The Adaptive Value and Clinical Significance of Allostatic Blood Pressure Variation

When blood pressure refuses to budge: exploring the complexity of resistant hypertension

Resistant hypertension, defined as blood pressure that remains above goal despite using three or more antihypertensive medications, including a diuretic, affects a significant proportion of the hypertensive population and is associated with increased cardiovascular morbidity and mortality. Despite the availability of a wide range of pharmacological therapies, achieving optimal blood pressure control in patients with resistant hypertension remains a significant challenge. However, recent advances in the field have identified several promising treatment options, including spironolactone, mineralocorticoid receptor antagonists, and renal denervation. In addition, personalized management approaches based on genetic and other biomarkers may offer new opportunities to tailor therapy and improve outcomes. This review aims to provide an overview of the current state of knowledge regarding managing resistant hypertension, including the epidemiology, pathophysiology, and clinical implications of the condition, as well as the latest developments in therapeutic strategies and future prospects.

Increased variability of mean arterial pressure is associated with increased risk of short-term mortality in intensive care unit: A retrospective study

Background

In intensive care unit (ICU), what thresholds of MAP variability are effective in distinguishing low- and high-risk patients for short-term mortality (in-hospital and 28-day) remains unclear.

Methods

Fifteen thousand five hundred sixty adult subjects admitted to ICU at Beth Israel Deaconess Medical Center (Boston, USA) between 2001 and 2012 were included in this retrospective study from MIMIC-III database. MAP within the first 24 h after admission were collected. Quantiles of MAP variability from 10% to 90% with 10% increasement each were considered to divide study participants into two groups, either having coefficients of variation of MAP greater or less than the given threshold. The threshold of MAP variability was identified by maximizing the odds ratio associated with increased risk of short-term mortality (in-hospital and 28-day). Logistic regression and Cox regression models were further applied to evaluate the association between increased variability of MAP and short-term mortality (in-hospital and 28-day).

Results

90% quantile of MAP variability was determined as the threshold generating the largest odds ratio associated with the increased risk of short-term mortality. Increased MAP variability, especially over 90% of MAP variability, was associated with increased risk of in-hospital mortality (odds ratio: 2.351, 95% CI: 2.064–2.673), and 28-day mortality (hazard ratio: 2.064, 95% CI: 1.820–2.337).

Conclusion

Increased MAP variability, especially over 90% of MAP variability, is associated with short-term mortality. Our proposed threshold of MAP variability may aid in the early identification of critically ill patients with a high risk of mortality.

Pseudo and resistant hypertension: A chaotic perspective

Systemic blood pressure (BP) may oscillate for homeostatic needs (equilibrium by constancy) or just as shifts in other intrinsic and extrinsic variables known as allostatic changes. This transitory pressure often rises alerts physicians to out‐of‐control hypertension or even hypertensive crisis. There is a very complex theory underlying these stochastic phenomena, which physicists and mathematicians translate into a single word: chaos. These changes happen according to a stochastic probabilistic pattern that presumes chaotic but somewhat predictable and nonlinear modeling of BP‐related dynamics as a mathematical approach. Based on the chaos theory, small changes at the initial BP (baseline overtime) values could disturb the homeostasis leading to extreme BP chaotic shifts. These almost insignificant oscillations may also affect other variables and systems, leading to the misdiagnosis of hypertension, “out‐of‐control” BP levels, and resistant hypertension (RHT). Thus, these unpredictable and transient increases in BP values may be improperly diagnosed as the white coat and masked or resistant hypertension. Indeed, the interference of the chaos in any phenotype of (true or false) hard to control BP is not considered in clinical settings. This review provides some basic concepts on chaos theory and BP regulation. Besides pseudoresistant hypertension (lack of adherence, circadian variations, and others (white‐coat, masked, early morning effects or hypertension), chaotic changes can be responsible for out‐of‐control hypertension.

Capnometric feedback training decreases 24-h blood pressure in hypertensive postmenopausal women

BACKGROUND

High normal resting pCO₂ is a risk factor for salt sensitivity of blood pressure (BP) in normotensive humans and has been associated with higher resting systolic BP in postmenopausal women. To date, however, no known studies have investigated the effects of regular practice of voluntary mild hypocapnic breathing on BP in hypertensive patients. The objective of the present research was to test the hypothesis that capnometric feedback training can decrease both resting pCO₂ and 24-h BP in a series of mildly hypertensive postmenopausal women.

METHODS

A small portable end tidal CO₂ (etCO₂) monitor was constructed and equipped with software that determined the difference between the momentary etCO₂ and a pre-programmed criterion range. The monitor enabled auditory feedback for variations in CO₂ outside the criterion range. 16 mildly hypertensive postmenopausal women were individually trained to sustain small decreases in etCO₂ during six weekly sessions in the clinic and daily sessions at home. 24-h BP monitoring was conducted before and after the intervention, and in 16 prehypertensive postmenopausal women in a control group who did not engage in the capnometric training.

RESULTS

Following the intervention, all 16 capnometric training participants showed decreases in resting etCO₂ (- 4.3 ± 0.4 mmHg; p < .01) while 15 showed decreases in 24-h systolic BP (- 7.6 ± 2.0 mmHg; p < .01). No significant changes in either measure was observed in the control group. In addition, nighttime (- 9.5 ± 2.6; p < .01) and daytime (- 6.7 ± 0.2 mmHg) systolic BP were both decreased following capnometric training, while no significant changes in nighttime (- 2.8 ± 2.2 mmHg; p = .11) or daytime (- 0.7 ± 1.0 mmHg; p ≤ .247) systolic BP were observed in the control group.

CONCLUSIONS

These findings support the hypothesis that regular practice of mild hypocapnic breathing that decreases resting etCO₂ reliably decreases 24-h blood pressure in hypertensive postmenopausal women. The extent to which these effects persist beyond the training period or can be observed in other hypertensive subgroups remains to be investigated.

Recognizing normal reproductive biology: A comparative analysis of variability in menstrual cycle biomarkers in German and Bolivian women

The idealized "normal" menstrual cycle typically comprises a coordinated ebb and flow of hormones over a 28-day span with ovulation invariably shown at the midpoint. It's a pretty picture-but rare. Systematic studies have debunked the myth that cycles occur regularly about every 28 days. However, assumptions persist regarding the extent and normalcy of variation in other cycle biomarkers. The processes of judging which phenotypic variants are "normal" is context dependent. In everyday life, normal is that which is most commonly seen. In biomedicine normal is often defined as an arbitrarily bounded portion of the phenotype's distribution about its statistical mean. Standards thus defined in one population are problematic when applied to other populations; population specific standards may also be suspect. Rather, recognizing normal female reproductive biology in diverse human populations requires specific knowledge of proximate mechanisms and functional context. Such efforts should be grounded in an empirical assessment of phenotypic variability. We tested hypotheses regarding cycle biomarker variability in women from a wealthy industrialized population (Germany) and a resource-limited rural agropastoral population (Bolivia). Ovulatory cycles in both samples displayed marked but nonetheless comparable variability in all cycle biomarkers and similar means/medians for cycle and phase lengths. Notably, cycle and phase lengths are poor predictors of mid-luteal progesterone concentrations. These patterns suggest that global and local statistical criteria for "normal" cycles would be difficult to define. A more productive approach involves elucidating the causes of natural variation in ovarian cycling and its consequences for reproductive success and women's health.

Stress-Induced Blood Pressure Elevation Self-Measured by a Wearable Watch-Type Device

BACKGROUND

Psychological stress contributes to blood pressure (BP) variability, which is a significant and independent risk factor for cardiovascular events. We compared the effectiveness of a recently developed wearable watch-type BP monitoring (WBPM) device and an ambulatory BP monitoring (ABPM) device for detecting ambulatory stress-induced BP elevation in 50 outpatients with 1 or more cardiovascular risk factors.

METHODS

The WBPM and ABPM were both worn on the subject's nondominant arm. ABPM was measured automatically at 30-minute intervals, and each ABPM measurement was followed by a self-measured WBPM measurement. We also collected self-reported information about situational conditions, including the emotional state of subjects at the time of each BP measurement. We analyzed 642 paired BP readings for which the self-reported emotional state in the corresponding diary entry was happy, calm, anxious, or tense.

RESULTS

In a mixed-effect analysis, there were significant differences between the BP values measured during negative (anxious, tense) and positive (happy, calm) emotions in both the WBPM (systolic BP [SBP]: 9.3 ± 2.1 mm Hg, P < 0.001; diastolic BP [DBP]: 8.4 ± 1.4 mm Hg, P < 0.001) and ABPM (SBP: 10.7 ± 2.1 mm Hg, P < 0.001; DBP: 5.6 ± 1.4 mm Hg, P < 0.001). The absolute BP levels induced by emotional stress self-measured by the WBPM were similar to those automeasured by the ABPM (SBP, WBPM: 141.1 ± 2.7 mm Hg; ABPM: 140.3 ± 2.7 mm Hg; P = 0.724). The subject's location at the BP measurement was also significantly associated with BP elevation.

CONCLUSIONS

The self-measurement by the WBPM could detect BP variability induced by multiple factors, including emotional stress, under ambulatory conditions as accurately as ABPM.

Dynamical interaction between heart rate and blood pressure of end-stage renal disease patients evaluated by cross recurrence plot diagonal analysis

The assessment of spontaneous variability of blood pressure and heart rate is based on specific physiological hypotheses about dynamic features, for example, the baroreflex modulation of heart rate over time in daily life. Usually, arterial baroreflex control of heart rate is explored without delays between blood pressure and heart rate data points, within a narrow range of values, excluding the analysis of saturation regions or low-threshold changes. In this work, we examine the dynamic interactions between systolic blood pressure (SBP) and interbeat interval (IBI), in 15-min length time series and for the first time using the analysis of diagonals derived from a cross-recurrence plots in healthy persons and end-stage renal disease (ESRD) patients. We found that ESRD patients have stronger intermittent dynamical interactions between IBI and SBP, but they lose most of the dynamical interactions. Although healthy subjects exhibit a continuously changing order of precedence between IBI and SBP at different lags, ESRD patients preserve this changing order of precedence only for lags >0 beats.NEW & NOTEWORTHY This study is the first to compare the time-variant pattern of systolic blood pressure (SBP) and interbeat interval (IBI) coupling between ESRD patients and healthy volunteers through the analysis of diagonal in cross-recurrence plots, and in the face of an orthostatic challenge. Our results demonstrated alternant interactions on the order of precedence (IBI → SBP or SBP→ IBI) at different time delays. This pattern is different in resting position and during active standing for the two groups studied, and interestingly, some association patterns are lost in ESRD patients. These patterns of alternant interactions on the order of precedence could be related to autonomic neural activities and cardiovascular synchronization at different scales both in time and space. This could reflect physiological adaptive flexibility of cardiovascular regulation. Losing some association patterns in ESRD may be the result of chronic adjustments of many physiological mechanisms (including chronic sympathetic hyperactivity), which could increase cardiovascular vulnerability to hemodynamic challenges.