Relationship between stroke volume and pulse pressure during blood volume perturbation: a mathematical analysis

Cardiovascular responses to leg-press exercises during head-down tilt

Introduction

Physical exercise and gravitational load affect the activity of the cardiovascular system. How these factors interact with one another is still poorly understood. Here we investigate how the cardiovascular system responds to leg-press exercise during head-down tilt, a posture that reduces orthostatic stress, limits gravitational pooling, and increases central blood volume.

Methods

Seventeen healthy participants performed leg-press exercise during head-down tilt at different combinations of resistive force, contraction frequency, and exercise duration (30 and 60 s), leading to different exercise power. Systolic (sBP), diastolic (dBP), mean arterial pressure (MAP), pulse pressure (PP) and heart rate (HR) were measured continuously. Cardiovascular responses were evaluated by comparing the values of these signals during exercise recovery to baseline. Mixed models were used to evaluate the effect of exercise power and of individual exercise parameter on the cardiovascular responses.

Results

Immediately after the exercise, we observed a clear undershoot in sBP (Δ = -7.78 ± 1.19 mmHg), dBP (Δ = -10.37 ± 0.84 mmHg), and MAP (Δ = -8.85 ± 0.85 mmHg), an overshoot in PP (Δ = 7.93 ± 1.13 mmHg), and elevated values of HR (Δ = 33.5 ± 0.94 bpm) compared to baseline (p < 0.0001). However, all parameters returned to similar baseline values 2 min following the exercise (p > 0.05). The responses of dBP, MAP and HR were significantly modulated by exercise power (correlation coefficients: rdBP = -0.34, rMAP = -0.25, rHR = 0.52, p < 0.001). All signals' responses were modulated by contraction frequency (p < 0.05), increasing the undershoot in sBP (Δ = -1.87 ± 0.98 mmHg), dBP (Δ = -4.85 ± 1.01 and Δ = -3.45 ± 0.98 mmHg for low and high resistive force respectively) and MAP (Δ = -3.31 ± 0.75 mmHg), and increasing the overshoot in PP (Δ = 2.57 ± 1.06 mmHg) as well as the value of HR (Δ = 16.8 ± 2.04 and Δ = 10.8 ± 2.01 bpm for low and high resistive force respectively). Resistive force affected only dBP (Δ = -4.96 ± 1.41 mmHg, p < 0.0001), MAP (Δ = -2.97 ± 1.07 mmHg, p < 0.05) and HR (Δ = 6.81 ± 2.81 bpm, p < 0.0001; Δ = 15.72 ± 2.86 bpm, p < 0.0001; Δ = 15.72 ± 2.86 bpm, p < 0.05, depending on the values of resistive force and contraction frequency), and exercise duration affected only HR (Δ = 9.64 ± 2.01 bpm, p < 0.0001).

Conclusion

Leg exercises caused only immediate cardiovascular responses, potentially due to facilitated venous return by the head-down tilt position. The modulation of dBP, MAP and HR responses by exercise power and that of all signals by contraction frequency may help optimizing exercise prescription in conditions of limited orthostatic stress.

Hemodynamic Support in Sepsis

This review discusses recent evidence in managing sepsis-induced hemodynamic alterations and how it can be integrated with previous knowledge for actionable interventions in adult patients.

A Lumped-Parameter Model of the Cardiovascular System Response for Evaluating Automated Fluid Resuscitation Systems

Physiological closed-loop controlled (PCLC) medical devices, such as those designed for blood pressure regulation, can be tested for safety and efficacy in real-world clinical settings. However, relying solely on limited animal and clinical studies may not capture the diverse range of physiological conditions. Credible mathematical models can complement these studies by allowing the testing of the device against simulated patient scenarios. This research involves the development and validation of a low-order lumped-parameter mathematical model of the cardiovascular system's response to fluid perturbation. The model takes rates of hemorrhage and fluid infusion as inputs and provides hematocrit and blood volume, heart rate, stroke volume, cardiac output and mean arterial blood pressure as outputs. The model was calibrated using data from 27 sheep subjects, and its predictive capability was evaluated through a leave-one-out cross-validation procedure, followed by independent validation using 12 swine subjects. Our findings showed small model calibration error against the training dataset, with the normalized root-mean-square error (NRMSE) less than 10% across all variables. The mathematical model and virtual patient cohort generation tool demonstrated a high level of predictive capability and successfully generated a sufficient number of subjects that closely resembled the test dataset. The average NRMSE for the best virtual subject, across two distinct samples of virtual subjects, was below 12.7% and 11.9% for the leave-one-out cross-validation and independent validation dataset. These findings suggest that the model and virtual cohort generator are suitable for simulating patient populations under fluid perturbation, indicating their potential value in PCLC medical device evaluation.

Estimation of cardiac stroke volume from radial pulse waveform by artificial neural network

BACKGROUND AND OBJECTIVES

Stroke volume (SV) and cardiac output (CO) are the key indicators for the evaluation of cardiac function and hemodynamic status during the perioperative period, which are very important in the detection and treatment of cardiovascular diseases. Traditional CO and SV measurement methods have problems such as complex operation, low precision and poor generalization ability.

METHODS

In this paper, a method for estimating stroke volume based on cascade artificial neural network (ANN) and time domain features of radial pulse waveform (SV_ANN) was proposed. The simulation datasets of 4000 radial pulse waveforms and stroke volume (SV_meas) were generated by a 55 segment transmission line model of the human systemic vasculature and a recursive algorithm. The ANN was trained and tested by 10-fold cross-validation, and compared with 12 traditional models.

RESULTS

Experimental results showed that the Pearson correlation coefficients and mean difference between SV_ANN and SV_meas (R=0.95, mean standard deviation (SD) = 0.00 ± 6.45) were better than the best results of the 12 traditional models. Moreover, as increasing the number of training samples, the performance improvement of the ANN (R=0.94(Δ + 0.04), mean ± SD = 0.00 ± 6.38(Δ± 2.02)) was better than the other best model, namely, multiple linear regression model (MLR) (R=0.93(Δ + 0.03), mean ± SD = 0.00 ± 6.99(Δ± 1.50)).

CONCLUSIONS

A method is proposed to estimate cardiac stroke volume by the ANN with time domain features of radial pulse wave. It avoids the complicated modeling process based on hemodynamics within traditional models, improves the estimation accuracy of SV, and has a good generalization ability.

Non-Invasive Assessment of Damping of Blood Flow Velocity Pulsatility in Cerebral Arteries With MRI

Background

Damping of heartbeat‐induced pressure pulsations occurs in large arteries such as the aorta and extends to the small arteries and microcirculation. Since recently, 7 T MRI enables investigation of damping in the small cerebral arteries.

Purpose

To investigate flow pulsatility damping between the first segment of the middle cerebral artery (M1) and the small perforating arteries using magnetic resonance imaging.

Study Type

Retrospective.

Subjects

Thirty‐eight participants (45% female) aged above 50 without history of heart failure, carotid occlusive disease, or cognitive impairment.

Field Strength/Sequence

3 T gradient echo (GE) T1‐weighted images, spin‐echo fluid‐attenuated inversion recovery images, GE two‐dimensional (2D) phase‐contrast, and GE cine steady‐state free precession images were acquired. At 7 T, T1‐weighted images, GE quantitative‐flow, and GE 2D phase‐contrast images were acquired.

Assessment

Velocity pulsatilities of the M1 and perforating arteries in the basal ganglia (BG) and semi‐oval center (CSO) were measured. We used the damping index between the M1 and perforating arteries as a damping indicator (velocity pulsatility_M1/velocity pulsatility_CSO/BG). Left ventricular stroke volume (LVSV), mean arterial pressure (MAP), pulse pressure (PP), and aortic pulse wave velocity (PWV) were correlated with velocity pulsatility in the M1 and in perforating arteries, and with the damping index of the CSO and BG.

Statistical Tests

Correlations of LVSV, MAP, PP, and PWV with velocity pulsatility in the M1 and small perforating arteries, and correlations with the damping indices were evaluated with linear regression analyses.

Results

PP and PWV were significantly positively correlated to M1 velocity pulsatility. PWV was significantly negatively correlated to CSO velocity pulsatility, and PP was unrelated to CSO velocity pulsatility (P = 0.28). PP and PWV were uncorrelated to BG velocity pulsatility (P = 0.25; P = 0.68). PWV and PP were significantly positively correlated with the CSO damping index.

Data Conclusion

Our study demonstrated a dynamic damping of velocity pulsatility between the M1 and small cerebral perforating arteries in relation to proximal stress.

Level of Evidence

4

Technical Efficacy

Stage 1

Genetic-fuzzy logic model for a non-invasive measurement of a stroke volume

BACKGROUND

Despite the importance of stroke volume readings in understanding the work of the cardiovascular system in patients, its routine daily measurement outside of a hospital in the absence of special equipment presents a problem for a comprehensive assessment of the heart performance.

OBJECTIVE

The purpose of this study was to develop a new non-invasive technique for measuring a stroke volume based on the relationship between time skin warming and a blood flow.

METHODS

. Ninety two randomly selected volunteers (54 males, aged 30.1 ± 11.9 years old, and 38 females, aged 35.8 ± 12.4 years old) were recruited for this study. The time skin warming was determined by applying on the wrist above the arterial pulsation a thermoelectric cooler using the Peltier effect. During recording the participants were in the supine position. Blood pressure was measured by sphygmomanometer. Heart performance was assessed by Murata ballistocardiographic sensor, detecting displacement of the whole body during each cardiac ejection of blood. The data provided by this sensor included heart rate, respiratory rate, heart rate variability and a stroke volume. Linear, non-linear statistical regression models and fuzzy logic were used to analyse the degree of interrelation between BCG-measured stroke volume and the time skin warming.

RESULTS

Comparative analysis of results indicated that the generic-fuzzy logic model demonstrated a high level of dependency (R = 0.803) between input (participants' time skin warming, pulse pressure and age) and output (ballistocardiographic stroke volume) parameters.

CONCLUSIONS

The method described in the paper offers a simple, portable, and low-cost solution that can even be used in a home setting to measure the stroke volume. The principle of the proposed method is based on the interrelation between time skin warming and blood flow. The latter, corrected by corresponding age and pulse pressure, expresses the participant's stroke volume. Adopting the genetic-fuzzy model significantly improved the accuracy of stroke volume's measurement and made the proposed method reliable for assessing of the cardiovascular system. This daily practice technique would help healthcare provider get an early diagnosis of cardiac dysfunctions and track heart changes during stress, e.g., in sport.

Symptoms upon postural change and orthostatic hypotension in adolescents with concussion

Objective: Concussion is associated with dysautonomia, altered blood pressure (BP) control, and may cause Orthostatic Hypotension (OH). We measured prevalence of OH using the 1-minute supine-to-standing OH Test in adolescents with concussion and controls.Participants: Adolescents within 10 days of injury (Concussion Group, n = 297, 15.0 ± 1.7 years, 59% male) were compared with controls (Control Group, n = 214, 15.0 ± 1.5 years, 58% male).Methods: BP, heart rate (HR), and complaints of lightheadedness/dizziness were measured after 2-minute supine and 1-minute standing. Control Group was assessed once. Concussion Group was assessed twice; (1) initial visit (mean 6.0 ± 3 days-since-injury) and (2) after clinical recovery (mean 46.3 ± 42 days-since-injury).Results: Initial visit; Concussion Group reported feeling lightheaded/dizzy on postural change more often than the Control Group (37% vs 4%, p < .001) but did not differ in meeting standard OH criteria (3% vs 5%, p = .32). Experiencing symptoms did not correlate with meeting OH criteria, but correlated with abnormal vestibulo-ocular reflex. After clinical recovery; Concussion Group did not differ in experiencing lightheaded/dizziness on postural change than controls (4%, p = .65).Conclusion: Adolescents commonly experience orthostatic intolerance after concussion without meeting the standard criteria for OH.

Hypotensive and antihypertensive effects of an aqueous extract from Guinep fruit (Melicoccus bijugatus Jacq) in rats

Melicoccus bijugatus Jacq (Mb) has been reported to have cardiovascular modulatory effects. In this study, we evaluated the antihypertensive effects and mechanism of action of Mb on N^G-Nitro-l-arginine Methyl Ester (l-NAME) and Deoxycorticosterone Acetate (DOCA) rat models. Aqueous extract of Mb fruit (100 mg/kg) was administered for 6 weeks to rats by gavage and blood pressure was recorded. Effects of the extract on vascular reactivity was evaluated using isolated organ baths, and tissues were collected for biochemical and histological analysis. The systolic blood pressure (SBP), diastolic blood pressure (DBP) and mean arterial pressure (MAP) were significantly (P < 0.05) reduced with extract (100 mg/kg) administration and treatment compared to the hypertensive models. Mb (100 µg/mL) reduced the vascular contractility induced by phenylephrine (PE), and caused a dose-dependent relaxation of PE-induced contraction of aortic vascular rings. The vasorelaxation properties seemed to be endothelium dependent, as well as nitric oxide (NO) and guanylyl cyclase, but not prostaglandin dependent. Histomicrograph of transverse sections of the ventricles from the Mb group did not show abnormalities. The extract significantly (P < 0.05) reduced an l-NAME induced elevation of cardiac output and Creatine Kinase Muscle-Brain (CKMB), but had no significant impact on the activities of arylamine N-acetyltransferase. In conclusion, Mb significantly decreased blood pressure in hypertensive models. The extract possesses the ability to induce endothelium dependent vasodilation, which is dependent on guanylyl cyclase but not prostaglandins.

Albumin Saturated With Fatty Acids Prevents Decompensation in a Rat Hemorrhagic Shock Trauma Model With Tourniquet and Hypotensive Resuscitation

ABSTRACT

Decompensation is a major prehospital threat to survival from trauma/hemorrhage shock (T/HS) after controlling bleeding. We recently showed higher than expected mortality from a combat-relevant rat model of T/HS (27 mL/kg hemorrhage) with tourniquet (TQ) and permissive hypotensive resuscitation (PHR) with Plasmalyte. Mortality and fluid requirements were reduced by resuscitation with 25% albumin presaturated with oleic acid (OA-sat) compared with fatty-acid -free albumin or Plasmalyte. The objective of this follow-up analysis was to determine the role of decompensation and individual compensatory mechanisms in those outcomes. We observed two forms of decompensation: slow (accelerating fluid volumes needed to maintain blood pressure) and acute (continuous fluid administration unable to prevent pressure drop). Combined incidence of decompensation was 71%. Nearly all deaths (21 of 22) were caused by acute decompensations that began as slow decompensations. The best hemodynamic measure for predicting acute decompensation was diastolic arterial pressure. Decompensation was due to vascular decompensation rather than loss of cardiac performance. Albumin concentration was lower in decompensating groups, suggesting decreased stressed volume, which may explain the association of low albumin on admission with poor outcomes after trauma. Our findings suggest that acute decompensation may be common after trauma and severe hemorrhage treated with TQ and PHR and OA-sat albumin may benefit early survival and reduce transfusion volume by improving venous constriction and preventing decompensation.

Modeling Arterial Pulse Pressure From Heart Rate During Sympathetic Activation by Progressive Central Hypovolemia

Heart rate (HR) has an impact on the central blood pressure (BP) wave shape and is related to pulse wave velocity and therefore to timing and duration of systole and diastole. This study tested the hypothesis that in healthy subjects both in rest and during sympathetic stimulation the relation between HR and pulse pressure (PP) is described by a linear effect model. Forty-four healthy volunteers were subjected to sympathetic stimulation by continuous lower body negative pressure (LBNP) until the onset of pre-syncopal symptoms. Changes in PP and HR were tracked non-invasively and modeled by linear mixed effect (LME) models. The dataset was split into two groups: the first was used for creating a model and the second for its evaluation. Models were created on the data obtained during LBNP. Model performance was expressed as absolute median error (1st; 3rd quantiles) and bias with limits of agreement (LOA) between modeled and measured PP. From rest to sympathetic stimulation, mean BP was maintained while HR increased (~30%) and PP decreased gradually (~20%). During baseline, PP could be modeled with an absolute error of 6 (4; 10) mm Hg and geometric mean ratio of the bias was 0.97 (LOA: 0.8–1.1). During LBNP, absolute median model error was 5 (4; 8) mmHg with geometric mean ratio 1.02 (LOA: 0.8–1.3). In conclusion, both during rest and during sustained sympathetic outflow induced by progressive central hypovolemia, a LME model of HR provides for an estimate of PP in healthy young adults.

Impact of Age and Target-Organ Damage on Prognostic Value of 24-Hour Ambulatory Blood Pressure

Markers of target-organ damage and 24-hour ambulatory blood pressure (BP) measurement improve cardiovascular risk stratification. The prevalence of target-organ damage and raised BP increases with aging. The study aim was to evaluate the impact of age and target-organ damage on the prognostic value of ambulatory BP. Markers of target-organ damage and ambulatory BP were measured in 1408 healthy people aged 41 or 51 (middle-aged group), and 61 or 71 (older group) years. The primary outcome was cardiovascular events after 16 years of follow-up, with data obtained from national registries. The prognostic value of BP was evaluated with Cox regression models, adjusted for traditional risk factors and target-organ damage, including left ventricular mass, pulse wave velocity, carotid plaques, and urine albumin/creatinine ratio. A total of 323 events were observed. In comparison with traditional risk factors, adding systolic BP and presence of target-organ damage improved risk stratification by increasing concordance index from 0.711 to 0.728 ( P =0.01). In middle-aged subjects with target-organ damage, increment in pulse pressure (hazard ratio, 1.70; 95% confidence interval, 1.31–2.21; P <0.01) and increment in average real variability (hazard ratio, 1.29; 95% confidence interval, 1.05–1.59; P =0.02) were associated with a greater risk of cardiovascular disease compared with subjects without target-organ damage: hazard ratio, 1.04 (95% confidence interval, 0.74–1.46; P =0.81); P for interaction, 0.02; and hazard ratio, 0.89 (95% confidence interval, 0.69–1.14; P =0.36); P for interaction, 0.01. Target-organ damage may be a marker of individual susceptibility to the harmful effects of pulse pressure and BP variability on the cardiovascular system in middle-aged individuals.