Camera-based photoplethysmography in critical care patients

BACKGROUND

Camera-based photoplethysmography (cbPPG) is an optical measurement technique that reveals pulsatile blood flow in cutaneous microcirculation from a distance. cbPPG has been shown to reflect pivotal haemodynamic events like cardiac ejection in healthy subjects. In addition, it provides valuable insight into intrinsic microcirculatory regulation as it yields dynamic, two-dimensional perfusion maps. In this study, we evaluate the feasibility of a clinical cbPPG application in critical care patients.

METHODS

A mobile camera set-up to record faces of patients at the bed site was constructed. Videos were made during the immediate recovery after cardiac surgery under standard critical care conditions and were processed offline. Major motion artefacts were detected using an optical flow technique and suitable facial regions were manually annotated. cbPPG signals were highpass filtered and Fourier spectra out of consecutive 10s signal segments calculated for heart rate detection. Signal-to-noise ratios (SNR) of the Fourier spectra were derived as a quality measure. Reference data of vital parameters were synchronously acquired from the bed site monitoring system.

RESULTS

Seventy patient videos of an average time of 28.6±2.8 min were analysed. Heart rate (HR) was detected within a±5 bpm range compared to reference in 83% of total recording time. Low SNR and HR detection failure were mostly, but not exclusively, attributed to non-physiological events like patient motion, interventions or sudden changes of illumination. SNR was reduced by low arterial blood pressure, whereas no impact of other perioperative or disease-related parameters was identified.

CONCLUSION

Cardiac ejection is detectable by cbPPG under pathophysiologic conditions of cardiovascular disease and perioperative medicine. cbPPG measurements can be seamlessly integrated into the clinical work flow of critical care patients.

The smelling of Hedione results in sex-differentiated human brain activity

A large family of vomeronasal receptors recognizes pheromone cues in many animals including most amphibia, reptiles, rhodents, and other mammals. Humans possess five vomeronasal-type 1 receptor genes (VN1R1-VN1R5), which code for proteins that are functional in recombinant expression systems. We used two different recombinant expression systems and identified Hedione as a ligand for the putative human pheromone receptor VN1R1 expressed in the human olfactory mucosa. Following the ligand identification, we employed functional magnetic resonance imaging (fMRI) in healthy volunteers to characterize the in vivo action of the VN1R1 ligand Hedione. In comparison to a common floral odor (phenylethyl alcohol), Hedione exhibited significantly enhanced activation in limbic areas (amygdala, hippocampus) and elicited a sex-differentiated response in a hypothalamic region that is associated with hormonal release. Utilizing a novel combination of methods, our results indicate that the putative human pheromone receptor VN1R1 is involved in extra-olfactory neuronal activations induced by the odorous substance Hedione. The activation of VN1R1 might play a role in gender-specific modulation of hormonal secretion in humans.

[Cardiogenic shock]

Cardiogenic shock is most commonly a complication of acute myocardial infarction. The ischemic loss of functional myocardium triggers distinct cardiovascular responses which can deteriorate to global pump failure with a mortality rate of more than 50%. Causes of cardiogenic shock beyond myocardial ischemia are very diverse. Decisive management with rapid evaluation, identification of the underlying disease and urgent initiation of supportive measures as well as definitive therapy is of prognostic value. Causal treatment of the cardiac disease is crucial but has to be weighed against the specific surgical circumstances of perioperative patients, particularly concerning anticoagulation, platelet inhibition and bleeding risks. Hemodynamic stabilization is achieved by pharmacological support of myocardial function, control of arrhythmia and volume load. Prevention and intensive care of shock-related multiorgan failure is of pivotal importance in the successful management of cardiogenic shock.

[Long QT syndrome and anaesthesia]

The long QT syndrome (LQTS) is a rare, congenital or acquired disease, which may lead to fatal cardiac arrhythmias (torsade de pointes, TdP). In all LQTS subtypes, TdPs are caused by disturbances in cardiac ion channels. Diagnosis is made using clinical, anamnestic and electrocardiographic data. Triggers of TdPs are numerous and should be avoided perioperatively. Sufficient sedation and preoperative correction of electrolyte imbalances are essential. Volatile anaesthetics and antagonists of muscle relaxants should be avoided and high doses of local anaesthetics are not recommended to date. Propofol is safe for anaesthesia induction and maintenance. The acute therapy of TdPs with cardiovascular depression should be performed in accordance with the guidelines for advanced cardiac life support and includes cardioversion/defibrillation and magnesium. Torsades de pointes may be associated with bradycardia or tachycardia resulting in specific therapeutic and prophylactic measures.

[The present and future status of "scarless" surgery]

The concept of scarless surgery aims at further minimization of diagnostic and therapeutic interventions. Based on the success of flexible gastroenterological endoscopy and laparoscopic surgery, it combines their advantageous approaches in a synergistic manner. Animal experiments have achieved encouraging results in respect to the feasibility of various types of interventions in the peritoneal and retroperitoneal cavity. Further studies and improvement of instruments will have to prove the practicality and superiority of this concept for medical outcome and efficiency compared to present standards of practice in the potential fields of application. The replacement of certain minimally invasive procedures with scarless intervention techniques seems reasonable, as do new fields of application. After further improvement of the methodology, adequate organization, infrastructure, and teaching structures will have to be developed. If they succeed, the concept of scarless surgery can expect a promising future.

Effects of inhalation of perfluorocarbon aerosol on oxygenation and pulmonary function compared to PGI2 inhalation in a sheep model of oleic acid-induced lung injury

OBJECTIVE

To evaluate the effects of PFC aerosol compared to PGI2 aerosol and NaCl aerosol on gas exchange and lung mechanics in oleic acid-induced acute lung injury.

DESIGN

A prospective, controlled, randomised, in vivo animal laboratory study.

SETTING

Research laboratory at an university hospital.

SUBJECTS

Twenty one (n = 21) adult sheep of either gender weighing 26.8+/-6.4 kg.

INTERVENTIONS

The animals were randomised to three groups: PFC aerosol (perfluorooctane), PFC group; prostacyclin aerosol (Flolan), PGI2 group; and NaCl aerosol (0.9% sodium chloride solution), control group. After induction of anaesthesia and placement of vascular catheters, lung injury was induced with 0.12 ml x kg(-1) oleic acid. Aerosols were continuously administered for 2 h using a jet nebuliser. Gas exchange, pulmonary mechanic, and haemodynamic parameters were obtained at regular intervals.

MEASUREMENTS AND MAIN RESULTS

PFC aerosol increased oxygenation (PaO2) 15 min after the initiation of treatment up to 120 min (P < 0.05). Transpulmonary shunt improved in the PFC group (P < 0.05) while it did not change in the two other groups. PFC aerosol reduced maximum airway pressure (Pmax) (median) significantly from (median) 38 mbar to 32 mbar (P < 0.05). Static compliance improved significantly in the PFC group (P < 0.05).

CONCLUSION

The inhalation of a PFC aerosol led to a significant improvement in pulmonary mechanics and gas exchange, which was not observed in the other two groups. These data suggest that a small dose of perfluorocarbon will have beneficial effects on gas exchange and respiratory mechanics. Therefore, the non-invasive aerosol application technique seems to be a reasonable alternative to administer perfluorocarbons in severe lung injury.

Vaporized perfluorocarbon improves oxygenation and pulmonary function in an ovine model of acute respiratory distress syndrome

BACKGROUND

Perfluorocarbon liquids are being used experimentally and in clinical trials for the treatment of acute lung injury. Their resemblance to inhaled anesthetic agents suggests the possibility of application by vaporization. The authors' aim was to develop the technical means for perfluorocarbon vaporization and to investigate its effects on gas exchange and lung function in an ovine model of oleic acid-induced lung injury.

METHODS

Two vaporizers were calibrated for perfluorohexane and connected sequentially in the inspiratory limb of a conventional anesthetic machine. Twenty sheep were ventilated in a volume controlled mode at an inspired oxygen fraction of 1.0. Lung injury was induced by intravenous injection of 0.1 ml oleic acid per kilogram body weight. Ten sheep were treated with vaporized perfluorohexane for 30 min and followed for 2 h; 10 sheep served as controls. Measurements of blood gases and respiratory and hemodynamic parameters were obtained at regular intervals.

RESULTS

Vaporization of perfluorohexane significantly increased arterial oxygen tension 30 min after the end of treatment (P < 0.01). At 2 h after treatment the oxygen tension was 376+/-182 mmHg (mean +/- SD). Peak inspiratory pressures (P < 0.01) and compliance (P < 0.01) were significantly reduced from the end of the treatment interval onward.

CONCLUSION

Vaporization is a new application technique for perfluorocarbon that significantly improved oxygenation and pulmonary function in oleic acid-induced lung injury.