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  • 1.
    Donald, Rob
    et al.
    Stats Res Ltd, Dingwall, Scotland.
    Howells, Tim
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Neuroscience, Neurosurgery.
    Piper, Ian
    Queen Elizabeth Univ Hosp, Inst Neurol Sci, Clin Phys, Glasgow, Lanark, Scotland.
    Enblad, Per
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Neuroscience, Neurosurgery.
    Nilsson, Pelle
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Neuroscience, Neurosurgery.
    Chambers, I.
    James Cook Univ Hosp, Dept Med Phys, Middlesbrough, Cleveland, England.
    Gregson, B.
    Newcastle Univ, Neurosurg Trials Grp, Newcastle Upon Tyne, Tyne & Wear, England.
    Citerio, G.
    Hosp San Gerardo, Neurorianimaz, Monza, Italy.
    Kiening, K.
    Ruprecht Karls Univ Hosp, Dept Neurosurg, Heidelberg, Germany.
    Neumann, J.
    Ruprecht Karls Univ Hosp, Dept Neurosurg, Heidelberg, Germany.
    Ragauskas, A.
    Kaunas Univ Technol, Kaunas, Lithuania.
    Sahuquillo, J.
    Vall dHebron Univ Hosp, Dept Neurosurg, Barcelona, Spain.
    Sinnott, R.
    Univ Melbourne, Dept Informat Syst, Parkville, Vic, Australia.
    Stell, A.
    Univ Glasgow, Dept Clin Phys, Glasgow, Lanark, Scotland.
    Forewarning of hypotensive events using a Bayesian artificial neural network in neurocritical care2019In: Journal of clinical monitoring and computing, ISSN 1387-1307, E-ISSN 1573-2614, Vol. 33, no 1, p. 39-51Article in journal (Refereed)
    Abstract [en]

    Traumatically brain injured (TBI) patients are at risk from secondary insults. Arterial hypotension, critically low blood pressure, is one of the most dangerous secondary insults and is related to poor outcome in patients. The overall aim of this study was to get proof of the concept that advanced statistical techniques (machine learning) are methods that are able to provide early warning of impending hypotensive events before they occur during neuro-critical care. A Bayesian artificial neural network (BANN) model predicting episodes of hypotension was developed using data from 104 patients selected from the BrainIT multi-center database. Arterial hypotension events were recorded and defined using the Edinburgh University Secondary Insult Grades (EUSIG) physiological adverse event scoring system. The BANN was trained on a random selection of 50% of the available patients (n = 52) and validated on the remaining cohort. A multi-center prospective pilot study (Phase 1, n = 30) was then conducted with the system running live in the clinical environment, followed by a second validation pilot study (Phase 2, n = 49). From these prospectively collected data, a final evaluation study was done on 69 of these patients with 10 patients excluded from the Phase 2 study because of insufficient or invalid data. Each data collection phase was a prospective non-interventional observational study conducted in a live clinical setting to test the data collection systems and the model performance. No prediction information was available to the clinical teams during a patient's stay in the ICU. The final cohort (n = 69), using a decision threshold of 0.4, and including false positive checks, gave a sensitivity of 39.3% (95% CI 32.9-46.1) and a specificity of 91.5% (95% CI 89.0-93.7). Using a decision threshold of 0.3, and false positive correction, gave a sensitivity of 46.6% (95% CI 40.1-53.2) and specificity of 85.6% (95% CI 82.3-88.8). With a decision threshold of 0.3, > 15min warning of patient instability can be achieved. We have shown, using advanced machine learning techniques running in a live neuro-critical care environment, that it would be possible to give neurointensive teams early warning of potential hypotensive events before they emerge, allowing closer monitoring and earlier clinical assessment in an attempt to prevent the onset of hypotension. The multi-centre clinical infrastructure developed to support the clinical studies provides a solid base for further collaborative research on data quality, false positive correction and the display of early warning data in a clinical setting.

  • 2.
    Howells, Tim
    et al.
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Neuroscience, Neurosurgery.
    Johnson, Ulf
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Neuroscience, Neurosurgery.
    McKelvey, Tomas
    Enblad, Per
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Neuroscience, Neurosurgery.
    An optimal frequency range for assessing the pressure reactivity index in patients with traumatic brain injury2015In: Journal of clinical monitoring and computing, ISSN 1387-1307, E-ISSN 1573-2614, Vol. 29, no 1, p. 97-105Article in journal (Refereed)
    Abstract [en]

    The objective of this study was to identify the optimal frequency range for computing the pressure reactivity index (PRx). PRx is a clinical method for assessing cerebral pressure autoregulation based on the correlation of spontaneous variations of arterial blood pressure (ABP) and intracranial pressure (ICP). Our hypothesis was that optimizing the methodology for computing PRx in this way could produce a more stable, reliable and clinically useful index of autoregulation status. The patients studied were a series of 131 traumatic brain injury patients. Pressure reactivity indices were computed in various frequency bands during the first 4 days following injury using bandpass filtering of the input ABP and ICP signals. Patient outcome was assessed using the extended Glasgow Outcome Scale (GOSe). The optimization criterion was the strength of the correlation with GOSe of the mean index value over the first 4 days following injury. Stability of the indices was measured as the mean absolute deviation of the minute by minute index value from 30-min moving averages. The optimal index frequency range for prediction of outcome was identified as 0.018-0.067 Hz (oscillations with periods from 55 to 15 s). The index based on this frequency range correlated with GOSe with rho = -0.46 compared to -0.41 for standard PRx, and reduced the 30-min variation by 23 %.

  • 3.
    Howells, Tim
    et al.
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Neuroscience, Neurosurgery.
    Johnson, Ulf
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Neuroscience, Neurosurgery.
    McKelvey, Tomas
    Chalmers, Dept Signals & Syst, Gothenburg, Sweden..
    Ronne-Engström, Elisabeth
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Neuroscience, Neurosurgery.
    Enblad, Per
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Neuroscience, Neurosurgery.
    The effects of ventricular drainage on the intracranial pressure signal and the pressure reactivity index2017In: Journal of clinical monitoring and computing, ISSN 1387-1307, E-ISSN 1573-2614, Vol. 31, no 2, p. 469-478Article in journal (Refereed)
    Abstract [en]

    In subarachnoid hemorrhage (SAH) patients intracranial pressure (ICP) is usually monitored via an extraventricular drain (EVD), which can produce false readings when the drain is open. It is established that both the ICP cardiac pulse frequency and long term trends over several hours are often seriously corrupted. The aim of this study was to establish whether or not the intermediate frequency bands [respiratory, Mayer wave and very low frequency (VLF)] were also corrupted. The VLF range is of special interest because it is important in cerebral autoregulation studies. Using a pattern recognition algorithm we retrospectively identified 718 cases of EVD opening in 80 SAH patients. An analysis of differences between closed and open-drain periods showed that ICP amplitude decreased significantly in all of the three lower frequency bands when the EVD was open. A similar analysis of systemic arterial pressure signal revealed similar changes in the same frequency bands that were positively correlated with the ICP changes. Therefore we concluded that the changes in the ICP signal represented real, physiological changes and not artifact. Pressure reactivity index (PRx) values were also computed during closed and open-drain periods. We found a small but statistically significant decrease during open-drain periods. Based on analysis of the change in the PRx distribution during open drainage we concluded that this decrease also represented physiological changes rather than artifact. In summary the ICP respiratory, Mayer wave, and VLF frequency bands are not corrupted when the EVD is open, and it safe to use these for autoregulation studies.

  • 4.
    Hällsjö Sander, Caroline
    et al.
    Karolinska Univ Hosp, Dept Anaesthesiol Surg Serv & Intens Care Med, S-17176 Stockholm, Sweden.;Karolinska Inst, Dept Physiol & Pharmacol, Stockholm, Sweden..
    Sigmundsson, Thorir
    Karolinska Univ Hosp, Dept Anaesthesiol Surg Serv & Intens Care Med, S-17176 Stockholm, Sweden.;Karolinska Inst, Dept Physiol & Pharmacol, Stockholm, Sweden..
    Hallbäck, Magnus
    Maquet Crit Care AB, Solna, Sweden..
    Suarez-Sipmann, Fernando
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Anaesthesiology and Intensive Care. Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Hedenstierna laboratory. Inst Carlos III, CIBER Enfermedades Resp CIBERES, Madrid, Spain..
    Wallin, Mats
    Karolinska Inst, Dept Physiol & Pharmacol, Stockholm, Sweden.;Maquet Crit Care AB, Solna, Sweden..
    Oldner, Anders
    Karolinska Univ Hosp, Dept Anaesthesiol Surg Serv & Intens Care Med, S-17176 Stockholm, Sweden.;Karolinska Inst, Dept Physiol & Pharmacol, Stockholm, Sweden..
    Björne, Hakan
    Karolinska Univ Hosp, Dept Anaesthesiol Surg Serv & Intens Care Med, S-17176 Stockholm, Sweden.;Karolinska Inst, Dept Physiol & Pharmacol, Stockholm, Sweden..
    A modified breathing pattern improves the performance of a continuous capnodynamic method for estimation of effective pulmonary blood flow2017In: Journal of clinical monitoring and computing, ISSN 1387-1307, E-ISSN 1573-2614, Vol. 31, no 4, p. 717-725Article in journal (Refereed)
    Abstract [en]

    In a previous study a new capnodynamic method for estimation of effective pulmonary blood flow (COEPBF) presented a good trending ability but a poor agreement with a reference cardiac output (CO) measurement at high levels of PEEP. In this study we aimed at evaluating the agreement and trending ability of a modified COEPBF algorithm that uses expiratory instead of inspiratory holds during CO and ventilatory manipulations. COEPBF was evaluated in a porcine model at different PEEP levels, tidal volumes and CO manipulations (N = 8). An ultrasonic flow probe placed around the pulmonary trunk was used for CO measurement. We tested the COEPBF algorithm using a modified breathing pattern that introduces cyclic end-expiratory time pauses. The subsequent changes in mean alveolar fraction of carbon dioxide were integrated into a capnodynamic equation and effective pulmonary blood flow, i.e. non-shunted CO, was calculated continuously breath by breath. The overall agreement between COEPBF and the reference method during all interventions was good with bias (limits of agreement) 0.05 (-1.1 to 1.2) L/min and percentage error of 36 %. The overall trending ability as assessed by the four-quadrant and the polar plot methodology was high with a concordance rate of 93 and 94 % respectively. The mean polar angle was 0.4 (95 % CI -3.7 to 4.5)A degrees. A ventilatory pattern recurrently introducing end-expiratory pauses maintains a good agreement between COEPBF and the reference CO method while preserving its trending ability during CO and ventilatory alterations.

  • 5.
    Karbing, D. S.
    et al.
    Aalborg Univ, Dept Hlth Sci & Technol, Resp & Crit Care Rcare, Aalborg, Denmark.
    Perchiazzi, Gaetano
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Hedenstierna laboratory.
    Rees, S. E.
    Aalborg Univ, Dept Hlth Sci & Technol, Resp & Crit Care Rcare, Aalborg, Denmark.
    Jaffe, M. B.
    Cardioresp Consulting LLC, Cheshire, CT USA.
    Journal of Clinical Monitoring and Computing 2017 end of year summary: respiration2018In: Journal of clinical monitoring and computing, ISSN 1387-1307, E-ISSN 1573-2614, Vol. 32, no 2, p. 197-205Article, review/survey (Refereed)
    Abstract [en]

    This paper reviews 32 papers or commentaries published in Journal of Clinical Monitoring and Computing in 2016, within the field of respiration. Papers were published covering airway management, ventilation and respiratory rate monitoring, lung mechanics and gas exchange monitoring, in vitro monitoring of lung mechanics, CO2 monitoring, and respiratory and metabolic monitoring techniques.

  • 6.
    Perchiazzi, Gaetano
    et al.
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Hedenstierna laboratory. Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Anaesthesiology and Intensive Care. Department of Emergency and Organ Transplant, Section of Anaesthesia and Intensive Care Medicine, University of Bari, Italy.
    Rylander, Christian
    Pellegrini, Mariangela
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Hedenstierna laboratory. Department of Emergency and Organ Transplant, Section of Anaesthesia and Intensive Care Medicine, University of Bari, Italy.
    Larsson, Anders
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Hedenstierna laboratory. Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Anaesthesiology and Intensive Care.
    Hedenstierna, Göran
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Hedenstierna laboratory. Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Medical Sciences, Clinical Physiology.
    Monitoring of total positive end-expiratory pressure during mechanical ventilation by artificial neural networks2017In: Journal of clinical monitoring and computing, ISSN 1387-1307, E-ISSN 1573-2614, Vol. 31, no 3, p. 551-559Article in journal (Refereed)
    Abstract [en]

    Ventilation treatment of acute lung injury (ALI) requires the application of positive airway pressure at the end of expiration (PEEPapp) to avoid lung collapse. However, the total pressure exerted on the alveolar walls (PEEPtot) is the sum of PEEPapp and intrinsic PEEP (PEEPi), a hidden component. To measure PEEPtot, ventilation must be discontinued with an end-expiratory hold maneuver (EEHM). We hypothesized that artificial neural networks (ANN) could estimate the PEEPtot from flow and pressure tracings during ongoing mechanical ventilation. Ten pigs were mechanically ventilated, and the time constant of their respiratory system (τRS) was measured. We shortened their expiratory time (TE) according to multiples of τRS, obtaining different respiratory patterns (Rpat). Pressure (PAW) and flow (V'AW) at the airway opening during ongoing mechanical ventilation were simultaneously recorded, with and without the addition of external resistance. The last breath of each Rpat included an EEHM, which was used to compute the reference PEEPtot. The entire protocol was repeated after the induction of ALI with i.v. injection of oleic acid, and 382 tracings were obtained. The ANN had to extract the PEEPtot, from the tracings without an EEHM. ANN agreement with reference PEEPtot was assessed with the Bland-Altman method. Bland Altman analysis of estimation error by ANN showed -0.40 ± 2.84 (expressed as bias ± precision) and ±5.58 as limits of agreement (data expressed as cmH2O). The ANNs estimated the PEEPtot well at different levels of PEEPapp under dynamic conditions, opening up new possibilities in monitoring PEEPi in critically ill patients who require ventilator treatment.

  • 7.
    Sander, Caroline Hällsjö
    et al.
    Karolinska Univ Hosp, Dept Anesthesiol Surg Serv & Intens Care Med, S-17176 Stockholm, Sweden.;Karolinska Inst, Dept Physiol & Pharmacol, Stockholm, Sweden..
    Lönnqvist, Per-Arne
    Karolinska Univ Hosp, Astrid Lindgrens Childrens Hosp, Paediat Anesthesia & Intens Care, Stockholm, Sweden..
    Hallbäck, Magnus
    Maquet Crit Care AB, Solna, Sweden..
    Suarez Sipmann, Fernando
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Anaesthesiology and Intensive Care. Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Hedenstierna laboratory. Inst Carlos III, CIBERES, CIBER Enfermedades Resp, Madrid, Spain..
    Wallin, Mats
    Karolinska Inst, Dept Physiol & Pharmacol, Stockholm, Sweden.;Maquet Crit Care AB, Solna, Sweden..
    Oldner, Anders
    Karolinska Univ Hosp, Dept Anesthesiol Surg Serv & Intens Care Med, S-17176 Stockholm, Sweden.;Karolinska Inst, Dept Physiol & Pharmacol, Stockholm, Sweden..
    Björne, Håkan
    Karolinska Univ Hosp, Dept Anesthesiol Surg Serv & Intens Care Med, S-17176 Stockholm, Sweden.;Karolinska Inst, Dept Physiol & Pharmacol, Stockholm, Sweden..
    Capnodynamic assessment of effective lung volume during cardiac output manipulations in a porcine model2016In: Journal of clinical monitoring and computing, ISSN 1387-1307, E-ISSN 1573-2614, Vol. 30, no 6, p. 761-769Article in journal (Refereed)
    Abstract [en]

    A capnodynamic calculation of effective pulmonary blood flow includes a lung volume factor (ELV) that has to be estimated to solve the mathematical equation. In previous studies ELV correlated to reference methods for functional residual capacity (FRC). The aim was to evaluate the stability of ELV during significant manipulations of cardiac output (CO) and assess the agreement for absolute values and trending capacity during PEEP changes at different lung conditions. Ten pigs were included. Alterations of alveolar carbon dioxide were induced by cyclic reoccurring inspiratory holds. The Sulphur hexafluoride technique for FRC measurements was used as reference. Cardiac output was altered by preload reduction and inotropic stimulation at PEEP 5 and 12 cmH(2)O both in normal lung conditions and after repeated lung lavages. ELV at baseline PEEP 5 was [mean (SD)], 810 (163) mL and decreased to 400 (42) mL after lavage. ELV was not significantly affected by CO alterations within the same PEEP level. In relation to FRC the overall bias (limits of agreement) was -35 (-271 to 201) mL, and percentage error 36 %. A small difference between ELV and FRC was seen at PEEP 5 cmH(2)O before lavage and at PEEP 12 cmH(2)O after lavage. ELV trending capability between PEEP steps, showed a concordance rate of 100 %. ELV was closely related to FRC and remained stable during significant changes in CO. The trending capability was excellent both before and after surfactant depletion.

  • 8.
    Sigmundsson, Thorir Svavar
    et al.
    Karolinska Univ Hosp, Dept Perioperat Med & Intens Care, Stockholm, Sweden.;Karolinska Inst, Dept Physiol & Pharmacol, Stockholm, Sweden..
    Öhman, Tomas
    Karolinska Univ Hosp, Dept Perioperat Med & Intens Care, Stockholm, Sweden.;Karolinska Inst, Dept Physiol & Pharmacol, Stockholm, Sweden..
    Hallbäck, Magnus
    Maquet Crit Care AB, Solna, Sweden..
    Redondo, Eider
    Hosp Navarra, Dept Intens Care Med, Pamplona, Spain..
    Suarez-Sipmann, Fernando
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Anaesthesiology and Intensive Care. Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Hedenstierna laboratory. Inst Salud Carlos III, CIBER Enfermedades Resp, Madrid, Spain..
    Wallin, Mats
    Karolinska Inst, Dept Physiol & Pharmacol, Stockholm, Sweden.;Maquet Crit Care AB, Solna, Sweden..
    Oldner, Anders
    Karolinska Univ Hosp, Dept Perioperat Med & Intens Care, Stockholm, Sweden.;Karolinska Inst, Dept Physiol & Pharmacol, Stockholm, Sweden..
    Sander, Caroline Hällsjö
    Karolinska Univ Hosp, Dept Perioperat Med & Intens Care, Stockholm, Sweden.;Karolinska Inst, Dept Physiol & Pharmacol, Stockholm, Sweden..
    Björne, Håkan
    Karolinska Univ Hosp, Dept Perioperat Med & Intens Care, Stockholm, Sweden.;Karolinska Inst, Dept Physiol & Pharmacol, Stockholm, Sweden..
    Performance of a capnodynamic method estimating effective pulmonary blood flow during transient and sustained hypercapnia2018In: Journal of clinical monitoring and computing, ISSN 1387-1307, E-ISSN 1573-2614, Vol. 32, no 2, p. 311-319Article in journal (Refereed)
    Abstract [en]

    The capnodynamic method is a minimally invasive method continuously calculating effective pulmonary blood flow (COEPBF), equivalent to cardiac output when intra pulmonary shunt flow is low. The capnodynamic equation joined with a ventilator pattern containing cyclic reoccurring expiratory holds, provides breath to breath hemodynamic monitoring in the anesthetized patient. Its performance however, might be affected by changes in the mixed venous content of carbon dioxide (CvCO2). The aim of the current study was to evaluate COEPBF during rapid measurable changes in mixed venous carbon dioxide partial pressure (PvCO2) following ischemia-reperfusion and during sustained hypercapnia in a porcine model. Sixteen pigs were submitted to either ischemia-reperfusion (n = 8) after the release of an aortic balloon inflated during 30 min or to prolonged hypercapnia (n = 8) induced by adding an instrumental dead space. Reference cardiac output (CO) was measured by an ultrasonic flow probe placed around the pulmonary artery trunk (COTS). Hemodynamic measurements were obtained at baseline, end of ischemia and during the first 5 min of reperfusion as well as during prolonged hypercapnia at high and low CO states. Ischemia-reperfusion resulted in large changes in PvCO2, hemodynamics and lactate. Bias (limits of agreement) was 0.7 (-0.4 to 1.8) L/min with a mean error of 28% at baseline. COEPBF was impaired during reperfusion but agreement was restored within 5 min. During prolonged hypercapnia, agreement remained good during changes in CO. The mean polar angle was -4.19A degrees (-8.8A degrees to 0.42A degrees). Capnodynamic COEPBF is affected but recovers rapidly after transient large changes in PvCO2 and preserves good agreement and trending ability during states of prolonged hypercapnia at different levels of CO.

  • 9.
    Suarez-Sipmann, Fernando
    et al.
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Hedenstierna laboratory.
    Santos, A.
    Peces-Barba, G.
    Bohm, S. H.
    Gracia, J. L.
    Calderón, P.
    Tusman, G.
    Pulmonary artery pulsatility is the main cause of cardiogenic oscillations2013In: Journal of clinical monitoring and computing, ISSN 1387-1307, E-ISSN 1573-2614, Vol. 27, no 1, p. 47-53Article in journal (Refereed)
    Abstract [en]

    The genesis of cardiogenic oscillations, i.e. The small waves in airway pressure (COSpaw) and flow (COSflow) signals recorded at the airway opening is under debate. We hypothesized that these waves are originated from cyclic changes in pulmonary artery (PA) pressure and flow but not from the physical transmission of heartbeats onto the lungs. The aim of this study was to test this hypothesis. In 10 anesthetized pigs, COS were evaluated during expiratory breath-holds at baseline with intact chest and during open chest conditions at: (1) close contact between heart and lungs; (2) no heart-lungs contact by lifting the heart apex outside the thoracic cavity; (3) PA clamping at the main trunk during 10 s; and (4) during manual massage after cardiac arrest maintaining the heart apex outside the thorax, with and without PA clamping. Baseline COSpaw and COSflow amplitude were 0.70 ± 0.08 cmH2O and 0.51 ± 0.06 L/min, respectively. Both COS amplitude decreased during open chest conditions in step 1 and 2 (p < 0.05). However, COSpaw and COSflow amplitude did not depend on whether the heart was in contact or isolated from the surrounding lung parenchyma. COSpaw and COSflow disappeared when pulmonary blood flow was stopped after clamping PA in all animals. Manual heart massages reproduced COS but they disappeared when PA was clamped during this maneuver. The transmission of PA pulsatilty across the lungs generates COSpaw and COSflow measured at the airway opening. This information has potential applications for respiratory monitoring.

  • 10.
    Tusman, Gerardo
    et al.
    Hosp Privado Comunidad Mar Del Plata, Dept Anesthesiol, 7600 Mar Plata, Buenos Aires, DF, Argentina.
    Acosta, Cecilia M.
    Hosp Privado Comunidad Mar Del Plata, Dept Anesthesiol, 7600 Mar Plata, Buenos Aires, DF, Argentina.
    Pulletz, Sven
    Klinikum Osnabrueck, Dept Anesthesiol & Intens Care Med, Osnabruck, Germany.
    Boehm, Stephan H.
    Rostock Univ, Med Ctr, Dept Anesthesiol & Intens Care Med, Rostock, Germany.
    Scandurra, Adriana
    Mar Del Plata Univ, Sch Engn, Elect Dept, Bioengn Lab, Mar Del Plata, Buenos Aires, Argentina.
    Martinez Arca, Jorge
    Mar Del Plata Univ, Sch Engn, Elect Dept, Bioengn Lab, Mar Del Plata, Buenos Aires, Argentina.
    Madorno, Matias
    ITBA, Buenos Aires, DF, Argentina.
    Suarez-Sipmann, Fernando
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Hedenstierna laboratory. CIBERES, Madrid, Spain;Hosp Univ La Princesa, Dept Crit Care, Madrid, Spain.
    Photoplethysmographic characterization of vascular tone mediated changes in arterial pressure: an observational study2019In: Journal of clinical monitoring and computing, ISSN 1387-1307, E-ISSN 1573-2614, Vol. 33, no 5, p. 815-824Article in journal (Refereed)
    Abstract [en]

    To determine whether a classification based on the contour of the photoplethysmography signal (PPGc) can detect changes in systolic arterial blood pressure (SAP) and vascular tone. Episodes of normotension (SAP 90-140 mmHg), hypertension (SAP > 140 mmHg) and hypotension (SAP < 90 mmHg) were analyzed in 15 cardiac surgery patients. SAP and two surrogates of the vascular tone, systemic vascular resistance (SVR) and vascular compliance (Cvasc = stroke volume/pulse pressure) were compared with PPGc. Changes in PPG amplitude (foot-to-peak distance) and dicrotic notch position were used to define 6 classes taking class III as a normal vascular tone with a notch placed between 20 and 50% of the PPG amplitude. Class I-to-II represented vasoconstriction with notch placed > 50% in a small PPG, while class IV-to-VI described vasodilation with a notch placed < 20% in a tall PPG wave. 190 datasets were analyzed including 61 episodes of hypertension [SAP = 159 (151-170) mmHg (median 1st-3rd quartiles)], 84 of normotension, SAP = 124 (113-131) mmHg and 45 of hypotension SAP = 85(80-87) mmHg. SAP were well correlated with SVR (r = 0.78, p < 0.0001) and Cvasc (r = 0.84, p < 0.0001). The PPG-based classification correlated well with SAP (r = - 0.90, p < 0.0001), SVR (r = - 0.72, p < 0.0001) and Cvasc (r = 0.82, p < 0.0001). The PPGc misclassified 7 out of the 190 episodes, presenting good accuracy (98.4% and 97.8%), sensitivity (100% and 94.9%) and specificity (97.9% and 99.2%) for detecting episodes of hypotension and hypertension, respectively. Changes in arterial pressure and vascular tone were closely related to the proposed classification based on PPG waveform. Clinical Trial Registration NTC02854852.

  • 11. Tusman, Gerardo
    et al.
    Gogniat, Emiliano
    Bohm, Stephan H.
    Scandurra, Adriana
    Suarez-Sipmann, Fernando
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Hedenstierna laboratory.
    Torroba, Agustin
    Casella, Federico
    Giannasi, Sergio
    San Roman, Eduardo
    Reference values for volumetric capnography-derived non-invasive parameters in healthy individuals2013In: Journal of clinical monitoring and computing, ISSN 1387-1307, E-ISSN 1573-2614, Vol. 27, no 3, p. 281-288Article in journal (Refereed)
    Abstract [en]

    The aim of this study was to determine typical values for non-invasive volumetric capnography (VCap) parameters for healthy volunteers and anesthetized individuals. VCap was obtained by a capnograph connected to the airway opening. We prospectively studied 33 healthy volunteers 32 +/- A 6 years of age weighing 70 +/- A 13 kg at a height of 171 +/- A 11 cm in the supine position. Data from these volunteers were compared with a cohort of similar healthy anesthetized patients ventilated with the following settings: tidal volume (VT) of 6-8 mL/kg, respiratory rate 10-15 bpm, PEEP of 5-6 cmH(2)O and FiO(2) of 0.5. Volunteers showed better clearance of CO2 compared to anesthetized patients as indicated by (median and interquartile range): (1) an increased elimination of CO2 per mL of VT of 0.028 (0.005) in volunteers versus 0.023 (0.003) in anesthetized patients, p < 0.05; (2) a lower normalized slope of phase III of 0.26 (0.17) in volunteers versus 0.39 (0.38) in anesthetized patients, p < 0.05; and (3) a lower Bohr dead space ratio of 0.23 (0.05) in volunteers versus 0.28 (0.05) in anesthetized patients, p < 0.05. This study presents reference values for non-invasive volumetric capnography-derived parameters in healthy individuals. Mechanical ventilation and anesthesia altered these values significantly.

  • 12. Tusman, Gerardo
    et al.
    Scandurra, Adriana
    Böhm, Stephan H
    Suarez-Sipmann, Fernando
    Clara, Fernando
    Model fitting of volumetric capnograms improves calculations of airway dead space and slope of phase III2009In: Journal of clinical monitoring and computing, ISSN 1387-1307, E-ISSN 1573-2614, Vol. 23, no 4, p. 197-206Article in journal (Refereed)
    Abstract [en]

    Background

    This study assessed the performance of a Functional Approximation based on a Levenberg-Marquardt Algorithm (FA-LMA) to calculate airway dead space (VDaw) and the slope of phase III (S III) from capnograms.

    Methods

    We performed mathematical simulations to test the effect of noises on the calculation of VDaw and S III. Data from ten mechanically ventilated patients at 0, 5 and 10 cmH2O of PEEP were also studied. FA-LMA was compared with the traditional Fowler’s method (FM).

    Results

    Simulations showed that: (1) The FM determined VDaw with accuracy only if the capnogram approximated a symmetrical curve (S III = 0). When capnograms became asymmetrical (S III > 0), the FM underestimated VDaw (−3.1% to −0.9%). (2) When adding noises on 800 capnograms, VDaw was underestimated whenever the FM was used thereby creating a bias between −5.54 and −1.28 ml at standard deviations (SD) of 0.1–1.8 ml (P < 0.0001). FA-LMA calculations of VDaw were close to the simulated values with the bias ranging from −0.21 to 0.16 ml at SD from 0.1 to 0.4 ml. The FM overestimated S III and showed more bias (0.0041–0.0078 mmHg/ml, P < 0.0001) than the FA-LMA (0.0002–0.0030 mmHg/ml). When calculating VDaw from patients, variability was less with the FA-LMA leading to mean variation coefficients of 0.0102, 0.0111 and 0.0123 compared to the FM (0.0243, 0.0247 and 0.0262, P < 0.001) for 0, 5 and 10 cmH2O of PEEP, respectively. The FA-LMA also showed less variability in S III with mean variation coefficients of 0.0739, 0.0662 and 0.0730 compared to the FM (0.1379, 0.1208 and 0.1246, P < 0.001) for 0, 5 and 10 cmH2O of PEEP, respectively.

    Conclusions

    The Functional Approxi- mation based on a Levenberg-Marquardt Algorithm showed less bias and dispersion compared to the traditional Fowler’s method when calculating VDaw and S III.

  • 13. Tusman, Gerardo
    et al.
    Suarez-Sipmann, Fernando
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences.
    Paez, Gabriel
    Alvarez, Jorge
    Bohm, Stephan H.
    States of low pulmonary blood flow can be detected non-invasively at the bedside measuring alveolar dead space2012In: Journal of clinical monitoring and computing, ISSN 1387-1307, E-ISSN 1573-2614, Vol. 26, no 3, p. 183-190Article in journal (Refereed)
    Abstract [en]

    We tested whether the ratio of alveolar dead space to alveolar tidal volume (VDalv/VTalv) can detect states of low pulmonary blood flow (PBF) in a non-invasive way. Fifteen patients undergoing cardiovascular surgeries with cardiopulmonary bypass (CPB) were studied. CPB is a technique that excludes the lungs from the general circulation. The weaning of CPB is a model that manipulates PBF in vivo because each time blood flow through the CPB decreases, expected PBF (ePBF) increases. Patients were liberated from CPB in steps of 20 % every 2' starting from 100 % CPB (very low ePBF) to 0 % CPB (100 % ePBF). During constant ventilation, volumetric capnograms were recorded and Bohr's dead space ratio (VDBohr/VT), VDalv/VTalv and the ratio of airway dead space to tidal volume (VDaw/VT) were calculated. Before CPB, VDBohr/VT was 0.36 +/- A 0.05, VDaw/VT 0.21 +/- A 0.04 and VDalv/VTalv 0.18 +/- A 0.06 (mean +/- A SD). During weaning from CPB, VDaw/VT remained unchanged while VDBohr/VT and VDalv/VTalv decreased with increasing ePBF. At CPB of 80, 60, 40 and 20 % VDBohr/VT was 0.64 +/- A 0.06, 0.55 +/- A 0.06, 0.47 +/- A 0.05 and 0.40 +/- A 0.04, respectively; < 0.001 and VDalv/VTalv 0.53 +/- A 0.07, 0.40 +/- A 0.07, 0.29 +/- A 0.06 and 0.25 +/- A 0.04, respectively; < 0.001). After CPB, VDBohr/VT and VDalv/VTalv reached values similar to baseline (0.37 +/- A 0.04 and 0.19 +/- A 0.06, respectively). At constant ventilation the alveolar component of VDBohr/VT increased in proportion to the deficit in lung perfusion.

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