Contactless video-based photoplethysmography technique comparison investigating pulse transit time estimation of arterial blood pressure

Abstract Background : Substantial investigation has been made into the correlation between Pulse Transit Time (PTT) and Blood Pressure (BP), as a possible route to achieve continuous non-invasive measurement of BP (cNIBP). We investigated whether PTT-trends could model BP-trends during episodes of rapid declines in Systolic Blood Pressure (SBP). Methods: From the freely available Medical Information Mart for Intensive Care (MIMIC-III) waveform database, we identified subjects who experienced a reduction in SBP from ≥ 120mmHg to ≤ 90 mmHg during a period of ≤ 15 minutes, for whom complete peak detection was possible. SBP was extracted from the Arterial Blood Pressure (ABP) waveform, and PTT was calculated from the R-peak of the ECG to the peak of the ABP waveform. Both SBP and PTT were processed using a moving average filter, yielding the variables SBP AV and PTT-RA AV . A moving average of continuous heart rate (HR AV ) was also analysed as a negative control to assess the effect of averaging. The intra-individual association between variables was assessed per subject using linear regression. Results: 511 patients were included for the main analysis. Median correlation coefficients (r) obtained from linear regression versus SBP AV were as follows: PTT-RA AV -0.93 (IQR -0.98 to -0.76), HR AV 0.46 (IQR -0.16 to 0.83). Regression slopes for the relationship between SBP AV and PTT-RA AV displayed a median of -2.46 mmHg/ms (IQR -3.47 mmHg/ms to -1.61 mmHg/ms). In supplementary analysis, results did not differ substantially when widening inclusion criteria, but the results were not always consistent within subjects across episodes of hypotension. Conclusions: In a large cohort of critically ill patients experiencing episodes of rapid declines in systolic blood pressure, there was a moderate-strong intra-individual correlation between averaged systolic blood pressure and averaged pulse transit time as measured from ECG R-peak to the peak of the arterial blood pressure waveform. Our findings encourage further investigation into using the pulse transit time for non-invasive real-time detection of hypotension.

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Physiological Amounts of Angiotensinogen Increase Blood Pressure in Sprague Dawley Rats After I.V. Administration.

Hypertension ◽

10.1161/hyp.36.suppl_1.694-d ◽

2000 ◽

Vol 36 (suppl_1) ◽

pp. 694-694

Author(s):

Christoph P R Klett ◽

Joey P Granger

Keyword(s):

Blood Pressure ◽

Arterial Blood Pressure ◽

Transit Time ◽

Mean Arterial Blood Pressure ◽

Time Lag ◽

Plasma Concentrations ◽

Sprague Dawley ◽

Angiotensin I ◽

Arterial Blood ◽

Sprague Dawley Rats

P9 The synthesis and secretion of hepatic angiotensinogen is controlled by a complex pattern of physiologic and pathophysiologic mediators including glucocorticoids, estrogens, thyroid hormones, cytokines, glucagon,insulin, and prostaglandins. Since plasma concentrations of angiotensinogen are close to the Michaelis Menten constant, it was hypothesized that changes in angiotensinogen plasma concentrations have an influence on the formation rate of angiotensin I and angiotensin II and, therefore, on blood pressure. To further test this hypothesis we injected purified rat angiotensinogen i.v. in Sprague Dawley rats via the femoral vein. Mean arterial blood pressure was measured after arterial cathederization. Control animals had a mean arterial pressure of 131 ± 2 mm Hg before and after the injection of vehicle (saline). The injection of 0.8, 1,2, and 2.9 mg/kg angiotensinogen caused a dose dependend increase in mean arterial blood pressure of 8 ± 0.4, 19.3 ± 2.1, and 32 ± 2.4 mm Hg, respectively. In contrast, the injection of a purified rabbit anti-rat-angiotensinogen antibody 1.4 mg/kg resulted in a significant decrease in blood pressure (-52 ± 3.2 mmHg). In an attempt to analyze how fast and efficient angiotensinogen production can sense regulatory input and convert into adaptation of secretion rate we determined the transit time (time needed for translation and post-translational modifications) for angiotensinogen in a pulse chase experiment employing 35 [S]-methionine as label in freshly isolated hepatocytes. During the chase periode, after quantitative immunoprecipitation, we determined the transit time for angiotensinogen with 2.5 h which is consistent with the constitutive type of angiotensinogen secretion and the time lag found for plasma concentrations to respond to regulatory mediators. In summary we conclude that variations in angiotensinogen plasma concentrations can result in changes in blood pressure. In contrast to renin known as a tonic regulator for the generation of angiotensin I, angiotensinogen seems to be a factor rather important for long-term control of the basal activity of the renin angiotensin system.

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