Utility of the Tympanic Membrane Pressure Waveform for Non-invasive Estimation of The Intracranial Pressure Waveform.

Time domain analysis of the intracranial pressure (ICP) waveform provides important information about the intracranial pressure-volume reserve capacity. The aim here was to explore whether the tympanic membrane pressure (TMP) waveform can be used to non-invasively estimate the ICP waveform. Simultaneous invasive ICP and non-invasive TMP signals were measured in a total of 28 individuals who underwent invasive ICP measurements as a part of their clinical work up (surveillance after subarachnoid hemorrhage in 9 individuals and diagnostic for CSF circulation disorders in 19 individuals). For each individual, a transfer function estimate between the invasive ICP and non-invasive TMP signals was established in order to explore the potential of the method. To validate the results, ICP waveform parameters including the mean wave amplitude (MWA) were computed in the time domain for both the ICP estimates and the invasively measured ICP. The patient-specific non-invasive ICP signals predicted MWA rather satisfactorily in 4/28 individuals (14%). In these four patients the differences between original and estimated MWA were <1.0 mmHg in more than 50% of observations, and <0.5 mmHg in more than 20% of observations. The study further disclosed that the cochlear aqueduct worked as a physical lowpass filter.

A novel rescue-tube device for in-water resuscitation.

BACKGROUND: In-water resuscitation (IWR) is recommended in the 2010 guidelines of the European Resuscitation Council. As IWR represents a physical challenge to the rescuer, a novel Rescue Tube device with an integrated "Oxylator" resuscitator might facilitate IWR. The aim of the present study was the assessment of IWR using the novel Rescue Tube device. METHODS: Tidal and minute volumes were recorded using a modified Laerdal Resusci Anne mannequin. Furthermore, rescue time, water aspiration, submersions, and physical exertion were assessed. In this randomized cross-over trial, 17 lifeguards performed four rescue maneuvers over a 100-m distance in open water in random order: no ventilation (NV), mouth-to-mouth ventilation (MMV), Oxylator-aided mask ventilation (OMV), and Oxylator-aided laryngeal tube ventilation (OLTV). RESULTS: OLTV resulted in effective ventilation over the entire rescue distance with the highest mean minute volumes (NV 0, MMV 2.9, OMV 4.1, OLTV 7.6 L · min(-1)). NV was the fastest rescue maneuver while IWR prolonged the rescue maneuver independently of the method of ventilation (mean total rescue time: NV 217, MMV 280, OMV 292, OLTV 290 s). Aspiration of substantial amounts of water occurred only during MMV (mean NV 20, MMV 215, OMV 15, OLTV 6 ml). NV and OLTV were rated as moderately challenging by the lifeguards, whereas MMV and OMV were rated as substantially demanding on a 0-10 visual analog scale (NV 5.3, MMV 7.8, OMV 7.6, OLTV 5.9). DISCUSSION: The device might facilitate IWR by providing effective ventilation with minimal aspiration and by reducing physical effort. Another advantage is the possibility of delivering 100% oxygen.

SCUBA-dive-related changes in heart rate in children.

The purpose of this study was to monitor heart rate (HR) and rhythm during open water SCUBA dives. Nine children performed 25-min open water SCUBA dives to 8 m depth. Before, during and after these dives, ECG was recorded. Compared with predive heart rate, heart rate declined by -24 ± 8% (range -36%; -15%) during the dive. In some children a further decline in HR was observed within the last minutes of the dive. Older and taller subjects and those with a high initial HR showed a more pronounced decline in HR. Furthermore singular supraventricular and ventricular extrasystoles were observed in some children. Immersion as well as facial and skin cooling presumably account for the initial decline in heart rate. A further drop in HR within the last minutes of the dive might be related to mild hypothermia. Single supraventricular and ventricular extrasystoles might occur in healthy children during dives.

Noninvasive intracranial pressure measurement using infrasonic emissions from the tympanic membrane.

OBJECTIVE: We investigated whether ICP can be assessed by measuring infrasonic emissions from the tympanic membrane. METHODS: An increase in ICP was induced in 22 patients with implanted ICP pressure sensors. ICP waveforms that were obtained invasively and continuously were compared with infrasonic emission waveforms. In addition, the noninvasive method was used in a control group of 14 healthy subjects. RESULTS: In a total of 83 measurements, the changes in ICP that were observed in response to different types of stimulation were detected in the waveforms obtained noninvasively as well as in those acquired invasively. Low ICP was associated with an initial high peak and further peaks with smaller amplitudes. High ICP was associated with a marked decrease in the number of peaks and in the difference between the amplitudes of the initial and last peaks. The assessment of infrasonic emissions, however, does not yet enable us to provide exact figures. CONCLUSION: It is conceivable that the assessment of infrasonic emissions will become suitable both as a screening tool and for the continuous monitoring of ICP in an intensive care environment.

Hypoxia and cardiac arrhythmias in breath-hold divers during voluntary immersed breath-holds.

The incidence and nature of cardiac arrhythmias during static apnea were studied by monitoring the electrocardiogram (ECG) and oxygen saturation (SaO(2)) of 16 recreational breath-hold divers. All subjects completed a maximal apnea with a mean (+/-SD) breath-hold duration of 281 (+/-73) s without clinical complications. Both heart rate (HR) and SaO(2) decreased significantly with breath-hold duration. The decline in SaO(2) was inversely related to the decline in HR (r = -0.55, P < 0.05). Cardiac arrhythmias (supraventricular and ventricular premature complexes, right bundle branch block) occurred in 12/16 (77%) subjects and were related to breath-hold duration. Subjects with atrial premature complexes (n = 9) had a reduced BMI (P = 0.016) and a higher decline of the terminal SaO(2) (P = 0.01). In conclusion, ectopic arrhythmias were common during maximal static apneas for training purposes. The results indicate that the occurrence of ectopic beats is associated with individual factors such as the tolerable SaO(2) decrease.

Noninvasive intracranial compliance monitoring. Technical note and clinical results.

Although invasive measurement of intracranial pressure (ICP) involving high-resolution waveform analysis allows assessment of intracranial compliance (ICC), it is only feasible in a few selected neurosurgical conditions. Intracranial compliance can be assessed using the high-frequency centroid (HFC), which is the power-weighted mean frequency within the 4 to 15-Hz band of the ICP waveform. The authors have systematically tested the utility, performance, and reliability of a noninvasive monitor of ICC. The underlying principle of this device is that the ICP transmission and its infrasonic waves are transmitted through the inner ear toward the tympanic membrane. If the outer ear is sealed in an airtight fashion, motions of the tympanic membrane cause air pressure fluctuations that can be recorded using a special sensor. The authors compared the HFC calculated from an intraparenchymal ICP sensor with that obtained simultaneously from an ipsilaterally placed noninvasive device during half of a respiratory cycle (peak to baseline) as well as for three random samples of three heart cycles. They analyzed 32 sessions in 13 patients in whom mechanical ventilation had been established. In four (11%) of 36 sessions they could not demonstrate an adequate signal. For the peak-to-baseline cycle, the mean invasively recorded HFC was 8.05 +/- 0.55 Hz (range 6.7-9 Hz) whereas the mean noninvasively recorded HFC was 8.04 +/- 0.49 Hz (range 7-9.3 Hz). The ICP was 8.5 +/- 5 mm Hg (range 2-24 mm Hg). For the three heart cycles randomly sampled, the values were 7.73 +/- 0.51 Hz (range 6.7-8.6 Hz) and 7.76 +/- 0.56 mm Hg (range 6.5-8.8 mm Hg), respectively. This device allows noninvasive assessment of ICC based on the HFC waveform analysis that is equivalent to that obtained by invasive intraparenchymal recording. The monitoring device may become a valuable tool for monitoring parameters in patients in whom placement of an intracranial sensor is not feasible but assessment of ICC as an alternative to ICP measurement is desired.