Implementation of a manually operated blood pressure monitor based on energy harvesting for use in resource-constrained settings.

Health workers who screen for hypertension in rural and resource-constrained settings face many challenges including limited training, difficulties in correctly performing blood pressure (BP) measurements, and electrical grid unreliability. The aim of this study is to present the implementation of a manually operated BP monitor which assists health workers in overcoming some of these challenges by harvesting energy during manual cuff inflation and then discharging it in a controlled manner to power BP data acquisition, storage and wireless transmission. A prototype device was fabricated using a rotary alternator, flywheel and capacitor which harvests and stores energy when the bulb is squeezed during cuff inflation. Testing of the prototype revealed that an average of 1.55 J of energy can be scavenged during 30 s of cuff inflation. This is sufficient for BP data acquisition, storage and wireless transmission to a near-by smartphone even when accounting for losses.

A ventilation technique for oxygenation and carbon dioxide elimination in CPR: Continuous insufflation of oxygen at three levels of pressure in a pig model.

AIM: Pulmonary ventilation remains an important part of cardiopulmonary resuscitation, affecting gas exchange and haemodynamics. We designed and studied an improved method of ventilation for CPR, constructed specifically to support both gas exchange and haemodynamics. This method uses continuous insufflation of oxygen at three levels of pressure, resulting in tri-level pressure ventilation (TLPV). We hypothesized that TLPV improves gas exchange and haemodynamics compared to manual gold standard ventilation (GSV). METHODS: In 14 pigs, ventricular fibrillation was induced and automated CPR performed for 10 min with either TLPV or GSV. After defibrillation, CPR was repeated with the other ventilation method. Gas exchange and haemodynamics were monitored. Data are presented as mean±standard error of the mean. RESULTS: TLPV was superior to GSV for PaO2 (163±36 mmHg difference; P=0.001), and peak AWP (-20±2 cmH2O difference; P=0.000) and higher for mean AWP (8±0.2 cmH2O difference; P=0.000). TLPV was comparable to GSV for CPP (5±3 mmHg difference; P=0.012), VCO2 (0.07±0.3 mL/min/kg difference; P=0.001), SvO2 (4±3%-point; P=0.001), mean carotid flow (-0.5±4 mL/min difference; P=0.016), and pHa (0.00±0.03 difference; P=0.002). The PaCO2 data do not provide a conclusive result (4±4 mmHg difference). CONCLUSION: We conclude that the ventilation strategy with a tri-level pressure cycle performs comparable to an expert, manual ventilator in an automated-CPR swine model.

Detection of a spontaneous pulse in photoplethysmograms during automated cardiopulmonary resuscitation in a porcine model.

INTRODUCTION: Reliable, non-invasive detection of return of spontaneous circulation (ROSC) with minimal interruptions to chest compressions would be valuable for high-quality cardiopulmonary resuscitation (CPR). We investigated the potential of photoplethysmography (PPG) to detect the presence of a spontaneous pulse during automated CPR in an animal study. METHODS: Twelve anesthetized pigs were instrumented to monitor circulatory and respiratory parameters. Here we present the simultaneously recorded PPG and arterial blood pressure (ABP) signals. Ventricular fibrillation was induced, followed by 20 min of automated CPR and subsequent defibrillation. After defibrillation, pediatric-guidelines-style life support was given in cycles of 2 min. PPG and ABP waveforms were recorded during all stages of the protocol. Raw PPG waveforms were acquired with a custom-built photoplethysmograph controlling a commercial reflectance pulse oximetry probe attached to the nose. ABP was measured in the aorta. RESULTS: In nine animals ROSC was achieved. Throughout the protocol, PPG and ABP frequency content showed strong resemblance. We demonstrate that (1) the PPG waveform allows for the detection of a spontaneous pulse during ventilation pauses, and that (2) frequency analysis of the PPG waveform allows for the detection of a spontaneous pulse and the determination of the pulse rate, even during ongoing chest compressions, if the pulse and compression rates are sufficiently distinct. CONCLUSIONS: These results demonstrate the potential of PPG as a non-invasive means to detect pulse presence or absence, as well as pulse rate during CPR.

The influence of nonlinear intra-thoracic vascular behaviour and compression characteristics on cardiac output during CPR.

Clinical observations suggest that the assumption of a linear relationship between chest compression pressure and cardiac output may be oversimplified. More complex behaviour may occur when the transmural pressure is large, changing the compliances and resistances in the intra-thoracic vasculature. A fundamental understanding of these compression induced phenomena is required for improving CPR. An extensively used, lumped element computer model (model I) of the circulation was upgraded and refined to include the intrathoracic vasculature (model II). After validation, model II was extended by adding variable compliances and resistances (model III) to the vascular structures. Successively, ranges of compression pressures, frequencies, duty cycles and compression pulse shapes were applied while controlling all other parameters. Cardiac output was then compared. The nonlinearities in compliance and resistance become important, limiting factors in cardiac output, starting in our experimental series at 70 mmHg peak compression pressure, and increasing with higher pressures. This effect is reproducible for sinusoidal and trapezoidal compression forms, resulting in lower cardiac output in all experiments at high compression pressures. Duty cycle and wait time are key parameters for cardiac output. Our data strongly indicate that vascular compliance, especially the ability of vessels to collapse (and potentially the cardiac chambers), can be a central factor in the limited output generated by chest compressions. Just pushing 'harder' or 'faster' is not always better, as an 'optimal' force and frequency may exist. Overly forceful compression can limit blood flow by restricting filling or depleting volume in the cardiac chambers and central great vessels.

Feedback control of retrograde peristalsis using Neural Gastric Electrical Stimulation.

Neural Gastric Electrical Stimulation (NGES) is a new method for invoking gastric contractions under microprocessor control. However, optimization of this technique using feedback mechanisms to minimize power consumption and maximize effectiveness has been lacking. The present work proposes a prototype feedback-controlled neural gastric electrical stimulator for the treatment of obesity. Both a force-based and an interelectrode impedance-based feedback neurostimulator were implemented and tested. Four mongrel dogs (2 M, 2 F, weight 14.9 ++/- 2.3kg) underwent subserosal implantation of 2-channel 1-cm bipolar electrode leads in the distal antrum. Two of the dogs were stimulated with a force-based feedback system and the other two animals were stimulated utilizing an interelectrode impedance-based feedback system. Both feedback systems were able to recognize Erythromycin-driven contractions of the stomach and were capable of overriding them with NGES-invoked retrograde contractions. The proposed technique could be helpful for retaining food longer in the stomach, thus inducing early satiety and diminishing food intake.