Continuous Arterial Pressure Measurements Research Articles

Tonometric Condition of Cellular Polypropylene Film Sensors in Measuring Arterial Pressure Waveform.

Tonometric continuous measurement of arterial pressure becomes feasible using a cellular polypropylene (Cellular PP) film sensor. A pulsatile arterial vascular phantom model was used to find the range of optimal tonometric conditions and the responsiveness to dynamic pressure changes. The optimal tonometric condition was assessed by the correlation coefficient between the hydraulic pressure and the Cellular PP output using two different types of tubes (the latex tube and the hydrogel tube) to simulate arteries. With a setting of the normal blood pressure range, the output of Cellular PP correlated strongly with the level of hydraulic pressure, 0.998 and 0.989 in the latex tube and the hydrogel tube, respectively. For maintaining the optimal tonometric condition, the depressed depths of the latex and the hydrogel tube were less than 1.2 and 0.6 mm, respectively. The phantom model also demonstrated that the Cellular PP sensor followed changes in a hydraulic pressure dynamically under the optimal tonometric conditions. The present results demonstrated the Cellular PP film sensor is applicable to the arterial tonometry in measuring the instantaneous blood pressure while the sensor is adjusted to maintain the minimal flatness of the underlying arterial wall.Clinical Relevance- To understand the physiological characteristics of blood pressure and arterial system, the instantaneous measurement of blood pressure is necessary. The present study suggests that Cellular PP films are applicable to peripheral arteries tonometrically to obtain simultaneously the respective blood pressure waveforms.

Validation of noninvasive continuous arterial pressure measurement by ClearSight System\u2122 during induction of anesthesia for cardiovascular surgery

BackgroundSince blood pressure tends to be unstable during induction of anesthesia in patients undergoing cardiovascular surgery, an artery catheter is often inserted before induction to continuously monitor arterial pressure during induction of anesthesia. ClearSight System™ enables noninvasive continuous measurement of beat-to-beat arterial pressure via a single finger cuff without pain using photoplethysmographic technology. If ClearSight System™ can replace intra-arterial pressure measurement, blood pressure could be easily and noninvasively assessed. However, the validity of ClearSight System™ during induction of anesthesia in patients undergoing cardiovascular surgery has not been evaluated. The aim of this study was to compare blood pressure measured by ClearSight System™ with intra-arterial pressure during induction of anesthesia for cardiovascular surgery.MethodsThis study was registered retrospectively. Data during induction of anesthesia for elective cardiovascular surgery were obtained for patients in whom noninvasive arterial pressure was measured by ClearSight System™ (APcs) and invasive radial arterial pressure (APrad) was measured simultaneously. According to the widely used criteria formulated by international standards from the Association for the Advancement of Medical Instrumentation, the acceptable bias and precision for arterial pressure measurements were fixed at < 5 mmHg and 8 mmHg, respectively.ResultsData for 18 patients were analyzed. For 3068 analyzed paired measurements, values of APcs vs APrad bias (precision) were 13.2 (17.5), − 9.1 (7.3) and − 3.9 (7.8) mmHg for systolic, diastolic, and mean arterial pressures, respectively.ConclusionsMean arterial pressure measured by ClearSight System™ could be considered as an alternative for mean radial arterial pressure during induction of anesthesia for elective cardiovascular surgery.

Performance of closed-loop resuscitation in a pig model of haemorrhagic shock with fluid alone or in combination with norepinephrine, a pilot study.

We evaluated the performance of a new device to control the administration of fluid alone or co-administration of fluid and norepinephrine in a pig model of haemorrhagic shock in two sets of experiments. In the first one, resuscitation was guided using continuous arterial pressure measurements (three groups: resuscitation with fluid by a physician, CL resuscitation with fluid, and CL resuscitation with fluid and norepinephrine). In the second one, resuscitation was guided using discontinuous arterial pressure measurements (three groups: CL resuscitation with fluid alone, CL resuscitation with fluid and moderate dose norepinephrine, and CL resuscitation with fluid and a high dose of norepinephrine). Pigs were resuscitated for 1h. In the first set of experiments, proportion of time spent in the target area of 78-88mmHg of systolic arterial pressure was not statistically different between the three groups: manual, 71.2% (39.1-80.1); CL with fluid, 87.8% (68.3-97.4); and CL with fluid and norepinephrine, 78.1% (59.2-83.6), p = 0.151. In the second set of experiments, performance of CL resuscitation with fluid or with combination of fluid and high or moderate dose of norepinephrine was not significantly different (p = 0.543 for time in target). Pigs resuscitated with norepinephrine required less fluid and had less haemodilution than pigs resuscitated with fluid alone. Performance of CL resuscitation using continuous arterial pressure measurement was not significantly different than optimised manual treatment by a dedicated physician. Performance of CL resuscitation was reduced with discontinuous arterial pressure measurements in comparison with continuous arterial pressure measurements.

Perioperative Quality Initiative consensus statement on the physiology of arterial blood pressure control in perioperative medicine

BackgroundPerioperative arterial blood pressure management is a physiologically complex challenge influenced by multiple factors. MethodsA multidisciplinary, international working subgroup of the Third Perioperative Quality Initiative (POQI) consensus meeting reviewed the (patho)physiology and measurement of arterial pressure as applied to perioperative medicine. We addressed predefined questions by undertaking a modified Delphi analysis, in which primary clinical research and review articles were identified using MEDLINE. Strength of recommendations, where applicable, were graded by National Institute for Health and Care Excellence (NICE) guidelines. ResultsMultiple physiological factors contribute to the perioperative physiological importance of arterial pressure: (i) arterial pressure is the input pressure to organ blood flow, but is not the sole determinant of perfusion pressure; (ii) blood flow is often independent of changes in perfusion pressure because of autoregulatory changes in vascular resistance; (iii) microvascular dysfunction uncouples microvascular blood flow from arterial pressure (haemodynamic incoherence). From a practical clinical perspective, we identified that: (i) ambulatory measurement is the optimal method to establish baseline arterial pressure; (ii) automated and invasive arterial pressure measurements have inherent physiological and technical limitations; (iii) individualised arterial pressure targets may change over time, especially in the perioperative period. There remains a need for research in non-invasive, continuous arterial pressure measurements, macro- and micro-circulatory control, regional perfusion pressure measurement, and the development of sensitive, specific, and continuous measures of cellular function to evaluate blood pressure management in a physiologically coherent manner. ConclusionThe multivariable, complex physiology contributing to dynamic changes in perioperative arterial pressure may be underappreciated clinically. The frequently unrecognised dissociation between arterial pressure, organ blood flow, and microvascular and cellular function requires further research to develop a more refined, contextualised clinical approach to this routine perioperative measurement.

PERFUSION INDEX AS AN INDICATOR OF COMPENSATION OF HYPOVOLEMIA AND POSSIBLE COMPLICATIONS IN PATIENTS WITH COMBINED TRAUMA

Hemorrhage in multiple trauma causes activation of a number of compensatory mechanisms, one of which is centralization of blood circulation and peripheral tissue hypoperfusion, which is accompanied by decrease in perfusion index (PI). PI is an indicator of volumetric peripheral blood flow and is measured with photoplethysmography method. This study was conducted to assess the relationship between the perfusion index, the degree of hypovolemia and its compensation after treatment with infusion-transfusion therapy in patients with multiple trauma in ICU settings. 32 patients (20 men and 12 women) aged from 32 to 46 years were examined. For the analysis were selected patients with multiple trauma - spleen rupture in combination with damage of one of the large tubular bone (femur, brachial or tibial bone). The obligatory inclusion criterion was the presence of clinical signs of compensated hypovolemic shock (arterial pressure lesser than 90, heart rate more than 100), a quick response to volemic resuscitation, without the use of additional inotropic support. As a result of the study, an increase in the perfusion index was noted already after 6 hours after damage control surgery and traumatology intervention with ongoing infusion-transfusion therapy in ICU, which indicates that perfusion of the peripheral pool of the bloodstream was improved and correlated with an increase in central venous pressure values, central hemodynamic parameters. It is advisable to use PI as one of the indicators of the degree of volemic status compensation in patients with multiple trauma. The growth of PI corresponds to the improvement of hemodynamic parameters. In some cases, the rapid recovery of volemic status after therapy according to continuous arterial pressure measurement, pulseoximetry, CVP, PI exacerbated anemia, caused by infusion associated hemodilution. This should be taken into account, because prolonged anemia can lead to diminished mental status of the patient. Also, an excessive increase in PI may indicate an over-activation of the sympathetic system due to exacerbated pain syndrome, which apparently can serve as an indicator of insufficient analgesia.

Quantification of peripheral and central blood pressure variability using a time-frequency method.

Systolic blood pressure variability (BPV) is associated with cardiovascular events. As the beat-to-beat variation of blood pressure is due to interaction of several cardiovascular control systems operating with different response times, assessment of BPV by spectral analysis using the continuous measurement of arterial pressure in the finger is used to differentiate the contribution of these systems in regulating blood pressure. However, as baroreceptors are centrally located, this study considered applying a continuous aortic pressure signal estimated noninvasively from finger pressure for assessment of systolic BPV by a time-frequency method using Short Time Fourier Transform (STFT). The average ratio of low frequency and high frequency power band (LFPB/HFPB) was computed by time-frequency decomposition of peripheral systolic pressure (pSBP) and derived central aortic systolic blood pressure (cSBP) in 30 healthy subjects (25-62 years) as a marker of balance between cardiovascular control systems contributing in low and high frequency blood pressure variability. The results showed that the BPV assessed from finger pressure (pBPV) overestimated the BPV values compared to that assessed from central aortic pressure (cBPV) for identical cardiac cycles (P<;0.001), with the overestimation being greater at higher power.

The dicrotic notch analyzed by a numerical model

Divergent concepts on the origin of the dicrotic notch are widespread in medical literature and education. Since most medical textbooks explain the origin of the dicrotic notch as caused by the aortic valve closure itself, this is commonly transmitted in medical physiology courses. We present clinical data and numerical simulations to demonstrate that reflected pressure waves could participate as one of the causes of the dicrotic notch. Our experimental data from continuous arterial pressure measurements from adult patients undergoing vascular surgery suggest that isolated changes in peripheral vascular resistance using an intravenous bolus of phenylephrine (a selective alpha 1-receptor agonist and thus a potent vasoconstrictor) modify the dicrotic notch. We then explore the mechanisms behind this phenomenon by using a numerical model based on integrated axisymmetric Navier-Stokes equations to compute the hemodynamic flow. Our model illustrates clearly how modifications in peripheral artery resistance may result in changes in the amplitude of the dicrotic notch by modifying reflected pressure waves. We believe that this could be a useful tool in teaching medical physiology courses.

Continuous noninvasive arterial pressure measurement using the volume clamp method: an evaluation of the CNAP device in intensive care unit patients

The CNAP system allows continuous noninvasive arterial pressure measurement based on the volume clamp method using a finger cuff. We aimed to evaluate the agreement between arterial pressure measurements noninvasively obtained using the CNAP device and arterial catheter-derived arterial pressure measurements in intensive care unit patients. In 55 intensive care unit patients, we simultaneously recorded arterial pressure values obtained by an arterial catheter placed in the abdominal aorta through the femoral artery (criterion standard) and arterial pressure values determined noninvasively using CNAP. We performed Bland-Altman analysis and calculated the percentage error. The mean difference (±standard deviation, 95% limits of agreement, percentage error) between noninvasive (CNAP) and invasively assessed arterial pressure was for mean arterial pressure +1 mmHg (±9 mmHg, -16 to +19 mmHg, 22%), for systolic arterial pressure -10 mmHg (±16 mmHg, -42 to +21 mmHg, 27%), and for diastolic arterial pressure +7 mmHg (±9 mmHg, -10 to +24 mmHg, 28%). Our results indicate a reasonable accuracy and precision for the determination of mean and diastolic arterial pressure by noninvasive continuous arterial pressure measurements using the volume clamp method compared with the criterion standard (invasive arterial catheter). Systolic arterial pressure is determined less accurately and precisely.

Noninvasive Hemodynamic Monitoring Devices

Noninvasive Hemodynamic Monitoring Devices

Minimally invasive intraoperative estimation of left-ventricular end-systolic elastance with phenylephrine as loading intervention

Left-ventricular end-systolic elastance (Ees) is an index of cardiac contractility, but the invasive nature of its assessment has limited perioperative application. We explored the feasibility of a minimally invasive method of Ees estimation for perioperative assessment of cardiac function and evaluated the suitability of phenylephrine as a loading intervention. In 17 surgical patients, Ees was determined as the slope of the end-systolic pressure-volume relation, which was obtained from non-invasive or invasive continuous arterial pressure measurements and left-ventricular volume determinations using transoesophageal echocardiography (TOE). Ees was determined using as loading interventions preload reduction by inferior vena cava compression (IVCC) and afterload increase by phenylephrine administration. Median invasive Ees determined with phenylephrine estimated 1.05 (0.59-1.21) mm Hg ml(-1) and with IVCC 0.58 (0.31-1.13) mm Hg ml(-1). Bland-Altman analysis to evaluate the level of agreement between minimally invasive and invasive Ees estimation revealed a bias of -0.03 (0.12) mm Hg ml(-1) with limits of agreement from -0.27 to 0.21 mm Hg ml(-1) and the percentage error was 33%. Agreement between Ees obtained with phenylephrine and IVCC revealed a bias of 0.15 (0.69) mm Hg ml(-1) with limits of agreement from -1.21 to 1.51 mm Hg ml(-1) and a percentage error of 149%. It is feasible to determine Ees combining continuous non-invasive arterial pressure measurements and left-ventricular volume determinations with TOE. However, administration of phenylephrine cannot substitute IVCC as a loading intervention, indicating that estimation of Ees in the intraoperative setting remains a challenge.

Influence of anesthetic agent, depth of anesthesia and body temperature on cardiovascular functional parameters in the rat

Sedating animals is sometimes necessary in experimental research. This paper presents and discusses the influence of four of the most common anesthetic agents on cardiovascular parameters in rats. We also studied the influence of body temperature. Ten-week-old Sprague-Dawley rats were anesthetized with either isoflurane, pentobarbital, ketamine/xylazine or tiletamine/zolazepam (n = 12 in each group). A pressure-sensing catheter was placed in the right carotid artery for the continuous measurement of arterial pressure, and echocardiography was performed. Indices of cardiac function were significantly higher in the tiletamine/zolazepam rats compared with the other groups. Heart rate was highest but stroke volume lowest with pentobarbital. Left ventricular diastolic dimension was lower in the pentobarbital and tiletamine/zolazepam rats compared with the isoflurane or ketamine/xylazine rats. Intraventricular diastolic pressure was similar in all groups whereas intraventricular systolic pressure, as well as both systolic and diastolic aortic pressures, was significantly higher in the tiletamine/zolazepam rats compared with the other groups. No hemodynamic indices differed significantly among the isoflurane, pentobarbital and ketamine/xylazine rats. Lowering body temperature significantly reduced heart rate and cardiac output but had no apparent effect on hemodynamic parameters. In conclusion, although cardiac functional parameters differed between the different anesthetic agents in ways that could be of relevance to the researcher, they may all have a role in experimental cardiology. Importantly, tiletamine/zolazepam anesthesia resulted in significantly higher indices of cardiac function and elevated blood pressures compared with the other anesthetic agents, a finding that should be kept in mind when interpreting data obtained in rats sedated on this regimen.

Non-invasive continuous arterial pressure measurement based on radial artery tonometry in the intensive care unit: a method comparison study using the T-Line TL-200pro device

BackgroundThe T-Line TL-200pro (TL-200pro) device (Tensys Medical, Inc., San Diego, CA, USA), based on radial artery tonometry, provides an arterial pressure (AP) waveform and beat-to-beat values of systolic arterial pressure (SAP), mean arterial pressure (MAP), and diastolic arterial pressure (DAP). The aim of the study was to evaluate this non-invasive technique for continuous AP monitoring in medical intensive care unit (ICU) patients. MethodsArterial pressure measurements obtained using the TL-200pro technology were compared using Bland–Altman analysis with values measured directly from a femoral arterial catheter in 34 ICU patients. ResultsArterial pressure values were analysed and compared in 4502 averaged 10-beat epochs. A bias of +0.72 mm Hg (95% limits of agreement −9.37 to +10.82 mm Hg) was observed for MAP. For SAP and DAP, there was a mean difference of −1.39 mm Hg (95% limits of agreement −18.74 to +15.96 mm Hg) and +4.36 mm Hg (95% limits of agreement −8.66 to +17.38 mm Hg), respectively. The percentage error for MAP, SAP, and DAP was 12%, 14%, and 21%, respectively. ConclusionsArterial pressure measurement based on radial artery tonometry using the TL-200pro technology is feasible in medical ICU patients. The TL-200pro system is capable of providing MAP values with high accuracy (low mean difference) and precision (narrow limits of agreement) compared with MAP measured invasively using a femoral arterial catheter. The TL-200pro technology is promising for the measurement of SAP and DAP but further development is necessary to improve accuracy and precision.

Reliability of radial arterial pressure monitoring after cardiac surgery

Invasive monitoring in critically ill patients allows a continuous measurement of arterial pressure, cardiac output, and the derivation of dynamic predictors of fluid responsiveness. However, the pressure signal may be altered by the dynamic characteristics of the fluid-filled tubing. The aim of the present study was to evaluate the reliability of radial artery blood pressure measurement and derived indexes during the early period after cardiac surgery.

Stretch syncope: Reflex vasodepressor faints easily mistaken for epilepsy

The pathophysiology of stretch syncope is demonstrated through the clinical, electrophysiological, and hemodynamic findings in three patients. Fifty-seven attacks were captured by video/EEG monitoring. Simultaneous EEG, transcranial (middle cerebral artery) doppler, and continuous arterial pressure measurements were obtained for at least one typical attack of each patient. They all experienced a compulsion to precipitate their attacks. Episodes started with a stereotyped phase of stretching associated with neck torsion and breath holding, followed by a variable degree of loss of consciousness and asymmetric, recurrent facial and upper limb jerks in the more prolonged episodes. Significant sinus tachycardia coincided with the phase of stretching and was followed within 9–16seconds by rhythmic generalized slow wave abnormalities on the EEG in attacks with impairment of consciousness. Transcranial doppler studies showed a dramatic drop in cerebral perfusion in the middle cerebral arteries during the episodes. The combination of the stereotyped semiology of the attacks, the pseudofocal myoclonic jerking, and the rhythmic generalized slow wave EEG abnormalities with the tachycardia make differential diagnosis from epilepsy challenging.

Increased phase synchronization and decreased cerebral autoregulation during fainting in the young

Vasovagal syncope may be due to a transient cerebral hypoperfusion that accompanies frequency entrainment between arterial pressure (AP) and cerebral blood flow velocity (CBFV). We hypothesized that cerebral autoregulation fails during fainting; a phase synchronization index (PhSI) between AP and CBFV was used as a nonlinear, nonstationary, time-dependent measurement of cerebral autoregulation. Twelve healthy control subjects and twelve subjects with a history of vasovagal syncope underwent 10-min tilt table testing with the continuous measurement of AP, CBFV, heart rate (HR), end-tidal CO2 (ETCO2), and respiratory frequency. Time intervals were defined to compare physiologically equivalent periods in fainters and control subjects. A PhSI value of 0 corresponds to an absence of phase synchronization and efficient cerebral autoregulation, whereas a PhSI value of 1 corresponds to complete phase synchronization and inefficient cerebral autoregulation. During supine baseline conditions, both control and syncope groups demonstrated similar oscillatory changes in phase, with mean PhSI values of 0.58+/-0.04 and 0.54+/-0.02, respectively. Throughout tilt, control subjects demonstrated similar PhSI values compared with supine conditions. Approximately 2 min before fainting, syncopal subjects demonstrated a sharp decrease in PhSI (0.23+/-0.06), representing efficient cerebral autoregulation. Immediately after this period, PhSI increased sharply, suggesting inefficient cerebral autoregulation, and remained elevated at the time of faint (0.92+/-0.02) and during the early recovery period (0.79+/-0.04) immediately after the return to the supine position. Our data demonstrate rapid, biphasic changes in cerebral autoregulation, which are temporally related to vasovagal syncope. Thus, a sudden period of highly efficient cerebral autoregulation precedes the virtual loss of autoregulation, which continued during and after the faint.

Mechanism of hypotensive transients associated with abrupt bradycardias in conscious rabbits

Transient bradycardic hypotensive events occur in resting rabbits. If the hypotension is due to vasodepression, these events may be a model for vasovagal syncope. To determine whether these events are responses to brief stimuli and whether the hypotensive episodes are solely due to rapid-onset bradycardia. Rabbits were instrumented with subcutaneous electrocardiogram leads, and cannulae were acutely inserted into an ear artery to obtain continuous arterial pressure measurements. Exposure to brief, low-level auditory stimuli at 5 kHz transiently increased the RR interval by approximately 70 ms and decreased mean arterial pressure by approximately 5 mmHg. These evoked bradycardic hypotensive events were almost identical to previously reported spontaneous bradycardic hypotensive events. Intra-aortic telemetric blood pressure monitoring was used to demonstrate that the evoked hypotension reflected prolonged diastole, rather than local ear arterial vasoconstriction. Furthermore, administration of the muscarinic blocker glycopyrrolate abolished not only bradycardia (RR interval 64+/-14 ms to 1+/-1 ms; P<0.0001), but also hypotension (--4.1+/-0.8 mmHg to --0.4+/-0.3 mmHg; P=0.0055). Finally, cardiac pacing abolished the inducible bradycardia (RR interval 51+/-10 ms to 2+/-1 ms; P=0.0006) and its associated hypotension (--4.1+/-0.7 mmHg to --1.2+/-0.3 mmHg; P=0.003). Brief auditory stimuli evoked a transient bradycardia mediated by cardiac muscarinic receptors and consequent hypotension. This is not a model for vasovagal syncope.

Prise en charge initiale d’un patient polytraumatisé aux urgences

The initial management of severe trauma patients is based on the search and early treatment of an hemorrhage and its consequences. There is no room for improvising and extensive team experience gathered in trauma centers improves outcome. But their potential distance from the accident scene in a pathology where time is essential gives a key role to the nearest hospitals in the initial management. Indeed any delay can have short and long term pejorative consequences because of tissular hypoperfusion which justifies advanced life-support procedures in prehospital setting and damage control surgical approach. Arterial catheterization for continuous measurement of arterial pressure is the cornerstone of monitoring. A simple and rapid initial imaging assessment at bedside enables appropriate emergency decisions before further imaging assessment is performed. Echocardiography and transcranial Doppler ultrasounds are non invasive promising techniques for initial assessment and monitoring of severe trauma patients.

A modified technique for tail cuff pressure measurement in unrestrained conscious rats.

In physiological experiments, it is essential to measure arterial pressure (AP) and heart rate (HR) in animals. Tail cuff pressure (TCP) measurement using photoelectric volume oscillometry has been commonly used. We designed a new technique for continuous measurement of AP and HR in conscious, unrestrained rats. This is based on the observation that fixation of the rat's tail with tape keeps the animal in position without struggling. The animal is free to move its body. To test the accuracy of this new technique, Sprague-Dawley rats underwent four AP and HR measurement techniques. These included a new unrestrained method (UR), which was compared to the following three methods: traditional restrained TCP method with restrainer, direct monitoring of AP and HR with femoral artery catheterization and a combination of photoelectric volume oscillometry (with body heating to 37 degrees C) and femoral arterial recording. The results show that the modified UR measurement provides accurate data on AP and HR. This method obtains a lower value of HR and similar mean AP when compared to direct monitoring from femoral arterial catheterization. Accordingly, the modified unrestrained TCP measurement can be used in conscious rats as a noninvasive method.

The chronic infusion of hexamethonium and phenylephrine to effectively clamp sympathetic vasomotor tone: A novel approach

There are several ways to assess the sympathetic nervous system (i.e., nerve recording, sympathectomy, etc.), each of which has its own limitations. The present study was conducted to establish a standard, testable chronic ganglionic blockade protocol with a fixed level of adrenergic vasomotor tone. Rats were instrumented with radio telemetry pressure transducers and venous catheters for continuous measurement of arterial pressure and infusion of pharmacologic agents, respectively. After 3 days of control measurements, rats were infused for 9 days with a continuous dose of the ganglionic blocking agent, hexamethonium and the alpha-adrenergic agonist, phenylephrine. In this way, sympathetic tone was effectively “clamped,” which maintained a normal level of arterial pressure. Control pressure between hexamethonium + phenylephrine (HEX + PE) treated rats (101 ± 2 mmHg) and saline (VEHICLE) treated rats (101 ± 2 mmHg) was not different. By day 9 of the infusion, there was no difference in arterial pressure between groups (VEHICLE: 101 ± 3 mmHg, HEX + PE: 103 ± 3 mmHg) or from the control period, although heart rate was significantly less in HEX + PE rats (VEHICLE: 406 ± 9 beats/min vs. HEX + PE: 343 ± 6 beats/min). The effectiveness of this technique was validated by measuring cardiac baroreceptor reflex sensitivity, as well as the pressor response to the direct ganglionic stimulating agent, 1,1-dimethyl-4-phenylpiperazinium iodide (DMPP). Compared to VEHICLE rats, HEX + PE rats showed no tachycardic response to depressor stimuli and an absence of a pressor response to DMPP. We conclude that this protocol is a useful technique to chronically, yet reversibly, block the sympathetic nervous system in experimental settings.

Continuous fiberoptic arterial oxygen tension measurements in dogs.

An experimental study using a new fiberoptic sensor for the continuous intraarterial measurement of oxygen tension is described. This "optode" sensor uses the phenomenon of fluorescence quenching to determine the oxygen tension of the surrounding medium. To assess the accuracy of this device, we anesthetized 4 dogs and monitored them continuously with arterial catheters and an intraarterial optode probe, and intermittently with arterial blood gas analysis. The inspired oxygen fraction was varied from 1.0 to 0.1, and arterial blood gases were measured for comparison with the optode reading. Two hundred ninety data sets yielded a correlation coefficient of 0.96, with a linear regression slope of 0.98 and intercept of 5.1 mm Hg. In the 72 data sets from the last dog, the bias and precision of the optode arterial oxygen tension values were -10.3 mm Hg and 20.0 mm Hg, respectively. The optode probe was easily inserted through a 20-gauge catheter and did not interfere with continuous arterial pressure measurement or blood sampling. This study suggests that the optode has great potential as a continuous, real-time monitor of arterial oxygen tension.