pressure monitoring in the management of hypertensive patients?

Noninvasive ambulatory blood pressure (BP) recording is now clinically available for the evaluation of hypertensive patients. It is well known that pressures measured in the office or clinic are unreliable and that repeated measurements are better at predicting outcome than are single measurements. Several studies have compared the correlation between target organ damage and different measures of BP, and in every instance ambulatory BP measurements have given better correlations than clinic readings. In one prospective study the ambulatory BP readings were more predictive of BP-related morbidity than were clinic readings. Data are now being obtained that will establish normal ranges of BP during ambulatory monitoring, against which values from patients being evaluated for hypertension can be compared. It is concluded that ambulatory BP monitoring is of clinical value for the evaluation of patients with mild hypertension.