Continuous Blood Pressure Measurement Research Articles

Cuff-less wearable biosensor in continuous noninvasive human radial artery pulse waveform and blood pressure measurement using self-mixing interferometry

In this paper, we propose a compact, wearable biosensor for the noninvasive measurement of human radial artery pulse waveform curve (PWC) and blood pressure (BP). In this system, self-mixing interferometry (SMI) technology is employed to measure the weak arterial vascular deformation, enabling accurate PWC retrieval. Based on the reconstructed PWC features, BP values are precisely estimated by means of deep learning method. Here continuous wavelet transform (CWT), enabling visualization of the relationship between the SMI signal temporal frequency components and the PWC characteristics, is highlighted for PWC flipping points seeking and convolutional neural network (CNN) input parameter acquisition. For the first time, a novel deep learning network preprocessing method is proposed that allows direct feature extraction from the CWT scalogram of SMI signal without the complicated PWC reconstruction algorithm. The robustness and accuracy of our device are validated by a series of clinical measurements, mean absolute error (MAE) and standard deviation (STD) values are calculated and compared with the existing models. We approach minimal BP estimation results (MAE ± STD) of 1.41 ± 1.89 mmHg for systolic blood pressure (SBP) and 1.78 ± 2.01 mmHg for diastolic blood pressure (DBP), respectively. The luxuriant novelties and remarkable performance clearly demonstrate our wearable sensor’s great potential in BP monitoring, and other clinical applications.

Raised blood pressure affects reactivity to expressive music features

Abstract Background Music has been shown to lower hypertensive patients’ blood pressure in the long-term, but predominant approaches overlook the wide range of complex real-time responses. Mapping the acute dynamics of music features can help discern blood pressure (BP) reactivity. Understanding the mechanisms of music BP effects can broaden the scope for precision medicine. Purpose The aims of this study are to determine: (1) if reshaped music features alter BP reactivity; and, (2) whether BP reactivity differs for individuals with high and normal BP. Methods Participants listened to music with computationally altered tempo and loudness played back on a Disklavier piano. We compared continuous BP measurements in 40 participants (23 females, mean age of 41.3 y (95%CI: 37.2-45.4)), 20 with baseline BP measurement above 140/90 mmHg (H-bBP) and 20 with bBP below (N-bBP), paired by playlist. Continuous BP was recorded while listening to a playlist of 9 reshaped versions of 8 distinct pieces (≈40 min) after a 5-minute baseline silence. Results The mean increase in systolic and diastolic BP during music (reactivity) was significantly higher for N-bBP than H-bBP (mean (95%CI); mmHg): systolic 8.6 (6.2-11.1) vs 5.0 (2.7-7.3); p=0.031; diastolic 7.7 (5.9-9.5) vs 4.6 (2.9-6.3); p=0.0046. No significant difference in pulse pressure (PP) reactivity was found; however, the N-bBP subjects had significantly lower mean PP during music than H-bBP subjects (45.2 (40.2-44.8) vs 54.2 (51.7-56.7) ; p<0.001). Based on mean tempos, N-bBP subjects had significantly lower average PP than H-bBP subjects during slow (<60bpm; 44.6 (40.6-48.6) vs 52.6 (48.9-56.3); p=0.016) and fast (>120bpm; 43.9 (39.9-47.9) vs 57.2 (52.9-61.5); p<0.001) music, though not medium pace music. Similarly, N-bBP participants had significantly lower PP during quiet (<13 dB; 44.0 (39.6-48.4) vs 55.7 (50.7-60.7); p<0.001) and loud (>17 dB; 44.0 (39.6-48.4) vs 55.5 (51.1-59.9); p<0.001) music, but not during moderately loud music. H-bBP and N-bBP participants’ PP measures are more similar during moderately fast and moderately loud music. In addition, N-bBP’s baseline-normalised mean PP was significantly lower only during fast music (3.3 (-2.3-8.6) vs 12.9 (6.9-18.9); p = 0.04). Separating responses to unaltered vs reshaped music––i.e. music made faster and/or louder, in the case of one piece, slower and/or quieter––significant differences are found between N-bBP and H-bBP groups only for reshaped music in baseline-normalised diastolic BP (6.8 (4.7-8.9) vs 3.9 (2.1-5.7); p=0.02) and PP (45.0 (42.2-47.8) vs 54.8 (51.8-57.8); p<0.001). Conclusions H-bBP subjects had less BP reactivity to music, especially in resting vascular tone PP. Reshaping of music can modulate the level of differences between groups, particularly for immoderate tempo and loudness. Music can induce significant changes in BP profile, which indicates that it could potentially be utilised as a tailored anti-hypertensive therapy.Differences between music and baselineDifferences in tempos and loudness cat.

BP-Diff: a conditional diffusion model for cuffless continuous BP waveform estimation using U-Net.

Continuous monitoring of blood pressure (BP) is crucial for daily healthcare. Although invasive methods provide accurate continuous BP measurements, they are not suitable for routine use. Photoplethysmography (PPG), a non-invasive technique that detects changes in blood volume within the microcirculation using light, shows promise for BP measurement. The primary goal of this study is to develop a novel cuffless method based on PPG for accurately estimating continuous BP.
Approach. We introduce BP-Diff, an end-to-end method for cuffless continuous BP waveform estimation utilizing a conditional diffusion probability model combined with a U-Net architecture. This approach takes advantage of the stochastic properties of diffusion models and the strong feature representation capabilities of U-Net. It integrates the continuous BP waveform as the initial status and uses the PPG signal and its derivatives as conditions to guide the training and sampling process.
Main results. BP-Diff was evaluated using both uncalibrated and calibrated schemes. The results indicate that, when uncalibrated, BP-Diff can accurately track BP dynamics, including peak and valley positions, as well as timing. After calibration, BP-Diff achieved highly accurate BP estimations. The mean absolute error (MAE) of the estimated BP waveforms, along with the systolic blood pressure (SBP), diastolic blood pressure (DBP), and mean arterial pressure (MAP) from the calibrated BP-Diff model, were 2.99 mmHg, 2.6 mmHg, 1.4 mmHg, and 1.44 mmHg, respectively. Consistency tests, including Bland-Altman analysis and Pearson correlation, confirmed its high reliability compared to reference BP. BP-Diff meets the American Association for Medical Instrumentation (AAMI) standards and has achieved a Grade A from the British Hypertension Society (BHS).
Significance. This study utilizes PPG signals to develop a novel cuffless continuous BP measurement method, demonstrating superiority over existing approaches. The method is suitable for integration into wearable devices, providing a practical solution for continuous BP monitoring in everyday healthcare.

Detection of hypertension using a target spectral camera: a prospective clinical study

Hypertension is a significant contributor to premature mortality, and the regular monitoring of blood pressure (BP) enables the early detection of hypertension and cardiovascular disease. There is an urgent need for the development of highly accurate cuffless BP devices. We examined BP measurements based on a target spectral camera’s recordings and evaluated their accuracy. Images of 215 adults’ palms and faces were recorded, and BP was measured. The camera captured RGB wavelength data at 640 × 480 pixels and 150 frames per second (fps). These recordings were analyzed to extract pulse transit time (PTT) values between the face and palm, a key parameter for estimating BP. Continuous BP measurements were taken using a CNAPmonitor500 for validation. Three frequency wavelengths were measured from video images. A machine learning model was constructed to determine hypertension, defined as a systolic BP of 130 mmHg or higher or a diastolic BP of 80 mmHg or higher, using the visualized data. The discrimination between hypertension and normal BP was 95.0% accurate within 30 s and 90.3% within 5 s, based on the captured images. The results of heartbeat-by-heartbeat analyses can be used to determine hypertension based on only one second of camera footage or one heartbeat. The data extracted from a video recorded by a target spectral camera enabled accurate hypertension diagnoses, suggesting the potential for simplified BP monitoring.

Abstract 33: CD4+ T Cell-Induced Renal Damage and Salt-Sensitive Hypertension is Not Modified by CD8+ T Cells

Salt-Sensitive (SS) hypertension and renal damage in the Dahl SS rat mirrors human disease with T cell infiltration in the kidney accompanying the development of SS hypertension and renal damage. Deletion of T cells on the Dahl SS genetic background (SS CD247-/- ) attenuates hypertension and renal damage, and subsequent replacement of CD4+ T cells alone restores the disease phenotype while the transfer of only CD8+ T cells had no significant effect on the disease phenotype. The present study tested the hypothesis that CD4+ and CD8+ T cells will synergistically act to enhance salt-sensitive hypertension and renal damage in the Dahl SS compared to the injection of only CD4+ T cells. This hypothesis was tested by adoptive transferring purified CD4+ T cells from Dahl SS (~5 million, CD4+ SS→), a combination of ~5 million CD4+ T cells with ~5 million CD8+ T cells from Dahl SS (CD4+CD8+ SS→) or PBS vehicle (PBS→) into the SS CD247-/- rat on postnatal day 5. Animals were instrumented with radiotelemeters at 8 weeks of age. After a week of recovery, baseline measurements of blood pressure and albumin excretion were obtained while rats were fed a low salt (LS, 0.4% NaCl) diet. Rats were then switched to a high salt (HS, 4.0% NaCl) diet for 21 days, with continuous blood pressure measurements and urine collections every 7 days. On day 21, the rats were euthanized, and their kidneys were perfused and collected for immune cell analysis by flow cytometry. During the LS baseline period there was no significant difference observed in mean arterial pressure (MAP) between the CD4+ SS→, CD4+CD8+ SS→, or PBS→ groups (121±2, 122±2, 119±1 mmHg; n=9, 10, 6, respectively). After three weeks of HS, both CD4+ SS→ and CD4+CD8+ SS→ rats demonstrated an equivalent amplification of SS hypertension (176±6 and 179±5 mmHg) and albuminuria (261±53 and 285±37 mg/day, respectively) which was significantly greater than the MAP (159±5 mmHg) and albuminuria (169±29 mg/day) in PBS→. Finally, a flow cytometric analysis at the end of the experiment confirmed the absence of CD3+ T cells in the PBS→ and documented the reconstitution of equal numbers of CD4+ cells in the blood and kidney of the rats receiving CD4+ cells or the combined CD4+ CD8+ cell transfer. We also confirmed the CD4+CD8+ was the only group that had reconstituted CD8+ T cells. These studies demonstrated that CD4+ T cells amplify salt-sensitive hypertension and renal damage in the Dahl SS independently from CD8+ T cells.

O57 NOCTURNAL BLOOD PRESSURE FLUCTUATION AND DIPPING PATTERNS IN PATIENTS WITH SEVERE OBSTRUCTIVE SLEEP APNOEA

Background and Objective: Nighttime blood pressure (BP) is important for diagnosis of hypertension and for cardiovascular risk stratification. Remarkably, a reverse dipping pattern is a strong and independent predictor of overall mortality and major adverse cardiovascular events. Therefore, the further clarification of the underlying mechanisms of non- and reverse dipping is crucial to improve the treatment of patients with nighttime hypertension. Methods: We investigated 97 patients with suspected obstructive sleep apnoea (OSA, AHI >30) using standard polysomnography and continuous BP measurement based on the pulse-transit-time method (SOMNOscreen Plus®, SOMNOmedics). Frequency and amplitude of fluctuations in systolic BP following sleep disturbances (OSA) were investigated. Results: Apnoeic events went along with transient increases of BP. In some cases, systolic BP did not reach the value before the apnoea but increased over time. We defined elevations of the systolic BP baseline by >10 mmHg with a duration of >10 min as BP superpositions. The superposition periods were also characterized by increased BP amplitudes with peak values of BP up to 220 mmHg. Superposition occurred in 48 patients. Further, 65% of the OSA patients were identified as non-dippers. However, nearly all the patients with superposition (98%) were identified to have non-dipper or reverse dipper patterns. Conclusions: Our study strongly suggests that non-dipping and reverse dipping in patients with severe OSA are causally linked to OSA related BP fluctuations. Further, continuous elevations in SBP baseline (superpositions) result in extreme BP values. This behaviour with high BP peaks may be contributing to the increased mortality in patients with reverse dipping. Therefore, identification and adequate treatment of patients with reverse dipping reduces the cardiovascular risk and may prolong their life.

Peripheral arterial catheters in extremely preterm infants born at less than 28 weeks of gestation—a single-center experience

The aim of this study was to perform a retrospective data analysis of established peripheral artery catheters (pAC) in extremely preterm infants. The primary outcome was the pAC life span and its correlation to gestational age, birth weight, localizations, and pAC removal. Retrospective data analysis of electronic patient records of all extremely preterm infants (born less than 28 weeks gestation) admitted to the neonatal intensive care unit in Graz (Austria) between January 2014 and December 2020. A total of 196 preterm infants with a median (IQR) gestational age of 25.7 (24.6–26.6) weeks and a birth weight of 730 (614–898) g were included. In 155 (79%) of these preterm infants, 286 pAC and six umbilical artery catheters were inserted successfully. The first pAC was inserted 2.5 (1.4–7.4) h after birth, and the median pAC life span was 57.5 (22.–107.2) h. Gestational age, birth weight, and catheter localization did not correlate with the pAC life span. The pAC localizations were the radial artery (63%), tibial posterior artery (21%), ulnar artery (6%), dorsal artery of the foot (6%), others (1%), and not documented (3%). Adverse reactions including temporarily impaired peripheral perfusion, local inflammation, extravasation, or bleeding were reported in 13% of all pAC, but none of these resulted in long-term sequelae. A median (IQR) of 9 (5–18) arterial blood samples were drawn via pAC, resulting in a notable reduction of pain stimuli.Conclusion: The use of pAC in extremely preterm infants is feasible and safe. Neither gestational age, birth weight nor localization did affect the life span of pAC. No long-term sequelae were observed, and pain events were reduced by using pAC for blood drawing.What is Known:• Peripheral artery catheters can be used for continuous blood pressure measurement and blood draw even in extremely preterm infants.• (Severe) adverse reactions such as bleeding, necrosis, or amputation occur between 1 and 4%.• What is New:• The median peripheral arty catheter life span is 58 h and is not affected by gestational age, birth weight, nor localization.• A median of nine blood samples can be taken per each single pAC and, therefore, prevent pain events in extremely preterm infants.

Resonance sonomanometry for noninvasive, continuous monitoring of blood pressure.

Cardiovascular disease is the leading cause of death worldwide. Existing methods for continuous, noninvasive blood pressure (BP) monitoring suffer from poor accuracy, uncomfortable form factors, or a need for frequent calibration, limiting their adoption. We introduce a new framework for continuous BP measurement that is noninvasive and calibration-free called resonance sonomanometry. The method uses ultrasound imaging to measure both the arterial dimensions and artery wall resonances that are induced by acoustic stimulation, which offers a direct measure of BP by a fully determined physical model. The approach and model are validated in vitro using arterial mock-ups and then in multiple arteries in human subjects. This approach offers the promise of robust continuous BP measurements, providing significant benefits for early diagnosis and treatment of cardiovascular disease.

Home blood pressure measurement days and changes in urinary sodium-to-potassium ratio, estimated salt and potassium intakes and blood pressure: 1-year prospective study.

Current international guidelines recommend home blood pressure (BP) measurement and low sodium and high potassium intakes for the management of hypertension. We hypothesized that increased home BP measurement may result in more effective management of sodium and potassium intakes and BP. We examined associations of home BP measurement days with changes in the urinary sodium-to-potassium (Na/K) ratio, estimated salt and potassium intakes and BP. We included 209 healthy participants (mean age, 55.9 years; 56.5% women) from a prospective cohort study. We examined 1-year data on self-measured home BP and spot urine samples. Median (interquartile range) days of home BP measurement was 324 (225-358) over 1-year. Baseline mean (SD) Na/K ratio, salt and potassium intakes, morning and evening SBP, and morning and evening DBP were 3.8 (2.3), 8.5 (1.9) g/day, 1833.5 (416.5) mg/day, 120.4 (14.0) mmHg, 118.2 (14.2) mmHg, 79.2 (10.1) mmHg, and 76.2 (10.1) mmHg, respectively. In multivariable-adjusted linear regression , β (standard error) per 10 days increase in number of home BP measurement were -0.031 (0.017) for Na/K ratio, -0.036 (0.015) for salt intake, -1.357 (2.797) for potassium intake, -0.178 (0.064) for morning SBP, -0.079 (0.041) for morning DBP, -0.109 (0.067) for evening SBP and -0.099 (0.045) for evening DBP. Additionally, relationships persisted for men and women, but changes in salt intake were more pronounced among participants taking antihypertensive medication (interaction P = 0.002). Continuous measurement of home BP may lead not only to self-monitoring of BP, but also to declines in salt intakes and some BP indices.

Calibration-Free Estimation Algorithm for Cuffless Continuous Blood Pressure Measurement based on ultrasonic devices

Calibration-Free Estimation Algorithm for Cuffless Continuous Blood Pressure Measurement based on ultrasonic devices

Atrial fibrillation ablation performed under general anesthesia is associated with significantly low arterial blood pressure and higher incidence of hypotensive events

Abstract Introduction Catheter ablation is a pivotal treatment for atrial fibrillation (AF). When performed under general anesthesia (GA), it may be associated to hypotensive events, with unclear prevalence and prognostic impact. Continuous non-invasive blood pressure (CNBP) measurement is a validated and reliable tool for intraprocedural beat-to-beat advanced hemodynamic monitoring. Purpose To assess and compare the hemodynamic impact of GA during AF ablation using a CNBP (ClearSight) system. Methods In an observational single large volume center study we prospectively enrolled all patients undergoing AF ablation at our institution with CNBP monitoring, as per local practice. Patients were assigned to deep sedation (DS) or general anesthesia (GA) group according to the chosen sedation regimen. The following parameters were compared between the two strategies: systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial pressure (MAP), cardiac output (CO), cardiac index (CI), stroke volume (SV), stroke volume index (SVI). Hypotension events (HE) (MAP < 65 mmHg) were counted and compared between groups. Results Two hundred patients were enrolled from September 2022 to August 2023. 170 patients underwent AF ablation under DS (76,7% male, mean age 56,77±15,76), while 30 patients were treated under GA (70% male, mean age 60,72±13,79). A total of 117709 measurements were analyzed and compared, for an overall monitoring time of 39293,66 minutes. Patients treated under GA had significantly lower average SBP (104,83±21,48 mmHg vs 138,05±22,09 mmHg, p<0,001), DBP (59,59±11,89 mmHg vs 76,12±12,75 mmHg, p<0,001), MAP (74,96±15,02 mmHg vs 97,12±15,38 mmHg, p<0,001). We also observed significantly lower CO (4,40±1,47 L/min vs 5,16±1,62 L/min, p<0,001), CI (2,22±0,71 L/min/m2 vs 2,61±0,78 L/min/m2, p<0,001) SV (62,37±18,04 mL/beat vs 70,65±24,95 mL/beat, p<0,001) and SVI (31,40±8,54 mL/beat/m2 vs 35,80±12,07 mL/beat/m2, p<0,001). Patients treated under GA witnessed a higher number of per-patient HE (10,53±9,16 vs 0,61±2,07, p<0,001), and higher HE duration (4,8±6,62 min vs 2,82±3,66, p<0,001). Conclusion AF ablation performed under general anesthesia is associated with significantly lower systolic, diastolic, and mean arterial pressure, reduced cardiac output, stroke volume and stroke volume index when compared to deep sedation. Patients undergoing AF ablation under GA witness higher incidence and duration of hypotensive events. CNBP is a valid tool for beat-to-beat procedural hemodynamic assessment and can help identifying and treat hypotensive events. Further studies are needed to assess the potential prognostic impact of intraprocedural hypotension during AF ablation.

The interactive effects of posture and biological sex on the control of muscle sympathetic nerve activity during rhythmic handgrip exercise.

Body posture and biological sex exhibit independent effects on the sympathetic neural responses to dynamic exercise. However, the neural mechanisms (e.g., baroreflex) by which posture impacts sympathetic outflow during rhythmic muscular contractions, and whether biological sex affects posture-mediated changes in efferent sympathetic nerve traffic during exercise, remain unknown. Thus, we tested the hypotheses that increases in muscle sympathetic nerve activity (MSNA) would be greater during upright compared with supine rhythmic handgrip (RHG) exercise, and that females would demonstrate smaller increases in MSNA during upright RHG exercise than males. Twenty young (30 [6] yr; means [SD]) individuals (9 males, 11 females) underwent 6 min of supine and upright (head-up tilt 45°) RHG exercise at 40% maximal voluntary contraction with continuous measurements of MSNA (microneurography), blood pressure (photoplethysmography), and heart rate (electrocardiogram). In the pooled group, absolute MSNA burst frequency (P < 0.001), amplitude (P = 0.009), and total MSNA (P < 0.001) were higher during upright compared with supine RHG exercise. However, body posture did not impact the peak change in MSNA during RHG exercise (range: P = 0.063-0.495). Spontaneous sympathetic baroreflex gain decreased from rest to RHG exercise (P = 0.006) and was not impacted by posture (P = 0.347). During upright RHG exercise, males demonstrated larger increases in MSNA burst amplitude (P = 0.002) and total MSNA (P = 0.001) compared with females, which coincided with greater reductions in sympathetic baroreflex gain among males (P = 0.004). Collectively, these data indicate that acute attenuation of baroreflex-mediated sympathoinhibition permits increases in MSNA during RHG exercise and that males exhibit a greater reserve for efferent sympathetic neural recruitment during orthostasis than females.NEW & NOTEWORTHY The impact of posture and sex on cardiovascular control during rhythmic handgrip (RHG) exercise is unknown. We show that increases in muscle sympathetic nerve activity (MSNA) during RHG are partly mediated by a reduction in sympathetic baroreflex gain. In addition, males demonstrate larger increases in total MSNA during upright RHG than females. These data indicate that the baroreflex partly mediates increases in MSNA during RHG and that males have a greater sympathetic vasoconstrictor reserve than females.

A Wireless Noninvasive Blood Pressure Measurement System Using MAX30102 and Random Forest Regressor for Photoplethysmography Signals

Hypertension, often termed “the silent killer”, is associated with cardiovascular risk and requires regular blood pressure (BP) monitoring. However, existing methods are cumbersome and require medical expertise, which is worsened by the need for physical contact, particularly during situations such as the coronavirus pandemic that started in 2019 (COVID-19). This study aimed to develop a cuffless, continuous, and accurate BP measurement system using a photoplethysmography (PPG) sensor and a microcontroller via PPG signals. The system utilizes a MAX30102 sensor and ESP-WROOM-32 microcontroller to capture PPG signals that undergo noise reduction during preprocessing. Peak detection and feature extraction algorithms were introduced, and their output data were used to train a machine learning model for BP prediction. Tuning the model resulted in identifying the best-performing model when using a dataset from six subjects with a total of 114 records, thereby achieving a coefficient of determination of 0.37/0.46 and a mean absolute error value of 4.38/4.49 using the random forest algorithm. Integrating this model into a web-based graphical user interface enables its implementation. One probable limitation arises from the small sample size (six participants) of healthy young individuals under seated conditions, thereby potentially hindering the proposed model’s ability to learn and generalize patterns effectively. Increasing the number of participants with diverse ages and medical histories can enhance the accuracy of the proposed model. Nevertheless, this innovative device successfully addresses the need for convenient, remote BP monitoring, particularly during situations like the COVID-19 pandemic, thus making it a promising tool for cardiovascular health management.

Salt-Sensitive Hypertension and Renal Damage are Amplified by Adoptive Transfer of CD4+ and Not CD8+ T Cells: A Role of NADPH Oxidase 2 (NOX2)

Infiltration of T cells into the kidney of the Dahl Salt Sensitive (SS) rat model of human disease accompanies the development of salt-sensitive hypertension and renal damage. Deletion of T cells on the Dahl SS genetic background (SSCD247−/−) attenuates hypertension and renal damage, and subsequent replacement of T cells by splenocyte transfer restores the disease phenotype. The present studies were performed to assess if the T cell subtype (CD4+ vs CD8+) is important in Dahl SS hypertension and interrogate the mechanism of action. In initial experiments, adoptive transfer of purified CD4+ or CD8+ T cells (~5 million) from splenocytes isolated from the Dahl SS (CD4+ SS→CD247 or CD8+ SS→CD247) or PBS vehicle (PBS→CD247) into the SSCD247−/− rat was performed on postnatal day 5. Animals were recovered and instrumented with radiotelemeters at 7 weeks of age. After a week of recovery, baseline measurements of blood pressure and albumin excretion were obtained while rats were fed a low salt (LS, 0.4% NaCl) diet. Rats were then switched to a high salt (HS, 4.0% NaCl) diet for 21 days, with continuous blood pressure measurements and urine collections every 7 days. On day 21, the rats were euthanized, and their kidneys were perfused and collected for immune cell analysis by flow cytometry. During the LS baseline period there was no significant difference observed in mean arterial pressure (MAP) between the CD4+ SS→CD247, CD8+ SS→CD247, or PBS→CD247 groups (113±1, 115±1, 114±1 mmHg; n=21, 10, 24, respectively). After three weeks of HS, rats receiving CD4+ T cells from the SS (CD4+ SS→CD247) demonstrated an amplified salt-sensitive hypertension (154±3 mmHg) and albuminuria (184±22 mg/day) compared to blood pressure (140±3 and 145±3 mmHg) and albuminuria (82±9 and 85±8 mg/day) in the CD8+ SS→CD247 or PBS→CD247 groups, respectively. Since the deletion of the p67phox subunit of NADPH oxidase 2 (NOX2) in adoptively transferred splenocytes attenuated Dahl SS hypertension and kidney damage, parallel studies examined the influence of deletion of p67phox in CD4+ (n=14) and CD8+ T cells (n=8). The adoptive transfer of either CD4+ or CD8+ T cells lacking functional NOX2 did not alter the LS or HS blood pressure or albuminuria when compared to the PBS control group. Finally, a flow cytometric analysis at the end of the experiment confirmed the absence of CD3+ T cells in the PBS→CD247 and documented the reconstitution of equal numbers of CD4+ cells in the blood and kidney of the rats receiving CD4+ cells with intact or deficient NOX2. Interestingly, no difference was observed in CD8+ T cells in the kidney and blood of rats receiving CD8+ cells with intact or deficient NOX2, but a significant number of CD4+ T cells were also observed in the SSCD247−/− rats receiving the purified CD8+ T cells. In summary, these studies demonstrate that CD4+ T cells amplify salt-sensitive hypertension and renal damage in the Dahl SS via a NOX2-dependent mechanism while CD8+ T cells do not alter disease phenotypes when compared to PBS control. GRANTS: HL161231, HL166458, Georgia Research Alliance. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Dynamic Shift Towards Increased O2 Consumption and Reduced Lactate Uptake During Acute Volume Expansion in Sprague Dawley (SD) Rats

Rationale: In a recent study (PMID: 37575482), we established a method to assess alterations in O2 and substance metabolism in the kidneys in conscious free moving rat. This involved the repeated collection of renal arteriovenous blood and urine, alongside continuous measurements (24/7) of renal blood flow (RBF) and blood pressure (BP). Our previous studies demonstrated that in SD rats, there is an augmentation in RBF and GFR following chronic salt loading. Additionally, total renal O2 consumption (VO2) increases while there is a decrease in the net consumption of lactate with a tendency for its increased production. We hypothesize that these changes are not exclusive to the chronic phase of salt-loading but can also manifest during rapid increases of RBF and GFR. The primary aim of this study was to establish an experimental model reflecting these dynamics. Methods: SD rat (male, 10 wk age fed 0.4 NaCl (LS) diet, n=8) were studied. The jugular vein and femoral vein and artery were catheterized together with the renal vein. FITC-inulin (2 mg/mL) dissolved in 2%BSA saline was infused at 1.0 mL/100 g body wt/h from jugular vein. RBF was measured with an ultrasonic flow probe (Transonic, Inc) on the left renal artery and BP was measured through an arterial catheter. Whole blood, collected from donor rats, was diluted by 20% with saline, and a 6 mL volume expansion was performed with this solution over 1 hour. Blood was collected from both the renal venous and arterial catheters and urine from a ureteral catheter before and after volume expansion. O2 content was measured by radiometer and plasma lactate measured with a high sensitivity L-lactate fluorescent assay kit (ab169557, abcam). The same experiment was performed without volume expansion (i.e., sham study). O2 and lactate delivery and consumption were calculated as follows: Delivery = arterial content (A) x RBF; Consumption = (A − renal venous content (RV)) x RBF; Extraction = (A-RV) / A. Results: BP increased from 101 ± 3 to 111 ± 4 mmHg (p&lt;0.05), RBF increased from 5.4 ± 0.5 to 7.9 to 0.6 mL/min/g kidney weight (gkw) (p&lt;0.05) by volume expansion. GFR increased from 0.94 ± 0.06 to 1.19 ± 0.08 mL/min/gkw (p&lt;0.05). O2 delivery increased from 1.06 ± 0.09 to 1.61 ± 0.12 mL/min/gkw (p&lt;0.05). O2 consumption (VO2) increased from 0.06 ± 0.01 to 0.08 ± 0.01 mL/min/gkw (p&lt;0.05). The O2 extraction ratio remained unchanged. Both lactate consumption (0.94 ± 0.11 to 0.47 ± 0.11 mM/gkw, p&lt;0.05) and extraction ratio (0.18 ± 0.01 to 0.11 ± 0.02, p&lt;0.05) were reduced by volume expansion. Conclusion: The increase of O2 consumption and reduction of lactate consumption with acute volume expansion model appear to be similar to those that we observed when SD rats were subjected to a chronic step increase of salt intake (from 0.4 to 4.0% NaCl). In contrast, however, an increase in O2 extraction was not observed with acute volume expansion as was the case with a high salt diet in which our studies have indicated that a prolonged tubular reabsorptive workload leads to enhanced oxidative stress with an uncoupling of oxidative phosphorylation. R01 HL151587, AHA 23POST1008714. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

ACNN-BiLSTM: A Deep Learning Approach for Continuous Noninvasive Blood Pressure Measurement Using Multi-Wavelength PPG Fusion.

As an essential physiological indicator within the human body, noninvasive continuous blood pressure (BP) measurement is critical in the prevention and treatment of cardiovascular disease. However, traditional methods of blood pressure prediction using a single-wavelength Photoplethysmographic (PPG) have bottlenecks in further improving BP prediction accuracy, which limits their development in clinical application and dissemination. To this end, this study proposed a method to fuse a four-wavelength PPG and a BP prediction model based on the attention mechanism of a convolutional neural network and bidirectional long- and short-term memory (ACNN-BiLSTM). The effectiveness of a multi-wavelength PPG fusion method for blood pressure prediction was evaluated by processing PPG signals from 162 volunteers. The study compared the performance of the PPG signals with different individual wavelengths and using a multi-wavelength PPG fusion method in blood pressure prediction, assessed using mean absolute error (MAE), root mean squared error (RMSE) and AAMI-related criteria. The experimental results showed that the ACNN-BiLSTM model achieved a better MAE ± RMSE for a systolic BP and diastolic BP of 1.67 ± 5.28 and 1.15 ± 2.53 mmHg, respectively, when using the multi-wavelength PPG fusion method. As a result, the ACNN-BiLSTM blood pressure model based on multi-wavelength PPG fusion could be considered a promising method for noninvasive continuous BP measurement.

AcumenTM hypotension prediction index guidance for prevention and treatment of hypotension in noncardiac surgery: a prospective, single-arm, multicenter trial

BackgroundIntraoperative hypotension is common during noncardiac surgery and is associated with postoperative myocardial infarction, acute kidney injury, stroke, and severe infection. The Hypotension Prediction Index software is an algorithm based on arterial waveform analysis that alerts clinicians of the patient’s likelihood of experiencing a future hypotensive event, defined as mean arterial pressure < 65 mmHg for at least 1 min.MethodsTwo analyses included (1) a prospective, single-arm trial, with continuous blood pressure measurements from study monitors, compared to a historical comparison cohort. (2) A post hoc analysis of a subset of trial participants versus a propensity score-weighted contemporaneous comparison group, using external data from the Multicenter Perioperative Outcomes Group (MPOG). The trial included 485 subjects in 11 sites; 406 were in the final effectiveness analysis. The post hoc analysis included 457 trial participants and 15,796 comparison patients. Patients were eligible if aged 18 years or older, American Society of Anesthesiologists (ASA) physical status 3 or 4, and scheduled for moderate- to high-risk noncardiac surgery expected to last at least 3 h. Measurements: minutes of mean arterial pressure (MAP) below 65 mmHg and area under MAP < 65 mmHg.ResultsAnalysis 1: Trial subjects (n = 406) experienced a mean of 9 ± 13 min of MAP below 65 mmHg, compared with the MPOG historical control mean of 25 ± 41 min, a 65% reduction (p < 0.001). Subjects with at least one episode of hypotension (n = 293) had a mean of 12 ± 14 min of MAP below 65 mmHg compared with the MPOG historical control mean of 28 ± 43 min, a 58% reduction (p< 0.001). Analysis 2: In the post hoc inverse probability treatment weighting model, patients in the trial demonstrated a 35% reduction in minutes of hypotension compared to a contemporaneous comparison group [exponentiated coefficient: − 0.35 (95%CI − 0.43, − 0.27); p < 0.001].ConclusionsThe use of prediction software for blood pressure management was associated with a clinically meaningful reduction in the duration of intraoperative hypotension. Further studies must investigate whether predictive algorithms to prevent hypotension can reduce adverse outcomes.Trial registrationClinical trial number: NCT03805217. Registry URL: https://clinicaltrials.gov/ct2/show/NCT03805217. Principal investigator: Xiaodong Bao, MD, PhD. Date of registration: January 15, 2019.

A continuous cuffless blood pressure measurement from optimal PPG characteristic features using machine learning algorithms

Background and objectiveHypertension is a potentially dangerous health condition that can be detected by measuring blood pressure (BP). Blood pressure monitoring and measurement are essential for preventing and treating cardiovascular diseases. Cuff-based devices, on the other hand, are uncomfortable and prevent continuous BP measurement. MethodsIn this study, a new non-invasive and cuff-less method for estimating Systolic Blood Pressure (SBP), Mean Arterial Pressure (MAP), and Diastolic Blood Pressure (DBP) has been proposed using characteristic features of photoplethysmogram (PPG) signals and nonlinear regression algorithms. PPG signals were collected from 219 participants, which were then subjected to preprocessing and feature extraction steps. Analyzing PPG and its derivative signals, a total of 46 time, frequency, and time-frequency domain features were extracted. In addition, the age and gender of each subject were also included as features. Further, correlation-based feature selection (CFS) and Relief F feature selection (ReliefF) techniques were used to select the relevant features and reduce the possibility of over-fitting the models. Finally, support vector regression (SVR), K-nearest neighbour regression (KNR), decision tree regression (DTR), and random forest regression (RFR) were established to develop the BP estimation model. Regression models were trained and evaluated on all features as well as selected features. The best regression models for SBP, MAP, and DBP estimations were selected separately. ResultsThe SVR model, along with the ReliefF-based feature selection algorithm, outperforms other algorithms in estimating the SBP, MAP, and DBP with the mean absolute error of 2.49, 1.62 and 1.43 mmHg, respectively. The proposed method meets the Advancement of Medical Instrumentation standard for BP estimations. Based on the British Hypertension Society standard, the results also fall within Grade A for SBP, MAP, and DBP. ConclusionThe findings show that the method can be used to estimate blood pressure non-invasively, without using a cuff or calibration, and only by utilizing the PPG signal characteristic features.

Can Currently Available Non-invasive Continuous Blood Pressure Monitors Replace Invasive Measurement With an Arterial Catheter?

Deviations from normal blood pressure (BP) during general anesthesia have been clearly linked to several adverse outcomes. Measuring BP accurately is therefore critically important for producing excellent outcomes in health care. Normal BP does not necessarily guarantee adequate organ perfusion however and adverse events have occurred even when BP seemed adequate. Invasive blood pressure monitoring has recently evolved beyond merely measuring BP. Arterial line-derived pulse contour analysis is used now to assess both cardiac output and stroke volume variation as indices of adequate intravascular volume. Confirmation of acceptable cardiac output with data derived from invasive intra-arterial catheters has become very important when managing high-risk patients. Newer devices that measure BP continuously and non-invasively in the digital arteries via a finger cuff have also become available. Many clinicians contemplate now if these new devices are ready to replace invasive monitoring with an arterial catheter. Unlike non-invasive devices, intra-arterial catheters allow frequent blood sampling. This makes it possible to assess vital parameters like pH, hemoglobin concentration, ionized calcium, potassium, glucose, and arterial partial pressure of oxygen and carbon dioxide frequently. Non-invasive continuous BP measurement has been found to be unreliable in critically ill patients, the elderly, and patients with calcified arteries. Pulse contour-derived estimates of cardiac output and stroke volume variation have been validated better with data derived from arterial lines than that from the newer finger cuff monitors. Significant advances have been recently made with non-invasive continuous BP monitors. Invasive monitoring with an arterial line however remains the gold standard for measuring BP and assessing pulse contour analysis-derived hemodynamic variables in critically ill patients. In the future, non-invasive continuous BP monitors will likely replace intermittent oscillometers in the operating room and the postoperative period. They will however not eliminate the need for arterial catheterization in critically ill patients.

Single-Cycle Pulse Signal Recognition Based on One-Dimensional Deep Convolutional Neural Network

Pulse signals carry comprehensive information regarding human cardiovascular physiology and pathology, providing a noninvasive and continuous method to assess cardiovascular health status in blood pressure monitoring. The blood pressure measurement method based on the pulse signal needs to extract the features of the single-cycle pulse signal, while the pulse signal pertains to the weak physiological signal of body surface. The acquisition process is susceptible to various factors leading to abnormal cycles, especially adjacent channel interference, affecting the subsequent feature extraction. To address this problem, this paper conducts an analysis of the formation mechanism of adjacent channel interference and proposes a single-cycle pulse signal recognition algorithm based on a one-dimensional deep convolutional neural network (1D-CNN) model. Radial pulse signals were collected from 150 subjects by pulse bracelet, and a dataset comprising 3446 single-cycle signals was extracted in total after denoising, single-cycle segmentation, and standardized preprocessing. The 1D-CNN model is trained to classify input signals into three categories: effective pulse signals, distortion, and interference signals. This classification is achieved by evaluating the waveform morphology of the signals within a single cycle. The results show that the overall classification accuracy of the algorithm on the test set is 98.26%, in which the classification accuracy of pulse waves is 99.8%, indicating that it can effectively recognize single-cycle pulse waves, which lays the foundation for subsequent continuous blood pressure measurement.